Impact of farm dams on river flows; A case study in the Limpopo River basin, Southern Africa

The study analysed the impact of a farm dam on the river flow in the Limpopo River basin. Two methods are used to calculate the water inflow: one uses the runoff component from the catchment water balance; the other uses the drainage output of the SIMFLOW model. The impact on the flow in a sub-catchment with and without the presence of a farm dam, has been analysed. Different farm dam storage capacities and infiltration rates of the soil were considered. In general, the change in natural flow is decreasing when the farm dam capacity becomes higher. On the other hand, the Remaining Natural Flow is increasing when the catchment area becomes larger. The Crop Water Availability was expressed as the relative difference between the crop water requirements and the amount of water supplied by precipitation and irrigation from the farm dam. For a given storage capacity of the farm dam the change in natural flow is calculated when the farm dam covers 90% of the potential evapotranspiration of maize.