FLOW ROUND RIVER BENDS 



831 



bend, in which the direction of flow was indicated by coloured stream 

 lines and by the behaviour of threads tied to pins fixed in the bed of the 

 stream, as well as by floating particles of matter, indicated a state of 

 affairs as represented in Fig. 145. Here the dotted line. A B indicates 

 the path of a particle floating in the surface, while the curves shown in 

 full represent the motion near the 

 bed of the stream. 



As indicated, a counter-current 

 flows from inner to outer bank over 

 the upper portion of the stream, 

 but since the same volume of water 

 is moved by the two currents, and 

 since the sectional area of the outer 

 current is comparatively very large, 

 its effect in carrying suspended 

 matter to the outer bank is negli- 

 gible. 



While this theory undoubtedly 

 accounts for a portion of the ero- 

 sion, and for the deposition of de- 

 tritus at the inner bank, it is 

 probable that the impact of the 

 stream on the concave bank is a 

 more potent factor in actually 

 causing erosion, and more par- 

 ticularly is this the case when 

 the stream is in flood and when 

 are most serious. 



secc/on on C-D. 

 FlG - li5 - 



in consequence the erosive effects 

 Under such circumstances observation shows that 

 the surface velocity is a maximum near the outer, and not the inner? 

 bank. 



ART. 94A. Loss OF HEAD PRODUCED BY BENDS IN AN OPEN CHANNEL. 



% 



Very little experimental evidence is available regarding the loss of head 

 due to bends in an open channel. Experiments on a cement lined 

 semicircular conduit, 9'8 feet in diameter, divided into four consecutive 

 sections A B G D, showed the following results. 1 



Section A is a tangent 640 feet long. 



B is 120 feet long and includes a curve of 100 feet radius. 



Engineering Record, Oct. 21st, 1911. By E. G. Hobaon. 



