| 02 Oct 2025
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.
General comments:
The authors presented an approach for an in-depth analysis of the hydrological response in a Cretaceous karst formation. The authors use own data from 20 drip rate loggers deployed in the cave system. In addition, precipitation, soil water content and evapotranspiration data were obtained for one location outside the cave system. The investigated time spans only one year. This was correctly mentioned by the authors and convincingly justified. For data evaluation, multidimensional scaling and agglomerative hierarchical clustering was used to classify drip types and find unique drip regimes. Generally, the manuscript is very well written and easy to follow. I also believe that the authors invested a significant proportion of time in field work and data evaluation. However, there are major issues that need to be addressed.
First and most importantly, the introduction (which is too long), the geological background and the hydrological background (also too long) refer to a very large aquifer system. A large proportion of text deals with the huge importance of this aquifer system as water source. The actual research work for this study, however, was done in one cave system by using loggers just a few meters apart. This is a substantial mismatch.
Also, there is no interpretation of the drip water amount beyond the standard techniques mentioned above and the authors only confirm the findings of already published studies. A quantitative consideration which could justify the framework given in the introduction is completely missing.
In summary, I am not convinced that this is sufficient for a publication in HESS.
Technical corrections:
Figure 1B: Add scale.