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tained load which overlies any particular spot on its channel 

 base, the stream must cut vertically into its channel base, 

 because it is a fact of observation that earth material 

 which is dragged across earth structures will corrade the 

 same, especially when the material of the stream load is 

 harder than the structure it traverses. In short until such 

 time the length O O will increase. Similarly while the 

 stream is strong enough to carry its load past a point on 

 its channel sides, so long will the length b grow along the 

 axis OB. In other words the cutting curve will extend 

 until the stream becomes unable to freely sweep the 

 channel sides with stream debris. Similar reasoning may 

 be extended to the case of the longitudinal axis. 



Having made this point clear, it will be interesting to 

 note the significance of the increase in volume of a stream 

 as regards its ability to corrade. The laws of mechanics 

 show that the kinetic energy of a stream apparently 

 increases directly as the product of the third power of the 

 velocity and the increase of the cross-section.' 



Let us suppose that a basin has been formed in the 

 ehanel base by the stream. Upon the increase of velocity, 

 all other tilings being equal, the new basin formed will be 

 similar in shape to that excavated under the less energetic 

 conditions, the ratios of the lateral, vertical and longi- 

 tudinal measures of stream strength being the same as 

 during the less energetic conditions, and the relative sizes 

 of the basins being those of the approximate ratios of the 

 two kinetic energies. From this knowledge the lateral, 

 vertical and longitudinal increases in stream strength 

 could be estimated. By increasing the depth and velocity 



:■- tin- channel base. 



