16 
BULLETIN 1486, U. S. DEPARTMENT OF AGRICULTURE 
increased and the stream bank on the convex side of the stream takes 
the position DEF. This new path is longer than the original. path 
and the velocity soon drops slightly as a result of the change. On 
the concave side of the stream, where velocity is lowest, a bar starts 
forming. As the flood recedes more sedimentation occurs and the 
bar is extended along points of least velocity. The next flood will 
probably cut the channel from the position DEF to the position 
DEF'. In the meantime, the convex stream bank below has moved 
to the dotted position and bars have formed on the upper shore 
through exactly the same process, Thus through a series of floods 
Fig. 15.— Channel change in a stream with wide flood plain due to erosion 
the tendency will nearly always be for movement as shown in Figure 
16. In general the principal channel current and also the deepest 
part of the channel will be found on the convex side of the stream. 
The above represents the general tendency for the stream as a 
whole. In addition there will be local erosion, shifting and cutting 
at many points due to cross currents, whorls, eddies, etc., these 
tending to erode at one point and silt up at another, so that the 
future behavior of any stream at any given point can only be pre- 
dicted after a careful study. In general, for any structure of material 
size, it will pay to go into the matter of location very thoroughly, 
studying the direction, velocity, and effect of flood currents at different 
