Sunday, November 23, 2014

Spring melt eyed closely

A long, cold winter has left significant snowpack in the Rainy River basin, meaning there’s an increased risk of high inflows to the Namakan Reservoir, Rainy Lake, and their tributaries as the spring melt begins.
As such, the Water Levels Committee of the International Rainy-Lake of the Woods Watershed Board is monitoring conditions closely.

On March 7, the owners of the dams at Rainy Lake and Namakan Reservoir were directed to operate them so as to target the lower end of the regulated lake level range (rule curves) defined by the International Joint Commission by the first week of April, Matthew DeWolfe, Canadian engineer advisor to the IRLWWB, noted yesterday.
This was to provide additional storage room in both lakes for the anticipated strong freshet (snow melt) flows.
In response to that directive, the dam owners—H2O Power and Boise—made modest adjustments to the outflows from the Namakan Reservoir and Rainy Lake to reach lake levels in the lower portion of the respective rule curve ranges as of April 1.
Under normal conditions, the dam owners are required to target the middle portion of the rule curves.
It was not necessary to open any dam gates to get the lakes down to the lower range—this was managed through turbine flows, said DeWolfe.
DeWolfe added that since last week, the dam owners have cut back the outflow on the lakes to hold them at the current level as they wait for the spring melt to really get underway.
Inflows to these lakes and their tributaries are slightly below normal for the start of April, but are expected to rise quickly as the snowpack begins to melt, he noted.
In response, outflows from the dams at Rainy Lake and the Namakan Reservoir will be adjusted with the goal of maintaining the lake levels within the range of the respective rule curves.
As of yesterday (April 8), no gates were open at the H2O Power dam here—all of the water passing through both the Canadian and U.S. sides is going through turbines.
Following the significant snowfall of March 31-April 1, there is no appreciable precipitation in the medium-range forecasts up to mid-April, said DeWolfe.
He added spring rainfall will affect what happens next.
“The risk of bringing the lake down too far is that the snow melts and you deal with that water, but then there’s no significant spring rainfall and you can’t get the lakes back up to preferred summer levels,” he explained.
“So it’s balancing the risk of increased snow melt inflows with not knowing what the spring rain will bring in.
“The biggest factor in determining whether you’ll have high spring or summer levels is really the amount of spring rainfall that comes and when it falls relative to when the snow melts,” DeWolfe stressed.
“So if everything comes at once, rain on top of significant snowpack, obviously inflow shoots up very quickly.”
The Water Levels Committee is monitoring conditions in the watershed regularly and will post updates as conditions warrant.
The latest information lake levels, dam settings, and basin flows can be found online at www.ijc.org/en_/RLWWB

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