 The USGS estimated that total water storage was about in 2005.This is a decline of about , or 9%, since substantial groundwater irrigation development began in the 1950s.Water conservation practices (terracing and crop rotation), more efficient irrigation methods (center pivot and drip), and reduced area under irrigation have helped to slow depletion of the aquifer, but levels are generally still dropping in areas including southwestern Kansas and the Texas Panhandle.