Conjunctive use of Geographic Information System (GIS) and 3-D Numerical Models (FEEFLOW) to characterize the groundwater flow regimes of the Lower Thal Doab, Punjab, Pakistan

Abstract

This dissertation documents the development of a steady-state and transient groundwater flow modeling of the Lower Thal Doab, Punjab, Pakistan including simulation of the high potential groundwater aquifer, prediction of future flow regimes, canal seepage, pumping effects on the water levels, management plan for safe aquifer yield, and a plan to avoid water logging. The three dimensional numerical groundwater flow model is constructed by using Feflow in conjunction with GIS. The model is comprised of four layers with a total depth of 100 meters i.e. equivalent to maximum depth of tubewells in the area. The study area is bounded by the Indus and Chenab Rivers, and Taunsa Punjnad Link Canal, as hydraulic head boundaries. The irrigation canals of the study area play an important role on flow regime and were treated as fluid flux boundaries and used in generating the mesh of the model. Triangular grid was overlaid on the study area, which was further refined along the canals to simulate the changes in flow and flux. Four recharge zones were identified based on administrative division of the area i.e. Tehsils of Muzaffargarh as Kot Adu, Muzaffargarh, Jotai and Alipur. Conductivity zones were established based on hydro-stratigraphy, lithology, pumping test data and physiographic features of the area. Groundwater levels data collected from Salinity Control and Reclamation Project (SCARP) and Land Reclamation Departments that was used in calibrating the model in steady and transient conditions. The model was calibrated in steady state for groundwater observed heads of year 1999 at 326 wells, well distributed in the area with a best match between the model and observed groundwater heads. The root mean square (RMS) is obtained to be 0.92 m. Similarly transient conditions were calibrated with known drawdown at observation points from year 1999 to 2004 and with observed heads of year 2004. Model verification was done by realization of the model from 2004 to 2010. Finally the calibrated and verified model was used for predictive simulation commencing from 2013 to 2030 to estimate the effect of future stresses and to predict changes in flow of the Lower Thal Doab. Model results have indicated shallow water table conditions that tend to persist in Kot Adu and northern part of Muzaffargarh tehsil area even in 2030 and onward, resulting twin menace of water logging and salinity. Contrarily, in south eastern parts of the area i.e. Alipur, and Jatoi water table is declining at the average annual rate of 0.33 meters that appears to be 12 meters in Alipur and Jatoi from 2013 to 2030. The obvious reasons of declining trend are excessive pumping for irrigation at tails of canals where supplies remain negligible. Different scenarios were run to achieve a practical plan that can be adopted as one of the optimal i solution to cater the groundwater problems in the Lower Thal Doab. It is somehow found with several model realizations that water table should be kept in between 3 to 6 meters, which would resolve and minimize the twin menace of water logging and salinity, and water table depletion could also be catered. The proposed solutions refer to cut supplies for all canals in Kot Adu and northern parts of Muzaffargarh area and instead use tube-well pumped water to supplement these canal supplies. Subsequently, these supplies will be used to feed the eastern and southern parts canals in Jatoi and Alipur to maintain a balance between canal supplies and tube-well pumping. The water table in these areas will then be controlled from further decline and ultimately will replenish due to reduction in pumping quantities and recharge from canal seepage.