Minnehaha, MN Creek Watershed District Assesses Stormwater Management Vulnerability

The Midwestern United States has already experienced large changes in very heavy precipitation. These changes in precipitation patterns and levels are projected to continue and worsen. The Minnehaha Creek Watershed District, responsible for Minneapolis, Minnesota and many of its western suburbs, wanted to better understand the threat to its stormwater management capabilities.

The District considered projections to assess stormwater system vulnerability and options for preparedness actions for two specific locations. The analysis used downscaled global model projections to identify the expected midcentury 1–10-year storm.

Stormwater system resilience was then considered under these conditions and a number of areas were identified as undersized. For these areas, estimated costs and feasibility comparisons of several stormwater management adaptation strategies were considered against a baseline of expected flooding damages caused by no-action.

The observed relevance and need to anticipate and plan for future storm events occurred mere months after completion of the study when over 24 inches of rain fell in the Minneapolis area over a period of 3 months. This heavy precipitation led to historic water levels and flooding. Using this study to identify and prioritize undersized portions of the stormwater management system will help the Watershed District’s communities prepare be more resilient to changes in the environment.

Recognizing the importance of its effort, the Watershed District developed a guidebook and held multiple outreach events to help other nearby communities replicate its approach and resiliency actions. (For more information about this case, view the U.S. Climate Resiliency Toolkit’s case study on the Minnehaha, MN Creek Watershed).

Minnehaha, MN Creek Watershed District Assesses Stormwater Management Climate Vulnerability

How did they do it?	Applicable EPA Tools
Assessed current vulnerability of stormwater drainage The watershed district used a grant from NOAA’s Climate Program Office to develop a vulnerability assessment and analyze adaptation options for two locations in Minnesota. The study used EPA’s Stormwater Management Model to simulate the stormwater system and rainfall runoff for the projected storm events and regionalized models from the CMIP 3 and CMIP 5 Models. The analysis focused on mid-century projections for managing the 1–10-year storm - the common design standard for local infrastructure. The study estimated cost per volume and feasibility for several adaptation strategies including: Pipe upsizing. Low impact development. Dry retention. Underground storage. The Weather and Extreme Trends projections estimated that for the two project areas as largely pipe upsizing as the most effective preparedness measure to manage projected future flooding. Local officials hope this information can better inform local public work projects. The analysis also noted the need for further research to analyze the potential water quality issues and prospects for downstream flooding from increased flows.	The EPA’s SWMM Model Climate Assessment Tool can help assess current vulnerability of stormwater drainage systems. SWMM Model Climate Assessment Tool
Engaged the community to provide information to prepare for future conditions Held a Climate Adaptation in Minnesota conference in 2013 to support local officials, planners, engineers, and natural resource practitioners to discuss adaptation strategies. Held four outreach events including three forums that presented and discussed the assessment, findings, and next steps with stakeholders in two focus areas. Created a Community Adaptation Planning for Changing Landscapes and Climate, which provided a step-by-step process for how the Minnehaha Creek Watershed District conducted their adaptation plan and the relevant process for completing a similar plan in other areas.	The Green Infrastructure Modeling Tools can help communities predict the environmental outcomes of different design and management approaches. Green Infrastructure Modeling Tools

How did they do it?

Applicable EPA Tools

Assessed current vulnerability of stormwater drainage

The watershed district used a grant from NOAA’s Climate Program Office to develop a vulnerability assessment and analyze adaptation options for two locations in Minnesota.
The study used EPA’s Stormwater Management Model to simulate the stormwater system and rainfall runoff for the projected storm events and regionalized models from the CMIP 3 and CMIP 5 Models.
The analysis focused on mid-century projections for managing the 1–10-year storm - the common design standard for local infrastructure.
The study estimated cost per volume and feasibility for several adaptation strategies including:
- Pipe upsizing.
- Low impact development.
- Dry retention.
- Underground storage.
The Weather and Extreme Trends projections estimated that for the two project areas as largely pipe upsizing as the most effective preparedness measure to manage projected future flooding.

Local officials hope this information can better inform local public work projects. The analysis also noted the need for further research to analyze the potential water quality issues and prospects for downstream flooding from increased flows.

The EPA’s SWMM Model Climate Assessment Tool can help assess current vulnerability of stormwater drainage systems.

SWMM Model Climate Assessment Tool

Engaged the community to provide information to prepare for future conditions

Held a Climate Adaptation in Minnesota conference in 2013 to support local officials, planners, engineers, and natural resource practitioners to discuss adaptation strategies.
Held four outreach events including three forums that presented and discussed the assessment, findings, and next steps with stakeholders in two focus areas.
Created a Community Adaptation Planning for Changing Landscapes and Climate, which provided a step-by-step process for how the Minnehaha Creek Watershed District conducted their adaptation plan and the relevant process for completing a similar plan in other areas.

The Green Infrastructure Modeling Tools can help communities predict the environmental outcomes of different design and management approaches.

Green Infrastructure Modeling Tools

Similar Cases and More Information

To see how Washington, D.C. is using green infrastructure to reduce stormwater impacts and combined sewer overflows view the DC Consent Decree. For more information on what a Washington, D.C. wastewater facility is doing to adapt to changing environmental conditions and the threats from flooding, view Blue Plains Wastewater Facility Case. For information on a city that is moving wastewater services away from an area vulnerable to flooding view the Iowa City Riverfront Master Plan.

Minnehaha, MN Creek Watershed District Assesses Stormwater Management Vulnerability

Similar Cases and More Information

References

Climate Change Adaptation Resource Center (ARC-X)