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Groundwater Overdraft Dramatized portrayals of the arid West and the region's perennial droughts often focus on the desperation of a well gone dry - the wind blows, the windmill turns, but fhe rain-starved earth has nothing more to give. In reality, that is only where the problem begins because overdrafting aquifers can have long- lasting consequences that are not resolved by a cloudburst or a flash flood. The groundwater supply for individual years varies considerably: In dry years, when there is less natural recharge and less surface water available, pumping typically goes up. In wet years, when more recharge occurs and more surface water is available, less pumping is needed to meet water needs. Overdraft occurs when over a period of years, more water is pumped from a groundwater basin than is replaced from all sources - such as rainfall, irrigation water, streams fed by mountain runoff and artificial recharge. As extensive pumping lowers the water table, the energy costs of lifting thaf water to the surface increases. In extreme cases, the water table can fall below the reach of existing wells, requiring costly extensions or new, deeper wells. But overpumping can lead to even more serious problems if the excessive extraction takes place over a long period of time - including land subsidence and, in areas along the coast, sea water intrusion. While some aquifers are in balance, California as a whole uses more groundwater than is replaced. Some 15 million acre-feet of water is pumped each year on average, About 6,5 million acre-feet of water seeps back into the ground as irrigation water is spread onto fields or run through irrigation canals. An additional 7 million acre-feet of water is naturally recharged by rain and runoff percolating into the ground, and still more is intentionally recharged through artificial replenishment projects, On average, California uses 1.3 million acre-feet of groundwater more than is naturally or artificially recharged, according to projected water budgets. In the Central Valley, the U.s. Geological Survey (USGS) estimates the aquifers are overdrafted by an average of 800,000 acre-feet of water a yeaL That is far less overdraft than in earlier decades, before dams and canals were constructed to help Central Valley farmers by capturing, storing and transport- ing Sierra runoff. The persistent overdraft, however, is troubling because groundwater is increasingly tapped to satisfy growing urban needs and to make up for surface water supplies that have been reallo- cated to restoring rivers and marshes. \\ ..... - " SIll..... I.Iurr - IIfSlll S'!!fIll IN -.,," ~ -- A statewide assessment by DWR in 1981 concluded that if trends continue, 11 of California's 450 ground- water basins were "subject to critical conditions of overdraft" that could lead to "significant adverse" social, environmental and economic consequences. Eight at these basins were in the San Joaquin Valley, and three were the coastal basins of Santa Cruz, Ventura and Santa Barbara counties, Another 42 basins throughout the state were found to be overdrafted and experiencing some - though less significant - consequences, Subsequently, a 1987 assessment by DWR concluded that the volume at overdraft represented a relatively small amount of the groundwater in storage - an improvement credited to the artificial recharge efforts by more than 65 local water agen- cies, Those management efforts were then tested by the 1987-1993 drought The drought revealed that in some places, the long-term consequences of over- pumping have not been resolved. Juseph !-~ Po/allllof the u..')', Geological Sun'ey, Irho pioneeral suhsidence research ill the Safl Joaquin ~~llley, stands Ilear II hClIchmark soutl/{'Wi! (~rM(,Jldotll, The /wlll slIf/ace in this area has subsided Ilearly 3U fet>t !Jecullse (~ri"tel1sh-e groundwater pumping, Signs 011 the fUHrer pole indicate the lel'e/ of the fund SIll/lice i1l /925, /955 <Illd /977. 11