HomeMy WebLinkAboutOrdinance No. 4288 - Second Reading: FloodplainRegulations.OrdinanceAmendment
ORDINANCE NO. ____
AN ORDINANCE CREATING AND ENACTING SECTIONS
60.324, 60.418, 60.4181, 60.4182, 60.4183, 61.117, 62.817,
62.818, 62.835, 62.836, 62.848, AND 62.857, AND
AMENDING AND REENACTING SECTIONS 60.200, 60.3501,
SUBDIVISON 2 OF SECTION 61.225, SECTIONS 62.800,
62.810, 62.811, 62.812, 62.813, 62.815, 62.830, 62.831,
62.832, 62.833, 62.841, 62.842, 62.843, 62.844, 62.846,
62.847, 62.850, 62.851, 62.852, 62.853, 62.871, 62.872,
62.873, 62.874, AND 65.440, AND REPEALING SECTIONS
60.110, SUBDIVISION 3 OF SECTION 60.410, 62.801,
62.802, 62.803, 62.812, 62.814, 62.816, 62.820, 62.856,
62.860, 62.875, 62.880, 62.881, 62.882, AND 62.883 OF THE
ROCHESTER CODE OF ORDINANCES, RELATING TO
FLOODPLAIN REGULATIONS.
THE COMMON COUNCIL OF THE CITY OF ROCHESTER DO ORDAIN:
Section 1. Section 60.324 of the Rochester Code of Ordinances is hereby
created and enacted to read as follows:
60.324 Flood Related Districts. The flood related districts are a set
of three districts established to Guide development within the flood plain
consistent with current flood plain management practices. The specific
purposes and regulations for the Flood Fringe, Floodway, and Flood
Prone districts are found in article 62.800.
Section 2. Section 60.418 of the Rochester Code of Ordinances is hereby
created and enacted to read as follows:
60.418 VARIANCES TO THE FLOOD DISTRICT REGULATIONS.
Variances shall be processed according to the Type III review procedure,
with the Phase III hearing process utilized. The Board of Appeals shall
substitute for the Commission in the Phase III process. The Board shall
consider the factors listed in section 62.824 for conditional use permits in
reviewing any variance application.
Section 3. Section 60.4181 of the Rochester Code of Ordinances is hereby
created and enacted to read as follows:
60.4181 CONSIDERATION. Subdivision 1. No variance to a
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flood plain regulation under this article shall be authorized unless the criteria
provided in this section are satisfied.
Subd. 2. Variances must not be issued within any designated
regulatory floodway if any increase in flood levels during the base flood
discharge would result.
Subd. 3. Variances may only be issued upon:
(A) A showing of good and sufficient cause;
(B) A determination that failure to grant the variance would
result in exceptional hardship to the applicant, not mere
inconvenience; and
(C) A determination that the granting of a variance will not result
in: increased flood heights; additional threats to public
safety; extraordinary public expense; creation of nuisances;
fraud on or victimization of the public; or a conflict with
existing local laws or ordinances.
(D) A determination that the variance is the minimum necessary,
considering the flood hazard, to afford relief.
Subd. 4. No variance shall have the effect of allowing in any
district uses prohibited in that district, permit a lower degree of flood
protection than the Regulatory Flood Protection Elevation for the
particular area, or permit standards lower than those required by State
law.
Section 4. Section 60.4182 of the Rochester Code of Ordinances is hereby
created and enacted to read as follows:
60.4182 Upon filing of an application for a variance to the
provisions of this article, the zoning administrator shall notify the applicant in
writing, to be maintained with the record of all variance actions, of the
following:
A. That the issuance of a variance to construct a structure
below the flood protection elevation will result in increased
premium rates for flood insurance up to amounts as high as
$25 for $100 of insurance coverage; and,
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B. Such construction below the flood protection elevation
increases risks to life and property.
Section 5. Section 60.4183 the Rochester Code of Ordinances is hereby created
and enacted to read as follows:
60.4183 Following approval of a variance to the provisions of this
article, the zoning administrator shall:
A. Maintain a record of the variance action, including the justification
for its issuance, and report such variances issued in his annual
report to the Administrator of the National Flood Insurance
Program, when requested by the Federal Emergency Management
Agency.
B. Submit a copy of the decision and its justification for issuance to
the Commissioner of Natural Resources within ten days of such
action.
Section 6. Section 61.117 of the Rochester Code of Ordinances is hereby
created and enacted to read as follows:
61.117 REQUIREMENTS FOR ALL FLOODPLAIN DISTRICTS.
Subdivision 1. A permit must be obtained from the Zoning Administrator to
verify a development meets the floodplain standards outlined in this
ordinance prior to conducting the following activities:
A. The erection, addition, modification, rehabilitation, or
alteration of any building, structure, or portion thereof.
Normal maintenance and repair also requires a permit if
such work, separately or in conjunction with other planned
work, constitutes a Substantial Improvement.
B. The use or change of use of a building, structure, or land.
C. The construction of a dam, on-site septic system, or fence,
although a permit is not required for a farm fence as defined
in this ordinance.
D. The change or extension of a nonconforming use.
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E. The repair of a structure that has been damaged by flood, fire,
tornado, or any other source.
F. The placement of fill, excavation of materials, or the storage
of materials or equipment within the floodplain.
G. Relocation or alteration of a watercourse (including new or
replacement culverts and bridges), unless a public waters
work permit has been applied for.
H. Any other type of Development.
Subd. 2. Building Sites. If a proposed building site is in a floodplain,
all new construction and substantial improvements (including the placement
of manufactured homes) must be:
A. Designed (or modified) and adequately anchored to prevent
floatation, collapse, or lateral movement of the structure
resulting from hydrodynamic and hydrostatic loads,
including the effects of buoyancy;
B. Constructed with materials and utility equipment resistant to
flood damage;
C. Constructed by methods and practices that minimize flood
damage; and
D. Constructed with electrical, heating, ventilation, plumbing,
and air conditioning equipment and other service facilities
that are designed and/or located so as to prevent water from
entering or accumulating within the components during
conditions of flooding.
Subd. 3. Certification. The applicant is required to submit
certification by a registered professional engineer, registered architect, or
registered land surveyor that the finished fill and building elevations were
accomplished in compliance with the provisions of this ordinance.
Floodproofing measures must be certified by a registered professional
engineer or registered architect. Accessory structures designed in
accordance with section 62.843 are exempt from certification provided
sufficient documentation is provided.
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Subd. 4. Certificate of Zoning Compliance for a New, Altered,
or Nonconforming Use. No building, land or structure may be occupied or
used in any manner until a certificate of zoning compliance has been
issued by the Zoning Administrator stating that the use of the building or
land conforms to the requirements of this ordinance.
Subd. 5. Record of First Floor Elevation. The Zoning
Administrator must maintain a record of the elevation of the lowest floor
(including basement) of all new structures and alterations or additions to
existing structures in the floodplain. The Zoning Administrator must also
maintain a record of the elevation to which structures and alterations or
additions to structures are Floodproofed.
Subd. 6. Notifications for Watercourse Alterations. Before
authorizing any alteration or relocation of a river or stream, the Zoning
Administrator must notify adjacent communities. If the applicant has
applied for a permit to work in public waters pursuant to Minn. Stat.
§103G.245, this will suffice as adequate notice. A copy of the notification
must also be submitted to the Chicago Regional Office of the Federal
Emergency Management Agency (FEMA).
Subd. 7. Notification to FEMA When Physical Changes
Increase or Decrease Base Flood Elevations. As soon as is practicable,
but not later than six months after the date such supporting information
becomes available, the Zoning Administrator must notify the Chicago
Regional Office of FEMA of the changes by submitting a copy of the
relevant technical or scientific data.
Section 7. Section 62.817 of the Rochester Code of Ordinances is hereby
created and enacted to read as follows:
62.817 Floodplain Limits. Where a conflict exists between the
floodplain limits illustrated on the Zoning Map and actual field conditions
including the natural or pre-existing grades, the Base Flood Elevation shall
be the governing factor in locating the regulatory floodplain limits.
Section 8. Section 62.818 of the Rochester Code of Ordinances is hereby created
and enacted to read as follows:
62.818. Delineation of Floodway in A Zones. Subdivision 1.
In A zones without a floodway, the floodway may be delineated using the
following procedures. Areas identified through these procedures as flood
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fringe may then be reclassified as Flood Fringe District, and will then be
subject to the requirements of sections 62.840 and 62.860, respectively.
The area determined to be Floodway shall be governed by section
62.850.
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Subd. 2. Upon receipt of an application for a permit or other
approval, the Zoning Administrator must obtain, review and reasonably
utilize any regional flood elevation and floodway data available from a
federal, state, or other source.
Subd. 3. If regional flood elevation and floodway data are not
readily available, the applicant must furnish additional information, as
needed, to determine the regulatory flood protection elevation and
whether the proposed use would fall within the Floodway or Flood Fringe
District. Information must be consistent with accepted hydrological and
hydraulic engineering standards and the standards in subdivision 4.
Subd. 4. The determination of floodway and flood fringe must
include the following components as applicable:
A. Estimate the peak discharge of the regional (1% chance) flood.
B. Calculate the water surface profile of the regional flood based
upon a hydraulic analysis of the stream channel and overbank
areas.
C. Compute the floodway necessary to convey or store the
regional flood without increasing flood stages more than one-
half foot. A lesser stage increase than 0.5 foot is required if, as
a result of the stage increase, increased flood damages would
result. An equal degree of encroachment on both sides of the
stream within the reach must be assumed in computing
floodway boundaries.
Subd. 5. The Zoning Administrator will review the submitted
information and assess the technical evaluation and the recommended
Floodway and/or Flood Fringe District boundary. The assessment must
include the cumulative effects of previous floodway encroachments. The
Zoning Administrator may seek technical assistance from a designated
engineer or other expert person or agency, including the Department of
Natural Resources. Based on this assessment, the Zoning Administrator
may approve or deny the application.
Section 9. Section 62.835 of the Rochester Code of Ordinances is hereby
created and enacted to read as follows:
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62.835. Adverse Effect on Unspecified Floodway. Flood
plain development should not adversely affect the hydraulic capacity of
the channel and adjoining flood plain of any tributary watercourse or
drainage system where a floodway or other encroachment limit has not
been specified on the Zoning Map.
Section 10. Section 62.836 of the Rochester Code of Ordinances is hereby
created and enacted to read as follows:
62.836 Critical Facilities. Critical Facilities are prohibited in all
floodplain districts.
Section 11. Section 62.848 of the Rochester Code of Ordinances is hereby
created and enacted to read as follows:
62.848 On-Site Water Supply and Sewage Treatment Systems:
Where public utilities are not provided:
A. On‐site water supply systems must be designed to minimize
or eliminate infiltration of flood waters into the systems and
are subject to the provisions in Minnesota Rules Chapter
4725.4350, as amended; and,
B. New or replacement on‐site sewage treatment systems must
be designed to minimize or eliminate infiltration of flood
waters into the systems and discharges from the systems
into flood waters, they must not be subject to impairment or
contamination during times of flooding, and are subject to
the provisions in Minnesota Rules Chapter 7080.2270, as
amended.
Section 12. Section 62.857 of the Rochester Code of Ordinances is hereby
created and enacted to read as follows:
62.857 On-Site Water Supply and Sewage Treatment Systems:
Where public utilities are not provided:
A. On‐site water supply systems must be designed to minimize
or eliminate infiltration of flood waters into the systems and
are subject to the provisions in Minnesota Rules Chapter
4725.4350, as amended; and,
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B. New or replacement on‐site sewage treatment systems must
be designed to minimize or eliminate infiltration of flood
waters into the systems and discharges from the systems
into flood waters, they must not be subject to impairment or
contamination during times of flooding, and are subject to
the provisions in Minnesota Rules Chapter 7080.2270, as
amended.
Section 13. Section 60.200 of the Rochester Code of Ordinances is hereby
amended and reenacted to delete the definitions of “Flood-Proofing,” “Flood Plain,”
“Freeboard,” Manufactured Home,” and “Obstruction,” and to add the definitions of the
terms “Base Flood,” “Base Flood Elevation,” “Critical Facilities,” “Floodplain,” “Flood
Insurance Rate Map,” “Floodproofing,” “Guide,” “Historic Structure,” “Lowest Floor,”
“Regulatory Flood Protection Elevation,” “Repetitive Loss,” “Special Flood Hazard Area,”
“Start of Construction,” “Substantial Damage,” and “Substantial Improvement” so as to read
as follows:
Base Flood: The flood having a one percent chance of being
equaled or exceeded in any given year.
Base Flood Elevation: The elevation of the “regional flood.” The
term “Base Flood Elevation” is used in the flood insurance study.
Critical Facilities: Facilities necessary to a community’s public
health and safety, those that store or produce highly volatile, toxic
or water-reactive materials, and those that house occupants that
may be insufficiently mobile to avoid loss of life or injury. Examples
of critical facilities include hospitals, correctional facilities, schools,
daycare facilities, nursing homes, fire and police stations,
wastewater treatment facilities, public electric utilities, water plants,
fuel storage facilities, and waste handling and storage facilities.
Floodplain: The beds proper and the areas adjoining a wetland,
lake or watercourse which have been or hereafter may be covered
by the regional flood.
Flood Insurance Rate Map: An official map on which the Federal
Insurance Administrator has delineated both the special hazard
areas and the risk premium zones applicable to the community. A
FIRM that has been made available digitally is called a Digital
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Flood Insurance Rate Map (DFIRM).
Floodproofing or Floodproofed: A combination of structural
provisions, changes, or adjustments to properties and structures
subject to flooding, primarily for the reduction or elimination of flood
damages.
Guide: To compel, direct, or force to move or occur in a particular
path or direction.
Historic Structure: See 44 Code of Federal Regulations, Part 59.1
or as amended.
Lowest Floor: The lowest floor of the lowest enclosed area
(including basement). An unfinished or flood resistant enclosure,
used solely for parking of vehicles, building access, or storage in
an area other than a basement area, is not considered a building’s
lowest floor; provided, that such enclosure is not built so as to
render the structure in violation of the applicable non-elevation
design requirements of 44 Code of Regulations, Part 60.3.
Regulatory Flood Protection Elevation: A level not less than one
foot above the regional (100 year frequency) flood plus any
increase in flood elevations that would be caused by the future
flood plain development outside the floodway. In Zone AO, the
RFPE is established by adding the depth number specified in feet
for the Zone AO on the Flood Insurance Rate Maps adopted in
section 62.800 of this ordinance to the highest adjacent grade at
the structure’s proposed location on the ground.
Repetitive Loss: Flood related damages sustained by a structure
on two separate occasions during a ten year period for which the
cost of repairs at the time of each such flood event on the average
equals or exceeds 25% of the market value of the structure before
the damage occurred.
Special Flood Hazard Area: A term used for flood insurance
purposes synonymous with “One Hundred Year Floodplain.”
Start of Construction: This term includes substantial improvement,
and means the actual start of construction, repair, reconstruction,
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rehabilitation, addition, placement or other improvement that
occurred before the permit’s expiration date. The actual start is
either the first placement of permanent construction of a structure
on a site, such as the pouring of slab or footings, the installation of
piles, the construction of columns, or any work beyond the stage of
excavation; or the placement of a manufactured home on a
foundation. Permanent construction does not include land
preparation, such as clearing, grading and filling; nor does it
include the installation of streets and/or walkways; nor does it
include excavation for a basement, footings, piers, foundations, or
the erection of temporary forms; nor does it include the installation
on the property of accessory buildings, such as garages or sheds
not occupied as dwelling units or not part of the main structure.
For a substantial improvement, the actual start of construction
means the first alteration of any wall, ceiling, floor, or other.
Substantial Damage: Damage of any origin sustained by a
structure where the cost of restoring the structure to its before
damaged condition would equal or exceed 50 percent of the market
value of the structure before the damage occurred.
Substantial Improvement: This term means, within any consecutive
365-day period, any reconstruction, rehabilitation (including normal
maintenance and repair), repair after damage, addition, or other
improvement of a structure, the cost of which equals or exceeds 50
percent of the market value of the structure before the “start of
construction” of the improvement. This term includes structures
that have incurred “substantial damage,” regardless of the actual
repair work performed. The term does not, however, include either:
A. Any project for improvement of a structure to correct existing
violations of state or local health, sanitary, or safety code
specifications which have been identified by the local code
enforcement official and which are the minimum necessary
to assure safe living conditions.
B. Any alteration of a Historic Structure provided that the
alteration will not preclude the structure’s continued
designation as a Historic Structure.
Section 14. Section 60.3501 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
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60.3501 Designation of Annexed Property: Flood Way and
Flood Fringe. Subdivision 1. The Flood Insurance Rate Map panels
adopted by reference into section 62.810 may include floodplain areas
that lie outside of the corporate boundaries of the City of Rochester at the
time of adoption of this ordinance. If any of these floodplain areas are
annexed into the City of Rochester after the date of adoption of this
ordinance, the newly annexed floodplain lands will be subject to the
provisions of this ordinance immediately upon the date of annexation.
Flood Insurance Rate Maps that are not listed in section 62.810 but that
contain newly annexed land shall automatically be adopted as part of this
code and zoning district designation shall be determined as stated in this
section.
Subd. 2. Lands designated as Floodway on the Flood Insurance
Rate Maps for Olmsted County shall be designated Floodway District
(FW) upon annexation. Lands designated as Flood Fringe A (FFA)
District under the Olmsted County Zoning Ordinance shall be designated
as Flood Fringe (FF) District upon annexation. Lands designated as
Flood Fringe B (FFB) District under the Olmsted County Zoning
Ordinance shall be designated as Flood Prone (FP) District upon
annexation. The designation of a floodplain district under this ordinance,
both Floodway and the Special Flood Hazard Areas shall be based on the
most current Flood Insurance Rate Maps and any amendments thereto.
Section 15. Subdivision 2 of Section 61.225 of the Rochester Code of Ordinances
is hereby amended and reenacted to read as follows:
Subd. 2. The findings for the approval of a land subdivision are as
follows:
A. The proposed land subdivision conforms to all relevant
requirements of this ordinance and variances have been
granted to permit any nonconformance.
B. The proposed water system and sanitary sewer system are
adequate to serve the normal and fire protection demands of
proposed development and to provide for the efficient and
timely extension to serve future development.
C. The plan for soil erosion and stormwater management
meets the adopted standards of the City of Rochester and is
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consistent with the adopted Stormwater Management Plan
or adopted drainage or stormwater policies.
D. The vehicular, pedestrian, transit and non-motorized system
is consistent with adopted transportation plans and is
consistent with the street layout standards listed in section
64.120 and traffic service standards in section 61.526.
E. The lot and block layout provide for safe and convenient
pedestrian, non-motorized vehicle, transit, vehicular, service
and emergency access, efficient utility service connections,
and adequate buildable area in each lot for planned uses.
F. The proposed land subdivision has taken into account the
current six-year and other Long-Range Capital
Improvements Programs and the elements listed therein in
the design of the subdivision.
G. The proposed subdivision, if in a residential zoning district,
addresses the need for spillover parking consistent with the
requirements of section 63.426.
H. The right-of-ways and easements of adequate size and
dimension are provided for the purpose of constructing the
street, utility, and drainage facilities needed to serve the
development.
I. The proposed parks, trail thoroughfares and open space
dedications are consistent with adopted plans, policies and
regulations.
J. The proposed subdivision will not have off-site impacts on
the street, drainage, water or wastewater systems that
exceed adopted standards.
K. The proposed subdivision will not have adverse impacts on
the safety or viability of permitted uses on adjacent
properties.
L. The proposed land subdivision is designed in such a
manner as to allow for continued development in an efficient
manner on adjacent undeveloped lands.
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M. The soils, topography and water tables have been
adequately studied to ensure that all lots are developable
for their designated purposes.
N. The proposed land subdivision is consistent with the
standards of the City’s adopted Comprehensive Plan.
O. Any land located within the Special Flood Hazard Area as
shown on the currently adopted Flood Boundary and
Floodway Maps of Flood Insurance Study, Rochester,
Minnesota, prepared by the Federal Emergency
Management Agency, is determined to be suitable for its
intended use and that the proposed subdivision adequately
mitigates the risks of flooding, inadequate drainage, soil and
rock formations with severe limitations for development,
severe erosion potential, or any other floodplain related
risks to the health, safety or welfare of the future residents
of the proposed subdivision in a manner consistent with this
ordinance.
P. The proposed land subdivision, if approved, would not result
in a violation of federal or state law, or city or county
ordinance.
Q. The proposed land subdivision permit is consistent with any
approved and applicable General Development Plan,
Conditional Use Permit or Traffic Impact Study.
R. All lots within the floodplain districts are able to contain a
building site outside of the Floodway District at or above the
regulatory flood protection elevation.
S. For all subdivisions in the floodplain, the Floodway, Flood
Prone, and Flood Fringe District boundaries, the regulatory
flood protection elevation and the required elevation of all
access roads are clearly labeled on all required subdivision
drawings and platting documents.
T. All subdivisions must have road access both to the
subdivision and to the individual building sites no lower than
two feet below the regulatory flood protection elevation.
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U. Subdivision proposals must be reviewed to assure that:
(1) All such proposals are consistent with the need to
minimize flood damage with the floodplain area;
(2) All public utilities and facilities, such as sewer, gas,
electrical, and water systems, are located and
constructed to minimize or eliminate flood damage; and,
(3) Adequate drainage is provided to reduce exposure of
flood hazard.
Section 16. Section 62.800 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.800 FLOOD DISTRICTS AND INTENT:
Subdivision 1. The intent of the flood district regulations is to Guide
development in the flood hazard areas of Rochester consistent with the
flood threat, in order to minimize loss of life and property, disruption of
commerce and governmental services, extraordinary public expenditure
for public protection and relief, impairment of the tax base and interruption
of transportation and communication, all of which adversely affect the
public health, safety and general welfare. Flood hazard regulations are
intended to minimize losses and disruptions.
Subd. 2. The flood district regulations are adopted to comply with
the rules and regulations of the National Flood Insurance Program
codified as 44 Code of Federal Regulations Parts 59 -78, as amended, so
as to maintain the community’s eligibility in the National Flood Insurance
Program.
Subd. 3. The regulations are also intended to preserve the natural
characteristics and functions of watercourses and floodplains in order to
moderate flood and stormwater impacts, improve water quality, reduce
soil erosion, protect aquatic and riparian habitat, provide recreational
opportunities, provide aesthetic benefits and enhance community and
economic development.
Section 17. Section 62.810 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
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62.810 DESIGNATION
Subdivision 1. Each individual flood district represents a set of
regulations superimposed upon the existing zoning districts, superseding
existing underlying regulations only to the extent that developments must
meet the additional standards of this chapter as well as those of the
underlying district in order to be in compliance with this ordinance.
Subd. 2. The Flood Fringe District (FF), the Floodway District
(FW), and the Flood Prone District (FP) are identified upon the zoning
map, and reference to the status of any property located in one of the
flood related districts is made by the District symbol (FF, FW, or FP)
being postfixed to a use district symbol (examples R-l/FF, B-4/FW, M-
2/FP). (Refer to section 60.3501, Designation of Annexed Property.)
Subd. 3. To aid in the identification and designation of properties
in the flood related districts, certain materials are attached and hereby
adopted by reference and declared to be part of this ordinance. These
materials include the Flood Insurance Study for Olmsted County,
Minnesota, and Incorporated Areas, and the Flood Insurance Rate Map
for Olmsted County and Incorporated Areas, all dated April 19, 2017 and
prepared by the Federal Emergency Management Agency, including the
following panels:
A. 27109CO141F
B. 27109CO142F
C. 27109CO143E
D. 27109CO144F
E. 27109CO153F
F. 27109CO154F
G. 27109CO155E
H. 27109CO166F
I. 27109CO168F
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J. 27109CO169E
K. 27109CO282F
L. 27109CO301F
M. 27109CO302F
N. 27109CO304E
O. 27109CO158E
P. 27109CO161F
Q. 27109CO162F
R. 27109CO163F
S. 27109CO164F
T. 27109CO306F
U. 27109CO307E
V. 27109CO313E
Section 18. Section 62.811 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.811 Designation of Floodway District (FW): The provisions in
this chapter relating to the floodway district shall apply to all lands designated
as floodway on the Flood Insurance Rate Map adopted in section 62.810.
The Floodway District also includes those areas designated as Zone A (that
do not have a floodway designated on the Flood Insurance Rate Map. For
lakes, wetlands, and other basins, the Floodway District includes those areas
that are at or below the ordinary high water level as defined in Minn. Stat.
§103G.005, subd. 14.
Section 19. Section 62.812 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
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62.812 Designation of Flood Fringe District: The Flood Fringe
District includes those areas within Zone AE and designated as floodway
fringe, or within Zone AO on the Flood Insurance Rate Map adopted in this
section, and were within the corporate boundaries of the City prior to
November 3, 1980. For lakes, wetlands, and other basins (that do not have
a floodway designated), the Flood Fringe District includes those areas
designated as Zone AE on the Flood Insurance Rate Map panels adopted
in this section that are below the one percent annual chance (100-year)
flood elevation but above the ordinary high water level as defined in Minn.
Stat. §103G.005, subd. 14.
Section 20. Section 62.813 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.813 Designation of Flood Prone District (FP): The Flood Prone
District includes those areas designated as floodway fringe on the Flood
Insurance Rate Map adopted in this section, as being within Zone AE but
being located outside of the floodway, and were annexed on or after
November 3, 1980, except as determined by the provisions of section
60.3501.
Section 21. Section 62.815 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.815 Reclamation: Nothing herein shall be so construed as to
prohibit the lawful rehabilitation or reclamation of any lands outside of the
floodway, provided that no filling, draining, construction of levees or other
improvements intended to eliminate or reduce the danger of the flood or
erosion shall be commenced until first reviewed and authorized by the
zoning administrator and the Commissioner, and, if revisions to floodplain
maps or designations are proposed, by the Federal Emergency
Management Agency.
Section 22. Section 62.830 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.830 USES PERMITTED
The regulations within this article establish those uses which are
permitted in each of the flood districts, subject to the further restriction
that any use contemplated shall also be permitted in the underlying
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zoning district. It shall be a misdemeanor for any person to establish a
use in a flood district which is not otherwise permitted in that district by
the following sections, or which is not permitted in the underlying zoning
district, and for any person to do any grading or filling in the flood plain
without first obtaining all necessary permits and approvals.
Section 23. Section 62.831 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.831 Permitted Uses, Floodway and Flood Prone Districts.
Subdivision 1. Permitted uses are those listed in subdivisions 2 through 6
which have a low flood damage potential and do not obstruct flood flows.
These uses are permitted within the Floodway and Flood Prone Districts
to the extent that they are not prohibited by the underlying zoning district
or any other ordinance and provided they do not require structures, fill, or
storage of materials or equipment except as permitted in section 62.800.
In addition, no use shall adversely affect the capacity of the channel or
floodways of any tributary to the main stream, or of any drainage ditch or
other drainage facility.
Subd. 2. Agricultural uses such as: general farming, pasture,
grazing, outdoor plant nurseries, horticulture, truck farming, forestry, sod
farming, and wild crop harvesting.
Subd. 3. Industrial-commercial uses such as: loading areas,
parking areas, billboards, airport landing strips.
Subd. 4. Private and public recreational uses such as: golf
courses, tennis courts, driving ranges, picnic grounds, boat launching ramps,
swimming area, parks, wildlife and nature preserves, fishing areas,
recreational trails.
Subd. 5. Channel modifications requiring a DNR permit where
there is no change in the flood profile.
Subd. 6. Any facility that will be used by employees or the
general public must be designed with a flood warning system that
provides adequate time for evacuation if the area is inundated to a depth
and velocity such that the depth (in feet) multiplied by the velocity (in feet
per second) would exceed a product of four upon occurrence of the
regional (1% chance) flood.
19
Section 24. Section 62.832 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.832 Uses in the Flood Fringe District: Uses permitted or
conditionally permitted in the Flood Fringe District are the same as those
identified in the underlying zoning district, subject to meeting the
construction standards established for the Flood Fringe District in section
62.840.
Section 25. Section 62.833 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.833 Conditional Uses, Floodway District: Subdivision 1. The
uses listed in subdivisions 2 through 6 involving structures (temporary or
permanent), fill, or the storage of materials or equipment, are permitted in the
Floodway District only after the issuance of a Type III conditional use Permit
as provide for in section 62.820.
Subd. 2. Structures accessory to open space or conditional uses,
in accordance with section 62.852.
Subd. 3. Placement of fill in accordance with section 62.851.
Subd. 4. Extraction of sand, gravel, and other minerals.
Subd. 5. Marinas, boat rentals, docks, and water control
structures.
Subd. 6. Railroads, streets, bridges, utility transmission lines and
pipelines, provided that the Department of Natural Resources’ Area
Hydrologist is notified at least ten days prior to issuance of any permit.
Section 26. Section 62.841 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.841 Standard for Principal Buildings. Subdivision 1. The
standards listed in subdivisions 2 through 5 shall apply to the construction of
principal buildings in the Flood Fringe District:
Subd. 2. Dwellings: New dwellings shall be constructed on fill
so that the lowest floor (including basement) is at or above the flood
20
protection elevation. The finished fill elevation shall be no lower than one
foot below the flood protection elevation and shall extend at such
elevation at least 15 feet beyond the limits of any structure or building
thereon. Residences that do not have vehicular access at or above an
elevation not more than two feet below the flood protection elevation shall
not be permitted. If a variance to the access requirement is granted, the
Board of Appeals must specify limitations on the period of use or
occupancy of the structure for times of flooding and only after determining
that adequate flood warning time and local flood emergency response
procedures exist.
Subd. 3. Dwellings in the AO Zone: New dwellings shall be
constructed on fill so that the lowest floor (including basement) is elevated
above the highest adjacent grade at least as high as the depth number
specified in feet on the Rochester Flood Insurance Rate Map. The
finished fill elevation shall extend at such elevation at least 15 feet
beyond the limits of any structure or building thereon. There must be
adequate drainage paths around structures on slopes to guide
floodwaters around and away from existing or proposed structures or
additions.
Subd. 4. Non-Residential Uses: New structures shall be
elevated so that their first floor (including basement) is at or above the flood
protection elevation. The finished fill elevation shall be no lower than one
foot below the flood protection elevation.
Subd. 5. Non-Residential Uses in the AO Zone: New
structures shall be constructed on fill so that the lowest floor (including
basement) is elevated above the highest adjacent grade at least as high
as the depth number specified in feet on the Rochester Flood Insurance
Rate Maps, or together with attendant utility and sanitary facilities be
completely Floodproofed in accordance with the State Building Code to
the FP-l or FP-2 classification without the utilization of dikes, dams or
levee. There must be adequate drainage paths around structures on
slopes to guide floodwaters around and away from existing or proposed
structures or additions.
Section 27. Section 62.842 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.842 Standards for Public Works. Subdivision 1. The standards
21
in this section shall apply to the construction of new public works in the Flood
Fringe District.
Subd. 2. Waste Treatment, Waste Disposal and Flood
Control Structures: No new construction, addition, or modification to
existing waste treatment facilities shall be permitted within the Flood Fringe
unless emergency plans and procedures for action to be taken in the event of
flooding are prepared, filed with, and approved by the Minnesota Pollution
Control Agency. The emergency plans and procedures must provide for
measures to prevent introduction of any pollutant or toxic material into the
flood waters.
Subd. 3. Utilities, Railroad Tracks, Streets and Bridges.
Public utility facilities, roads, railroad tracks, and bridges within the Flood
Fringe District shall be designed to minimize increase in flood elevations and
shall be compatible with local comprehensive flood plain development plans.
A. Protection to the flood protection elevation shall be provided
where failure or interruption of these public facilities would
result in danger to the public health or safety or where such
facilities are essential to the orderly functioning of the area.
B. Where failure or interruption of services would not endanger
life or health, a lesser degree of protection may be provided for
minor or auxiliary roads, railroads, or utilities.
Section 28. Section 62.843 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.843 Standards for Accessory Uses and Structures. Subdivision
1. The standards listed in subdivisions 2 and 3 shall apply to the
construction of accessory structures and the use of land for accessory
purposes:
Subd. 2. Accessory Structures: Such structures shall be
constructed on fill so that the lowest floor is at or above the flood protection
elevation or may be permitted below the flood protection elevation provided
that such structures are:
A. Not designed for human habitation;
22
B. Designed to have low flood drainage potential;
C. Constructed and placed on the building site so as to offer the
minimum resistance to the flood or floodwaters;
D. As an alternative to elevation on fill, accessory structures
that constitute a minimal investment and that do not exceed
500 square feet for the outside dimension at ground level
may be internally Floodproofed to the FP-3 or FP-4
standards in accordance with the State Building Code. To
meet this requirement, detached garages must be used
solely for parking of vehicles and limited storage. All such
structures must meet the following standards:
(1) To allow for the equalization of hydrostatic pressure,
there must be a minimum of two “automatic” openings
in the outside walls of the structure, with a total net
area of not less than one square inch for every
square foot of enclosed area subject to flooding;
(2) There must be openings on at least two sides of the
structure and the bottom of all openings must be no
higher than one foot above the lowest adjacent grade
to the structure. Using human intervention to open a
garage door prior to flooding will not satisfy this
requirement for automatic openings;
(3) The structure must be adequately anchored to
prevent flotation, collapse or lateral movement of the
structure and shall be designed to equalize
hydrostatic flood forces on exterior walls; and,
(4) Any mechanical and utility equipment in a structure
must be elevated to or above the Regulatory Flood
Protection Elevation or properly Floodproofed.
Subd. 3. Storage of Materials: The storage or processing of
materials that are, in time of flooding, flammable, explosive, or potentialloy
injurious to human, animal, or plant life is prohibited. Storage of other
materials or equipment may be allowed if readily removable from the area
within the time available after a flood warning and in accordance with a plan
approved by the zoning administrator.
23
Subd. 4. Accessory Land Uses: Accessory land uses for non-
residential uses, such as storage yards and parking lots, that are at
elevations below the flood protection elevation shall not be permitted
without a flood warning system that provides adequate time for
evacuation of the area if the area is inundated to a depth and velocity
such that the depth (in feet) multiplied by the velocity (in feet per second)
would exceed a product of four upon occurrence of the regional (1%
chance) flood.
Section 29. Section 62.844 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.844 Alternate Construction Standards. Subdivision 1. Alternate
standards for the construction of residential and non-residential uses are
permitted as follows:
Subd. 2. Residential Uses: Where existing streets, utilities, or
small lot size preclude the use of fill, other methods of elevating the first
flood (including basement) above the flood protection elevation may be
authorized by the issuance of a Type III Conditional Use Permit in
accordance with sections 61.140 and 62.820. These alternative methods
may include the use of stilts, pilings, parallel walls, etc., or above-grade
enclosed areas such as crawl spaces or tuck-under garages. The base
or floor of an enclosed area shall be considered above-grade and not a
structure’s basement or lowest floor if: 1) the enclosed area is above-
grade on at least one side of the structure; 2) it is designed to internally
flood and is constructed with flood resistant materials; and 3) it is used
solely for parking of vehicles, building access or storage. The above-
noted alternative elevation methods are subject to the following additional
standards:
A. The structure’s design and as-built condition must be
certified by a registered professional engineer or architect
as being in compliance with the general design standards of
the State Building Code and, specifically, that all electrical,
heating, ventilation, plumbing and air-conditioning
equipment and other service facilities must be at or above
the Regulatory Flood Protection Elevation or be designed to
prevent flood water from entering or accumulating within
these components during times of flooding.
24
B. Above-grade, fully enclosed areas such as crawl spaces or
tuck-under garages must be designed to internally flood and
the design must stipulate:
(1) The minimum area of openings in the walls where
internal flooding is to be used as a Floodproofing
technique. There shall be a minimum of two openings
on at least two sides of the structure and the bottom
of all openings shall be no higher than one foot above
grade. The automatic openings shall have a
minimum net area of not less than one square inch
for every square foot of enclosed area subject to
flooding unless a registered professional engineer or
architect certifies that a smaller net area would
suffice. When openings are placed in a structure’s
walls to provide for entry of flood waters to equalize
pressures, the bottom of all openings shall be no
higher than one foot above grade. Openings may be
equipped with screens, louvers, valves, or other
coverings or devises provided that they permit the
automatic entry and exit of flood waters without any
form of human intervention.
(2) The enclosed area will be designed of flood resistant
materials in accordance with FP-3 or FP-4
classifications in the State Building Code and shall be
used solely for building access, parking of vehicles or
storage.
Subd. 3. Non-Residential Uses: All areas of non-residential
structures, including basements, to be placed below the Regulatory Flood
Protection Elevation shall be Floodproofed in accordance with the
structurally dry Floodproofing classifications in the State Building Code.
Structurally dry Floodproofing must meet the FP-1 or FP-2 Floodproofing
classification in the State Building Code, without the use of dikes, dams or
levees, and this shall require making the structure watertight with the
walls substantially impermeable to the passage of water and with
structural components having the capability of resisting hydrostatic and
hydrodynamic loads and the effects of buoyancy. Structures
Floodproofed to the FP-3 or FP-4 standards shall not be permitted.
Whenever the zoning administrator determines that a particular use may
constitute an unusual hazard in the flood fringe, he may require the
25
issuance of a Type III conditional use permit as provided in section
62.820.
Section 30. Section 62.846 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.846 Additional Development Standards. Subdivision 1. The
standards in this section shall apply to the uses indicated. These standards
are imposed in addition to any other applicable standards in section 62.840.
Subd. 2. Manufacturing and Industrial Uses: Manufacturing
and industrial buildings, structures and appurtenant works shall be
protected to the flood protection elevation. Measures shall be taken to
minimize interference with normal plant operations, especially for streams
having prolonged flood durations. In considering permit applications, due
consideration shall be given to needs of an industry whose business
requires that it be located in Floodplain areas.
Subd. 3. Fill:
A. Fill shall be properly compacted and the slopes shall be
properly protected by the use of riprap, vegetative cover, or
other acceptable method. Permanent sand and gravel
operations and similar uses must be covered by a long term
site development plan as approved under other provisions of
this ordinance. The cumulative placement of fill where at any
one time in excess of 1,000 cubic yards of fill is located on the
parcel shall be allowable only as a conditional use unless the
fill is specifically intended to elevate a structure in accordance
with section 62.840.
B. When at any time more than 1,000 cubic yards of fill or other
similar material is located on a parcel for such activities as
on-site storage, landscaping, sand and gravel operations,
landfills, roads, dredge spoil disposal or construction of
flood control works, an erosion/sedimentation control plan
must be submitted unless the community is enforcing a state
approved shoreland management ordinance. In the
absence of a state approved shoreland management
ordinance, the plan must clearly specify methods to be used
to stabilize the fill on site for a flood event at a minimum of
the 100 year or regional flood event. The plan must be
26
prepared and certified by a registered professional engineer
or other qualified individual acceptable to the zoning
administrator. The plan may incorporate alternative
procedures for removal of the material from the flood plain if
adequate flood warning time exists.
Section 31. Section 62.847 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.847 Garbage and Solid Waste Disposal. There shall be no
disposal of garbage or solid waste materials within Flood Fringe areas.
No conditional use permits for garbage and waste disposal sites shall be
issued for Flood Fringe District. There shall be no further encroachment
upon the floodplain at existing sites.
27
Section 32. Section 62.850 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.850 CONSTRUCTION STANDARDS IN THE FLOODWAY DISTRICT
No structures (temporary or permanent); No fill, including fill for roads and
levees; No deposits, obstructions, storage of materials or equipment; or
No other uses allowed as Type III Conditional Uses which, acting alone or
in combination with existing or future uses, cause any increase in the
stage of the 1% chance or regional flood or cause an increase in flood
damages in the reach or reaches affected, shall be permitted.
Consideration of the effects of a proposed use shall be based on a
reasonable assumption that there will be an equal degree of
encroachment extending for a significant reach on both sides of the
stream. In addition, all floodway conditional uses shall be subject to the
regulations in the following sections.
Section 33. Section 62.851 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.851 Fill: Any fill deposited in the floodway shall be no more than
the minimum amount necessary to conduct a Type III Conditional Use
listed in section 62.833. Generally, fill shall be limited to that needed to
grade or landscape for that use and shall not in any way obstruct the flow
of flood waters or cause any increase in flood elevations. Such fill or other
material shall be protected against erosion by rip-rap, vegetative cover or
bulkheading. Dredge spoil sites and sand and gravel operations shall not
be allowed in the floodway unless a long term site development plan is
submitted which includes an erosion/sedimentation prevention element to
the plan.
Section 34. Section 62.852 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.852 Structures: Subdivision 1. Accessory structures (temporary
or permanent) permitted as conditional uses by section 62.833 shall be
subject to the following standards:
A. Not designed for human habitation;
B. Designed to have low flood damage potential; and,
28
C. Constructed and placed on the building site so as to offer the
minimum resistance to the flood or floodwaters:
(1) Whenever possible, structure shall be constructed with
the longitudinal axis parallel to the direction of flood
flow; and,
(2) So far as practicable, structures shall be placed
approximately on the same flood flow lines of those of
adjoining structures.
Subd. 2. Accessory structures shall be structurally dry
Floodproofed in accordance with FP-1 or FP-2 Floodproofing classifications
in the State Building Code. All Floodproofed accessory structures must meet
the following additional standards as appropriate:
A. The structure must be adequately anchored to prevent
flotation, collapse, or lateral movement of the structure
and shall be designed to equalize hydrostatic flood
forces on exterior walls.
B. Any mechanical and utility equipment in a structure
must be elevated to or above the Regulatory Flood
Protection Elevation or properly Floodproofed.
Subd. 3. As an alternative, an accessory structure may be
internally/wet Floodproofed to the FP3 or FP4 Floodproofing
classifications in the State Building Code provided the accessory
structure constitutes a minimal investment and that does not exceed 500
square feet for the outside dimension at ground level. Designs for
meeting this requirement must either be certified by a registered
professional engineer or meet or exceed the standards of subdivision 2
and also the following criteria. To meet this requirement, detached
garages must be used solely for parking of vehicles and limited storage.
Subd. 4. To allow for the equalization of hydrostatic pressure,
there must be a minimum of two “automatic” openings in the outside walls
of the structure, with a total net area of not less than one square inch for
every square foot of enclosed area subject to flooding; and,
Subd. 5. There must be openings on at least two sides of the
structure and the bottom of all openings must be no higher than one foot
29
above the lowest adjacent grade to the structure. Using human
intervention to open a garage door prior to flooding will not satisfy this
requirement for automatic openings.
Section 35. Section 62.853 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.853 Utilities, Railroad Tracks, Streets, and Bridges. Public
utility facilities, roads, railroad tracks, and bridges within the floodway
district shall be designed to minimize increases in flood elevations and
shall be compatible with local comprehensive flood plain development
plans. Such facilities must comply with section 62.850. Protection to the
flood protection elevation shall be provided where failure or interruption of
these public facilities are essential to the orderly functioning of the area.
Where failures or interruption of service would not endanger life or health,
a lesser degree of protection may be provided for minor or auxiliary roads,
railroads or utilities.
Section 36. Section 62.871 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.871 Manufactured Home Parks and Subdivisions. New
manufactured home parks and expansions to existing mobile/manufactured
home parks are prohibited in any Floodplain district.
Section 37. Section 62.872 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.872 Placement: Subdivision 1. Placement or replacement of
manufactured home units is prohibited in the Floodway District. In the
Flood Fringe and Flood Prone Districts, placement or replacement of new
or replacement manufactured homes in existing manufactured home
parks or on individual lots of record will be treated as new structures and
may be placed only if in compliance with section 62.800.
Subd. 2. All manufactured homes must be securely anchored
to an adequately anchored foundation system that resist flotation,
collapse and lateral movement. Methods of anchoring may include, but
are not to be limited to, use of over-the-top or frame ties to ground
anchors. This requirement is in addition to applicable state or local
anchoring requirements for resisting wind forces.
30
Subd. 3. If vehicular road access for preexisting manufactured
home parks is not provided in accordance with section 64.123, then
replacement manufactured homes will not be allowed until the property
owner(s) develops a flood warning emergency plan acceptable to the
zoning administrator.
Section 38. Section 62.873 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.873 Recreational Vehicles. Subdivision 1. New recreational
vehicle parks or campgrounds and expansions to existing recreational
vehicle parks or campgrounds are prohibited in any Floodplain district.
Placement of recreational vehicles in existing recreational vehicle parks
or campgrounds in the Floodplain must meet the exemption criteria in
subdivision 2 or be subject to section 62.874.
Subd. 2. Recreational vehicles are exempt from the provisions of this
section if they are placed in an existing recreational vehicle park or
campground and, further, they meet all of the following criteria:
A. Have a current license required for highway use.
B. Are highway ready meaning on wheels or the internal
jacking system are attached to the site only by quick
disconnect type utilities commonly used in campgrounds
and recreational vehicle parks, and the vehicle has no
permanent structural type additions attached to it.
C. The vehicle and associated use must be permissible in any
preexisting, underlying zoning district.
D. Accessory structures are not permitted within the Floodway
District. Any accessory structure in the Flood Fringe and
Flood Prone Districts must be constructed of flood-resistant
materials and be securely anchored, meeting the
requirements applicable to manufactured homes in section
62.872.
Section 39. Section 62.874 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
62.874 Additional Development. Recreational vehicles exempted
31
in section 62.873 lose this exemption when development occurs on the
parcel exceeding $500 for a structural addition to the vehicle or an
accessory structure such as a garage or storage building. The vehicle
and all additions and accessory structures will then be treated as a new
structure and shall be subject to the elevation/Floodproofing requirements
and the use of land restrictions specified in section 62.800.
Section 40. Section 65.440 of the Rochester Code of Ordinances is hereby
amended and reenacted to read as follows:
65.440 NONCONFORMING STRUCTURE CREATED BY FLOOD
DISTRICT REGULATION:
Subdivision 1. A lawful nonconforming use, structure or occupancy
created by flood district regulations may be continued in the same manner
as other nonconformities subject to the following additional standards that
are necessary to protect the public health, welfare or society. Historic
Structures are subject to the provisions of clauses A through I of this
subdivision.
A. A nonconforming use, structure, or occupancy must not be
expanded, changed, enlarged, or altered in a way that
increases its nonconformity. Expansion or enlargement of
uses, structures or occupancies within the Floodway District
is prohibited.
B. Any structural alteration or addition to a nonconforming
structure or nonconforming use which would result in
increasing the flood damage potential of that structure or
use must be protected to the regulatory flood protection
elevation in accordance with any of the elevation on fill or
Floodproofing techniques (i.e., FP-1 thru FP-4
Floodproofing classifications) allowable in the State Building
Code, except as further restricted in clauses C and D.
C. Whenever any alteration, addition or repair to a
nonconforming structure exceeds 50 percent of its current
market value as determined from the records of the Olmsted
County Assessor, the entire structure shall be made to
conform to all applicable flood plain regulations. This
requirement shall also apply at such time the cumulative
effect of all additions, alterations or major repairs since the
32
date the structure became nonconforming exceed 50
percent of the current market value.
D. The alteration, addition or repair to a nonconforming
structure, when the value of such work does not exceed 50
percent of its current market value as determined from the
records of the Olmsted County Assessor, shall not increase
the flood damage potential of the use or structure. Repair of
a nonconforming structure, if located in the floodway, shall
not increase the degree of obstruction to the flood flow.
E. If any nonconforming use, or any use of a nonconforming
structure, is discontinued for more than one year, any future
use of the premises must conform to this ordinance.
F. If any nonconformity incurs Substantial Damage, it may not
be reconstructed except in conformity with the provisions of
this ordinance. The applicable provisions for establishing
new uses or new structures will apply depending upon
whether the use or structure is in the Floodway, Flood
Fringe or Flood Prone Districts, respectively.
G. If any nonconforming use or structure experiences a Repetitive
Loss, it must not be reconstructed except in conformity with the
provisions of this ordinance.
H. Any Substantial Improvement to a nonconforming structure
requires that the existing structure and any additions must
meet the requirements of this ordinance for new structures.
Section 41. Sections 60.110, subdivision 3 of section 60.410, and sections
62.801, 62.802, 62.803, 62.812, 62.814, 62.816, 62.820, 62.856, 62.860, 62.875, 62.880,
62.881, 62.882, and 62.883 are hereby repealed.
Section 42. This ordinance shall become effective as of the date of its publication.
33
PASSED AND ADOPTED BY THE COMMON COUNCIL OF THE CITY OF
ROCHESTER, MINNESOTA, THIS ________ DAY OF _______________, 2017.
___________________________________
PRESIDENT OF SAID COMMON COUNCIL
ATTEST: __________________________
CITY CLERK
APPROVED THIS _______ DAY OF _________________, 2017.
___________________________________
MAYOR OF SAID CITY
(Seal of the City of
Rochester, Minnesota)
Ord15/FloodplainAmds
34
OLMSTED COUNTY,
MINNESOTA
AND INCORPORATED AREAS
Community Community
Name Number
*BYRON, CITY OF 270751
CHATFIELD, CITY OF 270125
DOVER, CITY OF 270566
EYOTA, CITY OF 270329
OLMSTED COUNTY 270626
(UNINCORPORATED AREAS)
ORONOCO, CITY OF 270330
PINE ISLAND, CITY OF 270145
ROCHESTER, CITY OF 275246
STEWARTVILLE, CITY OF 270332
*NO SPECIAL FLOOD HAZARD AREAS IDENTIFIED
FLOOD INSURANCE STUDY NUMBER
27109CV000A
Revised: April 19, 2017
OLMSTED COUNTY
NOTICE TO
FLOOD INSURANCE STUDY USERS
Communities participating in the National Flood Insurance Program have
established repositories of flood hazard data for floodplain management and flood
insurance purposes. This Flood Insurance Study (FIS) report may not contain all
data available within the Community Map Repository. Please contact the
Community Map Repository for any additional data.
The Federal Emergency Management Agency (FEMA) may revise and republish
part or all of this FIS report at any time. In addition, FEMA may revise part of
this FIS report by the Letter of Map Revision process, which does not involve
republication or redistribution of the FIS report. Therefore, users should consult
with community officials and check the Community Map Repository to obtain the
most current FIS report components.
Initial Countywide FIS Effective Date: April 17, 1995
Revised Countywide Date: February 4, 1998
April 19, 2017
i
TABLE OF CONTENTS
1.0 INTRODUCTION ................................................................................................................ 1
1.1 Purpose of Study ............................................................................................................. 1
1.2 Authority and Acknowledgments ................................................................................... 2
1.3 Coordination ................................................................................................................... 4
2.0 AREA STUDIED .................................................................................................................. 6
2.1 Scope of Study ................................................................................................................ 6
2.2 Community Description ................................................................................................ 12
2.3 Principal Flood Problems .............................................................................................. 14
2.4 Flood Protection Measures ........................................................................................... 19
3.0 ENGINEERING METHODS ............................................................................................ 21
3.1 Hydrologic Analyses ..................................................................................................... 21
3.2 Hydraulic Analyses ....................................................................................................... 36
3.3 Vertical Datum .............................................................................................................. 50
4.0 FLOODPLAIN MANAGEMENT APPLICATIONS ..................................................... 51
4.1 Floodplain Boundaries .................................................................................................. 51
4.2 Floodways ..................................................................................................................... 53
5.0 INSURANCE APPLICATIONS ....................................................................................... 85
6.0 FLOOD INSURANCE RATE MAP ................................................................................. 86
7.0 OTHER STUDIES .............................................................................................................. 88
8.0 LOCATION OF DATA ...................................................................................................... 88
9.0 BIBLIOGRAPHY AND REFERENCES ......................................................................... 88
ii
FIGURES
Figure 1 - Floodway Schematic ........................................................................................................ 85
TABLES
Table 1 – Streams Studied by Detailed Methods for the Initial Countywide FIS .............................. 7
Table 2 – Streams Revised for the February 4, 1998, Revision ......................................................... 8
Table 3 – Streams Studied by Detailed Methods in this Revision ...................................................... 9
Table 4 – Summary of Discharges .................................................................................................... 33
Table 5 – Summary of Stillwater Elevations .................................................................................... 36
Table 6 – Summary of Roughness Coefficients ............................................................................... 49
Table 7 – Vertical Datum Conversion .............................................................................................. 50
Table 8 – Floodway Data .................................................................................................................. 54
Table 9 – Community Map History .................................................................................................. 87
EXHIBITS
Exhibit 1 - Flood Profiles
Badger Run Panels 01P-03P
Bear Creek Panels 04P-10P
Carey Creek Panel 11P
Cascade Creek Panels 12P-14P
East Fork of Willow Creek Panel 15P
Hadley Valley Creek Panels 16P-17P
Hadley Valley Creek Split Flow Panel 18P
Middle Fork Zumbro River Panels 19P-20P
Mill Creek Panel 21P-22P
North Branch Root River Panels 23P-25P
North Run of the North Fork of Cascade Creek Panels 26P-28P
Silver Creek Panels 29P-33P
South Branch Middle Fork Zumbro River Panel 34P
South Fork of Bear Creek Panels 35P-36P
South Fork of Willow Creek Panel 37P
South Fork Whitewater River Panels 38P-39P
South Fork Zumbro River Panels 40P-44P
South Run of the North Fork of Cascade Creek Panels 45P-47P
Southeast Branch of Willow Creek Panel 48P
Tributary B Panel 49P
West Fork of Willow Creek Panel 50P
West Tributary to Willow Creek Panel 51P
Willow Creek Panels 52P-54P
Exhibit 2 - Flood Insurance Rate Map Index
Flood Insurance Rate Map
1
FLOOD INSURANCE STUDY
OLMSTED COUNTY, MINNESOTA AND INCORPORATED AREAS
1.0 INTRODUCTION
1.1 Purpose of Study
This Flood Insurance Study (FIS) revises and updates information on the
existence and severity of flood hazards in the geographic area of Olmsted
County, including the Cities of Byron, Chatfield, Dover, Eyota, Oronco, Pine
Island, Rochester, and Stewartville, and the unincorporated areas of Olmsted
County (referred to collectively herein as Olmsted County), and aids in the
administration of the National Flood Insurance Act of 1968 and the Flood
Disaster Protection Act of 1973. This study has developed flood-risk data for
various areas of the community that will be used to establish actuarial flood
insurance rates and to assist the community in its efforts to promote sound
floodplain management. Minimum floodplain management requirements for
participation in the National Flood Insurance Program (NFIP) are set forth in the
Code of Federal Regulations at 44 CFR, 60.3.
Please note that the City of Chatfield is geographically located in Olmsted and
Fillmore Counties, and the City of Pine Island is geographically located in
Olmsted and Goodhue Counties. See the separately published FIS report and
Flood Insurance Rate Map (FIRM) for flood-hazard information.
Please note that the City of Byron is located on the watershed divide of Cascade
Creek and the South Branch Middle Fork Zumbro River and has no mapped
special flood hazard areas. This does not preclude future determinations of
SFHAs that could be necessitated by changed conditions affecting the
community (i.e., annexation of new lands) or the availability of new scientific or
technical data about flood hazards.
In some states or communities, floodplain management criteria or regulations
may exist that are more restrictive or comprehensive than the minimum Federal
requirements. In such cases, the more restrictive criteria take precedence and the
State (or other jurisdictional agency) will be able to explain them.
The Digital Flood Insurance Rate Map (DFIRM) and FIS report for this
countywide study have been produced in digital format. Flood hazard
information was converted to meet the Federal Emergency Management Agency
(FEMA) DFIRM database specifications and Geographic Information System
(GIS) format requirements. The flood hazard information was created and is
provided in a digital format so that it can be incorporated into a local GIS and be
accessed more easily by the community.
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1.2 Authority and Acknowledgments
The sources of authority for this FIS are the National Flood Insurance Act of
1968 and the Flood Disaster Protection Act of 1973.
Precountywide Analyses
Information on the authority and acknowledgements for each jurisdiction
included in this countywide FIS, as compiled from their previously printed FIS
reports, is shown below:
Chatfield, City of: The hydrologic and hydraulic analyses for the
FIS report dated February 2, 1982, were
prepared by Toltz, King, Duvall, Anderson, and
Associates, Inc., for FEMA, under Contract No.
H-4706. That work was completed in March
1981 (FEMA, 1982a).
Dover, City of: The hydrologic and hydraulic analyses for the
FIS report dated October 15, 1981, were
prepared by Toltz, King, Duvall, Anderson, and
Associates, Inc., for FEMA, under Contract No.
H-4706. That work was completed in July 1980
(FEMA, 1981a).
Eyota, City of The hydrologic and hydraulic analyses for the
FIS report dated June 15, 1981, were prepared
by Toltz, King, Duvall, Anderson, and
Associates, Inc., for the Federal Insurance
Administration (FIA) under Contract No. H-
4706. That work was completed in May 1980
(FIA, 1981).
Olmsted County
(Unincorporated Areas):
The hydrologic and hydraulic analyses for the
FIS report dated November 19, 1980, were
prepared by Barr Engineering Company, for the
FIA, under Inter-Agency Agreement No. IAA-
H-9-77, Project Order No. 19, Amendment No.
1. That work was completed in February 1980
(FEMA, 1980b).
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Oronco, City of The hydrologic and hydraulic analyses for the
FIS report dated May 4, 1981, were prepared by
the U.S. Geological Survey (USGS), Water
Resources Division, for the FIA, under Inter-
Agency Agreement No. IAA-H-9-77, Project
Order No. 19, Amendment No. 1. That work
was completed in February 1980 (FEMA,
1981b).
Pine Island, City of For the September 2, 1980, FIS report and
March 2, 1981 FIRM, the hydrologic and
hydraulic analyses for the original study were
prepared by Edwards and Kelsey Inc. for the
FIA under Contract No. H-4540. That work was
completed in March 1979 (FEMA, 1980a).
For the February 16, 1994, FIS revision, the
hydrologic and hydraulic analyses were
prepared by the U.S. Army Corps of Engineers
(USACE), St. Paul District for FEMA under
Inter-Agency Agreement No. EMW-90-E-3286,
Project Order No. 3. This work was completed
in January 1992 (FEMA, 1994).
Rochester, City of The hydrologic and hydraulic analyses for the
original FIS report dated August 4, 1980, were
prepared by Barr Engineering Company, for the
FIA, under Contract No. H-3799. That work
was completed in November 1977. The
hydraulic analysis for the FIS report dated
August 4, 1987, was prepared by Barr
Engineering Company (FEMA, 1987).
Stewartville, City of
The hydrologic and hydraulic analyses for the
FIS report dated March 2, 1982, were prepared
by Toltz, King, Duvall, Anderson, and
Associates, Inc., for FEMA, under Contract No.
H-4706. That work was completed in March
1981 (FEMA, 1982b).
The City of Byron has no previously printed FIS report.
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April 17, 1995
Initial Countywide FIS Report
For the April 17, 1995, FIS, the updated hydrologic and hydraulic analyses were
prepared by the USACE, St. Paul District, for the City of Rochester and were
coordinated with FEMA. This work was completed in March 1993. Portions of
approximate flood hazard boundaries were delineated by Dewberry & Davis
under agreement with FEMA.
February 4, 1998
Countywide FIS Report
For the February 4, 1998, countywide revision, the hydrologic and hydraulic
analyses for Bear Creek, Cascade Creek, North Run of the North Fork of Cascade
Creek, South Run of the North Fork of Cascade Creek, the South Fork Zumbro
River, and Willow Creek were updated to reflect the completion of the Rochester
Flood Control Project. These analyses were prepared by the USACE, St. Paul
District, and were completed in September 1995.
This Countywide FIS Report
For this revision, the hydrologic and hydraulic analyses for Badger Run, Carey
Creek, Hadley Valley Creek, Hadley Valley Creek Split Flow, Mill Creek, North
Branch Root River, Silver Creek, and South Fork Whitewater River were
performed by Barr Engineering Company, for FEMA, under Contract No. EMC-
2005-GR-7024, Project Order No. 2. The work was completed in June 2008.
The hydrologic and hydraulic analysis for Mill Creek was performed by Atkins,
for FEMA, under Contract No. EMC-2005-GR-7024, Project Order No. 2. The
work was completed on May 25, 2011.
Base map information shown on the FIRM was provided in digital format by
Farm Services Administration. This information was photogrammetrically
compiled at a scale of 1:12,000 from aerial photography dated 2011 or later. The
projection used in the preparation of this map is Universal Transverse Mercator
(UTM) Zone 15, and the horizontal datum used is the North American Datum of
1983 (NAD83), GRS80 Spheroid.
1.3 Coordination
An initial meeting is held with representatives from FEMA, the community, and
the study contractor to explain the nature and purpose of a FIS, and to identify the
streams to be studied or restudied. A final meeting is held with representatives
from FEMA, the community, and the study contractor to review the results of the
study.
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Precountywide Analyses
The initial and final meeting dates for previous FIS reports for Olmsted County
and its communities are listed in the following tabulation:
Community FIS Date Initial Meeting Final Meeting
Chatfield, City of February 2, 1982 May 1978 September 2, 1981
Dover, City of October 15, 1981 April 1978 April 28, 1981
Eyota, City of June 15, 1981 April 1978 January 20, 1981
Olmsted County
(Unincorporated
Areas)
November 19, 1980 March 1975 August 9, 1978
Oronoco, City of May 4, 1981 January 17, 1977 November 24, 1980
Pine Island, City of September 2, 1980
February 16, 1994
June 1, 1977
January 14, 1992
September 11, 1979
January 25, 1993
Rochester, City of August 4, 1980 July 1977 January 14, 1980
Stewartville, City of March 2, 1982 March 1978 August 31, 1981
April 17, 1995
Initial Countywide FIS Report
For the April 17, 1995, initial countywide FIS, a final meeting was held on July
21, 1994, and was attended by representatives of the county, USACE, and FEMA.
February 4, 1998
Countywide FIS Report
For the February 4, 1998, countywide revision, a floodway coordination meeting
was held on May 17, 1995, and was attended by representatives of the Minnesota
Department of Natural Resources (MNDNR), the USACE, and the City of
Rochester. At this meeting, the USACE presented preliminary study data and
floodway alignments for the streams that were restudied by detailed methods. In
addition, FEMA notified the City of Rochester by letter dated July 8, 1996, that a
revision was being prepared using the data provided by the USACE.
This Countywide FIS Report
For this countywide revision, the initial meeting was held on August 12, 2005, and
attended by representatives of FEMA, MNDNR, Olmsted County, and elected
officials from townships, cities and county government in Olmsted County.
The results of the study were reviewed at the final meeting held on April 17, 2013,
and attended by representatives of FEMA, MNDNR and STARR. All issues
and/or concerns raised at that meeting have been addressed.
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2.0 AREA STUDIED
2.1 Scope of Study
This FIS covers the geographic area of Olmsted County, Minnesota including the
incorporated communities listed in Section 1.1. The areas studied by detailed
methods were selected with priority given to all known flood hazards and areas of
projected development or proposed construction.
The following lakes and streams are studied by detailed methods in this FIS report:
Badger Run Ponding Area 3
Bear Creek Ponding Area 4
Carey Creek Silver Creek
Cascade Creek South Branch Middle Fork Zumbro River
East Fork of Willow Creek South Fork of Bear Creek
Hadley Valley Creek South Fork Whitewater River
Hadley Valley Creek Split Flow South Fork of Willow Creek
Middle Fork Zumbro River South Fork Zumbro River
Mill Creek South Run of the North Fork of Cascade Creek
North Branch Root River Southeast Branch of Willow Creek
North Run of the North Fork
of Cascade Creek
Tributary B
West Fork of Willow Creek
Ponding Area 1 West Tributary to Willow Creek
Ponding Area 2 Willow Creek
The limits of detailed study are indicated on the Flood Profiles (Exhibit 1) and on
the FIRM (Exhibit 2).
April 17, 1995
Initial Countywide FIS Report
In the April 17, 1995, initial Countywide FIS, the flooding sources listed in Table
1 were revised.
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Table 1 – Streams Studied by Detailed Methods for the Initial Countywide FIS
Bear Creek From its confluence with the South Fork
Zumbro River to a point approximately 200
feet upstream of the confluence of Willow
Creek
Cascade Creek From its confluence with the South Fork
Zumbro River to a point approximately 50 feet
downstream of County Highway 34
East Fork of Willow Creek From its confluence with Willow Creek to
County Highway 101/45th Street Southeast
Silver Creek
From its confluence with the South Fork
Zumbro River to the walking bridge in Quarry
Hill Nature Center (formerly known as Silver
Creek Road)
South Fork Zumbro River
From a point approximately 1.1 miles
downstream of 37th Street Northwest/County
Highway 22 to Mayowood Road
Southwest/County Highway 125
Willow Creek From its confluence with Bear Creek to a point
approximately 0.7 mile upstream of 11th
Avenue Southwest
In addition, backwater elevations for the following streams were revised to reflect
the updated hydraulic analysis for Willow Creek: South Fork of Willow Creek,
Southeast Branch of Willow Creek, West Fork of Willow Creek, and West
Tributary to Willow Creek.
In the April 17, 1995, FIS, portions of the following flooding sources were newly
studied by approximate methods: Dry Run Creek, the Middle Fork Zumbro River,
the North Branch Root River, the South Fork Whitewater River, the South Fork
Zumbro River, and Tributary B.
The April 17, 1995, FIS reflected annexations by the Cities of Eyota, Oronoco,
Rochester, and Stewartville and the unincorporated areas of Olmsted County as
well as updated boundaries for the Richard J. Dorer Memorial Hardwood State
Forest.
The April 17, 1995, FIS incorporated the determinations of Letters of Map
Revision (LOMRs) issued by FEMA, which are shown in the following
tabulation:
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Stream Name Community and Description Date of Letter
Cascade Creek City of Rochester
Revised hydraulic analyses and
topographic information
September 7, 1990
South Run of the
North Fork of
Cascade Creek
Unincorporated Areas
Channel improvements, fill
placement, and bridge relocation
on the ROMAC plant site
December 26, 1991
North Run of the
North Fork of
Cascade Creek
City of Rochester
Quest International property
July 21, 1994
Cascade Creek Split Flow was revised using the updated hydraulic analysis and
topographic information submitted for the September 7, 1990, LOMR for Cascade
Creek.
February 4, 1998
Countywide FIS Report
In the February 4, 1998, revision the flooding sources listed in Table 2 were
restudied.
Table 2 – Streams Revised for the February 4, 1998, FIS
Stream Name
Limits of Revised or New Detailed Study
Bear Creek From its confluence with the South Fork
Zumbro River to a point approximately 265
feet upstream of the confluence of Badger
Creek
Cascade Creek
From its confluence with the South Fork
Zumbro River to County Highway 104
North Run of the North Fork
of Cascade Creek
From its confluence with Cascade Creek to a
point approximately 0.93 mile upstream of
19th Street Northwest
South Fork Zumbro River
From a point approximately 10,490 feet
downstream of 37th Street Northwest/County
Highway 22 to a point just upstream of
Mayowood Road/County Highway 125
Table 2 – Streams Revised for the February 4, 1998, FIS (Continued)
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Stream Name
Limits of Revised or New Detailed Study
South Run of the North Fork
of Cascade Creek
From the confluence with Cascade Creek to a
point approximately 1.1 miles upstream of
Dakota, Minnesota, & Eastern (DME) Railroad
Willow Creek From its confluence with Bear Creek to 11th
Avenue Southwest/County Highway 147
Also in the 1998 revision, the Cascade Creek split flow delineation in the area of
U.S. Highway 52 was removed. Water surface elevations along Cascade Creek
were reduced to a point where flow in this area was no longer diverted.
This Countywide FIS Report
The rivers and streams listed in Table 3 were studied using detailed methods in
this countywide FIS report.
Table 3 – Streams Studied by Detailed Methods in this Revision
Stream Name
Limits of Revised or New Detailed Study
Badger Run From the confluence with Bear Creek to
County Highway 36 / 50th Avenue Southeast
Carey Creek From the confluence with the North Branch
Root River to approximately 350 feet
upstream of County Highway 6 / 6th Street
Southwest
Hadley Valley Creek From the crossing of East River Road to
approximately 1.4 miles upstream of the
crossing at Hadley Valley Road Northeast
Hadley Valley Creek Split
Flow
From the downstream confluence with
Hadley Valley Creek to the upstream
confluence with Hadley Valley Creek
Mill Creek From the Olmsted/Fillmore County Boundary
to approximately 1 mile upstream of
Pedestrian Bridge
North Branch Root River
From approximately 1 mile downstream of
County Highway 120 / 15th Avenue Northeast
to approximately 1.5 miles upstream of
confluence with Carey Creek
Table 3 – Streams Studied by Detailed Methods in this Revision (Continued)
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Stream Name
Limits of Revised or New Detailed Study
Silver Creek From the walking bridge in Quarry Hill
Nature Center in Rochester to approximately
1.68 miles upstream of Silver Creek Road
Northeast
South Fork Whitewater River From approximately 250 feet upstream of U.S.
Highway 14 to the confluence of Tributary B
For this countywide revision, the FIS report and FIRM were converted to
countywide format, and the flooding information for the entire county, including
both incorporated and unincorporated areas, is shown. Also, the vertical datum
was converted from the National Geodetic Vertical Datum of 1929 (NGVD) to
the North American Vertical Datum of 1988 (NAVD). In addition, the
Universal Transverse Mercator coordinates, previously referenced to the North
American Datum of 1927, are now referenced to the NAD83.
The following flooding sources in the county were studied by approximate
methods for this revision: South Branch Middle Fork Zumbro River, Middle
Fork Zumbro River, Tributary A, Mill Creek, North Branch Root River, and
South Fork Whitewater River.
The South Fork Zumbro River was studied by approximate methods for this
revision from approximately 1,660 feet downstream of 90th Road Northeast to
the Olmsted County boundary.
This work was performed by the MDNR in 2013 using the USACE’s Hydrologic
Engineering Center’s (HEC) River Analysis System (RAS), Version 4.1.0
computer software. Cross section data was obtained from the 3-meter resolution
Light Detection and Ranging (LiDAR). The area below the water surface was
ignored in the cross-section geometry. The analyses included road crossings with
high embankments, substantial bridge openings or with bridge details readily
available from the Minnesota Department of Transportation hydraulic data site.
All or portions of the following flooding sources in the county were studied by
approximate methods in previous revisions: Dry Run Creek, Plum Creek, Badger
Run, and Tributary B.
The South Fork Zumbro River was studied by approximate methods in previous
revisions from approximately 570 feet downstream of 55th Street Northeast, to
approximately 1,660 feet downstream of 90th Road Northeast.
Approximate analyses were used to study those areas having low development
potential or minimal flood hazards. The scope and methods of study were
proposed to and agreed upon by FEMA and Olmsted County.
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The following tabulation presents Letters of Map Change (LOMCs) incorporated
into this countywide study:
LOMC Case Number Date Issued Project Identifier
LOMR 97-05-265P 02/27/1998 South Fork of Willow Creek &
Willow Creek – 2,400 feet
downstream of U.S. Highway
63 to U.S. Highway 63
LOMR 98-05-313P 02/11/1999 South Fork Zumbro River –
Bamber Valley Road
Southwest to Mayowood Road
LOMR 01-05-746P 07/18/2002 West Tributary to Willow
Creek & Willow Creek
LOMR 03-05-3988P 02/23/2004 North Run of the North Fork of
Cascade Creek-
Circle 19 Plaza
LOMR 05-05-1147P 07/28/2005 North Run of the North Fork of
Cascade Creek-
West 19th Development, LLC
LOMR 05-05-1180P 09/22/2005 Cascade Creek & South Run
of the North Fork of Cascade
Creek – Manorwoods Lake
Development
LOMR 06-05-BR73P 10/30/2006 Southeast Branch of Willow
Creek – Waterfront Business
Park/Southern Woods
Commercial Area
LOMR 06-05-B433P 02/14/2007 Cascade Creek – Meadow
Lakes Golf Course
LOMR 07-05-4071P 03/28/2008 Willow Creek – U.S. Highway
63 Improvements
LOMR 08-05-3390P 10/31/2008 Middle Fork Zumbro River -
U.S. Highway 52 Bridges
LOMR 09-05-1227P 05/15/2009 Mayowood Lake Floodway
Revision
LOMR 10-05-2736P 09/23/2010 South Run of the North Fork of
Cascade Creek – Csah 22/Th
14 Interchange
LOMR 12-05-4929P 03/21/2013 South Fork Zumbro River –
Rochester Public Utilities 4th
Street
LOMR 13-05-0422P 07/26/2013 Cascade Creek – Floodplain
Remapping
LOMR 13-05-8106P 10/17/2014 Bear Creek Revision
*Letter of Map Revision (LOMR)
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2.2 Community Description
Olmsted County is located in southeastern Minnesota. It is bordered by Mower
County to the south and southwest, Fillmore County and the City of Chatfield to
the south, Goodhue County and the City of Pine Island to the north, Wabash
County to the north and northeast, Winona County and the City of St. Charles to
the east, and Dodge County to the west. The county has a land area of 656 square
miles. The population in 2000 for Olmsted County was 124,277 (U.S. Census
Bureau, 2010).
The major highways crossing the county are: Interstate Highway 90 passing east-
west through the southern portion of the county; U.S. Highway 14 passing through
the central portion of the county; U.S. Highway 52 passes from the northwestern
to the southeastern portion of the county; and, U.S. Highway 63 passes north-south
through the center of the county. The Dakota, Minnesota, and Eastern Railroad,
formerly the Chicago and Northwestern Railroad, crosses the county east-west
along U.S. Highway 14.
The topography of Olmsted County varies from flat to gently rolling, with steep
slopes and bluffs along portions of the South Fork Zumbro River, North Fork Root
River and North Fork Whitewater River. Elevations range from 800 to 1,360 feet
(NAVD). The drainage system in the county is a well-established dendritic type
and was not significantly affected by the last glaciation that occurred in southern
Minnesota. The South Fork Zumbro River watershed extends over much of
Olmsted County. Outside of the City of Rochester many small tributaries to the
South Fork Zumbro River meander through wide bottomlands separated by
plateaus primarily west of the city. Bear Creek and Silver Creek, however, flow
through wooded, relatively steep, basins. Some of the stream valleys are highly
dissected with outcrops of limestone, shale and sandstone formations.
The land cover in Olmsted County is primarily agricultural cropland. Forest tracts
of elm, maple, basswood, and oak trees are found on steeper side slopes in the
northwestern, northeastern, and south central portions of the county, primarily
along river corridors. Scattered wooded and brushy areas exist in the alluvial
formations along many of the streams and in small wetlands located in upland
settings in the county.
The Olmsted County Soil Survey reports that there are nine soil associations in
four soil formation categories that describe distinct patterns of soils, topography
and drainage patterns. The first group is a broad upland area dominated by soils
formed in sediments and glacial till. The soil associations are remnants of
previous glacial deposits located in the higher elevations in the county in the
southwest, east central and northwestern portions of the county. These
associations are upland areas that have low relief and many long narrow
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drainageways and are well-drained to poorly-drained. This area includes gravel
knolls and low gravel ridges and is located in the City of Oronoco.
Most of the county is covered by uplands in the southern and northern portions of
the county and around the City of Rochester and are dominated by soils formed by
windblown material, loess, which comprises the second group. These soil
associations are generally well-drained to very poorly-drained areas with broad
summits and narrow drainageways. One soil association is also located in
floodplains along the floor of narrow ravines, some of which are tributaries that
flow into the City of Rochester.
A third area is dominated by soils formed in a mantle of glacial till and residuum
over bedrock located in upland areas in an east-west pattern through the southern
portion of the county. The soil association is level to sloping and has numerous
deep drainageways. Much of this area has bedrock located within five feet of the
soil surface.
The fourth group of soil associations are the sandy, silty or loamy materials on
terraces and outwash plains, exclusively located in the stream and river valleys
within the county. Much of the older portion of the City of Rochester is developed
within these terrace and outwash deposits. The major river valleys flow through
these soil associations and in some cases, such as the Root River and Whitewater
River, flow on the underlying bedrock.
Floodplain land use within all of the major watersheds in the unincorporated parts
of the county are dominated by agricultural uses and more specifically dominated
by cropland. Land use in the floodplain within the Cities of Eyota and Dover is
undeveloped, although bounded by low intensity commercial/industrial uses. The
floodplains in the Cities of Stewartville and the City of Chatfield are also generally
less developed and include parkland uses. Lake Florence in Stewartville was
removed due to a dam failure after the publication of the 1998 FIS. The floodplain
in both communities is bounded by low intensity residential and commercial
development. The City of Rochester is located on large terrace and alluvial
deposits that extend upstream within all of the tributaries to the South Fork
Zumbro River. The current floodplain is significantly narrower due to the
completion of the flood control project in 1998. The city includes a mix of low to
medium density residential areas and commercial and industrial development
adjacent to the floodplain. Development adjacent to the Cascade Creek floodplain
consists primarily of industrial and transportation uses.
The climatic classification of Olmsted County is humid continental characterized
by large seasonal variations in temperature, normally sufficient rainfall, and
moderate snowfall. Temperatures in the county range from an average high of 80
degrees Fahrenheit (°F) to an average low of 60°F in the summer, and from an
average high of 20°F to an average low of 4°F in the winter. The average annual
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precipitation is 31.4 inches, with the maximum average precipitation occurring in
the month of July (The Weather Channel, 2010).
2.3 Principal Flood Problems
Flooding on the streams studied in Olmsted County occurs primarily as a
result of spring runoff, although flooding has resulted from the occurrence of
short-duration, high-intensity rainstorms.
Stream-flow records for the South Fork Zumbro River basin have been
maintained by the USGS and the USACE. The USGS maintains a stream-flow
gaging station on the South Fork Zumbro River at the City of Rochester. This
station has a drainage area of approximately 304 square miles with records dating
back to 1951. The gage was moved upstream 0.4 mile in 1981. The USGS also
maintains four crest-stage, partial record stations on small tributaries on the South
Fork Zumbro River.
Runoff from the South Fork Zumbro River basin is subject to seasonal variations
in temperature and precipitation. The South Fork Zumbro River generally attains
its highest peak in March and April from runoff caused by snowmelt and often
augmented by rainfall. The months of May through September generally have
high flows consistent with the monthly precipitation pattern. Drainage throughout
the basin is well developed, and consequently the runoff is high and rapid. In the
vicinity of Rochester, the rate of rise during floods can be rapid and the duration
can be relatively short. At the USGS gaging station at Rochester, the South Fork
Zumbro River rose to its crest in 15 hours during the flood of 1978 at an average
rate of 1.3 feet per hour and a maximum rate of 3.25 feet per hour. The river
remained above bank-full stage for 35 hours. Extreme discharges observed were
a maximum of 30,500 cubic feet per second (cfs), with a gage height of 23.36 feet
on July 6, 1978, and a minimum of 8.4 cfs with a gage height of 1.6 feet on
December 7, 1955. The average discharge for 38 years was 166 cfs.
Descriptions of floods have been obtained from various sources such as gage
records, flood reconnaissance, personal interviews, and newspaper files. From
these sources, it has been possible to develop a history of the known floods on the
South Fork Zumbro River covering the past 135 years. Stage and discharge data
for past floods are available principally at the USGS gaging station on the river in
the City of Rochester.
The following descriptions are based on newspaper accounts, historical records,
field investigations, and other available data, and illustrate some of the flooding
problems in the City of Rochester.
October 1855
Few records of the October 1855 flood are available. One newspaper account of
the June 1908 flood referred to Mr. Thomas McCoy who remembered a major
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flood that occurred in October 1855. He recalled that Rochester was isolated to
such an extent that it could be reached from the southeast only by boat. Water
overflowed the west banks of the South Fork Zumbro River and flowed down
Broadway Avenue. He felt that this flood exceeded the one of June 1908,
however, other accounts of the 1908 flood indicate that it was the largest that any
residents living at the time could recall. Considering all available records, it has
been determined that the October 1855 flood was essentially of the same
proportions as the June 1908 occurrence. Subsequent hydraulic analysis
determined that the discharges associated with these two historic flood events of
1855 and 1908 were 16,900 cfs, making them the fourth and fifth largest events at
this location.
June 1908
The flood that crested in June 1908 was caused by heavy rainfall. The National
Weather Service (NWS) station at the City of Rochester reported 4.1 inches of
rain in 24 hours. At Grand Meadow, 24 miles south of the City of Rochester, 4.25
inches of rain fell in 24 hours and was preceded by 2.78 inches of rainfall 2 days
earlier.
June 1942
The largest known flood on Cascade Creek occurred in June 1942 and
approximated a 0.8-percent-annual-chance frequency event (USACE, 1958). A
major local flood occurred on Cascade Creek on June 4 and 5, 1942. Floodwaters
on Cascade Creek were up to 4 feet higher than any other known flood, while the
South Fork Zumbro River and other tributaries experienced only moderate rises.
Rainfall at the Rochester NWS station amounted to 2.33 inches on June 4, 1942,
and totaled 3.76 inches on June 3-5, 1942. Hourly records show that 1.11 inches
fell in 1 hour on June 4, 1942, and 0.97 inch of additional rain fell in the next 2
hours. The relative variation of runoff on the nearby streams indicates that much
heavier rainfall occurred on the Cascade Creek watershed than on other nearby
areas.
March 1965
As the result of runoff from spring snowmelt and generally light rainfall, a major
flood occurred in March 1965 with the crest stage approximately 0.7 foot higher
than the March 1962 flood at the USGS gaging station near Rochester. Another
flood occurred in the spring of 1965, which peaked on April 6, 1965, at
Rochester, with a crest stage almost 6 feet lower than the flood of March 1965.
Events preceding these floods included above normal precipitation in the fall of
1964 and below normal temperatures in December, which permitted deep frost
penetration into the ground. Early in the winter, a freezing rain formed a layer of
ice, sealing off the ground, and resulted in a high runoff rate from the subsequent
snowfall. Temperatures averaged below normal and remained below the thawing
point until late February, so there was little snowmelt runoff. In February, after
heavy snowfall and temperatures remaining well below 32°F during most of the
16
month, the temperature rose rapidly on February 27, 1965, to approximately 45°F
in the basin and remained above freezing for the next 2 days.
Steady but generally light precipitation, partly rainfall and partly snow, fell
throughout March 1 and 2, 1965. Snowmelt runoff along with rainfall generated a
rapid increase in stream flow, resulting in discharges of 19,600 cfs at the gaging
station near Rochester. After this flood peaked, above-normal snowfalls in March
produced accumulated snow depths of 7 inches at Rochester. Slowly rising
temperatures after March 30th gradually melted the snow, but with nearly an inch
of precipitation during this thawing period, the stream flow increased for several
days, resulting in a peak discharge of 8,010 cfs at Rochester. At the gaging
station, the flood of April had a smaller instantaneous peak discharge but a wider
crest, a longer period of rise, a longer period of recession, and twice the volume of
the March flood hydrograph.
July 1978
The largest known or recorded flood in the City of Rochester occurred on July 6,
1978. The largest known flood on Badger Run occurred in July 1978 (USGS,
1978). Floods exceeding a 1-percent-annual-chance frequency occurred on Silver
and Bear Creeks in July 1978 (USGS, 1978). This flood was caused by an intense
thunderstorm that produced a peak discharge of 30,500 cfs on the South Fork
Zumbro River. This flash flood that claimed five lives and caused property losses
to thousands of homes, hundreds of businesses, and numerous public properties
resulted from heavy rains of 6 inches or more. The NWS station at the Rochester
airport recorded 4.99 inches of rain in 3 hours. Total rain at the airport for this 8-
hour storm was 6.74 inches, whereas the average weighted rain over the 304
square mile drainage area was calculated to be 5.65 inches. At the USGS gaging
station at Rochester, the South Fork Zumbro River rose to its crest in 15 hours at
an average rate of 1.3 feet per hour and a maximum rate of 3.25 feet per hour. The
river remained above bank-full stage for 35 hours. Peak discharges on the
tributaries were published by the USGS as follows: Cascade Creek, estimated
1,000 cfs; Silver Creek, 9,290 cfs; Bear Creek on Belt Line, 24,900 cfs; and the
South Fork Zumbro River on Belt Line, 20,500 cfs.
No historic flood information is available for Willow Creek; West Tributary to
Willow Creek; East, South, and West Forks of Willow Creek; Southeast Branch
of Willow Creek; South Fork of Bear Creek; or the North and South Runs of the
North Fork of Cascade Creek.
Flood damage occurs along virtually all the streams that are tributaries to the
South Fork Zumbro River in Olmsted County because of the predominantly wide,
gently sloping floodplains.
Flooding in the Cities of Dover and Eyota occurred in June of both 1974 and 1978
as a result of heavy rainfall. From conversations with local officials and residents
of the City of Dover, homes near the confluence of Tributary B and the South
17
Fork Whitewater River and a home near the intersection of County Highway
10/Chatfield Street North and the Dakota, Minnesota, and Eastern Railroad
experienced some minor flooding problems. Also, water reportedly seeped
through the basement windows of a house at the north end of Sheek Street during
the 1974 storm, and it was necessary to evacuate the occupants of a mobile home
located across the street.
According to the City of Eyota utility superintendent, the intersection of Center
Avenue North and U.S. Highway 14 was inundated during both storms and the
box culvert on Center Avenue North was overtopped. The culverts carrying
Tributary A under Fifth Street, Madison Street, and Second Street were also
overtopped during both storms. The culvert under State Highway 42 near Second
Street was washed out in the 1974 storm, causing damage to the road bed. Some
of the businesses on Center and Front Streets suffered damage from basement
seepage, but this was due to street runoff rather than flooding effects from the
creek.
For the City of Dover, rainfall records from the NWS station in Rochester
(located 17 miles west of Dover) indicate that the frequency of the 1974 storm
was greater than a 0.2-percent-annual-chance flood event. The Minnesota
Department of Transportation (DOT) established a high watermark on the
roadside to the west of the Sheek Street house at an elevation of 1,144.7 feet
(NAVD). The hydraulic analysis performed for the City of Dover determined the
elevation of a 1-percent-annual-chance flood at this location to be 1,144.9 feet
(NAVD).
Floods such as the storm or July 1978 have passed through the Cities of Chatfield
and Stewartville, however, water damage has been limited by relatively steep
banks or wide floodplain, and the lack of development in the floodplain.
June 2004
Heavy rains fell in two waves over southeast Minnesota on June 8 and 9, 2004.
The remnants of the torrential rains that caused flooding and mudslides in the
Mankato area drifted east over southeast Minnesota late on June 8 and into the
early morning hours of June 9. Later in the morning of June 9, thunderstorms
redeveloped over south central and southeast Minnesota and continued throughout
the afternoon and early evening. The Rochester airport recorded 4.06 inches of
rain on June 9, setting a record for the date. Another 0.20 inch had fallen on June
8, leading to a two-day total of 4.26 inches. By late in the evening of June 9, most
of the heavy rain had moved into Wisconsin. The rains fell upon soil already
saturated from the heavy rains of May 2004.
The deluge led to street flooding and wet basements in the City of Rochester. One
apartment building had water flowing through the lowest floor. Numerous
accounts of water overtopping roads were reported throughout the region.
18
September 2004
On September 14 and 15, 2004, a series of disturbances along a stalled frontal
boundary dropped heavy rains in southern Minnesota with the heaviest rainfall
occurring in Faribault and Freeborn Counties to the west and outside of the
Zumbro, or Root River watersheds. The southeast and southwest corners of
Olmsted County received 6 inches of rainfall, 5 inches over the center of the
county and less than that over the northern portion of the county over a 24-hour
period. There were numerous reports in southern Minnesota of stream flooding,
urban flooding, mudslides, and road closures. Flash flood warnings were issued
for 13 Minnesota counties including all counties within the Zumbro and Root
River watersheds.
August 2007
A very moist warm air mass provided the fuel for showers and thunderstorms
along a warm front extending from northern Iowa to central Illinois from August
18th to 19th. Thunderstorms developed on Saturday moving west to east along
this line through southern Minnesota. Heavy rain persisted with rainfall rates of 1
to 2 inches per hour, common in southeastern Minnesota. Rochester International
Airport received 7.05 inches of rain over the period of the storm from Saturday
night into Sunday morning. Cascade Creek crested at 16.52 feet on Sunday
morning above the flood stage of 13.0 feet. Over a 24-hour period, Cascade Creek
received 10.45 inches, Silver Creek 10.17 inches, and Bear Creek 9.86 inches.
This amount of rain surpasses the 6 inch rainfall for a given location for a 24-hour
period that is said to be a 1-percent-annual-chance storm.
This storm event was one of the most extraordinary precipitation events in
Minnesota’s modern history according to the State Climatologist. During the
event a new Minnesota 24-hour rainfall record was broken. The State Climate
Extremes Committee agreed that the 15.10 inches total recorded on Sunday,
August 19, 2007, at Hokah in Houston County is the largest 24-hour total ever
measured at an official NWS observing station in Minnesota.
September 2010
On September 23 and 24, 2010, heavy rains led to the largest flood event to hit
southern Minnesota since the flood of August 2007. Wave after wave heavy
thunderstorms brought over 11 inches of rain in some areas in a 24-hour period, a
6 inch rainfall for a location in this region over a 24-hour period is said to be a
100-year storm. The large amount of rain, over such a wide area, in such a short
amount of time, caused record flooding, with Lake Shady Dam overtopping in the
City of Oronoco. Flood waters flowed over and around the north abutment and
washed out the embankment and north roadway approach to the U.S. Highway 18
bridge. The buried reinforced concrete core wall at the north abutment was
undermined, fractured and collapsed (Report, 2011). In the City of Pine Island,
more than 100 homes were affected, with damage varying from water in the
basements to water over the main floor structure. Additionally, more than 20
19
businesses were damaged and numerous roads and culverts were washed out
(USGS, 2011).
The effectiveness of the City of Rochester flood control project was evident as the
City of Rochester saw some street flooding, water seepage into basements, some
mudslides in the City of Rochester and in the unincorporated areas, and road
closures but not large scale flooding of portions of the city as happened in 1978.
The City of Eyota experienced basement flooding on a large scale that appears not
to have been due to surface flows of floodwater but a high groundwater table.
Some stream bank damage occurred on Cascade Creek within the City of
Rochester that threatened the loss of accessory buildings but no residences were
affected.
2.4 Flood Protection Measures
Floodplain development in the City of Rochester is controlled by the Rochester
Zoning Ordinance and Land Development Manual (City of Rochester, 1975). The
ordinance requires that plans for proposed structures in the floodplain meet
regulations set by the MNDNR in the following report: Flood Plain Information,
Supplemental Report on South Fork Zumbro River and Tributaries in the Vicinity
of Rochester, Minnesota (State of Minnesota, 1975).
A small check dam on Cascade Creek near the confluence with the South
Fork Zumbro River and dams on the South Fork Zumbro River in the City of
Rochester do not provide significant flood protection.
The USACE developed a local flood control plan for the City of Rochester, the
Rochester Flood Control Project, which is designed to reduce flood stages on the
South Fork Zumbro River, Cascade Creek, and Bear Creek through the
construction of a levee and floodwalls; alterations to bridges, sewers, and utilities
in the floodplains; and channel modifications.
The Rochester Flood Control Project is multifaceted and includes the construction
of seven Natural Resources Conservation Service (NRCS) (formerly the Soil
Conservation Service (SCS)) reservoirs on Silver, Bear, Willow, and Cascade
Creeks that impound water and reduce downstream peak flows in the City of
Rochester. All of the SCS reservoirs have been constructed and are operable.
The USACE's portion of the flood control project consisted of channel
improvements and construction of floodwalls, a levee, and hydraulic structures.
The USACE work was segmented into several stages and was completed in
September 1995. FEMA specifies that all levees must have a minimum of 3-foot
freeboard against a 1-percent-annual-chance flood in order to be considered a safe
flood protection structure. The Bear Creek levee meets FEMA freeboard
20
requirements. The February 4, 1998, FIS accounted for the following features of
the Rochester Flood Control Project:
• modifications to the South Fork Zumbro River from the downstream end of the
project upstream to the Fourth Street Southeast bridge and from upstream of
the South Broadway bridge to the upstream limit of work, including widening
and deepening the channel, low flow channel reaches, riprap lined channel and
slope protection, vertical concrete walls, bridge modifications, drop structures,
and U.S. Highway 14 bridge replacement;
• dam rehabilitation on Silver Lake;
• seven reservoirs located on Bear Creek, Silver Creek, Cascade Creek,
Willow Creek, East Fork of Willow Creek, and South Run North Fork Cascade
Creek; and
• a levee system is located along the Bear Creek upstream of U.S. Highway 14.
Please refer to the corresponding Flood Insurance Rate Map panels for the
protection status of this levee system.
There was a 70-acre lake, Lake Florence, that was small in relation to the 114
square mile drainage area of the North Branch Root River watershed at the dam;
therefore, the dam at the outlet of Lake Florence had little to no effect on the
flood flow peaks that pass through the City of Stewartville. The dam was
removed due to a severe flood after the publication of the 1998 FIS report and the
lake bottom is now a public park and the channel for the North Branch Root
River.
There are no permanent flood protection structures in the City of Oronoco and
none are proposed at this time. The volume available for floodwater storage in
Shady Lake is insignificant in comparison to the runoff volume of significant
flood events and no attenuation of the larger flood peaks occurs.
A holding pond on the West Fork of Willow Creek, approximately 1,000 feet
west of County Highway 147, provides some flood protection during the lower
frequency floods. A small check dam on Cascade Creek near its confluence with
the South Fork Zumbro River does not serve as a flood protection structure.
Floodplain development in Olmsted County is controlled by the Olmsted County
Zoning Ordinance (Olmsted County Board of Commissioners, 1970). The
ordinance has four floodplain districts that set standards for grading and
development within the floodplain. The ordinance requires that plans for proposed
fill and structures in the flood fringe, and flood-prone soils, as defined by the
SCS's Soil Survey for Olmsted County, be reviewed as conditional use permits.
The other communities with FEMA designated floodplains also have zoning
ordinance provisions that establish standards for development within the regulated
floodplain.
21
There are no other permanent flood protection structures in the county, and none
are proposed at this time.
3.0 ENGINEERING METHODS
For the flooding sources studied by detailed methods in the community, standard
hydrologic and hydraulic study methods were used to determine the flood hazard data
required for this study. Flood events of a magnitude that are expected to be equaled or
exceeded once on the average during any 10-, 50-, 100-, or 500-year period (recurrence
interval) have been selected as having special significance for floodplain management and
for flood insurance rates. These events, commonly termed the 10-, 50-, 100-, and 500-
year floods, have a 10-, 2-, 1-, and 0.2-percent chance, respectively, of being equaled or
exceeded during any year. Although the recurrence interval represents the long-term,
average period between floods of a specific magnitude, rare floods could occur at short
intervals or even within the same year. The risk of experiencing a rare flood increases
when periods greater than 1 year are considered. For example, the risk of having a flood
that equals or exceeds the 1-percent-annual-chance (100-year) flood in any 50-year period
is approximately 40 percent (4 in 10); for any 90-year period, the risk increases to
approximately 60 percent (6 in 10). The analyses reported herein reflect flooding
potentials based on conditions existing in the community at the time of completion of this
study. Maps and flood elevations will be amended periodically to reflect future changes.
3.1 Hydrologic Analyses
Hydrologic analyses were carried out to establish peak discharge-frequency r
relationships for each flooding source studied by detailed methods affecting the c
community.
Badger Run
New hydrologic modeling was performed for Badger Run for this countywide
analysis.
The Badger Run watershed is located in south central Olmsted County, southeast
of the City of Rochester. The detailed study portion of Badger Run extends from
County Highway 11 to the confluence with Bear Creek, with an average channel
slope of 0.5% for the study reach. The watershed of the study area is 16.37 square
miles. Much of the watershed is currently undeveloped with the majority of the
land being used for agricultural production. However, development has occurred
along the Badger Run corridor for more than 40 years primarily consisting of low
density residential subdivisions, and there is development occurring in the
northwestern portion of the watershed within the City of Rochester.
Flow values for each of the reaches for the 10-, 2-, 1-, and 0.2-percent chance
events were computed using the Environmental Protection Agency’s Storm Water
Management Model (SWMM), XP-SWMM, computer model (XP Software,
22
2005). The SCS Curve Number method was used to estimate peak runoff for each
subwatershed (SCS, 1975).
General routing information was built into the hydraulics module within XP-
SWMM to route runoff downstream and estimate peak flows. The hydraulic data
included survey information of structures at road crossings as well as a surveyed
cross section of the natural stream channel and extended cross section of the
overbank area (floodplain) using the two-foot topographic data (Horizons, Inc.,
April 2006) provided by the City of Rochester.
Flows estimated by the XP-SWMM models for Badger Run were verified using
regional regression methods (USGS, 1997). The National Flood Frequency
Program (NFF) (USGS, 2002), which incorporates the USGS regression
equations, was used to estimate flows for the 0.2-percent-annual-chance event for
each of the three detailed study areas.
Bear Creek
Hydrology for Bear Creek upstream of a point approximately 265 feet upstream of
the confluence of Badger Run was developed as part of a precountywide analysis.
In the City of Rochester, the 10-, 2-, 1- and 0.2-percent-annual-chance frequency
discharges were obtained from the Supplemental Report on South Fork Zumbro
River and Tributaries in the Vicinity of Rochester, Minnesota (State of Minnesota,
1975). The SCS calculated these discharges using a 24-hour rainfall event and the
unit hydrograph methods of the SCS TR-20 computer program (SCS, 1983). In
the unincorporated areas, hydrographs for Bear Creek upstream of a point
approximately 265 feet upstream of the confluence of Badger Run were developed
using a 24-hour rainfall event and the unit hydrograph methods of the SCS TR-20
computer program (SCS, 1983). Times of concentration and curve numbers were
estimated following procedures outlined in the SCS National Engineering
Handbook, using USGS topographic maps, MNDNR high altitude aerial
photographs, soil survey maps, and field inspection data (SCS, 1972a; USGS,
various dates (a); USGS, 1955; State of Minnesota, 1969; SCS, 1972b; SCS,
1961;. SCS, 1928). The 10-, 2-, and 1-percent-annual-chance precipitation
intensities were obtained from the National Weather Service (NWS) Technical
Paper No. 40; the 0.2-percent-annual-chance precipitation intensity was estimated
by extrapolating the 10-, 2-, and 1-percent-annual-chance precipitation intensities
on probability paper (NWS, 1961). Stage-discharge and stage-storage relationships
were developed using USGS topographic maps, highway culvert data, stage-
storage data and dike plans provided by the City of Rochester SCS, weir equations
and coefficients from Design of Small Dams, and field inspection data (USGS,
various dates (a); U.S. DOT, 1965; U.S. Department of the Interior, 1973).
The results from the hydrologic analyses of the South Fork Zumbro River basin
for the April 17, 1995, countywide FIS, were incorporated into the February 4,
1998, revision and expanded to further subdivide the drainage area (FEMA, 1995).
The analyses were updated to reflect the completed Rochester Flood Control
23
Project, including the completion of the final three of seven SCS reservoirs. It was
then calibrated to the computed pre-project discharge-frequency at the USGS
gaging station, while storage-outflow relationships were incorporated in the model
to determine the impact of the seven reservoirs. Peak flow discharges for Bear
Creek from its confluence with the South Fork Zumbro River to a point
approximately 265 feet upstream of the confluence of Badger Run were updated to
reflect the completed flood control project (FEMA, 1998).
For this revision, the 1992 USACE “City of Rochester, Minnesota, Interim Flood
Insurance Study, Hydrologic Analysis” is the source for discharges for Bear
Creek at the confluence with the South Fork of the Zumbro River. The upstream
discharges for Bear Creek were developed using the drainage area ratio method.
The discharges for the new Bear Creek Zone AE reach weren’t revised.
Carey Creek
The flows for Carey Creek were extracted from the existing TR-20 model for the
North Branch of the Root River developed for a pre-countywide analysis. This
hydrologic model was developed previously; however, the flows for Carey Creek
were not used for a detailed study until this revision of the FIS.
Cascade Creek
Hydrology for Cascade Creek upstream of a point approximately 250 feet
downstream of County Road 34 was developed as part of a pre-countywide
analysis. In the City of Rochester, the 10-, 2-, 1- and 0.2-percent-annual-chance
frequency discharges were obtained from the Supplemental Report on South Fork
Zumbro River and Tributaries in the Vicinity of Rochester, Minnesota (State of
Minnesota, 1975). The SCS calculated these discharges using a 24-hour rainfall
event and the unit hydrograph methods of the TR-20 computer program (SCS,
1983). In the unincorporated areas, discharges for floods of the selected
recurrence intervals for Cascade Creek upstream of a point approximately 250 feet
downstream of County Highway 34 were obtained from the SCS study of the
South Fork Zumbro River.
The results from the hydrologic model analyses of the South Fork Zumbro River
basin for the April 17, 1995, countywide FIS, were incorporated into the February
4, 1998, revision and expanded to further subdivide the drainage area (FEMA,
1995). The analyses were updated to reflect the completed Rochester Flood
Control Project, including the completion of the final three of the seven SCS
reservoirs. The model was calibrated to the computed pre-project discharge-
frequency at the USGS gaging station, while storage-outflow relationships were
incorporated in the model to determine the impact of the seven SCS reservoirs.
Peak flow discharges for Cascade Creek from its confluence with the South Fork
Zumbro River to a point approximately 250 feet downstream of County Highway
34 were updated to reflect the completed flood control project (FEMA, 1998).
24
East Fork of Willow Creek
As part of the April 17, 1995, FIS analyses, a discharge-frequency relationship
was developed for the South Fork Zumbro River at Rochester based upon 38
years of continuous records from 1951 to 1988 at the USGS gage (No. 05372995)
in the City of Rochester and from the information taken from Flood Control,
South Fork Zumbro River at Rochester, Minnesota, Design Memorandum No. 1,
Phase 2, General Project Design, published by the USACE, St. Paul District
(USACE, 1982). Included in the analysis were the historic flood events of 1855
and 1908. The USACE Hydrologic Engineering Center (HEC) Computer
Program, HEC-FFA (HEC, 1992) was used to develop the discharge-frequency
relationships. A log-Pearson Type III analysis was used according to the
guidelines outlined in U.S. Water Resources Council (WRC) Bulletin 17B (WRC,
1982).
Because of the existence of only one recording gage in the South Fork Zumbro
River basin, it was necessary to develop a basin model capable of determining
discharge-frequency relationships at several other locations in the watershed
including East Fork Willow Creek.
The South Fork Zumbro River basin was divided into 20 subbasins, with
boundaries partially dictated by seven SCS reservoirs. The necessary HEC-1
parameters were determined to allow the model to develop unit hydrographs for
each of the various subbasins, apply an exponential loss rate to non-uniform
rainfall events occurring over the subbasins, compute the local flow hydrographs,
route the flood hydrographs downstream, and combine this runoff with other
routed flows. The Clark method was used to develop unit hydrographs, and stream
routing was accomplished by use of the modified Puls method using a stage-
storage-outflow relationship.
Because the model is only representative of rainfall-runoff events, it was calibrated
to the summer-season discharge-frequency curve at the USGS gage in the City of
Rochester. A relationship was developed between the HEC-1 model summer-
season discharges and the all-season (combined snowmelt, rainfall, and runoff)
frequency curve discharges at the USGS gage. This relationship at the gage was
then applied to other points within the basin for adjustment from summer-season
conditions to the more critical all-season conditions. As indicated by this
relationship, the amount of adjustment decreases for increasing discharges. At the
USGS gage in the City of Rochester, the adjusted model frequency curve matches
the all-season instantaneous peak discharge-frequency curve.
Hadley Valley Creek and Hadley Valley Creek Split Flow
New hydrologic modeling was performed for Hadley Valley Creek and Hadley
Valley Creek Split Flow for this countywide analysis.
The Hadley Valley Creek watershed is located in central Olmsted County, just east
of the City of Rochester. The detailed study portion of Hadley Valley Creek
25
extends from 1.25 miles directly east of the intersection of Hadley Valley Road
Northeast/County Highway 124 and 48th Street Northeast/County Highway 124 to
the crossing of East River Road Northeast, with an average channel slope of 1.1%
for the study reach. The watershed of the study area is 8.82 square miles. Much
of the watershed is currently undeveloped with the majority of the land being used
for agricultural production. However, there is development occurring in the
western portion of the watershed near U.S. Highway 63 within the City of
Rochester.
Flow values for each of the reaches for the 10-, 2-, 1-, and 0.2-percent chance
events were computed using the XP-SWMM, computer model (XP Software,
2005). The SCS Curve Number method was used to estimate peak runoff for each
subwatershed (SCS, 1975).
General routing information was built into the hydraulics module within XP-
SWMM to route runoff downstream and estimate peak flows. The hydraulic data
included survey information of structures at road crossings as well as a surveyed
cross section of the natural stream channel and extended cross section of the
overbank area (floodplain) using the two-foot topographic data (Horizons, Inc.,
2006) provided by the City of Rochester.
Flows estimated by the XP-SWMM models for Hadley Valley Creek and Hadley
Valley Creek Split Flow were verified using regional regression methods (USGS,
1997). The NFF (USGS, 2002), which incorporates the USGS regression
equations, was used to estimate flows for the 0.2-percent-annual-chance event for
each of the three detailed study areas.
Middle Fork Zumbro River
As part of a pre-countywide analysis, the 1-percent-annual-chance flood frequency
discharges for the Middle Fork Zumbro River were determined from a drainage
area-discharge relationship developed by the USGS using stream gage data for the
Cannon, Zumbro, and Root River basins and established by inter-agency
agreement on March 1, 1977 (USGS, 1949-present; USGS, 1977). The 10-, 2-, and
0.2-percent-annual-chance discharge curves for the South Fork Zumbro River at
Rochester were plotted on probability paper along with the 1-percent-annual-
chance discharge for the Middle Fork Zumbro River. A line was drawn through
the 1-percent-annual-chance discharge for the Middle Fork Zumbro River and
parallel to the frequency curve of the South Fork Zumbro River to obtain the 10-,
2-, and 0.2-percent-annual-chance discharges for the Middle Fork Zumbro River in
the unincorporated areas. Discharge values for the 10-, 2-, and 0.2-percent-annual-
chance discharges for the Middle Fork Zumbro River in the City of Oronoco were
determined by ratio of other frequency flood discharges to the 1-percent-annual-
chance discharge for studies of communities adjacent to the City of Oronoco.
26
Mill Creek
As part of a pre-countywide analysis, the flow-frequency relationships were
determined using the TR-20 computer program, which uses the physical
characteristics of a watershed such as area, slope, land use, and soil types to
develop runoff hydrographs for the region (SCS, 1983). Design rainfall depths
were obtained from the NWS Publication Technical Paper No. 40 (NWS, 1961).
For Mill Creek, watershed areas and slopes were obtained from USGS topographic
maps, at a scale of 1:24,000, enlarged to 1:4,800, with a contour interval of 20 feet
(USGS, 1972). Rating curves for structures and cross sections were obtained from
field data and through manual calculations. A crest-stage gage is located
approximately 3.4 miles upstream from the City of Chatfield on Mill Creek. The
flow-frequency relationship for this gage was determined by the USGS by fitting a
log-Pearson Type III frequency distribution to 14 observed annual peaks from the
USGS gaging station No. 07040008, with a period of record from 1962 to 1976.
The results of the analysis was used to calibrate the computer model that was
developed for the entire watershed (USGS, 1977).
North Branch Root River
As part of a pre-countywide analysis, the flow-frequency relationships were
determined using the TR-20 computer program (SCS, 1983). Design rainfall
depths were obtained from the NWS Publication Technical Paper No. 40 (NWS,
1961).
For the North Branch Root River, the 24-hour duration rainfall from the NWS
Publication Technical Paper No. 40 was found to be the critical event (NWS,
1961). Flood hydrographs were then developed and peak discharges found for the
10-, 2-, 1-, and 0.2-percent-annual-chance frequency rainfall events.
North Run of the North Fork of Cascade Creek
The results from the hydrologic analyses of the South Fork Zumbro River basin
for the April 17, 1995, countywide FIS, were incorporated into the February 4,
1998, revision and expanded to further subdivide the drainage area (FEMA, 1995).
The analyses were updated to reflect the completed Rochester Flood Control
Project, including the completion of the final three of the seven SCS reservoirs. It
was then calibrated to the computed pre-project discharge-frequency at the USGS
gaging station, while storage-outflow relationships were incorporated in the model
to determine the impact of the seven SCS reservoirs. Peak flow discharges for
North Run of the North Fork of Cascade Creek from its confluence with Cascade
Creek to a point approximately 0.93 miles upstream of 19th Street Northwest were
updated to reflect the completed flood control project (FEMA, 1998).
Silver Creek
As part of the April 17, 1995, countywide FIS analyses, a discharge-frequency
relationship was developed for the South Fork Zumbro River at Rochester based
upon 38 years of continuous records from 1951 to 1988 at the USGS gage (No.
27
05372995) in Rochester and from the information taken from Flood Control,
South Fork Zumbro River at Rochester, Minnesota, Design Memorandum No. 1,
Phase 2, General Project Design, published by the USACE, St. Paul District
(USACE, 1982). Included in this analysis were the historic flood events of 1855
and 1908. The HEC-FFA computer program (HEC, 1992) was used to develop the
discharge-frequency relationships. A log-Pearson Type III analysis was used
according to the guidelines outlined in WRC Bulletin 17B (WRC, 1982).
Because of the existence of only one recording gage in the South Fork Zumbro
River basin, it was necessary to develop a basin model capable of determining
discharge-frequency relationships at several other locations in the watershed
including Silver Creek from its confluence with the South Fork Zumbro River to
the walking bridge in the Quarry Hill Nature Center.
The South Fork Zumbro River basin was divided into 20 subbasins, with
boundaries partially dictated by the seven SCS reservoirs. The necessary HEC-1
parameters were determined to allow the model to develop unit hydrographs for
each of the various subbasins, apply an exponential loss rate to non-uniform
rainfall events occurring over the subbasins, compute the local flow hydrographs,
route the flood hydrographs downstream, and combine the runoff with other routed
flows. The Clark method was used to develop unit hydrographs, and stream
routing was accomplished by use of the modified Puls method using a stage-
storage-outflow relationship.
Because the model is only representative of rainfall-runoff events, it was calibrated
to the summer-season discharge-frequency curve at the USGS gage in the City of
Rochester. A relationship was developed between the HEC-1 model summer-
season discharges and the all-season (combined snowmelt, rainfall, and runoff)
frequency curve discharges at the USGS gage. This relationship at the gage was
then applied to other points within the basin for adjustment from summer-season
conditions to the more critical all-season conditions. As indicated by this
relationship, the amount of adjustment decreases for increasing discharges. At the
USGS gage in the City of Rochester, the adjusted model frequency curve matches
the all-season instantaneous peak discharge-frequency curve.
New hydrologic modeling was performed for Silver Creek for this countywide FIS
from the walking bridge in Quarry Hill Nature Center to approximately 1.33 miles
upstream of the Silver Creek Road Northeast bridge crossing.
The Silver Creek watershed is located in central Olmsted County, just east of the
City of Rochester. The detailed study length for this revision of Silver Creek falls
between 40th Avenue Northeast and Silver Creek Road Northeast and the bridge
crossing at the end of Silver Creek Drive Northeast, with an average channel slope
of 0.4% for the study reach. The watershed of the study area is 17.59 square
miles. Much of the watershed is currently undeveloped with the majority of the
land being used for agricultural production. However, there has been limited
28
development in the City of Rochester along the creek due to the large public sector
land holdings.
For Silver Creek from the walking bridge in the Quarry Hill Nature Center to
approximately 1.33 miles upstream of the Silver Creek Road Northeast bridge
crossing, flow values for each of the reaches for the 10-, 2-, 1-, and 0.2-percent
chance events were computed using the XP-SWMM computer model (XP
Software, 2005). The SCS Curve Number method was used to estimate peak
runoff for each subwatershed (SCS, 1975).
General routing information was built into the hydraulics module within XP-
SWMM to route runoff downstream and estimate peak flows. The hydraulic data
included survey information of structures at road crossings as well as a surveyed
cross section of the natural stream channel and extended cross section of the
overbank area (floodplain) using the two-foot topographic data (Horizons, Inc.,
2006) provided by the City of Rochester.
Flows estimated by the XP-SWMM models for Silver Creek from the walking
bridge in Quarry Hill Nature Center to approximately 1.33 miles upstream of the
Silver Creek Road Northeast bridge crossing were verified using regional
regression methods (USGS, 1997). The NFF (USGS, 2002), which incorporates
the USGS regression equations, was used to estimate flows for the 0.2-percent-
annual-chance event for each of the three detailed study areas.
For this revision, the 1992 USACE “City of Rochester, Minnesota, Interim Flood
Insurance Study, Hydrologic Analysis” is the source for discharges for Silver
Creek at the confluence with the South Fork of the Zumbro River. The upstream
discharges for Silver Creek were developed using the drainage area ratio method.
South Branch Middle Fork Zumbro River
As part of a pre-countywide analysis, the 1-percent-annual-chance flood frequency
discharges for the South Branch Middle Fork Zumbro River were determined from
a drainage area-discharge relationship developed by the USGS using stream gage
data for the Cannon, Zumbro, and Root River basins and established by inter-
agency agreement on March 1, 1977 (USGS, 1949-present; USGS, 1977).
Discharge values for the 10-, 2-, and 0.2-percent-annual-chance discharges for the
South Branch Middle Fork Zumbro River in the City of Oronoco were determined
by ratio of other frequency flood discharges to the 1-percent-annual-chance
discharge for studies of communities adjacent to the City of Oronoco.
South Fork of Bear Creek
As part of a pre-countywide analysis, in the unincorporated areas, discharges for
floods of the selected recurrence intervals for South Fork of Bear Creek were
obtained from the SCS study of the South Fork Zumbro River.
29
South Fork Whitewater River
As part of a pre-countywide analysis, the flow-frequency relationships were
determined using the TR-20 computer program (SCS, 1983). Design rainfall
depths were obtained from the NWS Publication Technical Paper No. 40 (NWS,
1961).
For the South Fork Whitewater River, watershed areas and slopes were obtained
from USGS topographic maps (USGS, various dates(b)). Land use was determined
from field inspection, aerial photographs, SCS Soils Atlas Sheets, and USGS
topographic maps (Martinez Ortho-Mapping Corporation, 1979a; SCS, 1979;
USGS, various dates (b)). Soil types were determined from SCS Soils Atlas Sheets
for Olmsted County (SCS, 1979). Rating curves for structures and cross sections
were obtained from field data and through the use of the SCS WSP-2 Water
Surface Profile computer program (SCS, 1989). Decreasing discharges between
County Highway 10 and the downstream corporate limits of Dover are caused by
storage for peak flows available in overbank areas along the South Fork
Whitewater River.
South Fork of Willow Creek
Hydrology for the South Fork of Willow Creek was developed as part of a pre-
countywide analysis. Discharges were determined using drainage area-discharge
relationships.
South Fork Zumbro River
As part of the April 17, 1995 FIS, hydrologic analyses, a discharge-frequency
relationship was developed for the South Fork Zumbro River at the City of
Rochester based upon 38 years of continuous records from 1951 to 1988 at the
USGS gage (No. 05372995) in Rochester and from the information taken from
Flood Control, South Fork Zumbro River at Rochester, Minnesota, Design
Memorandum No. 1, Phase 2, General Project Design, published by the USACE,
St. Paul District (USACE, 1982). Included in this analysis were the historic flood
events of 1855 and 1908. The HEC-FFA computer program (HEC, 1992) was
used to develop the discharge-frequency relationships. A log-Pearson Type III
analysis was used according to the guidelines outlined in WRC Bulletin 17B
(WRC, 1982).
The South Fork Zumbro River basin was divided into 20 subbasins, with
boundaries partially dictated by the seven SCS reservoirs. The necessary HEC-1
parameters were determined to allow the model to develop unit hydrographs for
each of the various subbasins, apply an exponential loss rate to non-uniform
rainfall events occurring over the subbasins, compute the local flow hydrographs,
route the flood hydrographs downstream, and combine this runoff with other
routed flows. The Clark method was used to develop unit hydrographs, and stream
routing was accomplished by use of the modified Puls method using a storage-
outflow relationship.
30
Because the model is only representative of rainfall-runoff events, it was calibrated
to the summer-season discharge-frequency curve at the USGS gage in the City of
Rochester. A relationship was developed between the HEC-1 model summer
discharges and the all-season (combined snowmelt, rainfall, and runoff) frequency
curve discharges at the USGS gage. This relationship at the gage was then applied
to other points within the basin for adjustment from summer-season conditions to
the more critical all-season conditions. As indicated by this relationship, the
amount of adjustment decreases for increasing discharges. At the USGS gage in
Rochester, the adjusted model frequency curve matches the all-season
instantaneous peak discharge-frequency curve.
The results from the hydrologic analyses of the South Fork Zumbro River basin
for the April 17, 1995, countywide FIS, were incorporated into the February 4,
1998, revision and expanded to further subdivide the drainage area (FEMA, 1995).
The analyses were updated to reflect the completed Rochester Flood Control
Project, including the completion of the final three of the seven SCS reservoirs. It
was then calibrated to the computed pre-project discharge-frequency at the USGS
gaging station, while storage-outflow relationships were incorporated in the model
to determine the impact of the seven SCS reservoirs. Peak flow discharges for the
entire studied reach of the South Fork Zumbro River (from a point approximately
10,490 feet downstream of 37th Street Northwest to a point just upstream of
Mayowood Road/County Highway 125) were updated to reflect the completed
flood control project (FEMA, 1998).
For this revision, the 1992 USACE “City of Rochester, Minnesota, Interim Flood
Insurance Study, Hydrologic Analysis” is the source for discharges for South Fork
of the Zumbro River.
South Run of the North Fork of Cascade Creek
The results from the hydrologic analyses of the South Fork Zumbro River basin
for the April 17, 1995, countywide FIS, were incorporated into the February 4,
1998, revision and expanded to further subdivide the drainage area (FEMA, 1995).
The analyses were updated to reflect the completed Rochester Flood Control
Project, including the completion of the final three of the seven SCS reservoirs. It
was then calibrated to the computed pre-project discharge-frequency at the USGS
gaging station, while storage-outflow relationships were incorporated in the model
to determine the impact of the seven SCS reservoirs. Peak flow discharges for
South Run of the North Fork of Cascade Creek from the confluence with Cascade
Creek to a point approximately 1.1 miles upstream of Dakota, Minnesota and
Eastern Railroad were updated to reflect the completed flood control project
(FEMA, 1998).
Southeast Branch of Willow Creek
Hydrology for the Southeast Branch of Willow Creek was developed as part of a
pre-countywide analysis. Discharges were determined using drainage area-
discharge relationships.
31
Tributary B
As part of a pre-countywide analysis, the flow-frequency relationships were
determined using the TR-20 computer program (SCS, 1983). Design rainfall
depths were obtained from the NWS Technical Paper No. 40 (NWS, 1961).
For the Tributary B, watershed areas and slopes were obtained from USGS
topographic maps (USGS, various dates(b)). Land use was determined from field
inspection, aerial photographs, SCS Soils Atlas Sheets, and USGS topographic
maps (Martinez Ortho-Mapping Corporation, 1979a; SCS, 1979; USGS, various
dates (b)). Soil types were determined from SCS Soils Atlas Sheets for Olmsted
County (SCS, 1979). Rating curves for structures and cross sections were obtained
from field data and through the use of the SCS WSP-2 Water Surface Profile
computer program (SCS, 1989). Decreasing discharges between County Road 10
and the downstream corporate limits of the City of Dover are caused by storage for
peak flows available in overbank areas along the South Fork Whitewater River.
West Fork of Willow Creek
As part of a pre-countywide analysis, in the unincorporated areas, hydrographs for
West Fork of Willow Creek were developed using a 24-hour rainfall event and the
unit hydrograph methods of the SCS TR-20 computer program (SCS, 1983).
Times of concentration and curve numbers were estimated following procedures
outlined in the SCS National Engineering Handbook, using USGS topographic
maps, MNDNR high altitude aerial photographs, soil survey maps, and field
inspection data (SCS, 1972a; USGS, various dates (a); USGS, 1955; State of
Minnesota, 1969; SCS, 1972b; SCS, 1961;. SCS, 1928). The 10-, 2-, and 1-
percent-annual-chance precipitation intensities were obtained from the NWS
Technical Paper No. 40; the 0.2-percent-annual-chance precipitation intensity was
estimated by extrapolating the 10-, 2-, and 1-percent-annual-chance precipitation
intensities on probability paper (NWS, 1961). Stage-discharge and stage-storage
relationships were developed using USGS topographic maps, highway culvert
data, stage-storage data and dike plans provided by the Rochester SCS, weir
equations and coefficients from Design of Small Dams, and field inspection data
(USGS, various dates (a); U.S. DOT, 1965; U.S. Department of the Interior,
1973). Discharges were determined using drainage area-discharge relationships.
Flood discharges for West Fork of Willow Creek are lower downstream of the
earth dam because of attenuation effects of the holding pond just upstream of the
dam.
West Tributary to Willow Creek
Hydrology for the West Tributary to Willow Creek was developed as part of a pre-
countywide analysis. Discharges were determined using drainage area-discharge
relationships.
32
Willow Creek
As part of the April 17, 1995, FIS analyses, a discharge-frequency relationship
was developed for the South Fork Zumbro River at the City of Rochester based
upon 38 years of continuous records from 1951 to 1988 at the USGS gage (No.
05372995) in the City of Rochester and from the information taken from Flood
Control, South Fork Zumbro River at the City of Rochester, Minnesota, Design
Memorandum No. 1, Phase 2, General Project Design, published by the USACE,
St. Paul District (USACE, 1982). Included in this analysis were the historic flood
events of 1855 and 1908. The HEC-FFA computer program (HEC, 1992) was
used to develop the discharge-frequency relationships. A log-Pearson Type III
analysis was used according to the guidelines outlined in WRC Bulletin 17B
(WRC, 1982).
Because of the existence of only one recording gage in the South Fork Zumbro
River basin, it was necessary to develop a basin model capable of determining
discharge-frequency relationships at several other locations in the watershed
including Willow Creek upstream of 11th Avenue Southeast/County Highway 1.
The South Fork Zumbro River basin was divided into 20 subbasins, with
boundaries partially dictated by seven SCS reservoirs. The necessary HEC-1
parameters were determined to allow the model to develop unit hydrographs for
each of the various subbasins, apply an exponential loss rate to non-uniform
rainfall events occurring over the subbasins, compute the local flow hydrographs,
route the flood hydrographs downstream, and combine this runoff with other
routed flows. The Clark method was used to develop unit hydrographs, and stream
routing was accomplished by use of the modified Puls method using a storage-
outflow relationship.
Because the model is only representative of rainfall-runoff events, it was calibrated
to the summer-season discharge-frequency curve at the USGS gage in the City of
Rochester. A relationship was developed between the HEC-1 model summer-
season discharges and the all-season (combined snowmelt, rainfall, and runoff)
frequency curve discharges at the USGS gage. This relationship at the gage was
then applied to other points within the basin for adjustment from summer-season
conditions to the more critical all-season conditions. As indicated by this
relationship, the amount of adjustment decreases for increasing discharges. At the
USGS gage in the City of Rochester, the adjusted model frequency curve matches
the all-season instantaneous peak discharge-frequency curve.
The results from the hydrologic analyses of the South Fork Zumbro River basin
for the April 17, 1995, countywide FIS, were incorporated into the February 4,
1998, revision and expanded to further subdivide the drainage area (FEMA, 1995).
The analyses were updated to reflect the completed Rochester Flood Control
Project, including the completion of the final three of the seven reservoirs. It was
then calibrated to the computed pre-project discharge-frequency at the USGS
gaging station, while storage-outflow relationships were incorporated in the model
33
to determine the impact of the seven reservoirs. Peak flow discharges for Willow
Creek from its confluence with Bear Creek to 11th Avenue Southeast/County
Highway 1 were updated to reflect the completed flood control project (FEMA,
1998).
Peak discharge-drainage area relationships for each flooding source studied in
detail are shown in Table 4.
Table 4 – Summary of Discharges
Peak Discharges (cubic feet per second)
Flooding Source and Location
Drainage Area
(square miles)
10-Percent-
Annual-Chance
2-Percent-
Annual-Chance
1-Percent-
Annual-Chance
0.2-Percent-
Annual-Chance
BADGER RUN
At confluence with Bear Creek 16.37 1,376 2,335 3,070 5,661
At 30th Avenue Southeast 15.75 1,538 2,633 3,376 5,373
At 30th Street Southeast 13.40 1,739 3,512 4,543 7,132
At U.S. Highway 52 12.49 2,104 3,432 4,120 6,014
Approximately 2,800 feet
Northwest of 50th Avenue
Southeast/County Highway 11
9.72 1,801 2,867 3,465 4,998
At 50th Avenue Southeast /
County Highway 11
7.98 1,806 2,789 3,357 4,839
BEAR CREEK
At confluence with South Fork
Zumbro River
76.60 5,900 10,800 13,500 22,000
Above confluence of Willow
Creek
45.60 4,200 7,700 9,700 15,800
Above confluence of Badger
Run
29.70 3,200 5,900 7,400 12,000
Approximately 2,150 feet
upstream of County Highway
11/50th Street Southeast
5.64 1,040 1,930 2,430 3,950
Approximately 550 feet
upstream of County
Highway 19/ Chester Road
Southeast
3.35 830 1,260 1,460 2,050
At Dakota, Minnesota, and
Eastern Railroad
2.42 560 830 950 1,280
Approximately 1,400 feet
downstream of Field Road
0.80 220 360 420 600
Approximately 1,450 feet
upstream of Field Road
0.46 100 160 190 260
CAREY CREEK
At confluence with North
Branch Root River
18.25 2,624 3,939 4,773 6,466
CASCADE CREEK
At confluence with South Fork
Zumbro River
38.50 1,850 3,500 4,400 7,000
At 16th Avenue Northwest 37.00 1,850 3,500 4,400 7,000
Above U.S. Highway 52 36.90 1,900 3,650 4,600 7,200
Above confluence of North
Run of the North Fork of
Cascade Creek
33.20 1,800 3,250 4,000 6,200
Above confluence of South
Run of the North Fork of
Cascade Creek
20.40 1,700 3,000 3,650 5,500
Table 4 – Summary of Discharges (continued)
34
Peak Discharges (cubic feet per second)
Flooding Source and Location
Drainage Area
(square miles)
10-Percent-
Annual-Chance
2-Percent-
Annual-Chance
1-Percent-
Annual-Chance
0.2-Percent-
Annual-Chance
EAST FORK OF
WILLOW CREEK
At confluence with Willow
Creek
7.10 670 1,350 1,700 2,750
At U.S. Highway 52
6.40 560 1,100 1,380 2,200
HADLEY VALLEY CREEK
At East River Road 8.82 1,495 1,972 2,225 2,776
At U.S. Highway 63 8.23 1,434 1,897 2,141 2,673
At 48th Street Northeast/County
Highway 124
7.92 1,434 1,897 2,141 2,673
Approximately 2,100 feet west
of the crossing at Hadley
Valley Road Northeast/County
Highway 124
7.58 1,541 2,368 2,806 3,827
At Hadley Valley Road
Northeast/County Highway
124
4.31 911 1,203 1,345 1,669
Upstream from study area
(Approximately 6,600 feet
east of the Intersection of
Hadley Valley Road Northeast
and 48th Street Northeast)
3.19 1,029 1,662 2,026 2,923
HADLEY VALLEY CREEK
SPLIT FLOW
Approximately 1,350 feet
upstream of the downstream
confluence with Hadley Valley
Creek
* 883 1,175 1,317 1,641
Approximately 2,050 feet
upstream of the downstream
confluence with Hadley Valley
Creek
* 551 748 850 1,130
MIDDLE FORK ZUMBRO RIVER
Approximately 7,200 feet
downstream of County
Highway 18/Minnesota Avenue
South
427.63
11,700 22,500 28,300 46,600
Below confluence of South
Branch Middle Fork Zumbro
River
425.00 11,700 22,500 28,300 46,600
Above confluence of South
Branch Middle Fork Zumbro
River
207.00 9,180 15,800 19,000 27,800
MILL CREEK
At confluence with North
Branch Root River
30.00 4,660 8,540 10,260 14,370
NORTH BRANCH ROOT RIVER
Approximately 1,100 feet
upstream of U.S. Highway 63
114.00 10,540 15,640 18,680 25,210
NORTH RUN OF THE NORTH
FORK OF CASCADE CREEK
At confluence with Cascade
Creek
3.70 570 1,350 1,850 3,400
Approximately 2,100 feet
upstream of Seventh Street
Northwest
3.10 530 930 1,150 1,700
Approximately 300 feet
upstream of 19th Street
2.17 79 140 199 300
Table 4 – Summary of Discharges (continued)
35
Peak Discharges (cubic feet per second)
Flooding Source and Location
Drainage Area
(square miles)
10-Percent-
Annual-Chance
2-Percent-
Annual-Chance
1-Percent-
Annual-Chance
0.2-Percent-
Annual-Chance
Northwest
Approximately 2,200 feet
upstream of 19th Street
Northwest
*Data Not Available
1.62 21 74 90 93
SILVER CREEK
At confluence with South Fork
Zumbro River
17.80 2,250 4,100 5,200 8,500
At County Highway 22/East
Circle Drive Northeast
17.19 2,200 4,000 5,100 8,300
At Dakota, Minnesota, and
Eastern Railroad
16.79 2,200 3,900 5,000 8,200
Approximately 3,800 feet west
of the intersection of 50th
Avenue Northeast and Silver
Creek Road Northeast
11.68 1,700 3,100 4,000 6,500
SOUTH BRANCH MIDDLE
FORK ZUMBRO RIVER
At confluence with Middle Fork
Zumbro River
218.00 9,370 16,200 19,400 28,800
SOUTH FORK OF BEAR CREEK
At confluence with Bear Creek
22.60 2,660 5,080 6,450 11,000
SOUTH FORK WHITEWATER
RIVER
Approximately 1,830 feet
upstream of U.S. Highway
14
21.40 2,150 3,110 3,650 4,580
At Dakota, Minnesota and
Eastern Railroad
20.20 2,120 3,100 3,740 4,820
At County Road 10 20.10 2,130 3,210 3,850 4,910
At U.S. Highway 14 2.70 270 395 480 575
At Dakota, Minnesota and
Eastern Railroad
2.50 225 315 350 420
At Center Avenue South
2.10 210 295 330 390
SOUTH FORK OF WILLOW
CREEK
At confluence with Willow
Creek
1.00 440 790 1,000 1,120
At County Highway 20
0.60 340 620 780 1,070
SOUTH FORK ZUMBRO RIVER
At USGS gage 303.00 10,700 19,400 23,900 36,300
Above confluence of Cascade
Creek
252.20 9,600 17,300 21,500 33,000
Above confluence of Silver
Creek
233.20 9,100 16,800 20,800 32,000
Above confluence of Bear
Creek
155.00 6,900 12,000 14,800 22,500
SOUTH RUN OF THE NORTH
FORK OF CASCADE CREEK
At confluence with Cascade
Creek
11.70 1,260 1,580 1,750 2,200
At U.S. Highway 14 10.50 1,200 1,320 1,360 1,450
At Dakota, Minnesota, and
Eastern Railroad
10.50 1,250 2,000 2,400 3,400
Table 4 – Summary of Discharges (continued)
36
Peak Discharges (cubic feet per second)
Flooding Source and Location
Drainage Area
(square miles)
10-Percent-
Annual-Chance
2-Percent-
Annual-Chance
1-Percent-
Annual-Chance
0.2-Percent-
Annual-Chance
SOUTHEAST BRANCH OF
WILLOW CREEK
At confluence with Willow
Creek
0.70 890 1,670 2,130 3,450
TRIBUTARY B
At confluence with South Fork
Whitewater River
10.00 1,330 2,070 2,530 3,300
WEST FORK OF WILLOW CREEK
At confluence with Willow
Creek
0.70 50 77 100 140
At Earth Dam
0.55 150 240 290 390
WEST TRIBUTARY TO
WILLOW CREEK
At confluence with Willow
Creek
0.60 300 530 690 1,140
Approximately 2,100 feet
upstream of confluence with
Willow Creek
0.44 250 445 570 960
WILLOW CREEK
At confluence with Bear Creek 28.40 2,200 4,100 5,100 8,200
Above confluence of West
Tributary to Willow Creek
25.70 2,000 3,800 4,800 7,600
Above confluence of East
Fork of Willow Creek
18.50 1,250 2,550 3,300 5,400
Above confluence of South
Fork of Willow Creek
17.30 1,175 2,300 2,950 4,850
Above confluence of West
Fork of Willow Creek
16.00 1,050 2,100 2,700 4,500
Above confluence of
Southeast Branch of Willow
Creek
11.20 520 1,025 1,300 2,100
Stillwater elevations for Olmsted County are shown in Table 5.
Table 5 - Summary of Stillwater Elevations
Water Surface Elevations (Feet NAVD1)
Flooding Source
10-Percent-
Annual-Chance
2-Percent-
Annual-Chance
1-Percent-
Annual-Chance
0.2-Percent-
Annual-Chance
Ponding Area 1 * * 1048.8 *
Ponding Area 2 * * 1046.1 *
Ponding Area 3 * * 1048.8 *
Ponding Area 4 * * 1048.8 *
*Data Not Available
1 North American Vertical Datum of 1988
3.2 Hydraulic Analyses
Analyses of the hydraulic characteristics of flooding from the sources studied were
carried out to provide estimates of the elevations of floods of the selected
recurrence intervals. Users should be aware that flood elevations shown on the
37
FIRM represent rounded whole-foot elevations and may not exactly reflect the
elevations shown on the Flood Profiles or in the Floodway Data Table in the FIS
report. Flood elevations shown on the FIRM are primarily intended for flood
insurance rating purposes. For construction and/or floodplain management
purposes, users are cautioned to use the flood elevation data presented in this FIS
report in conjunction with the data shown on the FIRM.
Badger Run
In a pre-countywide hydraulic analysis, the approximate 1-percent-annual-chance
water-surface elevation for Badger Run, upstream of 50th Avenue
Southeast/County Highway 11, was computed using HEC-2 and the 1-percent-
annual-chance discharge obtained from the MNDNR (State of Minnesota, 1975).
For this countywide study, hydraulic analysis for Badger Run from the confluence
with Bear Creek to 50th Avenue Southeast/County Highway 11 was performed
using the USACE’s computer program HEC-RAS, version 3.1.3 (HEC, 2005).
The HEC-RAS model geometry was developed using Geographic Information
Systems (GIS) applications within the USACE computer program HEC-GeoRAS,
version 4.1.1 (HEC, 2006).
Cross section data for the hydraulic analyses for Badger Run were based on a
Digital Terrain Model (DTM) of the area provided by Olmsted County. The DTM
was certified to meet photogrammetric and aerial mapping standards. Surveyed
channel data were also incorporated into the cross sections.
Bridge/culvert and roadway survey data were also incorporated into the HEC-RAS
models. Survey points represented by stations and elevations were recorded in x-
y-z format, and sketches derived from field measurements provided additional
structural dimensions for culverts and bridges. Digital photographs were taken
during the survey.
Other parameters in the HEC-RAS model, including ineffective flow areas and
expansion and contraction coefficients, were based on the detailed DTM of the
study area. Starting water-surface elevations were determined using the water-
surface elevations computed for Bear Creek at the confluence with Badger Run.
Channel roughness factors (Manning’s “n” values) used in the model were
determined by both field reconnaissance and inspecting aerial photographs of the
study area.
Bear Creek
As part of a pre-countywide analysis, cross section data for Bear Creek upstream
of a point approximately 265 feet upstream of the confluence of Badger Run were
obtained from the MNDNR (State of Minnesota, 1975). Data for the dry portions
of the cross sections taken were obtained using photogrammetric methods with
aerial photographs taken in May 1974 and May 1975, and below-water cross
sections were obtained from field measurement (Mark Hurd Aerial Surveys, Inc.,
38
1974-1975). Water-surface elevations for floods of the selected recurrence
intervals on Bear Creek upstream of a point approximately 265 feet upstream of
the confluence of Badger Run in the unincorporated areas were obtained from the
MNDNR (State of Minnesota, 1975). In the unincorporated areas, the starting
water-surface elevations were obtained from the MNDNR (State of Minnesota,
1975). Roughness coefficients were chosen using field inspection data and aerial
photographs taken in May 1974 and 1975 (Mark Hurd Aerial Surveys, Inc., 1974-
1975).
As part of the February 4, 1998, revised countywide analysis, cross sections for
Bear Creek from the confluence of South Fork Zumbro River to a point
approximately 265 feet upstream of the confluence of Badger Run were obtained
from a 1980 field survey. Water-surface elevations of floods of the selected
recurrence intervals were computed using the USACE HEC-2 step-backwater
computer program (HEC, 1991). The hydraulic analyses for all revised streams
were updated to reflect completed construction of the Rochester Flood Control
Project. The starting water-surface elevations for Bear Creek were determined
from water-surface elevations computed for the South Fork Zumbro River at the
respective confluences. Manning's "n" values used in the hydraulic computations
for the revised streams in the February 4, 1998, revision were determined based
upon the previous HEC-2 models developed for the FIS for the City of Rochester
and the Rochester Flood Control Project (FEMA, 1987).
Carey Creek
For this countywide study, hydraulic analysis for Carey Creek was performed
using the USACE’s computer program HEC-RAS, version 3.1.3 (HEC, 2005).
The HEC-RAS model geometry was developed using GIS applications within the
USACE computer program HEC-GeoRAS, version 4.1.1 (HEC, 2006).
Cross section data for the hydraulic analysis for Carey Creek were based on full
cross section surveys (channel and overbanks) at specific locations. For additional
elevation points outside of the surveyed cross-sections and for floodplain mapping
between cross-sections, the best available topography data (USGS DTM) was
used.
Bridge/culvert and roadway survey data were also incorporated into the HEC-RAS
models. Survey points represented by stations and elevations were recorded in x-
y-z format, and sketches derived from field measurements provided additional
structural dimensions for culverts and bridges. Digital photographs were taken
during the survey.
Other parameters in the HEC-RAS model, including ineffective flow areas and
expansion and contraction coefficients, were based on the detailed DTM of the
study area. Starting water-surface elevations were determined using the water-
surface elevations computed for North Branch Root River at its confluence with
39
Carey Creek. Manning’s “n” values used in the model were determined by both
field reconnaissance and inspecting aerial photographs of the study area.
Cascade Creek
As part of a pre-countywide analysis, cross section data for Cascade Creek
upstream of a point approximately 250 feet downstream of County Highway 34
were obtained from the MNDNR (State of Minnesota, 1975). Data for the dry
portions of the cross sections taken were obtained using photogrammetric methods
with aerial photographs taken in May 1974 and May 1975, and below-water cross
sections were obtained from field measurement (Mark Hurd Aerial Surveys, Inc.,
1974-1975). Water-surface elevations for floods of the selected recurrence
intervals on Cascade Creek upstream of a point approximately 250 feet
downstream of County Highway 34 in the unincorporated areas were obtained
from the MNDNR (State of Minnesota, 1975). In the unincorporated areas, the
starting water-surface elevations were obtained from the MNDNR (State of
Minnesota, 1975). Roughness coefficients were chosen using field inspection data
and aerial photographs taken in May 1974 and 1975 (Mark Hurd Aerial Surveys,
Inc., 1974-1975).
As part of a pre-countywide analysis, depths for sheet flow areas were determined
using topographic maps and by field survey (USGS, various dates (a)). There are
areas of sheet flow with depths between 1 and 3 feet.
For the February 4, 1998, revised countywide analysis, cross sections for Cascade
Creek from its confluence with the South Fork Zumbro River to a point
approximately 250 feet downstream of County Highway 34 were obtained from a
MNDNR floodplain information report (State of Minnesota, 1975). All bridges,
dams, and culverts were field surveyed to obtain elevation data and structural
geometry. The starting water-surface elevations were determined from water-
surface elevations computed for the South Fork Zumbro River at the respective
confluences. Roughness factors (Manning's "n") used in the hydraulic
computations for the revised streams in the February 4, 1998, revision were
determined based upon the previous HEC-2 models developed for the FIS of the
City of Rochester and the Rochester Flood Control Project (FEMA, 1987).
East Fork of Willow Creek
For the April 17, 1995, initial countywide analysis, cross sections for East Fork
Willow Creek were obtained from a MNDNR floodplain information report (State
of Minnesota, 1975). All bridges, dams, and culverts were field surveyed to obtain
elevation data and structural geometry. Water-surface elevations of floods of the
selected recurrence intervals were computed using the USACE HEC-2 step-
backwater computer program (HEC, 1991). The starting water-surface elevation
for East Fork of Willow Creek was determined from the water-surface elevation
computed for Willow Creek. Manning's "n" values used in the hydraulic
computations were determined based upon the previous stream analyses for the
40
FIS of the City of Rochester and the Rochester Flood Control Project (FEMA,
1987).
Hadley Valley Creek
For this countywide study, hydraulic analysis for Hadley Valley Creek was
performed using the USACE’s computer program HEC-RAS, version 3.1.3 (HEC,
2005). The HEC-RAS model geometry was developed using GIS applications
within the USACE computer program HEC-GeoRAS, version 4.1.1 (HEC, 2006).
Cross section data for the hydraulic analysis were based on a DTM of the area
provided by Olmsted County. Surveyed channel data were also incorporated into
the cross sections. The cross sections were cut along each stream reach
perpendicular to both the stream lines representing the centroids of overbank flow.
Bridge/culvert and roadway survey data were also incorporated into the HEC-RAS
models. Survey points represented by stations and elevations were recorded in x-
y-z format, and sketches derived from field measurements provided additional
structural dimensions for culverts and bridges. Digital photographs were taken
during the survey.
Other parameters in the HEC-RAS model, including ineffective flow areas and
expansion and contraction coefficients, were based on a detailed DTM of the study
area (and the Hawthorne Hills proposed grading plan in the case of Hadley Valley
Creek). Starting water-surface elevations were determined using the normal depth
method in HEC-RAS based on the slope of the stream downstream of the study
area. Manning’s “n” values used in the models were determined by both field
reconnaissance and inspecting aerial photographs of the study area.
Hadley Valley Creek Split Flow
For this countywide study, hydraulic analysis for Hadley Valley Creek Split Flow
was performed using the USACE’s computer program HEC-RAS, version 3.1.3
(HEC, 2005). The HEC-RAS model geometry was developed using GIS
applications within the USACE computer program HEC-GeoRAS, version 4.1.1
(HEC, 2006).
Cross section data for the hydraulic analysis were based on a DTM of the area
provided by Olmsted County. Surveyed channel data were also incorporated into
the cross sections. The cross sections were cut along each stream reach
perpendicular to both the stream lines representing the centroids of overbank flow.
Bridge/culvert and roadway survey data were also incorporated into the HEC-RAS
models. Survey points represented by stations and elevations were recorded in x-
y-z format, and sketches derived from field measurements provided additional
structural dimensions for culverts and bridges. Digital photographs were taken
during the survey.
41
Other parameters in the HEC-RAS model, including ineffective flow areas and
expansion and contraction coefficients, were based on the detailed DTM of the
study area (and the Hawthorne Hills proposed grading plan in the case of Hadley
Valley Creek). Starting water-surface elevations were determined using the water-
surface elevations computed for Hadley Valley Creek at the downstream
confluence with Hadley Valley Creek Split Flow. Manning’s “n” values used in
the models were determined by both field reconnaissance and inspecting aerial
photographs of the study area.
Middle Fork Zumbro River
As part of a pre-countywide analysis of the Middle Fork Zumbro River, in the
unincorporated areas, data for the dry portions of the cross sections were obtained
using photogrammetric methods with aerial photographs taken in May 1974 and
May 1975, and below-water cross sections were obtained from field measurement
(Mark Hurd Aerial Surveys, Inc., 1974-1975).
In the City of Oronoco, the starting water-surface elevations for the Middle Fork
Zumbro River were obtained from the FIS for the unincorporated areas of Olmsted
County (FEMA, 1980b). The starting water-surface elevations for the Middle Fork
Zumbro River in the unincorporated areas were determined by critical depth.
Along certain portions of Shady Lake, a profile base line is shown on the maps to
represent channel distances as indicated on the flood profiles and floodway data
tables.
The approximate 1-percent-annual-chance water-surface elevation for Zumbro
Lake was determined from the water-surface profiles developed for the Middle
Fork Zumbro River.
Manning's "n" values for the Middle Fork Zumbro River in the City of Oronoco
were assigned on the basis of past experience and field inspection of the channel
and floodplain areas. In the unincorporated areas, roughness coefficients were
chosen using field inspection data and aerial photographs taken in May 1974 and
1975 (Mark Hurd Aerial Surveys, Inc., 1974-1975).
Mill Creek
For this countywide study, hydraulic analysis for Mill Creek from the county
boundary to approximately 1.83 miles upstream of the State Highway 30 bridge
crossing was performed using the USACE’s computer program HEC-RAS,
version 3.1.3 (HEC, 2005). The HEC-RAS model geometry was developed using
GIS applications within the USACE computer program HEC-GeoRAS, version
4.1.1 (HEC, 2006).
Cross section data for the hydraulic analysis for Mill Creek were based on full
cross section surveys (channel and overbanks) at specific locations. For additional
elevation points outside of the surveyed cross-sections and for floodplain mapping
42
between cross-sections, the best available topography data (USGS DTM) was
used.
Bridge/culvert and roadway survey data were also incorporated into the HEC-RAS
models. Survey points represented by stations and elevations were recorded in x-
y-z format, and sketches derived from field measurements provided additional
structural dimensions for culverts and bridges. Digital photographs were taken
during the survey.
Other parameters in the HEC-RAS model, including ineffective flow areas and
expansion and contraction coefficients, were based on the detailed DTM of the
study area. Starting water-surface elevations were determined using the normal
depth method in HEC-RAS based on the slope of the stream downstream of the
study area. Manning’s “n” values used in the model were determined by both field
reconnaissance and inspecting aerial photographs of the study area.
North Branch Root River
As part of a pre-countywide analysis, in the City of Stewartville, flood elevations
for areas studied by approximate methods were determined by field observation
and engineering judgment.
For this countywide study, hydraulic analysis for the North Branch of the Root
River from approximately 1.1 miles downstream of the second County Highway
120/20th Street Northeast bridge crossing to approximately 2.4 miles upstream of
the U.S. Highway 63 bridge crossing was performed using the USACE’s computer
program HEC-RAS, version 3.1.3 (HEC, 2005). The HEC-RAS model geometry
was developed using GIS applications within the USACE computer program
HEC-GeoRAS, version 4.1.1 (HEC, 2006).
Cross section data for the hydraulic analysis for North Branch of the Root River
were based on full cross section surveys (channel and overbanks) at specific
locations. For additional elevation points outside of the surveyed cross-sections
and for floodplain mapping between cross-sections, the best available topography
data (USGS DTM) was used. A few cross sections for the North Branch of the
Root River in Stewartville were extended using surveyed two-foot contour maps
provided by Olmsted County.
Bridge/culvert and roadway survey data were also incorporated into the HEC-RAS
models. Survey points represented by stations and elevations were recorded in x-
y-z format, and sketches derived from field measurements provided additional
structural dimensions for culverts and bridges. Digital photographs were taken
during the survey.
Other parameters in the HEC-RAS model, including ineffective flow areas and
expansion and contraction coefficients, were based on the detailed DTM of the
study area. Starting water-surface elevations were determined using the normal
43
depth method in HEC-RAS based on the slope of the stream downstream of the
study area. Manning’s “n” values used in the model were determined by both field
reconnaissance and inspecting aerial photographs of the study area.
North Run of the North Fork of Cascade Creek
As part of a pre-countywide analysis, depths for sheet flow areas were determined
using topographic maps and by field survey (USGS, various dates (a)). There are
areas of sheet flow with depths less than 1 foot on the North Run of the North Fork
of Cascade Creek. There are also areas of sheet flow with depths between 1 and 3
feet on the North Run of the North Fork of Cascade Creek. Weir equations and
coefficients from Design of Small Dams were used in the hydraulic analysis of
North Run of the North Fork of Cascade Creek in the areas of shallow flooding
(U.S. Department of the Interior, 1973). The depths of those shallow flooding
areas were developed using the weir equations and topographic information.
For the February 4, 1998, revised countywide analysis, cross sections for the North
Run of the North Fork of Cascade Creek from its confluence with Cascade Creek
to a point approximately 0.93 miles upstream of 19th Street Northwest were
obtained from Barr Engineering. All bridges, dams, and culverts were field
surveyed to obtain elevation data and structural geometry.
Water-surface elevations of floods of the selected recurrence intervals were
computed using the USACE HEC-2 step-backwater computer program (HEC,
1991). The hydraulic analyses for all revised streams were updated to reflect the
construction of the Rochester Flood Control Project.
The starting-water surface elevations for the North Run of the North Fork of
Cascade Creek were determined from water-surface elevations computed for
Cascade Creek at the confluences. Manning's "n" values used in the hydraulic
computations were determined based upon the previous HEC-2 models developed
for the FIS of the City of Rochester and the Rochester Flood Control Project
(FEMA, 1987).
Silver Creek
For the April 17, 1995, initial countywide analysis, cross sections for Silver Creek
from its confluence with the South Fork Zumbro River to the walking bridge in the
Quarry Hill Nature Center were obtained from a MNDNR floodplain information
report (State of Minnesota, 1975). All bridges, dams, and culverts were field
surveyed to obtain elevation data and structural geometry. Water-surface
elevations of floods of the selected recurrence intervals were computed using the
USACE HEC-2 step-backwater computer program (HEC, 1991). The starting
water-surface elevations were determined from water-surface elevations computed
for the South Fork Zumbro River its confluence. Manning's "n" values used in the
hydraulic computations were determined based upon the previous stream analyses
for the FIS of the City of Rochester and the Rochester Flood Control Project
(FEMA, 1987).
44
For this countywide study, hydraulic analysis for Silver Creek from the walking
bridge in the Quarry Hill Nature Center to approximately 1.33 miles upstream of
the Silver Creek Road Northeast bridge crossing was performed using the
USACE’s computer program HEC-RAS, version 3.1.3 (HEC, 2005). The HEC-
RAS model geometry was developed using GIS applications within the USACE
computer program HEC-GeoRAS, version 4.1.1 (HEC, 2006).
Cross section data for the hydraulic analysis were based on a DTM of the area
provided by Olmsted County. Surveyed channel data were also incorporated into
the cross sections. The cross sections were cut along each stream reach
perpendicular to both the stream lines representing the centroids of overbank flow.
Bridge/culvert and roadway survey data were also incorporated into the HEC-RAS
models. Survey points represented by stations and elevations were recorded in x-
y-z format, and sketches derived from field measurements provided additional
structural dimensions for culverts and bridges. Digital photographs were taken
during the survey.
Other parameters in the HEC-RAS model, including ineffective flow areas and
expansion and contraction coefficients, were based on the detailed DTM of the
study area. Starting water-surface elevations were determined using the water-
surface elevations computed as part of the 1995 FIS for Silver Creek at the
walking bridge in the Quarry Hill Nature Center (formerly known as Silver Creek
Road). Manning’s “n” values used in the model were determined by both field
reconnaissance and inspecting aerial photographs of the study area.
South Branch Middle Fork Zumbro River
As part of a pre-countywide analysis of the South Branch Middle Fork Zumbro
River, in the unincorporated areas, data for the dry portions of the cross sections
were obtained using photogrammetric methods with aerial photographs taken in
May 1974 and May 1975, and below-water cross sections were obtained from field
measurement (Mark Hurd Aerial Surveys, Inc., 1974-1975).
The starting water-surface elevations for the South Branch Middle Fork Zumbro
River were obtained from the water-surface elevations for the Middle Branch
Zumbro River.
Manning's "n" values for the South Branch Middle Fork Zumbro River in the City
of Oronoco were assigned on the basis of past experience and field inspection of
the channel and floodplain areas.
South Fork of Bear Creek
As part of a pre-countywide analysis of the South Fork of Bear Creek, in the
unincorporated areas, data for the dry portions of the cross sections were obtained
45
using photogrammetric methods with aerial photographs taken in May 1974 and
May 1975, and below-water cross sections were obtained from field measurement
(Mark Hurd Aerial Surveys, Inc., 1974-1975). In the unincorporated areas, the
starting water-surface elevations were obtained from the MNDNR (State of
Minnesota, 1975). Roughness coefficients were chosen using field inspection data
and aerial photographs taken in May 1974 and 1975 (Mark Hurd Aerial Surveys,
Inc., 1974-1975).
South Fork Whitewater River
As part of a pre-countywide analysis of the portion of the South Fork Whitewater
River within the limits of the City of Eyota, cross section data were obtained by
field survey; data on the overbank sections were obtained by photogrammetric
methods using aerial photographs (Martinez Ortho-Mapping Corporation, 1978;
Martinez Ortho-Mapping Corporation, 1979a; Martinez Ortho-Mapping
Corporation, 1979b). Starting water-surface elevations were determined using the
slope/area method. Manning's "n" values were chosen by engineering judgment
and based on field observations of the stream and floodplain areas.
For this countywide study, hydraulic analysis for the South Fork of the
Whitewater River from approximately 0.04 miles upstream of U.S. Highway 42 to
the confluence with Tributary B within the City of Dover, hydraulic analysis were
performed using the USACE’s computer program HEC-RAS, version 3.1.3 (HEC,
2005). The HEC-RAS model geometry was developed using GIS applications
within the USACE computer program HEC-GeoRAS, version 4.1.1 (HEC, 2006).
Cross section data for the hydraulic analysis for the portion of the South Fork of
the Whitewater River that is in the city of Dover was obtained from the original
HEC-2 model. The HEC-2 model was converted to HEC-RAS and was updated to
include new bridge survey data for County Highway 10.
Starting water-surface elevations were determined using the normal depth method
in HEC-RAS based on the slope of the stream downstream of the study area.
Manning’s “n” values used in the models were determined by both field
reconnaissance and inspecting aerial photographs of the study area.
South Fork of Willow Creek
As part of a pre-countywide analysis of the South Fork of Willow Creek, in the
unincorporated areas, data for the dry portions of the cross sections were obtained
using photogrammetric methods with aerial photographs taken in May 1974 and
May 1975, and below-water cross sections were obtained from field measurement
(Mark Hurd Aerial Surveys, Inc., 1974-1975). The starting water-surface
elevations were obtained from the water-surface elevations for Willow Creek.
Roughness coefficients were chosen using field inspection data and aerial
photographs taken in May 1974 and 1975 (Mark Hurd Aerial Surveys, Inc., 1974-
1975).
46
South Fork Zumbro River
As part of the hydraulic analysis for the February 4, 1998, revised countywide
analysis, channel cross sections for the South Fork Zumbro River from a point
approximately 10,490 feet downstream of 37th Street Northwest to a point just
upstream of Mayowood Road/County Highway 125 were obtained from USACE
construction drawings, and placed within the 1980 survey information that is used
for the overbank areas (USACE, 1988a; USACE, 1988b; USACE, 1989a;
USACE, 1989b; USACE, 1991; USACE, 1992; Mark Hurd Aerial Surveys, Inc.,
1980). All bridges, dams, and culverts were field surveyed to obtain elevation data
and structural geometry.
Water-surface elevations of floods of the selected recurrence intervals were
computed using the USACE HEC-2 step-backwater computer program (HEC,
1991). The hydraulic analysis for all revised streams were updated to reflect the
construction of the Rochester Flood Control Project.
The starting water-surface elevation for the South Fork Zumbro River was
determined by a rating curve developed at the site of the old USGS gaging station.
Manning's "n" values used in the hydraulic computations were determined based
upon the previous HEC-2 models developed for the FIS of the City of Rochester
and the Rochester Flood Control Project (FEMA, 1987).
South Run of the North Fork of Cascade Creek
As part of a pre-countywide analysis, depths for sheet flow areas were determined
using topographic maps and by field survey (USGS, various dates (a)). There are
areas of sheet flow with depths between 1 and 3 feet on the South Run of the
North Fork of Cascade Creek. Weir equations and coefficients from Design of
Small Dams were used in the hydraulic analysis of South Run of the North Fork of
Cascade Creek in the areas of shallow flooding (U.S. Department of the Interior,
1973). The depths of shallow flooding areas were developed using weir equations
and topographic information.
As part of the hydraulic analysis for the February 4, 1998, revised countywide
analysis, cross sections for the South Run of the North Fork of Cascade Creek
from its confluence with Cascade Creek to a point approximately 1.1 miles
upstream of Dakota, Minnesota and Eastern Railroad were obtained from the
Minnesota DOT. All bridges, dams, and culverts were field surveyed to obtain
elevation data and structural geometry.
Water-surface elevations of floods of the selected recurrence intervals were
computed using the USACE HEC-2 step-backwater computer program (HEC,
1991). The hydraulic analysis was updated to reflect the construction of the
Rochester Flood Control Project.
47
The starting-water surface elevations for the South Run of the North Fork of
Cascade Creek were determined from water-surface elevations computed for
Cascade Creek at the confluences.
Manning's "n" values used in the hydraulic computations were determined based
upon the previous HEC-2 models developed for the FIS for the City of Rochester
and the Rochester Flood Control Project (FEMA, 1987).
Southeast Branch of Willow Creek
As part of a pre-countywide analysis for the Southeast Branch of Willow Creek, in
the unincorporated areas, data for the dry portions of the cross sections were
obtained using photogrammetric methods with aerial photographs taken in May
1974 and May 1975, and below-water cross sections were obtained from field
measurement (Mark Hurd Aerial Surveys, Inc., 1974-1975).
Depths for sheet flow areas were determined using topographic maps and by field
survey (USGS, various dates (a)). There are areas of sheet flow with depths less
than 1 foot on Southeast Branch of Willow Creek and North Run of the North
Fork of Cascade Creek.
The starting water-surface elevations were obtained from the water-surface
elevations for Willow Creek. Roughness coefficients were chosen using field
inspection data and aerial photographs taken in May 1974 and May 1975 (Mark
Hurd Aerial Surveys, Inc., 1974-1975).
Tributary B
As part of a pre-countywide analysis, stream cross sections for Tributary B were
obtained by field survey; data on the overbank sections were obtained by
photogrammetric methods using aerial photographs (Martinez Ortho-Mapping
Corporation, 1978; Martinez Ortho-Mapping Corporation, 1979a; Martinez Ortho-
Mapping Corporation, 1979b).
At their confluence, the South Fork Whitewater River and Tributary B have
similar hydrologic and hydraulic characteristics; thus, the starting water-surface
elevations for the tributary would equal those on the South Fork Whitewater River
at the confluence. Accordingly, one continuous hydraulic model was developed for
the City of Dover.
Starting water-surface elevations were determined using the slope/area method.
Manning's "n" values were chosen by engineering judgment and based on field
observations of the stream and floodplain areas.
48
West Fork of Willow Creek
As part of a pre-countywide analysis of the West Fork of Willow Creek, in the
unincorporated areas, data for the dry portions of the cross sections taken were
obtained using photogrammetric methods with aerial photographs taken in May
1974 and May 1975, and below-water cross sections were obtained from field
measurement (Mark Hurd Aerial Surveys, Inc., 1974-1975).
The starting water-surface elevations were obtained from the water-surface
elevations for Willow Creek. Roughness coefficients chosen using field inspection
data and aerial photographs taken in May 1974 and May 1975 (Mark Hurd Aerial
Surveys, Inc., 1974-1975).
West Tributary to Willow Creek
As part of a pre-countywide analysis of the West Tributary to Willow Creek, in
the unincorporated areas, data for the dry portions of the cross sections taken were
obtained using photogrammetric methods with aerial photographs taken in May
1974 and May 1975, and below-water cross sections were obtained from field
measurement (Mark Hurd Aerial Surveys, Inc., 1974-1975).
The starting water-surface elevations were obtained from the water-surface
elevations for Willow Creek. Roughness coefficients chosen using field inspection
data and aerial photographs taken in May 1974 and May 1975 (Mark Hurd Aerial
Surveys, Inc., 1974-1975).
Willow Creek
As part of the hydraulic analysis for the April 17, 1995, initial countywide
analysis, cross sections for Willow Creek from 11th Avenue Southeast/County
Highway 1 to a point approximately 0.7 mile upstream of County Road 147 were
obtained from a MNDNR floodplain information report (State of Minnesota,
1975). All bridges, dams, and culverts were field surveyed to obtain elevation data
and structural geometry. Water-surface elevations of floods of the selected
recurrence intervals were computed using the USACE HEC-2 step-backwater
computer program (HEC, 1991). The starting water-surface elevations were
determined from water-surface elevations computed for the South Fork Zumbro
River at the respective confluences. Manning's "n" values used in the hydraulic
computations for the revised streams in the April 17, 1995, countywide FIS were
determined based upon the previous stream analyses for the FIS of the City of
Rochester and the Rochester Flood Control Project (FEMA, 1987).
As part of the hydraulic analysis for the February 4, 1998, revised countywide
analysis, cross sections for Willow Creek from its confluence with Bear Creek to a
point approximately 0.7 mile upstream of County Highway 147 were obtained
from a MNDNR floodplain information report (State of Minnesota, 1975). All
bridges, dams, and culverts were field surveyed to obtain elevation data and
structural geometry.
49
Water-surface elevations of floods of the selected recurrence intervals were
computed using the USACE HEC-2 step-backwater computer program (HEC,
1991). The hydraulic analyses for all revised streams were updated to reflect the
construction of the Rochester Flood Control Project. The starting water-surface
elevations for Willow Creek were adjusted to reflect revised Bear Creek flood
elevations. Manning's "n" values used in the hydraulic computations were
determined based upon the previous HEC-2 models developed for the FIS of the
City of Rochester and the Rochester Flood Control Project (FEMA, 1987).
The Manning’s “n” values for all detailed studied streams are presented in Table 6.
Table 6 – Summary of Roughness Coefficients
Stream Channel “n” Overbank “n”
Badger Run 0.035 0.035-0.100
Bear Creek 0.030-0.050 0.035-0.150
Carey Creek 0.035-0.050 0.035-0.100
Cascade Creek 0.030-0.050 0.035-0.150
East Fork of Willow Creek * *
Hadley Valley Creek 0.035-0.050 0.035-0.100
Hadley Valley Creek Split Flow 0.035 0.035-0.100
Middle Fork Zumbro River 0.030-0.050 0.035-0.090
Mill Creek 0.035-0.045 0.035-0.110
North Branch Root River 0.035-0.038 0.035-0.110
North Run of the North Fork of Cascade Creek 0.030-0.050 0.035-0.150
Silver Creek 0.030-0.050 0.035-0.150
South Branch Middle Fork Zumbro River 0.030-0.035 0.035-0.080
South Fork of Bear Creek 0.030-0.055 0.035-0.100
South Fork Whitewater River 0.035-0.040 0.040-0.100
South Fork of Willow Creek 0.030-0.050 0.035-0.150
South Fork Zumbro River 0.030-0.050 0.035-0.150
South Run of the North Fork of Cascade Creek 0.030-0.050 0.035-0.150
Southeast Branch of Willow Creek 0.030-0.055 0.035-0.100
Tributary B 0.035-0.040 0.040-0.100
West Fork of Willow Creek 0.030-0.050 0.035-0.150
West Tributary to Willow Creek 0.030-0.050 0.035-0.150
Willow Creek 0.030-0.055 0.035-0.150
*Data Not Available
Locations of selected cross sections used in the hydraulic analyses are shown on
the Flood Profiles (Exhibit 1). For stream segments for which a floodway was
computed (Section 4.2), selected cross section locations are also shown on the
FIRM (Exhibit 2).
Flood profiles were drawn showing computed water-surface elevations for floods
of the selected recurrence intervals.
The profile baselines depicted on the FIRM represent the hydraulic modeling
baselines that match the flood profiles on this FIS report. As a result of improved
topographic data, the profile baseline, in some cases, may deviate significantly
from the channel centerline or appear outside the Special Flood Hazard Area.
50
Although flood elevations on the streams and lakes in Olmsted County can be
raised by debris accumulation and ice jams at hydraulic structures, the hydraulic
analyses for this FIS were based only on unobstructed flow. The flood elevations
shown on the profiles are thus considered valid only if hydraulic structures remain
unobstructed, operate properly, and do not fail. Changes in existing bridge
dimensions and elevations could also affect the given water-surface elevations.
3.3 Vertical Datum
All FIS reports and FIRMs are referenced to a specific vertical datum. The vertical
datum provides a starting point against which flood, ground, and structure
elevations can be referenced and compared. Until recently, the standard vertical
datum in use for newly created or revised FIS reports and FIRMs was NGVD29.
With the finalization of NAVD88, many FIS reports and FIRMs are being
prepared using NAVD88 as the referenced vertical datum.
All flood elevations shown in this FIS report and on the FIRM are referenced to
NAVD. Structure and ground elevations in the community must, therefore, be
referenced to NAVD. It is important to note that adjacent communities may be
referenced to NGVD. This may result in differences in Base Flood Elevations
(BFEs) across the corporate limits between the communities. Some of the data
used in this study were taken from the prior effective FIS reports and adjusted to
NAVD. The average conversion factor that was used to convert the data in this
FIS report to NAVD was calculated using the U.S. Army Corps of Engineers
Corpscon for Windows, Version 5.11.08 (USACE, 1997). The data points used to
determine the conversion are listed in Table 7.
Table 7 – Vertical Datum Conversion
Conversion from
Quad Name Corner Latitude Longitude NGVD to NAVD (Feet)
Pine Island SE 44.125 92.625 0.10
Oronoco SE 44.125 92.500 0.08
Zumbro Lake SE 44.125 92.375 0.09
Millville SE 44.125 92.250 0.07
Plainview SE 44.125 92.125 0.04
Byron SE 44.000 92.625 0.01
Douglas SE 44.000 92.500 0.07
Rochester SE 44.000 92.375 0.07
Chester SE 44.000 92.250 0.07
Plainview SW SE 44.000 92.125 0.03
Rock Dell SE 43.875 92.625 0.10
Salem Corners SE 43.875 92.500 0.09
Simpson SE 43.875 92.375 0.05
Marion SE 43.875 92.250 0.02
Eyota SE 43.875 92.125 0.02
Average: 0.06
51
For additional information regarding conversion between NGVD and NAVD, visit
the NGS website at www.ngs.noaa.gov, or contact the NGS at the following
address:
Vertical Network Branch, N/CG13
National Geodetic Survey, NOAA
Silver Spring Metro Center 3
1315 East-West Highway
Silver Spring, Maryland 20910
(301) 713-3191
Temporary vertical monuments are often established during the preparation of a
flood hazard analysis for the purpose of establishing local vertical control.
Although these monuments are not shown on the FIRM, they may be found in the
Technical Support Data Notebook associated with the FIS report and FIRM for
this community. Interested individuals may contact FEMA to access these data.
To obtain current elevation, description, and/or location information for
benchmarks shown on this map, please contact the Information Services Branch of
the NGS at (301) 713-3242, or visit their website at www.ngs.noaa.gov.
4.0 FLOODPLAIN MANAGEMENT APPLICATIONS
The NFIP encourages State and local governments to adopt sound floodplain management
programs. Therefore, each FIS provides 1-percent-annual-chance (100-year) flood
elevations and delineations of the 1- and 0.2-percent-annual-chance (500-year) floodplain
boundaries and 1-percent-annual-chance floodway to assist communities in developing
floodplain management measures. This information is presented on the FIRM and in
many components of the FIS report, including Flood Profiles, Floodway Data Table, and
Summary of Stillwater Elevations Table. Users should reference the data presented in the
FIS report as well as additional information that may be available at the local map
repository before making flood elevation and/or floodplain boundary determinations.
4.1 Floodplain Boundaries
To provide a national standard without regional discrimination, the 1-percent-
annual-chance flood has been adopted by FEMA as the base flood for floodplain
management purposes. The 0.2-percent-annual-chance flood is employed to
indicate additional areas of flood risk in the community.
For each stream studied by detailed methods, the 1- and 0.2-percent-annual-chance
floodplain boundaries have been delineated using the flood elevations determined
at each cross section. Between cross sections, the boundaries were interpolated
using photogrammetrically compiled maps prepared from aerial photography,
photogrammetric methods with aerial photographs, a photogrammetrically
compiled planimetric map, topographic maps, flood profiles, and photogrammetric
compilation (USGS, various dates (a); Mark Hurd Aerial Surveys, Inc., 1974-
52
1975; Stanley Consultants, Inc., 1979; State of Minnesota, 1975; USGS, various
dates (c), Mark Hurd Aerial Surveys, Inc., 1955; Martinez Ortho-Mapping
Corporation, 1978; Mark Hurd Aerial Surveys, Inc., 1978; USGS, 1972; Martinez
Ortho-Mapping Corporation, 1979a; Martinez Ortho-Mapping Corporation,
1979b). Floodplain boundaries for sheet flow areas were determined using
topographic maps (USGS, various dates (a)).
For the streams revised in the April 17, 1995, countywide FIS and for the February
4, 1998, revision the boundaries were interpolated between cross sections using
photogrammetric methods with aerial photographs, topographic maps, and cross
section data (Mark Hurd Aerial Surveys, Inc., 1980; State of Minnesota, 1975;
Mark Hurd Aerial Surveys, Inc., 1974-1975; USGS, various dates (c); Mark Hurd
Aerial Surveys, Inc., 1955; USGS, various dates (d)).
For the streams revised during this countywide revision, the boundaries were based
on the following:
• North Branch Root River: Two-foot topographic data was collected by
Horizons in April of 1999, and mapped in November of 2001. The
projection is Olmsted County HARN, and the vertical datum is NAVD88.
• North Branch Root River: Two-foot topographic survey by Yaggy Colby
Associates compiled by stereophotogrammetric method from aerial
photography taken on December 19, 1984.
• Hadley Valley Creek: Two-foot contours provided by Yaggy Colby
Associates March, 2008.
• USGS (quad maps) with a contour interval of ten-feet was used for Mill
Creek, South Fork Whitewater River, Carey Creek, and portions of the
North Branch Root River
• Rochester two-foot topography was used for Silver Creek, Badger Run, and
portions of Hadley Valley Creek.
For the streams studied by approximate methods, the 1-percent-annual-chance
floodplain boundaries were delineated using photogrammetrically compiled maps
prepared from aerial photographs and approximate analysis, topographic maps,
photogrammetric methods with aerial photographs, historic records, field
observations, Flood Hazard Boundary Maps, and USGS Flood-prone quadrangles
(Martinez Ortho-Mapping Corporation, 1979b; USGS, 1955; Mark Hurd Aerial
Surveys, Inc., 1974-1975; FIA, 1976; FIA, 1981; USGS, 1975; USGS, various
dates (e)).
The 0.1- and 0.2-percent-annual-chance floodplain boundaries are shown on the
FIRM (Exhibit 2). On this map, the 1-percent-annual-chance floodplain boundary
corresponds to the boundary of the areas of special flood hazards (Zones A, AE,
and AO), and the 0.2-percent-annual-chance floodplain boundary corresponds to
the boundary of areas of moderate flood hazards. In cases where the 1- and 0.2-
percent-annual-chance floodplain boundaries are close together, only the 1-
53
percent-annual-chance floodplain boundary has been shown. Small areas within
the floodplain boundaries may lie above the flood elevations but cannot be shown
due to limitations of the map scale and/or lack of detailed topographic data.
For the streams studied by approximate methods, only the 1-percent-annual-chance
floodplain boundary is shown on the FIRM (Exhibit 2).
4.2 Floodways
Encroachment on floodplains, such as structures and fill, reduces flood-carrying
capacity, increases flood heights and velocities, and increases flood hazards in
areas beyond the encroachment itself. One aspect of floodplain management
involves balancing the economic gain from floodplain development against the
resulting increase in flood hazard. For purposes of the NFIP, a floodway is used as
a tool to assist local communities in this aspect of floodplain management. Under
this concept, the area of the 1-percent-annual-chance floodplain is divided into a
floodway and a floodway fringe. The floodway is the channel of a stream, plus
any adjacent floodplain areas, that must be kept free of encroachment so that the 1-
percent-annual-chance flood can be carried without substantial increases in flood
heights. Minimum Federal standards limit such increases to 1 foot, provided that
hazardous velocities are not produced. The floodways in this study are presented
to local agencies as minimum standards that can be adopted directly or that can be
used as a basis for additional floodway studies. In Minnesota, however, floodplain
encroachment is limited by Minnesota Regulations to that which would cause a
0.5-foot increase in flood heights above pre-floodway conditions at any point
(MNDNR, 1977). Floodways having no more than 0.5-foot surcharge were
delineated for this FIS. The floodway can be adopted directly or that can be used
as a basis for additional floodway studies.
The floodways presented in this FIS report and on the FIRM were computed for
certain stream segments on the basis of equal-conveyance reduction from each side
of the floodplain. Floodway widths were computed at cross sections. Between
cross sections, the floodway boundaries were interpolated. The results of the
floodway computations have been tabulated for selected cross sections (Table 8).
In cases where the floodway and 1-percent-annual-chance floodplain boundaries
are either close together or collinear, only the floodway boundary has been shown.
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) BADGER RUN A 134 447 2,958 1.0 1,016.6 1,016.6 1,016.6 0.0 B 810 516 2,949 1.0 1,017.4 1,017.4 1,017.4 0.0 C 2,561 560 1,929 1.6 1,018.9 1,018.9 1,019.0 0.1 D 3,853 580 957 3.2 1,019.6 1,019.6 1,020.1 0.5 E 4,573 547 659 4.7 1,020.5 1,020.5 1,020.6 0.1 F 7,139 730 944 3.3 1,023.6 1,023.6 1,024.1 0.5 G 9,715 690 2,535 1.3 1,029.0 1,029.0 1,029.4 0.4 H 11,017 480 1,380 2.5 1,030.1 1,030.1 1,030.4 0.3 I 12,039 455 1,413 2.4 1,031.8 1,031.8 1,032.3 0.5 J 12,929 680 1,961 1.7 1,033.1 1,033.1 1,033.5 0.4 K 14,564 610 1,387 2.4 1,034.3 1,034.3 1,034.8 0.5 L 15,286 440 940 3.6 1,036.2 1,036.2 1,036.3 0.1 M 16,654 388 1,077 3.1 1,038.7 1,038.7 1,039.2 0.5 N 17,562 335 1,120 3.0 1,039.7 1,039.7 1,040.2 0.5 O 18,768 372 1,087 3.1 1,041.6 1,041.6 1,041.7 0.1 P 20,288 520 2,438 1.9 1,046.5 1,046.5 1,046.7 0.2 Q 21,472 454 1,434 3.2 1,046.8 1,046.8 1,047.1 0.3 R 23,024 356 1,295 3.2 1,048.8 1,048.8 1,049.0 0.2 S 24,388 491 1,331 3.1 1,051.7 1,051.7 1,051.9 0.2 T 26,202 120 439 9.4 1,056.2 1,056.2 1,056.2 0.0 U 26,804 130 649 5.3 1,059.3 1,059.3 1,059.6 0.3 V 27,300 158 649 5.3 1,060.4 1,060.4 1,060.5 0.1 1Feet above confluence with Bear Creek TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA BADGER RUN
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) BADGER RUN (CONTINUED) W 28,673 292 1,142 3.0 1,062.1 1,062.1 1,062.3 0.2 X 30,003 376 1,056 3.3 1,063.1 1,063.1 1,063.3 0.2 Y 31,887 292 657 5.1 1,067.1 1,067.1 1,067.6 0.5 Z 33,432 380 727 4.6 1,070.9 1,070.9 1,071.3 0.4 1Feet above confluence with Bear Creek TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA BADGER RUN
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) BEAR CREEK A 106 144 1,204 7.4 986.1 982.22 982.52 0.0 B 792 133 1,107 8.0 986.1 983.62 983.62 0.0 C 1,267 101 866 10.3 988.4 988.4 988.4 0.0 D 2,006 115 1,067 8.3 992.6 992.6 992.6 0.0 E 2,587 122 1,029 8.7 994.0 994.0 994.0 0.0 F 3,326 154 1,213 7.3 996.0 996.0 996.0 0.0 G 4,858 178 1,307 6.8 998.7 998.7 998.7 0.0 H 5,861 178 1,306 6.8 1,000.7 1,000.7 1,000.7 0.0 I 6,706 171 1,252 7.1 1,001.5 1,001.5 1,001.5 0.0 J 8,870 799 3,173 3.0 1,006.9 1,006.9 1,006.9 0.0 K 10,613 808 3,555 2.9 1,007.8 1,007.8 1,007.9 0.1 L 14,000 936 4,287 2.1 1,011.2 1,011.2 1,011.2 0.0 M 14,337 851 3,959 2.3 1,011.6 1,011.6 1,011.8 0.2 N 17,369 738 3,276 1.6 1,017.0 1,017.0 1,017.4 0.4 O 19,559 459 2,134 2.4 1,019.1 1,019.1 1,019.4 0.3 P 20,775 641 2,061 2.5 1,021.5 1,021.5 1,021.8 0.3 Q 23,179 890 5,200 1.4 1,029.5 1,029.5 1,029.7 0.2 R 24,974 500 2,680 2.8 1,029.9 1,029.9 1,030.4 0.5 S 27,667 910 2,530 3.2 1,034.9 1,034.9 1,034.9 0.0 T 31,363 510 1,610 4.6 1,040.2 1,040.2 1,040.4 0.2 U 33,528 395 2,740 2.7 1,046.7 1,046.7 1,047.1 0.4 1Feet above confluence with South Fork Zumbro River 2Elevation computed without consideration of backwater effects from South Fork Zumbro River TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA BEAR CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) BEAR CREEK (CONTINUED) V 40,234 200 2,620 0.9 1,066.4 1,066.4 1,066.4 0.0 W 41,976 185 380 5.1 1,066.7 1,066.7 1,066.7 0.0 X 43,560 110 510 3.8 1,073.7 1,073.7 1,073.7 0.0 Y 44,880 65 400 4.8 1,077.6 1,077.6 1,077.6 0.0 Z 47,098 30 200 9.6 1,088.4 1,088.4 1,088.4 0.0 AA 48,259 75 350 5.5 1,095.7 1,095.7 1,095.7 0.0 AB 49,526 150 500 2.9 1,098.9 1,098.9 1,098.9 0.0 AC 51,110 410 1,310 1.1 1,107.0 1,107.0 1,107.0 0.0 AD 54,806 430 2,150 0.3 1,141.6 1,141.6 1,141.6 0.0 AE 55,968 20 300 2.8 1,142.2 1,142.2 1,142.2 0.0 AF 57,869 20 60 8.3 1,163.0 1,163.0 1,163.0 0.0 AG 60,509 60 70 7.1 1,188.0 1,188.0 1,188.0 0.0 AH 62,198 30 60 7.0 1,207.2 1,207.2 1,207.2 0.0 AI 65,102 55 40 4.6 1,262.5 1,262.5 1,262.5 0.0 1Feet above confluence with South Fork Zumbro River TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA BEAR CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) CAREY CREEK A 719 550 5,349 0.9 1,200.0 1,200.0 1,200.3 0.3 B 1,983 591 4,781 1.0 1,200.6 1,200.6 1,200.9 0.3 1Feet above confluence with North Branch Root River TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA CAREY CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) CASCADE CREEK A 995 92 546 8.1 980.5 980.5 980.5 0.0 B 1,545 111 730 6.1 981.9 981.9 981.9 0.0 C 2,125 137 786 5.6 983.0 983.0 983.0 0.0 D 2,810 103 745 5.9 984.1 984.1 984.1 0.0 E 3,640 102 533 8.3 985.0 985.0 985.0 0.0 F 4,365 113 643 6.9 988.7 988.7 988.7 0.0 G 4,910 226 1,144 5.8 990.5 990.5 990.5 0.0 H 5,845 110 792 5.6 991.6 991.6 991.6 0.0 I 6,690 191 712 8.6 994.1 994.1 994.1 0.0 J 7,415 277 868 8.1 996.3 996.3 996.3 0.0 K 8,030 107 523 9.3 997.9 997.9 997.9 0.0 L 8,545 140 824 6.7 1,000.5 1,000.5 1,000.5 0.0 M 9,065 91 680 6.9 1,001.0 1,001.0 1,001.1 0.1 N 9,392 119 1,041 6.6 1,004.1 1,004.1 1,004.1 0.0 O 11,072 320 1,518 4.2 1,004.2 1,004.2 1,004.3 0.1 P 13,718 216 1,968 2.1 1,005.7 1,005.7 1,005.9 0.2 Q 15,429 169 1,573 2.3 1,008.0 1,008.0 1,008.1 0.1 R 17,764 58 288 12.9 1,008.8 1,008.8 1,008.9 0.1 S 21,545 1,119 1,913 4.4 1,025.8 1,025.8 1,025.8 0.0 T 26,170 905 2,595 1.5 1,035.5 1,035.5 1,035.6 0.1 U 28,145 330 485 5.8 1,036.9 1,036.9 1,036.9 0.0 1Feet above confluence with South Fork Zumbro River TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA CASCADE CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) CASCADE CREEK (CONTINUED) V 29,775 230 785 3.5 1,043.6 1,043.6 1,043.6 0.0 W 32,205 245 685 4.1 1,049.0 1,049.0 1,049.0 0.0 X 36,545 330 745 3.8 1,056.5 1,056.5 1,056.5 0.0 1Feet above confluence with South Fork Zumbro River TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA CASCADE CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) EAST FORK OF WILLOW CREEK A 1,550 470 705 2.4 1,027.5 1,027.5 1,027.5 0.0 B 4,804 380 1,352 0.9 1,044.9 1,044.9 1,045.1 0.2 C 9,924 508 637 2.0 1,065.2 1,065.2 1,065.2 0.0 1Feet above the confluence with Willow Creek TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA EAST FORK OF WILLOW CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) HADLEY VALLEY CREEK A 1,046 245 1,660 1.3 976.5 976.5 977.0 0.5 B 1,565 216 871 2.5 977.2 977.2 977.6 0.4 C 2,045 189 794 2.7 979.3 979.3 979.7 0.4 D 2,509 179 554 3.9 980.7 980.7 981.1 0.4 E 3,065 70 452 4.7 983.0 983.0 983.4 0.4 F 4,401 280 1,141 2.5 991.8 991.8 992.2 0.4 G 5,265 178 1,035 2.7 993.0 993.0 993.3 0.3 H 5,568 308 1,284 2.2 993.5 993.5 993.8 0.3 I 5,931 245 1,067 2.6 993.6 993.6 993.9 0.3 J 6,295 253 1,102 2.6 994.3 994.3 994.5 0.2 K 4,322 210 790 3.6 994.5 994.5 994.7 0.2 L 6,829 197 593 4.7 994.8 994.8 995.0 0.2 M 7,720 12 19 1.5 997.4 997.4 997.5 0.1 N 8,024 10 15 1.8 997.9 997.9 998.0 0.1 O 8,403 9 9 3.1 999.6 999.6 999.7 0.1 P 8,690 9 14 2.0 1,003.6 1,003.6 1,003.7 0.1 Q 8,832 22 18 1.6 1,004.0 1,004.0 1,004.1 0.1 R 9,380 161 218 2.3 1,007.2 1,007.2 1,007.4 0.2 S 10,393 600 1,368 1.5 1,012.9 1,012.9 1,013.4 0.5 T 11,000 303 346 5.9 1,015.4 1,015.4 1,015.4 0.0 U 10,774 326 563 3.6 1,019.3 1,019.3 1,019.7 0.4 V 12,240 211 351 5.8 1,022.8 1,022.8 1,023.1 0.3 1Feet above Limit Detailed Study (Limit of Detailed Study is approximately 512 feet downstream of East River Road Northeast) TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA HADLEY VALLEY CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) HADLEY VALLEY CREEK (CONTINUED) W 12,961 351 553 3.7 1,027.8 1,027.8 1,028.2 0.4 X 13,559 355 415 4.9 1,031.7 1,031.7 1,032.0 0.3 Y 14,155 251 402 5.0 1,036.5 1,036.5 1,036.7 0.2 Z 15,311 317 470 4.3 1,044.0 1,044.0 1,044.3 0.3 AA 16,289 287 402 5.0 1,051.3 1,051.3 1,051.6 0.3 AB 16,585 241 367 5.5 1,053.8 1,053.8 1,054.1 0.3 AC 17,124 286 550 3.7 1,057.2 1,057.2 1,057.5 0.3 1Feet above Limit of Detailed Study (Limit of Detailed Study is approximately 512 feet downstream of East River Road Northeast) TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA HADLEY VALLEY CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) HADLEY VALLEY CREEK SPLIT FLOW A 7,208 93 172 7.6 1,000.4 1,000.4 1,000.5 0.1 B 7,512 122 320 4.1 1,002.5 1,002.5 1,002.9 0.4 C 7,891 200 2,483 0.5 1,002.8 1,002.8 1,003.2 0.4 D 8,178 332 4,541 0.3 1,002.8 1,002.8 1,003.2 0.4 E 8,320 240 3,497 0.4 1,002.8 1,002.8 1,003.2 0.4 F 8,868 187 2,665 0.3 1,002.8 1,002.8 1,003.2 0.4 1Feet above East River Road Northeast TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA HADLEY VALLEY CREEK SPLIT FLOW
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) MIDDLE FORK ZUMBRO RIVER A 24,725 320 4,085 6.9 937.5 937.5 937.5 0.0 B 25,485 400 6,875 4.1 938.5 938.5 938.5 0.0 C 27,005 160 3,850 7.4 938.7 938.7 938.7 0.0 D 28,620 400 2,640 10.7 940.2 940.2 940.2 0.0 E 30,010 172 2,623 10.8 945.4 945.4 945.9 0.5 F 31,100 470 6,123 4.6 947.7 947.7 948.2 0.5 G 31,839 197 3,043 9.3 947.8 947.8 948.3 0.5 H 32,051 205 3,444 8.2 959.8 959.8 959.8 0.0 I 32,579 240 4,053 7.0 960.4 960.4 960.5 0.1 J 33,001 820 11,672 1.6 961.2 961.2 961.4 0.2 K 34,057 1,471 22,954 0.8 961.3 961.3 961.4 0.1 L 34,796 915 12,323 1.5 961.3 961.3 961.4 0.1 M 35,694 495 7,176 2.7 961.3 961.3 961.4 0.1 N 36,222 527 8,180 2.3 963.4 963.4 963.5 0.1 O 37,753 1,049 14,880 1.3 963.5 963.5 963.7 0.2 P 38,809 856 10,056 1.9 964.0 964.0 964.1 0.1 Q 39,495 1,493 15,215 1.3 964.1 964.1 964.1 0.0 1Feet above the confluence with Zumbro River TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA MIDDLE FORK ZUMBRO RIVER
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) MILL CREEK A 1,392 160 1,403 7.3 975.3 975.3 975.4 0.1 B 3,695 475 3,522 2.9 978.5 978.5 978.8 0.3 C 5,490 440 1,792 5.7 980.3 980.3 980.5 0.2 D 5,642 595 2,253 4.6 982.8 982.8 983.2 0.4 E 8,015 695 2,776 3.7 986.4 986.4 986.6 0.2 F 11,445 510 2,202 4.7 992.5 992.5 992.9 0.4 1Feet above County Boundary TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA MILL CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) NORTH BRANCH ROOT RIVER A 146,253 296 3,274 5.7 1,176.0 1,176.0 1,176.2 0.2 B 147,156 380 4,381 4.3 1,176.9 1,176.9 1,177.1 0.2 C 149,220 1,350 9,885 1.9 1,178.5 1,178.5 1,178.7 0.2 D 150,334 1,450 8,680 2.2 1,178.7 1,178.7 1,179.1 0.4 E 153,306 1,250 10,389 1.8 1,184.4 1,184.4 1,184.4 0.0 F 154,613 1,328 9,734 1.9 1,184.6 1,184.6 1,184.6 0.0 G 156,659 1,150 8,680 2.2 1,185.3 1,185.3 1,185.5 0.2 H 159,234 630 3,712 5.0 1,187.0 1,187.0 1,187.2 0.2 I 159,607 650 4,759 3.9 1,188.1 1,188.1 1,188.4 0.3 J 161,514 688 5,257 3.6 1,190.6 1,190.6 1,190.8 0.2 K 163,874 426 3,538 5.3 1,195.1 1,195.1 1,195.3 0.2 L 164,328 351 3,111 6.0 1,195.5 1,195.5 1,195.7 0.2 M 166,100 406 3,659 5.1 1,198.1 1,198.1 1,198.2 0.1 N 166,597 370 3,454 5.4 1,198.6 1,198.6 1,198.8 0.2 O 167,377 626 5,797 3.2 1,200.0 1,200.0 1,200.3 0.3 P 168,789 1,213 6,919 2.7 1,200.9 1,200.9 1,201.2 0.3 Q 170,581 1,207 8,489 2.2 1,202.3 1,202.3 1,202.5 0.2 R 171,278 1,181 6,746 2.8 1,202.6 1,202.6 1,202.8 0.2 S 172,532 1,106 6,364 2.9 1,203.3 1,203.3 1,203.8 0.5 T 173,635 891 5,628 3.3 1,204.4 1,204.4 1,204.7 0.3 U 174,930 533 3,971 4.7 1,206.3 1,206.3 1,206.6 0.3 V 175,581 359 3,300 5.7 1,207.2 1,207.2 1,207.4 0.2 1Feet above Olmsted/Dodge County Boundary TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA NORTH BRANCH ROOT RIVER
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) NORTH RUN OF THE NORTH FORK OF CASCADE CREEK A 345 335 2,296 1.3 1,006.7 1,006.7 1,006.7 0.0 B 795 210 936 3.0 1,006.7 1,006.7 1,006.7 0.0 C 1,430 86 462 4.0 1,007.3 1,007.3 1,007.4 0.1 D 2,050 85 502 3.7 1,007.6 1,007.6 1,008.0 0.4 E 2,760 119 413 4.8 1,008.9 1,008.9 1,009.2 0.3 F 3,420 440 1,337 1.7 1,009.8 1,009.8 1,010.1 0.3 G 4,240 510 1,513 1.8 1,012.0 1,012.0 1,012.5 0.5 H 5,150 380 590 5.2 1,012.5 1,012.5 1,013.0 0.5 I 6,220 452 417 5.0 1,015.1 1,015.1 1,015.1 0.0 J 7,400 422 401 5.8 1,018.3 1,018.3 1,018.6 0.3 K 8,000 370 497 3.7 1,020.4 1,020.4 1,020.8 0.4 L 8,570 400 384 3.5 1,022.0 1,022.0 1,022.1 0.1 M 9,795 43 49 4.1 1,023.0 1,022.9 1,023.0 0.0 N 11,114 105 735 0.3 1,030.2 1,030.2 1,030.3 0.1 O 12,214 61 170 0.5 1,030.3 1,030.3 1,030.3 0.0 P 12,714 36 49 1.9 1,030.3 1,030.3 1,030.4 0.1 Q 13,584 30 28 3.2 1,033.8 1,033.8 1,033.8 0.0 1Feet above confluence with Cascade Creek TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA NORTH RUN OF THE NORTH FORK OF CASCADE CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SILVER CREEK A 745 107 694 5.0 982.7 982.7 982.7 0.0 B 2,365 135 570 6.1 985.5 985.5 985.5 0.0 C 2,555 149 708 4.9 986.5 986.5 986.5 0.0 D 3,435 220 794 4.3 988.6 988.6 988.6 0.0 E 4,485 386 1,051 3.3 992.1 992.1 992.2 0.1 F 5,085 312 905 3.8 994.6 994.6 994.6 0.0 G 6,785 96 313 11.0 1,003.9 1,003.9 1,003.9 0.0 H 6,985 128 934 3.7 1,007.2 1,007.2 1,007.2 0.0 I 8,845 286 551 6.3 1,010.5 1,010.5 1,010.5 0.0 J 9,395 200 924 3.4 1,015.1 1,015.1 1,015.1 0.0 K 10,294 192 744 4.2 1,018.1 1,018.1 1,018.6 0.5 L 10,824 140 601 5.2 1,020.6 1,020.6 1,020.8 0.2 M 11,241 99 469 6.6 1,022.2 1,022.2 1,022.3 0.1 N 11,623 121 722 4.3 1,025.1 1,025.1 1,025.1 0.0 O 12,394 240 944 3.4 1,026.1 1,026.1 1,026.1 0.0 P 13,254 335 1,004 3.2 1,028.3 1,028.3 1,028.3 0.0 Q 14,084 232 704 4.6 1,032.3 1,032.3 1,032.3 0.0 R 14,986 296 919 3.5 1,036.0 1,036.0 1,036.3 0.3 S 15,771 290 840 3.9 1,039.0 1,039.0 1,039.5 0.5 T 16,343 255 657 4.6 1,041.0 1,041.0 1,041.3 0.3 U 16,685 253 1,003 3.0 1,045.9 1,045.9 1,045.9 0.0 V 17,624 122 428 7.0 1,050.3 1,050.3 1,050.3 0.0 1Feet above confluence with South Fork Zumbro River TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SILVER CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SILVER CREEK (CONTINUED) W 18,297 156 639 4.7 1,055.3 1,055.3 1,055.5 0.2 X 18,855 86 513 5.8 1,059.2 1,059.2 1,059.2 0.0 Y 19,643 129 661 4.5 1,065.1 1,065.1 1,065.1 0.0 Z 20,841 165 612 4.9 1,072.4 1,072.4 1,072.7 0.3 AA 21,686 190 529 5.7 1,076.8 1,076.8 1,076.9 0.1 AB 22,442 165 657 4.6 1,080.8 1,080.8 1,081.1 0.3 AC 23,227 153 440 6.8 1,084.6 1,084.6 1,085.1 0.5 AD 24,215 200 588 5.1 1,092.3 1,092.3 1,092.7 0.4 AE 24,852 113 387 7.8 1,095.7 1,095.7 1,096.2 0.5 AF 25,433 87 432 6.9 1,099.4 1,099.4 1,099.5 0.1 AG 26,403 124 585 5.1 1,104.3 1,104.3 1,104.7 0.4 1Feet above confluence with South Fork Zumbro River TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SILVER CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SOUTH FORK WHITEWATER RIVER A 11,923 228 1,077 3.5 1,133.7 1,133.7 1,133.7 0.0 B 13,368 300 1,579 2.3 1,135.8 1,135.8 1,136.1 0.3 C 14,563 442 1,680 2.2 1,136.8 1,136.8 1,137.2 0.4 D 15,873 147 515 7.1 1,138.2 1,138.2 1,138.5 0.3 E 16,591 246 1,527 2.5 1,143.3 1,143.3 1,143.4 0.1 F 17,346 554 2,966 1.3 1,143.4 1,143.4 1,143.7 0.3 G 17,886 525 2,497 1.5 1,143.5 1,143.5 1,143.8 0.3 H 18,656 564 2,449 1.5 1,143.6 1,143.6 1,143.9 0.3 I 19,968 100 507 7.6 1,145.1 1,145.1 1,145.4 0.3 J 452 44 161 3.0 1,220.4 1,220.4 1,220.5 0.1 K 3402 70 161 2.8 1,222.0 1,222.0 1,222.0 0.0 L 1,5352 48 87 4.0 1,224.8 1,224.8 1,225.2 0.4 M 2,6002 70 129 2.7 1,228.5 1,228.5 1,228.5 0.0 N 2,9452 50 81 4.2 1,229.4 1,229.4 1,229.5 0.1 O 3,6252 21 71 4.8 1,231.1 1,231.1 1,231.6 0.5 P 4,1802 32 106 3.2 1,232.4 1,232.4 1,232.9 0.5 Q 4,3552 25 70 4.7 1,232.7 1,232.7 1,233.1 0.4 R 4,6802 31 82 4.0 1,234.2 1,234.2 1,234.3 0.1 1Feet above Olmsted / Winona County Boundary 2Feet above U.S. Highway 14 TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SOUTH FORK WHITEWATER RIVER
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SOUTH BRANCH MIDDLE FORK ZUMBRO RIVER A 306 807 10,309 2.8 961.2 961.2 961.4 0.2 B 1,098 735 10,363 1.9 963.8 963.8 963.9 0.1 C 2,048 725 9,910 2.0 963.9 963.9 964.0 0.1 D 3,051 860 11,100 1.8 964.0 964.0 964.1 0.1 E 3,686 418 4,721 4.1 964.0 964.0 964.3 0.3 F 5,005 602 6,840 2.8 964.6 964.6 964.7 0.1 G 5,427 153 10,979 1.8 964.8 964.8 964.9 0.1 H 6,325 972 9,769 2.0 964.9 964.9 965.1 0.2 1Feet above confluence with Middle Fork Zumbro TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SOUTH BRANCH MIDDLE FORK ZUMBRO RIVER
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SOUTH FORK OF BEAR CREEK A 2,350 600 2,080 3.1 1,052.8 1,052.8 1,052.9 0.1 B 3,105 815 5,720 1.1 1,056.4 1,056.4 1,056.4 0.0 C 5,180 500 2,170 3.0 1,057.1 1,057.1 1,057.1 0.0 D 6,640 450 1,310 4.9 1,062.1 1,062.1 1,062.5 0.4 E 8,275 490 2,780 2.3 1,065.6 1,065.6 1,065.7 0.1 F 9,895 495 2,410 2.7 1,067.5 1,067.5 1,067.7 0.2 G 12,115 605 2,110 3.1 1,071.6 1,071.6 1,071.9 0.3 H 15,115 350 2,130 3.0 1,077.8 1,077.8 1,078.1 0.3 1Feet above confluence with Bear Creek TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SOUTH FORK OF BEAR CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SOUTH FORK OF WILLOW CREEK A 2,025 239 1,432 0.6 1,046.6 1,046.6 1,046.6 0.0 B 2,720 53 53 4.4 1,049.5 1,049.5 1,049.5 0.0 1Feet above confluence with Willow Creek TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SOUTH FORK OF WILLOW CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SOUTH FORK ZUMBRO RIVER A 4,730 466 6,213 5.2 968.9 968.9 969.3 0.4 B 7,700 346 4,579 5.2 971.1 971.1 971.5 0.4 C 9,660 389 5,496 4.3 972.1 972.1 972.4 0.3 D 10,905 430 4,952 5.4 972.9 972.9 973.1 0.2 E 12,665 722 7,344 4.8 974.0 974.0 974.2 0.2 F 14,170 792 6,193 4.7 974.8 974.8 975.0 0.2 G 15,810 682 7,186 5.9 975.5 975.5 975.7 0.2 H 17,615 503 4,249 6.8 976.3 976.3 976.5 0.2 I 18,615 265 3,840 5.3 977.1 977.1 977.3 0.2 J 18,945 264 4,550 4.5 977.6 977.6 977.8 0.2 K 19,850 301 4,609 4.5 977.9 977.9 978.1 0.2 L 20,730 253 4,041 4.8 978.1978.1 978.2 0.1 M 21,140 222 3,209 6.1 978.1 978.1 978.4 0.2 N 21,450 234 2,647 7.4 979.0 979.0 979.0 0.0 O 22,950 872 8,045 2.4 980.8 980.8 980.8 0.0 P 24,375 301 3,517 5.5 980.9 980.9 980.9 0.0 Q 25,070 311 3,569 5.5 981.6 981.6 981.6 0.0 R 26,115 171 2,271 8.6 982.2 982.2 982.2 0.0 S 26,430 186 2,285 8.5 983.0 983.0 983.0 0.0 T 27,055 206 2,678 7.3 984.2 984.2 984.2 0.0 U 27,500 189 2,673 7.1 984.7 984.7 984.7 0.0 1Feet above Limit of Detailed Study (Limit of Detailed Study is approximately 10,490 feet downstream of 37th Street Northwest/County Highway 22) TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SOUTH FORK ZUMBRO RIVER
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SOUTH FORK ZUMBRO RIVER (CONTINUED) V 28,170 350 2,929 6.7 985.5 985.5 985.5 0.0 W 28,730 219 2,680 5.5 986.3 986.3 986.3 0.0 X 29,515 178 2,564 5.8 987.0 987.0 987.0 0.0 Y 30,530 122 1,568 9.3 988.5 988.5 988.6 0.1 Z 31,210 110 1,643 9.0 990.6 990.6 990.6 0.0 AA 31,790 114 1,772 8.4 992.4 992.4 992.5 0.1 AB 32,420 184 2,194 6.7 994.0 994.0 994.0 0.0 AC 32,910 153 1,619 9.1 994.4 994.4 994.4 0.0 AD 33,258 153 1,671 8.9 995.5 995.5 995.5 0.0 AE 33,545 326 2,254 6.9 996.5 996.5 996.5 0.0 AF 33,990 375 3,067 5.2 997.6 997.6 997.6 0.0 AG 34,715 112 1,776 8.3 997.6 997.6 997.6 0.0 AH 35,520 155 1,474 10.0 998.5 998.5 998.5 0.0 AI 35,800 151 1,480 10.0 999.4 999.4 999.5 0.1 AJ 36,020 248 2,820 5.3 1,001.3 1,001.3 1,001.3 0.0 AK 38,520 312 3,472 4.3 1,003.3 1,003.3 1,003.3 0.0 AL 39,190 287 3,222 4.6 1,003.6 1,003.6 1,003.6 0.0 AM 41,825 192 2,382 6.2 1,011.5 1,011.5 1,011.6 0.1 AN 45,320 490 3,120 5.8 1,015.2 1,015.2 1,015.7 0.5 1Feet above Limit of Detailed Study (Limit of Detailed Study is approximately 10,490 feet downstream of 37th Street Northwest/County Highway 22) TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SOUTH FORK ZUMBRO RIVER
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SOUTH FORK ZUMBRO RIVER (CONTINUED) AO 48,590 1,446 4,840 4.4 1,019.2 1,019.2 1,019.3 0.1 AP 54,650 864 3,977 5.0 1,027.8 1,027.8 1,028.0 0.2 1Feet above Limit of Detailed Study (Limit of Detailed Study is approximately 10,490 feet downstream of 37th Street Northwest/County Highway 22) TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SOUTH FORK ZUMBRO RIVER
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SOUTH RUN OF THE NORTH FORK OF CASCADE CREEK A 1,670 113 280 6.9 1,010.5 1,010.5 1,010.5 0.0 B 2,175 50 282 6.2 1,012.0 1,012.0 1,012.0 0.0 C 3,200 142 700 3.3 1,014.0 1,014.0 1,014.0 0.0 D 4,885 559 1,068 4.0 1,016.0 1,016.0 1,016.1 0.1 E 6,385 85 361 5.5 1,019.2 1,019.2 1,019.4 0.2 F 8,150 260 605 6.5 1,023.7 1,023.7 1,023.7 0.0 G 8,455 211 502 8.2 1,024.5 1,024.5 1,024.8 0.3 H 9,405 126 566 4.4 1,026.7 1,026.7 1,027.1 0.5 I 10,015 130 908 2.9 1,030.0 1,030.0 1,030.0 0.0 J 10,575 166 809 3.0 1,030.4 1,030.4 1,030.4 0.0 K 12,215 311 1,098 1.9 1,035.4 1,035.4 1,035.9 0.5 1Feet above confluence with Cascade Creek TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SOUTH RUN OF THE NORTH FORK OF CASCADE CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) SOUTHEAST BRANCH OF WILLOW CREEK A 1,400 229 610 3.5 1,080.6 1,080.6 1,080.9 0.3 B 2,475 53 459 4.6 1,089.1 1,089.1 1,089.2 0.1 C 3,745 77 252 8.5 1,094.7 1,094.7 1,094.8 0.1 D 5,180 220 980 2.2 1,105.7 1,105.7 1,105.7 0.0 E 6,045 180 245 8.7 1,107.3 1,107.3 1,107.7 0.4 F 6,795 135 465 4.6 1,111.9 1,111.9 1,112.3 0.4 1Feet above confluence with Willow Creek TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA SOUTHEAST BRANCH OF WILLOW CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) TRIBUTARY B A 120 155 492 5.1 1,145.3 1,145.3 1,145.3 0.0 B 180 206 576 4.4 1,145.6 1,145.6 1,145.6 0.0 C 825 584 1,785 1.4 1,146.1 1,146.1 1,146.1 0.0 1Feet above confluence with South Fork Whitewater River TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA TRIBUTARY B
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) WEST FORK OF WILLOW CREEK A 715 700 650 0.1 1,068.1 1,068.1 1,068.2 0.1 B 1,515 310 30 3.2 1,080.6 1,080.6 1,080.6 0.0 C 2,540 190 805 0.4 1,101.4 1,101.4 1,101.4 0.0 1Feet above confluence with Willow Creek TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA WEST FORK OF WILLOW CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) WEST TRIBUTARY TO WILLOW CREEK A 2,120 345 411 1.5 1,023.7 1,022.02 1,023.7 0.0 1Feet above confluence with Willow Creek 2Elevation computed without consideration of flooding controlled by Willow Creek TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA WEST TRIBUTARY TO WILLOW CREEK
FLOODING SOURCE FLOODWAY 1-PERCENT-ANNUAL-CHANCE-FLOOD WATER SURFACE ELEVATION CROSS SECTION DISTANCE1 WIDTH (FEET) SECTION AREA (SQUARE FEET) MEAN VELOCITY (FEET PER SECOND) REGULATORY (FEET NAVD) WITHOUT FLOODWAY (FEET NAVD) WITH FLOODWAY (FEET NAVD) INCREASE (FEET) WILLOW CREEK A 5,016 8102 2,818 1.8 1,019.6 1,019.6 1,019.7 0.1 B 11,352 500 2,936 1.1 1,033.0 1,033.0 1,033.4 0.4 C 16,526 1,0603 710 4.2 1,040.2 1,040.2 1,040.2 0.0 D 19,272 267 920 5.5 1,051.2 1,051.2 1,051.2 0.0 E 22,334 615 1,372 4.9 1,056.5 1,056.5 1,056.8 0.3 F 26,136 646 1,106 3.9 1,066.8 1,066.8 1,067.1 0.3 G 32,604 298 253 5.1 1,086.3 1,086.3 1,086.3 0.0 1Feet above confluence with Bear Creek 2Combined West Tributary to Willow Creek/Willow Creek Floodway 3Combined South Fork of Willow Creek/Willow Creek Floodway TABLE 8 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS FLOODWAY DATA WILLOW CREEK
85
The area between the floodway and 1-percent-annual-chance floodplain boundaries
is termed the floodway fringe. The floodway fringe encompasses the portion of
the floodplain that could be completely obstructed without increasing the WSEL of
the 1-percent-annual-chance flood more than 1 foot at any point. Typical
relationships between the floodway and the floodway fringe and their significance
to floodplain development are shown in Figure 1.
Figure 1 - Floodway Schematic
5.0 INSURANCE APPLICATIONS
For flood insurance rating purposes, flood insurance zone designations are assigned to a
community based on the results of the engineering analyses. These zones are as follows:
Zone A
Zone A is the flood insurance risk zone that corresponds to the 1-percent-annual-chance
floodplains that are determined in the FIS by approximate methods. Because detailed
hydraulic analyses are not performed for such areas, no BFEs or base flood depths are
shown within this zone.
Zone AE
Zone AE is the flood insurance risk zone that corresponds to the 1-percent-annual-chance
floodplains that are determined in the FIS by detailed methods. In most instances, whole-
foot BFEs derived from the detailed hydraulic analyses are shown at selected intervals
within this zone.
86
Zone AO
Zone AO is the flood insurance risk zone that corresponds to the areas of 1-percent-
annual-chance shallow flooding (usually sheet flow on sloping terrain) where average
depths are between 1 and 3 feet. Average whole-foot base flood depths derived from the
detailed hydraulic analyses are shown within this zone.
Zone X
Zone X is the flood insurance risk zone that corresponds to areas outside the 0.2-percent-
annual-chance floodplain, areas within the 0.2-percent-annual-chance floodplain, areas of
1-percent-annual-chance flooding where average depths are less than 1 foot, areas of 1-
percent-annual-chance flooding where the contributing drainage area is less than 1 square
mile, and areas protected from the 1-percent-annual-chance flood by levees. No BFEs or
base flood depths are shown within this zone.
Zone D
Zone D is the flood insurance risk zone that corresponds to unstudied areas where flood
hazards are undetermined, but possible.
6.0 FLOOD INSURANCE RATE MAP
The FIRM is designed for flood insurance and floodplain management applications.
For flood insurance applications, the map designates flood insurance risk zones as
described in Section 5.0 and, in the 1-percent-annual-chance floodplains that were studied
by detailed methods, shows selected whole-foot BFEs or average depths. Insurance
agents use the zones and BFEs in conjunction with information on structures and their
contents to assign premium rates for flood insurance policies.
For floodplain management applications, the map shows by tints, screens, and symbols,
the 1- and 0.2-percent-annual-chance floodplains, floodways, and the locations of selected
cross sections used in the hydraulic analyses and floodway computations.
The countywide FIRM presents flooding information for the entire geographic area of
Olmsted County. Previously, FIRMs were prepared for each incorporated community and
the unincorporated areas of the County identified as flood-prone. Historical data relating
to the maps prepared for each community are presented in Table 9.
Table 1 COMMUNITY NAME INITIAL IDENTIFICATION FLOOD HAZARD BOUNDAY MAP REVISION DATE FIRM EFFECTIVE DATE FIRM REVISION DATE 1Byron, City of N/A None N/A None Chatfield, City of August 13, 1976 None August 2, 1982 None Dover, City of November 1, 1974 October 17, 1981 April 15, 1982 None Eyota, City of April 12, 1974 October 17, 1975 December 15, 1981 None Olmsted County (Unincorporated Areas) May 19, 1981 None May 19, 1981 None Oronoco, City of May 10, 1974 June 11, 1976 November 4, 1981 None Pine Island, City of May 24, 1974 August 8, 1975 March 2, 1981 February 16, 1994 Rochester, City of March 27, 1971 None March 27, 1971 July 1, 1974 February 13, 1976 February 4, 1981 August 4, 1987 Stewartville, City of May 3, 1974 December 20, 1974 September 2, 1982 None 1No special flood hazard areas identified TABLE 9 FEDERAL EMERGENCY MANAGEMENT AGENCY OLMSTED COUNTY, MN AND INCORPORATED AREAS COMMUNITY MAP HISTORY Table 2 – Community Map History n
88
7.0 OTHER STUDIES
This report either supersedes or is compatible with all previous studies on streams studied
in this report and should be considered authoritative for purposes of the NFIP.
8.0 LOCATION OF DATA
Information concerning the pertinent data used in the preparation of this study can be
obtained by contacting FEMA, Federal Insurance and Mitigation Division, 536 South
Clark Street, Sixth Floor, Chicago, Illinois 60605.
9.0 BIBLIOGRAPHY AND REFERENCES
City of Rochester Flood Plain Zoning Regulations, adopted by Rochester Common
Council, December 1975.
Federal Emergency Management Agency, Flood Insurance Study, City of Pine Island,
Olmsted County, Minnesota, Flood Insurance Study Report, September 2, 1980a; Flood
Insurance Rate Map, March 2, 1981.
Federal Emergency Management Agency, Flood Insurance Study, Olmsted County,
Minnesota (Unincorporated Areas), Flood Insurance Study Report, November 19, 1980b;
Flood Insurance Rate Map, August 1, 1983.
Federal Emergency Management Agency, Flood Insurance Study, City of Dover, Olmsted
County, Minnesota, Flood Insurance Study Report, October 15, 1981a; Flood Insurance
Rate Map, April 15, 1982.
Federal Emergency Management Agency, Flood Insurance Study, City of Oronco,
Olmsted County, Minnesota, Flood Insurance Study Report, May 4, 1981b; Flood
Insurance Rate Map, November 4, 1981.
Federal Emergency Management Agency, Flood Insurance Study, City of Chatfield,
Fillmore and Olmsted County, Minnesota, Flood Insurance Study Report, February 2,
1982a; Flood Insurance Rate Map, August 2, 1982.
Federal Emergency Management Agency, Flood Insurance Study, City of Stewartville,
Olmsted County, Minnesota, Flood Insurance Study Report, March 2, 1982b; Flood
Insurance Rate Map, September 2, 1982.
Federal Emergency Management Agency, Flood Insurance Study, City of Rochester,
Olmsted County, Minnesota, August 4, 1987.
Federal Emergency Management Agency, Flood Insurance Study, City of Pine Island,
Goodhue County, Minnesota, February 16, 1994.
89
Federal Emergency Management Agency, Flood Insurance Study, Olmsted County,
Minnesota and Incorporated Areas, April 17, 1995.
Federal Emergency Management Agency, Flood Insurance Study, Olmsted County,
Minnesota and Incorporated Areas, February 4, 1998.
Federal Insurance Administration, Flood Hazard Boundary Map, City of Chatfield,
Fillmore and Olmsted Counties, Minnesota, August 1976.
Federal Insurance Administration, Flood Insurance Study, City of Eyota, Olmsted County,
Minnesota, Flood Insurance Study Report, June 15, 1981; Flood Insurance Rate Map,
December 15, 1981.
Hydrologic Engineering Center, HEC-2 Water Surface Profiles, U.S. Army Corps of
Engineers, Davis, California, May 1991.
Hydrologic Engineering Center, HEC-FFA, Flood Frequency Analysis, U.S. Army Corps
of Engineers, Davis, California, May 1992.
Hydrologic Engineering Center, HEC-RAS River Analysis System, Version 3.1.3, U.S.
Army Corps of Engineers, Davis, California, May 2005.
Hydrologic Engineering Center, HEC-GeoRAS, River Analysis System, U.S. Army Corps
of Engineers, Davis, California, January 2006.
Horizons, Inc., Two-Foot Topography derived from Orthophotographs for the City of
Rochester, Minnesota, April 12, 2006.
Mark Hurd Aerial Surveys, Inc., Topographic Maps, Contour Interval 2 Feet: Rochester,
Minnesota, April 1955.
Mark Hurd Aerial Surveys, Inc., Aerial Photographs for Olmsted County, Minnesota,
Scale 1:6,000, Contour Interval 2 Feet, May 1974 and 1975.
Mark Hurd Aerial Surveys, Inc., Planimetric Map, Scale 1:3,600: City of Oronoco,
Minnesota, 1978.
Mark Hurd Aerial Surveys, Inc., Aerial Photogrammetric Topography, Scale 1:2,400,
Contour Interval 2 Feet: South Fork Zumbro River Watershed, City of Rochester,
November 1980.
Martinez Ortho-Mapping Corporation, Aerial Photographs, Scale 1:7,200, No. 78543M-1-
1 through No. 78543M-1-8, City of Stewartville, November 15, 1978.
Martinez Ortho-Mapping Corporation, Dover Aerial Photographs, No. AD-9A-1 through
No. AD-9A-2, No. AD-9B-1 through AD-9B-2, Scale 1:9,600, April 23, 1979a.
90
Martinez Ortho-Mapping Corporation, Eyota Aerial Photographs, Scale 1:9,600, No. AD-
8-1 through AD-8-4, flown April 23, 1979b.
Minnesota Department of Natural Resources, Division of Water, The Regulatory
Floodway in Floodplain Management, Technical Report No. 6, September 1977.
National Weather Service, Rainfall Frequency Atlas of the United States, 30-Minute to
24-Hour Durations, 1- to 100-Year Return Periods, Technical Paper 40, U.S. Department
of Commerce, 1961.
Olmsted County Board of Commissioners, County of Olmsted Zoning Ordinance, adopted
January 2, 1970.
Report, Structural Condition Assessment of the Lake Shady Dam, Oronoco, MN, Olmsted
County, MN, February 2011.
Soil Conservation Service, Bureau of Chemistry and Soils, Soil Survey of Olmsted
County, Minnesota, U.S. Department of Agriculture, 1928.
Soil Conservation Service, Soil Survey, Dodge County, Minnesota, U.S. Department of
Agriculture, August 1961.
Soil Conservation Service, Engineering Division, Hydrology, U.S. Department of
Agriculture, National Engineering Handbook, Section 4, August 1972a.
Soil Conservation Service, Soil Survey, Steele County, Minnesota, U.S. Department of
Agriculture, August 1972b.
Soil Conservation Service, Technical Report No. 55, Urban Hydrology for Small
Watersheds, U.S. Department of Agriculture, 1975.
Soil Conservation Service, Soils Atlas Sheets for Olmsted County, Minnesota
(unpublished). Included in correspondence from George Poch of the Rochester,
Minnesota, Soil Conservation Service office to Deborah Hussey of TKDA, November
1979.
Soil Conservation Service, Technical Release No. 20, Computer Program, Project
Formulation, Hydrology, U.S. Department of Agriculture, September 1983.
Soil Conservation Service, Technical Release No. 61, WSP-2 Computer Program, U.S.
Department of Agriculture, March 27, 1989.
Stanley Consultants, Inc., Cascade Overflow Reach Map, Scale 1:1,200, April 1979.
91
State of Minnesota, Department of Natural Resources, Division of Waters, High Altitude
Aerial Photographs of Minnesota, St. Paul, Minnesota, 1969.
State of Minnesota, Department of Natural Resources, Division of Waters, Flood Plain
Information, Supplemental Report on South Fork Zumbro River and Tributaries in the
Vicinity of Rochester, Minnesota, October 1975.
U.S. Army Corps of Engineers, St. Paul District, Flood Plain Information, South Fork
Zumbro River and Tributaries, Rochester, Minnesota, St. Paul, Minnesota, August 1958.
U.S. Army Corps of Engineers, St. Paul District, Flood Control, South Fork Zumbro
River at Rochester, Minnesota, Design Memorandum No. 1, Phase 2, General Project
Design, September 1982.
U.S. Army Corps of Engineers, Stage 1A-1 Construction Drawings, July 1988a.
U.S. Army Corps of Engineers, Stage 1A-2B Construction Drawings, March 1988b.
U.S. Army Corps of Engineers, Stage 1B-1 Construction Drawings, March 1989a.
U.S. Army Corps of Engineers, Stage 1B-3 Construction Drawings, November 1989b.
U.S. Army Corps of Engineers, Stage 2B Construction Drawings, August 1991.
U.S. Army Corps of Engineers, Stage 2A Construction Drawings, June 1992.
U.S. Army Corps of Engineers, Topographic Engineering Center, Corpscon v. 5.11.08,
Computer Program, Alexandria, Virginia, September 1997.
U.S. Census Bureau, American Fact Finder, Olmsted County, Minnesota, 2010, Retrieved
April 29, 2010, from http://www.factfinder.census.gov.
U.S. Department of the Interior, Bureau of Reclamation, Design of Small Dams,
Second Edition, 1973.
U.S. Department of Transportation, Bureau of Public Roads, Hydraulics Branch, Manual
No. 6-294, Hydraulic Engineering Circular No. 5, Hydraulic Charts for the Selection of
Highway Culverts, Minnesota Department of Transportation Drainage Manual, December
1965.
U.S. Geological Survey, Water Resources Data for Minnesota, Annual Reports, 1949 to
Present.
U.S. Geological Survey, St. Paul, Minnesota, (open files). April 8, 1976, and July 20,
1978.
92
U.S. Geological Survey, Scientific Investigations Report 2011-5045, Floods of September
2012 in Southern Minnesota, U.S. Department of the Interior, 2011.
U.S. Geological Survey, Water-Resources Investigations Report 77-31, Techniques for
Estimating Magnitude and Frequency of Floods in Minnesota, U.S. Department of the
Interior, May 1977.
U.S. Geological Survey, Water-Resources Investigations Report 97-4249, Techniques for
Estimating Peak Flow on Small Streams in Minnesota, U.S. Department of the Interior,
Mounds View Minnesota, 1997.
U.S. Geological Survey, Water-Resources Investigations Report 02-4168, The National
Flood Frequency Program, Version 3: A Computer Program for Estimating Magnitude
and Frequency of Floods for Ungaged Sites, U.S. Department of the Interior, 2002.
U.S. Geological Survey, 7.5-Minute Series Topographic Maps, Scale 1:24,000, Contour
Interval 20 Feet: Chatfield, Minnesota, 1972.
U.S. Geological Survey, 7.5-Minute Series Topographic Maps, Scale 1:24,000, Contour
Interval 10 Feet: Oronoco, Minnesota, 1962; Douglas, Minnesota, 1966; Rochester,
Minnesota, 1972; Zumbro Lake, Minnesota, 1972; Chester, Minnesota, 1972; Plainview,
Minnesota, 1972, various dates (a).
U.S. Geological Survey, 7.5-Minute Series Topographic Maps, Scale 1:24,000, Contour
Interval 20 Feet: Dover, Minnesota, 1974; Marion, Minnesota, 1974; Plainview SW,
Minnesota, 1972, various dates (b).
U.S. Geological Survey, 7.5-Minute Series Topographic Maps, Scale 1:24,000, Contour
Interval 10 Feet: Douglas, Minnesota, 1966; Rochester, Minnesota, 1972; 15-Minute
Series Topographic Maps, Scale 1:62,500, Contour Interval 10 Feet: Stewartville,
Minnesota, 1955, various dates (c).
U.S. Geological Survey, 7.5-Minute Series Topographic Maps, Scale 1:24,000, Contour
Interval 10 Feet: Byron, Minnesota, 1982; Douglas, Minnesota, 1993; High Forest,
Minnesota, 1974; High Forest SW, Minnesota, 1974; Marion, Minnesota, 1974; Oronoco,
Minnesota, 1980; Pine Island, Minnesota. 1965; Rock Dell, Minnesota, 1974;
Stewartville, Minnesota, 1974; Contour Interval 20 Feet: Chatfield, Minnesota, 1974;
Chester, Minnesota, 1972; Elba, Minnesota, 1974; Millville, Minnesota, 1980; Pilot
Mound, Minnesota, 1974; Plainview, Minnesota, 1972; Rochester, Minnesota, 1993; St.
Charles, Minnesota, 1974; Salem Corners, Minnesota, 1993; Simpson, Minnesota, 1993;
Washington, Minnesota, 1974; Zumbro Lake, Minnesota, 1972, various dates (d).
U.S. Geological Survey, 15-Minute Series Topographic Maps, Scale 1:62,500, Contour
Interval 20 Feet: High Forest, Minnesota; Stewartville, Minnesota, 1955.
U.S. Geological Survey, Map of Flood-Prone Areas, Scale 1:62,500, Contour Interval 20
93
Feet: Rochester, Minnesota, 1969; Chatfield, Minnesota, 1975, various dates (e).
Water Resources Council, Hydrology Committee, Guidelines for Determining Flood Flow
Frequency, Bulletin #17B, Revised September 1981, Editorial Corrections March 1982.
The Weather Channel, Monthly Averages for Rochester, Minnesota, Retrieved on April
29, 2010, from http://www.weather.com.
XP Software, XP-SWMM EXPert Stormwater and Wastewater Management Model,
2005.
Yaggy Colby Associates, Two-Foot Topographic Survey Compiled by Stereo-
photogrammetric Methods from Aerial Photography, December 19, 1984.
DINANCE N8,d2C F I' CAT
AN Of7LINANCE CrtE-
ION
ATiNG AND ENACT-
ING SECTIONS 60.324,
60,418, 600161, 60.4182, State of Minnesota, Count of Olmsted
60.4183, 61,117,, 52.817, r
62,818; 62.835, 62.636,
62.848,AND 62.657,AND
AMENDING AND RE Sue Lovejoy, being duly sworn, on oath that she is the publisher or authorized
ENACTING SECTIONS
60.200, so.35c1, SUB-
' agent and employee of the publisher of the newspaper known as the Post-
DIVISON 2 of SEC Bulletin, and has full knowledge of the facts which are stated below:
TION 61,225, SECTIONS`
62.600, 62.610,
62,612, 62.613, rat 815, A The newspaper has co lied with all the requirements constituting
6x.830, 62.8x1, 82.832,' '� � complied rl g
62.833, 62.841, 7x2.842; qualifications as a legal newspaper, as provided by Minnesota Statute
62,843, 62.844,, 62.846,1
62.847, 62.850, 62.651,] 331A.02, 331A.07 and other applicable laws, as amended.
62.652, 62,853, 62.871„I
62.672, 62,073, 62.874„'
AND 65.+140, AND RE-
PEALING SECTIONS. (B) The printed notice
60,110, SUBDIVISION'
3 OF SECTION 60.410,
62.601, 62,802, 62,803„1 Which is attached was cut from the columns of said newspaper, and was
62,812, 62.856, 62.866, printed and published 1 times p p g
62,62x, 62.856, 62.860, p p ( ); it was Tinted and published on the following
62,875 62,880, 62.881, dates:
62,1182, AND 62.883 OF'
THE ROCHESTER CODE PB 04/08/20,17
OF ORDINANCES, RE-
LATING TO FLOODPLAIN IPB 04/08/2017
REGULATIONS.
The following is a sun7maay'
Floodplain paons Ordinance dopt Printed below is a copy of the lower case alphabet from a to z, both inclusive,
by the Rochester
c which is hereb acknowledged as being the size and kind of e used in the
Common Council on March y � g yp
20,2017,and Is published composition and publication of the notice:
pursuant to Section 6.07
of the Rochester Home
Rule Charter and Section abodefghiikimnopgrstowrxyz
331A.01, subd. 10 of the,
Minnesota Statutes, The POST-B ILL1=TIh4➢ CuMPAI�IY L.L.C,
Rochester Common Couin. B 1: Vis'
oil approved the publica
kion of this ordinance sum-'
wary at Its March 20,2017,
meeting. A copy of this or- TITLE: Media Sales Manager
dinance is on file at the Of-
fice of the City Clark, 201
Fourth Street S E, Doomu a
Subscribed and sworn to me on JL,^lVIJF3LIT
135 Rochester MN and yy F'w° ;
at the Rochester I'ulalia LI Tis I day 6af - ;,� t1 U NOTARY PUBLIC<MINNEOOTA
hrary, 101 second Street' �� My C"4rritlh.C xp,Jan.31,2020
S.E„Rochester,MIS, ?y r ”
This ordinance amends the
current floodplain regula-
tions b providingaddition-, Nota Public
al regulations for dove top-' 'PATE INFORMATION
merit actlVllies oddtrrring
within the City"s Iloodplain
as mapped by the 1=adaral i 1) Lowest classified rate paid by commercial user $21.95
Emergency Manogemont" For comparable space (per inch/per day/display rate)
agency and local flood-
plain reggutlations.
P SSE L7 AND ADOPT- 2ulicaon Fee ED BY THE COMMON ) PbtiF $172.65
COUNCIL OF THE CITY'.
OF ROCHESTER,MINNE-
SOTA,THIS 20th DAY OF
March,2,077, Ad If 205214:ORDINANCE N0.4288 AN ORDINANCE CREA
/s/Randy Slaver
PFIESIDENT OF SAID
COMMON COUNCIL
ATTEST:
/s/Anissa Hollingshead
CITY CLERK
APPROVED THIS 2411h
DAY OF March,2017.`
/S/Ardell E.Brede
MAYOR
Seal of the City of
Rochester,Minnesola
441(31
i
i
l