work underway on a water-discharge structure we designed for poor soil conditions
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inspection, modeling, and design for St. Mary's surge chamber

inspection, modeling, and design for St. Mary's surge chamber
client
City of Minneapolis
location
Minnesota

During heavy rainfall, geysers caused by trapped air pockets in a deep shaft of the Minneapolis stormwater-tunnel system spouted 15 to 20 feet high. The city hired Barr to model the hydraulics of this complex air-water mixing phenomena and design access-shaft modifications for the St. Mary’s/Hiawatha tunnel system.

The modeling evaluated transient flows, or pressure surges, within the tunnel system and the release of large air pockets, both of which can cause a geyser. We calibrated the model using historical precipitation and instrumentation data. The model was then used to develop hydraulic design criteria for a deflector plate at the top of the drop shaft that would redirect a geyser into a pressure chamber below the street. The model was also used to size the surge chamber, which stores 9,000 cubic feet of water and includes vented space to allow trapped air to dissipate safely. In addition, Barr completed an onsite inspection, utility locate, and civil and structural design services for the project.

Rehabilitating rather than replacing the 1940s-era stormwater infrastructure greatly reduced costs while significantly improving public safety during future extreme-storm events.