A GIS STUDY OF SINKHOLE MORPHOLOGY AND DISTRIBUTION IN RELATION TO STRUCTURAL FEATURES OF THE KAIBAB PLATEAU AS A MEANS OF UNDERSTANDING RECHARGE TO THE REDWALL-MUAV AQUIFER OF GRAND CANYON NATIONAL PARK, ARIZONA, USA

The Kaibab Plateau in Grand Canyon National Park and the Kaibab National Forest is unique in being one of Arizona’s largest and highest elevation karst areas, and yet, has been the focus of very few studies. This can be attributed to the challenging nature of the region, as little can be seen on aerial imagery through thick boreal and ponderosa pine forests. Field reconnaissance has several limitations due to the vastness of the watersheds and extremities of the region in weather and topography. Recent lidar data provides a detailed look at the plateau’s surface morphology, highlighting the highly-developed karst topography, with over 1,800 sinkholes, an increase of over 350% from the park’s original map and field-based karst features dataset.

Previous research suggests that the deep regional Redwall-Muav aquifer is recharged by meteoric waters travelling through faults and open joints fed by sinkholes. However, the locations and/or distribution of transmitting sinkholes are unknown. Geospatial sinkhole analysis was conducted, using ArcGIS (version 10.2.2.), to better understand how these surficial karst features are connected to the deep regional Redwall-Muav aquifer. Sinkholes identified with the use of lidar data were sub-classified based on calculated geometries into karst feature types: patterned ground, cleft (linear), escarpment, and large sinkholes. The relationships between these features and mapped structural geology were then assessed. We found cleft sinkhole groups to be most juxtaposed to or aligned with fractures and/or open joints, and therefore this sinkhole type is most likely to have the strongest hydrologic connection to the regional aquifer. This geospatial analysis of sinkhole morphology and distribution presents a GIS- based approach to modelling the relative importance of individual sinkholes or sinkhole complexes to aquifer recharge. Results suggest that sinkhole geometry can be used to interpret the overall importance of a sinkhole to aquifer recharge, and that observing the morphology of these features at a regional scale can improve our understanding of aquifer vulnerability, enabling improved monitoring and management decisions.