Fresh and saline ground-water zones in the Punjab region, West Pakistan

Abstract

An extensive program of test drilling and water sampling, undertaken by the Water and Soils Investigation Division (WASID) of the West Pakistan Water and Power Development Authority (WAPDA) to evaluate hydrologic problems related to waterlogging and soil salinity, has furnished data for the delineation of fresh and saline ground-water zones in the Punjab region of West Pakistan. Fresh ground water containing generally less than 500 ppm (parts per million) of total dissolved solids is found in wide belts paralleling the major rivers and in other areas of ground-water recharge. The fresh groundwater zone of upper (northeastern) Rechna Doab, where annual precipitation in places exceeds 30 inches, is the most extensive of the Punjab region and attains a depth of 1,700 feet or more below land surface near Gujranwala. Fresh ground water adjacent to the Indus River extends locally to depths of about l,500 feet. Saline ground water occurs downgradient from sources of recharge, particularly in the central parts of the interfluvial areas. Also, available data indicate a gradual increase in mineralization with depth and distance from sources of fresh-water recharge. Thus, even extensive fresh-water zones appear to be underlain, at variable depths, by saline ground water in most of the Punjab region. The saline ground waters of the Punjab region do not constitute, however, a distinct salt-water body that can be defined in terms of stratigraphic position, sea-level datum, particular lithology, or by chemical character. The ground waters of the Punjab region are characterized by a gradation from calcium magnesium bicarbonate types, near the sources of recharge, to waters containing a dominant proportion of sodium. Water containing from 500 to 1,000 ppm is commonly of the sodium bicarbonate type, or it may be of the mixed type, having about equal proportions of the common anions (bicarbonate, chloride, and sulfate). With increasing mineralization from about 1,000 to 3,000 ppm, ,the relative proportion of chloride and sulfate increases, and these waters are generally of the sodium chloride or sodium sulfate type. The highly mineralized waters of the Punjab region are generally of the sodium chloride type, whereas in Dera Ismail (D.I.) Khan District sodium sulfate waters predominate. The ground waters from more than 900 sampling sites have been classified into eight types, according to dominant cations and anions. These types have been further subdivided into groups containing different amounts of total dissolved solids. The pattern of distribution of saline ground-water zones in the Punjab region and the observed gradual increase in mineral content, downgradient from sources of fresh-water recharge, can be explained best by the processes of evaporation from the water table and solution of minerals within the alluvial aquifer.