drop along the edge exceeds about 6 feet. Municipal or county building and safety agencies 

 often provide design criteria for handrails. In the absence of handrail criteria, it is customary 

 to make the top rail 42 inches above the adjacent ground level and to design the top rail and 

 supporting posts for a minimum lateral thrust of 30 pounds per foot of rail. One secondary 

 rail should be provided about midway between ground level and the top rail. Some agencies 

 require a handrail system with no openings larger than 6 inches, necessitating insertion of 

 wire mesh panels or other means of compliance. 



The selection of materials for the handrail will depend on the type of bulkhead 

 construction. With timber bulkhead construction, the handrail is usually of timber. 

 Galvanized pipe handrails, are commonly used and provide long life except where subjected 

 to salt spray. One of the best handrail materials is aluminum with a hard anodize finish 

 1.5-millimeters thick. Some aluminum handrails have an experience record of over 15 years 

 without maintenance in a salt-air environment. They are available commercially, are 

 adaptable to almost any foundation or face-fastening situation, and have corner -turning and 

 termination systems to meet a variety of requirements. 



One type of perimeter treatment has been developed that produces a natural rustic 

 appearance and may be suitable for the channels and water areas adjacent to a marina where 

 bank erosion may be a problem. It consists of special molds for the exposed face and use of 

 colored concrete to blend with the native soil and, when completed, is similar to those 

 produced by natural weathering. Although the concrete must be placed in the dry, this 

 treatment could be the answer to many river- and lake-connecting channel problems where 

 preservation of esthetic quality is a requirement (Fig. 56). 



b. Basin Depths. The interior basin requirements of a smaU-craft harbor are determined 

 generally by the same criteria applied to entrance and basin approach channels. An 

 additional factor that must be considered, however, is the effect of bottom depth on 

 structures of the berthing system, such as fixed-pier supports, floating pier guide piles and 

 dolphins, and interior wave and surge baffles. The cost of each structure increases roughly 

 with the square of the depth; hence, the basins should be no deeper than navigational 

 considerations dictate. For this reason, as well as for space utilization economy, it is 

 customary to berth the larger and deeper-huUed craft near the entrance and to decrease 

 basin depths in step increments toward basins or parts of basins away from the entrance. 

 Thus, the narrower fairway and smaller turning area requirements of the small craft 

 decreases the amount of water area required for nonberthing use. Also, the shallower back 

 basin areas reduce pier and slip construction costs. In the berthing basins, assuming that the 

 maximum depression of a boat below the stillwater surface wiU be about 2 feet (due to wave 

 action and scend), the depth should be at least 2 feet below the keel of the deepest-craft 

 boat at extreme low water (see Sec. V, para. 4d, Fig. 63, for values of deepest draft). 



105 



