Image-based approach for calculating sediment transport rate and estimating seabed shear stress during scour

Draper, S., Cheng, L., White, D. and Leckie, S. (2015) Image-based approach for calculating sediment transport rate and estimating seabed shear stress during scour. Cheng, Liang, Draper, Scott and An, Hongwei (eds.) In Scour and Erosion - Proceedings of the 7th International Conference on Scour and Erosion, ICSE 2014. CRC Press. pp. 611-620 .

Abstract

In this paper an imaged-based approach is presented for calculating the sediment transport rate and estimating the seabed shear stress regularly in space and time during a model scale experiment involving scour. The approach works by solving the inverse form of the sediment continuity equation to determine the transport rate in terms of the seabed elevation using concurrent images recorded by a digital video camera. The calculated transport rate is then converted into an estimate of the seabed shear stress by (i) defining a functional relationship between the volumetric transport rate and shear stress, and (ii) estimating the free field shear stress. In this way the shear stress can be estimated without the need for any other form of measurement. Application of the approach requires that scour is confined to one plane (i.e. 2D) and that sediment transport is uni-modal (i.e. transport is via bedload or erosion only) and occurs at every point along the seabed. To demonstrate the new technique we present an example application to fixed pipelines located at different distances above a sand bed subjected to steady current. Results are in reasonable agreement with numerical models and indirect measurements of seabed shear stress.

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Contributors

Author: D. White

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