St. Mary's Gardens Subdivision Undergoes Flood Mitigation Project
New Storm Sewer and Pump Station Helps Alleviate Flooding in Monroe
CITY OF MONROE - The St. Mary’s Gardens subdivision has had a long history of flooding, spanning back to the early 2000s. After hearing the concerns from the residents, encouraging the City to help address the issue, Monroe made the decision to identify a solution to the flooding.
Efforts to find a solution began in 2015 when Spicer Group was hired to complete a study evaluating the stormwater concerns in the subdivision. Results of the study found that the existing storm sewer system was undersized, did not extend to every part of the subdivision, and was unable to properly convey stormwater into the Mason Run Drain which traverses along the northern end of the subdivision. Notably, the subdivision’s low-grade topography compounded the drainage issues, necessitating urgent intervention.
“The St. Mary’s subdivision, unfortunately, did not have enough grade to drain all the water to the Mason Run Drain, which presented a challenge in ensuring proper drainage,” Spicer Group Project Manager Jonathan Witham, P.E., said.
The study resulted in the identification of four modeling alternatives which evaluated the five-year and ten-year design storms of the stormwater sewer system.
“Spicer Group looked at various solutions for the flooding, such as installing detention ponds, increasing storm sewer pipe sizes on select streets, adding storm sewer to the streets without an existing system, and installing relief pipes to a secondary storm sewer system which drains the southern half of the subdivision,” Witham said. “We relied on software such as SWMM, or EPA Storm Water Management Model, which allowed us to analyze the existing pipe networks and to design alternatives throughout the project.”
After the initial study was complete and each option was evaluated closely, Spicer Group embarked on an additional design process to develop sustainable solutions tailored to the subdivision’s long-term stormwater management needs. Recognizing the limitations of the existing infrastructure, the design team explored innovative interventions for the 25-year-storm, per request of the City Council, to see what the impacts would be on each of the four design alternatives created. This necessitated careful planning and engineering of strategies to address the drainage issues effectively.
In 2019, the City sought further modeling alternatives to ensure all potential alternatives were evaluated to determine the best solution to the flooding. This led to designs for additional detention storage, relief pipes, and increased stormwater pipe capacities on each street. This time, Spicer Group also introduced the idea of adding a pump station as a viable solution to mitigate flooding by pumping excess stormwater away from the subdivision and into the Mason Run Drain.
Upon completion of the modeling phase, Spicer Group presented their findings to the City, suggesting the construction of a pump station with a wet well below grade to pump excess water during a storm event provided the best level of service for the subdivision. Calgary Park, situated adjacent to the Mason Run Drain and elevated from the subdivision, was deemed the ideal spot for the proposed pump station.
In 2021, Monroe requested Spicer Group to continue with providing final design for the construction of the pump station and sewer upgrades to Lavender St., Hendricks Dr., John L Dr., McCormick Dr., and Calgary Dr.
“Spicer Group gave a number of options at various levels of cost and complexity.” Patrick M. Lewis, P.E., Director of Engineering and Public Services for the City of Monroe, said. “Ultimately, we went with the option that solved the problem and would provide the best long-term solution.”
Community engagement also played a pivotal role throughout the project’s evolution, fostering collaboration between municipal stakeholders and residents. Two informational meetings were held that facilitated transparent communication and garnered overwhelming community support for the proposed project.
The project went to bid in September 2022 and construction kicked off in January 2023 with ER Zeiler Excavating as the contractor.
The project encountered several unique challenges, including the presence of substantial bedrock underneath the subdivision.
“What many people don’t know is that the City of Monroe has large amounts of bedrock for being in southern Michigan,” said Witham. “This did put some delays in the construction process because there was much more bedrock excavation than anticipated.”
The bedrock also affected the existing sanitary sewer beneath the subdivision, which was discovered to be quite shallow. This meant that the new storm sewer had to be installed underneath the existing sanitary sewer lines. This is very uncommon as usually sanitary sewer lines are much deeper in the ground than the storm sewer.
This meant the project team and excavators had to develop an adaptive approach and carefully maneuver the lines while installing the new storm sewer.
In the St. Mary’s Gardens subdivision, many houses have sub-slab drains commonly found in basements. These drains collect and remove water that accumulates beneath the concrete slab foundation of a building. As part of the project, the city aimed to provide every house with a sub discharge into the storm sewer. To achieve this, every other house received a drainage catch basin, ensuring direct connection to the new storm sewer.
Approximately 7,000 lineal feet of 8-inch plastic pipe was installed as header tiles, connecting the yard drain basins to the main storm sewer, and 5,000 lineal feet of new reinforced concrete pipe ranging from 12 to 42-inches in diameter was installed under the roads.
The newly installed pump station consists of a splitter chamber which directs water flow into two 14-foot diameter wet wells. The wet wells were supplied by Northern Concrete Pipe, Inc. and each contain two pumps that can run at a rate of 6,000 gallons per minute. Each pump turns on successively as the wet wells fill up, and the pumping rate was specifically designed to handle the 10-year storm. There is also a 27-inch diameter concrete overflow pipe for excess flow relief to the Mason Run Drain in the event of greater than a 10-year storm.
During the project’s progress, the City of Monroe received American Rescue Act Plan (ARPA) Funds due to COVID-19 circumstances, which aided in helping cover the $6.4 million in total construction costs. This financial aid allowed the City to push forward with the project and proceed with the full design of the project as planned.
“We were able to find funding through ARPA, and because of this, the City was able to make this the highest priority infrastructure project,” Lewis said. “Spicer Group was a great one-stop shop for everything we needed during the project and provided high-level design and detail.”
The installation of the pump station, storm sewers, and basins are complete, and the system is expected to be operational later this spring with final restoration efforts expected to conclude this June.