HYDROLOGIC IMPLICATIONS FROM AIRBORNE RESISTIVITY MAPPING OF THE SAND HILLS OF WESTERN NEBRASKA

The Sand Hills of western Nebraska are part of an extensive terrain of dunes distributed across the Great Plains. These dune complexes provide unique ecosystems, recharge to underlying aquifers including the Ogallala aquifer, and are very sensitive to short and longer term climate changes. Understanding the hydrogeologic framework of these dune systems and their underlying aquifers is essential in management of groundwater resources and ecosystems. The hydrogeologic framework is a critical component in understanding implications of climate change for one of the most productive agricultural regions of the United States

A frequency domain airborne electromagnetic (AEM) survey performed in 2010 in the area of Crescent Lakes National Wildlife Refuge (CLNWR) was extended several 10s of kilometers to the north and east with a time domain AEM survey conducted in early 2012. Previous hydrologic studies in the area have demonstrated that a dune dam has blocked the now partially buried Blue Creek. The dune dam is defined by a resistive zone that has a depth of 45 meters suggesting that it influences modern ground-water flow paths and surface-water features. In addition shallow lakes in the immediate area have variable salinity. This difference in salinity appears to be related to the lake interaction with the regional groundwater system. The resistivity depth sections interpreted from the AEM surveys show the subsurface distribution of dune sands and saline waters that act as a natural tracer for groundwater flow. The flow path of the saline waters follow the same patterns as classical groundwater models proposed nearly two decades ago. Some saline waters are perched above more resistive zones that may contain fresher waters. Other conductive zones suggest downward flow from saline lakes. In general interpreted flow paths are consistent with the trends previously suggested for paleo-channels of the ancestral Blue Creek. Ground-water flow paths controlled by buried topography interpreted from new geophysical surveys are important in predicting how possible deep and shallow groundwater are interconnected.