Peer ReviewedPostprint (published version

Calvete Manrique, Daniel

Kroon, Aart

Orfila, Alejandro

Ribas Prats, Francesca

Swart, Rinse Leendert de

English

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Geophysical Research AbstractsVol. 21, EGU2019-8879, 2019EGU General Assembly 2019© Author(s) 2019. CC Attribution 4.0 license.Obtaining directional wave characteristics in front of nearshore field sitesRinse de Swart (1), Francesca Ribas (1), Daniel Calvete (1), Alejandro Orfila (2), and Aart Kroon (3)(1) Universitat Politècnica de Catalunya, Department of Physics, Barcelona, Spain (rinse.de.swart@upc.edu), (2) IMEDEA(CSIC-UIB), Department of Operational Oceanography and Marine Technologies, Esporles, Spain, (3) University ofCopenhagen, Department of Geosciences and Natural Resource Management, Copenhagen, DenmarkWaves are the dominant forcing of the nearshore system and, in order to understand and predict beach morpholog-ical evolution, it is crucial to have a reliable source for wave characteristics at shallow water (about 20 m depth).The best sources of wave conditions are measurements devices (e.g., a wave buoy or AWAC) located directly infront of the study site. However, wave buoys are scarce and deploying and maintaining an AWAC is expensive.This means that wave conditions often have to be taken from a buoy located far from the study site or from alarge-scale global hindcast model and wave propagation is necessary. Mostly, propagation is done either by usinglinear wave theory and ray approximation or by using more advanced models such as SWAN. Such methods oftenlead to errors in quantifying wave conditions, especially in small fetch, complex geometry coasts such as theCatalan coast (Pallares et al., 2014). In particular, the reliability of the obtained wave angles is often questionable(see e.g. Amrutha et al., 2016 and Pallares et al., 2014), which is unfortunate because it is nowadays accepted thatthe wave angle plays a crucial role in nearshore evolution (e.g., Price and Ruessink, 2011).The objective of the present work is to investigate the best source for wave conditions in a low-fetch, com-plex geometry site (Castelldefels beach, Spanish Mediterranean coast), including the method of wave propagation.Although the study site and the closest permanent wave buoy are located relatively close to each other (approx-imately 20 km), a significant change in shoreline orientation occurs. Using data from this wave buoy or fromlarge-scale hindcast models as boundary conditions, both linear wave theory and SWAN are used to obtain thewave conditions at two locations closer to the study site. The effect of including different processes in SWAN isalso investigated. The results are compared with data measured at these two locations, paying special attention tothe wave angle. The first results indicate that the best wave conditions are obtained by forcing SWAN with themeasured directional spectra from the offshore buoy. Using either SWAN forced by statistical parameters or linearwave theory and ray approximation leads to equally good results for wave height and period but not for the waveangle, because wave refraction across the alongshore variable bathymetry is underestimated. Finally, large-scalehindcast models provide a much worse prediction of wave conditions at the study site, where particularly the waveangle is not reliable.ReferencesAmrutha, M. M., Kumar, V. S., Sandhya, K. G., Nair, T. B., & Rathod, J. L. (2016). Wave hindcast studies usingSWAN nested in WAVEWATCH III - comparison with measured nearshore buoy data off Karwar, eastern ArabianSea. Ocean Engineering, 119, 114-124.Pallares, E., Sánchez-Arcilla, A., & Espino, M. (2014). Wave energy balance in wave models (SWAN) forsemi-enclosed domains–application to the Catalan coast. Continental Shelf Research, 87, 41-53.Price, T. D., & Ruessink, B. G. (2011). State dynamics of a double sandbar system. Continental Shelf Research,31(6), 659-674.

Obtaining directional wave characteristics in front of nearshore field sites

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Obtaining directional wave characteristics in front of nearshore field sites

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