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Jordan University of Science and Technology (JUST) 2004

The Use of Modflow to Study the Possibility of Artificial Groundwater to charge to Mujib Watershed

Tamer Anthone Lafi Al-Assad

Titre : The Use of Modflow to Study the Possibility of Artificial Groundwater to charge to Mujib Watershed

Auteur : Tamer Anthone Lafi Al-Assad

Université de soutenance : Jordan University of Science and Technology (JUST)

Grade : Master of Science (MS) 2004

Résumé
Mujib watershed is located at the central of Jordan to the east of Dead Sea. It is considered as a one of the important basins in Jordan. The basin is a major source of drinking water for Amman, Madaba and Karak cities, in addition to the local agriculture. High abstraction rates in last years from more than 350 wells leads to major decline in water levels accompanied by deterioration in groundwater quality. Therefore, proper management of surface and groundwater resources is needed in order to protect Mujib basin from depletion. The artificial groundwater recharge is investigated in this study as one of the important options to face water scarcity and to improve aquifer storage. For this purpose, MODFLOW is used to build a groundwater flow model to simulate the behavior of the flow system under different stresses. The conceptual model B2/A7 aquifer system was simulated by one layer unconfined type overlaid by impervious layer (A1/6 aquitard). The system was discretized depending on the location and concentration of wells and springs, the presence of a geological structure as Siwaqa Fault, and water table gradient. An assessment of the natural recharge was performed as it is an important input for the groundwater model. Different approaches were performed but as the water balance approach gave high values of recharge (more than 10% of annual rainfall), the natural recharge was estimated as a percentage of the annual rainfall and this percentage is varied and depends on the rainfall amount and the degree of drought that are determined by using the Standardized Precipitation Index (SPI). Annual average value for the period 1970-2002 was used in the steady state simulation, and each year natural recharge value was used in the transient simulation distributed on five months. The model was calibrated for steady state condition by matching observed and simulated initial head counter lines, moreover some measures were performed to evaluate the calibrated model also ensure good calibration. Drawdown data for the period 1985-1995 were used to calibrate transient model by matching simulated drawdown with observed one, then the transient model was 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 0.001 to 40 m/d. No vertical hydraulic conductivity is required to calibrate one layer model. Calibrated specific yield ranges from 0.0001 to 0.15. The water balance for steady state condition of B2/A7 aquifer in Mujib basin can be summarized as follows : the total annual direct recharge is 20.4 MCM, the total annual inflow is 13.0 MCM, springs discharge are 15.3 MCM, and total annual outflow is 18.7 MCM. The possibility of artificial groundwater recharge is investigated by proposing different locations for water recharging. These locations are selected to be close as possible to the areas of high drawdown with smaller pipe length. The sources of recharged water are from existed and proposed dam locations and reclaimed municipal wastewater. Artificial recharging is considered to occur mainly by injecting water directly to the B2/A7 aquifer and through infiltration from reservoir. Seven different scenarios were performed to predict aquifer system response under different conditions ; three of them are included artificial recharge option. The best scenario that provides good recovery for the groundwater table and be applicably feasible is by reducing current abstraction rates by 20% and performing moderate artificial recharge rates reached 26 MCM/year. Sensitivity analysis has been conducted to assess the relative contribution of uncertainty of aquifer parameters on the accuracy of the predicting drawdown. The results show that the model is highly sensitive to horizontal hydraulic conductivity and anisotropy and with lower level to the recharge rates ; also the model is sensitive to specific yield. In general the model is more sensitive to decreasing aquifer parameters than increasing them.

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Page publiée le 4 novembre 2016, mise à jour le 23 mars 2019