Fish protections, irrigator access and hydro power generation are chief among the concerns at the mid-Columbia River’s Wanapum Dam, where on Feb. 27 a 65-foot long horizontal crack was discovered at one of the facility’s 12 spillways.
Grant County Public Utility District, the dam’s owner, opted for a steep drawdown of the reservoir behind the hydro project to reduce pressure on the damaged spill structure. The utility reported last week that steep drawdown to, at minimum, 541 feet elevation has served to stabilize the cracked spillway pier monolith. The Wanapum Dam forebay elevation had been maintaining at an average elevation of 568 feet through February.
The drawdown is the steepest ever since the dam when into operation in 1964. The resulting reduced “head” has cut the dam’s hydro production capabilities in half. Water pressure drives the turbines.
“There isn’t as much force, potential energy, above the dam,” said Grant spokesman Chuck Allen.
At the current reservoir level, the gravity fed fish ladders are left high and dry, and even if they weren’t salmon would now have a long drop once exiting the top of the ladders.
Fish biologists, engineers, and stakeholders are developing plans to modify the two fish ladders at Wanapum Dam to allow migrating salmon and steelhead to safely pass the dam when the adult spring Chinook salmon run begins in mid-April. Over the course of the spring, summer and fall, Chinook, coho and sockeye salmon, steelhead, bull trout, lamprey, shad and other fish species pass over the dam. Wild spring Chinook and steelhead stocks, as well as bull trout, are protected under the Endangered Species Act.
Such ladder fixes could include the installation of a water pumping system to feed the ladders and potentially some sort of slide to ease the fishes’ exit into the Wanapum pool.
The utility is also evaluating plans for capturing and transporting adult fish around the reservoir.
Even at current reservoir levels, downstream juvenile fish passage will occur as it has in the past.
If the Wanapum pool is drawn down for any length of time, it could cause problems for spawning salmon and steelhead that need access to Rock Island fish ladders. Rock Island, owned by Chelan PUD, is the next project upstream from Wanapum.
Grant is collaborating with other PUD and federal dam operators to assure adequate flows down through the system. The Hanford Reach below Grant’s Priest Rapids Dam will not likely be greatly affected, though Wanapum reservoir’s limited storage capabilities has been called on to make sure flows downstream were adequate to keep fall Chinook salmon eggs covered with water, and also protect fry that emerge from those eggs.
The Washington Department of Fish and Wildlife’s Bill Tweit called Wanapum pool “a 24-hour storage tool” that has been called on in the past to supplement downstream flows. The most utilized tool is Grand Coulee Dam 200 miles upstream. Its reservoir, Lake Roosevelt, has the most storage capacity in the mid-Columbia. Grand Coulee is operating throughout the winter and early spring to provide water to cover Hanford Reach, as well as chum eggs farther downstream.
Because of spring chinook returns that are imminent, “upstream passage is our first priority,” Tweit told the Northwest Power and Conservation Council on Wednesday. He filled the Council in on fish return projections for 2014.
Trapping and hauling fish, particularly late in the summer season, is likely not a top option, Tweit said. Sockeye salmon spawners, which migrate in summer toward the Okanogan and Wenatchee river basins, in particular are known often to be negatively affected by overhandling.
An evaluation of Wanapum Dam’s spillway pier monolith No. 4 is under way, with Grant PUD and contractors conducting studies to determine the fracture’s geometry, according to a Grant PUD press release.
The evaluation is expected to continue through next week. Once complete, the utility, along with an independent board of consultants and officials from the Federal Energy Regulatory Commission, will use the data to determine the best way to begin repairing the dam and raising the level of the reservoir.
Grant PUD is working in conjunction with the Washington State Department of Ecology to ensure that irrigators with land-use authorizations for surface-water withdrawals from the Wanapum reservoir have information and technical assistance they need to prepare for the upcoming irrigation season.
The 11 orchard irrigators affected by the reservoir drawdown have been contacted individually by Grant PUD. Affected irrigators can access information from the Department of Ecology on a web page devoted to the situation at www.ecy.wa.gov/programs/wr/dams/wanapum.html.
Grant PUD continues working with the sheriff’s offices of Grant, Chelan, Douglas and Kittitas counties to enforce the closure of the Wanapum reservoir shoreline to the public. The Washington Department of Fish and Wildlife has also closed its public-access sites on the shoreline and has increased patrol efforts. Sections of the shoreline, including the riverbank and mud flats are extremely unstable and have proven to be a serious safety hazard. The Wanapum Lower Boat Launch, Wanapum Heritage Center and day-use park remain closed.
Facilitating safe public recreation on the reservoir is one of Grant PUD’s goals as it moves forward in its response to the situation at Wanapum Dam. The utility has reopened public-access sites on the Priest Rapids reservoir, including the Priest Rapids Recreation Area at Desert Aire and the Buckshot Recreation and Wildlife Area. The Wanapum Dam Overlook is also open.
Methods used during the analysis of the fracture include precise drilling into the monolith, ground-penetrating radar and echo-imaging technology. Utilizing each form of technology allows the utility to determine the location and geometry of the fracture, according to Grant PUD.
Experts from the utility, a board of independent consultants and officials from the Federal Energy Regulatory Commission will use the data from the investigation to determine how best to move forward to repair the structure and possibly raise the elevation of the Wanapum reservoir to an intermediate level during the restoration phase.
Allen said that a boost of the reservoir level up to 560 feet would make the fish ladders operable.
No additional damage to the dam was found during a thorough inspection, other than some minor surface damage on spillways neighboring monolith No. 4.
To repair spillway pier No. 4, Grant PUD is exploring the possibility of using steel strand anchors that are drilled from the top of the dam through the concrete structure into bedrock. The steel strand anchors would be set into place with a specialized, high-strength grout, the utility says.
Data from the ongoing evaluation of the structure will help determine if this process would be an effective way to repair the spillway pier. The independent board of consultants and FERC will also evaluate the data and must approve any action before it is implemented by Grant PUD.
The utility is also working with Chelan PUD and other dam operators on the Columbia River, along with federal, state and local agencies, as well as tribes and other stakeholders impacted by the drawdown.
See CBB, March 7, 2014, “Crack In Wanapum Dam: Reservoir Drawn Down 26 Feet, Officials Assess Options, Fish Passage Strategies” http://www.cbbulletin.com/429942.aspx