EPISODIC SHINGLE SUPPLY AND THE MODIFIED DEVELOPMENT OF CHESIL BEACH,ENGLAND

This paper illustrates a budget approach to investigate and manage lit toral 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. Co mplex, long established links are demonstrated between eroding cliff s ediment sources and a sequence of pocket shingle beaches that they sup ply. Sediment inputs and subsequent transfers are found to be episodic so that the beaches naturally alternate between open and closed syste m 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 deve lop as a product of the Holocene transgression as often envisioned, bu t until recently, it formed part of a larger natural process system wi th the periodic input of additional shingle from the west, derived fro m the erosion of massive unstable cliffs. However, several interventio ns have dislocated these natural linkages, unwittingly reinforcing the closed system states. In the absence of natural replenishment, the mo dified beaches are becoming increasingly sensitive to the continuing r elative sea-level rise and storm activity that characterises this regi on. Attention is drawn to the need to establish such understanding pri or to undertaking additional interventions. Details are provided of th e ways in which this information has assisted in the control of beach mining and future management policies are suggested.