Alberta’s hydro facilities are showing their age
A little-known stock of hydroelectric plants face an infrastructure crunch
A wooden chute runs alongside a muddy dirt road high in the Kananaskis Valley. The device stretches 1.4 kilometers uphill from the Pocaterra hydro plant to Lower Kananaskis Lake, and it leaks like a punctured hose. “It looks like a sieve but it’s not structurally compromised,” says Roger Drury, a senior technical specialist and 14-year hydro veteran with TransAlta Corp., which owns and operates the 55-year-old power facility.
That is good news, because the chute – commonly called a penstock – functions much like a vital artery. It stands 11 feet (3.3 meters) high and looks like a long wooden culvert. When the plant is switched on to make electricity, the line carries a tremendous amount of water, as much as 1,100 cubic feet (31 cubic meters) per second, from the reservoir to a generator that produces 15 megawatts of electricity.
Attempts over the years to plug the holes with everything from small wood wedges to pieces of sheet metal and neoprene have helped a bit, but the infrastructure is starting to show its age.
Pocaterra is one of 11 hydro plants that make up the Bow River System in southwest Alberta. Most of them were built in the 1950s, but a few predate the First World War. The Horseshoe and Kananaskis power plants were commissioned by TransAlta ancestor Calgary Power Ltd. in 1911 and 1913, respectively. Both were run by operators who lived in a company town at Seebe, a once-thriving hamlet about 100 kilometers west of Calgary that became a ghost town as dams were increasingly automated in the 1950s.
By that time, too, coal was fast replacing hydro as the province’s generating mainstay. TransAlta cemented the shift to thermal power when it commissioned the Wabamun station west of Edmonton in 1956. The last major addition to hydro plants on the Bow came in 1961, Drury says. “It’s an aging set of facilities. All of them are facing issues.”
Pocaterra is a particularly dramatic example of wear and tear. Built in 1955 and named after George Pocaterra, an Italian-born rancher who was among the first to prospect for coal in the Kananaskis area, the plant depends on a system that looks cobbled together by today’s engineering standards.
Modern facilities favor buried penstocks made from steel, but wood was popular among engineers in the 1950s because it was cheap and easy to work with, Drury says. The long, culvert-like structure is cradled along its length by U-shaped frames called saddles. Its beveled boards are held together by taut steel bands that can be tightened as needed to close would-be gaps. The repair job to date is a bit like “patching a tire,” Drury says. “It’s pretty labor-intensive.”
Leaks are particularly bad at the 10 and 2 o’clock points on the circumference. “It’s one of the highest stress points,” says Drury. The strain shows. Enough water sprays out that summer maintenance crews had to don wetsuits to complete weekly inspections on the line. “They worked on the exterior, but it’s like working in your shower,” the hydro chief says.
The wooden penstock at the Pocaterra hydro plant stretches 1.4 kilometers between Lower Kananaskis Lake and a 15-megawatt power plant
Photo Courtesy of TransAlta
The fear is that water will eventually erode the hill that supports the saddles, which is why TransAlta is spending $20 million to replace the line and bury it. “You hit a point where there’s just nothing practical left that you can do.”
The plant is one of three on the Kananaskis River. Upstream, a five-megawatt unit commissioned in 1955 separates the Upper and Lower Kananaskis Lakes. Downstream, close to where the Bow River meets the Kananaskis, the 1947-era Barrier Plant produces 13 megawatts and kicks up strong currents popular among local kayakers.
The aging stock of hydro facilities is approaching an infrastructure crunch. “It’s a bit of dilemma,” says Drury. Big power plants that dot the Bow River watershed are characterized by low operating costs and high capital outlays for major upgrades. Improvements are typically required every 50 years or thereabouts, which puts the need to upgrade dam sites in southern Alberta somewhere between urgent and long overdue. “Most of them tend to be built in that 1900-1950 time frame” and are due for a “major rehabilitation,” Drury says.
The 11 plants that make up TransAlta’s hydropower portfolio in southern Alberta play an important role in regulating the company’s power supply. Their output helps satisfy sudden spikes in demand for power from consumers. The peaking units also offset unforeseen outages at the firm’s much larger coal-fired facilities. “Hydro is one of the backstop sources that can be dispatched under those kinds of conditions. It’s not common, but it is a very fundamental part of [TransAlta’s] operations.”
Water flows on the system are managed down to the hour. A plant like Pocaterra can fire up in about two to three minutes, Drury says. As a result, flow levels on the Kananaskis River tend to mirror scheduled periods of peak power demand throughout the day.
The result is a boon for whitewater enthusiasts, who have learned to time their recreational outings to match the system’s peaks and valleys. But the irregular flow is less kind to plants and fish. “There’s a tradeoff there,” Drury notes. “One of the downsides to a peaking plant is this exact issue, where you ramp up and release the flow and then you stop.”
The upside is more water for heavy users at periods when the river typically runs low. Choppy currents originate at the top of the system, in Upper Kananaskis Lake. Spring runoff fills the reservoir with snowmelt until roughly mid-September. The water is released beginning in November to augment low-flow periods throughout the winter, so “you’ve increased your minimum generation through your whole system. You’ve spread it out,” Drury says.
That in turn means more water is available for a parched region with no shortage of thirsty users. Heavy industries and a patchwork of irrigation and municipal intake systems depend on the Bow watershed. Sound reservoir management ensures there is enough of it to go around. “It’s only an issue when it’s dry.”
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