Several flood events in the past few years had limited or altogether cut off access to nearly 30 homes in the Lake Shure neighborhood located north of Fargo, ND. The new bridge that replaced the prior structure is now above the 100-year flood event level ensuring access during future flooding.
Following the historic 2009 spring flood event, the Cass County Highway Department engaged Houston Engineering, Inc. (HEI) to investigate alternatives with a hydraulic analysis for providing access to residents of Lake Shure during flood events. Lake Shure is a rural subdivision located in Reed Township near the City of Harwood, ND. During large flood events, access for residents of Lake Shure is limited to boats.
As part of this analysis, alternatives to raise 52nd Avenue North or 57th Street North were investigated. To complicate the analysis, FEMA has designated a floodway for Cass County Drain 45 and several breakout corridors in the vicinity of Lake Shure. As a result, any road raises will need to include increases in the hydraulic structure size so that base flood elevations are not impacted during a 100-year flood event.
The project consisted of performing a hydraulic analysis and preliminary bridge design for bridge replacement options on 52nd Avenue North and 57th Street North.
HEI developed a HEC-RAS hydraulic model using the effective Flood Insurance Study (FIS) HEC-2 hydraulic model. Hydrology for the hydraulic analysis was taken from the effective FIS. HEI evaluated grade raise and bridge alternatives to minimize stage increases during the 100-year flood event. This was done to provide consistency with the FEMA regulatory floodway requirements due to the defined floodways on Cass County Drain 45 and Breakout Floodway B.
Cost estimates were also prepared for the bridge alternatives to assist Cass County with completing a Hazard Mitigation Grant Application.
To avoid overtopping during flood events, HEI replaced the existing, single-span structure with a new
375-foot, five-span concrete bridge.
Client: Cass County Highway Department
Location: Harwood, ND
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