Using Modflow and MT3D Groundwater Flow and Transport Models As a Management Tool for the Azraq Groundwater System

Abstract

Numerical modeling has emerged as an effective tool for managing groundwater resources and predicting future responses, especially when dealing with complex aquifers systems and heterogeneous formations. Among these models, MODFLOW and MT3D are the most commonly used simulators for groundwater flow and solute transport in subsurface systems, respectively. These models have been used herein as a management tool for the Azraq basin, one of the most important groundwater resources for domestic and agricultural sectors in Jordan. Groundwater extraction from this basin already exceeded the safe yield of the aquifer, and a sharp drop in the water table, a dry out of the springs at the center of the basin and the problem of increased salinity in many parts of the aquifers have been reported. Currently, more than 600 wells including governmental, private and unauthorized wells are operating within the basin boundary. In its attempts to restore and sustain the aquifer, the Ministry of Water and Irrigation (MWI), the official entity in charge of water resources in Jordan, is considering several scenarios of controlled pumping. In this study, five suggested scenarios of pumping with different abstraction rates for years 2005 through 2020 have been explored by using the three dimensional finite difference flow model [MODFLOW (PM5)] to simulate the flow system, and the solute transport model (MT3D) to predict the transport of total dissolved solids given in terms of Electric Conductivity (EC). These scenarios include: first, maintaining the current pumping rate of 57 MCM for the study period; second, reducing the current pumping rates by half; third, increasing the pumping rate by half; fourth, reducing the pumping rates in public wells by half and maintaining the current rates for other wells; and finally reducing the pumping rates by half for the farm wells (private) and maintaining the rates at the other wells. Results indicate that the first and fourth scenarios have similar effect on the drawdown. Also, the second and fifth scenarios have similar effects and provide the lowest drawdown values. The third scenario gives the worst drawdown. The transport of Total Dissolved Solids (TDS) given in terms of Electric Conductivity (EC), has also been explored. Different parameters including EC, recharge, model boundary and advection parameters were adjusted to run the model. Simulation results indicated that the effect of the different scenarios on the values of EC is less profound than the effects on the drawdown values. The third scenario caused a slight increase of EC values over the values simulated by other scenarios.