198 



TRANSPORTATION OF DEBRIS BY RUNNING WATER. 



rUour interval O.O2 foot 

 Width oftroufffiJfoot 



FIGURE 68. Contoured plot of a stream bed, as shaped by a current. 



In view of these facts, the apparent results 

 of the experiments with crooked channels must 

 be received with caution, and probably nothing 

 more should be claimed for them than a general 

 indication that the capacity of a moderately 

 bent channel does not differ greatly from that 

 of a straight channel. 



FEATURES CAUSED BY CURVATURE. 



Incidentally the experiments illustrated sev- 

 eral consequences of curvature in addition to 

 the influence on slope and capacity. At each 

 turn the swiftest part of the current was thrown 

 to the outer or concave side of the channel, and 

 the slower parts moved toward the opposite 

 side, the transfers giving to the current as a 



whole a twisting motion. The action on the 

 debris became exceptionally strong near the 

 outer side and exceptionally weak near the 

 inner. A result of the strong action was that 

 part of the load was thrown upward, so as to 

 be temporarily suspended, and a result of the 

 diversity of velocity was the maintenance of 

 deep places near the outer wall and of shoals 

 near the inner. Associated with the twisting 

 motion were many whirls or eddies; and the 

 general obliquity of motion had the effect of 

 reducing the mean velocity in the direction of 

 the general flow. The reduction of mean 

 velocity was recorded in an increase of mean 

 depth, which amounted, in the average of all 

 examples, to 7 per cent and ranged from 2 to 

 14 per cent. 



