| dc.description.abstracteng | Natural groundwater replenishment in (semi-) arid areas is low and can be sometimes negligible as a result of low precipitation rates and high evapotranspiration. Therefore, groundwater resources in these areas can be considered as non-renewable. Due to increasing demand for water, aquifer systems have been subject to an over-abstraction depleting fossil water resources and causing numerous negative impacts; declining groundwater table and aquifer storage, salt water intrusion, land subsidence and other problems. Additionally, the disappearance of wetlands in many areas in the world has been associated with groundwater over-abstraction which constitutes a significant ecological lost. The Azraq oasis located in the heart of the desert in Jordan is an example of the degradation of an important ecosystem as a result of groundwater over-abstraction.
Azraq basin is characterized by high heterogeneity in groundwater recharge, where the main recharge area is in the north of the basin. The central part of the basin is covered by wetland known as the Azraq Oasis containing a wealthy biodiversity. Abstraction for agricultural and domestic purposes occur mainly around the oasis area, leading to drastic decline of groundwater table. In this study different management solutions for the basin including pumping strategies and application of Managed Aquifer Recharge are analyzed.
A groundwater model is first built and calibrated for the Azraq basin in order to understand the response of groundwater table at the oasis area to pumping practices as well as to remote groundwater recharge, and predict its behavior under possible future scenarios and management alternatives.
The application of Managed Aquifer Recharge (MAR) is then discussed with a focus on the analysis of subsurface characteristics which play the main role in determining the ability of an aquifer to accommodate a specific amount of infiltrated water. A new approach of employing numerical groundwater modeling in the generation of MAR suitability maps in terms of sub-surface characteristics is presented. A number of model-runs are conducted to simulate groundwater table’s response at different locations of the aquifer for different scenarios of infiltration water volumes. Simulation results are employed to calibrate an empirical equation that calculates the height of groundwater mound as a function of aquifer transmissivity and volume of infiltrated water, for a certain value of aquifer’ specific yield, a certain range of vertical hydraulic conductivity, and fixed design and operation conditions of MAR structure.
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This empirical equation is applied in GIS to spatially calculate the height of groundwater mounding beneath a hypothetical MAR structure, and generate based on that suitability maps for MAR implementation. Suitability maps are generated for different scenarios of aquifer’s hydraulic conductivity and assuming MAR structures capture the 50th and 80th percentile of monthly amount of surface runoff at the respective wadi in the study area.
Three surface factors are investigated in the basin for their suitability for MAR implementation; slope, soil texture and soil thickness, to generate a MAR suitability map in terms of surface factors where a new decision system is proposed for the integration of factors.
Based on MAR suitability map three MAR structures were proposed in the basin. MAR scenarios along with a number of pumping scenarios were tested using the calibrated groundwater flow model. The calibrated model was also used to define the safe yield of the aquifer and predict the behavior of the aquifer under scenarios of climate change.
The results show that by the year 2045 groundwater decline will range between 15 and 25 meters if current pumping practices continue. The safe yield of the aquifer where the groundwater table stabilizes was found to be 70% less than current pumping rates, indicating that the aquifer is being exploited largely beyond its limits. Two scenarios of future groundwater recharge, where recharge rates were reduced 25% and 50%, were tested. Under these two scenarios, negligible impacts on the groundwater table in the oasis area were realized indicating that the aquifer can be considered as non-renewable.
The results show that the application of MAR in the basin doesn’t contribute greatly to increasing the safe yield. Under MAR scenario where the capacity of MAR dam is designed based on the 50th and 80th percentiles of monthly surface runoff, groundwater head will increase 0.7 and 1 m by the year 2045 respectively.
Finally, a multi-criteria analysis was conducted for choosing abstraction rate in the basin based on conflicting environmental and socio-economic criteria under two scenarios of the future development of economic and other demographic issues.
the safe yield scenario was found to be the alternative that contributes the most to the goal of choosing the abstraction rate in the basin for the scenario of future economic prosperity, while keeping the current pumping rate was found to be the best alternative under a scenario of poor economic and social awareness. | de |