Aquifer Response to Record Low Barometric Pressures in the Southeastern United States

Abstract

A late-winter cyclone classified as one of the most intense of the 20th century moved across the Southeastern states of Georgia and South Carolina and onto the Northeast during March 12–14, 1993. Record low barometric pressures were recorded in Augusta, Georgia (28.93 inches of mercury) and Columbia, South Carolina (28.63 inches of mercury) on March 13, 1993, and pressures returned to normal values (near 30 inches of mercury) within one day following these record lows. This relatively unusual event provided an opportunity to examine the attendant water-level response in continuously monitored ground-water wells in regional Atlantic Coastal Plain, Piedmont, and Blue Ridge aquifers in the Southeast. Water levels in all wells examined responded inversely to the short duration, extreme drop in barometric pressure. Barometric efficiencies (Δground-water level/Δbarometric-pressure level) calculated were dependent on depth to screened- or open-interval midpoint (highest correlation coefficient, r 2 = 0.89) and, to a lesser extent, total thickness of confining material above the aquifer tapped (highest r 2 = 0.65). Wells in crystalline-rock aquifers had a correlation with depth to open-interval midpoint (r 2 = 0.89) similar to the sedimentary aquifers examined. The magnitude of barometric efficiency was also strongly related to a well's increased distance from aquifer outcrop areas in the Cretaceous aquifers in South Carolina (r 2 = 0.95) and the upper Brunswick aquifer in Georgia (r 2 = 0.90), because these aquifers are more deeply buried toward the coast. This relation between barometric efficiency, well depth, and extent of confinement suggests that barometric efficiency determinations can provide useful information to hydrologists concerned with examining an aquifer's degree of confinement and corresponding isolation from land surface, particularly when the aquifer is used as a source for public supply.