Hydrological processes and water resources management in a dryland environment II: Surface redistribution of rainfall within fields

摘要

Soil water movement was studied within fields on two different soil types, ared clay soil and a duplex soil of sand over clay, at the Romwe Catchment insouthern Zimbabwe. Each study site comprised two fields and formed a surfacewater sub-catchment (1.0-2.4 ha) from which runoff was gauged. Soil moisture wasmeasured in-situ at up to 20 locations within each sub-catchment over anentire cropping season and the following dry season. Maize was cultivated atboth sites according to the farmers' normal cropping practice and crop yieldswere recorded.Surface redistribution of rainfall through localised runon and runoff was shownto be an important process in both sub-catchments with rainfall concentrationfactors between 0.2 and 2.7 for major rainfall events. This process was a keyfactor controlling deep drainage to groundwater. Results indicate that surfacewater redistribution is of particular importance for groundwater recharge inyears with low or evenly distributed rainfall, when it would not otherwise haveoccurred. The soil water conditions created by surface redistribution ofrainfall are also actively exploited by farmers who vary cropping practiceswithin fields to maximise crop yields and reduce the risks of crop failure.