1512 



AMERICAN FORESTRY 



ged the topography, the more marked is this contrast, brought down by the streams and deposited in them 

 In hillv country some erosion is, of course, inevitable reduces their capacity and consequently their effective- 

 under any conditions. When the soil cover of trees, ness by just so much. This sedimentation is serious 



u n d e r b rush , 

 and litter is 

 kept intact, 

 however, this 

 is more often 

 beneficial than 

 otherwise, since 

 only the light- 

 er soil particles 

 are w ashed 

 away, to be- 

 later deposited 

 in the more 

 level lands be- 

 low, adding t<i 

 their fertility. 

 But when this 

 protective cov- 

 er is interfered 

 with, whether 

 by fire, destruc- 

 tive lumbering, 

 overgrazing, or 

 i n j u d i c ious 

 clearing of 

 land for agri- 

 culture, the 

 proportion of 

 coarser, infer- 

 tile materials 

 v/ashed away 

 increases great- 

 ly and trans- 

 forms erosion 

 from a con- 

 structive int( 1 

 a dangerously 

 d e s t r u c tivc 

 force, difficult 

 of control and 

 capable of do 

 ! 11 g untold 

 damage. 



From the 

 standpoint of 

 the water user, 

 the tendency of 

 the mountain 

 forests to pre- 

 vent erosion is 

 of the utmost 

 import ance. 

 Wherever stor- 



. ..•cnL-3iSei.lir 



^-«l_-4fc?.JAfcvJ??jUjta ^'l 



WATER FOR IRRIGATION AND POWER 



Upper. — Roosevelt Dam and power plant (in riRht center foreKround). This reservoir stores 1,140.000 acre- 

 feet of water and, together with the Verde River, furnishes the water supply for the Salt River 

 Reclamation Project in southern .'Xrizona. The hulk of the water for the project originates on 

 the Tonto National Forest and the White River Indian Reservation. 



Lower. — Minidoka D.im and power plant. This dam supplies water for the irrigation of 120,300 acres on the 

 Minidoka Reclamation Project in southern Idaho. The electricity developed at the power plant 



under any con- 

 il i t i o n , but 

 '1 () n b 1 y so 

 when, as not 

 i 11 f r e quently 

 h a p p e ns, no 

 nther satisfac- 

 tory dam sites 

 are available 

 and the reser- 

 voir can not be 

 icplaced at a 

 r e a s o n a b 1 e 

 cost. 



Water he.'ivi- 

 ly laden with 

 eroded ma- 

 terial often de- 

 creases the ef- 

 ficiency and in- 

 creases the cost 

 (if maintaining 

 diversion dams, 

 pipe lines, 

 t1 limes, canals, 

 and other irri- 

 gation works. 

 Sometimes 

 s u c h water 

 damages the 

 crops to which 

 if is a])|5lied, 

 and nut infrc- 

 (|ucntly it ser- 

 iously injures 

 or even ruins 

 the land by 

 burying it un- 

 der a mass of 

 s;iik1. gravel, 

 bowlders, and 

 other infertile 

 debris. Exces- 

 ■^ i V c erosion 

 may interfere 

 -■eriously with 

 iKivigation by 

 I' 1 1 i n g the 

 streams with 

 material which 

 is deposited in 

 their lower 

 reaches and in 



used on many farms for lighting, heating, and cooking, 



age reservoirs must be used, whether for municipal sup- the harbors into which they empty. The action of the 

 plies, irrigation, or water power, they are exposed to the forest in reducing surface run-off tends also to regulate 

 ever-present danger of silting up. Every bit of soil the flow of streams. Instead of rushing away in uncon- 



