Using Cave Drip Loggers to Characterize Groundwater Infiltration and Examine Hydrological Response in Cretaceous Karst Formation

Abstract. In Texas, groundwater from karst aquifers represents a significant percentage of the State's water supply. Karst regions are vital groundwater resources, and caves offer natural access points for observing long-term vadose zone water storage and fluxes, offering a better understanding of groundwater flow paths. Natural Bridge Caverns (NBC), which is situated within the recharge zone of the Cretaceous age Edwards (Balcones Fault Zone) aquifer and also recharges the Trinity aquifer below the Edwards, was monitored with a high resolution, spatially dense cave drip rate network during one hydrological year to characterize water infiltration within this karst system. Precipitation, soil water content (SWC), and evapotranspiration (ET) data were obtained for the location and used to evaluate the infiltration-discharge relationship for 20 drip loggers. All drip sites remained active throughout the monitoring period and generally exhibited low discharge rates during dry periods and high discharge rates in response to rainfall events. Discharge at the drip sites varied substantially, and analysis revealed a spatial relationship emerging from the dataset. Using Multidimensional Scaling (MDS) and agglomerative hierarchical clustering (AHC) we were able to classify similar drip types to obtain four unique drip regimes. A lithological assessment suggests that secondary porosity is influencing water movement rather than overburden thickness. Despite the relatively short time frame of this study, we find that the results shed valuable insights into the heterogeneity of hydrological flow within the vadose zone at NBC. It also emphasizes the importance of advancing our understanding and characterization of unsaturated zone hydrological processes to inform effective groundwater management policies.