Cottonwood Island Pile Dike Repair

Cottonwood Island Pile Dike System consists of 15 pile dikes located at Rile Miles 68.35, 68.57, 68.79, 69.01, 69.25, 69.51, 69.79, 70.07, 70.35, 70.77, 70.83, 71.17, 71.51, 71.59, and 71.87 on the Columbia River, along Howard-Cottonwood Island and on the Washington mainland: For 13 of the 15 pile dikes, the majority of the dike repair length will be replaced with enhanced enrockment that extends from the offshore end to 25 feet shoreward of existing +1.0 foot elevation (NAVD88). The enhanced enrockment sections will require removal of remaining existing timber piles to facilitate rock placement and provide for a uniform final rock structure. The offshore portions of the existing pile dike enrockment will be enhanced by raising the enrockment 4.0 feet above the original enrockment height. The enhanced enrockment will have a crest width of 8 feet and 1.5H:1V side slopes. The shoreside end will taper to existing enrockment at a 1.5H:1V slope. There will be no shoreward placement of stone beyond this location. The remainder of the pile dike repair length will be an offset timber pile dike section, with the offshore end starting at approximately the existing +1.0-foot ground elevation contour, which is 3.39 feet NAVD88. The in-shore end of the offset pile dike section will extend up the beach to existing +8.0-foot ground elevation contour. The timber pile dike sections will be offset 20 feet downstream and parallel to the existing pile dike structure. The new timber pile dikes will be installed using the same pile spacing and sizing as the original pile dikes. Other features of the work include installation of new steel king/marker piles at the offshore end of the offset timber piles structures and enrockments, placement of new rock scour aprons around the newly installed timber piles structures for the full length of pile installation, and installation of new rock shore connections from the newly installed timber piles structures connected to the landward end of the rock apron extending shoreward. The estimated material quantities for these pile dike repairs include 23,360 cubic yards of ODOT Class 1500 riprap for the enrockment, scour protection, and shore connections; 3,690 cubic yards of bedding material; 369 new 12-inche diameter timber piles of varying lengths from 20 feet to 30 feet; 39 new king steel piles with diameters from 10 to 24 inches. Demolition will include removal of approximately 756 piles for a total estimated length of 3,150 feet.

Dam/Tunnel, Renovation.

Division 02 -	Existing Conditions, Subsurface Investigation.
Division 31 -	Earthwork, Site Clearing, Grading, Excavation and Fill, Subgrade Preparation, Excavation, Shoring, Tunneling and Mining, Tunnel Excavation.
Division 35 -	Waterway and Marine Construction, Common Work Results for Waterway and Marine Construction, Waterway and Marine Construction and Equipment, Marine Construction and Equipment, Dam Construction and Equipment.