American Society of Civil Engineers

A New Sediment Transport Formula for Local Scour Prediction

by Xibing S. Dou, Ph.D., M.ASCE, (Senior Research Engineer, GKY & Associates, Inc., 5411-E Backlick Road, Springfield, VA 22151; Mailing Address: 6300 Georgetown Pike, McLean, VA 22101) and J. Sterling Jones, M.ASCE, (Hydraulic Research Engineer, Federal Highway Administration HRDI-07, 6300 Georgetown Pike, McLean, VA 22101)
Section: Bridge Pier Scour, pp. 1-8, (doi:

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Document type: Conference Proceeding Paper
Part of: Building Partnerships
Abstract: Numerical models have been developed to adequately simulate three dimensional flow around obstructions, such as bridge piers, in the flow field. Previously, however, sediment transport formulas available for predicting scour were developed for general scour in unobstructed flow. The capability for numerical models to predict local scour around bridge piers was severely restricted by the sediment transport formulas. This paper describes a new effective Sediment Transport Capacity (STC) formula which accounts for the dominate factors-diving currents, strong vortices and high turbulence-which characterize the local scour process. The new formula adds a new term to a classic sediment transport formula from the Chinese literature. Coefficients for the added term were derived from physical laboratory experimental data and it becomes zero when there is no flow obstruction. That means that the new formula can be used for both general scour and local scour when incorporated into a reliable numerical flow model. The new formula has been tested against independent physical model results and applied to a full scale study of the proposed Woodrow Wilson replacement bridge. Results from the Woodrow Wilson bridge study are presented in this paper. This paper presents an analogy between the Sediment Transport Capacity and Stream Power and shows that they are directly related. Just as an effective Sediment Transport Capacity is needed to predict local scour with a numerical model, an effective Stream Power is needed to analyze local scour with empirical methods.

ASCE Subject Headings:
Sediment transport
Empirical equations