NCM is currently performing work at Little Goose Lock and Dam that includes the installation of a boat barrier system and trash shear boom above the dam. The boat barrier system is designed to prohibit the entry of recreational craft and debris from entering the forebay, spillway gates and power unit intakes. The installation of the boat barrier system consists of the placement of precast concrete anchors at the river bottom, assembly and installation of floating Boatbuster buoy strings, as well as the installation of a floating work boat gate for maintenance and long term service access. The precast anchors vary in depth from 40 to 130 feet of water. A total of 25 concrete anchors were installed along with stackable supplemental weights. The weight of the concrete anchors are approximately 43,000 pounds and the supplemental weights are approximately 48,000 pounds. All concrete anchor and weight installation was performed without the use of divers saving the owner money and resources.
NCM utilized an underwater ROV and GPS survey equipment to accurately locate and place concrete anchors in their designed locations. All in-water work is being performed using an 110 foot x 50 foot derrick barge equipped with our Manitowoc 3900W Series II crawler crane. NCM fabricated and assembled the derrick barge in Tri-cities Washington and utilized our tugboat, the St. Helens, for the transportation and delivery to Little Goose Lock and Dam.
The trash shear boom consists of several precast concrete floats attached to a 2-7/8” stainless steel wire rope which is secured to the dam and then to a steel float just north of the navigational channel. The trash shear boom was a system that was previously in place, but suffered a catastrophic failure several years ago. NCM’s scope of work consisted of the refurbishment of the concrete floats, installation of new 2-7/8” cable, reattachment of existing anchor lines and hardware, fabrication and installation of roller assembly to allow the system to travel with varying forebay elevations, the re-installation of precast concrete floats, and the installation of wooden trash fence across the face of the concrete floats. The total length of the trash shear boom is approximately 1,000 feet long.
In addition to the installation of the trash shear boom, NCM was required to place quarry spalls into and around the existing anchors on the river bottom. NCM placed approximately 270 cubic yards of quarry spalls on the river bottom in less than 5 days at 3 different locations.
NCM and our subcontractors, Wilbert Precast, Worthington Products, Fabrication Products, Cascade Rigging, and Hancock Paint and Sandblast will be completed with all work on March 1st, 2018. This project required significant coordination between the Contractor, Owner, and Commercial River traffic to ensure that no parties experienced a negative impact as a result of the work.
US Army Corps of Engineers, Walla Walla District