On Wednesday, August 30th, the Bighorn Dam on the North Saskatchewan River was shutoff for approximately 24 hours to conduct a routine leakage test. The shutoff reduced river flow immediately beneath the dam to half a cubic metre per second, down from flows of 50 to 130 m³/s the previous day. The Bighorn Dam is located about 400 kilometres upstream of Edmonton.
With the river running at a mere trickle, standard operations involved crews walking through ankle deep water to salvage fish and return them to deeper waters further downstream. Calgary-based Transalta Corporation owns and operates the dam and conducts leakage tests each spring when reservoir levels are low and again each fall when levels are high.
Despite the routine nature of the operation, any paddlers or boaters on the upper reaches of the river last Wednesday were likely in for a disappointing surprise when the unannounced shutoff dropped water levels to a point that would potentially leave boaters stranded in the Rockies.
As the river meanders into the foothills, a number of tributaries contribute additional flow to the main stem and the effect of the shutoff becomes less dramatic. The Bighorn Dam controls approximately 20-25% of the North Saskatchewan Watershed’s source water, while the other 75-80% enters the river downstream of the dam, including at the confluence of the Brazeau River, which is also dam controlled.
In Rocky Mountain House, which is about 120 kilometres downstream of the Bighorn Dam, the lowest recorded flows remained above 50 m³/s from around midday on Thursday, August 31st into the morning of Friday, September 1st.
To see real-time flow data at various stations on the North Saskatchewan River, visit www.rivers.alberta.ca – note that the data is not validated.
Flows generally take about three days to reach Edmonton from the Bighorn Dam and will arrive in the City sometime this Saturday. Flow levels are already lower as we progress into the fall season and the dam shutoff may lead to the lowest levels yet this year. As always, boaters should be aware that some river channels may be particularly shallow and that rocky outcrops may be difficult to see just beneath the surface.
The low flow event will certainly keep a large expanse of sand above water at the increasingly popular Cloverdale Beach, which emerged earlier this summer as river levels declined following the spring freshet. If you’re headed there this weekend, avoid swimming in the current where the water is shallow, be aware of any risks associated with fluctuating water quality (click here for the latest test results), and enjoy the unusually sandy oasis right in the heart of our City!