Assessing sandy beach width variations on intertidal time scales using permanent laser scanning

Abstract

[EN] Coastal zones are highly dynamic, and their topography is subject to constant deformation. These deformations are governed by sediment transports that are forced by environmental conditions of waves, tides and wind which result in topographic changes at various spatial and temporal scales. In the view of climate change and intensification of extreme weather events, it is important for coastal management to monitor the deformation and coastal topography with high accuracy. To demonstrate a novel way of deriving these deformations and of analyzing the underlying processes, we use permanent laser scanning (PLS) to monitor part of the typical urban coastal beach in Noordwijk, The Netherlands. A laser scanner permanently installed on a hotel building acquired one 3D point cloud of the sandy beach and dunes every hour, continuously, for a duration of two years. The resulting spatio-temporal data set consists of ~ 15 000 point clouds and contains the evolution of a section of the coast of ~ 1 km length at great detail. The elevation changes are observed at centimeter level, allowing to monitor even small scale and slow processes. However, this information is not readily available from the extensive data set. By deriving digital elevation models (DEMs) from each point cloud and collecting elevation data as time series per spatial grid cell, we structure the data in an efficient way. We use the DEMs to estimate two parameters describing the coastal deformation, beach width and intertidal width. We also extract the shoreline at low and high tide for a part of the data set and estimate beach width and intertidal width from them. We find that heavy storms influence the location of the shoreline and the intertidal width in particular. Ultimately, the estimated beach width and intertidal width at high temporal frequency (monthly) and with high spatial accuracy (meters) helps coastal management to improve the understanding of coastal deformation processes.