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.
Highlights
Coastal dunes provide safety against flooding during storm events
Compared to hard engineering structures like sea dykes, coastal dunes are in favor because they are primarily being built by natural aeolian processes [1,2,3]
This study examines how annual to decadal variations in wind climate correlate with annual to decadal variations in dune volume along the Belgian coast
Summary
Coastal dunes provide safety against flooding during storm events. They have functions for recreation and nature conservation. Coastal dune development studies generally focus on the measurement of short-term transport processes in the timescale of hours to days [9,10,11,12,13] Sometimes, at these timescales, a one to one relation is found between predicted and observed values [14]. Coastal dune development is frequently studied by the measurement of long-term topographical elevation variations in the timescale of months to years [8,10,15,16,17] These topographical elevation changes are related to calculated potential transport rates [18]. When coastal dune development and its relation with potential aeolian sediment transport is studied on decadal timescales, the effects of erosive and accretive years should eventually average out. To explain longshore variations of the correlations by distinguishing between ‘natural’ and ‘managed’ beach sections of the Belgian coast featuring dunes
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