Episodic Shingle Supply and the Modified Development of Chesil Beach, England
Keywords:Cliff, bluff, sediment budget, erosion, shingle, gravel, beach, shoreline management, littoral, cell, drift, protection, Dorset
This paper illustrates a budget approach to investigate and manage littoral sediment for coastal defence within an integrated process system in west Dorset, England. The budget is quantified in terms of inputs, transfers, storage and outputs of sediment within a littoral cell. Complex, long established links are demonstrated between eroding cliff sediment sources and a sequence of pocket shingle beaches that they supply. Sediment inputs and subsequent transfers are found to be episodic so that the beaches naturally alternate between open and closed system states according to prevailing transport conditions. Interestingly, the major storm barrier of Chesil Beach is identified as the ultimate shingle sink. These results suggest that the beach did not simply develop as a product of the Holocene transgression as often envisioned, but until recently, it formed part of a larger natural process system with the periodic input of additional shingle from the west, derived from the erosion of massive unstable cliffs. However, several interventions have dislocated these natural linkages, unwittingly reinforcing the closed system states. In the absence of natural replenishment, the modified beaches are becoming increasingly sensitive to the continuing relative sea-level rise and storm activity that characterises this region. Attention is drawn to the need to establish such understanding prior to undertaking additional interventions. Details are provided of the ways in which this information has assisted in the control of beach mining and future management policies are suggested.