Determining the Relation between Soil Erodibility and Spatial Variability of Erosion Properties Using Geostatistical Techniques at the Alqueva Reservoir Area

Soil erosion risk assessment at the watershed of Alqueva is urgently needed to conserve water resources and prevent the accelerated dam siltation. The variation of soil properties is one of the most important reasons for the spatial variability of vegetation cover and erosion. In order to achieve more and better management of rangelands around the largest reservoir of Europe, it is essential to evaluate how the soil properties as well plant cover in regard to the introduced change in distribution are estimated. Therefore, using geo-statistical techniques, this study was conducted to assess the relation of the spatial variability of soil erosion to soil properties. The statistical results showed that most variables had a normal distribution. Graphical interpretation of soil properties was performed using ordinary kriging. There were high correlation between vegetation cover, soil texture (sand and silt fraction), hydraulic conductivity and soil erodibility values. The lowest and the highest coefficient of variation were found with organic matter (2.17%) and vegetation cover (60.14%), respectively. The semi-variogram analysis showed that the effective range vary from 150m for silt to 20100m for the K of the soil, with optimal distance to determine erodibility the 1250m. The parameters of soil texture showed more spatial dependency than those of the organic matter. As a whole, the maps obtained by Kriging showed that the soil properties and spatial variability of vegetation cover did not have a random pattern and depended on the conditions of the region. Key-words: Spatial variability; erosion; Geostatistic; land-use change; global change; Alqueva dam.