ECOHYDROLOGICAL--EROSION MODEL FOR SEMI-ARID MOUNTAIN CATCHMENT USING GIS TECHNIQUES: A CASE STUDY--WADI SURDUD CATCHMENT, REPUBLIC OF YEMEN.

An ecohydrological-erosion model for semi-arid mountain catchment has been developed and integrated with rainfall-runoff model for estimating upland delivery rates of sediments resulted from individual storm at the outlet of Wadi Surdud catchment (2370 km2), Tihama, Yemen. The degradation of soil resources in the mountainous areas of Yemen is evident due to long-term and intensive human impacts on those vulnerable ecological environments of the indigenous terraces. If current trends continue, Yemen may permanently lose a significant portion of its productive land to soil erosion due to lack of preservation of indigenous soil and water conservation systems. This area has been degraded into nearly desert-like condition. Yet, geological and even historic data indicate that the natural ecological environments should be much better than it appears. To restore the ecological environment, we need to know its potentials. The erosion and sedimentation processes of the upland watersheds have to be assessed by means which do not rely on historical storm flow data. Methods that depend on available or measurable representative data were developed for a deterministic approach of the erosion process. This study takes advantage of physically based methods and Geographic Information Systems (GIS) and uses the Digital Elevation Model (DEM) and observed meteorological and hydrological data to model the runoff and sediment yield in an attempt to assess the potential natural ecological environments. Our results show that the effective Curve Number (CN) and soil detachability are the factors that determine the potential natural ecological environments. In this paper the study of runoff and sediment delivery is based on one stream gauging station and 10 rainfall gauging stations. Discharge was calculated for the period from July, 15, 1998 to October, 10, 1998 which resulted from 10 rainfall storms. A comparison of observed and predicted sediment yield shows a good agreement with a coefficient of determination of 0.85. [ABSTRACT FROM AUTHOR]