View Summer 2022 issue

Summer 2022

Six large tanks extending 100 feet below ground were installed to collect stormwater that would otherwise spill onto a low-lying highway in Minneapolis during times of heavy rain.

Stormwater: Underground and under control

July 25, 2022

Interstate Highway 35 is a primary corridor for motorists traveling through Minneapolis. Historically, heavy spring and summer storms have shut down a low-lying stretch of the highway south of downtown, as the overwhelmed drainage system sends rainwater spilling onto the road and blocking traffic.

The Minnesota Department of Transportation hired Barr to design a stormwater surge system to deal with excessive stormwater in times of heavy rain. Our solution can be found underground in the form of six 42-foot-diameter storage tanks designed to capture above-normal stormwater from extreme precipitation events. The stormwater is then held until it can be slowly released back into the drainage system, thus providing more resiliency to the existing mainline stormwater infrastructure.

Stormwater tanks hold 4.56 million gallons of water, the equivalent of seven Olympic swimming pools.

When the system is activated, the six connected tanks fill concurrently and collectively can hold approximately 4.56 million gallons of water, the equivalent of seven Olympic swimming pools. A lift station located in the northernmost cell of the tank system pumps the water back into the existing stormwater drainage system after the storm has passed and the mainline system can handle the stored water.

Working in tandem as part of a Construction Manager/General Contractor (CMGC) project-delivery approach, Barr worked with Kramer North America and Nicholson Construction to address constructability issues such as wall construction to minimize noise impacts, hydraulic modeling to determine the location offering the highest stormwater-management benefit, and a geotechnical investigation to understand subsurface conditions and constructability risks.

“This was a partnered effort,” says Senior Geotechnical Engineer Mike Haggerty. “An integrated team with knowledge of hydraulics, geotechnical aspects, and constructability concerns was key to finding the optimal location and minimizing risk.” Barr led the design team with partners Brierley Associates and TKDA.

The system is planned to come online in 2023. To learn more about Barr’s stormwater-management services for transportation projects, contact us.

About the author

Mike Haggerty has been involved in multiple stages of this project. He has more than 15 years of geotechnical engineering experience on projects involving tunnels, mines, dams, and wind turbines. His work frequently involves the inspection and rehabilitation of existing tunnel infrastructure and the design of underground space.