CHAPTER V. RELATION OF CAPACITY TO DISCHARGE. 



FORMULATION AND REDUCTION. 



As a condition controlling the capacity of a 

 stream for the traction of debris, discharge is 

 the coordinate of slope. Each of the two fac- 

 tors is proportional to the potential energy of 

 the stream, on which traction depends; and the 

 control of each is exercised through the control 

 of velocity. Their fundamental difference in 

 relation to traction is connected with depth of 

 current. When velocity is augmented by in- 

 crease of slope, the depth is reduced; when it is 

 augmented by increase of discharge, the depth 

 is increased. Notwithstanding this difference, 

 the relations of capacity to discharge parallel 

 those of capacity to slope to a remarkable 

 extent. Thanks to this parallelism, the discus- 

 sions of the present chapter may be based in 

 considerable part on those which have preceded. 



The data for the comparison of capacity with 



discharge are contained in Table 12. In each 

 division of that table assigned to a grade of 

 d6bris are a number of subdivisions pertaining 

 severally to particular widths of channel. Each 

 column of such a subdivision pertains to a par- 

 ticular discharge and contains a series of ad- 

 justed capacities corresponding to an orderly 

 series of slopes. The values of capacity con- 

 nected with the same slope and comprised in 

 the same subdivision constitute a group illus- 

 trating the relation of capacity to discharge. 

 Table 32 contains in its upper part a number of 

 such groups, selected and arranged for the pres- 

 ent purpose. So far as practicable they per- 

 tain to the same slope, but it was not possible to 

 secure absolute uniformity in this respect and 

 at the same time make the representation in- 

 clude data of all the grades of debris. For 

 grades (A) to (E) the slope is 1.0 per cent; for 

 grades (F) to (H), 1.2 per cent. 



TABLE 32. Data on the relation of capacity to discharge, with readjusted values of capacity, C r , and values of the index of 



relative variation, i a . 



137 



