KARST GROUNDWATER VULNERABILITY MAPPING: APPLICATION OF THE COP AND EPIK METHODS TO THE KAIBAB PLATEAU, GRAND CANYON NATIONAL PARK

The Kaibab Plateau is a large uplifted karst region and host to thousands of sinkholes from which precipitation drains into the regional Redwall-Muav aquifer, the sole supply of drinking water to Grand Canyon National Park. The complex hydrogeological makeup of this semi-arid region, coupled with its overall importance to the hydrology of the Grand Canyon, makes improving our understanding of groundwater vulnerability a high priority. This study, the first of its kind for the park, will evaluate the intrinsic vulnerability of the karstic groundwater basins of the Kaibab Plateau. Two multi-attribute geospatial groundwater vulnerability analyses were conducted using the COP and EPIK methods, both of which have been specifically designed for karstic aquifer systems. Due to the unique geologic makeup of the Kaibab Plateau, these models were compared to assess their ability to quantify the variability in vulnerability and to determine which is the most appropriate for the study within Grand Canyon National Park. The COP method is based on three factors: concentration of flow (C), overlying lithological layers (O), and precipitation regime (P). The EPIK method takes into account: epikarst (E), protective cover (P), infiltration conditions (I), and karst development (K). For each method, the parameters are subcategorized by weighted attributes and rasterized in GIS. The finalized raster layers are combined and spatially analyzed in GIS to create the final groundwater vulnerability map. In both models, the results suggest there is a low to moderate level of vulnerability in the catchment basin. Because groundwater vulnerability maps of aquifers are an effective tool for resource and land use planning, the results of this study will help facilitate decision making regarding aquifer protection and sustainable management practices.