SUBSURFACE WATER FLOW CLASSIFICATION USING REMOTE SENSING LIDAR - A CASE STUDY AT NATURAL BRIDGE CAVERNS TX

The Trinity and Edwards aquifers, two of the 9 major groundwater systems in Texas, are significant sources of water in south-central Texas. The aquifers are primarily hosted in a network of fractured carbonate rock with substantial areas of cavernous porosity. Light Detection and Ranging (LiDAR) is a tool used broadly in geoscientific fields that uses light to create a three-dimensional point cloud in centimeter resolution and has been used to study water flow patterns within cavernous porosity.

Natural Bridge Caverns (NBC) is a karstic cave system in the northeast of San Antonio. NBC formed in cretaceous carbonate rocks located within Trinity and Edwards aquifers. This project investigates various spatial resolutions of LiDAR-acquired point clouds to map and assess the size and spatial distribution of cave ceiling features (stalactites). The assessment helps to investigate the impacts of data quality to identify the stalactites, hence understanding water infiltration patterns within the above limestone. First, we determine the best spatial resolution that accurately identifies stalactites based on manual counts of stalactites using various cave ceiling portions. We then classify areas of certain flow types using stalactite morphology and spatial distribution. We also determine the effect of LiDAR distance from the cave ceiling/wall surface in the identification process. With the optimal resolution of 6mm, we analyze larger ceiling sections from different cave chambers for flow classification to understand water infiltration patterns and processes in karst aquifers.