A raging mountain stream overflows a bridge. 



DISCUSSION 



The three examples illustrate how the tables may be used, and the practical signifi- 

 cance of the effects of clearcutting operations. We once again remind the reader that 

 the tabulated values are expressed in yield per unit area, and hence may be applied to 

 watersheds of any size or at any elevation. 



In illustrating the use of the tables, we used a potential water yield increase of 

 15 percent. Some readers may consider this figure as too conservative, because it is 

 considerably smaller than figures reported in the literature. At Fraser, Colorado, 

 for example, where 75 percent of the annual precipitation occurs as snow, a 40 -percent 

 commercial clearcut in strips yielded a first-year increase of 30 percent in annual 

 streamflow (Goodell 1958). We used the figure 15 percent as an example, and not as a 

 universal recommendation. In using the tables, the reader should consider the special 

 circumstances applying to his case. 



The tables may also be used to solve problems relating to channel stability, bank 

 cutting, and stream level. However, because the characteristics of stream channels 

 vary considerably from one segment to another, it is apparent that a particular problem 

 may not have a unique solution. Nevertheless, the land manager may sometimes be 

 particularly concerned with certain segments of a stream channel because they appear 

 vulnerable to changes in the hydrologic regime. In such cases, it may be worthwhile to 

 make the assumptions needed to perform the calculations and to determine the magnitude 

 of changes that can be expected. 



7 



