Retreat rate of cliffs and scarps with different geological properties in various locations along the Estonian coast

Recently reported increased water depths and greater wave heights, perhaps associated with increased storminess, are likely to lead to more active changes, such as increased beach erosion, faster shoreline migration and sediment redistribution. A coastal environment particularly sensitive to the impact of sea-level rise is that of highly erodible cliffs and scarps. As structures are often built close to such formations, it is important to determine the retreat rate of cliffs and scarps. Among other things, knowing the retreat rate can help regulators plan coastal protection measures and can help property owners decide where to place their structures to avoid damage. The principal objective of the current study is to find and analyze the retreat rate of cliffs and scarps in several locations along the Estonian coast. Variable geological conditions, exposure to the sea and human influence are considered. The study was carried out in five different locations along the Estonian coast representing different geological properties, variable human influence and hydrodynamic conditions. Aerial photographs, orthophotos, RTK-GPS, leveling survey and archive data was used to measure the changes on the edges of the scarps and cliffs. It was found that the fastest rate of retreat appears on the location where the softest sediments are exposed to the roughest wave conditions – in Cape Kiipsaare. Here the yearly scarp-line retreat reached over 7 m/y (17 m3/y per meter of shoreline) which is faster than the fastest retreat rate of soft cliffs recorded anywhere else, but still two times lower in terms of the eroded volume of sediments.