CONJUNCTIVE IRRIGATION IN PAKISTAN

A survey of tube wells was carried out in a surface hydrological unit (distributary canal command area) in Rechna Doab of the Punjab, Pakistan and results were compared with a tube well census conducted in the same area 20 years ago to update knowledge of the groundwater abstraction structures and find the changes occurring over two decades. Three water courses, located at the head, middle and tail regions of a distributary, were selected to carry out a survey of tube wells including information about ownership of each well, its installation year, bore depth, suction depth, power source, inner diameter of delivery pipe and discharge (which was determined by the trajectory method). Water table depth was collected twice from 11 hand pumps during the study (after rainy season in summer and in winter), six observation wells were also installed, two each in the command area of every sample watercourse, and monitored bi-weekly for a year. Electrical conductivity of groundwater samples collected from hand pumps, shallow and deep tube wells was also measured. Results were compared with those of Vander Velde and Johnson (1992) for the same water courses. Results show that number of tube wells increased by four and three folds in the command areas of the head and middle watercourses respectively, while the increase was 1.5 times at tail over the last two decades. Substantial increase in diesel engine and electric motor tube wells were observed while tractor driven tube wells decreased in number. Density of tube wells per 100 acres of GCA increased 4.3, 3.0 and 1.5 times in head, middle and tail regions respectively. Electric motor operated tube wells have higher discharge. Maximum average water table drop of 16.81 feet over 20 years was observed in the tail reach of the distributary canal. Shallow tube wells are disappearing from tail reach of the distributary. Most of the ground water pumped by these tube wells was of marginal quality