Influence of aspect on sediments and runoff production in semiarid environments

Abstract

By means of experiments with simulated rainfall the influence of aspect on runoff and erosion dynamics is analysed in a basin where the vegetation is distributed within a mosaic of Stipa tenacissima L. shrubs and inter-shrubs. In the inter-shrubs areas three different types of areas exist: Stone pavement (with rack fragments), Crusted surfaces (with surface crust) and vegetation covered areas (Brachypodium retusum). The erosion and runoff rates are very low beneath the vegetation (Esparto tussocks and Brachypodium retusum grass), while in the intershrubs areas (Crusted and Stone pavement) rates are higher. The vegetation controls runoff generation through its effect on the infiltration rates. Both runoff and erosion processes are influenced by aspect. The northjacing slopes have higher infiltration rates, and runojf is attenuated and reduced. The soil losses are neglegible in compararison to the southjacing slope. Vegetation cover is inversely and non-linearly related to the volume of overland flow, and the relationship exhibit a threshold due to the patch distribution of the vegetation. Modelling and predictioning the geomorphological processes under semiarid conditions is very complicated due to the high spatial variability of bis factors, specially the vegetation.