Prediction of Bay-Shaped Shorelines between Detached Breakwaters with Various Gap Spacings

Ching-Piao Tsai, Ying-Chi Chen () and Chun-Han Ko
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Ching-Piao Tsai: Department of Civil Engineering, National Chung Hsing University, Taichung 402, Taiwan
Ying-Chi Chen: Department of Civil Engineering, National Chung Hsing University, Taichung 402, Taiwan
Chun-Han Ko: Department of Civil Engineering, National Chung Hsing University, Taichung 402, Taiwan

Sustainability, 2023, vol. 15, issue 7, 1-15

Abstract: Detached breakwaters are widely used for shore protection. The planforms of tombolos or salients behind structures have also been used to provide a recreational and sustainable coastal environment. In this study, the comprehensive XBeach model was used to numerically simulate the evolution of wave transformation, nearshore current, and morphological changes in tombolo planforms behind detached breakwaters. Given various gap spacings between consecutive breakwaters, the numerical results indicated that both equilibrium bay-shaped shorelines and bottom profiles form in the lee of detached breakwaters after long-term persistent wave action. These equilibrium shorelines and bottom profiles were verified using well-known empirical formulas. Post-wave-action retreat displacement to the initial shoreline was analyzed, and an empirical relationship was proposed for predicting the equilibrium bay-shaped shoreline. By associating the empirical formula with a parabolic bay-shape equation, some actual beaches were evaluated to validate the predictions of equilibrium shorelines behind detached breakwaters. In conclusion, to appropriately plan the layouts of breakwaters, bay-shaped shorelines of tombolo planforms in the lee of detached breakwaters can be predicted at the design stage by using the proposed relationship.

Keywords: sustainable coastal environment; detached breakwater; tombolo; XBeach; wave transformation; nearshore current; morphological change; retreat displacement; equilibrium bay-shaped shoreline; parabolic bay-shape equation (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2023
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