Power Ops and Reservoir Management: The Year of the Perfect Storm
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There are probably few sets of circumstances to which the term “perfect storm” more aptly applies than those that confronted Rio Tinto Alcan Primary Metal BC’s power operations and reservoir management groups during 2007. Extreme weather – combined with an unexpected maintenance issue – created unprecedented challenges extending across the operation.
High precipitation in late 2006 set the stage for reservoir-management challenges. Then, on the night of March 28, 2007, a sudden power loss at the Kitimat smelter made it clear that the challenges were going to be multiple.
Use of one of two lines from the Kemano powerhouse was restored within a few hours. But when the Kildala Pass became accessible two days later, it was confirmed that a massive avalanche had destroyed a transmission tower and severed the second line.
This necessitated a repair effort of a nature and complexity that most of the people involved will likely only ever encounter once. It involved deployment of large and highly specialized teams, to a worksite that was accessible only by helicopter and that presented a narrow seasonal window and daunting safety and engineering challenges.
Power was fully restored across both lines in July, with a temporary replacement for the destroyed tower in place by August. Work on a permanent replacement was continuing when this report was prepared and had thus far been completed without a single accident or injury. A new configuration of suspended lines and conductors will replace two towers, and reduce the vulnerability to future avalanches.
Partial loss of transmission capacity represented a significant operational risk for the smelter, and this was compounded by a maintenance issue that took one of the eight generators at Kemano offline from July, 2007, to January, 2008.
Reservoir at Peak Levels
High precipitation continued into 2007 and monthly inflows into the reservoir were above the long-term average throughout the year, reaching a peak of twice the long-term average in July.
While more water than usual was diverted to the Kemano powerhouse during most of the year, the capacity to do so was limited by the hydroelectric system’s operational challenges. This increased the need for releases from the Skins Lake Spillway, on the eastern side of the reservoir, at a time when precipitation and inflows were already making flood-level flows necessary. These releases were timed and continually adjusted – based on routine and extensive data collection and forecasting – to limit downstream flooding as much as possible.
But the volume of inflows into the Nechako and natural inflows into other regional watersheds made it impossible to prevent flooding entirely. Weather conditions and a major ice obstruction on the Nechako in the spring further contributed to the flood risk.
Parts of the community of Vanderhoof were subject to an evacuation advisory, and flooding there lasted for nearly three months from June to September. Elsewhere in the region, agricultural land and sites of First Nations significance were also impacted.
2007 marked the first time that flooding has occurred on this scale since Rio Tinto Alcan Primary Metal BC established its community office in the watershed region. Rio Tinto Alcan Primary Metal BC personnel worked closely with provincial emergency management authorities and local governments and hosted public information meetings throughout the flood event.
Resources were dedicated to specific initiatives to mitigate and repair flood damage. This included rapid-response efforts to prevent a potential washout of a bridge, and removal and restoration of spirit houses in Cheslatta Carrier Nation cemeteries.
Reservoir monitoring and management efforts are believed to have reduced peak flood flows to about half of what they would otherwise have been.
| Sustainable Development Dimensions | ||
| Economic | Environmental | Social |
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