干旱区生态环境知识资源中心

Agriculture of arid and semi-arid regions is effected by over extraction of groundwater (GW) around the world especially in the developing countries like Pakistan. Groundwater (GW) should be properly recharged to overcome the issue of declining water levels. Analysis of GW use against recharge is done to address the issues of sustainable management and aquifer mining in Hakra branch canal system off-taking Eastern Sadiqia canal of Pakistan. Various water balance components were computed to estimate the net recharge using modeling as well as with remote sensing techniques. Soil profile data, water table depths, canals off take discharges and all the climatic data for the year 2006-11 were used as input data sets in Soil and Water Assessment Tool (SWAT) to compute GW recharge. Hakra branch canal system is divided into 17 off-taking distributaries and direct water courses. The SWAT model is calibrated and validated using in situ extents of soil, vegetation, evapotranspiration and surface supplies. Nash-Sutcliffe Efficiency (NSE) and coefficient of determination (R-2) were used as statistical parameters for calibration and validation of results. Using the net recharge, net GW abstraction was calculated for entire command area of Hakra branch canal system. SWAT was calibrated (NSE = 0.97, R-2 = 0.87) for the period of 2006-08 and validated (NSE = 0.98, R-2 = 0.90) for the period 2009-11. Average net recharge to the GW aquifer for the whole command area is estimated at -91 mm yr(-1), indicating abstraction is greater than recharge from all sources. Whereas, average net GW abstraction is calculated as 712 mm yr(-1) in the study area. The GW abstraction trend is increasing in the tail distributaries due to less canal water supplies. It is recommended to increase the head discharge of the main canal and share of the tail distributaries.