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Nearshore hydrodynamics and sediment transport patterns induced by waves and tide adjacent to a structured tidal inlet with complex bathymetry are investigated to determine the potential causes of downdrift beach erosion. A coupled wave and hydrodynamic model is used to simulate the nearshore hydrodynamics and morphodynamics. Near the inlet, the tidal-induced pressure gradient dominates the wave radiation stress gradient only in the first half of the flood duration. The nearshore hydrodynamic pattern for the rest of the tidal cycle is driven mainly by the wave-driven pressure gradient. The wave-driven pressure gradient results from alongshore variation of water surface elevation induced by nearshore wave focal points caused by wave refraction over irregular bathymetry (with ebb tidal shoals and nonparallel shoreline depth contours). The resulting alongshore sediment transport patterns suggest that the direction of the time-averaged alongshore sediment transport rate near the inlet and at the downdrift beach is against that of the larger-scale net sediment transport along the coast. The inlet-adjacent time-averaged alongshore sediment transport rate increases for waves with larger wave height and an incident angle closer to shore normal in contrast to expectations under the assumption of straight and parallel depth contours. [ABSTRACT FROM AUTHOR]

Beach profile evolution is a dynamic phenomenon that often leads to threatening consequences such as severe beach erosion and shoreline retreat. A new comprehensive morphodynamic model is introduced in this study that includes representation of bedload and suspended size-selective sediment transport and cross-shore sediment grain-sorting models. The model is capable of simulating the changes in cross-shore bathymetry and sediment grain size composition observed under laboratory conditions for both erosive- and accretive-type equilibrium beach profiles. The new model is most advantageous for scenarios with poorly sorted sediments or sites with strong cross-shore variability in sediment grain sizes. Information on sediment size composition in the domain and its history is also provided by the new model, which can be useful for engineering, recreational, or biological considerations. [ABSTRACT FROM AUTHOR]

A comprehensive study of swash-zone hydrodynamics and sediment transport was conducted on a macrotidal beach in Perranporth, United Kingdom. The unique study is the first to simultaneously measure suspended sediment and sheet flow sediment concentrations, water depth, near-bed velocity profiles, and high-resolution swash surface and bed-level changes on a natural beach. Data collected during the study are used to quantify the vertical profile of cross-shore and alongshore velocities and the importance of sheet flow sediment processes in the swash zone. The swash-zone boundary layer for cross-shore velocities is observed to generally occur over at least the lower 0.06 m of the water column. Alongshore velocities are often the same order of magnitude as the cross-shore velocities and are dominant near cross-shore flow reversal. Flows are often logarithmic in profile, but the instantaneous nature of the measurements renders application of the logarithmic model difficult. When valid, the logarithmic model enabled cross-shore shear stress estimates of up to with maximum alongshore shear stress estimates of , further highlighting the potential importance of alongshore flows. Friction coefficient estimates, assuming a quadratic drag law, showed no statistical difference between onshore- and offshore-directed motion, with typical values of (). Sheet flow concentrations exceeded the maximum measured suspended sediment concentrations of approximately . Sediment loads in the sheet layer are up to 10 times larger than the sediment loads in the lower suspension layer. Simplified sheet flow sediment transport estimates are 3.6 times larger on average than those in the suspension layer. The latter two findings indicate the importance of sheet flow processes in the swash zone that are generally ignored. [ABSTRACT FROM AUTHOR]

Our capability for predicting beach and dune erosion has improved in the last three decades, but the recovery of an eroded beach above the mean sea level (MSL) cannot be predicted at present. The cycle of beach erosion and recovery will need to be predicted for the long-term maintenance of a sand beach with a dune for coastal flooding reduction. The cross-shore numerical model (CSHORE) is extended and evaluated using natural beach erosion and recovery data along 16 cross-shore lines spanning 5 km alongshore for the duration of 272 days. The CSHORE predicts beach and dune erosion fairly well, as has been shown in previous comparisons. The bed-load formula used in the CSHORE is adjusted to predict the accreted beach profile with a berm. The computed beach profile evolutions are shown to be affected little by the alongshore gradient of the longshore sediment transport rate along the straight beach. The extended CSHORE predicts both erosion and accretion above MSL within a factor of about 2. [ABSTRACT FROM AUTHOR]

The Delaware Atlantic coast of 40 km length is suffering from beach erosion. The State of Delaware placed approximately 1,100,0001 m3 sand on its four beaches in 1998. Beach profiles were surveyed along fixed 65 cross-shore lines almost semiannually for 9–11 times until 2005. The measured profiles are analyzed to obtain the shoreline displacement and the area changes in the landward and shoreward zones between the two successive profile surveys. The relations among these profile change parameters indicate that a standard one-line model may not be applicable to these nourished beaches because of the dominant summer and winter profile changes. An inverse method based on a two-line model is developed to estimate the cross-shore sediment transport rate and the gradient of the longshore sediment transport rate. The estimated rates indicate the importance of both cross-shore and longshore sediment transport to predict the evolution of these nourished beaches with large variabilities in time and space. [ABSTRACT FROM AUTHOR]