HomeMy WebLinkAbout190716 Meeting 2 Staff Report
July 16, 2019
Flood Risk Reduction Strategy Task Force
Ross Bintner, P.E., Engineering Services Manager
Martha Allen, Water Resources Intern
Flood Risk Reduction Strategy Meeting 2 – Stormwater 101, Introduction to the
stormwater utility, infrastructure services in the Morningside focal geography.
This report outlines basic information related to stormwater and its context within Edina. Section 1
provides a high level overview of stormwater modeling, terminology, and the stormwater utility, and
responds to questions posed at the first meeting of the Flood Risk Reduction Strategy Task Force. Section 2
outlines the focal geography of Morningside neighborhood and the challenges involved with flood risk
reduction in that area.
1. Stormwater 101
Important terms and definitions
Capital expenditures (CAPEX): expenditures that are intended to purchase a new asset or improve an
existing asset or infrastructure. Capital projects are outlined in the City’s Capital Improvement Plan as part
of the comprehensive planning process.
Hydrology: the science that encompasses the occurrence, distribution, movement and properties of the
waters of the earth and their relationship with the environment within each phase of the hydrologic cycle.
Hydraulics: the branch of science and technology concerned with the conveyance of liquids through pipes
and channels.
Level of service: capacity of a drainage system to remove runoff water that interferes with normal daily
operations, commerce, and access.
Level of protection: capacity of a drainage system to prevent property damage and ensure public safety
during or after a storm.
Stormwater: Water that originates during a precipitation event and snow/ice melt. Stormwater can
infiltrated into groundwater, remain on the surface as surface water, or runoff into nearby stormwater
infrastructure, streams, rivers, or other water bodies.
Stormwater utility: The combined activities related to the control or treatment of stormwater. Funded by a
stormwater utility fee on your quarterly utility bill, fees collected from this utility fund operation,
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maintenance, education and outreach, capital improvement projects, and other infrastructure-related
services.
Stormwater Modeling
Stormwater modeling is a tool that can be used to understand and predict the complex processes involving
stormwater runoff. The most common types of stormwater models are classified as hydrologic, hydraulic,
and water quality.
Edina’s citywide stormwater computer simulation models can be used to evaluate the effects of small or
large scale changes within the city whether the changes are associated with either the hydrology or
hydraulics of the city. These models can (a) provide flood levels for interior water bodies, (b) identify
flooding issues (both street flooding and potential impact to homes), (c) identify storm sewer capacity
limitations, (d) evaluate peak flood elevation “timing” issues which is critical when evaluating the influence of
creek systems (Minnehaha Creek and Nine Mile Creek) that may be draining large upstream areas, and (e)
provide a tool for evaluating flood mitigation options.
Hydraulic parameters refer to any and all parameters related to conveyance of water through storage areas
(lakes, ponds, and wetlands), pipes, and overland flow channels (including streets). Hydrologic parameters
include information about the land use (e.g., perviousness/imperviousness), rainfall data, and soils data.
Hydraulic parameters refer to any and all parameters related to conveyance of water through storage areas
(lakes, ponds, and wetlands), pipes, and overland flow channels (including streets).
Attached to this report is a visual slide deck that staff will use to describe this topic.
Stormwater Utility Overview and Q&A
The following is an exploration of two guiding documents (The Edina Comprehensive Plan and the
Comprehensive Water Resources Management Plan (CRWMP) that describe and define the stormwater
utility and goals related to service provision. This section also outlines answers to key questions posed by
the Task Force and co-chairs. We hope to expand on the Q&A section during conversation with the Task
Force.
Guiding document 1; Chapter 7, Water Resources of the 2018 Comprehensive Plan (May 2018 Draft).
The overview and stormwater utility sections of the plan provide a high level view of the three utilities, and
the stormwater utility in detail.
Relevant sections:
Pages 7-1 to 7-6 from the overview section; Major challenges for the utilities include; aging infrastructure,
preparing for growth, and changing service expectations. Key initiatives include; renewal, asset management,
resilience, one-water, and public engagement.
Pages 7-23 to 7-33 from the stormwater utility section: This section outlines the stormwater service levels,
means, methods, resources, demands, organization, policy, implementation and improvement.
Core Service Concept; The core services of the Stormwater Utility are drainage and management of runoff
and flood risk, clean surface waters, and protection of natural waterbodies and wetlands. The purpose and
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interactions among the service levels is described in greater detail in CWRMP section 3. Overall, services
are improving and disruptions are less frequent citywide. Due to hydrologic and hydraulic modeling, services
and risks are increasingly better understood.
The core services of the stormwater utility also support other City core services, including transportation
and mobility, public health, sanitation and public safety.
Means of provision of service are separated into three categories; Infrastructure services, programmatic
services, and regulatory services.
1. Infrastructure (derived) services are provided by physical assets.
2. Programmatic services are provided by people using equipment, and/or technology.
3. Regulatory services are provided by people through the application of standards of practice or
setting and/or enforcing normative behavior.
Comprehensive Plan strategic goal areas and (infrastructure) lifecycle asset management:
The Comprehensive Plan outlines the following goals representing areas of strategic importance to the
utility. The Task Force will need to frame recommendations within the goals in these areas:
• Goal Area 1: Prioritization of service levels and rates of attainment
• Goal Area 2: Conservation and sustainability, one water
• Goal Area 3: Aging infrastructure and management of assets over generations
• Goal Area 4: Risk, health, and equity
ISO 55000 asset management standards and the Institute of Asset Management conceptual model (image
below) help show related workflow in an infrastructure owning organization. This model can be applied to
the stormwater utility to help understand the relationships in its organizational structure and
implementation workflow.
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Guiding document 2; The 2018 Comprehensive Water Resources Management Plan (July 2018 Final)
(CWRMP)
Relevant sections:
Chapter 1- Flood Risk Reduction Strategy development, Table 1.1 (included below)
Chapter 2 - Physical setting
Chapter 3 – Implementation, policy and practices to guide city projects, regulatory program
Chapter 15 - Possible actions to provide and manage flood risk, implementation, Table 15.2 (discussed
below)
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Table 1.1 displays potential strategies and actions that directly reduce flood risk. These options should only
serve to guide Task Force discussions and should not limit future recommendations or priorities.
Stormwater Q&A
• How is the stormwater utility organized?
o The new comprehensive plan provides the current vision and goals for the organization of
the utility.
• What are the stormwater utility’s top priorities?
o The comprehensive plan describes high level services (flood protection, drainage and
stormwater management, and clean surface waters) and their delivery, and the CWRMP
provides a review of issue and implementation actions (Table 15.1). The capital plan includes
projects in some of these issue areas (Table 15.2.) In the past the capital plan and CWRMP
have not been well coordinated and often we learn that we can’t come close to ‘solving’ the
problem with the capital allocated in the CIP. Attached is an example of projects in the focal
geography that staff will use to describe the change around our view of flood problems in
subsequent CWRMP and internal planning efforts.
• What are the stormwater utilities resources (dollars and people?)
o 2018 included $1.75M capital expense (CAPEX), $1.1M operations expense (OPX), and
0.12M Overhead. People are shared and allocated based on work, with the Sanitary, Water
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and road utilities. In 2018 the stormwater utility included approximately 5-6 FTE split across
15-20 positions.
• How are resources deployed (and split among priorities?)
o We split the program into operations expense (OPX), capital expense (CAPX) and
administration/overhead. Both OPX and CAPX maintain infrastructure. Overhead and OPX
include staff positions that provide non-infrastructure services.
• How does the storm system work?
o Part 2 of this report will go into specific issues and function in the Morningside focal
geography.
• How is the storm system paid for?
o The stormwater utility revenue is defined in City Code Chapter 28, Article III and the fee
schedule. The factors described in section 28-210 mean that acre for acre, more intense
land uses pay, commensurate with their runoff generation.
• How big are stormwater projects?
o The 2019-2023 Capital Improvement Plan (direct link) describes $21M in stormwater
improvements ranging from small to large, funded to unfunded.
• What is the history of areas prone to flooding?
o Attached to this report is a 1908 quad map with current day street centerlines overlaid.
While we see many of the regional flood areas align with creeks and former wetlands, of the
5 detailed local flood areas studied in the 2018 CWRMP, 2 related to former wetland areas
and 3 do not. Although each seems to have its own unique history, the trends described in
the first meeting seem to hold true. (perception/new data, climate change/more rain, more
runoff, increased service level expectations).
2. Infrastructure services in Morningside focal geography
There are diverse challenges that implicate flood risk in the Morningside neighborhood. The following
section will outline the process of issue discovery, detail the current status of flooding issues, and highlight
reasoning behind existing solutions and historical decision-making.
CWRMP Chapter 15: Table 15.2 outlines Potential Implementation Activities (including capital improvements)
that could reduce flood risk. The following issue ID’s are related to the Morningside focal geography.
D4 (studied in 2006 report); S17 (reviewed and found incorrect in response to resident query); S18;
and R35.
Prior to the 2018 CWRMP, there was no documented issue identification method or project selection
method, and no citywide visualization (mapping) of flood areas as well as potentially impacted structures.
Plan authors report that past City engineering and public works staff identified issue areas that generated
complaints and solutions were provided in the plan. The 2018 plan creation effort and visualization seemed
to change the scale of the issue and adds a caution to the prior one at a time approach, as a solution to one
problem may exacerbate a downstream.
During the development of the 2018 CWRMP, we found the list of flood issues was extensive. The lists
were sorted based on possible structural impacts. We chose to review the subsets of issues with the most
potential for structural impacts in detail and a larger group with lesser impacts using a quick desktop
analysis. A significant group of additional issues with even lesser impacts was not studied.
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Attached to this report is a visualization of the current focal geography, the storm network and inundation
areas from the 10% and 1% probability events labeled with issue areas from subsequent CWRMP updates
and studies. We will present and discuss this changing paradigm during our meeting.
In 2018 as the CWRMP was being finalized, staff conducted an internal effort to demonstrate a possible
project selection method for the focal geography. This analysis, that I have been calling our “rookie effort,”
took approaches borrowed from much larger work and tried to scale it down to the very local scale with
mixed results and is titled “Edina Morningside Neighborhood Flood Risk Reduction Concepts”. The analysis
includes a novel flood risk classification and the most detailed work we’ve done to characterize building
floor and low opening elevations. The method also proposed a damage / value at risk concept to try to
annualize flood risk to compare project cost benefit, which is the least certain part of the report. As staff
was drafting the analysis we asked Barr Engineering to iterate on possible infrastructure improvements in
the focal geography where upstream and downstream improvements were coordinated to manage risk in
both cases. Both documents are attached. Notable takeaways include;
• There is no widely understood measure of direct flood risk at the individual home scale. Somewhere
between no flooding and water coming in windows damage does occur, but we had to create our
own method to put numbers to varying levels of risk.
• The effect of neighboring homes flood risk may be significant. The concept conceptualized the effect
on sanitary backups for homes that may appear safe from surface flooding on maps. If this were
confirmed, in-home risk controls like overhead sanitary connections or backflow prevention devices
may be useful.
• Indirect risk from high groundwater was hard to quantify and the cost data was very sensitive to this
factor. The concept team guessed that if frequent basement flooding was an issue, many
homeowners would decide not to finish the space and reduce the potential for damage or invest in
retrofit sump pumps or other waterproofing.
• Good tools to judge various scenario levels of achievement or compare project cost and benefit are
hard to find. In this effort we had to make them ourselves and each rested on assumptions or
technical interpolations that are not easily accessible.
• The concept project selection method resulted in much wider scale projects with large associated
impacts and budgets and was very computationally intensive, and relied on methodologies that we
could find no precedent for at this small scale.
• The key technology that many of the downstream improvements relied on (predictive pumping) to
reduce excavation requirements relies on a technology that is untried in the local area.
Attachments
1908 Edina quad map with street overlay
Stormwater 101 slide deck
Morningside area CWRMP implementation history visualization
Edina Morningside flood risk reduction concept & associated summary memo