A preliminary estimation of groundwater recharge in Namman basin.

Abstract. In this paper, a simulation of a one-dimensional water movement in soil layers using Wave Model is presented. The model is utilized to investigate the groundwater recharge at varoius soil depths of Namman basin in western Saudi Arabia. The basin was divided into 35 sub-basins and the model was applied to the alluvial soils of the channels of the sub-basins. The study assumed that rainfall on moutainous areas of the basin will be transfered to the channels very fast and added to the direct rainfall as an accumulated water depth on the alluvium. Data of soil properties, soil-water relationship, rainfall and potential evaporation were collected for the study region and used by the model to estimate volumes of surface runoff, abstractions and groudwater recharge. Daily rainfall data for 1975 and 1980 which had largest and smallest annual rainfall depths during the period of the available rainfall records were used in the study. The results of the study indicated that values of infiltration rate were very high in most of the surface soil in the basin and their average was about 98% of rainfall volume. Most of runoff in Namman basin is produced by Yarij sub-basin and about a quarter of the hydrologic abstrations is contributed by Al-Shara sub-basin. Majareesh sub-basin has the largest contribution to groundwater rechage of Namman basin, while Arar and Yarij sub-basins have the smallest contributions. The study suggested a linear realtionship between groudwater recaharge volume and soil depth.