Stormwater Management in Detroit
Updated: Jun 10, 2020
Author: DBN intern John Bujdoso
Background
At its peak Detroit was home to 1.8 million residents, today that number is less than half. Yet the infrastructure of the past remains. Today the city is forced to maintain a large built area with a relatively small tax base, this is exemplified with the wastewater and sewerage systems. The Detroit Water and Sewage Department (DWSD) maintains 3,500 miles of sewer lines that, if stretched out in a straight line, would span from Boston to Los Angeles.
To treat the water running through the vast network of sewers, Detroit constructed one of the largest single-site Waste Water Treatment Plants (WWTP), in the United States. The Water Resources Recovery Facility located on the city's southwest side serves over 946 square miles (6). and prevents 550 million gallons of dilute sewage from discharging directly into the Detroit river every day. The DWSD also operates five purification sites to provide drinking water to over 3 million additional Michigan residents living in 125 communities throughout the Detroit metropolitan area (1).
Traditionally, sewage systems were designed in a way that sanitary sewers and storm sewers would combine prior to arriving at wastewater treatment plants. Such is the case in Detroit, (5). As the city expanded and grew, impervious concrete surfaces have paved the way for urbanization, today hard surfaces dominate the landscape. One issue with a heavily built area is that during intense rainfall events, there is nothing to slow down the storm surge and the runoff can overwhelm treatment facilities. This forces the facilities to release the untreated water into nearby waterways to prevent further backups (1), known as a combined sewer overflow or CSO.
CSOs degrade the quality of water and in turn the aquatic inhabitants living in the streams, rivers, and the connected lakes. A common result is bacterial and viral contamination which causes boil-water advisories and beach closings (5). Combined sewer overflows continue to be an issue today, contributing to contamination of drinking water supplies. The Detroit River has been the recipient of considerable amounts of pollutants over the years. In the 1960s, the Rouge River which drains into the Detroit River was one of three infamous rivers in the Great Lakes region to have caught fire (1). In the 1970s, a Rouge River study performed by the Michigan DNR deemed 40 miles of the river to be severely polluted. The principal contaminants were raw sewage and inorganic sediment that entered the river via combined storm sewers (1).
Investing in a clean water future
In 1985 a remedial action plan (RAP) was in the works for the Rouge River, with a heavy emphasis on sanitary sewer improvements and CSO reduction. There were approximately 7.8 billion gallons of combined sewage from 168 CSO points that were being discharged into the Rouge River and ultimately the Detroit River (1). From 1988 until 2003 over $900 million was spent on CSO projects as part of the Rouge River RAP, creating 9 retention basins that control 76 of the 157 outfalls in the Rouge River watershed. Though considerable effort and funding infrastructure has been put forth to separate storm sewers from sanity sewers, still a more dispersed and localized approached is needed to stabilize the impact of stormwater runoff on tributaries and other water bodies.
Today, 47% of the city’s land area is comprised of impervious surface (4). Detroit Water and Sewerage Department restructured its billing policy in 2016, charging all property owners for drainage based on their impervious acreage. According to DWSD, the drainage fee will be assessed at $602 per impervious acre. At this rate the university will be paying well over $1 million per year (6). To reduce these fees credits were put in place to encourage land owners to convert impervious surface to permeable, reducing the amount of runoff that reaches the sewer system and ultimately the treatment plant.
How DBN is getting involved
Larger land owners can receive drainage credits of up to 80% by implementing green stormwater infrastructure (GSI). Detroit Biodiversity Network sees this as an opportunity to increase native habitat, reduce stormwater runoff and save the university money in drainage fees. The Michigan native and prairie plants that we grow are known for their deep root systems that increase the permeability of the soil. By implementing plants into GSI features known as bioswales the root systems can greatly increase soil porosity and waster holding capacity.
DBN has already installed two bioswales throughout Wayne State University’s campus using native plants grown by students and staff on campus. DBN continues to design systems for future projects. The students and volunteers and employees working with DBN and Healthy Urban Waters believe that what was once a liability can become an asset. Slowing down and retaining water on site can be beneficial in a number of ways. Aside from saving money, it reduces the load on the treatment plant, and when native plants are used it increases wildlife habitat, and acts as a biofiltration system cleaning the water and the air.
Further reductions in WSU drainage costs will be achieved by incrementally by disconnecting buildings from the system and rerouting stormwater into GSI practices such as bioswales, detention and retention ponds, and by retrofitting parking structures, lots, and buildings with above and below-ground cisterns (6). It is important that DBN and Wayne State continue to innovate cost effective ways to deal with stormwater and improve the environmental quality of the city.
On a global level, urban areas are projected to experience more frequent and heavier rain events due to climate change, heightening the necessity for a more modular and decentralized stormwater management system (3). DBN sees the opportunity to save the university money through GSI retrofits as only the tip of the iceberg--our broader mission is to expand out into the community to assist local residents and businesses with community-based GSI projects. We are very excited to share our knowledge with the community and play a role in pushing this science forward.
FootNotes:
Hartig, John. Honoring Our Detroit River. 2003. Cranbrook Institute of Science. Print
http://historicdetroit.org/building/water-works-park-tower/
Foster, J., Lowe, A., & Winkelman, S. (2011). The Value of Green Infrastructure for Urban Climate Adaptation. Retrieved November 25, 2018, from http://ccap.org/assets/The-Value-of-Green-Infrastructure-for-Urban-Climate-Adaptation_CCAP-Feb-2011.pdf
Meerow, S., & Newell, J. P. (2017). Spatial planning for multifunctional green infrastructure: Growing resilience in Detroit. Landscape and Urban Planning,159, 62-75. doi:10.1016/j.landurbplan.2016.10.005
United States Environmental Protection Agency (U.S. EPA). National Pollutant Discharge Elimination System. February 2019.
Wayne State Rainworks Challenge