Erosion of the chalk coastal cliffs at Birling Gap, Sussex, UK. Correlation between rate of coastal retreat, geotechnical rocks properties and precipitation

Birling Gap forms part of the Seven Sister cliffs, East Sussex, UK. Geotechnically the area is characterized by the presence of a Devensian paleovalley developed in a shallow syncline within the Seaford Chalk Formation. It is a dynamic coast line which is subject to continual erosion. A detailed survey has been undertaken along the coast of Birling Gap from 1950 to 2000. Using these data, the spatial information is translated into geospatial elements of an ArcGIS platform. The geo-referencing process defines the position of the cliff in a specific period. Aerial photos and most recent mapping survey are used to extend and complete the temporal analysis to the 21st century. The outputs show that mean rate of coast retreat is 0.54 m/y and circa 30 m of coast has been lost in the last 60 years. Analysing the pluviometry data, it is possible to establish a relation between peak precipitation and high rates of coastal retreat. Higher rates of retreat are measured on the central portion of the studied area which is characterized by the deeply weathered paleovalley, which differs geotechnically from the surrounding more competent, less weathered chalk. The study shows how an accurate mapping survey translated into a GIS database can be a useful tool to understand the temporal geodynamic and hydrodynamic evolution of coastal environments. This work quantifies rapid erosion along this part of our chalk coastline and identifies that erosion is higher during periods of prolonged increased precipitation.