National Geographic : 1993 Mar
Feet above sea level 4,000 3,000 2,000 : Ogallala I cross section The aquifer ranges in thickness from less than a foot to 1,300 I feet, while averaging 200. Its I upper boundary varies in depth From surface level to 300 feet. By far the greatest volume of water underlies Nebraska. SOUTH s o U T H DA KO-TA l/i "4 . 'Itsor Rose more than 15 feet 7.5-14.9 2.5-7.4 No significant change 2.5-7.4 7.5-14.9 Declined more than 15 feet From the 1940s to 1980 the aquifer's average water level declined nearly ten feet, with declines exceeding 100 feet in some parts of Texas. During the 1980s the level declined only an additional foot-a result of increased rain and snow, water management, and new technol ogies. Still, serious depletion continued in parts of Kansas and Texas.