Morphometric analysis of slipface processes of an aeolian dune: Implications for grain-flow dynamics

Grain flows are an integral part of sand dune migration; they are a direct response to the local wind regime and reflect complex interactions between localized over-steepening of a dune slipface and complex turbulent airflow on the lee slope. Grain flows are primarily responsible for delivering sediment to the base of a dune, thus driving slipface advancement; yet, there are few constraints on their morphological and spatial characteristics or the amount of sediment that is redistributed by these flows. Using a combination of high-resolution terrestrial laser scanning and video recordings, four distinct grain-flow types are identified based on morphology and area on a dune slipface. Grain-flow morphologies range from small, superficial flows to larger flows that affect greater portions of the slipface, moving significant amounts of sediment. Detailed field observations are presented of the dynamics of lee slopes, including measurements of the initiation location, thickness, magnitude and frequency statistics of grain flows, as well as volume estimates of redistributed sediment for each grain flow observed. High-resolution laser scans enable accurate quantification of bulk sediment transfer from individual grain flows and can be used to study grain flows in a variety of environments. A categorization of grain-flow morphologies is presented that links styles of flows with wind strength and direction, turbulent airflow, sediment deposition and environment.