Development of a Process-Based Model of the Effects of Variable Lithology: An Isle of Wight Case Study

Process-based numerical modelling of soft rock cliffs is an important tool for predicting future rates of retreat. This is particularly important considering the potential impacts in climatic and environmental change. However, many existing model are criticised for the generalised manner in which the soft cliff system and retreat process is described. One key issue is the assumption of uniform vertical lithology when most natural cliffs are composed of interbedded stratigraphy of varying strength and composition. In response, this paper describes modifications to the 2D SCAPE (Soft Cliff and Platform Erosion) model to explore the influence of horizontal layers of varying material strength along a study frontage on the south west coast of the Isle of Wight, UK. Model validation against measured shore and bathymetric profiles of the study frontage has demonstrated improved fit when the effects of more resistant layers within the profile are incorporated into the model. Such layers influence the geomorphology of the profile, forming emergent ledge features which experience reduced erosion and increased profile slope with increasing resistance. The outcropping of such layers with respect to mean sea level is recognised as a key control on rates of cliff toe recession owing to the integrated erosive potential of the tide. Therefore, model results have highlighted the importance of considering interactions between layers of variable material strength and sea-level rise. As a consequence, the results highlight the important implications for studies involving historical extrapolation of retreat rates for coasts of interbedded stratigraphies.