Hydrochemical Characteristics of Groundwater in the Usfan Basin, Saudi Arabia

Abstract

The Usfan basin. covering some 2.000 krn-, includes two main plains in addition to a number of wadis. These wadis drain varied rock types and geomorphological features , crossing alternate horsts and grabens which are parallel to the Red Sea Rift. Representative groundwater samples were collected from 21 sites in the wadis and plains . Adjacent to 12 of these sites. geophysical measurements were made to deduce their geoelectric sequences, The samples were analysed for major dissolved cations and anions content in the laboratory . with the specific conductance for e ach well being measured in situ, The variation in TDS and concentration of the component ions dissolved in the groundwater along the course ofeach wadi and plain are interpreted in relation to the lithology of the aquifers. Construction of a linear bilogarithmic relationship between the specific conductance and both TDS (mgIL) and ~ ions (epm), allows a const ant to be deduced with maximum error ±9% of the actual values , Groundwater in the Usfan basin generally is of a chloride type with a predominance of Na though a few except ions trend towards a sulphate typc with dominant Ca-Mg, The groundwaters of wadis Haddat ash Sham and Shamiya, as well as those of Usfan Plain. are of secondary salinity hydrochemical facies, but thoseofBayadah plain and Wadi Ghulah are of primary salinity type, while those of wadis As Suqah and Fayidah range from secondary to primary in their direction of flow. The usability of the groundwaters for domestic uses , irrigation and breeding livestock is considered.