Land-use impacts on the hydrology of the Hidden River groundwater subbasin, Horse Cave, Hart County, Kentucky

Cesalea N. Osborne, David J. Keeling, Jason S. Polk, Patricia N. Kambesis, and Kevin B. Cary

ABSTRACT:

Hidden River Cave, located in the city of Horse Cave, Ky., forms one of the main tributaries of the Hidden River groundwater subbasin that spans multiple counties in south-central Kentucky. Hidden River Cave formed in Mississippian-aged carbonates and consists of a dendritic network of canyons and collapsed domes; a major trunk stream flows through the cave that supports myriad subsurface ecosystems and recharges the Mammoth Cave aquifer and the Green River, important water resources on which several communities depend. Poor land-use practices historically have contaminated the cave stream. As a result, the hydrology of the Hidden River groundwater subbasin has been extensively studied using fluorescent dye-tracing, and developments in groundwater resource management have improved cave conditions. However, land-use boundaries that intersect with areas of recharge still influence contaminant transport to groundwater. This study combined groundwater dye-tracing, high-resolution stage data collection, and supervised classification in a geographic information system (GIS) to assess land-use impacts on the hydrology of the Hidden River groundwater subbasin. Dye-tracing confirmed that stormwater infrastructure in Horse Cave discharges to Hidden River Cave, and, subsequently, the Hidden River groundwater subbasin. High-resolution stage data determined that the caveÂ’s major trunk streams respond to precipitation within 40 minutes to 1.5 hours, while baselevel conditions, except after sustained precipitation, are met three to four days after precipitation ends. Supervised classification determined that development is concentrated in Horse Cave and has increased by approximately 7 % between 1989 and 2017. These results suggest opportunities for the implementation of karst-specific stormwater management regulations where such regulations are weak.

SIMPLE LANGUAGE SUMMARY:

Hidden River Cave is found in Horse Cave, Kentucky, and it's an important part of a groundwater system that spreads across several counties in south-central Kentucky. This cave was formed in rock from the Mississippian age and has a complex network of canyons and collapsed domes. A significant stream flows through the cave, supporting various underground ecosystems and feeding into the Mammoth Cave aquifer and the Green River, which are crucial water sources for many communities. Historically, bad practices with how the land was used led to pollution in the cave's stream. Because of this, a lot of research has been done on the water system using fluorescent dyes to trace the water's path and efforts have been made to better manage the water resources, which has improved conditions in the cave. However, contamination can still make its way into the groundwater because of how land is used in areas where water gets absorbed into the ground. This study combined several methods: dye-tracing, detailed water level data collection, and the use of a geographic information system (GIS) to assess the impact of land use on the water system. The study found that stormwater systems in Horse Cave discharge into Hidden River Cave and, from there, into the groundwater system. The main streams in the cave react to rain in around 40 minutes to 1.5 hours, while it takes three to four days for things to go back to normal after the rain stops. It also found that development in Horse Cave has increased by about 7% between 1989 and 2017. These findings suggest that there might be opportunities to put in place better stormwater management rules that are specifically designed for areas with this type of landform, especially where current regulations aren't strong enough.