Abstract
Due to permanent dry conditions in arid land basins, channels experience a great quantity of water loss during the runoff process. The objective of this study is to quantify and delineate the spatial variability of channel losses over the contributing area of the upstream side of Wadi Al-Lith, in the western region of Saudi Arabia, by using Muskingum-Cunge flow routing method. HEC-HMS model was used here to simulate rainfall-runoff relationship, to route flood hydrograph, and to determine losses in the channel network of the basin. The required geomorphological parameters such as channel's geometry, roughness coefficient, and slopes obtained from GIS and field measurements. The model was calibrated and validated on real rainfall-runoff events and the optimized parameters were generalized. Results showed that both calibrated and validated hydrographs are in good agreement with observed hydrographs. Channel constituted the highest losses from the total rainfall and that these losses increased as the basin area increased and the slope decreased. The maximum percentage loss was 47.3% and the minimum percentage loss was 2.1%. Although these losses are from surface water, at the same time these losses are considered as gains to the subsurface storage. Therefore, such losses and gains should be considered in the water resources planning and management formulation.