equipment, and it may be important to provide the place and perhaps some of the means for 

 doing this. A shore-connected breakwater can be built entirely with land-based equipment, 

 but progress will be slowed by the single-point operation and congestion of haul traffic over 

 the breakwater crown. A two-stage construction program may be advisable, with the crown 

 being kept low (and wider) in the first stage and the capstone being appUed in4he final stage 

 (Fig. 23). 



A shore-cormected breakwater is usually an attractive structure to fishermen. During the 

 design stage, it must be determined if the top of the breakwater will be made available for 

 fishing and the conditions for this use. Additional provisions may be required to reduce the 

 hazards to those who avail themselves of such a concession. A level footpath along the top 

 of a rubble mound or a handrail along the cap may be required. Because of unexpectedly 

 high waves, people have been swept off these structures, especially along ocean shores. Users 

 must be warned of the danger by posted signs. This same consideration also appUes to 

 jetties. 



The wave diffraction pattern caused by a breakwater has a significant impact on the 

 adjacent shoreUne, and must be considered in project planning. A schematic analysis of this 

 diffraction effect on a typical sand beach is shown in Figure 24. This analysis should be 

 made whenever a breakwater is constructed off a shore area comprised of friable materials, 

 and the indicated effects should be accounted for in project design. The Shore Protection 

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

 contains instructions and data for analyzing wave diffraction under most conditions 

 encountered in harbor design. 



6. Entrance Channel and Structures. The design of harbors and entrance channels must 

 be related to the site selection and positioning of the protective structures. The jetties and 

 breakwater must permit construction, maintenance, and passage of tidal flows. AH these 

 aspects must be considered in harbor design. 



The channel ahnement should be as close to the natural channel aUnement as possible. 

 Any bends that are necessary should be gradual. The number and size of vessels must be 

 known to determine the design width and two-way traffic that must be accommodated. The 

 minimum width for small boat traffic should be about 50 feet or 5 times the beam of the 

 widest boat expected to be berthed in the harbor. If sailboats use the harbor, extra width 

 should be provided for tacking. When small craft are combined with a commercial fleet, 

 separate channels should be considered. Channel depth is usually measured from low water 

 datum and depends on many factors, including size and types of vessels, traveUng speed, and 

 wave magnitude. Traveling speeds govern the degree of squat which can be determined. An 

 overdepth of 1 foot in soft material and 2 feet in rock should be allowed for dredging 

 irregularities. The channel depth should be the sum of: (a) the draft, (b) squat, (c) one -half 

 the wave height, and (d) overdepth. A minimum of 6 feet is suggested for the channel depth. 



.56 



