US 80 and I-20/I-55 Over Pearl River Stream Instability Countermeasures

US 80 and I-20/I-55 cross the Pearl River at Jackson, Mississippi. Over the last 30-plus years, the channel banks have experienced natural erosion processes that jeopardize the bridge foundations at the crossings. Garver performed existing bridge scour evaluations and developed streambank stabilization countermeasure designs at both the US 80 and I-20/I-55 crossings. Site and stream reconnaissance was performed, and a geomorphic assessment was completed based on FHWA guidance. The USACE HEC-SSP software was used to perform a Bulletin 17C stream gage analysis for the Pearl River and tributaries. Stage-discharge relationships and specific discharge analyses were used to assess the vertical channel stability and to determine coincident discharge scenarios for countermeasure design. 

Garver utilized SMS with SRH-2D to develop a two-dimensional (2D) hydrodynamic model of the Pearl River floodplain due to multiple hydraulic structures and complex hydraulic flow conditions associated with a nearby tributary. In addition to the US 80 and I-20/I-55 crossings, the study area included a local roadway and two railroad crossings. Ten individual hydraulic bridge structures were incorporated within the model domain.