A numerical model based on the time-averaged continuity, cross-shore momentum, longshore momentum, and energy equations is developed to predict the cross-shore variations of the mean and standard deviation of the free surface elevation and depth-averaged cross-shore and longshore velocities under obliquely incident irregular breaking waves. The suspended sediment volume per unit horizontal area is estimated using the computed energy dissipation rates due to wave breaking and bottom friction. The longshore suspended sediment transport rate is estimated as the product of the longshore current and suspended sediment volume. The developed model is compared with limited field and laboratory data. The calibrated model is in fair agreement with the data. The longshore suspended sediment transport rate is shown to be approximately proportional to the square of the longshore current. The developed model appears promising but will need to be evaluated using extensive data sets.

Longshore Current and Sediment Transport on Beaches

Prediction of sediment transport in the swash-zone by using a nonlinear wave model

 In the present work, an advanced tsunami generation, propagation and coastal inundation 2-DH model (ie 2-D Horizontal model) based on the higher-order Boussinesq equations – developed by the authors – is applied to simulate representative earthquake-induced tsunami scenarios in the Eastern Mediterranean Two areas of interest were selected after evaluating tsunamigenic zones and possible sources in the region: one at the southwest of the island of Crete in Greece and one at the east of the island of Sicily in Italy Model results are presented in the form of extreme water elevation maps, sequences of snapshots of water elevation during the propagation of the tsunamis, and inundation maps of the studied low-lying coastal areas This work marks one of the first successful applications of a fully nonlinear model for the 2-DH simulation of tsunami-induced coastal inundation; acquired results are indicative of the model's capabilities, as well of how areas in the Eastern Mediterranean would be affected by eventual larger events

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Simulation of tsunami generation, propagation and coastal inundation in the Eastern Mediterranean

Soft shore protection methods: The use of advanced numerical models in the evaluation of beach nourishment

PURPOSE: The calculation of longshore sediment transport (LST) rates is a key component of most coastal engineering studies. While the LST process is conceptually simple, in practice the development of reliable rates is made difficult by problems associated with collecting accurate field data, by limitations to model predictions, and by substantial variations of the rates in time and space. This Coastal and Hydraulic Engineering Technical Note (CHETN) summarizes the state of understanding of the influence of grain size on surf zone sediment transport and is a companion to Smith et al. (2004). This CHETN discusses details of bed-load and suspended load transport, and the classical bed-load regime is shown to encompass two distinct modes of transport. Four LST models with varying levels of complexity are discussed to show how they incorporate the physics of grain size variation and its effect on the transport rate. In addition, a relationship between the K coefficient in the CERC formula (Coastal Engineering Manual (2002), Section III-2-3-a) and grain size is presented. Finally, some inconsistencies between theory and data are discussed in the context of the interrelationship between grain size and beach slope. The final conclusion is repeated here. In general, an increase in the median grain size will decrease LST rates in the surf zone. If a simple exponential relationship between transport rate and grain size (D) is needed (Equation 7: LST rate ∝ D n ), the most appropriate value for the exponent n should be of the order of -1, as seen from Equation 23. However, this tech note argues that this is clearly a simplistic view of surf zone sediment dynamics. A more realistic (though still highly simplified) approach would be that, for fine grain sediments (D50 on the order of 0.15 to 0.30 mm), suspended load transport should dominate and n should be somewhere within the range of -0.5 to -3.0. For coarse sands (D50 around 1.0 mm), sheetflow bed-load transport should dominate (Figure 6), and the transport rate should be nearly independent of grain size (n = 0). For large gravel and shingle (D50 > 20 mm), the dominant transport should be in the IM (Initial Motion) bed-load regime, with n within the range of -0.5 to -2.0. To state this another way, the exponent n in Equation 7 is itself a function of grain size. BACKGROUND: Though most researchers recognize the median grain size as a parameter of first order importance in its effects on the magnitude of sediment transport, its variation is not as easily studied as the variation of many of the other primary parameters. In the field, it is easy to obtain data for a range of values for wave heights and periods, for instance, as these vary constantly in time. However, the grain size on a beach typically shows no (or insignificant) variations in time. Similar problems can occur in the laboratory. Changing the wave height or period in a laboratory study is usually as simple as reprogramming a wave paddle. However, usually, changing the grain size in a large model is infrequently done because of the large cost in both time and money.

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Influence of Grain Size on Sediment Transport Rates with Emphasis on the Total Longshore Rate

A time-dependent model for obliquely incident nonlinear waves is developed and applied to predict longshore current and sediment transport. The wave model is based on the Boussinesq equations for breaking and nonbreaking waves. Wave breaking is introduced by adopting the surface roller concept. Longshore current velocity is calculated using the time-averaged alongshore momentum equation, including the effects of the cross-shore circulation on the dispersion of momentum. The wave module provides the longshore current and the sediment transport modules with all required hydrodynamic information such as radiation stress, bottom velocity, undertow velocity, and eddy viscosity coefficient. The Dibajnia and Watanabe formula is adopted to predict sheet-flow transport; whereas, for the suspended load, an energetics approach is used. Model results are compared with experimental data as well as with the Kamphuis and Costal Engineering Research Center formulas for the total alongshore sediment transport rate.

Ekaterini K. Karathanassi

Papers

Longshore sediment transport by nonlinear waves and currents