Implementation of a hydrologic model and GIS for estimating Wadi runoff in Dernah area, Al Jabal Al Akhadar, NE Libya

Abstract

This study has investigated the relationship between rainfall-runoff in Dernah area, Al Jabal Al Akhadar, NE Libya. It provides flash flood hazard warnings for ungauged basins using geographic information system (GIS). The study examined the morphometric parameters of four Wadis (Wadi Dernah, Wadi Bum Safer, Wadi Al Nagah and Wadi Bir Al Yajur) with emphasis on their implication for hydrologic processes through the integration analysis between morphometric parameters and GIS techniques. Data for this study were obtained from ASTER data for digital elevation model (DEM) with 30m resolution, topographic map (1:50,000), geological maps (1,250,000) which were checked during the field work. About 36 morphometric parameters were measured and calculated and interlinked to produce nine effective parameters for evaluating the flash flood hazard degree of the study area. The study basins are classified according to their hazards into three groups; Basins of low hazard degree (Wadi Al Nagah and Wadi Bir Al Yajur); Basins of medium hazard degree (Wadi Dernah); Basins of high hazard degree (Bum Safer). Software (SMADA 6) is applied to generate the hydrograph of subbasins of both medium and high hazard degrees. As a result of the model applied to Wadi Dernah, rainfall events of a total of 60, 70, 90, 110 and 120mm of return periods 5, 10, 25, 50 and 100years produce a discharge volume of 9.1×10 6, 13.5×10 6, 22.3×10 6, 34.0×10 6 and 39.7×10 6 m 3 respectively. While in case of Wadi Bum Safer the discharge volume is 22.1×10 6, 30.5×10 6, 46.1×10 6, 65.6×10 6 and 74.8×10 6 m 3.