such as chaparral to a shallower-rooted 

 species such as grass causes increases in 

 water yield." 



Water yield from headwater streams can be aug- 

 mented by reducing vegetation density by 20 percent 

 or more. The following sections explore the inherent 

 potentials in the forest and range environment for 

 increasing regional water supplies. None of these 

 estimates fully consider all the many environmental 

 issues involved. 



In one study,^^ the energy balance method was used 

 to estimate the potential for augmenting water sup- 

 plies through forest management in States east of the 

 Mississippi River. Estimates from this study are 

 adjusted here in table 7. 1 5 to include all of the forests 

 east of the 100th Meridian. These values are based on 

 the assumption of complete forest regulation for 

 increased water supplies and a rotation age of 120 

 years. 



The values in table 7.15 are considered applicable 

 to regions but not necessarily to individual water- 

 sheds. It has also been estimated that even-age man- 

 agement of some Southeastern watersheds could 

 increase water yield considerably more than the 

 values in table 7.15.^9 



Timing of increased water yield is important if 

 reservoirs are not available to store the extra water 



Table 7.15 — Estimated potential for increasing 



water yield from forested lands in the eastern 



States 



Forest type 



Forest 

 area 



Average annual yield 

 increase 





Thousand 



Inches 



Thousand 





acres 



acre-feet 



White-red-jack pine 



12,666.7 



0.45 



475 



Spruce-fir 



21,484.5 



.60 



1,465 



Longleaf-slash pine 



17,316.6 



.30 



433 



Loblolly-shortleaf pine 



50,245.1 



.35 



1,465 



Oak-pine 



34,948.6 



.20 



582 



Oak-hickory 



115,268.7 



.10 



961 



Oak-gum-cypress 



29,380.9 



.20 



490 



Elm-ash-cottonwood 



26,120.5 



.20 



435 



Maple-beech-birch 



35,271.6 



.15 



441 



Aspen-birch 



20,582.1 



.10 



172 



Total 



373,285.3 



2.65 



6,528 



3' Hibbert, Alden R., Edwin A. Davis, and Thomas E. Brown. 

 Managing chaparral for water and other resources in Arizona. 

 Proc. Watershed Management Symposium, ASCE Irrigation and 

 Drainage Division, Logan, Utah, p. 445^68. 1975. 



'* Lee. Richard. Opportunities for increasing water supplies in 

 the eastern United States by vegetation management. Unpublished 

 Rep. On file at the Forest Hydrology Laboratory, Wenatchee, 

 Wash., 78 p. 1977, 



5' Anderson, Hoover, and Reinhart, op. cit. 



until it is needed. Research in the East indicates that a 

 large part of the increased flow occurs in later 

 summer when flow is normally lowest.'"' Some 

 streams which dry up in late summer flow continu- 

 ously after vegetation on the basin is removed.'*' 



The potential for augmenting water supplies in the 

 western United States has received considerable atten- 

 tion during recent years and estimates vary according 

 to the assumptions used. An intensive study by a U.S. 

 Senate Select Committee'*^ evaluated the opportunity 

 for increasing water supplies in the 17 western States 

 through vegetation management. This study indi- 

 cated a potential initial water yield increase of about 

 12 million acre feet per year. Another study^^ esti- 

 mated that, in the western States (exclusive of the 

 Pacific coastal areas), the potential annual increase in 

 water yield from all cover types with sustained yield 

 and multiple-use considerations, but with intensive 

 management for water yield improvement, would be 

 about 4. 1 million acre-feet above natural levels. The 

 estimated average annual cost of producing this much 

 water was $21.42 per acre foot at 1967 price levels. 

 However, the greatest potential appeared on com- 

 mercial forest land; intensive management for water 

 yield of about 66 million acres of commercial forest 

 land in the West could potentially increase annual 

 water yield by 1.8 million acre-feet at a 1967 equiv- 

 alent cost of $1.23 per year per acre-foot. 



In a more recent analysis, the potential for increas- 

 ing water supplies in Oregon, Washington, Idaho, 

 Alaska, and (northern) California was estimated.'''' 

 These estimates, by precipitation zone and timber 

 type, are presented in table 7.16. The values are based 

 on the following assumptions: (1) Water yield in- 

 creases from small experimental watersheds can be 

 expanded to large areas, (2) rotation age will be 

 shortened and the harvest of old-growth inventory 

 will accelerate, and (3) the forest harvest will be by 

 clearcutting. 



"0 Ibid. 



■" Kochenderfer, James N., and Gerald M. Aubertin. Effects of 

 management practices on water quality and quantity: Fernow 

 Experimental Forest, West Virginia. In Municipal Water Manage- 

 ment Symposium Proc, U.S. Department of Agriculture, Forest 

 Service. General Tech. Rep. NE-13, p. 14-24. 1975. 



■•^U.S. Senate Select Committee on National Water Resources. 

 Water resources activities in the United States: Evapotranspiration 

 reduction. Part 2: Vegetation management. Comm. Print No. 20, 

 86th Congress, 2nd Session, p. 13-42. 1960. 



■" Reigner, I. C, R. C. Maloney, and E. G. Dunford. 

 Unpublished Rep. On file at U.S. Department of Agriculture, 

 Forest Service. Washington, D.C. 1969. 



"'' Wooldridge, David D. Opportunities for increasing water 

 supplies in the Pacific Coast States by vegetation management. 

 Unpublished Rep. on file at the Forest Hydrology Laboratory, 

 Wenatchee, Wash., 130 p. 1978. 



312 



