March 4 (Reuters) - Grant County Public Utility District said it expects to finish reducing the water behind the Wanapum Dam on the Columbia River in Washington state on Tuesday to allow crews to stabilize a 65-foot (20-meter) long crack in a spillway.
Grant PUD said the crack did not pose any danger to the public.
The company said on its website the 952-megawatt dam continues to generate electricity. Officials, however, were not immediately available to say how much power the dam was producing before and after the water drawdown.
Over the weekend, the company said lower water flows during repairs could force the utility to buy power on the open market and affect the broader Columbia River hydroelectric system.
Washington has more than 21,000 MW of hydropower generation, making up about 70 percent of the state's total capacity. Most of the state's hydropower facilities are part of the Columbia River system.
Grant PUD said the drawdown is a precautionary measure taken after divers inspecting the spillway discovered the 65-foot long by 2-inch (5-cm) wide horizontal crack across one of the dam's 12 spillways on Feb. 26.
Once the drawdown is complete, the company said the river will be the lowest it has been since the reservoir was filled in 1964.
Grant PUD said it is working with the U.S. Federal Energy Regulatory Commission, which regulates the nation's hydropower dams, and upstream dam operators and stakeholders.
The spillway is a portion of the dam that allows water to "spill" past the dam as opposed to running through the turbines. Each of Wanapum Dam's 12 spillway gates are capable of passing roughly 80,000 cubic feet of water per second based on current river conditions.
In a worst case scenario, if one of the spillway sections failed, the company said the remainder of the spillways and the main dam structure would remain intact.
The company said under current conditions, the amount of water that would flow through this section of the dam would be within the range of normal river conditions.
The utility serves about 46,000 customers in Grant County and sells electricity across the Pacific Northwest's coordinated electric power grid. (Reporting by Scott DiSavino; Editing by Marguerita Choy)