Longshore sediment transport in the nearshore zone: role of tides

Shoreline erosion presents a significant threat to coastal areas globally, highlighting the need for a thorough understanding of the underlying physical processes to formulate effective mitigation strategies (Luijendijk et al., 2018). Studies on shoreline evolution (Mutagi et al., 2022) often rely on empirical formulations to calculate longshore sediment transport induced solely by waves. However, the extent to which tides contribute to this transport, especially in meso- and macro-tidal coastal environments, remains poorly understood.This study, conducted as part of a research project (known as MOZES) funded by the Flemish government, aims to quantify the relative effects of tides on longshore sediment transport in the nearshore zone. To achieve this objective, an idealized model (known as Q2Dmorfo, Arriaga et al., 2017) and two complex numerical models (Scaldis-Coast and Flemco, Dujardin et al., 2023) are utilized. In the idealized model, wave- and tide-induced longshore sediment transports are computed using two analytical models inspired by the work of Longuet-Higgins (1970) and Southgate et al. (1989). The two complex models calculate longshore sediment transport by fully resolving the flow field, thereby considering tides, waves, and wind.Various scenarios are explored, forcing the models with tides and waves independently, as well as in combination. The study area selected for this research is the Belgian coastal zone, which is characterized by meso- to macrotidal conditions.ReferencesArriaga, J., Rutten, J., Ribas, F., Falqués, A., & Ruessink, G. (2017). Modeling the longterm diffusion and feeding capability of a mega-nourishment. Coastal Engineering, 121, 1 - 13. doi: 10.1016/j.coastaleng.2016.11.011Dujardin, A.; Houthuys, R.; Nnafie, A.; Röbke, B.; van der Werf, J.; de Swart, H.E.; Biernaux, V.; De Maerschalck, B.; Dan, S.; Verwaest, T. (2023). MOZES – Research on the Morphological Interaction between the Sea bottom and the Belgian Coastline: Working year 1. Version 4.0. FH Reports, 20_079_1. Flanders Hydraulics: AntwerpLonguet-Higgins, M. S. (1970). Longshore currents generated by obliquely incident sea waves: 1. Journal of Geophysical Research (1896-1977), 75 (33), 6778-6789. doi: 10.1029/JC075i033p06778.Luijendijk, A., Hagenaars, G., Ranasinghe, R., Baart, F., Donchyts, G., & Aarninkhof, S. (2018). The state   of the world’s beaches. Scientific reports, 8 (1), 6641.Mutagi, S., Yadav, A., Hiremath, C.G. (2022). Shoreline Change Model: A Review. In: Nandagiri, L., Narasimhan, M.C., Marathe, S., Dinesh, S. (eds) Sustainability Trends and Challenges in Civil Engineering. Lecture Notes in Civil Engineering, vol 162. Springer, Singapore. https://doi.org/10.1007/978-981-16-2826-9_64Southgate, H. N. (1989). A nearshore profile model of wave and tidal current interaction. Coastal Engineering, 13 (3), 219-245. doi: 10.1016/0378-3839(89)90050-1. Sedimentary Geology, 33(3), 195–216.