Predicting short term profile response for shingle beaches

Powell, K.A. (1990) Predicting short term profile response for shingle beaches. Project Report. HR Wallingford.

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Abstract

Recent years have seen a dramatic improvement in the prediction of inshore wave climates. Whilst this has brought obvious benefits to the design of many types of coastal structure, for beaches it has served only to emphasise the lack of a coherent design methodology. In recognition of this, a comprehensive series of physical model tests has been undertaken in order to examine more closely the behaviour of shingle beaches. The tests were carried out in a random wave flume, at a nominal scale of 1:17, and covered a range of both beach material characteristics (size and grading) and wave conditions. The material used to represent the model beaches was a graded anthracite, scaled to reproduce both the correct beach permeability, and threshold and direction of sediment motion. During the study measurements were taken of beach profiles, wave run-up exceedance levels and wave reflection coefficients. Additional tests, coupled with the analysis of results from previous site specific studies, allowed the model results to be extended to a wider range of conditions, including beaches with depth limited foreshores, and beaches overlying impermeable sloping sea walls. Methods for predicting wave run-up distributions, wave reflection coefficients and beach profile response have been derived. The development of a parametric profile model allows the quantification of shingle beach profile changes due to onshore/offshore sediment transport. Using the model, beach profiles can be predicted, and subsequently located against the initial profile through an area balance routine. The model also permits the derivation of confidence limits on the predicted profile. Where possible all model results have been validated against field data, much of which was collected specifically for the purpose. The results of this validation are encouraging, suggesting that the techniques developed will prove to be valuable tools in the design and management of shingle beaches.

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