Evaluation of water supply potential from small watersheds in Yemen

Abstract

An overview is given for the general characteristics of the Republic of Yemen (ROY) related to water resources management and developments. The hydrological data needed for development processes of water supply projects in ROY are scarce or do not exist especially for small scale projects. For this case of inadequate data, some theoretical and empirical models used in evaluating resources potentials from small watersheds are presented through the different chapters and applied in Wadi Surdud catchment area as a case study. The applied models include SCS curve number method and the Modified Universal Soil Loss Equation (MUSLE). Direct runoff estimations were computed using the curve number method with daily rainfall data for 1988- 1992. For this estimate, the catchment area was divided into three basins, and the average rainfall was obtained using Thiessen polygon method. The annual water yields for each basin were obtained from the estimated direct runoff. These annual water yield volumes are then used in constructing the needed flow duration curves and in obtaining a runoff general equation with curves for extraction the equation's coefficient of each basin for different conditions ofCNs. Due to the deficiency of the required data for applying the MUSLE, it was applied only for basin# 2 in Wadi Surdud. The purpose of this application was to demonstrate the procedures for determining the different variables of the equation and for developing general curves for use in estimating the sediment yield directly from the relationship between the peak flows and the cropping factor. The developed models of predicting both of water yields and sediment yields can be improved to produce more reliable results by obtaining more accurate data for Wadi Surdud.