CN-REM: A GIS MODEL FOR RAINFALL-RUNOFF ESTIMATION USING A SOIL CONSERVATION SERVICE METHOD

Visual BASIC for Applications (VBA) programming language techniques were used to formulate a computer model to be run under ArcMap software environment. Formulated Curve Number-Runoff Estimation Model (CN-REM) is formulated and tested to read input data in the form of digital maps (soil types, land uses and rainfall) for any study area. This procedure allows determination of the Curve Number (CN) for each polygon according to the Soil Conservation Service (SCS) method, developed by United States Department of Agriculture (USDA). Determination of CN is also based on antecedent moisture conditions (AMC) for the soil. Determined CN values were added as a new data field to be used for runoff discharge estimation for the whole area. This enables production of results in the form of a new map. Testing and operation of model was done for Greater Darfur area in western Sudan. Darfur was chosen as a study area for the importance of its hydrological study, and availability of water resources within this arid zone. Use of such maps enables proper planning of various water harvesting projects in the area.Analysis of produced maps emphasized the use of formulated CN-REM rather than relying on laborious manual processes. Time loss was dramatically reduced and resultant maps were highly adequate