Assessment ofSustainable Groundwater Extraction

Abstract

Pak. J. Engg. Appl. Sci. Vol. 24January, 2019(p.1–10)1Assessment ofSustainable Groundwater Extraction Rate for Quetta City Using MODFLOWAbdul Ghani1, Zulfiqar Ali Chaudary2,Habib-ur-Rehman2, Aftab H. Azhar3, Muhammad Masood*41.Construction and WorksDepartment, Govt. of Baluchistan, Quetta, Pakistan2.Department of Civil Engineering, University of Engineering and Technology, Lahore, Pakistan3.Directorate ofHydrology Mangla Dam Org. WAPDA. Mangla, Pakistan4.Centre of Excellence inWater Resources Engineering, UET, Lahore, PakistanCorresponding Author: E-mail: chmasoud@gmail.comAbstractQuetta is the largest population center in Baluchistan province. Its population entirely depends upon the groundwater. The increasing population of the city and unplanned use have depleted water table in the recent decades. USGS groundwater flow model MODFLOW (MODFLOW Pro) was applied for the Quetta city to simulate the behavior of aquifer under stresses. The model solves partial differential groundwater flow governing equation by finite difference method. The data regarding groundwater levels, tube wells, pumping rates and aquifer parameters etc. were collected from Water and Power Development Authority (WAPDA). The data showedthat the abstraction rate for the city has increased from 32.25MGPD to 57.76 MGPD over20 years. The model was calibrated and validated for the available data. Data from year 1995 to 1999 was used for calibration and from 2000 to 2005 for validation. The water balance showedthat 20% of the total precipitation was ultimately going to the groundwater as recharge. It was observed from the model results that the water table under Quetta city has declined at the average rate of 0.91 m/year since 1995 to 2014. The Vermont Storm Water Management (VSWM) method of volume recharge was used to calculate the fraction of recharge that is retained by the imperviousness caused by the urbanization of the city. This fraction comes out to be 0.6 MGPD to 2.9 MGPD per year, depending upon the amount of precipitation and the amount of imperviousness for the same year. The water budget calculated by the model showedthat the average recharge per year in the study period was 37.04 MGD and the average abstraction from the aquifer was 84.20 MGD, so there was annual deficit of 47.11MGD. The inflow through the boundaries was increasing with the passage of time due to fall of headinside the model area, whereas the outflow through the boundaries was almost zero during thestudy period because of higher heads outside the model boundary. The model was then used to predict different future scenarios by giving the same average recharge rates and varying abstraction rates, in order to predict the future behaviorof the aquifer