Abstract

Chaaban, F.; Darwishe, H.; Battiau-Queney, Y.; Louche, B.; Masson, E.; El Khattabi, J., and Carlier, E., 2012. Using ArcGIS® Modelbuilder and aerial photographs to measure coastline retreat and advance: North of France.

Coastal areas are naturally dynamic with changes occurring over periods of time. When the shoreline moves landward, coastal erosion becomes a serious problem, and the rate of change has to be calculated. Coastline retreat is one of the best indicators of coastal erosion. Here, the geographic information systems (GIS) platform (ArcGIS® 9.3.1; Esri software) is used to study the long-term (last 59 years) shoreline change in the area of Hardelot-Plage and Sainte Cécile–Plage (a north–south 14-km-long beach), in northern France. The primary aim of this study was to develop a methodology for calculating shoreline change using ArcGIS Modelbuilder and aerial photographs. Changes in 14 coastlines over the course of 59 years (from 1946 to 2005) were digitized and represented in ArcGIS 9.3.1 platform. Two hundred and ninety-two transects perpendicular to the shoreline were used to estimate coastal erosion and deduce the recession rate.

The Modelbuilders (two models) created and used in this work are generic models that can be used for geoprocessing linear features. One model can be used to ascertain the intersection between linear features (transects and shorelines), adding a new field to the attribute table and calculating the geometry of the intersection points. A second model can be used to add a new field to the attribute table and calculate the distance on the transect lines between the linear reference feature and other linear features, in this study between the baseline (established adjacent to the series of shoreline positions) and the shoreline. The results show that the shoreline change rates between 1947 and 2005 along the Hardelot and Sainte Cécile coasts are generally negative; 82.2% of transects have values less than zero (i.e., retreat) and outside of the error margin (±10 m). Nevertheless the shoreline change shows successive phases of advance and retreat over the same period.

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