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Accueil du site → Doctorat → Royaume-Uni → 1990 → Groundwater evaluation in a part of the Asir Highlands, Saudi Arabia.

University of East Anglia (1990)

Groundwater evaluation in a part of the Asir Highlands, Saudi Arabia.

Al-Yamani, Mahmoud S.

Titre : Groundwater evaluation in a part of the Asir Highlands, Saudi Arabia.

Auteur : Al-Yamani, Mahmoud S.

Université de soutenance : University of East Anglia

Grade : Doctor of Philosophy (PhD) 1990

The thesis describes the groundwater resources around Wadi Binhashbal village, in the southern province of Saudi Arabia which was selected to be representative of a wider area. Geological and hydrological data were collected and original geophysical investigations were made of the size, depth and extent of alluvial and bedrock aquifers. Studies of the hydrogeology and hydrochemistry of the groundwaters allowed a detailed conceptual model of groundwater flow in the area to be drawn up, and a tentative estimate of recharge and overall groundwater resources made. The area is underlain by crystalline rocks. The fractured and weathered parts of the bedrock constitute a major aquifer. A second aquifer is made up of the alluvial sediments on wadi floors. The two aquifers are hydraulically connected with groundwater flow generally moving from the bedrock to the alluvium. After a brief description of the background to the study in chapter 1, chapter 2 describes the geology and topography. In chapter 3 the hydrological data on rainfall, evaporation and runoff for the area is collected. The average rainfall is 232mm over the study area, and runoff generated by intense falls causes floods which are a major source of recharge to the wadi aquifer. The aquifer geometry is investigated by electrical resistivity soundings in chapter 4. The wadi and bedrock aquifers are both strongly affected by the varying degree of weathering and depth to rock head, which causes groundwater to be ponded in a series of closed basin-like aquifer bodies. In chapter 5 the hydrogeological properties (hydraulic conductivity, transmissivity, storativity and porosity) of both aquifers are assessed by means of measurements on laboratory samples and pumping tests in the field. A crude estimate is made of average annual recharge by combining the chloride budget method with hydrological data and wadi aquifer geometry. Average annual recharge is about 2.03m for the wadi alluvium, 1.74mm for the bedrock aquifer and 50mm as an average for the whole area. Chapter 6 gives the results of a chemical and isotopic survey of the groundwater which are used to develop a conceptual model of the hydrogeology. Evaporation and weathering reactions dominate the groundwater’s chemical evolution. Isotope studies show that much of the dissolved solids content of the water consists of salts which have been precipitated on or near the surface by evaporation of light to moderate falls of rain, then flushed into the aquifer by heavy rainfall. Groundwaters are also subjected to direct evaporation wherever the water table is close to the surface, especially in wadis. In the final chapter, further research requirements for monitoring water quality and planning the development of groundwater are discussed

Présentation : EThOS (UK)

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