328 E. C. ANDREWS. 



Let v be its velocity. 



Then \mv 2 — the energy of this mass m. 



Hence if a perfect barrier were suddenly presented at A 

 to the stream motion the energy destroyed per unit time 

 would be |w v 2 . 



But the mass is proportional to the volume of the stream 

 passing in unit time, and this is equal to s x v, where s is 

 the cross section of the stream at A. 



Therefore the total energy destroyed in unit time 



= \ m v 2 



= \ S V X V 2 = \ S V 3 



If now we suppose a flood to occur so that the cross 

 section of the stream at A becomes = k x s, and farther 

 suppose the velocity to be raised to I X v. 



Then the energy destroyed per second in this case 

 = ^ks x (lv) s 

 = ikl :i sv H 



Hence the ratio of the total energy of the flood stream 

 to that of the normal stream 



__ 2 tC I S V __ 7 j 3 



±sv A 



This ratio k I 3 should be therefore a minimum for the 

 corrasive strength of the stream. In the flood stream 

 therefore the vertical, lateral, and longitudinal measures 

 of strength all rapidly increase with the velocity. 



Literature. 

 1. Andrews, B. O. — (a) The Ice Flood Hypothesis of the 

 New Zealand Sound Basins. Journal of Geology, 

 Chicago, xiv, 1906, pp. 22-54. 



(b) The Geographical Significance of Floods. Proc. 

 Linn. Soc. N.S. Wales, 1907, xxxn, Part 4, pp. 795 - 834. 





