CHAPTER XI. EXPERIMENTS WITH CROOKED CHANNELS. 



EXPERIMENTS. 



In order to study the influence which bends 

 in the channel exert on capacity for traction, a 

 short series of experiments were made with 

 channels having angular bends and others with 

 channels having curved bends. Each of these 

 channels had a width of 1 foot and was shaped 

 by means of partitions within a trough 1.96 

 feet wide. (See fig. 67.) Above and below the 

 bends were straight reaches of the same width. 

 All the experiments were made with de"bris of 



grade (C) and with a discharge of 0.363 ft. 3 /sec. 

 The loads were measured. In some experi- 

 ments the head lost in the region of the bends 

 was measured by means of level readings on the 

 water surface above and below. 



After each experiment the profile of the bed 

 was determined by levelings at intervals of 1 

 foot, and in several cases the region of the 

 bends was covered by such levelings and 

 sketches as to make it possible to construct a 

 contour map of the bed. 



I 7 



n ? 



m T 



iv 



FIGURE 67. Plans of troughs used in experiments to show the influence of bends on traction. 



SLOPE DETERMINATIONS. 



The profiles of the channel beds as shaped 

 by the current were plotted. Through that 

 part of the profile corresponding to the straight 

 channel above the bends was drawn a straight 

 line representing the mean slope for that region, 

 and a similar straight line was drawn below the 

 region of the bends. From a point on the first 

 line near the position of the first bend to a point 

 on the second line corresponding to a position 

 several feet below the last bend a straight line 

 was drawn, and this was assumed to represent 

 the mean slope of the channel in the region 

 affected most by the bends. The profiles above 

 the bends showed evidence of the rhythms com- 

 monly observed in the straight^channel experi- 

 ments. The profiles below the bends showed 

 steeper undulations, which were ascribed to 

 196 



the influence of the strong agitation of the 

 water in passing the bends. In estimating 

 the slopes in the region of the bends the dis- 

 tance used was the length of the medial line of 

 the channel. 



The observations for head were made at 

 points 2 feet and 4 feet above the first bend 

 and 3 feet and 5 feet below the last bend, and 

 the slopes were computed for the distances, on 

 the medial line, between the points. 



Check estimates of slope for straight chan- 

 nels were obtained by interpolation from Table 

 12, the determinations of load being used as 

 arguments. 



The data are assembled in Table 64, where 

 the stronger and weaker determinations of the 

 slope of the debris surface are severally indi- 

 cated by the letters a and &. The measure- 

 ments of water slope are thought to be coordi- 



