A multi-scale and multi-disciplinary approach for the study and monitoring of rocky coastlines
Rendiconti Online della Società Geologica Italiana
Societá Geologica Italiana
Slope instability is one of the main natural hazards which can affect hard rock coastlines. Different failures mechanisms may be possible depending on the influence of the rock mass discrete fracture network and the relative orientation of the coastline: failures may be either discontinuity controlled or dominated by rock mass behaviour. Using the north coast of Cornwall as an example the paper presents a multi-scale and multi-disciplinary approach for study and monitoring of coastal instability. Several cliff failures have occurred in recent decades, indicating the need for further research and monitoring to reduce the risk to both infrastructures and persons. Analysis of multi-temporal aerial LiDAR data and orthophotos, available through the Channel Coastal Observatory, was undertaken to locate recent landslide failures. Three different LiDAR data sets, acquired from 2008 and 2014, were used to highlight failed areas and their geometry and orthophotos were used for subsequent validation. In addition, terrestrial LiDAR point clouds were also used to identify the structural and geomorphic features that characterize these coasts; special emphasis was given to identification of joint sets, tension cracks and recent landslide headscarps. This information was then integrated with the available geological data to create a GeoDatabase using GIS techniques. This combined dataset was then used to select areas for more detailed (small-scale) study. These detailed studies included an engineering geological evaluation and use of terrestrial LiDAR and photogrammetric surveys. Data gained from these surveys were used to complement the slope geometry data obtained from aerial LiDAR and to provide further understanding of scale effects (differences between large scale structural studies performed with aerial remote sensing techniques and small scale studies with terrestrial remote sensing techniques). Finally, integration of data from both large and small scale studies was performed to undertake back analyses of the observed failures. These analyses were performed using a combination of conventional approaches and more sophisticated numerical simulations. The aerial and terrestrial LiDAR data was used to assist generation of numerical models. The geometry of the slope instabilities and the location of the identified (and active) tension cracks were then utilized to calibrate the numerical simulations. The results of these analyses are important to improve our understanding of coastal instability mechanisms and also provide a framework for understanding future coastal recession and factors controlling potential instability.
Abstract from 88th Congress of the Italian Geological Society, 2016-09-07, 2016-09-09, Naples
Vol. 40, Supplemento no. 1, p. 350