Tsunami waves behave like a very rapid tide impressed on the lunar tide at whatever stage it 

 happens to be. The rapid flushing of channels and basins tliat results may cause unusual 

 amplifications and channel velocities that scour banks and make navigation of any size vessel 

 extremely hazardous. The tsunami wave may rise above the adjacent land surface of a 

 harbor and flood marginal lands. 



Little can be done to prevent a tsunami wave penetration in a small-craft harbor, but 

 precautions can be taken to minimize the damage. A site should be selected where the 

 perimeter land surface is above the level to which tsunamis might raise the water surface. If 

 this is not practical, the floors of buildings in the perimeter area should be kept above this 

 level. Another precaution is to keep the tops of the anchor piles of floating slips well above 

 this level so that the floats will not rise above them. 



Anchorages should be designed to resist the lateral loads that may be imposed by 

 tsunami-generated currents. The trough of a tsunami wave might lower some of the berthed 

 craft to the bottom. To prevent damage from such an occurrence, shearing off the barnacles 

 from guide piles below the normal low tide level by a cutting device could prevent a pile 

 guide from sticking on their rough surface in a tsunami drop and capsizing the berthed craft 

 on the tsunami crest. In regions where tsunami flooding has been serious, a warning signal 

 and emergency evacuation system should be devised. 



d. Tides. Lunar tides vary from place to place along the shores of all oceans. Tide 

 prediction tables, published annually by the National Oceanic and Atmospheric 

 Administration, are available for most locations where smaU-craft harbors may be built. 

 Ocean tides may extend many miles upstream from the mouths of large rivers and are 

 semipredictable for most potential harbor sites. If a coastal site is chosen that is remote 

 from any of the stations listed in the tables, it is possible to interpolate predictions for the 

 site from values given in the tables for the two nearest stations. The extremes of the 

 predicted spring tides provide criteria for designing the harbor to accommodate any water 

 level fluctuation that may occur. 



Interior surge, boat-wake waves, tsunamis, and hurricane surge should be considered in 

 conjunction with the tidal fluctuations. In determining the project bottom depths of 

 interior channels and basins, consideration must also be given to the drafts of the largest 

 vessels that will be using the facility and to effects of squat, roll, pitch, and heave on these 

 vessels in maneuvering areas. For example, the berthing basins of one marina were dredged 

 to what was thought to be sufficient depth below the predicted extreme low tide level to 

 provide adequate clearance for the keels of the deepest-draft boats to be accommodated; 

 yet, after a short period of operation, there were complaints of groundings. Investigations 

 showed that the maneuvering habits of the larger power craft in some areas resulted in a 

 combined squat and resonant pitch that "kicked up" bottom materials into submerged 

 "windrows." In other instances, designers have neglected to take into account internal wave 

 action, and during the first extreme low water, the normal wave penetration into the 

 berthing area caused some boats to strike bottom. 



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