The hydroelectric potential of the Keenleyside Dam remained untapped for 34 years. This changed in February 2002, when the 185 MW Arrow Lakes generating station began commercial operation after 24 years of efforts to add generation at the dam.
The Columbia River is the fourth largest river in North America, exceeded in length and flow only by the Mississippi, Mackenzie and St. Lawrence Rivers. It drains an area of 670,520 km2, of which 102,260 km2 are in Canada. The main stem of the river rises in Canada some 772 km from the Canada/USA border, and then continues for about 1,191 km to join the Pacific Ocean at Portland, Oregon.
The 1964 Columbia River Treaty (The Treaty) between Canada and the USA included a requirement for the construction of a storage dam at Lower Arrow Lake in British Columbia. Arrow dam, subsequently renamed the Hugh Keenleyside Dam, was completed in 1968. At that time it was not economic to install generating facilities at the dam, and no provisions were made for the future addition of generation.
Existing Keenleyside Dam
The Hugh Keenleyside Dam is on the Columbia River, 7 km upstream of Castlegar near the downstream end of Lower Arrow Lake. Construction of the dam raised the level of two natural lakes to form the Arrow Lakes reservoir, which has a live storage volume of 8.8 X 109 m2, and an area of 51,600 ha, and extending 235 km upstream. The dam is owned by BC Hydro, which operates it in accordance with the terms of the Treaty.
The reservoir is drawn down each autumn and winter to provide water for generation at downstream hydroelectric projects. It reaches the minimum level in the spring, providing flood control storage, and refills during the late spring and summer. The mean annual flow at the dam is 1160 m3/s. Discharges from the dam vary from 142 m3/s to about 850 m3/s during the refill period, and from 1,000 m3/s to 2,700 m3/s in the summer when the reservoir is full and while the reservoir is drafted through the autumn and winter. The available head at the dam varies from a maximum of about 21.5 m in the summer to as low as 2.5 m in the spring.
The site is typical of river valleys in British Columbia that have been formed by several glacial advances and retreats, with a complex mix of deep glaciofluvial and alluvial soils overlying bedrock in the valley floor and steep valley walls of rock. The overburden in the riverbed at the site has a depth of more than 150 m, and bedrock outcrops only on the north side of the valley floor. This site was the only location on Lower Arrow Lake where there was sufficient bedrock located at a relatively shallow depth to construct a dam.
The dam consists of a concrete gravity section and an earth fill section. The concrete structures are founded on granodiorite bedrock, and have a total length of 360 m and a maximum height of 58 m. The discharge facilities through the concrete dam consist of four spillway bays controlled by 15.2 m-wide by 16.8 m-high vertical lift gates and four submerged low level outlets on each side of the spillway.
The low level outlets are 6.1 m-wide by 7.3 m-high rectangular conduits, which slope down to the energy dissipator and are controlled by vertical lift gates. The energy dissipator is a short basin with a vertical dented end sill which induces a high degree of turbulence with a corresponding high energy loss.
The navigation lock allows for the passage of marine traffic, primarily the downstream movement of recreational boaters on log rafts to mills. It has a maximum lift of 23 m, with an overall length of 128 m and a width of 15.2 m.
The 450 m-long earthfill dam has a maximum height of 52 m and is founded on overburden. It is a zoned embankment, constructed from sand and gravel with an upstream sloping impervious core of glacial till, which continues 670 m upstream to form an impervious blanket across the full width of the reservoir.