Sandbags and tubes may easily be cut 

 open by vandals (Marks and Clinton 

 1974) and deteriorate quickly, thus re- 

 quiring frequent repair. 



Biological . The Buffalo Army Engi- 

 neer District (U.S. Army Engineer Dis- 

 trict, Buffalo undated a) in issuing a 

 general permit for shore protection in 

 Lake Erie listed several biological con- 

 straints on the revetment construction 

 which may be applied to all coastal re- 

 gions: 



o Armor unit revetments should 

 be made of clean, non-pollut- 

 ing material. Any material 

 contaminated with grease, 

 phenol, lead, or other toxic 

 elements should not be used. 



o Revetments should not be 

 constructed during the fish 

 spawning periods. 



o Revetments should not be 

 constructed in wetlands; in 

 areas serving as habitat for 

 threatened or endangered 

 species; in important fish 

 spawning areas; or in signi- 

 ficant waterfowl or shorebird 

 nesting, feeding, and resting 

 areas. 



Revetments with facings that are 

 highly irregular (such as riprap) and 

 have a shallow slope have a greater abi- 

 lity to support marine life (Gantt 1975). 

 Although revetments do provide a new 

 irregular habitat which does support 

 greater marine life than vertical sea 

 walls, there is an initial loss of organ- 

 isms and habitat by placement of revet- 

 ments. 



Construction Materials 



There are two structural classes of 

 revetments (U.S. Army Corps of Engi- 

 neers 1973b): rigid, cast-in-place, and 

 flexible or articulated armor unit revet- 

 ments. Rigid, cast-in-place types of 

 revetments are constructed of cement, 

 asphalt, or bitumen grouted stone. A 

 concrete revetment is very effective 

 against wave attack, but water must be 

 removed from the construction area to 



pour the concrete. A concrete revet- 

 ment is depicted in Figure 34. Compo- 

 nents of armor unit revetments include 

 an armor face, filter, and protective 

 toe (McCartney 1976). 



The armor face is the outer layer 

 of the structure which serves to dissi- 

 pate wave energy as waves are deflected 

 landward. Materials commonly used as 

 armor facino are shown in Table 2 

 (McCartney 1975, 1976; U.S. Army Corps 

 of Engineers 1973b). Riprap revetments 

 are illustrated in Figures 30 and 31. A 

 Nami ring revetment and an interlocking 

 concrete block revetment are shown in 

 Figures 35 and 36. 



A filter serves as an interface be- 

 tween the armor facing and the native 

 soils which the structure protects. Some 

 commonly used filters include gravel, 

 auarry spalls, filter cloth, and combi- 

 nations of gravel and a filter cloth, 

 and quarry spalls and a filter cloth. 



Toe protection is necessary to pre- 

 vent scouring at the base of revetments 

 and to protect the structure against 

 changing beach profiles in front of the 

 structure. Common types of revetment 

 toe protection include aprons which will 

 sag into any scour hole that develops, 

 buried toes, toes weighted with extra 

 layers of armor units (armor units are 

 not necessarily the same as those used 

 on the rest of the structure), flexible 

 mats such as gabions or filter cloth 

 filled with sand, bag or rock sills 

 placed seaward of the toe to trap sand 

 and bury the toe, sand or gravel stock- 

 piles, cutoff walls, and anti-erosion 

 rings (McCartney 1976). 



Expected Life Span 



The expected life span of revet- 

 ments ranges from 5 to 30 yr or more. 

 Expected life span will vary depending 

 upon construction materials, the wave 

 height and period the structure was de- 

 signed to withstand, and the climatic 

 conditions to which the structure is ex- 

 posed. Damage to rubble-mound structures 

 is generally progressive, and the Shore 

 Protection Manual (U.S. Army Corps of 

 Engineers 1973b) recommends considering 

 both the frequency of damaging waves and 



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