Block removal and step backwearing as erosion processes on rock shore platforms: A preliminary case study of the chalk shore platforms of south-east England

摘要

Shore platforms frequently exhibit steps or risers facing seaward, landwards or obliquely across-shore. A combination of soft copy photogrammetry, ortho-rectification, geo referencing and field measurement of step height are linked in a GIS environment to measure step retreat on chalk shore platforms at sample sites in the south of England over two periods, 1973-2001, 2001-2007. The methods used allow for the identification, delineation and measurement of historic change at high spatial resolution. The results suggest that while erosion of chalk shore platforms by step backwearing is highly variable, it appears to be of similar magnitude to surface downwearing of the same platforms measured by micro-erosion meters (MEMs) and laser scanning, in a range equivalent to 0·0006 - 0·0050my~(-1) of surface downwearing. This equates to annual chalk volume loss from the platforms, by the two erosion processes combined, of between 0·0012m~3m~(-2) and 0·0100m~3m~(-2). Results from the more recent years' data suggests that step retreat has variability in both space and time which does not relate solely to climatic variability. The results must be viewed with caution until much larger numbers of measurements have been made of both downwearing and step erosion at higher spatial and temporal resolution.