THE WORK OF RUNNING WATER. 



191 



The straightening of the channel is often accomplished in another 

 way. Even before the meanders reach the stage represented by Fig. 1, 

 Plate XVI; the position of the channel becomes unstable. In time of 

 flood, the whole flat is covered with flowing water. The greater depth 

 of water in the channel tends to give it a velocity greater than that of 

 the water on the flat outside. But the distance from a to c via b (Fig. 

 181) is much greater than that in a direct line. It follows that the 

 slope from a to c direct is greater than that by way of h. If the current 

 between a and c in time of flood be strong enough to erode, it may 



Fig. 181. — Diagram illustrating later stages in the development of meanders. 



deepen its bed, and thereby increase the volume of water following this 

 course. The increased volume gives increased velocity, and the result 

 may be the opening of a channel between a and c direct. The channel 

 may be worn so deep that when the flood subsides, the stream will 

 follow it. So long as the abandoned channel-curve remains unfilled 

 with sediment, it is often called a cut-off. If it contains standing 



