Abstract
Gravel beaches and barriers form a valuable natural protection for many shorelines. The paper presents a numerical modelling study of gravel barrier beach response to storm wave conditions. The XBeach non-hydrostatic model was set up in 1D mode to investigate barrier volume change and overwash under a wide range of unimodal and bimodal storm conditions and barrier cross sections. The numerical model was validated against conditions at Hurst Castle Spit, UK. The validated model is used to simulate the response of a range of gravel barrier cross sections under a wide selection of statistically significant storm wave and water level scenarios thus simulating an ensemble of barrier volume change and overwash. This ensemble of results was used to develop a simple parametric model for estimating barrier volume change during a given storm and water level condition under unimodal storm conditions. Numerical simulations of barrier response to bimodal storm conditions, which are a common occurrence in many parts of the UK were also investigated. It was found that barrier volume change and overwash from bimodal storms will be higher than that from unimodal storms if the swell percentage in the bimodal spectrum is greater than 40%. The model is demonstrated as providing a useful tool for estimating barrier volume change, a commonly used measure used in gravel barrier beach management.
Highlights
Received: 17 December 2020Gravel beaches and barriers form a significant proportion of world’s beaches at mid to high latitudes [1]
Similar observations were found in Sallenger [49]; Crest accumulation—In cross sections with small freeboard and/or barrier area, crest build-up due to overtopping was observed under moderate storm conditions
There were several cases where crest was lowered through avalanching of the barrier beach face; Barrier Overwash—Once a barrier had started experiencing overwashing, the general trend was that an increase in surge, Hs and Tp resulted in more overwash, leading to more sediment being deposited further behind the barrier (Figure 8D)
Summary
Gravel beaches and barriers form a significant proportion of world’s beaches at mid to high latitudes [1] They act as natural means of coast protection and are capable of dissipating a large portion of incident wave energy under highly energetic wave conditions (e.g., [2,3]). Powell [8] presented a parametric model for gravel beach morphodynamic evolution against short term wave attack, based on a comprehensive series of physical model tests. The application of his model to a number of field sites proved it to be a useful tool to determine short term cross-shore profile evolution of gravel beaches. Bradbury [9] investigated a relationship between incident wave conditions and the geometry of barrier beaches under storm wave conditions using an extensive series of physical model experimental results on cross-shore profile
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