I-35W Bridge Replacement Hydraulic and Scour Analyses

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Ayres played an important role in the extraordinary project that quickly reconstructed the I-35W bridge over the Mississippi River in Minneapolis in the wake of the previous bridge’s tragic August 2007 failure.

The Minnesota Department of Transportation set an aggressive completion target of December 24, 2008, for the project and hired the design-build team of Figg Bridge Engineers and Flatiron-Manson Joint Venture. The team retained Ayres to provide hydraulic and scour analyses early in the project. Ayres was responsible for conducting a hydraulic analysis of the Mississippi River at the bridge crossing, conducting a scour analysis for Piers 2 and 3 adjacent to the river banks, and designing riprap for the channel bank. Ayres used complex 2-dimensional modeling to verify that the design would have no adverse impact on nearby structures, such as the 10th Avenue Bridge immediately downstream, an adjacent lock chamber, and a storm tunnel underneath Pier 3. Scour calculations were based on HEC-18 methods, including the complex pier method.

Our ability to complete the analyses under a nearly impossible schedule of approximately two weeks was essential in getting the project moving on the established timeline. The hydraulic analyses would have taken several months under a typical schedule. Ultimately the vital Minneapolis link, which in 2007 carried approximately 140,000 vehicles a day, opened on September 18, 2008, more than three months early.

Project Information

Client's Name

Minnesota Department of Transportation, Metro District


Minneapolis, MN

Primary Service

River Engineering + Water Resources


State + Federal + Tribal