PREDICTION OF SOFT-CLIFF RETREAT WITH ACCELERATING SEA-LEVEL RISE

Reliable estimates of future cliff recession are needed to assess coas tal vulnerability and evaluate management policies with regard to the widespread sea-level rise thought likely to result from global warming . A research gap is identified in providing appropriate predictive met hods. This paper reviews the possible effects of sea-level rise upon s oft-rock cliffs over a 50-100 year planning timescale. It evaluates di fferent methods of analysing historical recession and highlights the m ain assumptions and rules governing future extrapolation of retreat ra tes. Simple predictive models including a modification of the Bruun Ru le are developed and applied to estimate cliff sensitivity to sea-leve l rise in southern England. The complexity of factors interacting over variable spatial and temporal scales is identified as a major problem . Irrespective of sea-level rise, recession assessments need to accomm odate episodic cliff failures occurring within regular erosion cycles and differentiate instances of runaway systems change. Predictions mus t rely upon methods of extrapolating historical retreat. Different met hods are applicable according to the presence or absence of shoreface sediments. The modified Bruun Rule appears the most appropriate for si tuations where cliff sediments accumulate on the shore profile. Result s obtained using this model indicated that recession could increase by between 22% and 133% by 2050 according to site. Cliffs on exposed coa sts and those containing high proportions of clay appear the most sens itive to change. Attention is drawn to some of the inherent uncertaint ies including those caused by different landslide types, lags in respo nse and the effect of protective beaches.