Rapid Recharge Events in a Karstic Aquifer: An Example from Lake of the White Roses, Lechuguilla Cave, New Mexico

A short-term rise in pool levels in Lechuguilla Cave in response to extreme precipitation and flash-flooding events demonstrates the connectivity between the cave and the regional aquifer system. Lechuguilla Cave, currently ranked as the deepest limestone cave in the continental United States, is formed in middle Permian carbonates in the Guadalupe Mountains of southeastern New Mexico. Lake of the White Roses, the lowermost pool in the cave, is thought to intersect the regional water table in the Capitan Reef Aquifer, which provides the water supply for the city of Carlsbad and much of surrounding Eddy County. Direct measurements and datalogger records show that pool levels had steadily declined by over 5 meters since the pool was discovered in 1989, a period during which New Mexico was subject to episodic drought conditions. In 2004 Eddy County experienced unusually high rainfall that included a severe storm in early April. This extreme precipitation event caused flash flooding in the Pecos River and in arroyos in the Guadalupe Mountains, which serve as line sources of recharge to the Reef Aquifer. Within 3 days, pool levels in Lake of the White Roses began to rise, reversing a 13-year declining trend. Water levels in the pool eventually rose 4 cm above pre-flood conditions, then began to decline over the next two weeks. However, beginning in September, pool levels began to rise again, ultimately increasing by almost a meter relative to levels recorded at the beginning of 2004. The higher water levels persisted for several months, consistent with the longer-term precipitation record in Eddy County, which was twice the annual average in 2004. The short and medium-term increases in pool levels in Lechuguilla Cave also correlate to increases in hydraulic head recorded in a monitoring well completed in the Reef Aquifer more than 32 km northeast of the cave, and appear to reflect the triple porosity system — conduit + fracture + matrix — that is typical of karstic aquifers.