Fear of a blowout has been reduced, but Grant County Public Utility District officials are still puzzling over what to do about a worrisome 2-inch, 65-foot long horizontal crack discovered late last month along one of the 12 spillways at central Washington’s Wanapum Dam on the Columbia River.
The damage was first discovered on Feb. 24 by a dam worker who noticed a section of the spillway deck had shifted slightly. Utility engineers then examined the area and found that one of the spillway pier monoliths had moved 2 inches out of alignment.
Divers inspecting the spillway on Feb. 27 saw a horizontal fracture about 2 inches wide at the base of the monolith.
To take pressure off the damaged spillway pier, the utility began to draw down the reservoir behind the dam by about 26 feet. The reservoir above the dam is now at its lowest level since the hydro project began operating 1964.
The drawdown is intended to take pressure off the damaged structure, and allow better assessments of the damage and judge what might be done to correct the problem. Overall the structure, with its 10 turbines and generators, is 8,637 feet long and 180 feet tall. Its construction began July 1959 and was completed in October 1963.
“It’s something that we’re taking very seriously,” said Grant PUD spokesman Chuck Allen. “It’s going to be this low until we come up with a long-term plan.”
On Tuesday, Grant PUD lowered its Emergency Action Plan classification for the Wanapum Dam spillway incident to a “non-failure emergency.” The utility had been operating under the condition of a “developing failure” since Feb. 28.
Grant announced Wednesday that its Emergency Action Plan (EAP) includes the notification procedures in the event of a “non-failure emergency” at Wanapum Dam, including situations that would necessitate the utility maintaining low water levels behind the dam to prevent a more serious emergency. The EAP describes the initial roles and responsibilities of Grant PUD personnel and other agencies based on the capabilities of each agency to respond in the event of an emergency situation at Wanapum Dam.
The news of a downgrade comes as a result of engineering surveys conducted March 3 and 4 that show continued stabilization of the fractured area found on the spillway. As of 6 p.m. Tuesday, survey results show that the impacted area is stable, according to a Grant press release. The fracture has closed and the damaged section of the spillway monolith has moved back upstream by nearly 1.75-inches as a result of the utility’s actions to lower water above Wanapum Dam and reduce pressure on the damaged spillway.
Grant PUD continues to work in conjunction with the Federal Energy Regulatory Commission as well as upstream dam operators and stakeholders to monitor and evaluate this incident. Public safety and the safe operation of the dam is the utility’s top priority.
Grant PUD in collaboration with other entities is also actively studying options to assure safe passage of adult and juvenile salmon and steelhead past Wanapum Dam if the current drawdown of the Wanapum reservoir continues into the migration season.
Adult upstream passage begins in April and continues into mid-November. Juvenile salmon and steelhead begin to swim downstream around the third week of April. In the event that water remains low into the migration season, options to provide upstream passage include modifications to existing Wanapum Dam fish ladders as well as the potential to trap and haul fish via trucks around the reservoir, according to a Grant PUD press release.
At current water levels, the Wanapum Fish Bypass would be operational, allowing juvenile salmon and steelhead to safely pass over the dam. The utility will continue to coordinate with partner agencies, tribes and Chelan PUD to determine the best options moving forward.
Wanapum Dam, 415 river miles from the mouth of the river at the Pacific Ocean, is the sixth dam that, as an example, migrating salmon and steelhead must negotiate on their way up the Columbia to spawn. Those fish include wild spring chinook salmon and steelhead stocks that are listed under the Endangered Species Act. Listed bull trout also travel up and down the system.
Wanapum is located downstream of Vantage, Wash., and 18 miles upstream of Priest Rapids Dam, which is also owned by Grant PUD.
Priest Rapids Dam is located on the Columbia River, 24 miles south of Vantage and 200 miles downstream from Grand Coulee Dam.
The next hydro project, nearly 40 miles upstream, is Chelan County PUD’s Rock Island Dam at Wenatchee.
Chelan County PUD announced Tuesday that it has stopped generating power at Rock Island Dam in response to drawdown by Grant County PUD at Wanapum Dam. With the lowered river level below Rock Island Dam, Chelan PUD is taking steps to protect its generating equipment and to safely operate its generators within design criteria during the Wanapum drawdown.
For the time being, the river flow will be managed by spilling water through the spillways at Rock Island. Rock Island Dam has a generating capacity of 629 megawatts.
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. Those spring chinook and steelhead are headed for such rivers as the Wenatchee, Entiat, Methow and Okanogan. Such fish runs typically start showing up in number in mid- to late April. Runs of summer Chinook and sockeye salmon come later.
The two PUDs, and others, are “having multiple daily conversations” to plot strategy to assure that fish can proceed up and downstream unimpeded, according to Keith Truscott, Chelan PUD’s Natural Resources director.
“We don’t want to have that happen,” he said of the possibility that fish can’t access fish ladder entrances or safely exit such systems.
“We’re going to look at the entire system,” Truscott said of juvenile and adult passage routes at Chelan’s Rock Island and Rocky Reach dams. The Wanapum reservoir situation should not impact juvenile fish migrations.
With the impacted portion of Wanapum now stable, Grant PUD staff, consultants and regulators are developing a plan to determine the root cause of the spillway monolith fracture, which was discovered on Feb. 27, and how best to repair the structure.
The utility has reopened public-access sites below Wanapum Dam, including the Priest Rapids Recreation Area at Desert Aire and the Buckshot Recreation and Wildlife Area. Those sites had been closed shortly after the crack discovery and Wanapum drawdown.
The Wanapum Lower Boat Launch, the Wanapum Heritage Center and day-use park remain closed. However, the Wanapum Dam Overlook is open.
Working under the authority of its federal license, the utility has temporarily closed the Wanapum reservoir shoreline. Article 18 of the utility’s operating license with the Federal Energy Regulatory Commission states that Grant PUD “… may reserve from public access such portions of the project waters, adjacent lands, and project facilities as may be necessary for the protection of life, health and property.”
Only authorized personnel are allowed access to the Wanapum reservoir shoreline. Sections of the shoreline, including the riverbank and mud flats are extremely unstable and have proven to be a serious safety hazard.
The utility continues to post signs informing the public of the shoreline closure and is actively working to patrol the area. State and local law enforcement agencies will be notified whenever anyone is observed trespassing in areas closed to the public. All boat launches on the Wanapum reservoir are closed to the public.
Grant PUD remains able to meet customer electricity needs with its current power supply portfolio. Wanapum Dam continues to generate electricity, yet at a reduced rate. Under normal river conditions, and considering that three of the dam’s 10 turbines are offline because of maintenance and turbine replacement, the dam has the capacity to generate roughly 700 megawatts. Given the drawdown in the water levels behind Wanapum Dam, capacity has been reduced to approximately 360 megawatts.
A spillway is the portion of the dam that allows water to “spill” past the dam as opposed to running through the turbines. The spillway consists of multiple, independent structural sections that support the spillway gates.
After drawing down the level of water behind Wanpum Dam, if two of the dam’s 12 spillway sections failed now, the amount of water that would flow through the spillway sections is 100,000 cubic feet of water per second.
“This amount of water is significantly less than under normal operations and would be within the range of average river flow, approximately 120,000 cubic feet per second,” according to a Grant PUD press release.
For up-to-date information on this issue, please visit www.grantpud.org