In a Nutshell:

• Recent funding for flood relief and stormwater management is not enough to prevent future flooding events in Southeast Michigan
• Larger and more frequent storms will continue to cause safety risk and property damage in developed and low-lying areas
• Increased regional cooperation and dedicated infrastructure funding is required to significantly reduce the risk of future flooding events

By: Eric Paul Dennis, PE – EPDennis@CRCMich.org

Michigan received some good news along with this week’s spring rainshowers. The U.S. Department of Housing and Urban Development (HUD) has allocated nearly $86 million in Community Development Block Grant-Disaster Recovery (CDBG-DR) funds in response to the June 2021 flood in Southeast Michigan. The City of Detroit will be the largest beneficiary of these funds with $57.6 million allocated. The City of Dearborn is allocated $16.3 million, and the remaining $12 million will go to the State of Michigan.

It is not yet determined exactly how the funds will be spent. Detroit Mayor Mike Duggan has stated that the city will look to use the funds to “pursue permanent measures to protect residents in Jefferson Chalmers from rising water levels and from basement flooding,” including supporting the city’s new basement backup and flood protection program. According to the Detroit News, the city is required to develop an “action plan” before funds are released, as is Dearborn and the State of Michigan.

Hopefully this grant money will help to compensate the losses suffered by residents in 2021 and provide some protection from future flood events. However, this $86 million is only a drop in the bucket compared to what would be needed to prevent widespread flooding if a storm like the June 2021 event happens again. 

In June 2021, areas of Southeast Michigan received more than six inches of precipitation over just a few hours. Stormwater collection and treatment systems were already operating near capacity due to receiving up to two inches of rain over the previous 48 hours. When the deluge came, there was nowhere for the additional water to go, so it went nowhere, backing-up into basements and low areas.

Total rainfall from June 25 – June 27, 2021

Source: Presentation to the GLWA Board of Directors October 27, 2021.

A post-event analysis of the June 25/26 event concluded that operational and maintenance issues related to sewage pump stations contributed to the damage from the flood. However, the analysis also concluded that the contribution of operational and infrastructure deficiencies was marginal in comparison to the severity of the damage due to the volume and intensity of the rainfall. The capacity of the regional stormwater management infrastructure to manage such a precipitation event was substantially overwhelmed. Widespread flooding would have happened regardless. Even the hundreds of millions of dollars of planned sewage infrastructure improvements or now under construction throughout southeast Michigan are insufficiently resilient against such a rainstorm as occurred in June 2021.

Disasters like the 2021 floods and those from 2014 become high-profile examples of regional stormwater infrastructure deficiency, but even smaller storms with an inch or two of rainfall can create local flooding issues, and recent research shows that many Detroit households experience recurrent home flooding that often goes unreported. 

Many residents are most at risk simply by way of living in older, low-lying neighborhoods where stormwater from other areas tends to accumulate. Watersheds are complex systems that do not follow property lines or municipal boundaries. The Greater Detroit Regional Sewer System connects multiple watersheds and municipal sewer systems. As such, lower-lying regions are often inundated by stormwater that flows into the system from upstream communities, and even the Great Lakes Water Authority (GLWA) has limited control over how much stormwater enters the system. 

Much of Southeast Michigan was developed decades ago when it was common practice to build combined sanitary and stormwater sewer systems. In such combined sewage overflow (CSO) systems, runoff from rainstorms is directed by storm-drains into the same sewers that carry domestic sewage and commercial/industrial wastewater. During heavy rainstorms, the stormwater demand on these systems can exceed the capacity to route the water to treatment plants. Heavy rainfall can put increased pressure on even separated sewers due to infiltration at access points and degradation sewers. 

When combined or sanitary sewers are overwhelmed, the systems overflow and untreated sewage is released directly into the environment. In extreme events, the sewers can completely back-up, flooding basements, roadways, and low-lying properties.

Combined Sewer Overflow systems tied-in to the Greater Detroit Regional Sewer System (GDRSS)

Southeast Michigan Watersheds

Watershed management across Southeast Michigan is a shared responsibility. Major players include the Southeast Michigan Council of Governments (SEMCOG), the Great Lakes Water Authority (GLWA), the Michigan Department of Environment, Great Lakes, and Energy (EGLE), the Michigan Department of Transportation (MDOT), and the many contributory municipalities. Each of these stakeholders has done much to improve stormwater infrastructure in recent decades, including separating and managing combined sewage systems. However, the challenge of stormwater management has expanded as continued development has increased impervious surfaces (such as pavement and building rooftops), as well as an increasing frequency of high-intensity rain events.

Stormwater management will be a generational project in Michigan. Changing weather and land-use patterns have assured that rainstorms will more frequently overwhelm our ability to manage the runoff. While many stakeholders understand the challenges, more effort and resources are needed to coordinate regional approaches and fund solutions.

An emerging approach to stormwater management is to leverage natural or engineered “green stormwater infrastructure” such as bioretention systems, bioswales, and even rain gardens. These devices, along with natural analogs such as forests and wetlands, both reduce the quantity of water that must be managed by traditional stormwater infrastructure, and improve the quality of the water through natural filtering. Green infrastructure has historically been overlooked as critical components of a regional stormwater management system, but is becoming increasingly popular and viewed as an essential tool in flood management. 

The benefit:cost ratio of green infrastructure is usually overwhelmingly positive from a systems/network perspective. However, under existing Michigan policies, individual users of a stormwater management system (i.e., property owners) often find it less costly to allow stormwater to drain away as surface runoff or into a storm drain, imposing external costs on the public stormwater management system.

There are various government efforts to fund stormwater management utilities by assessing property owners, but legal issues related to vote requirements for new taxes and the definition of fees have stymied many efforts and convinced some municipalities to avoid any attempt at raising revenue for infrastructure improvements.

Without an approach to stormwater management that crosses watersheds and political boundaries that fairly distributes the cost of conveying and treating runoff, we can expect many Michigan sewer systems to continue to be overwhelmed. Policymakers would be wise to pursue cooperative regional solutions that incentivize infrastructure projects that relieve pressure on our sewer systems and treatment plants by encouraging onsite retention and treatment.