174 



TRANSPORTATION OP DEBRIS BY RUNNING WATER. 



The corresponding curves for the finer com- 

 ponent (at the right in fig. 56) show that 

 capacity for finer de'bris is influenced by the 

 admixture of coarser, but not in the same 

 way. Each addition of the coarser reduces 

 capacity, the rate of reduction being at first 

 gradual, then more rapid, and afterward 

 gradual. 



The general effect of the addition of fine 

 material being to increase capacity, and the 

 effect of adding coarse material to reduce 

 capacity, let us now inquire the effect of 



diversifying the material of the load by ex- 

 changing part of it for a finer grade and part 

 for a coarser. Probably no general answer to 

 this question may be derived from our data, 

 but a partial answer is possible if we assume 

 that the initial grade is separated from each 

 of the substituted components by the same 

 contrast of fineness, expressed as a ratio. 

 To take a concrete example, from Table 61, 

 the capacity for grade (A) is 185 gm./sec., 

 for grade (G) 16 gm./sec., and for (A,Gj), 

 their equal mixture, 89 gm./sec. When for 



(> 



..(G) 



IE)- 



FIGURE K. Tractional capacities of components of mixed grades, in relation to the percentages of the components in the mixtures. Curves 

 at left show capacities for coarser component, at right for finer. Katios at left show percentages of finer component , at right of coarser. 



half of (A) there is substituted an equal 

 amount of (G), which is 16.2 times coarser, 



89 

 the capacity is changed in the ratio 



When for half of (G) there is substituted an 

 equal amount of (A), which is 16.2 times finer, 



89 

 the capacity is changed in the ratio .-^ = 5.56. 



The geometric mean of these ratios, 1.64, may 

 plausibly stand for the effect of substituting 

 an equal mixture of (A) and (G) for a grade 

 symmetrically intermediate between (A) and 

 (G). The method is easily criticized, and its 

 assumptions will certainly not bear close 



scrutiny, but it nevertheless yields a sort of 

 composite which is of use in showing that the 

 general effect of diversifying a stream's trac- 

 tional load is to enlarge capacity. Corre- 

 sponding composite ratios have been obtained 

 from the other examples of Table 61 and are 

 given below. 



