Report: Historic Rainfall, Not Defective Sewer System Caused 2021 Detroit Flooding

Heavy and historic rainfalls that exceeded the design capacity of the wastewater system caused the surface flooding and basement backups experienced in the city of Detroit last June and July.
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An independent investigation of last summer’s flooding in Detroit determined that heavy and historic rainfalls exceeded the design capacity of the wastewater system. // Photo by Dan Austin
An independent investigation of last summer’s flooding in Detroit determined that heavy and historic rainfalls exceeded the design capacity of the wastewater system. // Photo by Dan Austin

Heavy and historic rainfalls that exceeded the design capacity of the wastewater system caused the surface flooding and basement backups experienced in the city of Detroit last June and July.

Those were the findings of the independent investigative team reviewing the rain events of June and July 2021 that presented its final report Thursday to the Great Lakes Water Authority (GLWA) Board of Directors.

The report also stated that even if every piece of piping and equipment in the regional system worked in an ideal manner during the July 25-26 storm, basement backups and surface flooding still would have occurred in GLWA’s system, or any other collection system designed to today’s standard.

The standard reflects a collection system designed to handle 1.7 inches of rain in one hour (with no rain before/no rain after) or 3.31 inches in 24 hours. On June 25, more than six inches was experienced in only half that time, which is double the maximum design standard for 24 hours.

“While it is not possible to eliminate the chance of flooding given these circumstances, we are taking actions that can help mitigate the extent of the flooding,” says Suzanne R. Coffey, interim CEO of GLWA.

Over the last year, GLWA took the following actions to improve climate resiliency in the regional system in the short-term:

  • Installed three new transformers at the Freud Pump Station and successfully converted the external power supply feeding the transformers to DTE Energy power via three independent power feeds.
  • Converted external power such that all wastewater facilities operated by GLWA in the collection system are serviced by DTE Energy.
  • Installed Power Quality Monitoring Systems (PQMs) on the Conners Creek, Freud and Blue Hill Pump Stations and all wet weather treatment facilities, which provide advance notice regarding power outages and help in diagnostics of power quality-related issues.
  • Developed additional operational strategies to improve system response for larger rain events.
  • Reviewed and recalibrated instrumentation throughout the system.
  • Reinspected approximately more than 20 miles of the regional system, which is about 13 percent of the total GLWA regional sewer system.
  • Increased frequency of notification of extreme wet weather events to the public through digital channels and the media.
  • Expanded coordination with member partner communities on both the eastside and westside of the regional system, including establishing lines of communication with public works directors to optimize flow through the regional system.
  • Ongoing government outreach to discuss resources available for flood mitigation, including more than two dozen meetings with state and federal legislators. Initial outcomes of this outreach include a $27 million in appropriations from state and federal budgets for wastewater collection system improvements.

GLWA also has begun working with legislators to identify funding at the federal level for a Flood Risk Mitigation Study for southeast Michigan. The comprehensive feasibility study, which will be conducted in partnership with the Army Corps of Engineers, would evaluate the implementation of concepts such as wastewater storage at grade or deep tunnel levels, using pumping stations for discharge, constructing large diameter relief sewers, and strategic sewer separation to address the long-term impacts of climate change.

Contained within the report was a series of short-, medium-, and long-term operational and programmatic recommendations. GLWA will immediately begin reviewing these recommendations to see if there are items:

  • That have already been accomplished.
  • Can help inform adjustments/improvements to currently underway projects.
  • Offer new approaches to ongoing concerns.
  • Are not entirely feasible within the operation of the regional system.

With the independent investigation complete and the report presented to the GLWA board, the authority expects to make a decision on claims within the next several weeks.

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