The Delaware Department of Transportation (DelDOT) requested a study of the hydrology, hydraulics, and scour evaluations around the two bridges carrying US 13 over the Leipsic River near the Town of Smyrna, Delaware. Scour around the piers and abutment of bridges is one of the top three causes of bridge failure. Inspections of these scour critical bridges found minor scour is exposing the bridge piers and abutment foundations.
Straughan evaluated the potential maximum scour depths at the bridges to develop recommendations for scour countermeasures. The evaluation looked at floods from the upstream watershed and ones from tidal storm surges. Using these outputs from the riverine and tidal events as the boundary conditions and survey data of the channel, Straughan created a two-dimensional (2D) HEC-RAS hydraulic model of the bridge piers and abutments in the storm. Straughan estimated the final scour depths using methods from Federal Highway Administration. The final analysis allowed DelDOT to make an informed assessment of the risk of failure due to scour and to estimate the required scour protection for the bridges.