Determination of Bridge Scour Velocity in an Estuary

by Billy L. Edge, (M.ASCE),
Stephan N. Vignet,
John S. Fisher, (M.ASCE),



Document Type: Proceeding Paper

Part of: North American Water and Environment Congress & Destructive Water

Abstract:

Determination of the appropriate design for protection against bridge pier scour depends significantly upon the design velocities at the project site. In estuaries with large influences by tides or storm surges, the velocity is controlled by the dynamic change in water level. These changes at the ocean boundary together with the upland runoff drive the hydrodynamics of the system. Because the ocean water surface is aflinction of the characteristics of storm surges, the velocity is likewise similarly affected Thus in order to determine the velocity at the proposed project site, a simulation of the hydrodynamics is required using the ocean storm surge as the driving boundary condition. A problem arises however in defining an appropriate method to correctly describe the ocean boundary. This paper describes three methods for determining the boundary condition based upon historical and stochastic representations of tropical storms (hurricanes) at the ocean boundary of a particular estuary. Each of the three methods are applied to the Indian River estuary in Delaware. For a simple and conservative approach the Single Design Hydrograph (SDH) method yields good results for the Indian River example.

Subject Headings: Ocean engineering | Fluid velocity | Estuaries | Storm surges | Scour | Hydrodynamics | Domain boundary | Delaware | United States

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