Abstract
The United States Soil Conservation Service (SCS) curve number method is used to estimate rainfall runoff from three sub-watersheds in South-Eastern Botswana. This approach uses the NASA Endeavour Shuttle Radar Topography Mission (SRTM) DEMs, digital soil data from the Botswana Ministry of Agriculture, rainfall data from the Department of Meteorological Services and land-use data derived from Landsat ETM+ imagery. Runoff predicted from the SCS method is compared with the runoff calculated using the Pitman and Monash models and the gauged runoff. The Thagale River system watershed produces a mean annual volume of 7.2 Mm3 while the Notwane and Metsimotlhabe runoff volumes are 19.9 Mm3 and 17.8 Mm3 respectively. The SCS Model is found to be either over- or under-estimating the mean annual runoff volumes found using the other two models. It is concluded that more mean annual runoff volumes should be established for the whole country using the three models and a correlation analysis made in order to determine the superior model. The SCS Model uses a lot of Earth Observation (EO) and other data found in different government departments, hence this encourages collaboration. It is further observed 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. Water SA Vol 32(1)pp:29-36
Highlights
Botswana is a totally landlocked country lying between latitudes 18oS and 27oS and longitudes 20oE and 29oE in Southern Africa
It is crucial that the watershed runoff or inflows, which are used as inputs for the modelling of water resources, are accurate as erroneous values could have serious implications
BNWMP (1991) concluded that the Monash Model was superior to the Pitman Model and it was adopted for water resource planning in Botswana
Summary
Botswana is a totally landlocked country lying between latitudes 18oS and 27oS and longitudes 20oE and 29oE in Southern Africa. Botswana covers about 528 000 km with a generally uniform topography varying from 600 m in the northeast of Tuli Block where the major rivers converge into the Limpopo River, to about a local maxima of 1 400 m. Botswana climate is described as arid to semi-arid with generally low and erratic rainfall. Because of the aridness of the country, the government of Botswana has invested heavily on studies to evaluate potential of water resources in the country. These studies are meant to indicate the water resources that could be developed to meet the ever-increasing water demands for domestic, industrial and agriculture use (BNWMP, 1991; NAMPAD, 2000). It is crucial that the watershed runoff or inflows, which are used as inputs for the modelling of water resources, are accurate as erroneous values could have serious implications
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