Hydrological processes and water resources management in a dryland environment. III, groundwater recharge and recession in a shallow weathered aquifer

In crystalline basement regions of Africa, shallow weathered aquifers provide vital water resources for rural communities. To quantify evidence of the behaviour of these shallow aquifers, groundwater levels were observed at a network of 65 boreholes within the Romwe Catchment in southern Zimbabwe. Soil moisture was monitored at selected sites. Groundwater hydrographs showed considerable spatial and temporal variation. Where the soil profile was freely draining, groundwater levels typically responded within a few days of major rainstorms and large annual fluctuations in the water table of up to 7 m were recorded. In areas where a thick clay layer exists, annual fluctuations were smaller and groundwater levels rose more gradually in response to rainfall. In cultivated areas, vertical drainage was an important recharge mechanism. Groundwater hydrographs typically have an exponential recession and, by the end of the dry season in the years studied, levels were close to the base of the weathered aquifer. Variations in hydrograph response between years illustrate the importance of rainfall amount, intensity and distribution on groundwater recharge.