THE LATERAL EROSION OF STREAMS 443 



case, however, the velocity data are taken from measurements on a 

 straight reach of the river having a very symmetrical profile. The 

 distribution of velocities being very different on curves, different rela- 

 tions would probably hold between the mean velocity and mean 

 squared velocity, and the above ratio would be changed. The 

 computation, the result of which is given above, involves less assump- 

 tion than any other method of attacking the problem discovered and 

 the figure, 18 per cent, may be safely considered of the same order 

 of magnitude as that expressing the actual difference of potential 

 lateral gradients on right-and-left curves in this case. The relation 



Fig. 3 



between potential lateral gradient and consequent lateral erosion 

 varies with other factors so that an attempt to compare the actual 

 erosion on right-and-left curves would be idle. It is readily seen that, 

 as the radius of curvature increases, the relative value of F^ decreases, 

 until on straight reaches it becomes zero. On straight reaches, then, 

 Fj is acting alone, and the tendency is 100 per cent to the right, 

 its strength depending on the velocity of the stream and the latitude. 



Boring Currents in a Meandering Stream 



In a meandering stream the potential lateral gradient is reversed 

 on each successive bend. The tendency is for all particles in motion 

 to move toward the outer bank, establishing an actual lateral gradient 

 corresponding to the potential. For a period, friction being low, 

 the actual gradient will be high, since the momentum of the boring 

 currents developed on the preceding curve must be checked and 

 lateral inertia overcome before the boring currents normal to the 



