148 



TRANSPORTATION OF DEBRIS BY RUNNING WATER. 



ered that is, the superiority of the control by 

 slopes, as compared with the control by dis- 

 charge, is more strongly marked in the case of 

 duty than in the case of capacity. 



i. 1.93 

 For general averages, - = r-j-= 1.36, and 



. *t _ L93 ^1. 3 . 



^ 



In Table 41 the values of . _^ ^ correspond to 



those of t 1 in Tables 37 to 40 that is, they 



are based on the partial means of those tables 

 and are arranged under the same groups, the 

 purpose being to show how the dominance of 

 control by slope, as expressed by a ratio, varies 

 with certain conditions. 



TABLE 41. Variations of the ratio . ' in relation to dis- 

 charge, width of channel, fineness of debris, and slope. 



In comparing this table with the tables of 

 -^, the most conspicuous feature noted is that the 



variation of 



with all conditions is much 



more pronounced than the variation of A 



*3 



Associated with this is the fact that the excep- 

 tions or apparent reversals observed in Tables 

 37 and 39 are not repeated in Table 41. 



In verbal generalization of the tabulated 

 results it is to be borne in mind (1) that the 

 alphabetic order in which the grades are 

 arranged is the order from fine to coarse, and 

 (2) that variation with respect to form ratio 



is the inverse of variation with respect to 

 width of channel. The general fact is that 

 the dominance of control by slope, as com- 

 pared with control by discharge a dominance 

 always pronounced is notably increased by 

 increase of slope, discharge, fineness, or form 

 ratio. 



(73) 



CONTROLS OF EFFICIENCY. 



The index of relative variation of efficiency 

 in relation to slope (p. 144) is i l 1; and the 

 corresponding index for efficiency in relation to 

 discharge is i 3 l. The ratio of these indexes 



n "| n 



^r is greater than =*, the corresponding ratio 



in the case of capacity, with exception of those 

 doubtful cases in which i l <i 3 . That is, the 

 superiority of the control by slope, as com- 

 pared to the control by discharge, is more 

 strongly marked in the case of efficiency than 

 in the case of capacity. It is also true that 



n 1 o 



-r<- *-;-; or that the superiority of control 



l,n 1. tro ~~ -1 



by slope is less strongly marked for efficiency 

 than for duty. For the general averages 

 i, = 1 .93 and i, = 1 .42 the computed values of 

 the ratios expressing superiority of control by 

 slope are, as to capacity 1.36, as to efficiency 

 2.21, as to duty 4.3. 



TABLE 42. -Variations of the ratio ^T in relation to dis- 

 charge, width of channel, fineness of debris, and slope. 



