PROBLEMS FROM DEVELOPMENT 87 



brought under irrigation, many of these bottom lands have 

 been afflicted by rising water table. Currently about 8,000 

 acres in Helena Valley is waterlogged. It has been proposed 

 that a 3-mile tunnel be constructed from the Canyon Ferry 

 Dam to divert into Helena Valley enough water to irrigate 

 10,000 acres of new land and to supplement the water sup- 

 ply to another 15,000 acres of land, chiefly on the upper 

 slopes of the valley. This proposed diversion may well in- 

 crease the waterlogged areas in the lower part of the 

 valley. 



Helena Valley's ground-water reservoir is tapped by a few 

 irrigation wells, and it is capable of producing much larger 

 quantities than now developed. There is a good possibility 

 that pumping from wells for irrigation of the lower part 

 of the valley would lower the water table in waterlogged 

 areas and also release surface-water supplies for use on lands 

 higher on the slopes. 



San Luis Valley, Colo. zo San Luis Valley in the Upper Rio 

 Grande basin has a valley floor generally more than 7,000 

 feet above sea level. Irrigation is accomplished mainly by 

 diversions from the Rio Grande and other streams tributary 

 to the valley but is supplemented to considerable extent by 

 water from approximately 5,000 flowing wells and 2,000 

 pumped irrigation wells of large capacity. Since irrigation 

 began about 1874, the ground-water storage in the valley 

 has increased; the area of artesian flow has expanded, and 

 some shallow gravels have been saturated and subsequently 

 tapped by wells for supplemental irrigation. Farmers have 

 found the coarse, permeable soils to be ideal for subirriga- 

 tion along the west slope, where it is possible to maintain 



so References: Robinson, T. W., and H. A. Waite, "Ground Water in the 

 San Luis Valley, Colorado," U.S. Geol. Survey (Contribution 

 to the Rio Grande Joint Investigation), 1937, 119 pp. 

 "Water Facts in Relation to a National Water-resources 

 Policy," U.S. Geol. Survey, Mimeo. rept., Appendix C, 

 pp. 24-26, April 1950. 



