AbstractInvestigation of cliff recession along 20km of the West Wales coastline has recognised erosion processes and mechanisms. Cartographic evidence has established considerable spatial variability in long-term retreat rates between the solid rock sections and those of tills and glacial clays. Mean contemporary recession rates of 13cm yr1 have been measured in the glacial embayments where storm wave action is considered the primary direct agent initiating cliff erosion. Morphological evidence suggests that different mechanisms have produced recession in other areas.
Cardigan Bay is a medium-to-high energy storm-wave dominated environment receiving on average twelve storms per year. A wave-hindcast 5 procedure provided measures of storm intensity (maximum value of 4.8x10 5 Joules/m crest width), those from the north-westerly quadrant contributing 82% of all destructive waves. Climatic and tidal influences were assessed in terms of tidal coverage of different cliff heights along the coastline.
Theoretical wave refraction modelling has predicted a series of longshore residual littoral sediment cells. The position of such cell boundaries in terms of 'high' and 'low' beaches has been assessed by extensive field surveys. Longshore variation in beach levels was considered to be constant over the study period while changes in 'sweep' zones were seasonal though single storm events did result in a significant lowering of beach level by up to 1.5m.
Field and laboratory determination of basic physical properties of the tills did not differentiate between them although inherent variations of grading were found within each till unit. Comparative values of uniaxial compressive strength were obtained to represent the geotechnical properties of the various cliff materials.
Temporal and spatial variation in erosion rates were considered to be a function of environmental, beach and cliff factors. The significance of each factor was tested statistically using stepwise multiple regression. Beach volumes were most significant in explaining spatial variation whereas no consistent relations hip was evident for strength of materials.
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