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Facts about Dearborn’s sewer system and the June 26, 2021 flooding and sewer backups (as of July 14, 2021)  
Document originally created June 28, 2021
Updated July 8, 2021
Updated July 12, 2021
Updated July 14, 2021

Update as of July 14, 2021:

The City Council has requested an assessment from an independent third party to take a look at the events that occurred June 25 and 26, 2021, and, separately, to examine the City’s overall sewer system. It is hoped that this review will also result in recommendations for steps that can be taken in the future.

These recommendations may include addressing broader issues related to climate change, the recognition that development and actions in the 43 communities in the Rouge River watershed can impact Dearborn, which is near the end of the river before it reaches the Detroit River, the recognition of the importance of storm water management for private and public development in the region, and the recognition that regional cooperation and regional solutions may be required.
Information published prior to July 14, 2021 is below. Note language has been updated to refer to the events following the June 25-26 rainstorms as flooding and sewer backups.

Q: What is believed to have caused the significant flooding and sewer backups that occurred June 26?
A. The storm that led to severe flooding and sewer backups on June 25-26 was historic. As of July 14, the City of Dearborn is looking into the cause, but preliminary assessments have shown that our sewer system is working as designed.
All sewers are designed to flow by gravity, meaning that the pipes slope downward. During high-intensity rain events, rainwater and wastewater drain into the Rouge River, without pumps.
The city’s sewer system is designed to handle three inches of rain within 24 hours. During the June 25-26 storm, Dearborn received over seven and a half inches of rain. Most of this rain occurred within seven hours. Comparatively, surrounding cities received an average of five inches of rain. Dearborn received the largest amount of rainfall in the area. These figures were at least two inches higher than those recorded during the flood that occurred in 2014.

Q: What was the federally-mandated Combined Sewer Overflow (CSO) project intended to do?
A: The Combined Sewer Overflow (CSO) project that the City has been working on for years was intended to reduce pollution in the Rouge River, as mandated by the federal government. This is done in Dearborn through separating storm and sanitary sewers, and/or through chemically-treating any wastewater that does flow into the Rouge River during heavy rain.
The CSO project was not intended to increase the sewer system’s capacity in order to prevent flooding. The CSO permit was issued by the Michigan Department of Environment, Great Lakes and Energy (EGLE) and was required by a federal mandate to reduce pollution in the Rouge River. More than 40 communities, including Dearborn, are in the Rouge River watershed, and many were affected by the federal mandate to clean up the river.
Frequently, during almost all rain events, storm water would become combined with waste water and drain into the Rouge River. Thus, the CSO project was enacted to mitigate pollution to the Rouge River through allowing only chlorine-treated wastewater to drain into the river.
Dearborn was required to fully finance the CSO project. The federal government did not provide financial assistance.

Q: Why was east Dearborn impacted so severely in June 2021?
A: East Dearborn sits at a lower ground elevation than west Dearborn, rendering it more vulnerable to flooding. In addition, east Dearborn was developed prior to World War II, meaning that the sewer system was built according to standards at that time.
Furthermore, continuing housing and building development in that area over the years resulted in the removal of several surface streams that led to the Rouge River, which reduced drainage options during storms.
In east Dearborn, storm water is carried by an outlet consisting of two large diameter pipes constructed in the 1920s that outfall into the Rouge River via the Ford Turning Basin. Another large outlet was added in the 1960s in order to provide some relief. However, due to the intensity and magnitude of the June 25-26 storm, these two storm outlets were completely submerged, limiting their ability to discharge water as designed from east Dearborn into the Rouge River.
Due to the elevation level in east Dearborn and its close proximity to the Rouge River, it was not possible to build a deeper sewer system.

Q: What is the City doing to address/prevent this in the future?
A: Unfortunately, retrofitting the sewer system to fit today’s standards, if it were possible, would come with an astronomical cost. The ideal fix would cost roughly $500M, which would lead to a 110 percent increase in residents’ water and sewage bills. That amounts to a total of $170 additional cost on residents’ bills per quarter.
The City also explored constructing a $100M retention basin (pipe storage) along Oakman Boulevard, but it was deemed unviable due to rising river elevation.
Furthermore, there is no guarantee that these systems would have prevented the floods that occurred on June 25-26, or will prevent similar floods in the future.
The City is currently exploring options in the interim that will assist in alleviating future flooding.

Q: Is a regional approach needed to address flooding issues?
A: The City is advocating for an examination of how regional development have impacted the Rouge River as well as sewer systems within the Rouge watershed.
The Rouge watershed is approximately 480 square miles. All the storm water runoff falling into the Rouge watershed drains to the Detroit River through the Rouge River main stem located at Michigan Avenue, south of the Detroit River.
The upstream development in the watershed, the historic high water levels in the Great Lakes and climate change have all contributed the greatest impact to the increased elevations being experienced on the Rouge River in the vicinity of the two outfalls serving east Dearborn. To address this problem, it will be necessary to expand our understanding of the dynamics taking place for what will be not only a solution for Dearborn, but for the entire region and all the Great Lakes communities.

Q: How did the rainfall on June 25-26 compare with annual and monthly averages?
A: Dearborn received 7.5 inches of rain within 24 hours.

For comparison, the average annual rainfall in the State of Michigan is 30 – 48 inches.

For the Detroit area, the average monthly rainfall during its wettest months of April through September is 3.05-3.27 inches.

This means that Dearborn received more rain in a 24-hour period on June 25-26, 2021 than the Detroit area typically receives in an entire month.