Groundwater Numerical Modelling of Amman-Zarqa Basin-Jordan

Abstract

Amman Zarqa Basin (AZB) is the most developed groundwater basin in the arid region of Jordan and faces water shortage and declining water table due to overexploitation to meet irrigation and domestic water demands. Therefore, groundwater flow modeling for this watershed is a necessary tool for proper management of groundwater resources to protect AZB from depletion. MODFLOW was calibrated and used to simulate the behavior of the flow system under different pumping rates scenarios. The conceptual model for Amman-Wadi Sir (B2/A7) aquifer system was formulated by one layer unconfined type overlaid by impervious layer (A1/6 aquitard) and calibrated for steady state condition by matching observed and simulated initial head contour lines. Drawdown data for the period 1985–1995 was also used for calibration of the transient model by matching simulated drawdowns with observed ones, and then validated by using drawdown data for the period 1996–2002. The results of the calibrated model showed that the horizontal hydraulic conductivity of the B2/A7 aquifer ranges between 0.007 to 45 m/d. Calibrated specific yield ranges from 0.001 to 0.15.

Three scenarios were conducted to predict the B2/A7 aquifer system response under different conditions during the period 2020–2030. The first scenario assumed that the pumping rates of year 2005 (110.4 MCM/year) are constant for 15, and 25 years. The maximum drawdowns where found reached about 99.9 and 104.9 m in the years 2020, and 2030, respectively. The second scenario assumed that the present abstraction rates (110.4 MCM/year) is reduced to 80 MCM/year. The maximum drawdowns were reduced to about 90, and 94.8 m in the years 2020 and 2030, respectively. The third scenario assumed an abstraction rate of only 65 MCM/year. The maximum drawdowns in this case will be decreased to only 76.8, and 72.5 m for the years 2020 and 2030, respectively; this scenario (abstraction rate of 65 MCM/year) has been found to provide a safe recovery and stability in the drawdown and therefore, could be considered as the safe yield of AZB.