AbstractBeach topography quickly changes in response to the action of storm waves, resulting in erosion of the foreshore with accretion under a calm wave condition after a storm. These seasonal beach changes may occur on beaches with protective measures or artificial beaches produced by beach nourishment. On these beaches, the shore protection function of a sandy beach is reduced when a trough is formed immediately offshore of the shoreline and the foreshore slope increases, indicating the importance of the study on topographic changes. Moreover, the time required for a beach recovery in response to wave conditions has not been sufficiently studied, along with the 3-D topographic changes associated with beach cycles. In this study, we aim to investigate these issues using the Narrow Multi-Beam survey data, wave data, and seabed materials data, taking the Chigasaki coast as an example. It was found that a seabed shallower than 2 and 3 m depths was eroded by rapid offshore sand transport during a storm event with the deposition of sand in a zone between 3 and 5 m depths, and then the beach recovered within 1-2 years after the storm. It was also confirmed that a bar and trough disappeared in 1-2 months under the conditions of HE = 0.5 m, TE = 8 s, and H/L = 0.005 when the crown depth of the bar was smaller than approximately 2 m. Thus, the topography after the storm waves recovers within several months or 1-2 years depending on wave conditions and the crown depth of the bar.
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Davis Jr, R. A. and Fitzgerald, D. M.: Beaches and Coasts, Blackwell Publishing, Malden, USA, 2004, p. 419.
Ishikawa, T., Uda, T., San-nami, T., Aoshima, G., and Yoshioka, A. 2009. Comprehensive management of sand considering grain size on Shonan coast, Proc. Coastal Dynamics 2009, Paper No. 71, pp. 1–12.
Ishikawa, T., Uda, T., San-nami, T., and Hosokawa, J. 2013. Verification of shore protection effect of beach nourishment on Chigasaki coast, Asian and Pacific Coasts 2013, Proc. 7th Inter. Conf., pp. 1–8.
Ishikawa, T., Uda, T., San-nami, T., Hosokawa, J., and Tako, T. 2018. Possibility of offshore discharge of nourishment sand in terms of sand volume and grain size composition, Proc. 36th Conf. on Coastal Eng., Baltimore, Maryland, papers.47, pp. 1–14.
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