The importance of grain-related shear velocity in predicting multi-monthly dune growth

This study assesses the accuracy of the aeolian transport model proposed by van Rijn and Strypsteen in 2020 in predicting sediment transport rates for dune growth, with a focus on the importance of grain-related shear velocity. A 9-month dataset of local and regional wind characteristics and dune growth from a new artificial dune with planted marram grass in an environment with minor supply limitations was analysed. The study site is located in Oosteroever, Belgium. The results revealed that utilizing local measured overall shear velocities resulted in significant overprediction of dune volume changes. Incorporating sub-models for grain-related bed roughness and shear velocity improved the predictions of dune growth drastically with high statistical results (r² = 0.98 and RMSE = 0.64 m³/m). The primary driver contributing to dune growth at the study site was due to oblique onshore moderate winds of 10 m/s, as revealed from a frequency-magnitude analysis. The model could be used with either local wind measurements or regional data transformed to local beach conditions. The study highlights the importance of considering grain-related shear velocity in future studies to improve the prediction of sand transport rates and enhance our understanding of dune evolution.