Mapping Groundwater Infiltration in Karst Using LIDAR at Natural Bridge Caverns, Texas
Publication Date: 2026/09/01
Publication Volume: Journal of Cave and Karst Studies 88 #3
DOI Link: https://dx.doi.org/10.4311/2025ES0109
ABSTRACT:
The Trinity and Edwards Aquifers, two of the nine 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. This study used Light Detection and Ranging (LiDAR) to generate a three-dimensional point cloud in centimeter resolution to study water flow patterns within cavernous porosity. The research was conducted at Natural Bridge Caverns (NBC), a cave system northeast of San Antonio, Texas. The NBC cave system formed within Cretaceous carbonate rocks that host the Trinity and Edwards Aquifers. Our investigation focused on various spatial resolutions of LiDAR point cloud data to map and assess the size and spatial distribution of cave ceiling features (stalactites). The best spatial resolution to accurately identify and count stalactites, when compared to manual counts of stalactites, was established. Areas of specific flow types were classified using stalactite morphology and spatial distribution. Additionally, the effect of LiDAR distance from the cave ceiling/wall surface on the identification process was evaluated. We found that the number of LiDAR scans has a greater effect on data quality than scan distance. For the analysis of larger ceiling sections in various cave chambers, we established an optimal resolution of 10 mm (~0.39 in.). We established an optimal threshold of 97th percentile for stalactite identification and a threshold of 93rd percentile for flow classification. The flow classification based on stalactite morphological analysis shows that the Castle of the White Giants exhibits the highest amount of flow despite the chamber having the thickest overburden. The chamber also presents the greatest flow rate within the caverns.
SIMPLE LANGUAGE SUMMARY:
Much of the water used in south-central Texas comes from two large underground water sources (aquifers), the Trinity and the Edwards. The water moves through cracks and caves in limestone rock. This study looked at how water drips into Natural Bridge Caverns, a cave near San Antonio, by studying its stalactites, the icicle-shaped mineral formations that grow down from the ceiling where water drips. The researchers used LiDAR, a laser scanner that measures millions of points to build a detailed 3D model of the cave ceiling, accurate to about a centimeter. They tested different levels of detail to find the best one for counting stalactites by computer, and compared the results with counts done by hand. A detail level of 10 millimeters (about 0.4 inch) worked best. They also found that taking more scans mattered more than how close the scanner was to the ceiling. Using the shape and spread of the stalactites, they mapped where water flows into the cave. A room called the Castle of the White Giants had the most water flow, even though it has the most rock above it.
REFERENCES:
Barker, R. A., Bush, P. W., and Baker, E. T. Jr., 1994, Geological history and hydrogeologic setting of the Edwards-Trinity aquifer system west-central Texas: U.S. Geological Survey, Water-Resource Investigations Report 94-4039, 51, p. 27–44, https://doi.org/10.3133/wri944039
Bellian, J., Kerans, C., and Jennette, D., 2005, Digital outcrop models: Applications of terrestrial scanning LiDAR technology in stratigraphic modeling: Journal of Sedimentary Research, v. 75, no. 2, p. 166–176. https://doi.org/10.2110/jsr.2005.013
Brown, K., Mahmud, K., Katumwehe, A. B., Price, J. D., and B. Vauter, 2023, Morphological and spatial analysis of cave LiDAR remote sensing to identify karst water infiltration pathways: AGU23, San Francisco, California, 11–15 December, American Geophysical Union, H51P-1304.
Bruun, B., Jackson, K., Lake, P., and Walker, J., 2016, Texas aquifers study groundwater quantity, quality, flow, and contributions to surface water: Texas Water Development Board Report, p. 74–81, https://digitalcommons.usf.edu/kip_articles/4891.
Chang, C and Liu, L., 2021, Investigating the formation of the Cretaceous Western Interior Seaway using landscape evolution simulations: GSA Bulletin, v. 133, no. 1–2, p. 347–361.
Clark, A. K and Morris, R. R., 2017, Bedrock geology and hydrostratigraphy of the Edwards and Trinity aquifers within the Driftwood and Wimberley 7.5-minute quadrangles, Hays and Comal Counties, Texas: U.S. Geological Survey Scientific Investigations Map 3386, 12, pp. 2–8, https://doi.org/10.3133/sim3386
Ford, D and Williams, P. D., 2007, Karst Hydrogeology and Geomorphology: Hoboken, NJ, USA, Wiley, 562 p.
Gary, M. O., 2011, Geological Assessment for Natural Bridge Caverns Comal County: Texas, Zara Environmental LLC, 40 p.
George, P. G., Mace, R. E., and Petrossian, R., 2011, Aquifers of Texas, Texas Water Development Board Report 380, 172 p, https://doi.org/10.3133/wri944039
Heidmann, H. K., 2018, Lidar Base Specification Version 1.3: United States Geological Survey, National Geospatial Program, Chapter 4 of Section B: U.S. Geological Survey Standards Book 11, Collection and Delineation of Spatial Data: p. 5–52, https://doi.org/10.3133/tm11b4.
Kastning, E. H., 1983, Geomorphology and hydrogeology of the Edwards Plateau Karst, Central Texas [Ph.D. thesis]: University of Texas at Austin, Texas Speleological Survey Reissue, 657 p., https://texasspeleologicalsurvey.org/PDF/Kastning.pdf.
Klimchouk, A. B., Ford, D. C., Palmer, A. N., and Dreybrodt, W., 2000, Speleogenesis and Evolution of Karst Aquifers: Huntsville, AL, USA, National Speleological Society, 514 p.
Lindgren, R. J., Dutton, A. R., Hovorka, S. D., Worthington, S. R. H., and Painter, S., 2004, Conceptualization and Simulation of the Edwards Aquifer, San Antonio Region, Texas: United States Geological Survey Scientific Investigations Report 2004-5277, p. 27–31.
Mahmud, K., Mariethoz, G., Pauline, C. T., and Baker, A., 2015, Terrestrial Lidar survey and morphological analysis to identify infiltration properties in the Tamala Limestone, Western Australia: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, v. 8, no. 10, p. 4871–4881.
Mahmud, K., Mariethoz, G., Baker, A., Treble, P. C., Markowska, M., and McGuire, E., 2016, Estimation of deep infiltrating unsaturated limestone environments using lidar and drip count data: Hydrology and Earth System Sciences, v. 20, no. 1, p. 359–373.
Maclay, R. W and Small, T. A., 1986, Carbonate Geology and Hydrology of the Edwards Aquifer in the San Antonio Area: Texas: Texas Water Development Board Report, p. 13–28, https://digitalcommons.usf.edu/kip_articles/612/.
Pringle, J. K., Howell, J. A., Hodgetts, D., Westerman, A. R., and Hodgson, D. M., 2006, Virtual outcrop models of petroleum reservoir analogues: A review of the current state-of-the-art: First Break, v. 24, no. 3, p. 33–42.
Remie, R., Mahmud, K., Gary, M., Price, J. D., Katumwehe, A., and Vauter, B., 2025, Using Cave Drip Loggers to Characterize Groundwater Infiltration and Examine Hydrological Response in Cretaceous Karst Formation: EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-2623.
Shindel, G. M., 2019, Genesis of the Edwards aquifer, in Sharp, J. M., Green, R. T., and Shindel G. M., eds., The Edwards Aquifer: The Past, Present and Future of a Vital Water Resource: Boulder Colorado, Geological Society of America Memoir, 215, p. 9–18. https://doi.org/10.1130/2019.1215(02).
USGS, 2021, Water Resource Mission Area, Principal Aquifers of the United States, United States Geological Survey: https://www.usgs.gov/mission-areas/water-resources/science/principal-aquifers-united-states (accessed April 28 2025).
Weary, D. J. and Doctor, D. H., 2014, Karst in the United States: A digital map compilation and database, U.S. Geological Survey Open-File Report 2014-1156, p. 23.
