Reclamation by tubewell drainage in Rechna Doab and adjacent areas, Punjab region, Pakistan

Abstract

Around the turn of the century, a network of more than 40,000 miles of canals was constructed to divert water from the Indus River and its tributaries to about 23 million acres of largely unused desert in the Punjab region of Pakistan. The favorable climate and the perennial supply of irrigation water made available through the canals instituted the beginning of intensive farming. However, because of generally poor drainage and the high rate of canal leakage, the water table began to rise. As the population increased and agriculture expanded, the demand for irrigation water soon exceeded the available supply. Spreading of the canal supply to meet the expanded needs locally created shortages that prevented adequate leaching. Increased evaporation from the rising water table further contributed to the progressive accumulation of soluble salts in the soil. By the late 1930's the combined effect of waterlogging and salinity had reduced the agricultural productivity of the region to one of the lowest in the world. In 1954, after several unsuccessful projects were undertaken to reclaim affected areas and to stop the progressive encroachment of waterlogging and salinization, the Government of Pakistan in cooperation with the U.S. International Cooperation Administration undertook a study of the geology and hydrology of the Indus Plain that ultimately resulted in the formulation of a ground-water reclamation program. The principal feature of the program is the utilization of a network of deep wells spaced about a mile apart for the dual purpose of lowering the water table and for providing supplemental irrigation water. Through financial assistance and technical and engineering support principally from the United States, construction began in 1960 on the first of 18 proposed reclamation projects that eventually will include 21 million acres and more than 28,000 wells having an installed capacity of more than 100,000 cubic feet per second. An area of about 1.3 million acres a few miles west of the City of Lahore was selected for the pilot project. The first Salinity Control and Reclamation Project (SCARP-l) was completed in 1962. Within the project area about 2,000 wells were drilled as deep as 350 feet and equipped with turbine pumps having a capacity of up to 5 cubic feet per second each and a combined operating capacity of about 3.5 million acre-feet per year. To July 1968 pumping from project wells and from private and other governmental agency wells supplied about 12 million acre-feet of water. This pumping more than doubled the available irrigation supply and lowered the water table to a depth of 10 feet or more below most of the project area. As a result, approximately 66 percent of the 400,000 acres of land damaged by waterlogging and accumulation of excessive salt was wholly or partially reclaimed. The cropping intensity was increased from about 77 percent in 1962 to 101 percent in July 1968, and the annual value of crops increased 186 percent over 1962. Annual water budgets for the first 6 years of project operation indicate that pumping caused a decrease in annual ground-water outflow from the project area from about 57,000 acre-feet to 32,000 acre-feet, caused an increase in annual ground-water inflow to the project area from 35,0'00 acre-feet to 52,000 acre-feet, and depleted about 1.71 million acre-.feet of groundwater storage. Net annual recharge to the ground-water reservoir during this same period ranged from a high of slightly more than 2 million acre-feet in 1964 to a low of about 1 million acre-feet in 1965. The budgets suggest that perhaps as much as half the net canal' inflow to the project area is lost through leakage. This leakage is the principal source of recharge to the ground-water reservoir. Pumping has caused widespread changes in the chemical quality of ground water by chanelling the rate and direction of flow, inducing infiltration from canals, and mixing of indigenous waters of dif