Electric analog analysis of the groundwater system in Chaj Doab area, West Pakistan

Abstract

The extensive canalization of the Doab, which was necessary to the development of irrigation agriculture induced added recharge to the ground-water system from the canal leakage. Disruption of the hydrologic balance of the regional flow system resulted in water-logging and soil salinization on a scale that threatens the entire economy of the region. The report establishes the cause-effect relationships involved and defines the functioning of the hydrologic system. Analog-simulation techniques for the analyses of ground-water systems in the Doab is developed. Analyses are made for (a) steady-state conditions that prevailed prior to the canal-irrigation period, and (b) non-steady state conditions for the canal-irrigation period from the year 1900 to 1960. The rise in ground-water levels, rate of infiltration from the main canals and their distributaries, net recharge rate to ground-water reservoir, and the effect of evapotranspiration on the rising groundwater levels are determined. Recharge to ground-water from the rivers Jhelum and Chenab and discharge through evapotranspiration are found to be the main sources for maintaining hydraulic dynamic equilibrium during the pre-irrigation period. Further analysis indicates that, during the canal-irrigation period, the infiltration from the main canals and their distributaries is the cause of rise in ground-water levels. The net infiltration rate is of the order of 1767 million gallons per day and is a function of canal size. Out of this, 867 million gallons per day is the loss due to evapotranspiration, showing its importance in the ground-water system of the area. Information resulting from this study provides a guide for more detailed study of the problem and establishes significant guidelines for future ground-water development in the Doab.