PROBLEMS FROM DEVELOPMENT 71 



lower end of the valley is made up largely of return flow 

 from irrigation. A substantial part, perhaps half, of the 

 water that enters the valley in streams serves to recharge 

 the ground-water reservoir, either by seepage from stream 

 channels and irrigation canals or by percolation from irri- 

 gated lands. The pumping draft throughout the valley is 

 believed to exceed average ground-water replenishment by 

 about 1,500,000 acre-feet, and for many years there has been 

 a progressive depletion in ground-water storage. Water 

 deficiencies — in precipitation, stream flow, and ground- 

 water replenishment — are generally greatest near the south 

 end of the valley and become progressively less toward the 

 north. 



This short statement of the over-all conditions in San 

 Joaquin Valley indicates the basis for a fundamental part 

 of the Central Valley Project: importation of water from 

 Sacramento Valley, which constitutes the northern part of 

 the Central Valley and annually discharges sizable surpluses 

 into San Francisco Bay. Present plans call for ultimate con- 

 struction of 38 reservoirs with capacity of 30 million acre- 

 feet, approximately equivalent to the annual flow of all 

 streams in the Central Valley; major canals to transport 

 water southward; and extensive utilization of ground-water 

 reservoirs for annual and cyclic storage. The conditions of 

 infiltration, storage, movement, and discharge of ground 

 water are so diverse in various parts of San Joaquin Valley 

 that detailed hydrologic knowledge is prerequisite to maxi- 

 mum utilization of the imported water. Basic data are now 

 being obtained and analyzed but in some instances not soon 

 enough to influence the design and construction stages of 

 the project. 



In several places in San Joaquin Valley there are problems 

 of excessive overdraft from pumping. For example, in the 

 Delano-Earlimart area static water levels in some wells are 

 as much as 250 feet lower than in 1905, and the pumping 

 lifts in many wells are between 300 and 400 feet. In the 

 Arvin-Edison area, average water levels dropped at a rate 



