HomeMy WebLinkAboutFlood Risk Reduction Strategy
CITY OF EDINA
FLOOD RISK REDUCTION
STRATEGY
March 4, 2020 – City Council Work Session Draft
City of Edina, Engineering Department
www.EdinaMN.gov
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Table of Contents
Executive Summary ................................................................................................................................. 3
Problem statement.................................................................................................................................. 5
Project initiation .................................................................................................................................. 5
How flooding occurs ............................................................................................................................ 6
Groundwater levels are increasing: summary of monitoring data..................................................... 8
What is flood risk? ............................................................................................................................... 8
Drivers of increasing flood risk ............................................................................................................. 9
Getting to scale: a challenging problem made even more challenging, climate change impact
analysis .......................................................................................................................................... 11
Climate Action Plan: in progress item ............................................................................................. 11
Formulating a Strategy .......................................................................................................................... 12
Comprehensively Reduce Flood Risk throughout the Community ...................................................... 12
The gap between the current Comprehensive Water Resources Management Plan and the Strategy 13
City Sectors of Work and Service ........................................................................................................... 14
Infrastructure .................................................................................................................................... 14
Go Big, Go Bigger: infrastructure analysis ....................................................................................... 15
Morningside Roadway Reconstruction Engineering Study: in progress item ................................... 16
Regulation ......................................................................................................................................... 18
Keep your water to yourself: private infrastructure analysis .......................................................... 20
From ‘ill-drained’ to impervious: impervious surface analysis ........................................................ 21
Impervious limit: in progress item .................................................................................................. 22
Outreach and Engagement ................................................................................................................ 22
Outreach products: in progress item .............................................................................................. 23
Emergency Services ........................................................................................................................... 23
Strategy Development ........................................................................................................................... 24
Task Force role and process ............................................................................................................... 24
Brainstorming, prioritizing, and categorizing possible actions ............................................................ 26
Conclusion ............................................................................................................................................. 26
Next steps ............................................................................................................................................. 27
Acknowledgement................................................................................................................................. 28
Appendix ............................................................................................................................................... 29
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Appendix A: ‘Groundwater levels are increasing: summary of monitoring data’, technical memo ...... 29
Appendix B: ‘Getting to scale: a challenging problem made even more challenging, climate change
impact analysis’, technical memo ...................................................................................................... 29
Appendix C: ‘Go Big, Go Bigger: infrastructure analysis’, technical memo .......................................... 29
Appendix D: ‘Keep your water to yourself: private infrastructure analysis’, technical memo .............. 29
Appendix E: ‘From ‘ill-drained’ to impervious: impervious surface analysis’, technical memo............. 29
Appendix F: Actions for Flood Resilient Homes, fact sheets ................................................................ 29
Appendix G: Task Force charge .......................................................................................................... 29
Appendix H: Potential action matrix key, ranked response, and potential action matrix ..................... 29
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Executive Summary
This draft of the flood risk reduction strategy summarizes a ten-month task force effort where staff and
community members worked to come to a shared understanding of what flooding is, and how we can
connect on the promise to comprehensively reduce the risk of flooding throughout the community.
We expanded and developed our understanding of how we view flood risk, to include;
The key equation; 𝐹𝑘𝑘𝑘𝑎 𝑟𝑖𝑟𝑘=𝑎𝑘𝑖𝑘𝑎𝑟𝑎× 𝑎𝑥𝑘𝑘𝑟𝑟𝑟𝑎 × 𝑟𝑟𝑘𝑘𝑎𝑟𝑎𝑎𝑖𝑘𝑖𝑟𝑥
o Flooding starts with the weather and climate, requiring an awareness of short- and long-
term risks. Rainfall varies over time, and climate change increases the extremes.
o Flood exposure depends of landform, runoff, flow, drainage, and groundwater. These
factors vary spatially, some areas having higher exposure to flood waters or flow.
o Flood vulnerability depends on the assets, public and private, that are on the land and
exposed to flooding. Increasing climate extremes drive flood exposure and demands
adaptation or resilience increase commensurately to keep risk constant.
Pathways for structural risk;
o Over the land surface; Intense storms can cause high water in both local and regional
low areas, and overland flow paths
o Groundwater seepage; Long term wet periods can raise groundwater putting stress on
building foundations, and flood low-lying landlocked areas
o Sanitary backflow; Flooding in nearby structures can overwhelm the sanitary system and
cause backups
Risk reduction efforts depend on the time
o The best time to reduce flood vulnerability is before the flood
o During a flood focus shifts to staying safe from harm, or sustaining or restoring services
o After the flood, we focus on recovering and reviewing risk
We explored the community aspects of flooding, and the City’s role.
Problem; We will make flood information available to all and promote flood awareness
People; We will work to help people stay safe in floods
Property; We will help people protect their properties from flooding and the effects of floods
Places; We will plan public streets and parks to accept and transmit flood waters to reduce risk
and disruption of related city services
We reviewed City areas of work, and the relationships to flood risk.
Infrastructure: We will renew our infrastructure and operate it to reduce risk
Regulation: We acknowledge competing demands of land use, solving drainage, groundwater,
and surface water issues. We help people solve issues without harming another.
Outreach and Engagement: We make flood information available and give people tools for flood
resilience.
Emergency Services: We help people prepare for floods, remove people from harm during
floods, and help people recover after floods.
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We reviewed key drivers of increasing risk and areas of work to inform questions about the pace of
implementation and possible next step actions;
Climate; Climate change is making storms more intense and increasing the chance of extended
wet periods or drought. This is the overwhelming driver increasing future flood exposure.
Aging and obsolete infrastructure; Our pipes are old and not up to the current demands. This is
a significant driver as infrastructure provides most stormwater service.
Demand for well drained landscapes; Development has connected the landscape to the water to
make land well drained. While this a major historic driver, it is a minor driver increasing future
flood exposure. Most of the drainage and land development decisions have been made, but
there are some public and private system retrofits that continue to connect landscape and water
bodies, marginally affecting flood exposure.
Imperviousness; Community demand for garages, parking areas, patios, decks, pools, and bigger
homes has increased the hard cover of soils. This is a minor driver increasing future flood
exposure. Most of the land development decision have been made, but small additions to
impervious cover marginally affect flood exposure. Soils can’t soak up the amounts of water
floods provide.
We reviewed possible actions, evaluating effectiveness, value, and community support to map out future
planning. A few quick-win items were started where existing resources allowed and are presented as
appendix to this report. Other items were classified as planning or development items that imagine a
future level of implementation with expanded skill and resources.
These efforts to put flooding into focus have resulted in the creation this framework and draft strategy
for Council and task force review, to connect on the promise to comprehensively reduce the risk of
flooding throughout the community.
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Problem statement
Flooding can affect people, damage property, threaten health and safety, and disrupt transportation and
business. Flooding is common in Edina and climate change is expected to make flooding worse.
Flooding has historically been considered a technical problem, requiring a technical solution. Land
ownership, space, legislation, and hydrology are interwoven with values about problem ownership,
water stewardship, service tradeoffs, and transferring risk. What was once considered purely a technical
problem may be more of a mix of a technical, scientific, political, and social one. This type of problem
requires a different set of strategies, skill sets, and tools.
Timothy M. Gieseke. Shared Governance for Sustainable Working Landscapes
Project initiation
In September 2018 City Council adopted the 2018 Comprehensive Water Resources Management Plan.
The implementation section of the plan included development of a Flood Risk Reduction Strategy.
A City Manager Task Force of Edina residents was formed to provide a community voice to the process.
The City recognizes the contribution of these individuals and appreciates the value they’ve provided.
Task Force members;
Nora Davis (co-chair), Lake Cornelia Neighborhood
Kathy Amlaw (co-chair), Lake Edina Neighborhood
Greg Lincoln, Morningside Neighborhood
Michael Platteter, Morningside Neighborhood
Louise Segreto, Indian Hills Neighborhood
Roxane Lehmann, Sunny Slope Neighborhood
Richard Strong, Concord Neighborhood
Richard Manser, Todd Park Neighborhood
The Task Force was charged with supporting and providing recommendations to inform the
development of this strategy, specifically to;
Incorporate local challenges, opportunities, knowledge, and community values
Incorporate voices from throughout the City of Edina. While the Morningside neighborhood has
been identified as a focal geography for case study, strategies and outcomes ought to be scalable
city-wide.
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Identify action steps for building community capacity to address flood risk and resiliency in
Edina.
In July 2019 staff began working with a resident Task Force to develop a Flood Risk Reduction Strategy.
The group met over a dozen times, investing hundreds of hours collectively.
The strategy doesn’t solve flooding. We’ve learned that it’s too big of a problem to solve outright;
however, we’ve charted a path to reduce the risk of flooding. Through this effort, we;
Explored technical questions like, “How much does impervious cover matter?”, “What kind of
flood risk does the future hold in the wake of a changing climate?”, “How much benefit can
private storage provide?”, and “How much benefit can bigger infrastructure provide?”
Interviewed the operators and maintainers of the system to better understand the level of
service the system currently provides and its vulnerabilities.
Gained a better understanding of the factors and drivers that influence flood risk.
Described the various ways in which structural flooding occurs; over the land surface, through
groundwater seepage, and sanitary sewer backflow.
Defined the areas within which we already work and identified other actions the City could
undertake, connecting these areas of work to Council work plan goals.
Widened our approaches for reducing flood risk.
Heard people share their experience and knowledge about flooding. The Task Force shared
their community values around flood risk and informed the framework and strategy.
Based on Council and community feedback, the Morningside neighborhood was selected as the focal
geography for the Flood Risk Reduction Strategy. Further description about how the neighborhood was
used to test ideas is provided in the Strategy Development section of this report.
Throughout this report, we briefly highlight relevant in-progress items and summaries of the technical
analyses – more detailed memorandums describing the technical analyses are provided in the Appendix.
How flooding occurs
Too much water from rain or melting snow can overwhelm the system. Pipes run full, intersections
flood, lakes and creeks overtop their banks, water flows over the land surface, sidewalks and paths
become impassible, yards are inundated, groundwater builds up, water seeps through basement walls
and floors, and water can back up into homes through sanitary sewers.
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Groundwater levels are increasing: summary of monitoring data
Groundwater levels are increasing: summary of monitoring data
In the winter of 2020 Nine Mile Creek Watershed District and Minnehaha Creek Watershed District
separately convened local water resources and emergency managers to share their groundwater level
monitoring data.
After a string of exceptionally wet years and a record-breaking precipitation year in 2019, lakes and
creeks are high, the ground is saturated and, in many places, groundwater level monitoring records
show water table elevations are on the rise. One groundwater monitoring well in Edina near
Bredesen Park shows an increase of about 15 feet since 2010. In areas where the depth to the
regional groundwater table is shallow, structures with basements are at an increased risk for flooding
from groundwater seepage.
Groundwater is difficult to map. It’s dynamic, inconsistent, and the distribution can vary drastically
from what we see on the land surface.
More information about local groundwater level monitoring data is available in the appendix.
What is flood risk?
Flood Risk: Flood risk is determined by climate, exposure, and vulnerability.
Flood Exposure: The degree to which property, homes, buildings, infrastructure, and other assets
come into contact with flood water.
Flood Vulnerability: The degree to which exposed assets are unable to resist flooding and are
damaged by floods.
For example, two homes side-by-side might have the same flood exposure, but one home might be less
vulnerable to the exposure. Vulnerability can be decreased with the installation of downspouts, proper
grading, a basement sump pump, waterproof or reinforced foundations, mature trees with strong root
systems, and excellent drainage through well-designed rain gardens, among other things.
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Flood risk factors and definitions adapted from IPCC, 2012: Managing the Risks of Extreme Events and
Disasters to Advance Climate Change Adaptation. A Special Report of Working Groups I and II of the
Intergovernmental Panel on Climate Change.
Drivers of increasing flood risk
Flooding issues within the City of Edina continue to increase in frequency and severity. The following
have been identified as primary drivers leading to increased flood risk.
Climate change and changing weather patterns:
Climate change is the lead driver of increasing flood risk in Edina. Climatologists indicate that
large, intense rainfall events are occurring more frequently, and models predict that large rainfall
events will become more intense in the future. Minnesota is already experiencing prolonged wet
periods; in fact, the years between 2015 and 2019 were the wettest in Minnesota history and we
can expect more wet years in the future. This increase is also impacting neighboring
communities, is occurring at the international, national, state, and watershed levels, and is
expected to get much worse.
With the update to the Comprehensive Water Resources Management Plan, the most recent
precipitation frequency estimates were incorporated into the City’s flood model which showed
increased flood risk throughout the City. It should be noted that this data only brings us to
current climate conditions and does not provide protection for additional future risk caused by
climate change.
Modeling of storms and flood risk, and visualization of that risk has improved dramatically in
recent decades, leading to better community perception of risk.
See ‘Getting to scale: a challenging problem made even more challenging, climate change impact
analysis’ and ‘Climate Action Plan: in progress item’ sections of this report.
Aging and obsolete infrastructure:
Infrastructure is aging, and much is in poor repair, stretching maintenance and operations staff
thin. Current resources dictate a reactive approach instead of a proactive approach.
The current stormwater system was built for a different time and standard. Climate change has
already increased the risk and made most of the system obsolete.
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Needs far exceed available resources. Flooding issues are extensive and improvements that
address the 1%-annual-chance storm are often out of reach at current levels of funding.
Demand for well-drained landscapes:
Development has connected the landscape to the water to make land well drained. Demand for
well-drained landscapes has led to private and public drain line and gutter expansion. This
expansion directly connects the landscape and the water generated there to downstream
properties and waterbodies.
While this a major historic driver, it is a minor driver increasing future flood exposure. Most of
the drainage and land development decisions have been made, but there are some public and
private system retrofits that continue to connect landscape and water bodies, marginally
affecting flood exposure.
Imperviousness:
Community demand for garages, parking areas, patios, decks, pools, and bigger homes has
increased the hard cover of soils.
There is an increasing trend of imperviousness in the City of Edina. Specifically, within the focal
area of Morningside, nearly one million square feet of impervious surfaces (homes, structures,
driveways, patios, swimming pools, etc.) have been added since 1950. This equates to about 14%
of the total size of occupied parcels in the Morningside neighborhood (2019, City of Edina staff).
This is a minor driver increasing future flood exposure. Most of the land development decision
have been made, but small additions to impervious cover marginally affect flood exposure. Soils
can’t soak up the amounts of water floods provide.
See ‘Keep your water to yourself: private infrastructure analysis’, ‘From ‘ill-drained’ to
impervious: impervious surface analysis’, and ‘Impervious limit: in progress item’ sections of this
report.
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Getting to scale: a challenging problem made even more challenging, climate change impact
analysis
Getting to scale: a challenging problem made even more challenging, climate
change impact analysis
Through the Task Force process, staff heard the sentiment, “stop studying the problem, you have the
answer, it’s time to act.” While action is needed now, this report rebuts the sentiment that we have
the answers. Our new understanding of risk in the 2018 Comprehensive Water Resources
Management Plan show the system is overloaded. We now can more easily see how ‘solving’ a
problem in one area can make a downstream problem worse. ‘Solutions’ need to review downstream
risk and be packaged together comprehensively, acknowledging or mitigating the risk transfer.
Packaging problems requires a scale of effort that has not been attempted in Edina, and the scales
contemplated still do not totally ‘solve’ the problem, instead they may not even be keeping up with
climate change.
Climate change is changing the target. Solutions of today have to accommodate more water than in
the past, and solutions have to withstand the effects of climate change in the future. We need a new
approach to planning. It is necessary to shift the approach from trying to reduce flood exposure for
some, to reducing the vulnerability to flooding for all.
A memorandum describing the analysis in more detail is available in the appendix.
Climate Action Plan: in progress item
Climate Action Plan: in progress item
Development of a Climate Action Plan would further outline and prioritize actions for climate change
mitigation and adaptation. City staff is working to scope a process for creating a Climate Action Plan
for Edina. The Energy and Environment Commission recently completed a study and report on a
timeline and parameters for such a plan, including the City’s leadership role.
Undoubtedly, carbon reduction in both the private and public sectors will be an area of opportunity.
In order to meet community-wide emission reduction goals, it will take a process that includes the
community to understand what actions are important and how to prioritize them. There is a clear
overlap between addressing flood risk and mitigating climate change. To that end, it is prudent that
the Flood Risk Reduction Strategy inform the larger Climate Action Plan work of the City’s
Sustainability Manager and Energy and Environment Commission.
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Formulating a Strategy
Comprehensively Reduce Flood Risk throughout the Community
Flooding in Edina is not only common, it’s increasing. The City of Edina’s strategy is to
comprehensively reduce risk throughout the community. This means we address flooding
through a broad range of actions and that decisions consider the assets and people that characterize the
City. Approaches for managing risk include reducing exposure, reducing vulnerability, transferring and
sharing risks, increasing resilience to changing risks, and preparing, responding and recovering from
floods.
Adapted from IPCC, 2012: Managing the Risks of Extreme Events and Disasters to Advance Climate Change
Adaptation. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change
Strategy helps answer the question, “What are we trying to accomplish?” Every community has limited
resources and deals with its own unique challenges – strategy acts as a guide to a set of actions and
filters out those that do not fit.
Tactics help answer the question, “How are we going to accomplish our goal?” Tactics are the actions
within the following City sectors of work; infrastructure, regulation, outreach and engagement, and
emergency services. Each sector of work supports a City Council work plan goal.
Flood Risk
Reduction
Approaches
Reduce
Exposure
Reduce
Vulnerability
Transfer and
Share Risks
Increase
Resilience to
Changing Risks
Prepare,
Respond, and
Recover
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These areas of work and the current state of practice are spelled out in greater detail in the water
resources chapter of the Comprehensive Plan and the Comprehensive Water Resources Management
Plan.
The gap between the current Comprehensive Water Resources Management Plan and
the Strategy
Past iterations and the current Comprehensive Water Resources Management Plan have focused
primarily on reducing exposure to flooding or transferring risk, although sometimes in unknown or
unexpected ways. This often means capital infrastructure projects to modify the flood or regulatory
standards applied when properties develop or redevelop. The current Comprehensive Water Resources
Management Plan outlines projects that add or upsize pipes or surface flood storage. This narrow
approach has some pitfalls.
First, it limits the approaches, and thereby the actions that could be implemented to reduce
flood risk. The actions focus on reducing exposure only. Many opportunities exist using
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approaches to reduce vulnerability, transfer and share risks, increase resiliency to changing risks,
and preparing, or responding, and recovering from flooding.
Second, it ignores the risk transferred to downstream people and assets. Many of the capital
infrastructure projects don’t consider impacts outside the immediate project area. In a fully
developed landscape, many of the downstream storage areas in Edina and in our neighboring
communities are already full.
Third, it implies that the public realm is the only opportunity space to reduce risk – some of the
simplest and most cost-effective ways to reduce risk are for people to reduce the vulnerability
of their structures and property. Some resources to this end have been developed as part of
this process (see Outreach Products in the Outreach and Education section of this report).
Fourth, it doesn’t recognize the lead driver; climate change, and sets us on a path in which we
cannot catch up to the increasing risk. The strategy and associated actions must be able to scale
to the problem.
City Sectors of Work and Service
The City of Edina works in the following four sectors to reduce community flood risk. Detailed in each
sector overview is; a statement of the intended outcome of the work, a list of the City departments and
partners who lead the work, a list of City departments and partners who help, are involved, or are part
of the process, a description of when and how flood risk is considered, and a summary of gaps identified
during detailed discussions with the Task Force.
Infrastructure
What is the outcome; Building stormwater infrastructure that manages areas of flood flow and
storage that with the landscape, define areas of vulnerability. Reducing the vulnerability of infrastructure
so they are durable to extreme events or fail safe. Reducing exposure and vulnerability of related
sanitary sewer infrastructure that can serve as a conduit for flood waters between structures. The
service provided by water resource and other infrastructure is defined in the 2018 City of Edina
Comprehensive Plan and Comprehensive Water Resources Management Plan.
Who does the work; Public Works Department, Engineering Department, property owners, private
redevelopment, and contractors.
Who is involved; Planning Department, Building Department, and future property owners.
When flooding risk is considered; At decision points, in projects, design, failure analysis, during
infrastructure planning.
Gaps; Actual service level falls short of expected service, aging infrastructure, reactive maintenance,
reactive emergency response, capital improvements do not have scale to ‘fix it’ or even keep up with
climate change trend.
Pace of redevelopment: Currently driven by owners of at-risk properties. The City could establish a
program including eligibility and standards for purchasing, redeveloping to a flood-resilient standard, and
selling properties.
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Enhancing public infrastructure by building new, retrofitting old, and keeping what we have in working
condition is a key action to reducing flood exposure.
Stormwater systems route water to low areas where it is temporarily stored, and then they work to
convey water downstream. The stormwater system is made up of 127 miles of gravity main ranging from
12-84” in diameter, 6800 manholes, 900 outlets, 38 miles of small diameter sump drain, 11 stormwater
lift stations, one half mile of stormwater force main, and 150 ponds and wetlands (2018 Draft
Comprehensive Plan Chapter 7).
The City’s stormwater system was designed to convey a certain amount of water and protect against
impacts at a certain level. This “level of protection” is based on the capacity of public infrastructure to
handle stormwater and on the likelihood, or probability, that a storm will occur. When storms are
bigger or more intense than the infrastructure is designed to handle, or when it clogs, there are
consequences such as disruptions to services, facilities, or damage to property. The city stormwater
system is exposed to flooding and also determines the flood exposure of people and assets.
Risk is changing primarily because climate is changing and the level of protection for design is a moving
target. Designs from the past are undersized for today and there is a growing realization in technical
circles that even if designs were revised to reflect today’s climate they would quickly be obsolete due to
the changing risk brought by climate change.
Go Big, Go Bigger: infrastructure analysis
Go Big, Go Bigger: infrastructure analysis
To test the possible scale of implementation in the face of projected climate change impacts, a
preliminary evaluation and conceptual design of potential flood risk reduction options for the
Morningside neighborhood was completed.
A cursory evaluation was conducted to assess which option reduced flood exposure for the most
homes. This was completed for a range of storm events from the 20%-annual-chance storm event (5-
year storm which is 3.6 inches in 24 hours) to the 1%-annual-chance storm event (100-year storm
which is 7.5 inches in 24 hours). Infrastructure options that were evaluated included increasing storm
sewer pipe sizes, constructing flood walls, creating additional flood storage by excavating (lowering)
the ballfield area of Weber Park and then reconstructing the fields, creating additional flood storage
by excavating the wooded area north of Weber Pond and excavating and re-grading existing low
areas (e.g. low area at Lynn Avenue and Kipling Avenue north of West 42nd Street), excavating
backyards in key locations, installing predictive pumping systems for a few key areas (including Weber
Pond), and installing underground flood storage.
Seven infrastructure options were developed using combinations of some of the mitigation options
identified above with planning-level costs estimated between $3.4M and $31.6M. The option with the
largest benefit in terms of homes that would no longer be exposed to flooding up to the 1%-annual-
chance storm event (Option 7b, the ‘Go Bigger’ option) has an estimated cost of $8.5M and
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completely removes approximately 24% of the homes potentially impacted under existing conditions.
The next best infrastructure option (Option 2b, the ‘Go Big’ option) removes approximately 16% of
the homes currently impacted and would cost approximately $4.5M.
Baseline; the current replacement value of stormwater infrastructure in the City is about $70M.
Over 16 square miles this is approximately;
$6,800/acre
Baseline replacement value of stormwater infrastructure
The ‘Go Big’ option contemplated a $4.5M project serving about 630 properties and 185 acres.
$24,300/acre
Cost 3.6 times larger than the baseline
The ‘Go Bigger’ option contemplated an $8.5M project serving about 630 properties and 185
acres.
$45,900/acre
Cost 6.7 times larger than the baseline
In addition to costs, the projects come with tradeoffs, contemplating major changes in parks, open
spaces, existing water bodies, and piping and utility operations changes. The projects also present
opportunity for co-planning around park and sustainability improvements as sections of aging
infrastructure are renewed.
A memorandum describing the analysis in more detail is available in the appendix.
Morningside Roadway Reconstruction Engineering Study: in progress item
Morningside Roadway Reconstruction Engineering Study: in progress item
Infrastructure options remain the foundation of reducing flood exposure, but the scale of climate
change will make transformation change a challenge. In April 2020 staff will ask Council to consider a
scope of service for preliminary engineering for the street reconstruction project in the Morningside
D/E and Morningside C neighborhoods in 2022 and 2023, respectively. Staff will also ask Council to
consider the engagement plan to go along with the project design. This would be the first major
street reconstruction project to be designed under the proposed flood risk reduction strategy.
The operations and maintenance of public infrastructure is a key component of reducing flood risk.
Operations includes inspection and condition assessment, street cleaning, catch basin clog clearing, pipe
and outlet clog clearing, sediment control, pump and power system monitoring, and emergency
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operations. Maintenance includes catch basin repair, pipe repair, outlet repair, sediment removal, weed
and woody debris removal, and other actions.
Stormwater models that predict flood problems assume that all pipes, catch basins, inlets, and outlets
are in good working order and free from obstructions. The reality is that material and debris often enter
the system before or during storms and can cause service disruptions. Aging infrastructure also lends to
more failures.
Staff prioritizes their stormwater operation and maintenance work based on opportunity and requests
for service within the constraints of their resources. Opportunities include repairing and renewing
stormwater infrastructure in areas where other work is already planned. For example, crews inspect
and repair stormwater catch basins in neighborhoods where street improvements are planned, thereby
extending the life of the street improvement and providing real value to the public. Requests for service
also get prioritized. As storm events occur, staff evaluate the risk and respond as resources allow.
Operations and maintenance staff were invited to talk about their work with the Task Force. Some
themes related to the challenges and opportunities emerged.
Challenges related to operation and maintenance:
Much of the system aside from pump and power systems are managed with reactive,
run-to-failure approach and there is significant deferred maintenance in the system
leading to small items remaining unaddressed, leading to larger issues.
The program for evaluating maintenance needs meets the minimum regulatory standard.
It is not comprehensive.
The system is aging, much of it originating in the 1950s and 1960s.
During events, stormwater systems and sanitary sewer systems are stressed at the same
time. When flood events coincide with snow and ice events, staff are further stretched
to provide services and must make decisions about priorities, constrained by their
resources.
Some stormwater features in the city have been installed to intentionally capture
pollutants and debris in order to protect clean water. When not properly maintained,
they can interfere with overlapping drainage and flood protection services.
Service levels are not clearly defined. During the peak of events, staff are receiving,
prioritizing, responding to, and communicating on requests for service. Residents often
don’t know where their issue ranks or what service level they can expect.
Opportunities for operation and maintenance:
Proactive maintenance, the benefits of which go beyond flood protection. Proactively
cleaning and maintaining stormwater infrastructure can support clean water goals by
properly managing accumulated pollutants.
Increased street sweeping to keep stormwater conveyances clear. This also has a clean
water benefit.
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Promotion of the new metro-wide adopt-a-drain program to augment city street
sweeping. Residents are asked to adopt a storm drain in their neighborhood and keep it
clear of leaves, trash, and other debris to reduce water pollution. The program also
works to provide flood protection. Often, once a system is flooded, the primary
objective for maintenance staff is to clear the obstruction. At this point, the opportunity
to clear and dispose of clogging debris before its transported to downstream
waterbodies is largely lost.
High value infrastructure retrofits. In some cases, maintaining and optimizing existing can
be more cost effective than new infrastructure.
Better definition of service levels residents can expect for given issues.
More general communication about the City’s flood response during and after events.
Continued investment in the sanitary sewer system and its resiliency during floods.
An increase in resources dedicated to public works staff would be required in order to address issues
and capitalize on opportunities in operations and maintenance.
Regulation
What is the outcome; Homes and buildings have reduced exposure to floods. Those that are
exposed to floods take actions to reduce vulnerability. Private improvements such as structures,
landscaping, grading and other private systems manage their own risk, and take actions that do not
increase exposure of neighboring properties, reducing it if possible.
Who does the work; Engineering Department, Building Department, private permit applicants.
Who is involved; Public Works Department, Planning Department, future property owners.
When flooding risk is considered; At application and permit, during construction, at final inspection
and permit close.
Gaps; Added impervious marginally increases community risk, long term maintenance of private
drainage systems is uncertain, “retail” nature of permitting a variety of single family improvements is
time intensive, regulation in limited areas due to limited resources, the first point of contact that
interfaces with builders, homeowners, and describes issues in homes with existing exposure is time
intensive.
Redevelopment provides a once in a generation opportunity to build-in resilience. City staff are actively
engaged with the development community through regulatory programs and provide technical support
to permitted and affected private parties. In response, new structures or additions can be required to
meet minimum elevations for low floors (such as basements) or low openings (such as windows wells).
Another response to redevelopment includes requiring durable flow paths to route water away from
structures. The City could consider enhancing standards for resilience in redevelopment plans or
encourage a deeper risk conversation with the development community to promote resilient decision-
making within the permit process. Increased regulation of redevelopment in Edina would reduce risk. A
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tradeoff would be that a change in regulation could impose additional costs to developers and impact
overall market conditions.
Future flooding is projected to get worse. The models that predict flood risk use data from the past to
estimate precipitation. The City could consider a flood risk standard that incorporates future risk due
to climate change to match the lifecycle of the private improvements that rely on them. By planning
street flood storage, lowering roads, managing overflow paths, and taking other actions based on a
future flood risk level due to climate change, capacity could be built into the system to make them
future ready for their expected design lives.
Land use is often cited as a key sector for managing flood risk, though fully developed communities such
as Edina may not be able to realize the same returns in this sector as a less developed community. Many
of the decisions about land use in Edina have already been made – that is to say that neighborhoods
emerged in places and at times that might not have otherwise happened if those land use decisions were
made today.
The regulatory program remains an effective way to reduce the consequences of flooding for the
developing property. The City could consider further enhancing the outreach to property owners,
builders and developers to promote resilient design.
Where they work: As private improvements are made, or properties redevelop, the City
provides flood risk information and holds standards that control or mitigate the exposure to
flooding through its regulatory program. Existing controls through the regulatory program are
working to raise the low elevations or low opening of structures. This raising of structures
reduces the exposure to flooding.
Where they don’t work: While the regulatory program is good to reduce exposure and
vulnerability to the property or improvement that is changing and its immediately adjacent
neighbors, it is a poor tool to reduce the flood exposure downstream.
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Keep your water to yourself: private infrastructure analysis
Keep your water to yourself: private infrastructure analysis
The impact of comprehensive stormwater storage including underground storage within private
property, the right of way, or under streets in the Morningside neighborhood was evaluated. This
analysis was conducted as a result of Task Force discussions about the potential impacts of requiring
private homeowners to store stormwater running off from their impervious areas on-site similar to
requirements for commercial development.
The benefits achieved by storing the first 1-inch, 2-inches, and 3-inches of precipitation from storm
events of varying size, from the 20%-annual-chance storm event (5-year storm) to the 1%-annual-
chance storm event (100-year storm) are summarized in the table below. For the private storage
evaluation underground storage vaults were assumed under a portion of each of the 570 residential
parcels within the Morningside neighborhood. The analysis showed that storing the first 1-inch of
storms of this magnitude had a negligible impact on flood levels. Storing the first 2-inches and 3-inches
showed a more significant benefit with regards to reduction in peak flood levels. Depending on the
storm event, and depending on the location within in the neighborhood, the results varied anywhere
from flood level decreases of a few inches to decreasing nearly a foot and a half. However, this
apparent benefit comes at an initial cost of approximately $15,000 per inch of stormwater stored per
residential parcel. To store 2-inches of runoff in the entire neighborhood would cost approximately
$17 million. In addition, while the flood levels may be lowered, the number of homes that are
removed from potential impacts from flood inundation is small. For example, one home may
potentially be removed from flood inundation at Weber Pond depending on the storm event. Finally,
the management and maintenance of these underground stormwater storage vaults distributed
throughout an entire neighborhood is expected to be complicated and unprecedented.
This solution would provide a moderate benefit for a very high cost. Additionally, a preliminary look
at the compounding effect of climate change suggests that any improvement realized by implementing
additional storage would be taken back by climate change (i.e., increased precipitation amounts).
Inches of
Runoff Stored
on Private
Property
Approximate Cost for
All Parcels in
Morningside to Store
Runoff
Flood Level Reduction Benefit (in feet) for Weber Pond
Subwatershed (MS_40)
5-yr Storm
(3.6" of
precipitation)
10-yr Storm
(4.3" of
precipitation)
50-yr Storm
(6.4" of
precipitation)
100-yr Storm
(7.5" of
precipitation)
1 inch $ 8,550,000 0.1 <0.1 <0.1 0
2 inches $ 17,100,000 0.6 0.3 0.5 0.3
3 inches $ 25,650,000 0.7 0.9 0.6 0.5
A memorandum describing the analysis in more detail is available in the appendix.
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From ‘ill-drained’ to impervious: impervious surface analysis
From ‘ill-drained’ to impervious: impervious surface analysis
The Task Force wanted to explore the impact of limiting impervious cover through regulating
development and redevelopment. The impact of decreased imperviousness across the Morningside
neighborhood was evaluated.
The analysis showed an impervious limit would have little impact on flood risk. Although an
impervious limit or reduction supports other values such as open space, room for trees,
neighborhood character, and limiting heat island effect, the case for flood risk reduction was weak.
Additionally, setting impervious limits would require a large financial investment.
The impervious area that is directly connected to the storm sewer system in the Morningside
neighborhood is estimated to be about 25% of the total land area, in aggregate. The analysis tested
the sensitivity to changes in impervious by modifying the stormwater model so that the
imperviousness of the entire contributing drainage area was increased, decreased, and even lowered
all the way to 0%, which reflects a pre-development condition. This sensitivity test was also
completed for a range of storm events, from the 20%-annual-chance storm event (5-year storm) to
the 1%-annual-chance storm event (100-year storm). As expected, the imperviousness sensitivity test
showed that less impervious area generates less stormwater runoff and more impervious area
generates more stormwater runoff. However, the magnitude of the runoff changes generated by
adjusting imperviousness were not as impactful as may have been expected. Additionally, the little
flood reduction benefit shown in the analysis does not consider future climate change.
A memorandum describing the analysis in more detail is available in the appendix.
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Impervious limit: in progress item
Impervious limit: in progress item
At their February 12th, 2020 Planning Commission meeting heard an introduction to a zoning
ordinance amendment which would limit impervious cover. Current code includes only a building
coverage limit.
Outreach and Engagement
What is the outcome; People understand their vulnerability and exposure to flooding, know what
action to take to reduce each in the immediate, short and long term. People have the knowledge and
resources to take action. People are motivated to take action to protect themselves.
Who does the work; Engineering Department, Communications Department, partner agencies,
community groups.
Who is involved; The public, and public and private organizations.
When flooding risk is considered; In anticipation of spring melt, during flood events, post-hazard
recovery, property transfers, upon FEMA flood hazard map update.
Gaps; No coordinated plan and message, limited public and private resources. Knowledge alone doesn’t
equal action. Although not at the same scale as a capital item, engaging the public still costs money.
Equity should be considered in tactics.
When people understand the risks of flooding, they can take actions to reduce the consequences of
flooding. Actions could range from simple things, like moving valuables to higher floors, to more
complex retrofit improvements like flood proofing and sanitary sewer backflow prevention.
Risk awareness could be encouraged by improved distribution of information products like the existing
flood risk map available on the City’s website. This local map is industry leading, with few small cities
producing and publicly sharing detailed local flooding information. Although the information had been
public for a long time, it had been in a format that required some technical knowledge to interpret.
With new mapping tools, increasingly detailed digital stormwater system data, and more precise data
about topography of the landscape, we’re better able to visualize risk.
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Outreach products: in progress item
Outreach products: in progress item
Through the process, we uncovered some ‘quick-win’ actions that could be implemented immediately.
Actions for Flood Resilient Homes Fact Sheets. These two-page fact sheets describe common
actions that people can take to reduce their own exposure and vulnerability to flooding. A
copy of the draft fact sheets are provided in the Council work session meeting packet. The
complete set of fact sheets is expected to be finalized within the month.
“What is my flood risk?” interactive map. This application allows users to visualize the
flooding on the land surface for any property in the City of Edina. This information is already
available on the interactive water resources map; however, this application is more focused
on communicating flood risk specifically. Once finalized, the map will be available on the Maps
page of the City website. The application can be previewed at a temporary weblink at;
https://barrgisonline.maps.arcgis.com/apps/webappviewer/index.html?id=79c2a16b53af475dbc2
84cd2df9e4fee
Sandbagging how-to videos. The City provides sandbags, free of charge. This series of videos
will be used to promote the service, inform people on how to request sandbags, demonstrate
how to build a sandbag dike, and describe how to dispose of sandbags after a flood. Video
production is anticipated to occur this spring.
Emergency Services
What is the outcome; Parties respond to remove people from harm, or prevent damage to property
if possible, or provide aid after damage occurs. Limited disturbance/damage. Rapid return to normalcy.
Who does the work; Police Department, Fire Department, Engineering Department, Public Works
Department, County/State/Federal Emergency Responders, other infrastructure owners, and private
contractors.
Who is involved; Emergency operations command, emergency responders, the public, property
owners, visitors, other infrastructure owners.
When flooding risk is considered; In emergency operations plans, disaster planning, training and
drills, post-hazard recovery.
Gaps; Current response is triggered in major/severe events, the utility group’s first priority is to
maintain or reestablish function of infrastructure systems, call centers can be overwhelmed and need
clear triage procedure, there is nearly no service available for property owners during a flood, process
of after-action inquiry, questions and blame that realize long-known service gaps is adversarial and leads
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to rushed planning. A request or complaint-based response may not provide an equitable distribution of
services.
The City’s role in emergency situations include responding to life, health and safety calls and supporting
or restoring the operation of the utilities. When floods occur the ability to respond effectively quickly
degrades as phone lines and other communications channels fill with requests and reports. The ability
to sort and serve these requests goes into triage with critical system function and support measures
competing with urgent requests from the public.
Empowering people to adapt to flood risk, prepare for flood events, and mitigate the impacts of climate
change all contribute to a more resilient community. Adaptation and preparedness actions work to
mitigate the consequences of flooding.
Strategy Development
Task Force role and process
In order to incorporate community values into the process, a volunteer Task Force of eight Edina
residents was formed. Members represent homeowners with a range knowledge and experience. Most
have experienced flooding on their properties or have engaged with flood issues in the larger
community. Members came from all across the City of Edina. Task Force members met 12 times and
attended two City Council work sessions between July 2019 and March 2020.
The Morningside neighborhood was selected as the focal area of study due to the presence of significant
modeling and research in the area. The Morningside neighborhood faces a range of flooding challenges
that past efforts have struggled to address. As part of this effort, a 2-dimensional model was developed
and field calibrated to better refine the flood model and relate the models of St Louis Park and
Minneapolis. The Morningside neighborhood was also used as the case study neighborhood for
evaluating impervious limits, private storage, big infrastructure, and future climate change as noted in the
various analysis sections of this report.
The Task Force’s charge was to “Provide recommendations to inform a Flood Risk Reduction Strategy
to be considered for adoption by the City Council and incorporation as a major amendment to the
City’s Comprehensive Water Resources Management Plan.” The products of this process including
meeting agendas, minutes, and analyses are available for review in the Water Resources Library on the
City of Edina website.
To better understand the nature of the issue, Task Force members requested and were presented with
the following:
Overview of the focal area of Morningside neighborhood, its historical and current flood
challenges, and previous efforts to evaluate flood risk reduction options.
A technical exploration of City-owned stormwater infrastructure, maintenance operations,
levels of service, and the stormwater utility.
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Regulatory options that have been implemented in other comparable communities and
associated challenges and trade-offs.
Modeled sensitivity analysis completed by Barr Engineering to explore the potential impact of
comprehensive impervious limits, private stormwater storage, and enhanced infrastructure
including larger pipes and stormwater storage.
Communications strategies that promote preparedness and connect residents with resources
during flood events.
Overview of the City’s floodplain management ordinance and participation in the National Flood
Insurance Program.
The City’s policy and standards for stormwater management through the permit process,
related to development and redevelopment.
A conversation with maintenance staff to understand routine operation and maintenance as well
as storm response.
Interacting directly with the Task Force has provided staff members with insight into public perception
of their role in flood risk reduction. During these conversations, staff began to see certain discrepancies
between the following City assumptions; perception of risk, interpretation of the term ‘flooding’, and the
role of City services.
How does the City define flood risk? Flood risk has been seen as a combination of the statistical
probability of a flood event happening and the potential community-wide losses that occur as a
consequence of that event. In the City of Edina, the increasing value of homes located within the
floodplain is occurring in tandem with changing weather patterns that increase intensity of storm
events, both of which increase the overall risk. The City’s idea of current flood risk is also being
shaped by changing community expectations for service.
Defining “flooding” is similarly complicated by social perception. FEMA defines flooding as “A
general and temporary condition of partial or complete inundation of 2 or more acres of
normally dry land area or of 2 or more properties…” When intense or prolonged rain events
occur, the system can become overwhelmed. A wet basement, flooded garage, or standing
water may not fit FEMA’s definition, but each impacts the community and was considered
“flooding” by Task Force members.
City services play a critical role in the following common flooding issues; creeks outside their
banks, curb lines flowing full, storm drains clogging, pipes running full, low points in streets or
yards filling up and threatening structures, flow paths eroding, sump pumps flowing, basement
foundations leaking, and sanitary sewers backing up. Community service expectations are
mismatched with available resources for preventative maintenance and timely emergency
response to these issues.
Staff heard the following sentiments from the Task Force;
Flooding affects quality of life by disrupting daily activities, risking safety, and damaging
structures.
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A priority should be to reduce risk to residential structures.
Help property owners protect themselves and prevent damage to structures.
Be ready to help the community recover after floods.
Maintain the function of the existing system to maintain service.
Be a good neighbor.
Brainstorming, prioritizing, and categorizing possible actions
A series of actions were proposed for a possible menu or toolbox of actions as a result of discussions
with the Task Force. Each action was accompanied by a detailed description, justification/motivating
factors, tradeoffs and other considerations, cost score, staff-ranked effectiveness score, community
enthusiasm ranking, and action category. The brainstorming exercise resulted in more than 40 potential
actions. Reviewing and ranking these actions was no small task.
Task Force members were asked to rank possible flood risk reduction actions based on community
enthusiasm, informed by community held positions and interests related to flooding. Positions are
surface statements of where a person or community stands. Interests are the underlying reasons, values
or motivations that explain a certain position. Based on perceived community position and interests, the
Task Force was asked to rank the action items in terms of community enthusiasm. Enthusiasm is the
community’s interest or approval of the action. Considerations for community enthusiasm include
tradeoffs, community impacts, land, sustainability, environmental outcomes, and social outcomes.
Task Force members shared their hesitation in representing the community with their rankings because
they felt that each flood experience was unique and they hadn’t had sufficient information or
opportunity to gauge community enthusiasm at this detailed level. A summary of the aggregated Task
Force rankings is included in the appendix with this caveat - in the end, the conversations around actions
provided the most value for staff in forming the framework and strategy. The process helped to identify
quick-win actions that could be implemented immediately, clarified areas of agreement and disagreement
between the Task Force and staff, and will be used as a starting point for future Comprehensive Water
Resources Management Plan program development work. We would expect rankings to be continually
refined as more people participate and more information becomes available. The exercise itself
outweighs the absolute ranking of the actions.
The full set of possible actions as well the Task Force ranking summary is included in the appendix of
this report.
Conclusion
The process has reiterated the need to address flooding with a range of strategies that span technical,
scientific, political, and social approaches. Many communities are struggling with managing increasing
flood risk.
Key takeaways:
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The current stormwater model helps to better visualize where the issues are; they are
extensive, interwoven, and difficult to solve. The existing stormwater system is overloaded and
the strategy to put water somewhere else is limited.
Climate change impacts are significant.
Groundwater levels are increasing. The years between 2015 and 2019 were the wettest in
Minnesota history.
The Flood Risk Reduction Strategy widens our approaches, and thereby actions, to reduce flood
risk. The current Comprehensive Water Resources Management Plan is narrow and can’t keep
up with the lead driver; climate change.
There are opportunities to empower people and institutions to adapt, prepare, and mitigate.
The Strategy opens the approach of reducing vulnerability. Often, some of the simplest and
most cost-effective ways to reduce risk are for people to reduce the vulnerability of their
structures and property.
Impervious surfaces matter; however, the opportunity to reduce flood risk by limiting or
reducing impervious cover in the City of Edina is limited.
Additional resources are needed to implement actions.
Residents have high expectations for service.
Other promising opportunities exist for operation and maintenance, public infrastructure
(though climate change will make transformational change a challenge), and redevelopment
standards anchored in resiliency.
Lastly, there is an opportunity to knit together the emerging Flood Risk Reduction Strategy with the
existing Living Streets Plan and forthcoming Climate Adaptation Plan. Bringing these efforts into focus
and examining strategies through an equity lens are necessary to deliver high-value benefits to the
community.
Next steps
Staff will finalize the Flood Risk Reduction Strategy based on Council and task force feedback from the
work session and propose to bring the finalized report to the April 7th City Council meeting for final
approval.
Staff will prepare a scope of service for preliminary engineering for stormwater infrastructure related to
the roadway reconstruction projects in the Morningside C, D and E maintenance groups scheduled for
reconstruction in 2022 and 2023. Staff will also ask Council to consider the engagement plan to go along
with the project design. This would be the first major roadway reconstruction project to be designed
under the proposed Flood Risk Reduction Strategy.
Staff will prepare a scope of service to complete a major amendment to the Comprehensive Water
Resources Management Plan in order to incorporate the Flood Risk Reduction Strategy into the policies
and implementation actions of that Plan.
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Summary of proposed next steps;
1. Council considers approval of Flood Risk Reduction Strategy.
2. Council considers approval of preliminary engineering scope of service for the Morningside D/E
and Morningside C neighborhood roadway reconstruction projects in 2022 and 2023,
respectively.
3. Council considers approval of Morningside Neighborhood roadway reconstruction design
engagement plan.
4. Council considers approval of scope of service for major amendment to Comprehensive Water
Resources Management Plan.
Acknowledgement
Staff would like to thank the Task Force for their contributions. The experience, knowledge, and
curiosity they brought to the process added value and influenced the Strategy.
Nora Davis (co-chair), Lake Cornelia Neighborhood
Kathy Amlaw (co-chair), Lake Edina Neighborhood
Greg Lincoln, Morningside Neighborhood
Michael Platteter, Morningside Neighborhood
Louise Segreto, Indian Hills Neighborhood
Roxane Lehmann, Sunny Slope Neighborhood
Richard Strong, Concord Neighborhood
Richard Manser, Todd Park Neighborhood
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Appendix
Appendix A: ‘Groundwater levels are increasing: summary of monitoring data’, technical
memo
In development, memo to be included in appendix for final report.
Appendix B: ‘Getting to scale: a challenging problem made even more challenging,
climate change impact analysis’, technical memo
Draft graphics to visually show the impact of climate change (191015 Climate visualization_1of2.PDF and
191015 Climate visualization_2of2.PDF) are available for review in the Water Resources Library on the
City of Edina website, to be finalized and included in appendix for final report.
Appendix C: ‘Go Big, Go Bigger: infrastructure analysis’, technical memo
Draft concept analysis report (191015 Infrastructure analysis_1of2.PDF and 191015 Infrastructure
analysis_2of2.PDF) is available for review in the Water Resources Library on the City of Edina website,
to be finalized and included in appendix for final report.
Appendix D: ‘Keep your water to yourself: private infrastructure analysis’, technical
memo
Draft analysis report (191015 Private infrastructure analysis.PDF) is available for review in the Water
Resources Library on the City of Edina website, to be finalized and included in appendix for final report.
Appendix E: ‘From ‘ill-drained’ to impervious: impervious surface analysis’, technical
memo
Draft versions (191015 Map of Edina_1908.PDF and 191015 Impervious surface analysis.PDF) are
available for review in the Water Resources Library on the City of Edina website, to be finalized and
included in appendix for final report.
Appendix F: Actions for Flood Resilient Homes, fact sheets
Draft fact sheets provided, to be finalized and included for final report.
Appendix G: Task Force charge
Available for review in the Water Resources Library on the City of Edina website, to be included in
appendix for final report.
Appendix H: Potential action matrix key, ranked response, and potential action matrix