DUNE MIGRATION AND AEOLIAN TRANSPORT ALONG CEARÁ STATE, BRAZIL: DOWNSCALING AND UPSCALING AEOLIAN INDUCED PROCESSES

Abstract

Dune evolution and aeolian sediment transport have been studied along the coast of Ceara State, Brazil. Barchan dune fields were found to be in equilibrium, with morphometric relationships such as H/W and W/L being constant in the area. Dune migration rates depend on dune size, with migration rates decreasing as dune size increases. Barchans in Jericoacoara beach migrate at an average rate of 17.5 m.yr-1 whereas sand-sheets do it at 10.0 m.yr-1. This dependence stresses the existence of equilibrium in the dune field, i.e. a constant aeolian transport exists and dunes migrate according to their sand volume. Aggregated sediment transport obtained from dune migration was in the order of 78 m3 /m/yr for barchan fields in Jericoacoara beach and 89 m3 /m/yr in Pecem beach and it was found to be uncorrelated with dune size. When the aeolian transport was calculated by using a predictive model as a function of a power of the wind velocity and results were integrated at a yearly scale a maximum difference of 30% was obtained. This agreement between the two approaches to estimate yearly aeolian transport was associated with specific climatological conditions in the area, i.e. wind direction restricted to easterly components and rainfall concentrated in few months.