The Impact of Unsaturated Zone Heterogeneity and Land Use/Cover on Groundwater Recharge: A Case Study of the Densu River Basin of Ghana

Characterisation of groundwater recharge in the Densu basin of Ghana has been undertaken and the extent of the effects of heterogeneity of the unsaturated zone on present and future groundwater recharge evaluated using a distributed physically based hydrological model (MIKE SHE Code) in a 1-D mode. The unsaturated zone flow was simulated using a fully implicit finite difference solution technique whereas the governing processes of the evapotranspiration are based on empirically derived equations. Within the framework of the 1-D model, it has been possible to demonstrate the sensitivity of groundwater recharge on land use/cover and soil types through vertical discretisation of the unsaturated zone according to a set of relevant properties determined through averaging of different sample points. The land use/cover was also classified in both space and time. The main aim of the study was to elucidate the effects of soil types and land use/cover on groundwater recharge and evapotranspiration. Vegetation dynamics from satellite images, root depths and the hydraulic properties in the form of the Van Genuchten model of the different soils were the main variables used as inputs in the model. With a constant precipitation rate, the exchanges of water between the Unsaturated and Saturated zones vary greatly from one set of combination of soil type and land use/cover to another set.