pressure differentials, wind setup, surf beats, shelf resonance, edge 

 waves, internal waves, and tsunamis. The heights of the intermediate- 

 and long-period waves range from about 1 inch to 3 feet for the forced 

 oscillation, seich-type waves, and up to 30 feet or more for tsunamis. 

 Tides are also long-period waves, but they are seldom reproduced in 

 harbor wave action models. Instead, selected Stillwater levels, repre- 

 senting high and low stages of the tide, and considering the effects of 

 local wind setup and hurricane surge, are used for testing. Waves are 

 also conveniently classified according to the ratio of water depth to 

 wavelength, d/X, called velative depth. Eagleson and Dean (1966) 

 suggested the following classification (Table 4-1) of small -amplitude 

 waves according to relative depth. 



Table 4-1 . Classification of small-amplitude waves 

 (Eagleson and Dean, 1966). 



Range of d/X 



Wave type 



to 0.05 

 0.05 to 0.5 

 0.5 to oo 



Shallow-water waves 

 Intermediate-depth waves 

 Deepwater waves 



Shallow-water and deepwater waves are also referred to as long and 

 short waves, respectively. The classification according to the wave 

 period is useful because the magnitudes of movements (roll, pitch, heave, 

 surge, sway, and yaw), for vessels moored elastically at piers in the 

 ordinary manner, are sensitive to the period of the incident waves meas- 

 ured in terms of the resonant periods of oscillation of the moored vessel. 

 Likewise, amplitudes of the oscillations of the water masses in harbor 

 basins are sensitive to the period of the incident waves measured in terms 

 of the resonant periods of oscillations of the basin waters. According 

 to Wilson (1967), the critical oscillations for ordinary-sized ships 

 moored in commercial harbors with elastic lines lie in the intermediate- 

 period wave range from about 25 seconds to 2 minutes. Raichlen (1968) 

 states that the critical oscillations for the ordinary-sized boats that 

 moor in small-craft harbors lie in the short -period wave range of about 

 10 seconds and less. The classification of waves according to relative 

 depth is useful because the wave velocity and the degree of refraction 

 of waves approaching a problem area from deep water through water of de- 

 creasing depth is a function of the d/A ratio. The phenomenon of wave 

 diffraction is also a function of relative depth. 



The perimeter walls of most harbor basins are usually prime wave 

 reflectors, and the reflection coefficient increases as the wave period 

 increases. Thus, for intermediate- and long-period waves the harbor 

 boundaries are nearly perfect wave reflectors, and standing-wave systems 

 are generated in the harbor basins for such waves with little reduction 

 in energy due to friction. Such waves oscillating in harbor basins are 

 usually called seiches, a French term which was used originally to desig- 

 nate the free oscillations of relatively long-period standing waves in 

 lakes or other enclosed bodies of water. Seiches in lakes were usually 

 caused by the piling up of water on the windward side of the lake (wind 



204 



