traffic lanes, channel depth, width, length, and alinement. Control structure 

 considerations include the selection of the protective works by evaluating 

 type, use, effectiveness, economics, and environmental impact. In selecting 

 the shape, size, and location of shore protection works, the objective should 

 be not only to design an engineering work that will accomplish the desired 

 results most economically, but also to consider effects on adjacent areas. An 

 economic evaluation includes the maintenance costs, along with the interest on 

 and the amortization of the first cost. If any plan considered would increase 

 the problem by extending its effects to a larger coastal stretch or preventing 

 an extension, the economic effect of each such consequence should be evalu- 

 ated. A convenient measurement for comparing various plans on an economic 

 basis is the total cost per year per meter of shore protected. 



Effects on adjacent land areas are considered to the extent of providing 

 the required protection with the least amount of disturbance to current and 

 future land use, ecological factors, and esthetics of the area. The form, 

 texture, and color of material should be considered in the design, as well as 

 how the material is used. Proper planning analysis also requires the con- 

 sideration of legal and social consequences where shore protection measures 

 may result in significant effects on physical or ecological aspects of the 

 environment . 



The following sections describe the most common structural solutions now 

 used to meet functional requirements and provide guidelines for the applica- 

 tion of these solutions. The environmental effects of all such solutions 

 must, by law as well as normal engineering concerns, be studied. 



II. SEAWALLS, BULKHEADS, AND REVETMENTS 



1 . Functi ons. 



Seawalls, bulkheads, and revetments are structures placed parallel, or 

 nearly parallel, to the shoreline to separate a land area from a water area. 

 The primary purpose of a bulkhead is to retain land or prevent landsliding, 

 with the secondary purpose of affording protection to the upland against 

 damage by wave action. Bulkheads may also serve as moorings and cargo trans- 

 fer points for vessels. The primary purpose of a seawall or revetment is to 

 protect the land and upland areas from erosion by waves and currents, with an 

 incidental function as a retaining wall or bulkhead. There are no precise 

 distinctions between the three structures, and often the same type of struc- 

 ture in different localities will bear a different name. Thus, it is 

 difficult to indicate whether a stone or concrete facing designed to protect a 

 vertical scarp is a seawall or a revetment, and often just as difficult to 

 determine whether a retaining wall subject to wave action should be termed a 

 seawall or bulkhead. All these structures, however, have one feature in 

 common — they separate land and water areas. The structures are generally used 

 where it is necessary to maintain the shore in an advanced position relative 

 to that of adjacent shores, where there is a scant supply of littoral material 

 and little or no protective beach, as along an eroding bluff, or where it is 

 desired to maintain a depth of water along the shoreline, as for a wharf. 



2. Limitations . 



These structures afford protection only to the land immediately behind 



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