Coastal dune behavior and the role of sediment supply in the aeolian system

Abstract

This thesis explores the nature of coastal dune behavior and the role of sediment supply in the aeolian system. The first part of the thesis conducts a data analysis based on the Dutch JARKUS dataset, which provides yearly measured profiles along the Dutch coast. A series of parameters derived from the profile measurements have been used to represent the dune behavior quantitatively. Two locations with different coastal orientations, the Rijnland and Ameland coasts, have been studied. The theoretical wind transport capacity calculated for the two coasts showed very different results, where the transport capacity in cross shore direction for Ameland was found offshore dominant with very small onshore component while the one for Rijnland was found onshore dominant with much larger onshore component. The calculated actual dune growth rates along the two coasts had much less values than the transport capacity but demonstrated similar trend: Rijnland experienced more dune accretion than Ameland. The spatial variations in coastal morphology derived from the measurements have been correlated to the alongshore varying dune behavior, showing that a larger dune accretion is usually linked to a wider active dune but no obvious relationship can be identified between beach width and dune growth rate. The second part of the thesis discusses a modeling study using the AeoLiS model. The inconsistency between the actual dune accretion and the theoretical onshore wind transport capacity was probably because the sediment availability dominated the aeolian sediment transport, which inspired an attempt to analyze the role of sediment supply in the aeolian system through a modeling study. Therefore AeoLiS has been used to simulate aeolian sediment transport, dune volume changes and the combined effect of erosion and accretion processes in the coastal systems. In the modeling study, 11 scenarios have been simulated. By comparing the simulation results of the different scenarios, the influences of several different processes on the aeolian sediment transport have been analyzed. Dune vegetation was found to be necessary to acquire dune accretion. Sediment sorting and beach armoring were found to be able to significantly reduce the aeolian sediment transport, indicating the important role of sediment supply in the aeolian system. And the more the nonerodible roughness elements existed on the bed, the more the aeolian transport could be reduced. In the onshore wind dominant system, the existence of the offshore wind reduced the onshore aeolian transport in the model. In the offshore wind dominant system, the offshore wind needed to be filtered out to enable the model to reproduce the pattern of onshore aeolian transport and dune accretion. For Rijnland which experienced mainly onshore winds, the modeled dune accretion volume was relatively larger than the measured dune accretion based on the data analysis. For Ameland where the present winds were mainly offshore, the simulated and measured dune accretion volumes were quite close. Similar to the trends in the wind transport capacity and the dune growth rate, the modeled dune accretion volume for Rijnland was also larger than the one for Ameland.