Building a Pier for Fish Transportation
The barges that travel the Snake and Columbia Rivers with cargoes of young fish will soon have new mooring facilities to aid in their effectiveness.
By Ken Almberg
The existing pier below Lower Granite Dam no longer has the maintenance capacity for the additional and larger barges being put into service the past few years. Photos courtesy WCC
The hydroelectric dams on the Columbia and Snake Rivers provide inexpensive electric power to millions of customers in the northwestern United States. But those dams have also made breeding difficult for several species of fish, including native steelhead and Chinook salmon. These anadromous fish live in the Pacific Ocean and migrate upriver to spawn in the freshwater streams in which they were born. Getting upstream past all the dams is not their only problem: The juvenile fish that travel downstream to reach the sea also face a much longer journey than they did previously. With the river current slowed by dams, it can take the fish months instead of weeks to complete their journey.
Walla Walla District of the U.S. Army Corps of Engineers (USACE) has been addressing the problem in several ways. As it has on all dams downstream, the district has installed fish ladders at the Lower Granite Dam site, constructed at mile marker 107.5 on the Snake River, to help the adult fish move upstream to spawn. In 2001, for instance, Walla Walla District built a spillway to make it easier for the juvenile fish to move back down to the ocean. However, the district’s earliest efforts to save the steelheads and salmon date back to the severe drought year of 1977, when it began collecting juvenile fish at the dam and transporting them via specially designed trucks and barges to release sites below the Bonneville Dam on the Columbia River, where they can easily reach the sea.
These barges have a pumping system that brings the river water into their tanks, giving the juvenile fish an opportunity to imprint the distinct smell of that water so they will return back to their birthplace to spawn when they are mature.
Working in cooperation with the National Oceanic and Atmospheric Administration Fisheries Service, USACE transports between 15 and 22 million fish each year from various dam sites along the Snake and Columbia Rivers. Lower Granite is the first collector dam on the Snake River, and thus the primary component of the fish transportation program. In 2011, Walla Walla District collected a total of 6.3 million juvenile fish at Lower Granite Dam. According to USACE, close to 100 percent of the barged fish survive their trip downstream.
In recent years, Walla Walla District has doubled the number of fish transport barges from four to eight. This increase has put pier space at Lower Granite Dam at a premium—barges at the dam are docked three deep, making it difficult to stock and service them. In 2012, Walla Walla District requested bids for a pier expansion. It awarded the $6.9 million project to a joint venture of Spokane-based Garco Construction and Total Site Services, which operates out of Richland, Wash. TSS/GARCO chose West Coast Contractors (WCC), Coos Bay, Ore., as the subcontractor responsible for the pier construction.
IN-WATER WINTER WORK
With conservation of the fish a major priority on the project, the in-water work on the new pier was scheduled to extend from Nov. 14, 2013, to Feb. 28, 2014. After that date, all, barges and construction equipment were to be removed from the water. While the time frame may be optimal for the fish, it can be difficult for the crews who must perform the work in temperatures that drop -0°F on many nights.
The pier will rest on two rows of pilings, constructed from 32 steel casings, 54-in in diameter and 41-ft in length. Each of the casings has rock teeth welded to the bottom. Since the riverbed consists of hard trap rock with a compressive strength of approximately 35,000-psi, the casings are being set in a two-step process. Using a vibratory hammer to reduce the impact on the marine wildlife, WCC first inserts the casings a short depth into the rock to ensure correct placement. Then its subcontractor, Pacific Foundation of Vancouver, Wash., uses a drill rig to rotate the casing and seat it further into the hard rock layer.
The 16 casings closest to shore go through roughly 39-ft of alluvium, while the second row, which sits further out in the Snake River, has only about 15 to 20-ft of material to travel through. These spoils are removed from water with a rock auger bit and discharged into a skip box before being stockpiled at the project site.
WCC is working from shore to set the first row of pilings in the proper alignment. For the second row of pilings, the contractor will create temporary pilings, cap them with a steel cap beam and put stringers on top of the cap beam to create a work platform for the drill rig. Templates that rest on the close-to-shore pilings define the placement of the outmost row of pilings. (Because of the difficulty in finding nearby sources in this remote area of Washington, WCC fabricated the templates at its own plant in Oregon and brought them to the site.)
The pier also will include a mooring dolphin, which is a free standing marine structure used to moor ships. The dolphin will be constructed using a 15-ft diameter, 42-ft long casing that is held in place by a post-tensioned anchoring system composed of 12 rock anchors. The 62-ft-long anchors are made from 4-in diameter, high-strength threaded rod and extend down into the rock 20-ft below the casing.
To set these anchors, the contractor will insert 8-in, post-tensioned tubing before the concrete is poured. After the concrete is set, the 12 tubes will be drilled out, the anchors inserted and grouted back in halfway up. A hydraulic ram tensioning system will pull the anchors to a strength of 52 kits.
A fish barge being transported downstream. Salmon and steelhead fry are transported just downstream of Bonneville Dam, then released to continue their journey to the Pacific Ocean.
Walla Walla District specified that an airlift system be used to clean out the interior of the mooring dolphin casing in preparation for the tremie concrete pour. In fact, this system is similar to a process used by some underwater recovery teams that removes layers of sand and other materials from a shipwreck site.
After using a clamshell to remove as much material from the interior of the casing as possible, WCC will construct a manifold around the structure and force air from a barge-mounted compressor into it via small holes in the casing exterior. The air will force the unwanted material up. Water removed via this process will be discharged into a weir tank, and after some time there it will be pumped into a ponding basin for settling.
The concrete will be tremie-poured once the casing has passed inspection. The entire process is expected to take approximately two weeks. The smaller pier casings will also be filled with a tremie concrete pour.
To finish the pier construction, two cranes (a 100-ton and 160-ton) will set precast pier caps in place and then fit pre-cast, pre-stressed slabs on the caps to form the pier itself. TSS/Garco will finish the dock with a layer of concrete and add all utilities and railings. The new pier will be able to accommodate 8 barges at one time.
PLANS IN MOTION
Although the percentage of juvenile steelhead and salmon being transported is going down (USACE and the other government agencies involved in the fish recovery program are finding other methods, such as spillways, to keep the fish moving) the barges will continue to play a key role in ensuring that the steelhead and the salmon are preserved.
Now with sufficient space at the Lower Granite Dam pier, the transport barges will be able to do their jobs more effectively and more efficiently.