Long Waves in Canals and Standing Waves in Closed Basins 235 



they occur so frequently that the people have named these devastating waves 

 "tsunami". The meteorologic tsunami are nothing but seiches of bays 



' B otto m 

 Fig. 99. Upper: seiches over a submarine bank, lower: seiches on the shelf (Hidaka). 



and of the shelf, but they exceed in intensity the normally smaller ampli- 

 tudes of the seiches on the shelf. Consequently, we can refer to the pre- 

 ceding paragraph for their explanation and theory. We have to consider, 

 however, that the amplitude of the variations in level, particularly in the 

 case of tsunami, is no longer small in comparison to the depth. Thereby 

 the equation of continuity has to be adjusted to the change in the surface 

 level. Nomitsu (1935) showed that the corresponding equations have their 

 depth h replaced by h + rj. This has a considerable influence, especially in 

 computing the rise in water level when the sea bottom slopes up towards 

 the coast. If tp is the slope of the surface, T is the wind stress and e is 

 a coefficient smaller than §, we can use for this computation simp = —eT/gQd, 

 which gives the slope of the surface in relation to the wind (see vol. I, 

 equation XIII. 45). We replace d or h by h + rj, so that we can consider 

 greater amplitudes of the waves: 



efy T^_ 



(VI. 144) 



Here T is the stress of the wind and £ a numerical factor which, in case of 

 no bottom friction, is equal to 1. With friction and the water sticking to the 



