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Cedar River Watershed

Water Storage and Climate Resiliency

Cody Fox, CRWD Administrator

Bret Zimmerman PE, Houston Engineering, Inc.

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OVERVIEW

  • Background
  • Existing Projects
  • Climate Resiliency Study
  • Collaborating with local landowners and producers

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CEDAR RIVER WATERSHED

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  • Austin, MN
  • Established in 2007
  • ~ 435 square miles

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BACKGROUND

  • Frequent flooding 🡪 Flash flooding
  • Flooding occurring more often
  • Sediment into east side lake
  • Flooding in Austin
  • Flooding of rural roads
  • Ag flooding and streambank erosion
  • Goal of Delisting Dobbins Creek

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  • 2015 – CRWD and Hormel Foundation Partnership = 8% reduction on Dobbins

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EXISTING CAPITAL IMPROVEMENT SITES

  • 11 Existing Sites in Dobbins Creek
  • 13% Reduction in Peak Flows upstream of East Side Lake
  • Over 1,400 ac/ft storage @ aux spillway
  • $7M in engineering, �easements, construction �on 13 projects.
  • Primary funding from �MN Bonding, Hormel �Foundation and �Clean Water Legacy.

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EXISTING CAPITAL IMPROVEMENT SITES

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“TYPICAL” DESIGN

  • Upstream of Public Waters
  • No permanent pool
  • 100-year below spillway
  • 500-year below top of berm

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  • Drawdown
    • 10-year < 24-hour
    • 100-year < 36-hour

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  • 100-year flowage easement
  • Temporary easement
  • Multiple landowner
  • ~80% Flow Reduction from site

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2022 STUDY

  • MPCA Stormwater Community Resilience Planning Grant
  • Total Project Budget $86,500
  • Local match of 10% (Cash or In-kind)
  • Environmental Justice Areas of Concern
  • Develop conceptual projects…not just a study
  • Public Engagement

https://mpca.maps.arcgis.com/apps/MapSeries/index.html?appid=f5bf57c8dac24404b7f8ef1717f57d00

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FUTURE CLIMATE HYDROLOGY

This was NOT a Climate Change Study

18% Increase in Rainfall Depth

Return Period

Probability

100-year

1% Chance

500-year

0.2% Chance

NOAA Atlas 14

7.8

10.7

Future Climate Hydrology

9.2

12.6

Stormy/Not as Stormy

Warm/Wet

Hot/Dry

High/Low Emissions

End of Century

Far Term Projections

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STACKED HYDROGRAPH ANALYSIS

  • Where is the runoff coming from?
  • Systematically “turn off” the subwatersheds

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Where to prioritize

storage

…where not to

store water

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STACKED HYDROGRAPH ANALYSIS

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IDENTIFIED POTENTIAL CIP LOCATIONS

18 Identified Sites

1 – Upper Cedar River

2 – Roberts Creek

2 – Wolf Creek

4 – Middle Cedar River

9 – Dobbins Creek

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PROJECT PORTFOLIOS

Design Criteria

100-yr < spillway

500-yr < TOD

Targeted 4” of �runoff storage

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MODELING AND RESULTS

  • 25 Scenarios
    • Pre-CIP
    • Base Condition (2022)
    • Individual Sites
    • Grouped by Subwatersheds
    • All Sites
  • 10 Reporting Model Outputs

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OUTLET OF DOBBINS CREEK

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2022 STUDY SUMMARY

  • 18 Potential Sites Identified
  • Not all sites provide downstream peak reductions
  • Benefits:
    • Water Quality
    • Downstream Flood Damage Reduction
  • Opportunity for other conservation practices� (i.e., grassed waterways)

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2023 CAPITAL IMPROVEMENT PROJECTS

  • Combined 20,020 CY of clay
  • 155-ac-ft storage (A.S.)
  • 38-57% reduction downstream (10-yr – 500-yr)
  • 1.5% reduction at East Side Lake
  • ~$335M Construction

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LOCAL SUPPORT

  • Building Support
    • Took time and a few projects to go very well- attention to detail & COMMUNICATION with landowners, neighbors, and townships was key.
    • Not everyone is in support, which may lead to plans changes (curved berms, etc.)

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  • Two projects dealt with 4 properties and 27 needed signatures (land in trusts, etc.)

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  • Funding- Had to build support. $3.1M initially from Hormel Foundation for initial Vision 2020 request for 8% reduction. Delivered by exceeding 100 yr flow reduction prediction and on time & on budget.

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  • State folks bought in after tours and seeing success with voluntary work. These aren’t community saving projects (ring dikes), rather they are multi-faceted. Flood reduction for local roads, homes, ag fields, and major water quality improvements by alleviating flows that are damaging streambanks at a very fast rate.

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Tracking and showing projects for public to follow along and understand projects and their locations.

EDUCATION AND OUTREACH

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TAKE-AWAYS

  • Having a working district-wide H&H model to be able to assess/analyze
  • Collaboration with landowners- *Important to have relationship prior to projects as there is built in trust.
  • Creative solutions- No project is/should be similar.
  • Education and Outreach
  • Identify funding sources
  • Engaged staff and community

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Questions

Cody Fox, CRWD Administrator

Bret Zimmerman PE, Houston Engineering, Inc.