Station 2
Assessment

The engineering team was tasked with finding solutions to the 5 failed dams, as well as evaluate the condition of the remaining 18 within the watersheds. The alternatives are designed for failed dams, however, it is assumed that the decision of what to do with the failed dams will influence future watershed management decisions. The 5 dams that failed in the 2018 storm all failed in similar ways, where the dam embankment meets the sandstone wall of the valley. 

 

For more information on each failed dam with pictures of the failures, click on the names of the dams in the images of the watersheds below.

Remaining Dams

The remaining dams are susceptible to the same failure mode due to the similar age, construction method, and highly fractured sandstone foundation in the Driftless Region. 

  • The remaining dams have been inspected by the local dam tender and a geotechnical engineering team to provide information on their current condition.

  • Based on those inspections, dams were ranked in terms of hazard classification and risk of failure.

  • Significant deficiencies were identified in some of the dams:

    • joint deterioration in the principal spillway pipes, ​

    • corrosion of corrugated metal pipes in the foundation drains,

    • uncontrolled seepage through the dam abutments

Coon Creek Remaining Dams Condition Assessment Summary

CC Cond Assess Sum.PNG

West Fork Kickapoo Remaining Dams Condition Assessment Summary

WFK Cond Assess Sum.PNG

Failed Dams

  • The 5 failed dams are out of compliance with the Wisconsin Department of Natural Resources and cannot remain in their current state.

  • The team looked at breadth of alternatives, eliminating those that would not be viable or feasible. Eliminated from further consideration include:

    • Repairing the dams in their existing locations. In order to repair the failed dams with Federal funds, the dams would need to be upgraded to current standards. This upgrade would likely include (1) replacement of foundation drains, (2) replacement of principal spillway pipe, and (3) installation of a foundation cutoff wall. There would not be much of the original structure left after these replacements. Trying to preserve portions of the original structure would likely increase construction costs.

    • Building new dams in a more optimal location within the watersheds. Only one potential location was found.

  • Remaining alternatives considered include:

    1. Dam Decommissioning

    2. Dam Replacement

    3. Land Use Changes

    4. Small Dams in Upper Watershed

    5. Floodplain Improvements.

 

Water modeling was completed to evaluate the amount of flood protection these alternatives could provide.​ Land Use Changes, Small Dams in the Upper Watershed and Floodplain Improvements were shown to not reduce peak flows enough meet the purpose and need of the project on their own. They are considered supplemental to the alternatives of Dam Decommissioning and Downstream Dam Replacement.

Coon Creek Watershed

West Fork Kickapoo Watershed