Assessing scour model performance with experimental data

Equations by Soulsby and Whitehouse have been applied to predicting mine burial by scour in tidal estuaries. The main equation, which has the functional form of [1-exp(-t/T)], computes the depth of the scour pit with time under steady state conditions. This theory may be applied to changing conditions by using the RMS values of the frictional stress at the bed and assuming a quasi-steady state of the RMS values over a small time period. From 1999-2002, the Naval Research Laboratory conducted scour burial experiments using instrumented mines that measure mine motion (heading, roll, and pitch) and percent burial (surface area covered with sediment). Using oceanographic and sediment data obtained during these experiments, this study examines how well the predictions match the mine burial measurements.

I. Introduction

The Navy has recently shown increased interest in predicting mine burial, both because of mining activities in the Persian Gulf and because the state of prediction has arguably been poor [1]. For sandy environments, mine burial often occurs from scour – the erosion of sediment around an obstacle due to intensified shear stresses and vortices caused by the object's presence. (Other burial processes can include sand ridge migration, liquefaction, and global sediment transport; impact burial usually is insignificant for sandy bottoms.) The most commonly used scour mine burial models, until recently, were based on equations presented in a 1963 report by Carsten and Martens [2]. Their measured rates of burial are based on scaled laboratory experiments, which may not represent in situ conditions where the mines are much larger than mean grain size or rippled bed forms.