Utrecht, Netherlands
Utrecht, Netherlands
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Ridderinkhof W.,IMAU | Hoekstra P.,IMAU | van der Vegt M.,IMAU | de Swart H.E.,IMAU
Continental Shelf Research | Year: 2016

Ebb-tidal deltas are bulges of sand that are located seaward of tidal inlets. Many of these deltas feature shoals that cyclically form and migrate towards the coast. The average period between successive shoals that attach to the coast varies among different inlets. In this study, a quantitative assessment of the cyclic behavior of shoals on the ebb-tidal deltas of the Wadden Sea is presented. Analysis of bathymetric data and Landsat satellite images revealed that at the majority of inlets along the Wadden Sea migrating shoals occur. The average period between succeeding shoals correlates to the tidal prism and has values ranging between 4 and 130 years. A larger tidal prism favors larger periods between successive shoal attachments. However, such a relationship was not found for wide inlets with multiple channels. There is a positive relationship between the frequency with which the shoals attach to the coast and their migration velocity, and a negative relationship between the migration velocity of the shoal and the tidal prism. Finally, the data were too sparse to assess whether the longshore sediment transport has a significant effect on the period between successive shoals that attach to the coasts downdrift of the observed tidal inlets. © 2016 Elsevier Ltd.

van der Grinten R.M.,KNMI | de Vries J.W.,KNMI | de Swart H.E.,IMAU
Natural Hazards | Year: 2013

Storm surge models usually do not take into account the explicit effect of wind gusts on the sea surface height. However, as the wind speed enters quadratically into the shallow water equations, short-term fluctuations around the mean value do not average out. We investigate the impact of explicitly added gustiness on storm surge forecasts in the North Sea, using the WAQUA/DCSM model. The sensitivity of the model results to gustiness is tested with Monte Carlo simulations, and these are used to derive a parametrisation of the effect of gustiness on characteristics of storm surges. With the parametrisation and input from the ECMWF model archive, we run hindcasts for a few individual cases and also the 2007-2008 winter storm season. Although the explicit inclusion of gustiness increases the surge levels, it does not help to explain, and hence reduce, the errors in the model results. Moreover, the errors made by ignoring gustiness are small compared to other errors. We conclude that, at present, there is no need to include gustiness explicitly in storm surge calculations for the North Sea. © 2012 The Author(s).

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