Staff Directory

Hydraulic and Coastal Engineering Study for US-331 over Choctawhatchee Bay, Florida

Client: Florida Department of Transportation (FDOT)
Location: Walton County, Florida, USA

Challenge. Provide coastal engineering and bridge hydraulics/scour calculations in support of the design/build project and develop the Bridge Hydraulics Report (BHR) in accordance with FDOT requirements

Project-Choctawatchee-BaySolution. The proposed location is exposed to wind setup and waves, which, when combined with hurricane surge, could produce high water surface elevations and wave heights. The approach involved an application of the tightly coupled SWAN+ADCIRC models. Model calibration and verification occurred via comparisons of hindcast simulations of hurricanes Ivan (2004) and Opal (1995) to gage measurements. The AASHTO Level III approach to determining design hydraulic parameters involved hindcasting hurricane surge and waves at the site and developing design parameters through application of extreme value statistics. For this project, we identified the 20 most severe storms affecting the area and extended them to 60 hindcast simulations by shifting hurricane paths. The maximum values at each model node provided the inputs for the extreme value analysis to develop the 100- and 500-year return period value at each node. These return period values provided input to calculate long-term scour processes (channel migration and aggradation/degradation), contraction scour depths, and local scour at new bridge piers. Developed “long-term scour” for vessel collision loading from normal everyday conditions at the bridge.