2025-09-09 WS City Council Agenda
Richfield City Council Agenda
September 9, 2025 -- 5:45 PM
Richfield Municipal Center
Council Chambers
6700 Portland Avenue South
1. Call to Order
2. Item Discussion
a. Discuss proposed 2026 Utility Rates and potential revisions to the 2026-2030 Utilities
CIB/CIP.
b. Flood-Risk Area Prioritization Presentation
3. Adjournment
Auxiliary aids for individuals with disabilities are available upon request. Requests must be made at least 96 hours in advance to the
City Clerk at 612-861-9739.
Includes Materials - Materials relating to these agenda items can be found in the Council Chambers Agenda Packet book located by
the entrance. The complete Council Agenda Packet is available electronically on the City of Richfield website.
Page 1 of 78
City Council Meeting 9/9/2025
Agenda Section: Item Discussion
Agenda Item: 2.a.
Report Prepared By:
Scott Kulzer, Senior Analyst
Department Director:
Kristin Asher, Public Works Director
Item for Consideration:
Discuss proposed 2026 Utility Rates and potential revisions to the 2026-2030
Utilities CIB/CIP.
EXECUTIVE SUMMARY
The purpose of the work session is to discuss the 2026 Utility Rates. Staff will present
recommended adjustments in the proposed Capital Improvement Plan that will
accommodate the corrected cash balances that were recently discovered for the three
Enterprise Funds (Water, Sewer, Storm). The goal is to keep sufficient cash balances in
the accounts and continue progress on needed capital improvements for the systems.
HISTORICAL CONTEXT
RECOMMENDED ACTION
Provide staff direction on 2026 Utility Rates and potential revisions to the 2026-
2030 Utilities CIB/CIP.
EQUITABLE OR STRATEGIC CONSIDERATIONS OR IMPACTS
POLICIES (RESOLUTIONS, ORDINANCES, REGULATIONS, STATUTES, ETC.)
CRITICAL TIMING ISSUES
FINANCIAL IMPACT
LEGAL CONSIDERATIONS
ALTERNATIVE RECOMMENDATION(S)
ATTACHMENTS
Page 2 of 78
1. 09092025 Utility Rates - Slides - Final
Page 3 of 78
2026 Utility Rates
September 9, 2025
Page 4 of 78
5-2-5 August 12 CIP
Page 5 of 78
Updated cash balances w/Aug 12 CIP
Page 6 of 78
Originally Included in 2026 –2030 CIP
Water –51000
•Bonding for Nicollet Avenue (2026) –2027 Debt Service
•Bonding for Water System Interconnect (2027) –2028 Debt Service
•Water Treatment Plant (WTP) Generator (2026-27)
•WTP Improvements (2026-2028)
•Watermain Rehabilitation (2030)
•Nicollet Park Watermain (beyond 2030)
Storm – 53000
•Bonding for Nicollet Ave (2026) – 2027 Debt Service
•HUB Storm Improvements (2026)
•Rehabilitation of Storm Manholes (annually)
•PW Storage Facility (2026)
•Wilson Pond Flood Mitigation (2027-2030)
•Pond Dredging (2027, 2030)
•Lift Station Upgrades (2030)
•Bonding for 69th Street & Penn Ave (2028) – 2029 Debt Service
Sewer – 52000
•Sanitary Sewer Lining (annually)
•Sanitary Sewer Hot Spots (2026)
•Lift Station Reconstructions (2027; 2029)
Page 7 of 78
Recommended Changes to CIP
•Remove 2027 & 2030 Pond Dredgings
•Reorganized projects
–Move up lower cost projects (WTP bathrooms; pipe gallery coatings)
–Reduce & delay higher cost projects (watermain rehab moved to 2030)
–Moved out HUB to 2028 (from 2026)
•Eliminated sewer lining project for 2029
Page 8 of 78
Water – 51000
•Bonding for Nicollet Avenue (2026) – 2027 Debt Service
•Bonding for Water System Interconnect (2027) – 2028 Debt Service
•Water Treatment Plant (WTP) Generator (2026-27)
•WTP Improvements (2026-2028)
•Watermain Rehabilitation (2030) –reduced to $2M
•Nicollet Park Watermain (beyond 2030)
Storm – 53000
•Bonding for Nicollet Ave (2026) – 2027 Debt Service
•HUB Storm Improvements (2026 28)
•Rehabilitation of Storm Manholes (annually)
•PW Storage Facility (2026)
•Wilson Pond Flood Mitigation (2027-2030)
•Pond Dredging (2027, 2030) –moved to beyond 2030
•Lift Station Upgrades (2030)
•Bonding for 69th Street & Penn Ave (2028) – 2029 Debt Service
Sewer – 52000
•Sanitary Sewer Lining (annually)
–Eliminated for 2029
•Sanitary Sewer Hot Spots (2026)
•Lift Station Reconstructions (2027; 2029)
Adjusted 2026-2030 CIP
Page 9 of 78
5-2-5 with changes to CIP
Page 10 of 78
7-2-7 with changes in CIP
Page 11 of 78
Utility Customer Impacts
Page 12 of 78
2026 Proposed Annual
Impact on the Average
Richfield Home
Recommended 7-2-7% Increase
Property Tax:$ 82
Water fees-7%:$ 22
Wastewater-2%:$ 7
Stormwater-7%:$ 7
Streetlight fees:$ 0
Franchise fees:$ 0
TOTAL $118
Page 13 of 78
Utility Rates Study Overview
Step 1: Establish written financial/rate setting policies for adoption
•Review/revise existing policies
•Set minimum cash balance targets
Step 2: Capital Funding/Asset Replacement Analysis
•Objective is to adequately fund capital through annual rate revenues
Step 3: Development of the Financial Plan
•Long-term financial plan for each utility
•Identification of rate impacts based on capital funding analysis
•Considerations: debt service; capital replacement; reserve levels
Step 4: Develop Rate Design Alternatives
•2 rate structures per utility will be developed
•Affordability impacts will be reviewed
Page 14 of 78
City Council Meeting 9/9/2025
Agenda Section: Item Discussion
Agenda Item: 2.b.
Report Prepared By:
Olivia Wycklendt, Project Engineer
Department Director:
Kristin Asher, Public Works Director
Item for Consideration:
Flood-Risk Area Prioritization Presentation
EXECUTIVE SUMMARY
As part of the Strategic Plan (Sustainable Infrastructure), the City has completed a
Flood-Risk Area Prioritization study to determine where significant flooding may occur
within the City of Richfield during strong storm events. This study included updating the
City's stormwater model and developing possible solutions to mitigate flooding in these
areas. This study may be used in the future to determine possible projects for the City's
Capitol Improvement Plan. City staff will be giving a brief informational presentation on
the stormwater model update and the findings from the model analysis.
HISTORICAL CONTEXT
Historically, Richfield has several flood-prone areas throughout the City, which played a
role in deciding which projects to prioritize. Barr Engineering created a stormwater
modeling report in 2019, which they have now updated to reflect new construction and
more detailed modeling data.
RECOMMENDED ACTION
Staff will be providing an informational presentation on the stormwater model update
conducted primarily using grant funds from the Minnesota Pollution Control Agency
(MPCA). This is an opportunity for the City Council to ask questions; no formal action or
direction is needed. Per the City grant agreement with the MPCA, staff is required to
present the final results of the study to City Council and the public.
EQUITABLE OR STRATEGIC CONSIDERATIONS OR IMPACTS
• This effort is alignment with the Sustainable Infrastructure goals of the Strategic
Plan.
• The findings from the stormwater modeling were made using a scoring system
with different weighted categories, including using a social vulnerability index and
census data to identify which Richfield residents may be more significantly
impacted in a major flood event.
POLICIES (RESOLUTIONS, ORDINANCES, REGULATIONS, STATUTES, ETC.)
Page 15 of 78
CRITICAL TIMING ISSUES
FINANCIAL IMPACT
The total cost of the study is $115,000. $91,500 was provided by the Mn Pollution
Control Agency (MPCA).
LEGAL CONSIDERATIONS
ALTERNATIVE RECOMMENDATION(S)
ATTACHMENTS
1. Flood Risk Prioritization Final Report
2. 2025 Citywide Stormwater Model Council Presentation
Page 16 of 78
4300 MarketPointe Drive, Suite 200
Minneapolis, MN 55435
952.832.2600
barr.com
Stormwater Model Update and Flood-Risk Area
Identification and Prioritization
Prepared for
City of Richfield
Prepared by
Barr Engineering Co.
August 2025
This study was paid for in part by a grant from the MPCA.
Page 17 of 78
barr.com
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Certification
I hereby certify that this report was prepared by me or under my direct supervision and that I am a duly
Licensed Professional Engineer under the laws of the State of Minnesota.
August 15, 2025
Kelly Miller
PE #: 52619
Date
Page 18 of 78
barr.com
i
\\barr.com\projects\Mpls\23 MN\27\23272085 Richfield Model Update Project\WorkFiles\05 Report\Richfield_FloodRiskPrioritization.docx
Stormwater Model Update and Flood-Risk
Area Prioritization Identification
August 2025
Contents
1 Introduction ...................................................................................................................................... 1
2 Stormwater Model Updates ............................................................................................................. 3
2.1 2022 USGS LiDAR Model Updates ............................................................................................. 3
2.2 Model Update Areas .................................................................................................................... 3
2.3 Taft Lake Review ......................................................................................................................... 5
2.3.1 Minneapolis Model Edge Matching North of Mother Lake and Taft Lake ................................ 5
3 Rainfall Events, Climate Adaptation Assessment, and Model Results ............................................ 8
4 Environmental Justice Analysis and Project Prioritization ............................................................. 13
4.1 Methodology ............................................................................................................................... 13
4.1.1 Storm System Conditions ...................................................................................................... 13
4.1.2 Critical Infrastructure .............................................................................................................. 16
4.1.3 Frequency of Flooding ........................................................................................................... 18
4.1.4 Social Vulnerability Index ....................................................................................................... 20
4.1.5 Number of Flood-Prone Structures ........................................................................................ 22
4.2 Results ....................................................................................................................................... 24
5 Flood Control Project Identification and Alternatives Study ........................................................... 26
5.1 Flood-Risk Area Near Wilson Pond ........................................................................................... 26
5.1.1 Wilson Pond Flood Mitigation Concept A .............................................................................. 27
5.1.2 Wilson Pond Flood Mitigation Concept B .............................................................................. 30
5.1.3 Wilson Pond Flood Mitigation Concept C .............................................................................. 32
5.2 Flood-Risk Area Northwest of Roosevelt Park ........................................................................... 34
5.2.1 Northwest of Roosevelt Park Flood Mitigation Concept A ..................................................... 34
5.3 Flood-Risk Area Near Woodlawn Terrace ................................................................................. 37
5.3.1 Near Woodlawn Terrace Flood Mitigation Concept A............................................................ 37
5.3.2 Near Woodlawn Terrace Flood Mitigation Concept B............................................................ 40
5.4 Limitations and Considerations .................................................................................................. 42
6 Conclusions .................................................................................................................................... 43
7 References ..................................................................................................................................... 44
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Tables
Table 2-1 Updated Boundary Conditions with Minneapolis ................................................................ 6
Table 3-1 Precipitation Depth for Design Storm Events ..................................................................... 8
Table 4-1 Storm System Conditions Scoring .................................................................................... 14
Table 4-2 Critical Infrastructure Scoring ............................................................................................ 16
Table 4-3 Frequency of Flooding Scoring ......................................................................................... 18
Table 4-4 Social Vulnerability Index Scoring ..................................................................................... 20
Table 4-5 Number of Flood-Prone Structures Scoring ...................................................................... 22
Table 4-6 Top 10 Flood-Risk Locations in the City of Richfield ........................................................ 24
Table 5-1 Wilson Pond Flood Mitigation Concepts - Cost Estimate Comparison ............................. 27
Table 5-2 Modeled Peak Water Levels Wilson Pond Flood Mitigation Concept A: Reduce the
Water Level in Wilson Pond Ahead of a Storm Event ...................................................... 28
Table 5-3 Modeled Peak Water Levels Wilson Pond Flood Mitigation Concept B: Increase Storm
Sewer Capacity ................................................................................................................. 30
Table 5-4 Modeled Peak Water Levels Wilson Pond Flood Mitigation Concept C: Increase Storm
Sewer Capacity and Number of Pipes .............................................................................. 32
Table 5-5 Northwest of Roosevelt Park Flood Mitigation - Cost Estimate ........................................ 34
Table 5-6 Modeled Peak Water Levels Northwest of Roosevelt Park Flood Mitigation Concept A:
Add Underground Storage Chamber ................................................................................ 35
Table 5-7 Near Woodlawn Terrace Flood Mitigation - Cost Estimate Comparison .......................... 37
Table 5-8 Modeled Peak Water Levels Near Woodlawn Terrace Flood Mitigation Concept A:
Add Underground Storage Chamber ................................................................................ 38
Table 5-9 Modeled Peak Water Levels Near Woodlawn Terrace Flood Mitigation Concept B:
Increase Storm Sewer Capacity ....................................................................................... 40
Figures
Figure 1-1 Study Area .......................................................................................................................... 2
Figure 2-1 Model Update Areas ........................................................................................................... 4
Figure 2-2 Minneapolis Model Edge Matching North of Mother Lake and Taft Lake ........................... 7
Figure 3-1 Inundation Areas 2-year 24-hour Storm.............................................................................. 9
Figure 3-2 Inundation Areas 10-year 24-hour Storm.......................................................................... 10
Figure 3-3 Inundation Areas 100-year 24-hour Storm ....................................................................... 11
Figure 3-4 Inundation Areas MCE100-year 24-hour Storm ............................................................... 12
Figure 4-1 Flood-Risk Prioritization Criteria 1: Storm Sewer Conditions ........................................... 15
Figure 4-2 Flood-Risk Prioritization Criteria 2: Critical Infrastructure ................................................. 17
Figure 4-3 Flood-Risk Prioritization Criteria 3: Frequency of Flooding .............................................. 19
Figure 4-4 Social Vulnerability Index Factors ..................................................................................... 20
Figure 4-5 Flood-Risk Prioritization Criteria 4: Social Vulnerability Index Areas ............................... 21
Figure 4-6 Flood-Risk Prioritization Criteria 5: Number of Flood-Prone Structures ........................... 23
Figure 4-7 Flood-Risk Areas with Combined Prioritization Scores .................................................... 25
Figure 5-1 Wilson Pond Concept A: Reduce the Water Level in Wilson Pond Ahead of a Storm
Event ................................................................................................................................. 29
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Figure 5-2 Wilson Pond Concept B: Increase Storm Sewer Capacity ............................................... 31
Figure 5-3 Wilson Pond Concept C: Increase Storm Sewer Capacity and Number of Pipes ............ 33
Figure 5-4 Northwest of Roosevelt Park Concept A: Add Underground Storage Chamber .............. 36
Figure 5-5 Near Woodlawn Terrace Concept A: Add Underground Storage Chamber ..................... 39
Figure 5-6 Near Woodlawn Terrace Concept B: Increase Storm Sewer Capacity ............................ 41
Appendices
Appendix A Opinion of Probable Construction Cost
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Abbreviations
Barr Barr Engineering Co.
BMP Best Management Practice
city City of Richfield
H&H hydrologic and hydraulic
LiDAR Light Detection and Ranging
MCE100-year Mid-21st century 100-year moderate rainfall estimate
MSE3 Midwest Southeast 3
PCSWMM Personal Computer Stormwater Management Model
SVI Social Vulnerability Index
USGS United States Geological Survey
Page 22 of 78
1
1 Introduction
In 2018 and 2019, Barr Engineering Co. (Barr) helped the city of Richfield (city) develop a hydrologic and
hydraulic (H&H) stormwater model that covers the municipal boundary [reference (1)]. The model covers
the entire city and the areas of adjacent cities that drain into Richfield. The model study area covers the
total watershed area included in the H&H model which is approximately 8.8 square miles and is shown in
Figure 1-1. The stormwater model was originally developed for multiple purposes, which include:
• Identifying inundation extents for the 2-, 10-, and 100-year 24-hour precipitation events
• Identifying potentially flood-prone structures
• Assessing the performance of existing stormwater infrastructure
• Prioritizing areas for infrastructure upgrades and stormwater BMP implementation
• Evaluating the impact of development and redevelopment within the city
The city has experienced redevelopment since the original model development, and the city’s goals for
this project were to:
• Update the existing H&H stormwater model
• Climate adaptation evaluation by simulating a larger storm in the model
• Prioritize flood-risk project areas through environmental justice and additional factors
• Evaluate concept-level flood-risk reduction projects at selected locations.
This report is organized following the chronological order of the project. Stormwater model updates are
discussed in Section 2, followed by the climate adaptation assessment in Section 3, the environmental
justice analysis and project prioritization in Section 4, the flood-risk reduction project identification and
alternatives in Section 5, and conclusions in Section 6.
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Study Area
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park Pond
Study Area
Municipal Boundary
Lakes and Ponds
Page 24 of 78
3
2 Stormwater Model Updates
The original stormwater model was developed using the Personal Computer Stormwater Management
Model (PCSWMM) and had not been updated since provided to the city. Updates to the model as part of
this project included:
• New topographic information published by the USGS since the original model development,
which was incorporated in the updated model, as discussed in Section 2.1.
• City staff provided information about construction projects with stormwater impacts that have
occurred in the study area since 2018, as discussed in Section 2.2.
• Barr added additional data to the PCSWMM model based on collected survey data and
information from the city of Minneapolis stormwater model, which is discussed in Section 2.3
In addition to the changes listed above and described in more detail below, the existing model was
divided into two PCSWMM model files (East and West) which required intermediate boundary conditions
or flows from one file to the other. The model has been updated to be one PCSWMM model file that
covers the entire city. This removed the need for intermediate boundary conditions.
2.1 2022 USGS LiDAR Model Updates
Barr updated the existing PCSWMM model to incorporate the Light Detection and Ranging (LiDAR) data
collected in 2022 and published by the United States Geological Survey (USGS) [reference (2)]. The
2018 model was based on LiDAR data collected in 2011 [reference (3)]. Model updates included revisions
to storage curves and overland flow paths. Storage curve updates included adjustments to inverts and
initial depths in natural depressions where the updated LiDAR data provided additional data at lower
elevations. Overland flow paths were reviewed for LiDAR elevation changes of greater than 0.5 feet and
new overland flow paths were added to the model using the updated LiDAR data to simulate a larger
rainfall event, as discussed in Section 3.
2.2 Model Update Areas
Barr updated the existing PCSWMM model for areas identified by the city as shown in Figure 2-1. These
update areas included redevelopments, pond improvement projects, street and storm sewer projects, and
areas of the city that had been part of stormwater evaluations since 2018. Updates in these areas were
based on data provided by the city and available data including the city’s updated GIS storm sewer data,
as-built drawings, and the 2022 LiDAR data. The 2022 LiDAR dataset was used for watershed boundary
updates, except locations with specific grading plans available.
Additionally, the city provided updated storm lift station data, and where applicable, Barr updated the
model inputs in the PCSWMM model. As part of the model update areas the storm pump station at Taft
Park was added to the model.
The methodology outlined in the original model development report Richfield Hydrologic and Hydraulic
Modeling Report [reference (1)] was followed to update the model.
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Model Update Areas
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
Best Buy Corporate
and Metro Transit
Orange Line
65th Street
Christian
Park
Pond
Sheridan
Park Pond
Lunds
Apartments Taft Park
Lift
Station
Rya/RF64
Hope
Church
77th Street
Underpass
Novo
Apartments
Lyndale
Avenue
Chamberlain
Apartments/
Richfield
Parkway South
LynVue
Taft Lake Review
and Minneapolis
Model Edge Matching
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Study Area
Model Update Areas
Municipal Boundary
Lakes and Ponds
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5
2.3 Taft Lake Review
Available storm sewer and outlet structure data on the lake connections between Mother Lake and Taft
Lake, and Taft Lake north of Highway 62, were identified as high importance to the city for current
stormwater-related efforts. Barr surveyed from the outlet structure on Mother Lake to Taft Lake and from
Taft Lake north of Highway 62. This survey data consisted of pipe inverts, material, shape, diameter, and
additional details on the Mother Lake outlet structure. Information from the survey was used to update the
PCSWMM model in this area. Survey locations are shown on Figure 2-2.
2.3.1 Minneapolis Model Edge Matching North of Mother Lake and Taft
Lake
As part of the Taft Lake Review, the extent of the modeled watersheds and boundary conditions north of
Mother and Taft Lake in Minneapolis was reviewed. Additional watershed area in the city of Minneapolis
was added to the city of Richfield PCSWMM model that was previously accounted for in model inflows.
Including this area in the model allows for a greater understanding of the direct watershed runoff to the
two lakes and the contributing watershed area. Along with the additional watershed area, the connecting
storm sewer pipes were also added to the model.
Boundary conditions were re-evaluated with the expansion of the watershed area. Inflow boundary
conditions were set to locations where surface overflows during the peak of storm events occur. The
downstream boundary condition along the outflow path from Taft Lake to Lake Nokomis in Minneapolis
was set just downstream of the outlet control from the wetland area north of Highway 62 and Taft Lake.
The updated boundary conditions are shown on Figure 2-2 and summarized in Table 2-1.
The additional watershed area, connecting storm sewer pipes, and boundary condition timeseries data
were originally sourced from the city of Minneapolis stormwater model, with their approval [reference (4)].
Page 27 of 78
6
Table 2-1 Updated Boundary Conditions with Minneapolis
Added or
Removed
Inflow
or
Outflow
Richfield PCSWMM
Junction/ Storage
ID
Boundary Condition Data Source
Removed Outflow 432571Z Minneapolis South Region XP-SWMM Model1
Removed Outflow 432526Z Minneapolis South Region XP-SWMM Model1
Removed Outflow 432577Z Minneapolis South Region XP-SWMM Model1
Removed Outflow 432577Z2 Minneapolis South Region XP-SWMM Model1
Removed Outflow 433867Z1 Minneapolis South Region XP-SWMM Model1
Removed Outflow 433867Z2 Minneapolis South Region XP-SWMM Model1
Removed Outflow 545102 Minneapolis South Region XP-SWMM Model1
Removed Inflow MOL01 Minneapolis South Region XP-SWMM Model1
Removed Inflow 979959A Minneapolis South Region XP-SWMM Model1
Removed Inflow 692463 Minneapolis South Region XP-SWMM Model1
Removed Inflow 509725 Minneapolis South Region XP-SWMM Model1
Removed Inflow 433860 Minneapolis South Region XP-SWMM Model1
Removed Inflow 433789 Minneapolis South Region XP-SWMM Model1
Removed Inflow 433530 Minneapolis South Region XP-SWMM Model1
Removed Inflow 433326 Minneapolis South Region XP-SWMM Model1
Added Outflow 9OUT03 Minneapolis South Region XP-SWMM Model2
Added Outflow 9OUT02 Minneapolis South Region XP-SWMM Model2
Added Outflow 9OUT01 Minneapolis South Region XP-SWMM Model2
Added Inflow 559084 Minneapolis South Region XP-SWMM Model2
Added Inflow 559120 Minneapolis South Region XP-SWMM Model2
Added Inflow 9C538983 Minneapolis South Region XP-SWMM Model2
Added Inflow 9A441934 Minneapolis South Region XP-SWMM Model2
Added Inflow 9A433585 Minneapolis South Region XP-SWMM Model2
Added Inflow 9A632715 Minneapolis South Region XP-SWMM Model2
Added Inflow 632715 Minneapolis South Region XP-SWMM Model2
Added Inflow 433536 Minneapolis South Region XP-SWMM Model2
Added Inflow 432521 Minneapolis South Region XP-SWMM Model2
1 - City of Minneapolis ‘MPLS_So_Region.xp’ provided in 2017 during original model development [reference (5)]
2 - City of Minneapolis ‘MPLS_So_Region.xp’ provided in 2024 during model updates [reference (6)]
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Minneapolis Model
Edge Matching North of
Mother Lake and Taft Lake
Richfield, MN
62
77
RICHFIELD
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT 12thAveSE 66th St
Taft Lake
Legion Lake
Milner
Pond
Mother Lake
Study Area
Watersheds Added From
Minneapolis Model
Model Subwatersheds
MnDOT Survey Points
Updated Boundary Condition
Added Inflow
Deleted Inflow
Added Outflow
Deleted Outflow
Municipal Boundary
Lakes and Ponds
Page 29 of 78
8
3 Rainfall Events, Climate Adaptation Assessment, and
Model Results
The PCSWMM model was used to simulate four design rainfall events. Three design rainfall events were
simulated in the original model developed in 2018 and 2019 and are the Atlas 14 2-year, 10-year, and
100-year 24-hour storm events [reference (7)]. To provide additional information for the city to assess
climate adaptation, the updated model also represents the Mid-21st century 100-year moderate rainfall
estimate (MCE100-year) 24-hour storm event [reference (8)]. The MCE100-year 24-hour storm event is
intended to estimate the long-term extreme weather trends on flood mitigation. The four design storm
events use the Midwest Southeast 3 (MSE3) rainfall distribution [reference (9)]. Rainfall depth for the four
design storm events is listed in Table 3-1.
Table 3-1 Precipitation Depth for Design Storm Events
Storm Event and Return
Period
Duration Precipitation Depth (inches)
Atlas 14 2-year 24-hour 2.83
Atlas 14 10-year 24-hour 4.24
Atlas 14 100-year 24-hour 7.50
MCE100-year 24-hour 10.20
The larger precipitation depth for the MCE100-year 24-hour storm event resulted in more stormwater
runoff conveyed through the stormwater system, causing greater surface ponding and overland flow rates
compared to the 100-year MSE3 event. To account for additional surface flow directions additional
overland flow paths were added to the model using transects developed from the 2022 LiDAR data or
standard street cross sections consistent with the methodology outlined in the original model
development report [reference (1)]. To account for additional surface ponding, rim elevations were
increased at modeled junctions and storages. The MCE100-year storm event used the 100-year 24-hour
storm event boundary conditions. For model consistency, all four storm events were simulated in the
updated model.
Model results of the peak water level for the 2-, 10-, 100-, and MCE100-year 24-hour rainfall events were
used to create inundation areas. Inundation areas were delineated where water is stored in ponds,
wetlands, and topographic depressions using level pool mapping in ArcGIS (i.e., inundation mapping of
sloped water surface along roadways and through the floodplain was not completed). Inundation areas
were adjusted in locations where the LiDAR surface did not accurately represent existing topographic
conditions. This typically occurred near bridges or large buildings where the 2022 LiDAR data set does
not capture the features accurately. The inundation maps for each rainfall event are shown in Figure 3-1
through Figure 3-4.
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Inundation Areas
2-year 24-hour Storm Event
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park Pond
Study Area
2-year 24-hour
Storm Event
Inundation Extent
Municipal Boundary
Note: Inundation areas were
delineated where water is stored
in ponds, wetlands, and topographic
depressions using level pool mapping
in ArcGIS (i.e., inundation mapping of
sloped water surface along roadways
and through the floodplain was not
completed).
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Inundation Areas
10-year 24-hour Storm Event
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park Pond
Study Area
10-year 24-hour
Storm Event
Inundation Extent
Municipal Boundary
Note: Inundation areas were
delineated where water is stored
in ponds, wetlands, and topographic
depressions using level pool mapping
in ArcGIS (i.e., inundation mapping of
sloped water surface along roadways
and through the floodplain was not
completed).
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Inundation Areas
100-year 24-hour Storm Event
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park Pond
Study Area
100-year 24-hour
Storm Event
Inundation Extent
Municipal Boundary
Note: Inundation areas were
delineated where water is stored
in ponds, wetlands, and topographic
depressions using level pool mapping
in ArcGIS (i.e., inundation mapping of
sloped water surface along roadways
and through the floodplain was not
completed).
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Inundation Areas
MCE100-year
24-hour Storm Event
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park Pond
Study Area
MCE100-year 24-hour
Storm Event
Inundation Extent
Municipal Boundary
Note: Inundation areas were
delineated where water is stored
in ponds, wetlands, and topographic
depressions using level pool mapping
in ArcGIS (i.e., inundation mapping of
sloped water surface along roadways
and through the floodplain was not
completed).
Page 34 of 78
13
4 Environmental Justice Analysis and Project Prioritization
Using the inundation areas discussed in Section 3 and the criteria the city identified for prioritizing flood-
risk areas, a tool was developed to help the city identify the general prioritization of flood-risk areas for
further evaluation. This process is described in Section 4.1 and the results of the analysis are described
in Section 4.2.
4.1 Methodology
Multiple criteria were considered in the evaluation to identify potential multi-faceted mitigation measures
to address potentially flood-prone areas. Barr consulted with the city to identify criteria that would be
considered in prioritizing flood-risk areas, and the city provided the scoring and weight applied to each
criterion. While the approach has limitations, it provides a consistent methodology to determine where to
begin evaluating and planning stormwater improvements that align with the city’s priorities. The criteria
selected to score the flood-risk areas are:
• Storm system conditions
• Critical infrastructure
• Frequency of flooding
• Social vulnerability index (SVI)
• Number of flood-prone structures
Each of the criteria was assigned a score. A score of zero represents that the criteria do not apply for a
given area, whereas a higher score indicates that it is a high priority for the area. Each of the criteria was
also assigned a weight to allow the city to prioritize the criteria relative to each other.
Using the 100-year 24-hour inundation areas based on the model results, shown on Figure 3-3 flood-risk
areas were developed by grouping inundation areas where the inundation polygons touched across
watershed boundaries.
The model study area extends beyond the city municipal boundary, so flood-risk areas outside or mostly
outside of the municipal boundary were identified within the prioritization tool spreadsheet. Results
include scores for all flood-risk areas, but those outside of the municipal boundary naturally scored lower,
as the majority of the data sets used for the prioritization did not extend outside of the municipal
boundary.
The following sections describe the prioritization criteria that were considered.
4.1.1 Storm System Conditions
Scoring from the Stormwater Infrastructure Qualitative Risk Analysis for the City of Richfield memo was
used for the analysis of storm system conditions [reference (10)]. This scoring system was created to
identify pipe segments or culverts with a higher likelihood of failure due to age, material, and ground
slope. The identified infrastructure was also assessed to determine the consequences of pipe failure,
including the potential for roadway or railway collapse, inundation or washout, flooding or settlement of
structures, flooding or critical or high-value public buildings, and slope failure. The combined risk score
percentiles are based on all pipes included in the analysis of the memo, and percentiles were selected at
identified percentile breaks in the data.
Page 35 of 78
14
Table 4-1 defines the scoring and weighting associated with the storm system conditions criteria. To
score and weigh each flood-risk area for the storm system condition, the city’s storm sewer pipe network
was intersected with the 100-year flood-risk areas. Then the average combined risk score from all
intersected pipes per flood-risk area was calculated, and the score and weight shown in Table 4-1 was
applied. The pipes within each flood-risk area are shown on Figure 4-.
Table 4-1 Storm System Conditions Scoring
Criteria Score Weight
Low risk (combined risk score 0-34th percentile) 0
10%
Low to moderate risk (combined risk score 34-59th percentile) 1
Moderate to high risk (combined risk score 59-91st percentile) 4
High risk (combined risk score 91-96th percentile) 7
Highest risk (combined risk scores 96-100th percentile) 10
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Flood-Risk
Prioritization Criteria 1:
Storm Sewer Conditions
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park Pond
Municipal Boundary
100-year 24-hour Storm Event
Inundation Extent
Storm Sewer Conditions*
Low Level of Combined Risk
Low to Moderate Risk
Moderate to High Risk
High Risk
Highest Risk
*Storm sewer within 100-year
24-hour Storm Event Inundation
Extent is shown in bold.
Page 37 of 78
16
4.1.2 Critical Infrastructure
Critical infrastructure for this analysis was identified by the city to include critical transportation routes, city
infrastructure for specific utilities, emergency service locations, and schools. These types of infrastructure
were identified by the city as providing essential services during a flood event. For scoring, three
categories of critical infrastructure were identified:
• Critical transportation routes – these are roadways that need to remain open to allow for
evacuation or access by emergency services. Critical transportation routes were defined by the
city.
• Critical city utility infrastructure – city staff identified critical utility infrastructure that includes
sanitary and storm lift stations. These locations were determined to provide critical services, and
it is critical that they continue to operate during a flood event.
• Emergency service locations and schools – these are defined as locations that provide essential
services before, during, or following a flood event. These include hospitals, police stations, fire
stations, local government buildings, and schools.
Table 4-2 defines the scoring and weighting associated with the critical infrastructure criteria. To score
each flood-risk area for critical infrastructure, points were awarded for each structure that was located
within the 100-year flood-risk area, following the scores outlined in Table 4-1. The critical infrastructure
within each flood-risk area is shown on Figure 4-2.
Table 4-2 Critical Infrastructure Scoring
Criteria Score Weight
Critical infrastructure is not located in flood-risk area 0
15%
Critical transportation route is located within a flood-risk area 1 per each 600
feet of route
Critical city infrastructure is located within a flood-risk area (specifically
utilities)
4 per each
location
Emergency service(s) locations and schools are located within a flood-risk
area
3 per each
location
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Flood-Risk
Prioritization Criteria 2:
Critical Infrastructure
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
Grass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park PondBloomingtonAveS RichfieldPkwyW 70th St
W 76th St
W 77th St
E 70th St
E 77th St
E 76th St
E 66th St
12thAveSNicolletAveSPortlandAveSPennAveSLyndaleAveSYorkAveSW 66th St
Municipal Boundary
100-year 24-hour Storm Event
Inundation Extent
Critical Transit Route
Critical Infrastructure:
Emergency Services or School
Critical Infrastructure: Utility
Impacted Critical Transit Route
Impacted Critical
Infrastructure: Emergency
Services or School
Impacted Critical
Infrastructure: Utility
Critical transportation routes –
These are roadways that need to remain
open to allow for evacuation or access
by emergency services. Critical
transportation routes were defined by
the city.
Critical city utility infrastructure –
City staff identified critical utility
infrastructure that includes sanitary and
storm lift stations. These locations were
determined to be providing critical
services, and it is critical that they
continue to operate during a flood event.
Emergency service locations and
schools – These are defined as locations
that provide essential services before,
during, or following a flood event. These
include hospitals, police stations, fire
stations, local government buildings,
and schools.
Page 39 of 78
18
4.1.3 Frequency of Flooding
The frequency of flooding refers to how often a location is potentially inundated. Areas that could be
inundated more frequently generally also have larger inundation depth during less frequent events (i.e.,
deeper inundation depth during the 100-year event). Therefore, areas that are inundated more frequently
received higher scores than areas that do not flood as often. Scores were determined by considering the
lowest structure within a given floodplain area (i.e., the structure that floods the most frequently).
Table 4-3 defines the scoring and weighting associated with the frequency of flooding criteria. Structures
are shown on Figure 4-3 that intersect the inundation areas and are color-coded by the first storm event
that impacts the structure.
Table 4-3 Frequency of Flooding Scoring
Criteria Score Weight
No flooding of structure(s) during a 100-year event 0
25%
Flood-prone structure(s) in estimated MCE100-year event 1
Flood-prone structure(s) in 100-year event 3
Flood-prone structure(s) in 10-year event 5
Flood-prone structure(s) in 2-year event 10
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Flood-Risk
Prioritization Criteria 3:
Frequency of Flooding
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park Pond
Flood-prone structure(s)
in 2-year event
Flood-prone structure(s)
in 10-year event
Flood-prone structure(s)
in 100-year event
Flood-prone structure(s) in
estimated MCE100-year event
2-year 24-hour Storm Event
Inundation Extent
10-year 24-hour Storm Event
Inundation Extent
100-year 24-hour Storm Event
Inundation Extent
MCE100-year 24-hour Storm
Event Inundation Extent
Municipal Boundary
Page 41 of 78
20
4.1.4 Social Vulnerability Index
Social vulnerability is a measure of a community’s ability to respond to a natural disaster. The database
referenced to determine the social vulnerability index for this scoring is the Centers for Disease Control
and Prevention/Agency for Toxic Substances and Disease Registry Social Vulnerability Index (SVI)
[reference (11)]. This database was created to help public health officials and emergency response
planners identify and map areas of the community that would most likely need support before, during, and
after a hazardous event. The SVI indicates the relative vulnerability of every U.S. census tract to prepare
for and respond to hazardous events, whether a natural disaster like a flood or a disease outbreak, or an
anthropogenic event such as a harmful chemical spill. The social factors incorporated in SVI are shown in
Figure 4-4.
Image from Centers for Disease Control and Prevention / Agency for Toxic Substances and Disease Registry SVI [reference (11)]
Figure 4-4 Social Vulnerability Index Factors
Table 4-4 defines the scoring and weighting associated with the social vulnerability index of the floodplain
area. To score each flood-risk area using the social vulnerability index, the area weighted average was
computed based on the 100-year flood-risk area over the SVI value by census tract [reference (11)]. The
area weighted average method means that if a flood-risk area was entirely within one census tract the
value would be the same as the census tract; alternatively, if a flood-risk area crosses a census tract
boundary the area in each census tract is multiplied by the SVI rating of the census tract, then those two
values are added and divided by the total area of the flood-risk area. The flood-risk areas over the SVI
census tract data are shown on Figure 4-5.
Table 4-4 Social Vulnerability Index Scoring
Criteria Score Weight
Low level of vulnerability (SVI 0-25th percentile) 1
10% Low to moderate level of vulnerability (SVI 25-50th percentile) 4
Moderate to high level of vulnerability (SVI 50-75th percentile) 7
High level of vulnerability (SVI 75-100th percentile) 10
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Flood-Risk
Prioritization Criteria 4:
Social Vulnerability Index Areas
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park Pond
High level of vulnerability
(SVI 75-100th percentile)
Moderate to high level of
vulnerability (SVI 50-75th
percentile)
Low to moderate level of
vulnerability (SVI 25-50th
percentile)
Low level of vulnerability
(SVI 0-25th percentile)
Social Vulnerability Index
100-year 24-hour Storm Event
Inundation Extent
Municipal Boundary
Page 43 of 78
22
4.1.5 Number of Flood-Prone Structures
The number of potentially flood-prone structures was calculated by intersecting building outlines provided
by the city of Richfield with the 100-year flood-risk areas. Areas where more structures were located
within an inundation area were assigned a higher score. Table 4-5 defines the scoring and weighting
associated with the number of flood-prone structures criteria, and flood-prone structures are shown on
Figure 4-6.
Table 4-5 Number of Flood-Prone Structures Scoring
Criteria Score Weight
No flood-prone structures 0
40%
1-5 flood-prone commercial structures 1
1-5 flood-prone commercial structures OR greater than 5 flood-prone
commercial structures 3
6-10 flood-prone residential structures OR 1 high-density housing
structure 5
Greater than 10 flood-prone residential structures OR greater than 1 high-
density housing structure 10
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Flood-Risk
Prioritization Criteria 5:
Number of Flood-
Prone Structures
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park Pond
Municipal Boundary
100-year 24-hour Storm Event
Inundation Extent
Building Footprint
Flood-Prone Structures
Commercial
High-Density Housing
Residential
Page 45 of 78
24
4.2 Results
Each flood-risk area was assigned scores and weights based on the criteria listed in Section 4.1.1
through Section 4.1.5 and ranked based on the total score. Areas with higher scores indicate locations
that are a higher priority for mitigating flood-risk.
A total of 746 flood-risk areas were evaluated from the study area with 601 flood-risk areas located within
or primarily within the municipal boundary. The top 10 locations are summarized in Table 4-6. The
locations of all flood-risk areas evaluated are shown on Figure 4-7.
Table 4-6 Top 10 Flood-Risk Locations in the City of Richfield
Flood-Risk Area Total Score
FPA_1913 9.4
FPA_581 9.1
FPA_1889 8.5
FPA_3434 8.05
FPA_1054 7.9
FPA_2134 7.9
FPA_763 7.65
FPA_2353 7.6
FPA_2501 7.6
FPA_2874 7.6
This prioritization by flood-risk area is a framework to help the city identify flood-risk areas that have a
larger impact on buildings or critical infrastructure, have storm sewer infrastructure that has been
identified as higher risk, and are impacting community areas that most likely need support before, during,
and after a hazardous event. While evaluating future flood-risk reduction projects, the prioritization
scoring should be considered with other factors which may include the following:
• Opportunities for improvement from other public works projects (i.e., road reconstruction projects)
• Potential project partners for improvements to offset project costs
• Solving flood-risk areas from upstream to downstream to account for additional volume or flow
rate to downstream projects
As such, the prioritization list of potentially flood-prone areas within the city is not intended to be used as
a defined order for evaluating areas. Rather, it should be used to provide guidance to the city when
determining where to begin with further evaluation of system modifications that could be implemented to
reduce the risk of flooding within the city.
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Flood-Risk Areas with
Combined Prioritization Scores
Richfield, MN
456732
456753
121
62
77
§¨¦35W
§¨¦494
§¨¦35W
RICHFIELD
EDINA
BLOOMINGTON
MINNEAPOLIS
MINNEAPOLIS-ST PAUL
INTERNATIONAL
AIRPORT
WPleasantAveSW 73rd St
W 70th St XerxesAveS LyndaleAveSW 77th St
E 73rd St
W 69th St
E 70th St PortlandAveSE 66th St
E 77th St
E 76th St 12thAveS PennAveSW 76th St
W 66th St NicolletAveSGrass
Lake
Taft
Lake
Richfield
Lake
Legion
Lake
Adams
Hill
Pond
Milner
Pond
Norby's Pond
Wood Lake
Mother Lake
Wilson
Pond
Augsburg
Pond
Sheridan
Park Pond
Christian
Park Pond
Municipal Boundary
Prioritization Scores
0.0 - 2.4
2.5 - 4.4
4.5 - 6.4
6.5 - 10
Page 47 of 78
26
5 Flood Control Project Identification and Alternatives Study
The prioritization by flood-risk area was reviewed by city staff who identified three locations for a
planning-level evaluation. For each of these three areas, concept level flood-risk reduction projects were
modeled to evaluate the reduction in flood risk. Based on the concept level design, a planning-level cost
estimate was developed for city staff to consider when planning for further evaluation of each project.
Section 5.1 through Section 5.3 describe the details of the three selected flood-risk areas and identified
potential projects. Additional notes on limitations and additional considerations are included in Section
5.4. The cost estimates provided are described in more detail in Appendix A.
5.1 Flood-Risk Area Near Wilson Pond
The area around Wilson Pond is one of the locations with the largest risk of flooding in the city. This area
impacts the most residential structures in a single location, the lowest structures are affected during the 2-
year 24-hour rainfall event, Wilson Pond is located within an area of the city with a high social
vulnerability index, and surface inundation impacts a critical transportation route through the city as well
as a school. For these reasons the city selected this area to evaluate concepts for system modifications
to reduce flood risk.
Options that were considered but not pursued for the area near Wilson Pond include adding surface
storage areas, underground storage, and a pump to lower the water level in Wilson Pond ahead of a
storm event. Surface storage was not considered due to a lack of undeveloped space near the flood-risk
area and the city’s direction to not consider property acquisition for flood-risk reduction. Underground
storage was not considered due to the expected shallow groundwater in the area. The groundwater atlas
of Hennepin County shows that groundwater in this area is expected to be less than 10 feet below the
ground surface [reference (12)]. The pump option was not considered after review of the volume of water
stored in Wilson Pond and an assumed predictive timeframe of 24 hours to lower the water level resulted
in a high pumped flow rate for a stormwater system.
Three potential project flood-risk mitigation concepts were identified for the Wilson Pond area:
• Flood Mitigation Concept A: Reduce the water level in Wilson Pond ahead of a storm event and
modify the outlet by lowering the invert and increasing the storm sewer capacity from Wilson
Pond south, discussed in Section 5.1.1.
• Flood Mitigation Concept B: Increase the storm sewer capacity from Wilson Pond south,
discussed in Section 5.1.2.
• Flood Mitigation Concept C: Increase the storm sewer capacity and number of pipes from Wilson
Pond south, discussed in Section 5.1.3.
A comparison of the concept level cost estimate for these three potential projects is provided in Table 5-1.
The cost estimate is further described in Appendix A.
Page 48 of 78
27
Table 5-1 Wilson Pond Flood Mitigation Concepts - Cost Estimate Comparison
Concept Description Cost Estimate
A
Reduce the water level in Wilson Pond ahead of a storm
event and modify the outlet by lowering the invert and
increasing the storm sewer capacity
$8,853,000
$6,198,000 – $15,493,000
B Increase storm sewer capacity $11,536,000
$8,076,000 – $20,188,000
C Increase storm sewer capacity and number of pipes $17,333,000
$12,134,000 – $30,333,000
Note: Total project cost accuracy range is -30% to +50%.
Each of these concepts evaluated from the discharge from Wilson Pond to Highway 494. Model results
assume sufficient capacity to route the additional flow away from the city which may need to be conveyed
through the city of Bloomington or along the Highway 494 corridor to the Minnesota River. This
assumption is not accounted for in the planning-level cost estimates, and further coordination will be
required with the city of Bloomington or MnDOT if the city of Richfield decides to further evaluate one of
the flood mitigation concepts.
5.1.1 Wilson Pond Flood Mitigation Concept A
This flood mitigation concept is to leverage the existing surface storage in Wilson Pond for storm volume
retention and increase the storm sewer capacity downstream of Wilson Pond. This mitigation concept is
shown on Figure 5-1. By lowering the water level in the pond ahead of a storm event there is additional
capacity to route the runoff from upstream and attenuate the flow before discharging downstream.
The concept design includes a gate with remote access controlled based on weather forecasts to lower
the water level in Wilson Pond ahead of a storm event. This concept design would leverage the existing
storage in Wilson Pond and result in approximately 5 acre-feet of additional storage ahead of a storm
event with an assumed draw down time of 24-hours. A pumped option was not considered based on the
high flow rate needed to lower the water level in the assumed 24-hour period. The storm sewer pipe out
of Wilson Pond would be lowered and the storm sewer pipe downstream lowered until the pipe grade was
able to re-connect at the existing elevation. A larger pipe size was included downstream of Wilson Pond
to Highway 494 to increase both the ability to draw down the water level of Wilson Pond ahead of the
storm event as well as increase conveyance capacity during the storm event. For this concept storm
sewer pipe changes would be required within the city from Wilson Pond to Highway 494 and from there
continued into the city of Bloomington or along the Highway 494 corridor. This concept would result in a
larger volume and a higher peak rate of discharge leaving the municipal boundary.
Model results of this concept design are shown in Figure 5-1 with inundation comparison for the 10-year
24-hour storm event and a summary of modeled peak water levels at a few locations around the flood-risk
area are compared to the existing condition model results in Table 5-2. The locations summarized in
Table 5-2 are also shown on Figure 5-1.
Page 49 of 78
28
Table 5-2 Modeled Peak Water Levels Wilson Pond Flood Mitigation Concept A: Reduce the
Water Level in Wilson Pond Ahead of a Storm Event
Storm Event Model Condition
Modeled Peak Water Level by Location (feet)
Wilson Pond
Upstream of
Wilson Pond at E
73rd St. and S 17th
Ave.
Downstream of
Wilson Pond at E
75th St. and S 15th
Ave.
2-year 24-hour
Existing Conditions 823.9 825.3 825.9
Mitigation Concept A 822.0 825.2 821.6
Lowered Water Level 1.9 0.1 4.2
10-year 24-hour
Existing Conditions 826.9 826.8 827.3
Mitigation Concept A 825.4 826.0 823.4
Lowered Water Level 1.4 0.8 3.9
100-year 24-hour
Existing Conditions 828.6 828.4 828.6
Mitigation Concept A 828.3 828.1 828.3
Lowered Water Level 0.3 0.3 0.3
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Wilson Pond Concept A:
Reduce the Water Level in
Wilson Pond Ahead of a
Storm Event
Richfield, MN
Upstream of Wilson
Pond at E 73rd St.
and S 17th Ave.
Downstream of Wilson
Pond at E 75th St.
and S 15th Ave.
Outlet Control Gate
Connection to south requires coordination with
MnDOT and Bloomington. Coordination with
other entities did not occur as part of this study.
Volume of Storage Gained from
Lowering Water Level: 5 acre-feet
(approx.) based on a 24-hour draw
down period
Wilson
Pond
E 73rd Ave
Chicago Ave SFer
n
D
r
Bloomington Ave SCedar Ave S75th ST EW 76 1/2th St
Cargo Rd
77th St
1
4
t
h
A
v
e
S
73rd ST EDiagonal BlvdE 71st St
16th Ave SL
S
e
r
v
i
c
e
R
D
E 78th St
E 73rd St
E 74th St 15th Ave S17th Ave S11th Ave S18th Ave S10th Ave SLongfellow Ave SPark Ave SOakland Ave SChicago AVE S13th Ave SE 78th STColumbus Ave SElliot AVE SMNTH 77E 77th St
E 76th ST
E 75th St
E 72nd ST
12th Ave S77
§¨¦494
Existing 10-year 24-hour
Storm Event Inundation
Extent
10-year 24-hour Storm Event
Inundation Extent with
Lowered Normal Water Level
in Wilson Pond Ahead of
Storm Event, Lowered Pipe
Inverts, and increased Storm
Sewer Capacity
Generalized Flood Risk Area
Flood-Prone Structure(s) in 10-
year Event
Flood-Prone Structure No
Longer Impacted as Result
of Concept A
Flood-Prone Structure Still
Impacted with Concept A
Storm Sewer Pipe
Model Result Locations
Storm Sewer Pipe Changes
Increase to 5.5 foot diameter
Lower pipe inverts and
increase to 4 foot diameter
Lower pipe inverts and
increase to 5.5 foot diameter
Municipal Boundary
Flood-Prone Structures Impacted by
Existing 10-year Inundation Extent 126 structures
Flood-Prone Structures No Longer
Impacted as a Result of Concept A 80 structures
Flood-Prone Structures Still Impacted with
Concept A 46 structures
Number of Structures within Generalized Flood-Risk Area
Page 51 of 78
30
5.1.2 Wilson Pond Flood Mitigation Concept B
This flood mitigation concept is to increase the storm sewer capacity downstream of Wilson Pond by
increasing the size of the pipe from Wilson Pond to Highway 494. This mitigation concept is shown on
Figure 5-2.
The storm sewer pipe is currently circular with a diameter ranging from 2.5 feet to 4.5 feet. This flood
mitigation concept represents a single box culvert with dimensions of 5 feet by 5 feet downstream of
Wilson Pond to Highway 494. For this concept storm sewer pipe changes would be required within the
city from Wilson Pond to Highway 494 and from there continued into the city of Bloomington or along the
Highway 494 corridor. This concept would result in a larger volume and a higher peak rate of discharge
leaving the municipal boundary.
Model results of this concept design are shown in Figure 5-2 with inundation comparison for the 10-year
24-hour storm event and a summary of modeled peak water levels at a few locations around the flood-risk
area are compared to the existing condition model results in Table 5-3. The locations summarized in
Table 5-3 are also shown on Figure 5-2.
Table 5-3 Modeled Peak Water Levels Wilson Pond Flood Mitigation Concept B: Increase
Storm Sewer Capacity
Storm Event Model Condition
Modeled Peak Water Level by Location (feet)
Wilson Pond
Upstream of
Wilson Pond at E
73rd St. and S 17th
Ave.
Downstream of
Wilson Pond at E
75th St. and S 15th
Ave.
2-year 24-hour
Existing Conditions 823.9 825.3 825.9
Mitigation Concept B 824.3 825.3 823.9
Lowered Water Level -0.41 0.0 2.0
10-year 24-hour
Existing Conditions 826.9 826.8 827.3
Mitigation Concept B 826.3 826.4 825.4
Lowered Water Level 0.6 0.4 1.9
100-year 24-hour
Existing Conditions 828.6 828.4 828.6
Mitigation Concept B 828.3 828 828.0
Lowered Water Level 0.3 0.4 0.6
1 – Model shows increased backflow in the pipe out of Wilson Pond during the 2-year 24-hour event resulting in an increased
modeled peak water level in Wilson Pond.
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Wilson Pond Concept B:
Increase Storm Sewer Capacity
Richfield, MN
Upstream of Wilson
Pond at E 73rd St.
and S 17th Ave.
Downstream of Wilson
Pond at E 75th St.
and S 15th Ave.
Connection to south requires coordination with
MnDOT and Bloomington. Coordination with
other entities did not occur as part of this study.
Wilson
Pond
E 73rd Ave
Chicago Ave SFer
n
D
r
Bloomington Ave SCedar Ave S75th ST EW 76 1/2th St
Cargo Rd
77th St
1
4
t
h
A
v
e
S
73rd ST EDiagonal BlvdE 71st St
16th Ave SL
S
e
r
v
i
c
e
R
D
E 78th St
E 73rd St
E 74th St
15th Ave S17th Ave S11th Ave S18th Ave S10th Ave SLongfellow Ave SPark Ave SOakland Ave SChicago AVE S13th Ave SE 78th STColumbus Ave SElliot AVE SMNTH 77E 77th St
E 76th ST
E 75th St
E 72nd ST
12th Ave S77
§¨¦494
Existing 10-year 24-hour
Storm Event Inundation
Extent
10-year 24-hour Storm Event
Inundation Extent with
Increased Storm Sewer
Capacity from Wilson Pond
Generalized Flood Risk Area
Flood-Prone Structure(s) in 10-
year Event
Flood-Prone Structure No
Longer Impacted as Result
of Concept B
Flood-Prone Structure Still
Impacted with Concept B
Model Result Locations
Storm Sewer Pipe
Increased Storm Sewer Pipe
to 5’x5’ Box Culvert
Municipal Boundary
Flood-Prone Structures Impacted by
Existing 10-year Inundation Extent 126 structures
Flood-Prone Structures No Longer
Impacted as a Result of Concept B 58 structures
Flood-Prone Structures Still Impacted with
Concept B 68 structures
Number of Structures within Generalized Flood-Risk Area
Page 53 of 78
32
5.1.3 Wilson Pond Flood Mitigation Concept C
This flood mitigation concept is to increase the storm sewer capacity downstream of Wilson Pond by
increasing the number of pipes and size of the pipe from Wilson Pond to Highway 494. This mitigation
concept is shown on Figure 5-3.
This flood mitigation concept represents a double box culvert with dimensions of 5 feet by 5 feet
downstream of Wilson Pond to Highway 494, or twice the cross-sectional area as Concept B discussed in
Section 5.1.2. For this concept storm sewer pipe changes would be required within the city from Wilson
Pond to Highway 494 and from there continued into the city of Bloomington or along the Highway 494
corridor. This concept would result in a larger volume and a higher peak rate of discharge leaving the
municipal boundary.
Model results of this concept design are shown in Figure 5-3 with inundation comparison for the 10-year
24-hour storm event and a summary of modeled peak water levels at a few locations around the flood-risk
area are compared to the existing condition model results in Table 5-4. The locations summarized in
Table 5-4 are also shown on Figure 5-3.
Table 5-4 Modeled Peak Water Levels Wilson Pond Flood Mitigation Concept C: Increase
Storm Sewer Capacity and Number of Pipes
Storm Event Model Condition
Modeled Peak Water Level by Location (feet)
Wilson Pond
Upstream of
Wilson Pond at E
73rd St. and S 17th
Ave.
Downstream of
Wilson Pond at E
75th St. and S 15th
Ave.
2-year 24-hour
Existing Conditions 823.9 825.3 825.9
Mitigation Concept C 824.5 825.3 824.0
Lowered Water Level -0.61 0.0 1.9
10-year 24-hour
Existing Conditions 826.9 826.8 827.3
Mitigation Concept C 826.3 826.3 825.0
Lowered Water Level 0.6 0.5 2.3
100-year 24-hour
Existing Conditions 828.6 828.4 828.6
Mitigation Concept C 827.9 827.8 827.5
Lowered Water Level 0.7 0.6 1.1
1 – Model shows increased backflow in the pipe out of Wilson Pond during the 2-year 24-hour event resulting in an increased
modeled peak water level in Wilson Pond.
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Wilson Pond Concept C:
Increase Storm Sewer Capacity
and Number of Pipes
Richfield, MN
Upstream of Wilson
Pond at E 73rd St.
and S 17th Ave.
Downstream of Wilson
Pond at E 75th St.
and S 15th Ave.
Connection to south requires coordination with
MnDOT and Bloomington. Coordination with
other entities did not occur as part of this study.
Wilson
Pond
E 73rd Ave
Chicago Ave SFer
n
D
r
Bloomington Ave SCedar Ave S75th ST EW 76 1/2th St
Cargo Rd
77th St
1
4
t
h
A
v
e
S
73rd ST EDiagonal BlvdE 71st St
16th Ave SL
S
e
r
v
i
c
e
R
D
E 78th St
E 73rd St
E 74th St
15th Ave S17th Ave S11th Ave S18th Ave S10th Ave SLongfellow Ave SPark Ave SOakland Ave SChicago AVE S13th Ave SE 78th STColumbus Ave SElliot AVE SMNTH 77E 77th St
E 76th ST
E 75th St
E 72nd ST
12th Ave S77
§¨¦494
Existing 10-year 24-hour
Storm Event Inundation
Extent
10-year 24-hour Storm Event
Inundation Extent with
Increased Storm Sewer
Capacity and number of
Pipes from Wilson Pond
Generalized Flood Risk Area
Flood-Prone Structure(s) in 10-
year Event
Flood-Prone Structures No
Longer Impacted as a Result
of Concept C
Flood-Prone Structures Still
Impacted with Concept C
Model Result Locations
Storm Sewer Pipe
Increased Storm Sewer Pipe
to two parallel 5’x5’ Box
Culverts
Municipal Boundary
Flood-Prone Structures Impacted by
Existing 10-year Inundation Extent 126 structures
Flood-Prone Structures No Longer
Impacted as a Result of Concept C 61 structures
Flood-Prone Structures Still Impacted with
Concept C 65 structures
Number of Structures within Generalized Flood-Risk Area
Page 55 of 78
34
5.2 Flood-Risk Area Northwest of Roosevelt Park
The flood-risk area Northwest of Roosevelt Park was selected by the city for further evaluation. This flood-
risk area impacts multiple structures in a single location, the lowest structures are affected during the 10-
year 24-hour duration rainfall event, the flood-risk area is located within an area of the city with a high
social vulnerability index, and surface inundation impacts a critical transportation route through the city.
For these reasons, as well as the potential for flood reduction with open space near the flood-risk area,
the city selected this area to evaluate concepts for system modifications to reduce flood risk.
Options that were considered but not pursued for the area Northwest of Roosevelt Park include adding
surface storage areas and increasing capacity downstream of the flood-risk area. Surface storage was
not considered because the undeveloped portion of Roosevelt Park is at a higher elevation than the
nearby flood-risk area. Preliminary grading of a potential pond at this site did not add significant storage
volume below the modeled water level of the flood-risk area and getting the water to the pond by gravity
drainage was not feasible. Increasing capacity of the downstream storm sewer system was not evaluated
further as the flood-risk area drains to Norby’s Pond which is also identified as a flood-risk area.
One potential project flood-risk mitigation concept was identified for the area Northwest of Roosevelt
Park, adding an underground storage chamber upstream of the flood-risk area. This concept is discussed
more in Section 5.2.1. A concept level cost estimate for this potential project is provided in Table 5-5. The
cost estimate is further described in Appendix A.
Table 5-5 Northwest of Roosevelt Park Flood Mitigation - Cost Estimate
Concept Description Cost Estimate
A Add underground storage chamber $15,491,000
$10,844,000 – $27,110,000
Note: Total project cost accuracy range is -30% to +50%.
5.2.1 Northwest of Roosevelt Park Flood Mitigation Concept A
This flood mitigation concept is to add an underground storage chamber beneath the baseball fields at
Roosevelt Park and is shown on Figure 5-4. Surface drainage upstream of the flood-risk area from
Roosevelt Park and along 76th Street would be diverted to the underground storage chamber. The
underground storage chamber would retain runoff from the upstream contributing watersheds and
attenuate the flow rate to the flood-risk area during the peak of the storm event.
The concept design includes adding approximately 354,000 cubic feet of underground storage for water
retention based on a surface area of 300-foot by 300-foot, a depth of 5.25 feet, and an assumed 75% of
underground volume available for stormwater storage. An outlet control structure would be used to retain
water in the underground storage but still allow the underground storage to drain completely after the
storm event. Along 76th Street the downstream invert of one storm sewer pipe would need to be adjusted
and a new pipe added to direct drainage towards the new underground storage. Additional pipe
modifications would be required to connect the surface drainage around the baseball fields to the
underground storage chamber.
Model results of this concept design are shown in Figure 5-4 with inundation comparison for the 10-year
24-hour storm event and a summary of modeled peak water levels at a few locations around the flood-risk
Page 56 of 78
35
area are compared to the existing condition model results in Table 5-6. The locations summarized in
Table 5-6 are also shown on Figure 5-4.
Table 5-6 Modeled Peak Water Levels Northwest of Roosevelt Park Flood Mitigation Concept
A: Add Underground Storage Chamber
Storm Event Model Condition
Modeled Peak Water Level by Location (feet)
Baseball
Fields
Upstream of
Underground
Storage at 76th
St. and S
Clinton Ave.
Downstream of
Underground
Storage at 76th
St. and S 3rd
Ave.
2-year 24-hour
Existing Conditions 842.3 842.0 840.6
Mitigation Concept A 837.7 839.9 840.2
Lowered Water Level 4.6 2.2 0.4
10-year 24-hour
Existing Conditions 842.5 842.9 842.2
Mitigation Concept A 838.8 841.9 841.7
Lowered Water Level 3.7 1.0 0.5
100-year 24-hour
Existing Conditions 843.6 843.6 843.6
Mitigation Concept A 842.9 843.1 842.9
Lowered Water Level 0.7 0.5 0.7
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Northwest of Roosevelt Park
Concept A: Add Underground
Storage Chamber
Richfield, MN
Outlet control structure from
new underground storage
chamber to existing pipe
leaving to the north
Volume of Storage Chamber:
354,000 cubic feet (approx.)
Location of storage to be
determined during next
phase of design.Baseball Fields
Upstream of Underground
Storage Chamber at 76th
St. and S Clinton Ave.
Downstream of
Underground Storage
Chamber at 76th St.
and S 3rd Ave.
W 76 1/2th St
4th Ave S5th Ave S4th AVE SClinton AVE S2nd Ave S3rd Ave S1st Ave SStevens Ave SPortland Ave SE 75th St
E 77th St
E 76th ST
456735
Existing 10-year 24-hour
Storm Event Inundation
Extent
10-year 24-hour Storm Event
Inundation Extent with
Underground Storage
Generalized Flood Risk Area
Proposed Underground
Storage Chamber
Flood-Prone Structure(s) in 10-
year Event
Flood-Prone Structures No
Longer Impacted as a Result
of Concept A
Flood-Prone Structures Still
Impacted with Concept A
Storm Sewer Pipe
Model Result Locations
Storm Sewer Pipe Changes
Add
Remove
Replace with new slope
Note: Additional pipe modifications
needed around baseball field area to
connect stormwater pipes to
underground storage chamber.
Flood-Prone Structures Impacted by
Existing 10-year Inundation Extent 9 structures
Flood-Prone Structures No Longer
Impacted as a Result of Concept A 6 structures
Flood-Prone Structures Still Impacted with
Concept A 3 structures
Number of Structures within Generalized Flood-Risk Area
Page 58 of 78
37
5.3 Flood-Risk Area Near Woodlawn Terrace
The flood-risk area near Woodlawn Terrace was selected by the city for further evaluation. This flood-risk
area impacts multiple structures in a single location, the lowest structures are affected during the 2-year
24-hour duration rainfall event, the storm sewer pipes are classified as moderate to high risk, the flood-
risk area is located within an area of the city with a high social vulnerability index, and the surface
inundation impacts three high-density housing structures. For these reasons, as well as the potential for
flood reduction with open space near the flood-risk area, the city selected this area to evaluate concepts
for system modifications to reduce flood risk. Options that were considered but not pursued for the area
near Woodlawn Terrace include adding surface storage areas. Surface storage was not considered
because while the area has open space, the space is developed with baseball fields and parking lots.
Two potential project flood-risk mitigation concepts were identified for the area near Woodlawn Terrace:
• Flood Mitigation Concept A: Add underground storage chamber below the parking lot, discussed
in Section 5.3.1.
• Flood Mitigation Concept B: Increase the storm sewer capacity from the flood-risk area to Wood
Lake by increasing the pipe sizes, discussed in Section 5.3.2.
A comparison of the concept level cost estimate for these two potential projects is provided in Table 5-7.
The cost estimate is further described in Appendix A.
Table 5-7 Near Woodlawn Terrace Flood Mitigation - Cost Estimate Comparison
Concept Description Cost Estimate
A Add underground storage chamber $1,540,000
$1,078,000 - $2,695,000
B Increase storm sewer capacity $7,440,000
$5,208,000 - $13,020,000
Note: Total project cost accuracy range is -30% to +50%.
5.3.1 Near Woodlawn Terrace Flood Mitigation Concept A
This flood mitigation concept is to add an underground storage chamber under the parking lot next to
Lynwood Commons Apartments as shown in Figure 5-5. The underground storage chamber would retain
runoff from the upstream contributing watersheds and attenuate the flow rate to the flood-risk area during
the peak of the storm event.
The concept design includes adding approximately 24,000 cubic feet of underground storage for water
retention based on a surface area of approximately 8,000 square feet, a depth of 3 feet, and an assumed
75% of underground volume available for stormwater storage. To achieve the 3-foot depth with 2 feet of
cover, the parking lot would have to be re-graded. Additional pipe modifications would be required to
connect the existing storm sewer pipes under the parking lot to the proposed storage chamber. This
mitigation concept would require agreements with the owner of the parking lot next to the Lynwood
Commons Apartments.
Model results of this concept design are shown in Figure 5-5 with inundation comparison for the 10-year
24-hour storm event and a summary of modeled peak water levels at a few locations around the flood-risk
Page 59 of 78
38
area are compared to the existing condition model results in Table 5-8. The locations summarized in
Table 5-8 are also shown on Figure 5-5.
Table 5-8 Modeled Peak Water Levels Near Woodlawn Terrace Flood Mitigation Concept A:
Add Underground Storage Chamber
Storm Event Model Condition
Modeled Peak Water Level by Location (feet)
Parking lot in
flood-risk area
Downstream at
Wood Lake
Upstream at
Lincoln Baseball
Fields
2-year 24-hour
Existing Conditions 842.5 822.1 841.9
Mitigation Concept A 841.9 822.1 841.7
Lowered Water Level 0.6 0.0 0.2
10-year 24-hour
Existing Conditions 843.3 823.7 842.9
Mitigation Concept A 843.2 823.7 842.8
Lowered Water Level 0.1 0.0 0.1
100-year 24-hour
Existing Conditions 844.5 827.1 844.5
Mitigation Concept A 844.5 827.1 844.5
Lowered Water Level 0.0 0.0 0.0
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Near Woodlawn Terrace
Concept A: Add Underground
Storage Chamber
Richfield, MN
Parking Lot in
Flood-Risk Area
Upstream at Lincoln
Baseball Fields
Volume of Storage Chamber:
24,000 cubic feet (approx.)
Location of storage to be
determined during next
phase of design.
W 73 1/2rd St
W 75th St
Grand Ave SHarriet Ave SGarfield Ave SW Pleasant Ave SW 75th ST Lyndale AVE SE Pleasant Ave SW 74th St
Bryant Ave SWentworth Ave SPillsbury Ave SAldrich Ave SW 76th ST
Existing 10-year 24-hour
Storm Event Inundation
Extent
10-year 24-hour Storm Event
Inundation Extent with
Underground Storage
Generalized Flood Risk Area
Proposed Underground
Storage Chamber
Flood-Prone Structure(s) in 10-
year Event
Flood-Prone Structures Still
Impacted with Concept A
Flood-Prone Structures No
Longer Impacted as a Result
of Concept A
Storm Sewer Pipe
Model Result Locations
Note: Additional pipe modifications
needed around baseball field area to
connect stormwater pipes to
underground storage chamber.
Flood-Prone Structures Impacted by
Existing 10-year Inundation Extent 6 structures
Flood-Prone Structures No Longer
Impacted as a Result of Concept A 0 structures
Flood-Prone Structures Still Impacted with
Concept A 6 structures
Number of Structures within Generalized Flood-Risk Area
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5.3.2 Near Woodlawn Terrace Flood Mitigation Concept B
This flood mitigation concept is to increase the storm sewer capacity downstream of the northwest corner
of the parking lot next to Lynwood Commons Apartments by increasing the size of the pipe to Wood Lake.
This mitigation concept is shown on Figure 5-6.
The storm sewer pipe is currently circular and arch pipes with a diameter ranging from three feet to four
feet. This flood mitigation concept increases the pipe diameter to range from three feet to six feet. The
pipe upstream of northwest corner of the parking lot next to Lynwood Commons Apartments to the middle
of the parking lot is not currently included in this mitigation concept to be increases in size due to shallow
cover over the existing pipe.
Model results of this concept design are shown in Figure 5-6 with inundation comparison for the 10-year
24-hour storm event and a summary of modeled peak water levels at a few locations around the flood-risk
area are compared to the existing condition model results in Table 5-9. The locations summarized in
Table 5-9 are also shown on Figure 5-6.
Table 5-9 Modeled Peak Water Levels Near Woodlawn Terrace Flood Mitigation Concept B:
Increase Storm Sewer Capacity
Storm Event Model Condition
Modeled Peak Water Level by Location (feet)
Parking lot in
flood-risk area
Downstream at
Wood Lake
Upstream at
Lincoln Baseball
Fields
2-year 24-hour
Existing Conditions 842.5 822.1 841.9
Mitigation Concept B 841.4 822.1 841.6
Lowered Water Level 1.1 0.0 0.3
10-year 24-hour
Existing Conditions 843.3 823.7 842.9
Mitigation Concept B 842.5 823.7 842.4
Lowered Water Level 0.8 0.0 0.5
100-year 24-hour
Existing Conditions 844.5 827.1 844.5
Mitigation Concept B 843.4 827.1 843.8
Lowered Water Level 1.1 0.0 0.7
Page 62 of 78
0 400 800
Feet
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Nearmap Imagery, 2024
Barr Footer: ArcGISPro 3.3.2, 2025-06-25 10:39 File: I:\Client\Richfield_MN\Work_Orders\23272085_Model_Updates\Maps\Final_Report\Final Report Figures.aprx Layout: Figure 5-6 Near Woodlawn Terrace Concept B-Increase Storm Sewer Capacity User: EMAFIGURE 5-6
Near Woodlawn Terrace
Concept B-Increase
Storm Sewer Capacity
Richfield, MN
Parking Lot in
Flood-Risk Area
Downstream at
Wood Lake
Upstream at Lincoln
Baseball Fields
Wood Lake
Augsburg
Pond
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W 73 1/2rd St
Pleasent LaLyndale
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SHumboldt AveW 7
7
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t W Pleasant Ave SAugsburg AVE SW 71st St
Irving Ave SW 72nd St
W 75th St
W 72nd ST
Grand Ave SFremont Ave SOak Grove BLVDGirard Ave SGarfield Ave SHarriet Ave SColfax Ave SW 73rd St
Emerson Ave SE Pleasant Ave SW 75th STDupont Ave SAldrich Ave SBryant Ave SHumboldt Ave SWentworth Ave SBlaisdell Ave SPillsbury Ave SW 74th St
W 76th ST
Existing 10-year 24-hour
Storm Event Inundation
Extent
10-year 24-hour Storm Event
Inundation Extent with
Increased Storm Sewer
Capacity to Wood Lake
Generalized Flood Risk Area
Flood-Prone Structure(s) in 10-
year Event
Flood Prone Structures No
Longer Impacted as a Result
of Concept B
Flood Prone Structures Still
Impacted with Concept B
Storm Sewer Pipe
Model Result Locations
Storm Sewer Pipe Changes
Increase to 5 foot diameter
Increase to 6 foot diameter
Flood-Prone Structures Impacted by
Existing 10-year Inundation Extent 6 structures
Flood-Prone Structures No Longer
Impacted as a Result of Concept B 1 structures
Flood-Prone Structures Still Impacted with
Concept B 5 structures
Number of Structures within Generalized Flood-Risk Area
Page 63 of 78
42
5.4 Limitations and Considerations
The projects, model results, and cost estimates presented in Section 5 are represent a concept level
design. Each flood-risk area was evaluated at a high level for potential flood-risk mitigation options and
those discussed were identified as potential options while some other options were not considered based
on available information and city direction. Some of the limitations identified to rule out mitigation options
were expected shallow groundwater levels, flood-risk areas identified downstream, and the city’s direction
to not consider property acquisition for flood-risk reduction.
Additional evaluations of each site and mitigation concept will need to be completed as they are pursued
further. This includes design optimization, evaluating utility conflicts, reviewing permitting requirements, in
some cases agreements with private landowners or other public entities, and additional considerations
specific to each project. For example, the three mitigation concepts for Wilson Pond include increased
flow to Highway 494 which would need to be conveyed to the Minnesota River through the city of
Bloomington or along the Highway 494 corridor. The details of this stormwater routing beyond the city
boundary have not been determined and would also require additional permitting discussions to find an
acceptable solution. Other mitigation options presented do not have this exact challenge but are expected
to have other challenges that would be identified as the design progresses and becomes more detailed.
Additional limitations and description of the cost estimates included for each mitigation concept in
Section 5 are described in Appendix A.
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6 Conclusions
The prioritization framework was developed with the city. The prioritization framework can be used as one
tool to determine where to begin with further evaluation of flood-risk mitigation projects. This provides the
city a methodology to compare potential benefits of flood-risk mitigation projects and prioritize how to
invest limited resources for mitigating flood-risk.
It is anticipated that overtime the prioritized list of areas will change. For example, as flood-risk mitigation
projects are completed or as city census data changes. When these changes occur or new information
becomes available, the prioritized list could be updated to reflect changing priorities.
Finally, this prioritization framework provides a consistent methodology to evaluate how to prioritize flood-
risk mitigation projects for the city. Additionally, this framework uses a similar methodology, though with
some different criteria, than the city of Bloomington for work within the Richfield Bloomington Watershed
Management Organization.
Three flood-risk areas were selected by the city based on the project prioritization framework developed.
For these three flood-risk areas a total of six mitigation concepts were identified and evaluated in the
updated stormwater model. Each concept provides some level of flood-risk mitigation but at varied cost
and with additional project considerations. Additional design and evaluation of the alternatives will be
required as the city plans for future flood-risk mitigation projects. The project prioritization process identified
multiple flood-risk areas across the city. The framework outlined in this report will be used by the city to
inform future flood-risk mitigation studies.
Data sets used for model development are not always complete or error-free. As additional information is
collected or provided by the city, the prioritized list of areas may be affected. For example, no survey data
was collected to verify flood-prone structures. However, if surveys are completed in the feasibility study
phase of flood-risk mitigation projects to better address the cost-benefit relationship of specific projects,
new survey information may demonstrate that existing structures are or are not flood-prone.
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7 References
1. Barr Engineering Co. Richfield Hydrologic and Hydraulic Modeling Report. Minneapolis : s.n., 2019.
2. U.S. Geological Survey. 3D Elevation Program: LiDAR point cloud data for Minnesota, 2022
collection. The National Map. [Online] 2023. https://apps.nationalmap.gov/downloader/.
3. Furgo Horizons Inc. and Minnesota Department of Natural Resources. LiDAR Elevation Twin
Cities Metro Region. Saint Paul, Minnesota : Minnesota Department of Natural Resources, 2011.
4. Ranschau, Heidi, City of Minneapolis Public Works - Surface Water & Sewer Division. Email
Subject: RE: [EXTERNAL] RE: Model request for Richfield. Minneapolis : s.n., November 19, 2024.
5. Paul Hudalla, City of Minneapolis Public Works, Surface Water & Sewer Division. RE: Mpls S.
Region subwatersheds and modeling related to Richfield H&H modeling. Minneapolis : s.n., November 2,
2017.
6. Heidi Ranschau, City of Minneapolis Public Works, Surface Water & Sewer Division. RE:
[EXTERNAL] RE: Model request for Richfield. Minneapolis : s.n., Nov 19, 2024.
7. Perica, Sanja, et al. NOAA Atlas 14, Volume 8, Version 2, Precipitation-Frequency Atlas of the United
States, Midwest States. Silver Spring, MD : National Oceanic and Atmospheric Administration, 2013.
8. Stack LJ, Simpson MH, Gruber J, Moore TL, Yetka L, Eberhard L, Gulliver J, Smith J, Mamayek
T, Anderson M and Rhoades J. . Long-term climate information and forecasts supporting stakeholder-
driven adaptation decisions for urban water resources: Response to climate change and population
growth. Final project report: Sectoral Applications Research Program FY2011. s.l. : Climate Program
Office, National Oceanic and Atmospheric Administration, 2014.
9. USDA Natural Resources Conservation Service, Minnesota. NOAA_Rainfall_Distributions. 2015.
10. Barr Engineering, Co. . Stormwater Infrastructure Qualitative Risk Analysis for the City of Richfield.
Minneapolis : s.n., March 14, 2018.
11. Centers for Disease Control and Prevention/ Agency for Toxic Substances and Disease
Registry/ Geospatial Research, Analysis, and Services Program. CDC/ATSDR Social Vulnerability
Index. Database Minnesota. [Online] 2022. [Cited: July 15, 2024.]
https://www.atsdr.cdc.gov/placeandhealth/svi/data_documentation_download.html.
12. Minnesota Department of Natural Resources. Groundwater Atlas of Hennepin County, Minnesota.
St. Paul : Minnesota Department of Natural Resources, 2021.
13. Barr Engineering, Co. . Stormwater Model Update and Flood-Risk Area Prioritization Identification.
Minneapolis : s.n., 2021.
Page 66 of 78
Appendix A
Opinion of Probable
Construction Cost
Page 67 of 78
1
1 Opinion of Probable Construction Cost
There are several factors that affect the cost of implementing a flood-risk reduction project:
• The volume of stormwater that must be stored within the watershed or conveyed downstream;
• The potential to reduce flood-risk by retrofitting existing stormwater infrastructure;
• The potential to reduce flood-risk by constructing new flood detention facilities; and
• The potential need to acquire property when other flood-reduction alternatives are not feasible.
Evaluating the most cost-efficient flood reduction project for a given flood-risk area requires (1) review of
the source(s) and cause(s) of flooding (requiring detailed hydrologic and hydraulic review), (2) high-level
review of available options to mitigate flooding (e.g., is there sufficient available space for a flood
detention project? Is there sufficient grade to excavate and tie-in to existing storm sewer utilities, etc.),
and (3) preliminary design and cost-comparison analysis of feasible flood-mitigation alternatives. Due to
the large number potential system modifications identified, it was not practical to perform detailed review
of flood-mitigation alternatives for each location within the study area, and it is anticipated that the
configuration of system modifications to reduce flood-risk will change during subsequent phases of
design.
An important note is that, based on a more-detailed review of flood-mitigation alternatives, optimization of
potential system modifications, and completion of detailed design, the final cost of flood-mitigation may be
lower or higher than the concept level opinions of cost included in this report. The costs provided in this
report are intended to provide a planning-level estimate for the potential system modifications that were
evaluated.
The opinions of cost, project reserves, contingency, documentation and discussion presented in this
report are intended to provide background information for concept-level alternatives assessment, analysis
purposes, and budget planning. The cost of time escalation is not included in the opinions of probable
cost. All costs are presented in 2025 US dollars.
Quantities were estimated with calculations based on available information presented. Dimensions,
areas, and volumes for construction were estimated using excel, GIS, and manufacturer information.
Unit costs are based on recent bid prices, published construction cost index resources, and similar
stormwater BMP projects.
Costs associated with Base Planning Engineering and Design (PED), Construction Management (CM),
Permitting, and Property or Easement acquisition are not included in the overall estimate for construction
costs.
The opinions of cost also do not include other tasks following construction of each alternative presented
such as operations and maintenance, or monitoring.
Contingency used in these opinions of probable cost are intended to help identify an estimated
construction cost amount for the minor items included in the current Project scope but have not yet been
quantified or estimated directly during the feasibility evaluation. Stated another way, contingency is the
resultant of the pluses and minuses that cannot be estimated at the level of project definition that exists.
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2
The contingency includes the cost of ancillary items not currently itemized in the quantity summaries but
commonly identified in more detailed design and required for completeness of the work. A 25%
contingency is applied to the estimated construction cost to account for the costs of these items.
Industry resources for cost estimating (AACE International Recommended Practice No. 18R-97, and
ASTM E2516-06 Standard Classification for Cost Estimate Classification System) provide guidance on
cost uncertainty, depending on the level of project design developed. The opinion of probable cost for the
alternatives evaluated generally corresponds to a Class 4 estimate characterized by completion of limited
engineering and use of deterministic estimating methods. As the level of design detail increases, the level
of uncertainty is reduced. Figure A-1 provides a graphic representation of how uncertainty (or accuracy)
of cost estimates can be expected to improve as more detailed design is developed.
Figure A-1 Relationship between Cost Accuracy and Degree of Project Definition
At this early stage of planning, the range of uncertainty of total project cost is high. Due to the early stage
of the project, it is standard practice to place a broad accuracy range around the point cost estimate.
The accuracy range is based on professional judgment considering the level of design completed, the
complexity of the project, and the uncertainties in the project scope; the accuracy range does not include
costs for future scope changes that are not part of the project as currently defined or risk contingency.
The estimated accuracy range for this point estimate is -30% to +50%.
The opinion of probable construction cost is made on the basis of Barr Engineering’s experience and
qualifications and represents our best judgment as experienced and qualified professionals familiar with
the project. It is acknowledged that additional investigations and additional site-specific information that
becomes available in future stages of design may result in changes to the proposed configuration, cost
and functioning of project features. This opinion is based on project-related information available to Barr
Engineering at this time and includes a concept-level feasibility design of the project. In addition, because
we have no control over the eventual cost of labor, materials, equipment or services furnished by others,
or over the contractor’s methods of determining prices, or over competitive bidding or market conditions,
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3
Barr Engineering cannot and does not guarantee that proposals, bids, or actual costs will not vary from
the opinion of probable cost presented. If the city wishes greater assurance as to the probable
construction cost, the city should authorize further investigation and design of a selected alternative.
Page 70 of 78
4
2 References
American Society for Testing and Materials. 2006. ASTM E2516-06 Standard Classification for Cost Estimate Classification System. ASTM International, West Conshohocken, PA, DOI:
10.1520/E2516-06
Association for the Advancement of Cost Estimating. 2005. AACE International Recommended Practice
NO. 18R-97, February 2, 2005.
Page 71 of 78
Stormwater Model Updates and Flood-Risk Area Identification
Page 72 of 78
Citywide Stormwater Model -Background
•Existing citywide stormwater model was developed in 2018 for PCSWMM
•Changes to the stormwater system from redevelopment and public projects required model updates
•Stormwater modeling helps guide decision making for municipal projects
•In 2024, city staff secured a $91,500 MPCA grant to undertake this work
Page 73 of 78
Updates Made
•Incorporating new (2022) USGS LiDAR data
•Merging existing East/West models
•Changes from redevelopments, pond improvement projects, street and storm sewer projects
•Updated storm lift station data
•Matching boundary conditions with Minneapolis’ model
•Modeling an additional storm event based on future climate projections
Page 74 of 78
Flood Risk Area Prioritization
•Developed a quantitative scoring framework for flood risk areas:
•Storm system condition (10%)
•Critical infrastructure (15%)
•Frequency of flooding (25%)
•Social vulnerability index (SVI) (10%)
•Number of flood-prone structures (40%)
•High-scoring areas were evaluated by City staff
•Downstream impacts
•Upcoming public works projects
Page 75 of 78
Model Results
Page 76 of 78
Concept-Level Alternatives Analysis
Page 77 of 78
Next Steps
•Leverage model to guide design and decision-making
•Maintain and continue to refine model
•Changes to stormwater system
•Updated rainfall estimates
•Incorporating more accurate data
•Begin long-term planning for flood mitigation projects
Page 78 of 78