Comparison between the United States Soil Conservation Service (SCS) and the two models commonly used for estimating rainfall-runoff in south-eastern Botswana

The United States Soil Conservation Service ( SCS) curve number method is used to estimate rainfall runoff from three watersheds in South-Eastern Botswana. This approach uses the NASA Endeavour Shuttle Radar Topography Mission DEMs, digital soil data from the Botswana Ministry of Agriculture, rainfall data from the Department of Meteoro-Services and land-use data derived from Landsat ETM+ imagery. Runoff predicted from the SCS method is compared the runoff calculated using the Pitman and Monash models and the gauged runoff. The Thagale River system watershed a mean annual volume of 7.2 Mm(3) while the Notwane and Metsimotlhabe runoff volumes are 19.9 Mm(3) and 17.8 respectively. The SCS Model is found to be either over- or under- estimating the mean annual runoff volumes found using other two models. It is concluded that more mean annual runoff volumes should be established for the whole country using three models and a correlation analysis made in order to determine the superior model. The SCS Model uses a lot of Earth (EO) and other data found in different government departments, hence this encourages collaboration. It is further that the SCS Model is quick to produce results, does not require stream gauging and can also easily be updated as the land use/land cover changes.