Frost formation at night followed by thawing in the daytime may cause damage in some 

 regions. Frost or freezing of water trapped in crevices between structural members may pry 

 them apart or loosen connections. Eliminating the crevices through careful design and 

 construction can avoid this type of ice damage. Figure 10 shows how frost and ice action 

 can damage a concrete parking area. 



Damage from ice-floe impact is common in rivers, but it may also occur in harbors as a 

 result of floes drifting with the wind or with circulatory currents in lakes or arctic waters. 

 Deflecting booms made of logs or heavy timbers can often be devised to protect the 

 berthing area from drifting ice. Fixed-pile structures that break the ice sheets into smaller 

 pieces are discussed later in Section V. 



d. Fog. Although fog causes little damage in a smaU-craft harbor, the reduced visibility 

 is a serious navigational problem. Most water areas have occasional foggy conditions and 

 most recreational boaters have Umited skill in navigating their craft under poor visibility 

 conditions. For this reason, entrance channels and main fairways in a harbor should be as 

 straight as possible. There is no method of dispelling fog at a reasonable cost, and although 

 radar and infrared devices have helped the navigator, such sophistication is seldom available 

 to the small-craft operator. SmaU-craft harbor entrances and fairways should therefore be 

 designed so that they can be navigated in dense fog by following marker buoys and other 

 channel-marking devices, witli as few turns as possible. 

 2. Wave Factors. 



a. Sea and Swell. These factors have been mentioned as they apply to site selection. 

 Once the site has been fixed, the harbor must be planned so as to reduce wave action from 

 the entrance and interior basins to acceptable heights. This is done through a combination 

 of entrance-channel orientation, protective breakwaters and jetties, and interior 

 wave-dissipating devices. Where a harbor opens into the ocean or a large lake, the entrance 

 should be oriented for a boat to enter without turning broadside to the incoming waves and 

 thus risk broaching or being "surf-boarded" into a jetty during high wave conditions. Both 

 historical wave data and the statistical hindcast data required for site selection can be useful 

 in orienting the entrance and designing the protective structures. Wave -dissipation structures 

 can often be used in reducing to acceptable heights the waves that do find their way into the 

 entrance. The normal criteria for acceptable maximum wave heights are about 2 to 4 feet in 

 the entrance channel and 1 to 1.5 feet in the berthing areas, depending on the characteristics 

 of the using craft. 



Generally, if waves can be attenuated to a height of about 1 foot in the berthing areas, 

 their horizontal oscillations will not be troublesome, and any longer -period resonant effects 

 will go unnoticed. In initial planning, the best orientation of the entrance and location of 

 protective structures can be obtained by refraction and diffraction diagram analysis 

 (U.S. Army, Corps of Engineers, Coastal Engineering Research Center, 1973), (Fig. 11). 



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