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Scour and stream stability at U.S. 98 over the Pearl River
Proceedings of the 2023 Mississippi Water Resources Conference

Year: 2023 Authors: Quick K.

In February 2020, a major flood event occurred on the Pearl River that caused significant bridge scour, bank erosion, and the failure of existing streambank stabilization countermeasures at U.S. Highway 98 (US 98) near Columbia, MS. The Mississippi Department of Transportation (MDOT) maintains US 98, and in 2018 began planning and designing a new structure over the Pearl River to replace the 90-year-old eastbound bridge that was constructed in 1933. The US 98 westbound bridge was built in 1970 and was not originally scheduled to be replaced. The Pearl River is significantly meandering, and in 1986 MDOT constructed a series of five (5) jetties along the left descending channel bank to stabilize the lateral channel migration that was occurring immediately upstream of US 98. The 2020 flood caused significant scour along the jetty system, causing failure of one of the structures and severe bank erosion at a second structure. The scour along the jetties contributed to additional local scour at the US 98 bridge opening which led MDOT to implement a real time scour monitoring plan of action, and accelerated plans to replace the US 98 westbound bridge. This presentation will provide background for the US 98 bridge replacement project, lateral stream migration, and will discuss how technologies such as multi-beam bathymetric surveying, two-dimensional (2D) hydraulic modeling, and underwater acoustic imaging lead to a more informed and accurate decision-making process for MDOT. This will include both short-term and long-term plans to address stream and scour issues at the US 98 crossing over the Pearl River.

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