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http://weather.gov/portland
Boaters, beware.
The Columbia and lower Willamette rivers are running unusually low, even by traditional end-of-summer measures.
“People who aren’t real familiar with the river need to be aware,” said Andy Bryant, a hydrologist for the National Weather Service in Portland. “There are a lot more shallow areas than there would normally be, and a lot more exposed sandbars.”
The weather service expects the most extreme low to occur between 9 a.m. and noon on Sunday, when the official gauge below the Interstate 5 Bridge drops to a half-foot below zero.
That doesn’t mean the river will be empty — river level zero means the surface is 1.8 feet above mean sea level — but it’s plenty low enough to create problems for houseboat owners, recreational boaters and heavily loaded deep-draft ships.
“They have to be more cognizant of when they’re loading,” Bryant said. “If they’re loading a ship at deep draft, they may need to adjust the timing to catch the higher part of the tidal cycle.”
The Columbia’s ordinary flood height is 16 feet in Vancouver.
Mitch Cline, with the U.S. Coast Guard command center in Astoria, Ore., said the Coast Guard has issued a broadcast notice about the dicey situation on the Columbia and lower Willamette this weekend.
“The prudent mariner should own a marine VHF radio and monitor it,” Cline said. “Unfortunately, that’s not always the case.”
Bryant attributed the situation to minimal water flowing downriver from Bonneville Dam, combined with weak tidal conditions reaching upstream from the Pacific Ocean. Ocean tides influence the Columbia 143 miles upriver to Bonneville Dam and as far up the Willamette as the waterfalls in Oregon City. Tidal influence varies by as much as 4 feet in Vancouver, Bryant said. However, the variance between high and low tides will be unusually meager this weekend.
“We’re not getting as much tidal energy coming up the river,” he said.
Federal dam managers, meanwhile, expect to run the minimum amount of water through the Columbia system.
Bryant said the river’s flow below Bonneville Dam will be less than a quarter of the volume that flowed past the dam just three months ago. Overcast skies this weekend will reduce the use of air-conditioning in the region, minimizing the need to push water through dam turbines.
“Temperatures are going to be right at comfortable room level,” Bryant said.
