Ground Water Inflow to a Karst Environment During Periods of Low Precipitation: Kartchner Caverns, Arizona (USA)

Beginning in January 2005, water inflow and cave formation wetness were monitored in Kartchner Caverns in southern Arizona during a period of less than average precipitation. This monitoring was conducted to determine whether observed cave formation drying was attributed to changes in inflow of water to the cave as a result of lower than average precipitation or because of opening of the cave for public tours.  Since 1994 the average annual Palmer Drought Severity Index has risen above normal only three years (1995, 1998, and 2001). A combination of precipitation gages, stream gages, electrical resistance sensors, and temperature sensors were used to detect the presence of water and measure rates of water movement.  Results from the monitoring were compared to a survey conducted in the 1980s and early 1990s during a period of wetter than normal conditions.  The main difference in ground-water inflow to the cave between the wet period (1980s and early 1990s) and dry period (2005 – 2008) was infiltration from ephemeral stream-flow channels surrounding the cave. During the dry period channel recharge from the three ephemeral streams surrounding the caverns did not provide any inflow to the cave even though channel flow occurred. Direct infiltration of precipitation through the limestone rocks overlying the caverns continued to provide periodic inflow to the cave during the dry period; however, the annual volume of infiltration was reduced compared to the wet period. As a consequence of less infiltration and inflow into the cave during the dry period, ponded water was not observed in portions of the cave compared to the wet period. Finally, electrical resistance sensors proved valuable for detecting thin films of water on cave formations (stalactites, ribbons, and stalagmites). The timing and duration of water detected on formations was directly attributed to overhead infiltration.