Groundwater Modeling: A Tool for Groundwater Management to Support Urban Water Supply and Food Security

Abstract

Faisalabad is the 3rd largest city of Pakistan where underlying aquifer mostly contains saline water. Heavy population of the city needs huge quantity of fresh water. Water requirements for the existing Faisalabad city are being met by installation of well-fields along Jhang Branch canal, where groundwater is fresh. The increasing population pressure requires more water and identify more suitable sites for installation of well-field on sustainable basis. It was deemed imperative to elevate the existing well field. The MODFLOW, a numerical groundwater model developed by United States Geological Survey (USGS) for simulation and future prediction of aquifer behavior in response to pumping by various well fields was developed, calibrated and validated satisfactorily. A groundwater decomposition approach was also developed to tune various coefficients used in estimation of inflow and outflow components of groundwater system. The calibrated model was used to predict the future response of aquifer under different scenarios of pumping by existing and future/proposed wellfields. Calibrated flow model revealed that a sink has already been developed at the center of existing well-field of Water and Sanitation Agency (WASA) due to excessive pumpage. Future predictions of model indicate that there is no conspicuous change in regional groundwater flow pattern, even with all the existing tubewells remain in operation. However, the sink in the WASA well field area further deepens, and flow gradients become comparatively steep showing increase in groundwater flow velocity. Depth to watertable has already increased from 12 m in 2005 to 16 m in 2011 in the critical area of WASA well field. Model has predicted that this depth will further increase to 24 m in 2018. It has also been observed that groundwater quality along the river is fresh and becomes saline towards Faisalabad city. Due to pumpage in the freshwater zone model predicts that saline water will rush towards well fields deteriorating the quality of fresh water along Jhang Branch Canal. Therefore, it has been suggested that site for further pumping should be moved towards upstream of Jhang Branch Canal at least up to RD 180-187 and possibly on right side of the canal instead of left side