Why the High Water at Otter Falls

Energy Supply

Aug 07, 2012  Comment

Question: Why is there so much water running over Otter Falls this summer? Have you changed the way you are operating your Aishihik hydro plant?

Answer: Otter Falls (seen here on the right) was designed and built in 1975 to be an ‘overflow structure’. That means that when the water in Aishihik Lake gets a certain height, the Otter Falls control structure releases some of that water to keep the lake at an acceptable level (to avoid flooding on the lake). That’s when you will see lots of water flowing over Otter Falls.

Even when water levels are lower, you will always see a certain amount of water flowing over Otter Falls, because our water license requires that we maintain a minimum flow at all times.

This year we are well over the minimum (about 40 cm over the minimum). That’s because it  happens to be a high water year at Aishihik Lake, as it is in many other parts of the territory. These kinds of levels have been seen three or four years in the last ten at Aishihik. So while it’s not uncommon, it doesn’t happen all the time, and when it does people really notice it.

This year’s high water is a result of a combination of things: a high snowpack, lots of rain, and the fact that there were eight days this summer when our Aishihik plant was completely shut down for maintenance and an additional 20 days when we were only feeding Haines Junction due to maintenance on the transmission line. That means water usage through the plant was minimum. When the water doesn’t run through the generating units, it gets spilled over Otter Falls.

Just as an aside, did you know that Otter Falls was on the 1954 Canadian five-dollar bill?

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