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This study investigates the influence of tidal straining in the generation of turbidity maximum zones (TMZ), which are observed to extend for tens of kilometers along some shallow, open coastal seas. Idealized numerical simulations are conducted to reproduce the cross-shore dynamics and tidal straining in regions of freshwater influence (ROFIs), where elliptical current patterns are generated by the interaction between stratification and a tidal Kelvin wave. Model results show that tidal straining leads to cross-shore sediment convergence and the formation of a nearshore TMZ that is detached from the coastline. The subtidal landward sediment fluxes are created by asymmetries in vertical mixing between the stratifying and destratifying phases of the tidal cycle. This process is similar to the tidal straining mechanism that is observed in estuaries, except that in this case the convergence zone and TMZ are parallel to the shoreline and perpendicular to both the direction of the freshwater flux and the major axis of the tidal flow. We introduce the term minor axis tidal straining (MITS) to describe the tidal straining in these systems and to differentiate it from the tidal straining that occurs when the major axis of the tidal ellipse is aligned with the density gradient. The occurrence of tidal straining and the coastal TMZ is predicted in terms of the Simpson (Si) and Stokes (Stk) numbers, and top–bottom tidal ellipticity difference (Δε). Based on our results, we find that SiStk2 > 3 and Δε > 0.5 provide a limiting condition for the required density gradients and latitudes for the occurrence of MITS and the generation of a TMZ. [ABSTRACT FROM AUTHOR]

Observations from a field experiment along the south-Holland coast, the Netherlands, were carried out in order to obtain new insights about the impacts of the Rhine ROFI (Region of Freshwater Influence) on the sand transport patterns. The net alongshore sand transport is generally governed by tides. The sediment concentration in the middle shoreface increased significantly with approaching waves of higher than ~1 m and Tm0 > 5 s. The southward net transport of the alongshore component does not agree with the literature. Modulations of the net cross-shore transport direction were observed. The net transport is more relevant during the neap tides where the velocity magnitudes are smaller. [ABSTRACT FROM AUTHOR]

Abstract: In the future it is believed that extreme coastal flooding events will increase (in frequency and intensity) as a result of climate change. We are investigating the flood risks in the eastern Irish Sea posed by extreme storm events. Here, an 11-year simulation (01/01/1996–01/01/2007) including wave–current interaction has been validated. These data can then be used to investigate the potential for coastal flooding in the study area. To accurately model a storm event in the eastern Irish Sea both wave effects and the influence of the external surge need to be considered. To simulate the waves, we have set up a one-way nested approach from a 1° North Atlantic model, to a 1.85km Irish Sea model, using the state-of-the-art 3rd-generation spectral WAve Model (WAM). This allows the influence of swell to be correctly represented. The Proudman Oceanographic Laboratory Coastal-Ocean Modelling System (POLCOMS) has been used to model the tide–surge interaction. To include the external surge we have set up a one-way nested approach from the 1/9° by 1/6° operational Continental Shelf surge model, to a 1.85km Irish Sea model. For the high resolution Irish Sea model we use a POLCOMS–WAM coupled model, to allow for the effects of wave–current interaction on the prediction of surges at the coast. Using two classification schemes the coupled model is shown to be good and often very good at predicting the surge, total water elevation and wave conditions. We also find the number of low level surge events has increased in the study area over the past decade. However, this time period is too short to determine any long-term trends in the wave and surge levels. [Copyright &y& Elsevier]