Spatial Distribution Of Runoff In Ungauged Catchments In Tanzania

Abstract

This paper presents a preliminary map of average annual runoff of Tanzania using a conceptual rainfall runoff model to predict the amount of water directed to base flow of the rivers with the application of Geographic Information System (GIS). Average annual runoff is a fundamental hydrological variable which serves many purposes in hydrological research particularly in stream flow estimation for hydropower plant allocation and development. Still the runoff data can serve during irrigation and flood control situation. The Pacific Southwest Inter-Agency Committee (PSIAC) model was utilized to rate the surface geology, soil-infiltration rate, topography, ground cover, land use, upland and channel erosions parameters which have been applied to estimate the Curve Number (CN). Subsequently, CN and rainfall data have been employed in the Soil Conservation Service (SCS) runoff equation to estimate the direct runoff data. The results of the study show the combination of PSIAC and SCS models were useful in studying of runoff response of the Tanzania’s catchments. Once the preliminary runoff map was evaluated depends on the three climate zones of Tanzania indicated to have high annual runoff in wet zone compared with moderate and dry zones. The runoff map can be applied during preliminary study, however the author acknowledged the primary source of data for the average annual runoff estimation is preferable to be taken at the gauged river flow stations.