Cross-shore distribution of longshore sediment transport: comparison between predictive formulas and field measurements

The skill of six well-known formulas developed for calculating the longshor e sediment transport rate was evaluated in the present study. Formulas prop osed by Bijker [Bijker, E.W., 1967. Some considerations about scales for co astal models with movable bed. Delft Hydraulics Laboratory, Publication 50, Delft, The Netherlands; Journal of the Waterways, Harbors and Coastal Engi neering Division, 97 (4) (1971) 687.], Engelund-Hansen [Engelund, F., Hanse n, E., 1967. A Monograph On Sediment Transport in Alluvial Streams. Teknisk Forlag, Copenhagen, Denmark], Ackers-White [Journal of Hydraulics Division , 99 (1) (1973) 2041], Bailard-Inman [Journal of Geophysical Research, 86 ( C3) (1981) 2035], Van Rijn [Journal of Hydraulic Division, 110 (10) (1984) 1431, 110(11) (1984) 1613; 110(12) (1984) 1733], and Watanabe [Watanabe, A. , 1992. Total rate and distribution of longshore sand transport. Proceeding s of the 23rd Coastal Engineering Conference, ASCE, 2528-2541] were investi gated because they are commonly employed in engineering studies to calculat e the time-averaged net sediment transport rate in the surf zone. The predi ctive capability of these six formulas was examined by comparison to detail ed, high-quality data on hydrodynamics and sediment transport from Duck, NC , collected during the DUCK85, SUPERDUCK, and SANDYDUCK field data collecti on projects. Measured hydrodynamics were employed as much as possible to re duce uncertainties in the calculations, and all formulas were applied with standard coefficient values without calibration to the data sets. Overall, the Van Rijn formula was found to yield the most reliable predictions over the range of swell and storm conditions covered by the field data set. The Engelund-Hansen formula worked reasonably well, although with large scatter for the storm cases, whereas the Bailard-Inman formula systematically over estimated the swell cases and underestimated the storm cases. The formulas by Watanabe and Ackers -White produced satisfactory results for most cases, although the former overestimated the transport rates for swell cases and the latter yielded considerable scatter for storm cases. Finally, the Bijke r formula systematically overestimated the transport rates for all cases. I t should be pointed out that the coefficient values in most of the employed formulas were based primarily on data from the laboratory or from the rive r environment. Thus, re-calibration of the coefficient values by reference to field data from the surf zone is expected to improve their predict ive c apability, although the limited amount of high-quality field data available at present makes it difficult to obtain values that would be applicable to a wide range of wave and beach conditions. (C) 2001 Elsevier Science B.V. All rights reserved.