Artificial groundwater recharge in Kuwait : planning and management

Abstract

Storing freshwater in brackish aquifers using artificial recharge has been predicted (using a rigorous numerical modelling technique) to be a very beneficial water management alternative for Kuwait. Two possible practices of freshwater injection and recovery have been identified. First, through a seasonal cycle, desalination plants can operate at their optimum capacity all over the year irrespective of seasonal fluctuations in water demand, and also the aquifer yield can be increased at the same time. The optimum location for this storage is suggested to be the Shigaya-B well field, mainly because of the high specific injection rates of the injection wells, and its location in a highly depleted area. The other benefit of artificial recharge to Kuwait is using the aquifer as a long-term strategic reserve for freshwater to be used later during the emergency conditions. The Shigaya-A wellfield is suggested to be the optimum site for this storage, mainly because of the high freshwater recovery efficiency, and the sufficient depth of aquifer head allowing additional build-up inside the injection wells due to well face clogging. Using a sub-regional numerical model, the optimum management variables required to inject and recover freshwater at the two types of storages have been identified, including; number and geometry of injection/recovery wells, their injection/recovery rates, and the duration of injection necessary to recover the intended quantity and quality of freshwater. Also, the recovery efficiency of freshwater storage and recovery practice has been estimated. From an analysis of freshwater injection-withdrawals field experimental data (for a single well, SU-IO), using a single-well numerical model, it was possible to quantify the clogging factor, and differentiate between its different causes. It has been found that most of the clogging occurred due to air entrapment, and not due to the formation or recharge water properties. This means that clogging during this experiment is due to a fault in the injection system, and that well injection capacity is likely to be higher if this avoided. Further modelling was implemented to devise methods for minimising displacement and quality deterioration of the artificially-recharged freshwater mound, by the regional groundwater flow, if it is stored for a long time. The preferred methods involve operation of "hydraulic gradient-control" pumping wells outside the storage area to create a zone of zero hydraulic gradient ( stagnation zone) around the stored water mound. A management model using the response matrix approach was implemented to determine the optimum pumping rates of these wells necessary to produce the intended hydraulic gradient. By the time all the usable stored water is irrecoverable without these controls (after 4 years), it was possible using this technique to recover about 55 % of this water.