under anticipated environmental condi- 

 tions. Armor facings constructed of 

 materials such as riprap or rubble 

 should have components which are 

 dense and heavy enough not to be mov- 

 ed by waves. Revetments with perme- 

 able armor units (such as gabions) or 

 interlocking armor units rely less on 

 mass of the individual structural compo- 

 nents to withstand wave energy than do 

 more solid type revetments (Docks and 

 Harbor Authority 1965). More detailed 

 discussions of the various types of ar- 

 mor units, their advantages and disad- 

 vantages, are found in the Shore Pro- 

 tection Manual (U.S. Army Corps of 

 Engineers 1973b) and the Survey of 

 Coastal Revetment Types (McCartney 

 1976). 



Socioeconomic . Social and economic 

 considerations can affect the location 

 and type of structure built at a site. 

 Local laws, costs of structural alterna- 

 tives, historical points of interest, cur- 

 rent and future uses of the area, and 

 aesthetic values are some of the criteria 

 which influence the placement of a re- 

 vetment. Current and future uses of 

 an area help to determine the need for 

 a revetment at a given location. Beach 

 use influences the type and location of 

 the structure on the shoreline. 



The design life of a temporary re- 

 vetment to protect an exposed embank- 

 ment during construction activities 

 would be shorter than the design life of 

 a revetment built to protect a shore- 

 front dwelling from damage due to 

 beach recession. Revetments can se- 

 verely affect waterfront recreational 

 activities, such as swimming, boating, 

 and shell- fishing. McCartney (1976) 

 points out that a beach used "for re- 

 creation and other purposes may dictate 

 use of upper beach revetment to contain 

 runup and sandfill on the beach face 

 seaward of the revetment." 



Several authors have commented on 

 the visual impact revetments have on 

 the shoreline. Structures which resem- 

 ble and follow the natural shoreline 

 seem to have less adverse impact on the 

 scenic or aesthetic values of an area. 

 For example, gabions are sometimes 

 viewed as a more aesthetically pleasing 

 type of revetment than either brickwork 



or concrete slabbing because of their 

 resemblance to the natural stonework 

 (Docks and Harbor Authority 1965). A 

 rock revetment which was to be built at 

 Sunset Cliffs, San Diego County, Cali- 

 fornia, was viewed as more aesthetically 

 acceptable than a more formal structure 

 (U.S. Army Engineer District, Los Anqeles 

 1970). Bel lis et al. (1975) point out 

 that "the availability of 'free' mate- 

 rials such as demolished buildings, old 

 tires, junked cars, and other debris all 

 too often leads to really bizarre shore- 

 lines..." An example of such a shore- 

 line is found in Figure 33. Some au- 

 thors, however, view any type of revet- 

 ment as an artificial intrusion that is 

 an aesthetic affront to the shore envi- 

 ronment. Bauer (1975) made the following 

 comment with reference to riprap revet- 

 ments: 



"The most negative feature of rip- 

 rap, however, resides in the of- 

 fending visual impact and environ- 

 mental degradation of the shore 

 resource. The use of such rock 

 heaps, Just as in the case of the 

 streambank revetments, has now 

 mushroomed into a serious shore 

 despoilage - a syndrome that is 

 lining our beautiful beach environ- 

 ments with ugly, incompatible bor- 

 ders and backdrops of rubble." 



Economic feasibility often deter- 

 mines the number and types of structural 

 alternatives available for a given loca- 

 tion. Initial construction and mainte- 

 nance costs for the design life of the 

 project vary depending upon site condi- 

 tions, geographic region, and materials 

 used. Initial construction costs can 

 range from $25.00 to $200.00 or more per 

 linear foot of protection. While revet- 

 ments tend to be less expensive than 

 bulkheads, those constructed along the 

 open coasts or to protect barrier beach- 

 es are expensive to build and maintain 

 relative to those built in semiprotected 

 and protected environments. Local avail- 

 ability of the suitable construction 

 materials influences cost of the struc- 

 ture. The cost of maintenance depends 

 upon the labor expenses, material costs 

 and frequency of repair. For example, 

 nylon bag and polyethylene tube revet- 

 ments are relatively inexpensive to in- 

 stall, but may be expensive to maintain. 



64 



