Simulation of the effect of wind speedup in the formation of transverse dune fields

A computer simulation model for transverse-dune-field dynamics, correspondi ng to a uni-directional wind regime, is developed. In a previous formulatio n, two distinct problems were found regarding the cross-sectional dune shap e, namely the erosion in the lee of dunes and the steepness of the windward slopes. The first problem is solved by introducing no erosion in shadow zo nes. The second issue is overcome by introducing a wind speedup (shear velo city increase) factor, which can be accounted for by adding a term to the o riginal transport length, which is proportional to the surface height. By i ncorporating these features we are able to model dunes whose individual sha pe and collective patterns are similar to those observed in nature. Moreove r we show how the introduction of a non-linear shear-velocity-increase term leads to the reduction of dune height, and this may result in an equilibri um dune field configuration. This is thought to be because the non-linear i ncrease of the transport length makes the sand trapping efficiency lower th an unity, even for higher dunes, so that the incoming and the outgoing sand flux are in balance. To fully describe the inter-dune morphology more prec ise dynamics in the lee of the dune must be incorporated. Copyright (C) 200 0 John Wiley & Sons, Ltd.