Watersheds and How to Care for Them 



607 



may be so great as to warrant a fire- 

 control program tight enough to pre- 

 vent the occurrence of any man-made 

 fire, with provision for the immediate 

 suppression of naturally caused fires. 



Construction improvements, such as 

 roads, trails, airfields, and the like, are 

 potentially hazardous from the stand- 

 point of runoff and erosion because 

 they uncover extensive land areas. The 

 construction of such projects calls for 

 special precautions. 



First, roads, trails, and other clear- 

 ings should be located and designed so 

 as to cause the least possible soil dis- 

 turbance. Provision should be made for 

 the immediate stabilization of cut and 

 fill slopes. Because such projects in- 

 variably produce some runoff, experi- 

 ence shows that adequate provision is 

 needed for safely passing the drainage 

 water to the natural channels, or for 

 storing the runoff in the adjacent 

 mantle by contour trenching or ter- 

 racing the land. Provision for regular 

 maintenance and prompt repair of cut 

 and fill slope stabilization works and of 

 drainage facilities is essential. Where 

 it is not feasible physically or eco- 

 nomically to meet these requirements 

 of satisfactory watershed maintenance, 

 the improvements should not be built. 



The construction of water facilities, 

 such as dams, canals, and transmoun- 

 tain diversions, present other problems. 

 These require consideration of all pos- 

 sible adverse effects as well as bene- 

 ficial effects on watershed conditions. 

 All, of course, must be designed against 

 failure. Adequate provision should be 

 made in the design and operation of 

 impounding dams for maintaining an 

 effective habitat for fish and other 

 aquatic life. Transmountain diversions 

 should be constructed and operated so 

 as not to cause the scouring of chan- 

 nels and consequent sedimentation in 

 the areas to which water is diverted. 

 Full advantage should be taken of op- 

 portunities to spread the store water 

 underground. 



HARVEST CUTTINGS, timber-stand 

 improvement, thinnings, and the other 



cultural treatments of the forest and 

 range cover offer possibilities of im- 

 proving the usefulness of stream flow 

 in two ways. Some types of treatment 

 will result in increased, or more timely, 

 yields of water; others, in less runoff. 



Removal of trees and shrubs from 

 along stream banks and on valley bot- 

 toms where the plant roots have con- 

 tinuous access to free water in the 

 channels or valley fill is an effective 

 means of reducing transpiration losses 

 and thus increasing stream flow during 

 the growing season. Conversion of a 

 forest type to a plant cover that re- 

 quires less water for growth offers an- 

 other possibility of increasing water 

 yields. It may be desirable on some 

 western watersheds, for example, to 

 suppress the deep-rooted aspen, which 

 consumes up to about 20 inches of 

 water in a growing season, and encour- 

 age a plant cover of more shallow- 

 rooted grasses and herbs that require 

 several inches less water for growth. 



In other areas, where most of the 

 stream flow is derived from winter 

 snow, harvest cuttings of the conifers, 

 which create openings for deeper ac- 

 cumulation of snow and decrease in- 

 terception losses, offer another chance 

 of obtaining a greater or a more pro- 

 longed yield of stream flow. Studies in 

 Utah indicate the use of snowdrift 

 fences may accomplish similar results 

 on high-elevation and windswept snow 

 fields. All such measures should be un- 

 dertaken, however, only when they can 

 be accomplished without causing ac- 

 celerated erosion or a serious increase 

 of flood discharges. 



In many parts of the country the 

 flood hazard is high because of pro- 

 longed, copious rainfall, or very high 

 rates of rainfall and of snow melt. 

 Flood control in such areas generally 

 requires the maximum possible cover 

 of vegetation and litter. Here harvest 

 operations should be aimed at main- 

 taining a canopy that will intercept 

 and evaporate the greatest possible 

 amount of precipitation before it 

 reaches the ground. There should be a 

 minimum of disturbance to the litter 



