146 



TRANSPORTATION OF DEBRIS BY RUNNING WATER. 



charge. The second group gave comparative 

 ratios for discharges of 0.182, 0.363, and 0.734 

 ft. 3 /sec., by means of five sets of index values; 

 and two other groups made other comparisons, 

 as shown in Table 37. The upper division of 

 the table gives mean values of i t and i a ; the 



that within each group the values of the 

 indexes decrease as discharge increases, while 

 the values of the ratio, as a rule, increase with 

 the increase of discharge. To the first rule 

 there are no exceptions; the exceptions to the 

 second are not so important as to leave the 

 principle in doubt. 



lower division, their ratios. It will be observed 



TABLE 37. Variations of the indexes i t and 13, and their ratio, in relation to discharge. 



The variations of the indexes with discharge as a factor controlling capacity, is more pro- 

 have already been illustrated in another way nounced for large discharges than for small, 

 (pp. 107, 143). The new fact brought out is under like conditions of slope, width, and 

 that the superiority of slope over discharge, fineness. 



TABLE 38. Variations of the indexes i t and i 3 , and their ratio, in relation to width of channel. 



A different grouping of the index values, 

 but similar in principle, gave the means and 

 ratios of Table 38, which is related to channel 

 width just as Table 37 is related to discharge. 

 With a single exception, the mean values of 

 indexes increase with width; thus illustrating 

 general facts previously noted on pages 104 

 and 143. Without exception, the ratios of 

 ij to i s decrease with increase of width. The 

 new fact brought out is that the superiority of 

 slope over discharge, as a factor controlling 

 capacity, is more pronounced for narrow chan- 

 nels than for wide, under like conditions of 

 slope, discharge, and fineness. 



As form ratio varies inversely with width, it 

 follows that the superiority of slope is more 



pronounced, under like conditions, when form 

 ratio is large than when it is small. 



A third grouping of the index values, making 

 a similar comparison of their averages and 

 ratios with fineness of debris, is reported in 

 Table 39 (p. 147). The mean values of indexes 

 increase on the whole in passing from finer to 

 coarse grades, but there is much irregularity. 

 The same irregularity was encountered when 

 these relations were examined in other con- 

 nections. (See pp. 108 and 143.) The ratios 

 decrease on the whole from finer to coarser, 

 and there is but one discordance among the 

 sequences. 



To compare the variations of the indexes 

 with changes in slope, the 32 pairs of values of 



