88 CONSERVATION OF GROUND WATER 



the water table under a crop at any desired depth merely by 

 adjusting the gates and check dams along the surrounding 

 ditches. 



The Rio Grande has piled alluvium along its course and 

 thus created a closed basin in the north half of the valley. 

 Surplus irrigation water moves toward the sump area of this 

 closed basin and accumulates in numerous small lakes. 

 There has been a progressive accumulation of salts in the 

 low areas, and, as the water table has risen, some valuable 

 lands have become waterlogged. A project to drain the 

 closed basin by means of a canal to the Rio Grande is now 

 being studied and may ultimately result in reclaiming some 

 of the land and in making more water available for benefi- 

 cial use downstream, and if transfer arrangements can be 

 worked out, to the upper reaches of the San Luis Valley. 



In several ground-water reservoirs of the West where the 

 annual replenishment is in excess of the present ground-water 

 draft, the surplus is discharged into streams. In Willamette 

 Valley, Ore., for example, only a very small proportion of the 

 annual replenishment to the ground-water reservoir is used 

 by wells, and the remainder is discharged to streams chiefly 

 during the dry part of the year. The ground-water reservoir 

 under the Snake River Plain in Idaho discharges some of its 

 surplus into the Snake River at the famed large springs along 

 the north wall of the canyon. Ground-water reservoirs in many 

 of the higher mountain valleys likewise discharge surpluses 

 into streams; indeed, these areas are generally located where 

 the climate is sufficiently humid during some part of the year 

 so that the hydrologic conditions approach those of the humid 

 East. 



Willamette Valley, Ore. 31 The three largest cities and 

 two-thirds of the population of Oregon are located in Wil- 



si Reference: Piper, A. M., Ground-water Resources of the Willamette Val- 

 ley, Oregon, U.S. Geol. Survey Water Supply Paper 890, 

 1942, 194 pp. 



