Incident Wove Crest 



Figure 39. Mach-stem formation, solitary wave. Lines of equal 



surface elevation above still water normalized to unit 

 incident wave amplitude (after Perroud, 1957) . 



Chen (1961) studied Mach-stem development using a range of values 

 for the nearshore slope. He showed that where the angle of the nearshore 

 slope 3 < 60°, and a-, > 55°, the Mach stem formed a breaking wave along 

 the shoreline. The relationship between the wavelength and the slope 

 length was not considered in this case, and was not varied during the 

 experiments . 



It was generally found by Perroud (1957) and Chen (1961) that the 

 incident waves neither reflected from the shoreline nor formed Mach stems 

 when a-y > 70°. This would be the case for an incident wave traveling 

 nearly parallel to the section of shoreline; e.g., a wave entering an 

 inlet with a gradually varying cross section. 



7. Bay and Harbor Resonance . 



When a bay or harbor is very long in relation to the tsunami wave- 

 length, the tsunami may cause resonance if a natural mode of oscillation 

 of a bay or harbor corresponds to the period of the tsunami. Murty, 

 Wigen, and Chawla (1975) have tabulated the approximate periods of inlets 

 on the Pacific coast of North and South America based on the formula 



4L, 



(293) 



131 



