Wholly owned and operated by a First Nation, the 2.1MW Atlin hydro plant is a perfect example of how water power can be environmentally beneficial and socially responsible, writes Lara Taylor
On 9 September 2009, the community of Atlin, British Columbia, Canada, gathered to celebrate the official grand opening of the Atlin hydroelectric project. The community as a whole, and the Taku River Tlingit First Nation (TRTFN) in particular, had much to celebrate. The 2.1MW Atlin project had been commissioned and operating smoothly for more than five months.
Until recently, the community of Atlin’s electricity was provided using diesel generators. These necessitated the delivery of more than 1M litres of diesel fuel per year to the 400 residents of Atlin, which is located in the far northwest of British Columbia. The pollution associated with this was becoming a cause for concern and, consequently, hydro power became a focal point in the community.
The directors of the Taku Land Corporation (TLC), a company wholly owned by the TRTFN, envisioned a project that would embody the fundamental principles presented in the TRTFN Constitution. The project would prevent the air pollution created by the diesel generators, thereby protecting the TRTFN traditional territory. Project revenues would remain in the community, strengthening the local economy and creating employment and contracting opportunities for TRTFN members and local residents.
In 2003, the Atlin Tlingit Development Corporation (ATDC) began work with BC Hydro, the provincial power utility, to develop a community energy plan, which led to TLC submitting an expression of interest to BC Hydro in July 2005. This EOI in turn, led to the signing of a 25-year power purchase agreement in November 2006.
TLC engaged Sigma Engineering of Vancouver to provide technical expertise for the development of the project. Sigma already had experience of working in the Atlin area. In a 1990 BC Hydro request for proposals, Sigma and its sister company Synex Energy Resources prepared a successful proposal to develop a 7.1MW project on Pine Creek. This project would have supplied electricity to Atlin with the surplus energy being sold to the Yukon Territory (north of British Columbia); however, it was deferred when the energy needs of the Yukon Territory declined.
The Atlin project conceptualised by TLC and Sigma was a low impact 2.1MW modified run-of-river plant (see figure 1). The scheme includes a low control structure at the outlet of Surprise Lake, hence the modified run-of-river operation. This control structure creates additional storage on the lake and allows project operators to control the flow being released into Pine Creek. Since the project displaces diesel generation on a non-integrated grid, the project’s capacity factor is extremely important, and the use of Surprise Lake storage is a key factor.
The project also includes an intake and weir that divert water into the penstock and to the powerhouse. The powerhouse includes an outdoor switchyard and a 25kV powerline that connects the project to the local Atlin grid.
Water power potential
The mean annual flow at the project intake was estimated at 4.2m3/sec. This estimate was calculated from a 36-year long streamflow record that Sigma synthesised based on two gauges: one on Pine Creek and the other on the nearby Gladys River.
Pine Creek is a snowmelt driven system with very low precipitation; an average of 347mm of precipitation falls annually (1971-2000). High flows occur in June as the result of snowmelt. Since the period of low flows coincides with the period of high electricity demand, storage was required on Surprise Lake to displace diesel generation year-round. Surprise Lake levels were modelled based on Pine Creek outflow over the period of record to determine the amount of storage required. The model showed that 1.1m of storage would be required on Surprise Lake to meet the community of Atlin’s projected electricity needs 20 years in the future. Atlin’s current electricity demand is approximately 4.67GWh annually; this demand is projected to increase to 6.98GWh in 2034.
Environmental studies for the project began in 2004. These addressed the full range of possible impacts: fish and fish habitat, wildlife and archaeology. The project team also assessed potential effects on TRTFN traditional use of the land, cultural resources, recreation and public safety.
Prior to construction commencing, TLC project manager, Stuart Simpson, worked with provincial and federal agencies to ensure that all required permits and authorisations were in place. Before a water licence and crown land tenure were issued, TLC submitted a development plan to the appropriate ministries describing the project, its potential effects, and the mitigation measures that would be undertaken to minimise these.
The project triggered an environmental assessment under the Canadian Environmental Assessment Act based on three factors: there are arctic grayling in the control structure area, Pine Creek is a navigable water body, and federal funding was received. A provincial environmental assessment was not triggered since the project is smaller than the BC Environmental Assessment Office’s 50MW threshold.
A number of characteristics contributed to making it particularly environmentally beneficial and socially responsible. These are:
• The project replaces diesel generation and is expected to prevent the emission of over 100,000 tonnes of greenhouse gasses (CO2 and NO2) over the next 25 years.
• It is locally owned by the TRTFN; all revenue will be reinvested into the local economy creating local employment and contracting opportunities.
• The Atlin region has a long history of placer mining. The settlement of Discovery, home to approximately 10,000 people during the 1898 gold rush, was located on Pine Creek. The project is located in areas that were previously impacted by placer mining. There was even a small hydro project in operation during the gold rush days.
• Fish access to the upper portion of Pine Creek is restricted by a set of falls. Arctic grayling (Thymallus arcticus) and slimy sculpin (Cottus cognatus) are present in the control structure area, but no fish were caught in the intake area.
In situations where foreseeing the magnitude of environmental impact was difficult, an adaptive management plan was implemented to ensure that these effects are mitigated. For example, fluctuating Surprise Lake levels could have a negative impact on nesting shorebirds and waterfowl. In response to this concern, a set of interim lake level guidelines was drafted. Nesting habitats will be monitored during critical nesting periods for shorebirds, and the lake level guidelines will be adjusted as appropriate.
The project was funded through a combination of grants, equity financing and debt financing. The cost was higher than would usually be expected for a project of its size due to its remote location and the moderate penstock gradient (average slope 2.7%). However, it is financially viable because it replaces diesel generation and, therefore, receives a higher electricity purchase price than projects connected to the main British Columbia grid.
The project, particularly during the development stage, received grants from a number of government sources aimed at reducing climate change:
• Indian and Northern Affairs Canada.
• Aboriginal and Northern Communities Action Programme.
• British Columbia Ministry of Energy Mines & Petroleum Resources.
Equity financing was provided by other TRTFN corporations and EcoTrust Capital Canada. The majority of the project’s construction was funded through debt financing provided by the Canada Life Insurance Company of Canada.
Design and construction
Sigma was the prime engineering consultant for the design and construction. The sub-consultants were Schneider Canada of Victoria, BC (electrical engineering), Sargent and Associates of Victoria, BC (structural engineering), and EBA of Whitehorse, Yukon Territory (geotechnical engineering). BC Hydro conducted the interconnection work.
Construction was completed in two stages. The control structure was designed first and built in the spring of 2007 by Johnston Construction of Galloway, BC. The remainder was built between May 2008 and March 2009 by Arctic Construction of Fort St. John, BC (general contractor). This construction sequence allowed the additional storage at the control structure to fill during the spring freshet before being required for project operation.
Atlin is located in a very cold and relatively remote area of British Columbia. Both of these factors provided additional challenges for the team. When possible, TLC engaged local people and businesses to provide materials and services. Hiring locally helped to keep costs down and was consistent with the TLC’s goals for the project. There were approximately 200 individuals and 35 companies involved and of these, approximately 10 were from the Atlin area and 20 were northern companies.
A brief summary of each of the project components is included in the sections below (also see Table 1).
The control structure includes a sheet pile and rip-rap weir built at the outlet of Surprise Lake. The weir is at an existing road bridge and ties into the road embankments. To lengthen the seepage path under the weir, a 45mm EPDM membrane sandwiched between two layers of non-woven geotextile was extended 10m upstream of the weir. The membrane and geotextile layers were protected by a layer of drain rock. A geotextile filter was extended 7m downstream of the weir and protected using a layer of pea gravel and a layer of rip rap.
A 1.8m diameter culvert through the left road embankment releases flow from Surprise Lake into Pine Creek. An orifice-type fishway also passes through the left road embankment. This fishway has improved arctic grayling migration between Pine Creek and Surprise Lake.
The timing of control structure construction was extremely important. Construction occurred during the spring low flow period and needed to be completed before the start of the freshet. This construction window meant that crews had to begin work when temperatures were still well below freezing. Excavation of the frozen road embankment was extremely difficult, and concrete had to be covered and heated following pours.
The Atlin intake consists of a small concrete gravity dam and a reinforced concrete intake that is located approximately 25m upstream of the dam. The concrete gravity dam has a maximum height of 9.25m from its bedrock base. During typical flows water not required by the project flows over the 14m wide ogee-type spillway. During flood flows, water also flows over the 14.4m wide secondary spillway.
The intake structure includes a penstock slide gate as well as coarse and fine trashracks. Water flows from the intake into a short section of 1.52m diameter steel pipe. This portion of the penstock was designed to allow the reducer to be exchanged for a bifurcation if the plant is expanded in the future.
Atlin’s cold climate was considered in the design of the intake and weir, including winter operation and the impacts of ice. The weir is higher than for comparable projects because the required submergence over the penstock inlet includes a 0.5m thick ice allowance. Non-metallic trashracks were used at the project intake to reduce the tendency of frazil ice to stick to these structures. The coarse trashrack can be removed during the winter months to prevent it from being damaged by ice. The fine trashrack is submerged and therefore less susceptible to ice damage.
The buried penstock is 3910m long and made of 1.22m HDPE and steel pipe. The minimum depth of fill over the penstock is 1.35m; this burial depth ensures that water in the penstock does not freeze. Burying the penstock also guarantees that wildlife migration across the penstock route is unimpeded.
The powerhouse is a prefabricated steel building on a concrete foundation. The building houses the generating equipment, crane and controls. The switchyard is located adjacent to the powerhouse.
The generating equipment consists of 2x1MW horizontal axis Pelton wheels, double overhung on a single generator. The turbine and generator were supplied by the Chongqing Yunhe Industry (Group) Co of Chongqing, China.
Since the community of Atlin is not connected to the provincial electricity grid, the controls for the turbine and generator needed to be different from conventional run-of-river projects. Rather than constantly adjusting to meet the community’s electricity needs, the project generates electricity at a constant rate greater than the demand. A load bank is used to disperse the excess energy.
A 750m long, 25kV powerline and 3.15km of 25kV express feeder connect the project to the diesel generating station and the local Atlin grid.
For long-term operations, TLC transferred ownership of the project to the Xeitl Limited Partnership (XLP), which is also wholly owned by the TRTFN. (Xeitl is the Tlingit word for lightning, which is the closest Tlingit word relating to electricity.) The project is one of the first small hydroelectric projects in Canada to be wholly owned and operated by a First Nation.
The project generated 1.95GWh of electricity over its first six months of operation. Stuart Simpson, now operations manager, reports that the plant is running nearly flawlessly. There have been eight outages since project commissioning, but none of these have been caused by project breakdowns. The outages have been caused by a combination of operator error during training, trees falling on the powerline and ravens landing on neighbourhood transformers.
Simpson also reports that the XLP has been very impressed with the facilities.
The Atlin hydro project has been extremely successful from a number of aspects. The plant has been operating smoothly since commissioning, and it will meet Atlin’s electricity needs for many years to come. Although the current project configuration has been sized to provide Atlin with electricity for the next 25 years, it has also been built to be expandable if the area’s energy demands increase faster than forecasted.
The project’s success is largely due to the resolve of TLC, XLP and the people who have spent the past five years advancing the work, including Peter Kirby (president) and Stuart Simpson (project manager). Good teamwork and effective communication, despite large geographic separations, were also paramount.
The project is a perfect example of how water power can be environmentally beneficial and socially responsible. The XLP team is now frequently solicited to speak at conferences as well as to provide advice to other First Nations in western Canada about building their own small hydro projects. It demonstrates what can be accomplished when people strive to reach a common goal.
Lara Taylor, Environmental Coordinator, Sigma Engineering Ltd, Vancouver, British Columbia, Canada. Email: email@example.com
All photos were taken by Stuart Simpson