Timber Cutting and Water Yields 



601 



her cutting and the associated site 

 deterioration is not serious, the open- 

 ing of the forest should increase total 

 yields of usable water, build up peak 

 discharges to a minor extent, and still 

 permit a normal supply of water to pass 

 through the soil into ground water and 

 therefore to produce sustained stream 

 flow from deep sources, such as peren- 

 nial springs. 



These principles are not yet com- 

 pletely established, and they may be 

 expanded or altered considerably as 

 further knowledge is obtained. But it 

 is interesting to see how, even now, 

 they can be applied to a variety 

 of watershed-management problems, 

 varying from the control of erosion and 

 floods to the production of maximum 

 supplies of water. 



Consider the first of these, for ex- 

 ample. Where floods and sediment 

 cause damage, the streams have too 

 much water and it is concentrated too 

 much in short, abrupt peaks. At the 

 same time they carry large amounts of 

 sterile sediment that clogs channels 

 and ruins farm lands. Forest vegeta- 

 tion cannot do all that is necessary to 

 remedy such conditions, but it does 

 stabilize the soil and minimize erosion. 

 It also intercepts and evaporates rain- 

 fall and tends to dry out the soil mois- 

 ture, making as much space available 

 as possible in the great storage reservoir 

 of the soil on watershed land. 



To help solve such problems, it is 

 advisable to keep the forest cover as 

 dense as possible in order to provide 

 maximum soil protection and oppor- 

 tunity for the consumption of water. 

 This may mean only the lightest and 

 most careful timber cutting, or perhaps 

 no cutting at all. Then the forest will 

 reduce floods and erosion from its own 

 area, even though its benefits may have 

 to be supplemented by engineering 

 works and by soil and water conserva- 

 tion measures on agricultural and 

 other nonforest land. 



As a variation of this problem, per- 

 haps our watershed may be located in 

 an area of considerable erosion hazard, 

 but where there is an intense demand 



for water from the irrigated valleys 

 below. A good example is provided by 

 the cut-over, deteriorated watershed 

 land in the ponderosa pine belt of the 

 Rocky Mountain Front Range, with 

 credible soil derived from the red 

 Pike's Peak granite. In such cases there 

 is little question as to the proper 

 method of watershed management. 

 The land must be protected and ero- 

 sion rates slowed down and finally con- 

 trolled as much as possible, even at the 

 cost of lowered water supplies. Again, 

 this means building the best possible 

 cover of forest and other vegetation 

 and using any other measure neces- 

 sary to remedy the cause. When the 

 spiral of flash floods and erosion has 

 been started to any serious degree, the 

 losses due to land depletion and sedi- 

 mentation far exceed the nominal 

 benefits of augmented supplies of silt- 

 laden water. 



At the other extreme of watershed 

 problems, suppose we are concerned 

 with an area within the millions of 

 acres of high mountain country that 

 are quite safe and stable. It produces 

 water for urban and irrigated areas, 

 but the area itself is not susceptible to 

 floods or erosion unless it is severely 

 abused. Here the watershed manager 

 can relax in comparative security, 

 looking at clear, perennial streams 

 with high yields but small annual vari- 

 ations in flow. In such an area he can 

 design the silvicultural treatment of 

 the forest so as to provide the best sup- 

 ply of all its resources, without having 

 a constant fear of upsetting a delicate 

 balance. His management may be var- 

 ied according to the combined needs 

 of forest and watershed benefits, from 

 light selection cutting to clear cutting 

 if that seems necessary. But whatever 

 methods he deems desirable, his sound 

 and well-planned management of this 

 watershed will pay dividends to the 

 people in the valleys below, through 

 more adequate supplies of usable 

 water. 



H. G. WILM is a silviculturist who 

 has specialized in research on the 



