some bottom habitats and creates new 

 ones. Rubble mound structures provide 

 attachment sites for sessile organisms, 

 and the irregular surface can support a 

 diverse community of rocky shore plants 

 and animals (Ortolano and Hill 1972). 

 Sand accretion areas can provide new 

 habitats for shellfish and shorebirds 

 (Snow 1977). Areas where erosion takes 

 place often become populated by fish 

 which require deeper water. Jetty relat- 

 ed fisheries can develop (Ortolano and 

 Hill 1972). However, the presence of 

 jetties may limit or alter the normal 

 movement of fish and crustaceans into 

 and out of estuaries (Cronin et al. 

 1971). Physical changes in water circu- 

 lation, flushing, current patterns, and 

 shoaling within the estuary may severe- 

 ly degrade or alter existing habitats 

 (U.S. Army Engineer District, Portland 

 1975b). In some cases altered circula- 

 tion patterns are beneficial. 



C umulative effects . Most of the 

 effects due to jetties are noticeable in 

 the immediate vicinity and in the em- 

 bayment or river and coastal area where 

 they are constructed. There is gener- 

 ally little reason to construct several 

 pairs of jetties in proximity. Therefore, 

 cumulative effects due to proliferation 

 of jetties are not obvious. It is possi- 

 ble, however, that numerous jetties 

 along a coastline could have the same 

 cumulative effects upon littoral trans- 

 port as a numer of groins could. 



Structural and Nonstructural 

 Alternatives 



Jetties are normally used to pro- 

 vide channel or inlet stabilization and to 

 reduce the amount of dredging required 

 to maintain the inlet or channel. There 

 are different materials and configura- 

 tions available for jetty construction. It 

 is also possible to use other structures, 

 such as groins, in conjunction with jet- 

 ties to reduce or modify effects of the 

 jetty on adjacent areas. 



Nonstructural alternatives fall into 

 two categories. The first is to do noth- 

 ing and forego the use of the waterway 

 for navigation and possibly adjacent 

 lands for some form of development. 

 The second alternative is to maintain 

 naviration by means of dredging. This 



alternative can be very costly and can 

 result in the channel being unusable for 

 certain periods due to the inability of 

 dredging equipment to provide and to 

 maintain desired depths for navigation. 

 It is also possible that the dredging 

 and disposal process will have an impact 

 on the surrounding environment which is 

 far greater than the impact due to jet- 

 ties. 



Regional Considerations 



Jetties have been built, or are 

 planned, for virtually every inlet of 

 significant size in the North Pacific 

 (Coastal Region 1). In some cases only a 

 single jetty has been placed but most 

 inlets are stabilized by a pair of jet- 

 ties. All are placed perpendicular to 

 the shore and are of rubble mound or 

 quarried stone construction. No unique 

 placement constraints apply to this 

 coastal region. Construction materials 

 include rock (usually basalt), quarry 

 stone, and, in at least one case, dolos- 

 se. Average life span of jetties in this 

 area is about 50 yr with major repairs 

 expected to be necessary during that 

 period (U.S. Army Engineer District, 

 Portland 1975c, 1976e). 



Long-term impacts include erosion 

 and accretion changes, habitat altera- 

 tions at the jetties and within estuar- 

 ies, and changes in tidal patterns and 

 water quality. Storm waves have caused 

 severe damage to jetties as a result of 

 scouring (Wong 1970). A number of sand 

 spits have been altered, breached, or 

 destroyed as a result of jetty-caused 

 current changes. The foredune at Tilla- 

 mook, Oregon, is many times higher than 

 it was before construction of the Tilla- 

 mook jetty. No summer return of winter 

 sand loss was observed in the first few 

 years following extension of Yaquina 

 Bay, Oregon, jetty (Demory 1977). Jef- 

 ferson (1974) reported that configura- 

 tion of some of Oregon's coastal bays 

 has been changed by the construction of 

 jetties. All" along the Oregon coast, 

 changes in habitat, apparently connected 

 with presence of or changes in jetties, 

 have been observed (Snow 1977). In one 

 case, a jetty's influence on littoral 

 transport contributed to the breaching 

 of a sand spit. This allowed sand and 

 boulders to enter a protected lagoon and 



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