THE RELATIONSHIP BETWEEN WAVE ACTION AND BEACH PROFILE CHARACTERISTICS

Abstract

The rational design of coast protection works requires a knowledge of the behaviour of the beach under natural conditions. The understanding of the relationship between the waves acting on the beach and the characteristics of the beach profile produced, is thus a necessary preliminary to the analysis of the causes of beach erosion and the evaluation of the effect of projected remedial measures. The present paper describes the results of a series of preliminary hydraulic model experiments carried out by the author prior to a model study of the behaviour of groynes in stabilising beaches. Most of the beach materials used represented coarse sand or shingle in nature. The results demonstrate the fundamental importance of the "phase difference" in terms of wave period between the break-point and the limit of uprush, in relation to flow conditions, cusp formation, and the change from "step" to "bar" type profiles. Within the limits of the experiments an expression connecting the breaker height, beach profile length, and grain diameter is developed, and its implications examined in relation to beach slope, and to the previous "wave steepness" criterion for the change from step to bar type profiles. Observations are included on the rate of recession of a shoreline due to the onset of more severe wave conditions.