Maximum fluctuation of the shoreline due to tidal fluctuation, In: beach erosion monitoring - results from BEACHMED-e/ OpTIMAL Project

The advance of modern satellites (e.g. Quickbird, Ikonos) made possible to extract the “instantaneous” shoreline with a very good accuracy (1 to 3 pixels i.e. less than 2 m). The horizontal instantaneous shoreline shift, due to fluctuation of the sea surface elevation, is significant for beaches comprising fine sand and should always be taken into account when dealing with shorelines extracted from aerial or satellite images. In this paper a) we describe the methodology used to study this problem, b) we find the maximum error which is introduced when we assume that the instantaneous shoreline - extracted from satellite images - is identical to the MHWL shoreline, c) we give two empirical equations which can be used as a “rule of thumb” to calculate the maximum fluctuation of the horizontal position of the instantaneous shoreline, d) we suggest that by knowing the exact time that the image is taken, the mean grain size of the beach material and the sea surface fluctuation in the area under investigation, it is possible to correct the instantaneous shoreline to produce the MHWL shoreline.