Abstract
The present study aimed to develop an integrated approach that utilized field geology, remote sensing and airborne magnetic data to identify the Quaternary aquifers impounded by dykes and explain the dykes/lineaments relationship and their effects on the storage and flow of the groundwater of Sadiyah sub-basin, lower part of Wadi Yalamlam basin, Western Arabian Shield, Saudi Arabia. Field visits supported by Landsat ETM+ratio images (5/7, 5/4 and 5/1) revealed the presence of three main dyke types that can be chronologically arranged from older to younger as: Sheared mafic and acidic dykes (D1); Damm dyke complex (D2); and Ghumayqah dykes (D3). Two dykes referred to the first type (D1) were traced with depth using airborne magnetic survey crosscutting the main course of Wadi Yalamlam around Sadiyah village at high angle. According to water table elevation measurements, the aquifer of lower Wadi Yalamlam area is divided into three parts namely I, II and III. The water table elevations decreased from 158 m in the first part (I) to reach 66 m in the third part (III) of the aquifer. This drop is attributed to the effect of dykes which act as natural barriers. The study area was affected by three major fault systems as confirmed by field study and total magnetic map. Two of these systems have NE-SW to ENE-WSW and N-S to NNW-SSE directions, whereas the third one represents the Najd fault system trends in NW-SE direction. The present study identifies two locations valid for agricultural expansion lie just to the north of Sheikh Said and Abu Helal Farms.