BC Hydro will be closely monitoring water levels in the Columbia River drainage system as a wet spring and above average snow pack have begun to influence area lakes and reservoirs.
Even though the winter was dryer than normal, things changed quickly in the spring with most year-to-date precipitation levels in the area being higher than normal.
Even though water levels are forecast to be high, they are not expected to reach the levels of 2012, the last high-water year.
Of special concern is Kootenay Lake which sits at 1,749 ft., three feet below the onset of flood concerns. The lake is forecast to peak at about 1,752 ft. in late May. In 2012, Kootenay Lake peaked at 1,753.4 ft.
Kootenay Lake levels have been at record highs, in spite of the fact that outflows have been running to the maximum capacity that the natural restriction at Grohman Narrows can take.
“We have already been putting out as much as can since beginning of March,” said Gillian Kong, a specialist engineer with BC Hydro, in a conference call last week. “As soon as the lake starts to draft, we will turn around and reduce discharge.”
BC Hydro will be coordinating with the United States Army Corp of Engineers which operates the Libby Dam upstream on the Kootenay River in Montana. The U.S. portion of the drainage system actually saw even higher levels of precipitation, further complicating water management scenarios. They also have a lot of high level snow pack.
Flows at Duncan Dam will also be reduced to manage water levels at Kootenay Lake.
Also of concern is the Arrow Lakes Reservoir which is forecast to peak within two feet from full at 1,444 ft. in mid/late July. The lake is currently at 1,420 ft., but that is expected to increase steadily over the next few months. Arrow Lakes will be undergoing a controlled refill to a maximum level of 1,427 ft. on May 31 and 1,440 ft. on June 30.
“However, due to uncertainties in weather and runoff, if Arrow is full and flows are high, BC Hydro would be required to store up to two feet above full supply level (1,446 ft.) between June 15 and Aug. 31, 2017 for flood protection at Castlegar and Trail,” explained the BC Hydro presentation. In 2012, Arrow Lake peaked at 1,445.3 ft. on July 22.
If the reservoir is filled too slow it causes an increased flood risk in the U.S. If it is filled too fast it will result in going above full pool level at Arrow Lake.
“A four-foot buffer going into July will help reduce downstream flood risk and help manage the high water levels later in July at Arrow,” said Kong.
“Because we never know what the weather and runoff will bring us later in the year, in order to be prepared for the unexpected — especially if Arrow is full … we may be required to store two feet above the flood levels to manage the high flows downstream at Castlegar and Trail,” explained Kong. “At this point we do not plan on using the additional two feet unless there is a bona fide flood concern downstream.”
All of this trouble is caused by the exceptionally high spring rains. As of May, yearly precipitation levels, calculated using a water year of Oct. 1 to Sept. 30, are 91 per cent of average at Mica, 110 per cent at Revelstoke, 115 per cent at Arrow Lake, 118 per cent at Duncan and a record high 149 per cent at Kootenay Lake.
“All this rain translates to building snow pack,” said Kong. “Particularly for the past several months it has been cooler than average — all that rain went to building snow pack at higher elevations.”
Snow pack levels were below average until the last two months where almost all measuring stations are reporting above average levels.
The 2016 water supply forecast at The Dalles, Ore. — which represents the overall runoff for the Columbia — is 131 percent of average. This is the ninth-highest level since 1961, and close to the 2012 level of 135 per cent.
The water supply forecast for Birchbank (between Castlegar and Trail) is 115 per cent of average. Levels should increase and peak in early June.
BC Hydro does not expect flooding concerns at Castlegar and Trail, but to prepare for the unexpected has requested additional storage space at Kinbasket (1 ft.), Arrow (2 ft.), Duncan (1 ft.) and Libby (1 ft.) if available.