Estimation of the surface runoff depth of Wadi Derna Basin by integrating the geographic information systems and Soil Conservation Service (SCS-CN) model

Abstract

Precipitation and runoff are the important hydrologic component in the water resources assessment. Many methods are available to estimate surface runoff from rainfall; however, the SCS-CN method remains the most popular and frequently used method as runoff curve number (CN) is a crucial factor of the SCS-CN method and depends on land use/land cover (LC/LU), soil type, and antecedent soil moisture (AMC). This approach with the geographic information system (GIS) was applied for estimating runoff volume of Wadi Derna Basin. Soil maps were processed and classified into hydrologic soil groups (HSG), where the dominant HSG in the study area is D. The HSG and LULC layers were intersected and the CN values and the weighted curve number for each antecedent moisture (AMC) condition were assigned. As a result of the model applied, the annual runoff volume for forty years during 1960–2000 in the study area was estimated by 138.51 Mm3. Furthermore, a volume flood has been estimated, based on the flood of October 1945 and late November 1986. Those events called for average precipitation of 145 and 64.14mm respectively. The rainfall of 1945 produced a volume flood of 53.36 Mm3, which represents 40 % of annual runoff volume, while the flood of November 1986 was 14.8 Mm3, which is in good agreement with the recorded flood in the basin. The results demonstrated that the study area has a high potential for flood risk. Therefore, dams of Wadi Derna basin is needed periodic maintenance. Moreover, increasing vegetation cover is required to reduce the phenomenon of desertification.