Objectives
In Pakistan, where agriculture production is of prime importance for its economic development, the increasing dependence on groundwater for irrigation and drinking purposes makes it vitally important to assess underground water balance to recommend policy measures for its sustainable management. The key objectives of this study are to enhance groundwater management and to develop sub-regional groundwater model for informed decision making.
Design and Methodology
First objective was achieved by developing a geo-database for the groundwater information available with departments. Historical data sets were digitized, and additional data sets for groundwater level and quality were acquired by installation of data loggers in newly established observation wells in the command area. With the available data, a physical process based groundwater model was developed for achieving second objective. Calibrated model of sub-regional level was used to assess the policy scenario for sustainable water use and protection against water logging and salinization. The assessment of the scenarios were performed by aquifer stress analysis, water level threshold assessment, and water balance impact assessment.
Original data and results
Lithologically, the area consists of sands of various grades with silt and clay down to several hundred feet. Sand is predominant, and is highly transmissive and constitutes the potential aquifer in the area. The groundwater flow in the region is divided into two directions, with the hydrological divide seen near the Rohri canal-constituting world largest single canal area for irrigated agriculture. There are zones of shallow to deep water tables in the area. Depth to water table increases near the river Indus and decreases near the main canals. The Indus River and the canals are the main sources of groundwater recharge in the area. The area has recently seen an increase in groundwater pumping, especially at the tail reaches of canals. Reasons for this growth include less availability of water at these tail reaches, and subsidized cost of tube well installation.
Conclusion
Tail reach of canal commands are highly dependent on groundwater, and long term trends shows that water balance will become negative if high pumping continue in regions near the Indus River. There will be positive impact on water logged area with water levels going below root zones, which will ultimately bring good crop yields. Government has to cap the groundwater in regions near the river, and should allow pumping of groundwater in water logged area where the groundwater quality is suitable for irrigation.