Soil water movement in semi-arid climate. An isotopic investigation

Soil moisture movement in the arid region of Thar desert, Rajasthan, has been studied using the tritium tagging method. It was found that groundwater recharge in the area varies between 6-14% of the precipitation input. The important factors which control the groundwater recharge are: i) vegetation cover; ii) nature of surface soil; and iii) topography. It was found that groundwater recharge is higher in the regions of shifting unconsolidated sands as compared to stabilised sand dunes having vegetation cover. In addition, a slight inclination of the land surface results in considerable reduction in the soil moisture transfer as compared to flat areas or areas which are situated in slight depression. A simple conceptual model has been employed to understand the mechanism of soil moisture movement. The model involves estimation of precipitation excess for individual months taking into account the requirement of soil moisture storage and evapotranspiration. Using this model, the computed groundwater recharge for the semi-arid regions of Gujarat has been found to be in very good agreement with the experimental values obtained by the tritium tagging method. (author)