Local Sediment Scour Model Tests for the Woodrow Wilson Bridge Piers: Final Report
anadromous fish, critical velocity, design, flow velocities, flume, hydraulics, Massachusetts, model studies, Potomac River, prototype, scour, Turners Falls, upstream
Small scale physical model tests were performed on four different pier configurations for the Woodrow Wilson Replacement Bridge that is located on the I-95 and I-495 over the Potomac River near Washington D.C. The model tests were conducted in the Hydraulics Flume at the USGS Conte Anadromous Fish Research Center in Turners Falls, Massachusetts. All tests were conducted at velocities just below critical velocity (i.e. just below the velocity needed to initiate sediment movement on the flat bed upstream of the structure) for the uniform diameter 0.8 mm sand used in the flume. For the prototype pier, local scour depths were computed two different ways from the measured model scour depths corrected to critical velocity. The 'Conventional Method' assumes that the scour depth at transition from clearwater to live bed scour conditions in the model study should be multiplied by the geometric scale of the model to obtain the prototype scour depth. Sheppard's Method takes into consideration the fact that the sediment in the model test is not scaled properly and that the prototype scour depth depends on the design flow velocity. The model parameters with the measured and corrected (corrected for test velocity being less than critical) scour depths are given in Table ES-1. The prototype scour depths for four different velocities believed to span 100 and 500 year return interval flows are given in table ES-2.