Minnehaha, MN Creek Watershed District Assesses Stormwater Management Climate Vulnerability

Minnehaha, MN Creek Watershed District Assesses Stormwater Management Climate Vulnerability

Project Summary

 

The National Climate Assessment shows the Midwestern United States has already experienced large changes in very heavy precipitation and projects such changes to continue and worsen. The Minnehaha Creek Watershed District, responsible for Minneapolis, Minnesota and many of its western suburbs, wanted to better understand the climate threat to its stormwater management capabilities. The District considered climate projections to assess stormwater system vulnerability and adaptation options for two specific locations. The analysis used downscaled global climate model projections to identify the expected mid-century 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 relevance and need to anticipate and plan for future storm events was observed mere months after completion of the study when over 24 inches of rain fell in the Minneapolis area over a period of three 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 adapt to climate change. 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 adapt to climate change.

(For more information about this case, view the U.S. Climate Resiliency Toolkit’s case study on the Minnehaha, MN Creek Watershed District Assesses Stormwater Management Climate Vulnerability.)

Implementation

The Watershed District started by assessing current climate vulnerabilities of stormwater drainage. The 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 the U.S. Environmental Protection Agency's Stormwater Management Model to simulate the stormwater system and rainfall runoff for the projected storm events and regionalized climate 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 and underground storage. The Weather and Extreme Trends projections estimated that for the two project areas, the most effective adaptation measure to manage projected future flooding was largely pipe upsizing. Local officials hope this information can better inform local public 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.

Community Engagement 

The Watershed District provided information to the community about adapting to future conditions.They held the Climate Adaptation in Minnesota conference in 2013 to support local officials, planners, engineers and natural resource practitioners to discuss adaptation strategies. The District also held four outreach events including three forums that presented and discussed the assessment, findings and next steps with stakeholders in two focus areas. 

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