USING TIME-DOMAIN ELECTROMAGNETICS AND LIDAR DATA TO CHARACTERIZE WATER FLOW PATHS AND VOID SPACES IN THE WATER SINKS AREA, HIGHLAND COUNTY, VA, USA

The Water Sinks area has a karst topography replete with sinkholes, a steep depression, and at least three known cave systems– Helictite, Owl, and Water Sinks. All three of these cave systems are located along the axis of the Chestnut Ridge anticline and occur in successively older strata. The water table in and around the Water Sinks depression has shifted over the past few decades, and the reasons for its migration and specific pathways have not previously been studied. In this study, we used time-domain or transient electromagnetics (TDEM or TEM) resistivity tomography data and a water flow model derived from airborne LiDAR (Light Detection and Ranging) using ArcGIS, in an attempt to characterize the water flow paths, groundwater movement, and void spaces in the study area. We collected nine TEM datasets using the Geonics G-TEM system at various stations throughout the area, many of which were in close proximity (if not coincident) to the locations where DC resistivity data for a concurrent study by Valle-Hernández et al. were collected. We generated inverse models for the TEM data using Interpex IXG-TEM software. Combining the TEM results with the resistivity data and streamflow analysis, we are able to locate the groundwater flow paths both past and present. By evaluating these data within the context of the geology near the anticline, we are able to show that the evolution of the cave systems were primarily driven by the presence of an impermeable sandstone layer.