Abstract
In the absence of permanent rivers, groundwater is one of the major water resources in Southern Tihama plain, in the Southwestern Saudi Arabia. Hydrogeological investigation, as well as hydrogeochemical analyses, of 272 groundwater samples was performed to evaluate groundwater resources of shallow alluvial aquifer and their quality for different purposes in the Southern Tihama plain. Hydrogeological investigation revealed that groundwater occurs mainly in alluvium deposits under free water table conditions that range between 9 and 33 m. The calculated hydraulic gradient is inclined towards the west and southwest direction, ranging from 0.001 to 0.005, and soil infiltration rate of coastal plain soils is higher than other soil types. Hydrochemical analysis results indicate that groundwater type is mainly sodium chloride reflecting high amount of minerals. Groundwater in Tihama plain is not suitable for direct drinking and domestic purposes; therefore, it needs a proper treatment to remove high salinity and chloride concentrations. Result also shows that most of the groundwater has high salinity and low sodium hazard, suggesting little danger of exchangeable sodium. Other quality indices such as salinity, chloride, sulfate, and alkalinity range from suitable to high restricting water suitability for some industrial purposes without special treatment or mixing with low saline water.