It seems reasonable to conclude from the foregoing discussion that 

 the velocity of the water u at the front of a bore or surge advancing over 

 dry land as an inundation, or over a channel bed that has been einptied by 

 a preceding withdrawal of water will be fairly well represented by the 

 formula 



u^ = K ygd^ (D-17) 



in which d is the height of the general surge level above the land level 

 at any point occupied by the front of the surge, and K is a numerical 

 coefficient with a value between say 1. 5 and 2. 0. For conservative design 

 purposes it would seem desirable to adopt the value K = Z. 0. 



We return to our comment made at the beginning of this Appendix 

 regarding the extremely wide range of periods of tsunami waves engendered 

 by the Alaskan earthquake. The findings of this report are that for the most 

 part the very long period waves of the tsunami merely inundated the land 

 like fast-rising tides. Since there was neither wave-breaking nor bore- 

 formation in this action, the formulas considered above obviously do not 

 apply. However, we need to know what velocities of flow developed in these 

 cases. 



If we consider the crest of a wave of period T = 1. 8 hrs. to have 

 reached a coastline, it is of interest to determine where its still-water 

 level crossing point would be located, seaward of the coast. To a first 

 approximation we may assume the wave speed to be that of Eq. (4) in the 

 text, so that the quarter wave length X/4 of the wave is given by the 

 definition formula 



Td' (D-18) 



J^ - I 

 4 4 



D-7 



