Bifurcation Patterns in Linear Dunes

Abstract:

This study aims to understand the pattern of bifurcations in linear sand dunes and analyzed the relationship of local boundary conditions to the bifurcation pattern. Bifurcations, or “Y-junctions”, in fields of linear dunes represent interactions between the bedforms and disrupt the pattern of straight, parallel crestlines. Y-junctions have been suggested to open primarily in the upwind direction, but inspection of dune-fields on Earth shows that this is often not the case. In this study, the directions of bifurcations were mapped in a survey of fifteen dune fields. The distribution of up- and downwind opening bifurcations was compared with enhanced vegetation indices (EVI), vegetation modal percentages, dune spacing, grain size, and wind regime collected from various sources. The wind data for each location were filtered to sample only sand-transporting winds. The proportion of upwind-opening bifurcations in the studied dune fields ranges from 1% to 100%. The sixteen dunes mapped were split into two groups based on EVI; a non-vegetated and vegetated group. Within the vegetated dunes, we found dune fields with less vegetation variability between the dunes and interdune had more unidirectional Y-junctions while dune fields with more vegetation variability had more bidirectional Y-junctions.