Quantification of the Normandy and Picardy chalk cliff retreat by photogrammetric analysis
S. Costa, D. Delahaye, S. Freiré-Diaz, L. Di Nocera, R. Davidson, E. Plessis, 2004. "Quantification of the Normandy and Picardy chalk cliff retreat by photogrammetric analysis", Coastal Chalk Cliff Instability, R. N. Mortimore, A. Duperret
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The chalk cliffs of Normandy and Picardy are retreating rapidly and approaching the built-up areas located near the shore. Previous studies of cliff retreat in this area suffer from a large margin of error (absolute error in cliff position is ±7m) due to the techniques and methods used. This paper présents a recent study which aims to quantify the chalk cliff retreat between 1966 and 1995 by means of photogrammetric analysis. In addition to the very high accuracy of the results (absolute error in cliff position is ±0.3 m), this technique gives geo-referenced numeric data allowing the creation of a geographical databank intended to become a tool for hazard management in coastal zones. Three scales of analysis have been used: a retreat value per hydro-sedimentary cell, per sub-cell and one every 50m. These scales show that this regressive dynamic is spatially very variable. However, three zones of distinct retreat rates are apparent. These appear to be linked with the lithological characteristics of the chalk. Furthermore, the quantification associated with the flint content of the cliff allows an assessment of the flint shingle provision from the cliff to the shore.
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Most of the rocky coastlines around the world are subject to active erosion processes. Because of the growing hazard to local communities from coastal cliff retreat, it is necessary to investigate where, when and how cliffs collapse. The results of these studies are vital for the planners and local authorities responsible for safety and access to cliffs and beaches. This volume focuses on the coastal chalk cliffs of the English Channel, where a multidisciplinary approach has been used to understand active coastal cliff recession.
The book is organized around three main themes: the geological factors controlling cliff instability, the marine parameters influencing coastal erosion and the use of some new tools for hazard assessments.
This volume will be of use to academics and professionals working on rocky shores, with an interest in sedimentary geology, stratigraphy, tectonics, geomorphology, engineering geology, coastal engineering and GIS.