PURPOSE:Total longshore sediment transport (LST) rate and its cross-shore distribution in the surf zone are essential to many coastal engineering and science studies. Practical engineering applications such as predicting beach response in the vicinity of coastal structures, beach-fill evolution and renourishment requirements, and sedimentation rates in navigation channels all require accurate predictions of LST rates. Present predictive tools have been developed based primarily on field studies; however, obtaining high-quality data in the field is difficult (Wang and Kraus 1999). Arguably the most widely used model for estimating total longshore sediment transport rate is the "CERC" formula (Coastal Engineering Manual 2002, Shore Protection Manual 1984, which is based on field measurements and is often applied to calculate the total LST rate. Accuracy of the CERC formula is believed to be ± 30-50 percent at best; and several parameters that logically might influence LST are excluded in the formula, such as breaker type and grain size.This CHETN summarizes results of experiments conducted in the Large-scale Sediment Transport Facility (LSTF) Fowler et al. 1995) to investigate the importance of wave height, period, and breaker type (spilling and plunging breakers) on total LST and the cross-shore distribution of LST. The LSTF is capable of simulating wave conditions that are almost directly comparable to annual averages along many low-wave-energy coasts, for example a majority of estuarine beaches (Nordstrom 1992) and many beaches along the Gulf of Mexico and the Great Lakes in the United States.
BACKGROUND:A common tool for predicting the total rate of longshore transport is the CERC formula. The model, based on the assumption that the total longshore sediment transport rate is proportional to longshore energy flux, is given as: