PART II: SUMMARY OF CORPS BREAKWATER AND JETTY PROJECTS IN NPD 



3. NPD presently maintains 68 breakwaters and 35 jetties located in 48 

 of their coastal projects. Thirty-eight breakwaters and 5 jetties are located 

 in 20 projects in US Army Engineer District, Alaska (NPA) ; 9 breakwaters and 

 22 jetties are located in 12 projects in US Army Engineer District, Portland 

 (NPP); and 21 breakwaters and 8 jetties are located in 16 projects in US Army 

 Engineer District, Seattle (NPS). 



4. Nearly all of the breakwaters and jetties are of rubble-mound con- 

 struction, although steel pilings, steel sheetpilings, timber pilings (with or 

 without planks), and concrete have also been used. Early structures were 

 built primarily by dumping stone from railroad cars on a tramway constructed 

 above the jetty or breakwater. Where the in situ material provided an insuf- 

 ficient foundation, structures were constructed on blankets of brush or 

 gravel. Otherwise, structures were built directly on the existing bottom 

 material. 



5. New construction, repair, and rehabilitation work carried out on 

 rubble-mound structures in NPS and NPP since 1961 have used placed-stone con- 

 struction techniques. Due to quality control, random armor stone placement 

 is specified for NPA structures, but use of placed-stone construction is 

 encouraged . 



6. Most of the jetty repair work is for wave-induced localized damage 

 on the sea side of the jetty trunks. The damage consists primarily of down- 

 slope slumping of the primary armor stone as a result of both individual armor 

 stone displacement and toe damage that allow slippage of the outer armor 

 layers. Both NPA and NPP have constructed sacrificial toe berms of core-size 

 material to provide added toe stability, trip incident waves to reduce runup 

 and overtopping, and protect against scour and undermining. 



7. Most of the jetty rehabilitation work consists of rebuilding jetty 

 heads that have been lost due to scour and undermining combined with storm 

 wave-induced armor stone displacement. Typical jetty head rehabilitation 

 includes filling scour holes and forming a bedding foundation with minus 

 400-lb material then reconstructing the head using only class "A" stone. 



8. Concrete armor units are not used by the division. Repair work has 

 generally consisted of placement of additional stone, frequently of a larger 

 size. Many of the structures have been raised and/ or extended. 



