Flood worries could happen all over again next year
Editor: Watching the lake rise to neverbefore-seen levels and the damage being done, I decided to do some research on the management of Okanagan Lake levels.
I came across the Okanagan Basin Implementation Agreement adopted in 1982 where Okanagan Lake levels established by the Province of British Columbia were finalized.
See: obwb.ca/obwrid/docs/050_ Summary%20Report%20on%20the %20Okanagan%20Basin%20Imple mentation%20Agreement.pdf
Lake management levels were set with the low target being 341.3 metres above sea level, the upper target being 342.5, resulting in a normal range of 1.2 metres.
Oct. 1 and Feb. 1 were identified as key dates. The Oct. 1 lake-level target was set at 341.92 and the Feb. 1 target at 341.77.
These targets were set to ensure no more than a 15 -centimetre drawdown during the late fall and winter months to benefit the shore-spawning Kokanee and to ensure river flows for salmon runs.
The agreement recognized, because of large storage in Okanagan Lake in relation to discharge capability at Penticton, adjustment of lake levels takes many days and weeks of outflows to significantly change the water surface level of Okanagan Lake.
After Feb. 1, the lake should then be drawn down to its low target of 341.3 in advance of the spring’s melt/freshet. In anticipated flood years, read higher-than-normal snowpacks, the lake could be drawn down a further 30 cm, to approximately 341.0 metres
So if the low target is 341.3 and the high level target is 342.5, and years of historical data to draw on, it would appear the assumption is that the spring melt/freshet will add one to 1.2 metres to the lake elevation in a normal year. So now we get to this year. Here are some lake elevation measurements taken over the winter and into May: Sept 12 – 341.98; Sept 30 – 341.92; Oct. 17 – 341.89; Nov. 1 – 341.92; Jan. 20 – 341.75; Feb. 6 – 341.74; Feb. 28 – 341.73; March 16 – 341.74; April 19 – 341.92; April 24 – 342.02; May 1 – 342.11; May 8 – 342.40; May 15 – 342.66; May 23 – 342.89; May 29 – 343.05.
It looks like lake-level targets were met Oct. 1, 2016, and Feb. 1, 2017.
After Feb. 1, the lake drawdown to the low target of 341.3, on or about April 15 should have started. March and April were wetter than normal throughout the Okanagan basin, but much of that moisture fell as snow at higher elevations. Witness the increase in the snowpack from February to May 1.
Looking at the measurements, the lake level did not budge Feb. 1 through late-March and after that date started to climb. So the question is – were outflows being maximized starting Feb. 1 to draw down the lake?
It was reported May 8 by environment ministry officials that the lake was about 0.2 metres below the ministry’s target. The lake that day measured 342.4 metres.
That statement, in my opinion, was misleading, because 342.6 metres is the upper target at the peak of the melt/freshet in midJune, not early May.
With the estimate that the spring melt/freshet adds approximately 1-1.2 metres to the lake level, if the lake was at 342.4 May 8, with the spring melt/freshet having barely started, adding the 1-1.2 metres of the melt/freshet would result in a lake level approaching 343.4-plus at its peak in mid-June, which it appears is going to be close to what is now being predicted.
So now what we need the Environment Ministry to do is learn from what has happened and figure out what measures need to be put in place to ensure there is not a repeat next year or in future years
Because it’s certainly possible that May 1, 2018 we could see a largerthan-normal snowpack again, and we could see wetter than normal months of March and April in 2018.
Don Renoe, Peachland