We’ve had about 250 mm of rain hit above the Comox Lake reservoir over 48 hours. About 70 mm has fallen so far today though precipitation rates are tapering off now. The daily volume of water inflows into the Comox Lake Reservoir of 520 m3/s on Tuesday hit a 50-year return period. The highest on BC Hydro’s record for a daily inflow average was 522 m3/s – we were close. This was and remains a major water event for BC Hydro to try manage through.
The Comox Lake Reservoir has risen about 2.6 metres in the past 48 hours. The reservoir is currently at 135.85 m and rising. The water inflows into the reservoir are around 500 m3/s – the Cruikshank River is flowing in at about 275 m3/s. About half-a-metre of water is free spilling over the over flow spillway section of the dam.
BC Hydro decreased the water release from the Comox dam from about 225 m3/s to about 45 m3/s well in advance of the high tide this morning. A water survey gauge at the 5th Street Bridge reached a maximum of 4.28 m (it hit a high of 4.61 m yesterday) before slowly receding but has since come up and is hovering around 4.2-4.4 m. Isolated flooding can begin at 4.2 metres.
As the tide moved out this morning, BC Hydro increased water discharges from the dam by about 50 m3/s every 30 minutes in consideration of the Browns and Tsolum rivers that were rising from today’s rain event. The release from the dam is currently about 240 m3/s.
The Tsolum is currently flowing at 230 m3/s and the Browns River at 140 m3/s – they are flowing at high levels. The total river flow at Gauge 10 is about 700 m3/s.
The highest level the Comox Lake Reservoir has reached in some 50 years of record is around 136.2 m. That level was hit twice, including the flood event in January 2010. BC Hydro forecasts the reservoir potentially hitting 136.7 m by end of day Thursday. With the high reservoir level, BC Hydro’s downstream operational flexibility continues to diminish as we consider the high tides. The Comox dam is made of concrete and founded on bedrock, and is safe and being well managed under the flood risk management conditions. It is designed for these events.
The silver lining is the weather is anticipated to turn drier by Friday. After a smaller storm tomorrow, the long-term forecast into next week looks much drier.
The water inflows into the reservoir, averaged over the whole day, are forecasted to be 460 m3/s. For the next four days, they are forecasted to be 310 m3/s, 190 m3/s, and 110 m3/s. BC Hydro updates its five-day forecast each day.
BC Hydro continues to work very closely with the City of Courtenay and other key emergency responder agencies with many calls and emails per day. It’s critical that we are all on the same page and aware of each other’s situations. The two-way communication has worked very well.
(BC Hydro update)