From Drought to Monsoon on Vancouver Island

The 2009 weather year on Vancouver Island, from the perspective of rain and snow abundance and the challenge that presented BC Hydro in its hydroelectric operation, was unprecedented.

The extreme bookends of very dry and then very wet within a calendar year was impressive, yet harrowing. How BC Hydro was able to manage through this extreme year was very challenging yet successful--the social and environmental impacts were generally limited and to the external eye, perhaps even unnoticeable.

The only real impact was some flooding in the City of Courtenay that was beyond BC Hydro control. What happened or unfolded weather-wise to present this situation, and how it was dealt with, is what is intended to be conveyed.

Last winter BC Hydro identified a weather pattern of cool and dry weather, and acted to begin conserving water on the first day of 2009. Beyond July, weather conditions remained very dry and maintained a drought condition through to October--the lowest water inflows in 46 years for hydroelectric operations for the Puntledge River and Campbell River systems. There was no significant rain.

Then things began to shift to the other extreme--wet. Rains began in late October and culminated into major storm events in November. Heavy rain and record mountain snow falls, and the subsequent rain and snow melt from warmer storm systems, combined to raise the Upper Campbell Reservoir/Buttle Lake by over 5 meters in four weeks. For two large storm events only nine days apart, this large 6,730 hectare reservoir increased 1.4 meters and 1 meter respectively in a 24-hour period.

To protect fish habitat in the Campbell River, but with the overall goal of flood management, BC Hydro prefers to spill a smaller amount of water over a long period of time. BC Hydro was spilling water through the system that culminated with an amount that had not been seen since 2003. Peak hourly system inflows were 1,400 cubic metres per second (m3/s) yet the downstream discharge into the Campbell River hit a maximum of 350 m3/s, with flooding beginning at 450 m3/s.

Gravel in the Campbell River begins to move and potentially impact salmon eggs at around 350 m3/s and above. It was very fortunate the reservoir was so low back in October. BC Hydro allowed the reservoir to move into a reservoir flood buffer zone, but today, it has since drafted out of that zone and is ready to potentially attenuate a future storm.

For the Puntledge River, a much smaller reservoir system, the November storm events led to record peak flows for the Tsolum River and led to flooding in Courtenay--the first time since 1994. Up to an incredible 200 mm of rain fell in a 24-hour period. The high flows from the Puntledge, Browns, and Tsolum rivers that feed into the Courtenay River, and the high tide, led to that event. The Tsolum River reached a peak flow of 275 m3/s per second, the highest in the past 50 years, and the peak inflow into the Comox Lake reached a high of 730 m3/s.

The Comox Dam and the water release downstream is the only part of these river systems under BC Hydro management. Comox Dam discharge varied between 100-200 cubic metres per second, and the flooding would have been much worse had BC Hydro not had room in the reservoir to attenuate the very high inflows. It also reacted by releasing only 50 m3/s during high tide, and up to 230 m3/s at low tide.

It takes about two hours for water released from the dam to reach key City of Courtenay locations. BC Hydro was therefore communicating often with the City's Emergency Operations Centre. At the Comox Lake Reservoir, BC Hydro was also able to avoiding flooding of cabin properties around the lake. About a week later, BC Hydro was able to lower the reservoir in time to absorb another, but smaller, storm event that led to no flooding.

Return to January 2010 Western Energy News

To sponsor Western Energy News, please contact WEI at 503 231-1994.