Shingle beach

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.

Abstract: The 24-km long beach of the LincoIn City littoral cell on the central Oregon coast is bound by pronounced headlands that prevent bypassing of beach sands, in effect making this a large pocket beach. There is a seasonal reversal in the sand transport along this embayed shoreline, but the net littoral drift is zero. The wave energy is extreme with storms generation 7-meter significant wave breaker heights. This wave energy is essentially uniform along the Lincoln City littoral cell; in spite of t this uniformity there is a marked longshore variation in grain sizes of the beach sediment and an accompanying change in beach morphology from dissipative to reflective beaches. These variations in the beach sediment grain sizes parallel those found in the sea cliffs which consist of Pleistocene beach and dune deposits apparently formed in environments similar to those found today. Gravel and coarse sand layers are exposed in the sea cliff along the south-central portion of the littoral cell, and these constitute the major source of coarser sizes in the modern beach. By dissecting the multimodal grain size distributions of beach sediments into individual modes having log-normal distributions, we have been able to trace the coarse modes back to their sea-cliff sources. The proportions of these modes within the beach rapidly decrease away from their sources indicating a relatively small degree of longshore dispersal in spite of the high energy wave environment. The persistence of the dispersal pattern suggests a period of time that has been insufficient to produce the longshore homogenization of the sediments. It is suggested that the sea cliff erosion which introduces the coarse modes into the beach sediments did not begin or was insignificant until about 300 years ago, at which time a major subduction earthquake caused subsidence of this portion of the coast and rapid cliff recession. The longshore variation in beach sand grain sizes and accompanying beach morphology are playing an important role in the continuing sea cliff erosion with cliffs backing the coarse-grained reflective beaches eroding more rapidly than the cliffs buffered by the fine-grained dissipative beaches.

Abstract: Beach erosion, a problem along most sandy shores, can be caused by man-induced interventions to the coast or natural processes. Remediation of beach erosion (i.e., beach restoration) along eroding developed beachfronts is commonly practiced in the United States by periodic beach renourishment with or without coastal structures. Rates of erosion within beach fills generally vary greatly, and areas that erode faster than the nourishment average are commonly termed erosional hot spots (EHSs). Delray Beach, located on the southeast coast of Florida, was renourished for the fourth time on December of 1992 with about 914,000 m3 of sand dredged from offshore and placed along 2.7 km of beach. About 448,000 m3 of the fill had eroded away by 2001, about eight and a half years after initial construction. Two beach segments with erosion rates higher than the nourishment average were identified based on analysis of annual beach profile data. About 40% of the eroded volume accrued from one of these beach segme...

Abstract: On beaches where natural shoreline variability is significant, beach nourishment is a useful engineering method to augment the dry beach and protect infrastructure and/or unstable cliffs. In this study, a low-cost video monitoring system is used to monitor the shoreline response to a nourishment operation on a dynamic gravel embayed beach in Central Italy. Video-derived shorelines were collected over a 15-month period to measure the evolution of the beach with regards to three specific parameters: the dry beach width, the dry beach area and the beach orientation. Moderate increases in the dry beach width of 3.6 m and 6.7 m across the embayment were observed in response to two different gravel nourishments of approximately 40,000 m3 and 46,000 m3 respectively. The orientation of the beach meanwhile was found to rotate rapidly in the clockwise direction and more gradually in the counter-clockwise direction. Analyses of individual storm events suggest these rapid clockwise rotations are caused by ESE storms, which result in beach retreat particularly at the southern end. The combination of an overall narrow beach width and a clockwise beach orientation is observed to cause a cliff erosion event at a vulnerable point along the embayment.