Critical Zone Assessments of an Alluvial Aquifer System Using the Multi-influencing Factor (MIF) and Analytical Hierarchy Process (AHP) Models in Western Iran

Many arid regions in the world suffer from over-exploitation of local groundwater resources leading to the degradation of freshwater aquifer systems, drying of spring discharges, and other damage to land and infrastructure. The development of groundwater critical zone maps (GCZMs) using the best available data is one important method that can be used by decision makers to develop a justifiable regulatory framework that may ban future use of wells. The multi-influencing factor (MIF) and the analytical hierarchy process (AHP) methods were used to create GCZMs for the Kangavar sub-catchment basin (aquifer system) of western Iran. Seven mapped factors were used as input into the models that included spatial occurrence of geological formations, aquifer lithologies, aquifer thickness, aquifer recharge, annual groundwater discharge (including water use), water-well density, and groundwater quality (degradation). Weighting factors were placed on the input data based on expert opinions, and the created thematic maps were combined using the weighted sum tool within a GIS framework to create two separate GCZMs. It was found that both methods produced acceptable and similar results, but based on a receiver operating characteristic curve analysis of internal error the MIF model (0.82) was > 10% more accurate compared to the AHP model (0.72). Critical and subcritical classification areas within the basin covered areas of 94 and 77.7 km(2) in the MIF and AHP maps, respectively. Banning of water-well construction in these areas is therefore technically justifiable and demonstrates the need to use two methods for development and verification of GCZMs with varying assumptions.