Assessing the Site Suitability of Managed Aquifer Recharge (MAR) Projects in Karst Aquifers in Lebanon - A Multi Criteria Analysis
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Groundwater overexploitation in Lebanon has led to severely decreased groundwater reserves and enhanced seawater intrusion at the coast. To improve freshwater availability much attention has recently been given to Managed Aquifer Recharge (MAR), a groundwater management technique that employs artificial replenishment of aquifers. In Lebanon the potential of a MAR scheme lies in storing excess winter runoff underground and recovering it during the dry summer. In coastal aquifers infiltrating surface water would also counteract the increasing salinity. While numerous authors have discussed potential MAR schemes in Lebanon no successful project has been implemented yet. This is certainly related to the complicated geology in Lebanon, where 70% of the aquifers are karstic. Globally, various designs of MAR schemes have successfully been implemented in unconsolidated aquifers, but there is little experience with artificially recharging karstic aquifers even though karst shows considerable potential for MAR. Karstified aquifers often feature high well productivity and are less prone to clogging. However, the high heterogeneity of karst aquifers with high transmissivity values along conduits and a generally low purification potential make them a challenging medium for successful MAR schemes. In this research a 2-step framework for assessing the suitability of potential MAR sites in karstic aquifers is presented. The core of this approach is a criteria catalogue that guides the assessment of each potential MAR site with regards to physical, social, and economical aspects. The criteria were developed based on an extensive literature and expert interviews. The criteria catalogue helps to structure collected data and gives a good overview of possible proxies that indicate suitable conditions. The alternative sites are compared and ranked in a comprehensive multi criteria analysis. The methodology is demonstrated for Lebanon. Based on a pre-selection carried out in a previous research by UNDP (2014) nine potential MAR sites are compared. Sufficient data was collected to score 38 of 141 developed criteria. Focus lies on assessing the site-specific physical properties of the aquifers. Monte Carlo Simulations to account for score and weight uncertainties reveal that the ranking is relatively robust, especially the first and last positions.