Water resources and related geology of Dera Ismail Khan district, West Pakistan, with reference to the availability of ground water for development

Abstract

Dera Ismail (D.I.) Khan District contains an area of 3,450 square miles between the right bank of the Indus River and the Sulaiman Range in westcentral West Pakistan. Agriculture is the principal source of income in the District, but only a small part of the arable land is fully utilized. The region is semiarid and has an average annual rainfall of about 9 inches and a potential evapotranspirational rate of eight to nine times the annual rainfall. Thus, rainfall alone is not adequate for high-intensity cropping. Irrigation is practiced near the Indus River; the Paharpur Canal is used, as well as the traditional inundation method. Elsewhere in the District, adequate water is supplied to local areas by karezes, perennial streams from the mountains, and some recently installed tubewells (see 'Glossary'). Further development of ground-water supplies would permit a more effective utilization of most of the presently tilled land and would allow additional land to be farmed. D.I. Khan District is primarily an alluvial plain that slopes from the mountain ranges in the northern and western parts of the District toward the Indus River. Rocks in the bordering mountains are of Paleozoic to early or middle Pleistocene age. The unconsolidated rocks of the plain, of middle (?) Pleistocene to Holocene (Recent) age, consist of piedmont deposits derived from the hills to the north and west and of alluvium laid down by the Indus River. These deposits interfinger in a transitional zone about 8 to 12 miles west of the river. Lithologic and structural features indicate that the unconsolidated rocks possibly may be divided into broad units. The investigations in D.I. Khan District have revealed two main areas of potential ground-water development based on considerations of both permeability and chemical quality of the ground water: 1. A belt about 10 miles wide parallels the Indus River from the Khisor Range southward to the area immediately south of D.I. Khan town. In this belt, the material penetrated by test holes and tubewells consists predominantly of sand, which in tubewells can yield from 2 to 3 cfs (cubic feet per second) of water with only moderate drawdown. Also in this belt, ground water of good chemical quality extends to depths of 1,000 feet or more. 2. The area from the mouth of the Gumal River gorge to the vicinity of Kot Azam contains sand and gravel strata that may yield from 1 to 3 cfs of water, which contains 500 to 1,500 ppm (parts per million) of total dissolved solids. Other marginal parts of the District also contain water of good chemical quality, but developmental prospects are somewhat poorer because of greater depths to water, lower permeabilities, or greater depths to aquifers, all of which would require greater costs in the tubewell installations. The stratification or zoning of water of different chemical qualities to some extent governs the local availability of useful water. Generally, the ground water of poorest quality is found in the shallow zone, and quality improves with depth. The central part of the District, in a belt reaching from the vicinity of Tank southward to the Indus River near Dera Ghfizi Khan District, contains highly mineralized water and few aquifers. The mineralization of water in this belt is due primarily to large concentrations of sodium and sulfate and thus differs from the main part of the Punjab region where highly mineralized waters are generally chloride waters. Radical changes in water quality, both horizontally and vertically, are common in the District. Changes in chemical quality of water from large-capacity wells near areas of highly mineralized water are taking place, and further changes may be expected as withdrawals continue and increase in magnitude. Under present conditions, surface-water supplies are fully utilized, and ground water is the largest supply available for development-other than that from the Indus River.