Edenville Dam interim Repair Measures

Phase I Interim Stabilization Measures at Tobacco Spillway

1. Lowering and filling existing concrete spillway.
   
2. Restoring base flow in the Tobacco River.
   
3. Lowering water level upstream of dam.
   
4. Stabilizing River immediately downstream of dam.
   
5. Spillway designed to convey approximately 11,300 cfs – approximately 200-year flood flow.
   
6. MDOT constructing temporary M-30 causeway.
   
7. Embankment stabilization adjacent to concrete.

Phase II Interim Stabilization Measures at Edenville Spillway

1. Remove Edenville spillway to it’s base.
   
2. Install low dike across the breach channel.
   
3. Install sheet pile cut off wall across breach channel.
   
4. Restore base flow to original river channel.
   
5. Convey 200 storm year inflow without overtopping into breach channel.
   
6. Exploring options for the powerhouse – either demolish or re-use water passages as a low level outlet. Hydro generation is not an option.
   
7. Stabilize and restore downstream portions of the Tittabawassee River channel.
   
8. Exploring embankment stabilization options along upstream face of dike from spillway to M-30.
   
9. Installing boom on Tobacco River for safety.

Quick Facts

$121 million	2,875	2025-2026	$1,720
Cost to Repair	Waterfront Properties	Estimated Lake Return Date	Estimated Annual Capital Assessment Range

Edenville Dam will require demolition of damaged structures - the spillway and powerhouse - and construction of new primary and auxiliary spillways.

Tobacco River Proposed Plan View of Permanent Repairs

Tittabawassee River Proposed Plan View of Permanent Repairs

Edenville Proposed Embankment at Breach Channel

Tobacco Proposed Embankment Stabilization

Proposed Tittabawassee Spillway

Example crest gate with gate closed on the far/left side and the gate open on the right side

Wixom Lake Recovery and REstoration Timeline

Click to enlarge

Long-Term Restoration

Critical items

Spillway Adequacy

• Edenville is classified a high hazard dam. Prior to May 2020 flood, the total spillway capacity (Edenville + Tobacco) was approximately 20,670 cubic feet per second (cfs) before water would begin overtopping embankments
  
• Prior State of Michigan 1/2 PMF was 25,000 cfs
  
  • Based on current on-going studies and recent flood, this will increase
    
• FLTF study currently estimating future spillway requirement being 52,275 cfs
  
• Spillway requirements still being finalized based on
  
  • PMP and PMF studies
    
  • Inflow Design Flood Study
    
  • State of Michigan Dam Safety Task Force
    
  • EGLE approval 

Water Retaining Structures

• The left embankment completely breached. Portions of the remaining embankments were damaged due to rapid reservoir drawdown and scour
  
• Remaining embankment slopes are steep and don’t meet stability criteria
  
• Embankments leak excessively. No seepage cutoff and no internal filter zones to protect against seepage-induced internal erosion
  
• Total spillway capacity is significantly lacking
• Geotechnical investigations and structural analyses are required to support design of new embankments and repair of existing embankments
  
• All water retaining structures will need to be thoroughly evaluated and designed to meet State and federal dam safety standards
  

Risk-based design approach

• The IDF/risk-based approach aligns with FEMA guidelines and recommendations of the Michigan Dam Safety Task Force guidelines for Michigan dams
  
• Inflow Design Flood that requires these steps:
  

1. Site-specific Regional Probable Maximum Precipitation (PMP) studies which are underway.
2. Perform downstream Inundation mapping assuming dam failure for a range of flows starting from the 100-year flood up to the PMF
3. Determine the incremental hazard increase and consequences of failure for a range of flood flows up to the PMF
4. Use risk-based, IDF approach to inform the design spillway capacity – no less than 200-year but possibly less than the ½ PMF

Resources

FAQs

Will wixom Lake Be Split Into Two lakes?

No. The current design has Wixom Lake to continue as one lake as legally defined.  

Why can't Wixom lake come up sooner?

We are running parallel paths to get to the start of construction. A significant amount of work must be done before construction can begin:

• Independent forensic investigation report
• Engineering
  • Preliminary engineering reports
  • Inflow Design Flood needs to be established
  • Final design and construction plans
• Submittal and approval for USDA funding approval
• Environmental studies and EGLE permitting
• Bid letting and computation of costs
• Special assessment hearings and appeals
• Approval of special assessment roll by county 

Documents

• 9/9/2021 | ​Wixom Lake Restoration Activity and Timeline
• ​2/18/2021 | Wixom Lake Webinar, PowerPoint

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• 8/31/2020 | EGLE Preliminary Report on the Edenville Dam Failure, Response Efforts, and Program Reviews
• 8/3/2020 | Wixom Lake Webinar, PowerPoint ​
• 6/9/2020 | Clarification on Details Related to Sanford and Edenville Dams

Contacts

• Wixom Lake Association: Facebook • website • email • Larry Woodard, President
• ​FLTF Board Representatives: 
  • ​Don Zakett, Wixom Lake, 2020-2022
  • Dave Rothman, Wixom Lake, 2020-2023