Application of a hydrological model in a data-poor arid region catchment: a case study of Wadi Ham, United Arab Emirates

Many arid region Wadi catchments are facing increasing water scarcity due tothe unsustainable human practises such as the over expansion of irrigatedagriculture and over exploitation of their groundwater aquifers.The “Soil and Water Assessment Tool” (SWAT) model, which is acomprehensive conceptual, semi-distributed watershed scale model, wasselected after a review of the hydrological processes occurring in arid regioncatchments to simulate the hydrological processes of the Wadi Ham catchmentin northeast United Arab Emirates.A sensitivity analysis conducted for SWAT for the total runoff, maximum runoffand days of runoff showed that a DEM resolution of no more than 100 m shouldbe used for proper representation of such mountainous arid catchments. Theappropriate size of defined sub-basins was found to be about 18 km2. Thesensitivity analysis also demonstrated that the most sensitive parameters thataffect the ephemeral streamflow are mainly related to the soil and channelproperties of the catchment soil depth, soil available water capacity, soil bulkdensity, soil clay percentage, soil curve number, baseflow recession constantand channel effective hydraulic conductivity.SWAT simulated the ephemeral streamflow in Wadi Ham acceptably. For thecalibration period of 1981 and 1982, the performance statistics for DRMS,PBIAS, NSE and PEM were 1.10 m3/s, 27.12%, 0.78 and 0.80 respectively.During the validation period between 1983 and 1988, the DRMS, PBIAS, NSEand PEM were 0.93 m3/s, -27.30%, 0.57 and 0.70 respectively. SWAT showedvery plausible behaviour for reservoir sedimentation, plant growth, irrigation abstraction and groundwater recharge via the transmission losses mechanism.However, SWAT was not able to adequately simulate the recharge from thebottom of the recharge dam reservoir due to an inappropriate maximumeffective hydraulic conductivity defined by the model.Two management scenarios were simulated. The first scenario related to theconstruction of an additional dam upstream and its effect on sedimentation ratein the main reservoir. The second scenario found that the recharge volumescould be enhanced through the construction of a discharge inlet point into themain stream channel for the treated wastewater from the principal townupstream of the catchment.The successful simulation of Wadi Ham represents the first use of SWAT in atruly arid climate. This research has therefore established the feasibility ofusing SWAT as a tool for integrated catchment modelling in arid region data-poor Wadi catchments and to support improved water resources managementin this water stressed environment.