Generalized potentiometric-surface map and groundwater flow directions in the Madison aquifer near Jewel Cave National Monument, South Dakota

A generalized potentiometric-surface map of the Madison aquifer near Jewel Cave National Monument was constructed using water levels measured from calendar years 1988 to 2019 in 24 groundwater wells and 4 subterranean cave lakes interpreted to be in hydraulic connection with the aquifer. The map indicated that groundwater near Jewel Cave National Monument originates from recharge sources to the Madison aquifer in the higher elevations in the north-central area of the map, flows west to south-southwest through the Jewel Cave network, then southeast.

Hydrographs were constructed using water levels from four observation wells and one subterranean lake (Hourglass Lake) in the Jewel Cave network to evaluate historical and current groundwater recharge to the Madison aquifer in the study area. Hydrographs from 1992 through 2018 indicated water levels were lowest from the early to mid-1990s, increased through the late 1990s, peaked in the early 2000s, decreased until 2010, and then increased to the highest levels during 2016–18. A visual comparison of the Hourglass Lake hydrograph with cumulative precipitation, and quantitative (statistical) comparison of lake-water levels with cumulative precipitation, indicated that lake-water levels increased as cumulative precipitation increased, most likely due to some degree of precipitation recharge to hydraulically connected Madison Limestone outcrops.

Comparing the potentiometric-surface map constructed for this study, with a map by Strobel and others (2000) of the same region and aquifer, indicated similarity and, therefore, provided some validation of map construction. The potentiometric-surface map constructed for this study could be used by park managers and others as a tool to evaluate the hydrogeologic characteristics of the Madison aquifer in the study area.