Optimum Strategies of Groundwater Pumping Regime under Scavanger Tubewells in Lower Indus Basin, Sindh, Pakistan

In general Pakistan is an agricultural country, most of its area including lower Indus basin (LIB) lies in arid and semi-arid zones, where irrigation by canal water and groundwater is only option. Due to continuous seepage from canal irrigation network and infiltration from irrigated lands; without adequate provision of natural and artificial drainage and its appropriate outlet, water-logging and soil salinity problems were developed. To combat these problems and to supplement canal water irrigation, 357 scavenger tubewells were installed in two districts (Nawabshah and Sanghar) of Sindh, Pakistan, under Left Bank Outfall Drain (LBOD) stage-1 project with the cost of US$ 12.75 funded by World Bank. In this paper, already calibrated groundwater flow model (MODFLOW) was linked with solute transport model (MT3D), and several simulation runs were performed using range of solute transport parameter of this region till the MT3D model was calibrated successfully for two sampled sites located at JRS-57 and JRS-60 tubewells during pumping tests. Using the calibrated MT3D model, various scenarios were developed using suitable fresh-saline water pumping ratios and daily operational hours for achieving optimum management strategy for better control of fresh and saline water interface. The study revealed that optimum management strategy to control saline water and fresh water interface was to operate scavenger wells at the operational factor of 0.55 (i.e. 13.2 hr/day) for JRS-57 and 0.5 (i.e. 12 hr/day) for JRS-60 with recovery ratio of 0.5:0.5 for both the tube-wells.