Dependence of Total Longshore Sediment Transport Rates on Incident Wave Parameters and Breaker Type

Abstract

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:

A Hybrid Model of Swash-Zone Longshore Sediment Transport on Reflective Beaches

“…Previous studies have found that a significant part of the longshore sediment transport occurs in the swash zone and may account for a large portion of the total littoral drift (Bodge and Dean, 1987, Kamphuis, 1991, Smith et al, 2009, especially on steep reflective beaches (Van Wellen et al, 2000), where alongshore sediment transport in the swash zone can be significantly greater than that in the surf zone (Hughes et al, 2007). In the present study, model predicted alongshore swash-zone transport may account for 34%-100% of the total littoral drift under the wave conditions simulated at the study site.…”

“…Offshore and onshore sediment transport in the swash zone, therefore, contributes significantly to shoreline accretion and erosion. Secondly, a significant part of the longshore sediment transport occurs in the swash zone and may account for a large portion of the total littoral drift (Bodge and Dean, 1987, Kamphuis, 1991, Smith et al, 2009, especially on steep reflective beaches (Van Wellen et al, 2000), where the surf zone is typically narrow or even absent, with wave breaking occurring practically on the beachface. Alongshore sediment transport in the swash zone can be significantly greater than that in the surf zone on such beaches (Hughes et al, 2007).…”

A method to estimate the longshore sediment transport at ebb‐tidal deltas based on their volumetric growth: Application to the Guadiana (Spain–Portugal border)

“…Moreover, the simplified bulk formulations fail to account for morphological features on the beach that affect the breaking type of waves and accuracy of LST rate predictions (Kamphuis and Readshaw, ; Smith et al ., ). As an example, if plunging breaking were more frequent than spilling for the more energetic conditions which in turn generate the larger transport rates, then one of the main hypotheses of the bulk expressions (spilling breaking) would not be fulfilled (Smith et al ., ). Yet, the results from bulk equations are still highly variable when averaged for the period 1995–2017, characterized by a more typical beach morphological setting (Table ).…”

“…However, the wave propagation processes were altered by a submerged nearshore bar welding to the beach during the initial development of the modern delta (until ~1995; see Supporting Information and Garel et al ., ). Moreover, the simplified bulk formulations fail to account for morphological features on the beach that affect the breaking type of waves and accuracy of LST rate predictions (Kamphuis and Readshaw, ; Smith et al ., ). As an example, if plunging breaking were more frequent than spilling for the more energetic conditions which in turn generate the larger transport rates, then one of the main hypotheses of the bulk expressions (spilling breaking) would not be fulfilled (Smith et al ., ).…”

“…In particular, LST predictions can vary widely depending on the bulk formula used (Fowler et al ., ; Wang et al ., ; Van Wellen et al ., ; Schoonees and Theron, ; Tonk and Masselink, ; Güner et al ., ; Mil‐Homens et al ., ). Direct quantifications at the site are required to calibrate (or improve, at least) bulk equations or validate their results, but are rarely available (Cooper and Pilkey, ; Smith et al ., ).…”