Dune volume changes at decadal timescales and its relation with potential aeolian transport

Abstract

Long-term changes in dune volume at the Belgian coast are analyzed based on measured data by airborne surveys available from 1979. For most of the 65 km long coastal stretch, dune volume increases linearly in time at a constant rate. Dune growth varies between 0-12.3 m3/m/year with an average dune growth of 6.2 m3/m/year, featuring large variations in longshore directions. Based on a wind data set from 2000-2017, it is found that potential aeolian sediment transport has its main drift from the west to southwest direction (onshore to oblique onshore). Based on a modified Bagnold model, onshore potential aeolian sediment transport ranges to a maximum of 9 m3/m/year, while longshore potential aeolian sediment transport could reach up to 20 m3/m/year. We found an important correlation between observed and predicted dune development at decadal timescales when zones with dune management activities are excluded. Most of the predicted data are within a factor of two of the measured values. The variability in potential transport is well related to the variability in dune volume changes at the considered spatial-temporal scale, suggesting that natural dune growth is primarily caused by aeolian sediment transport from the beach. It also suggests that annual differences in forcing and transport limiting conditions (wind and moisture) only have a modest effect on the overall variability of dune volume trends.