The Comox Valley's dry period was interrupted briefly with a decent storm system, the first since late September, that hit Vancouver Island on Jan. 10, BC Hydro summarized Wednesday.
The 24-hour storm brought about 50 mm of rain recorded at Comox Dam and about 100 mm at the upstream Cruikshank River weather station. The reservoir rose about 40 centimetres over that weekend.
"It was not a large storm but it certainly gave us a bit of reprieve from the dry conditions," said Stephen Watson of BC Hydro.
"The warm alpine temperatures in the weeks that followed resulted in some modest snowmelt inflows with the reservoir rising another 20 centimetres. The double-edged sword is that while this added water to the reservoir, it depleted the snowpack that was already near a record low."
From Oct. 9 to date, the low water inflows into the reservoir for this time of year continues to be an occurrence rarely seen in BC Hydro’s 50 years of record.
"The dry conditions during the so-called storm season we’ve just passed through have been the second lowest on record. Since October, remarkably, we have only received about 35 per cent of normal water inflows into the reservoir from storm runoff and snowmelt.
After slowly declining for months, the Comox Lake Reservoir rose slightly in mid-January to hit a high of 132.47 metres Jan. 19, but the reservoir has slowly declined to the current elevation of about 132.10 metres.
At 131.4 metres BC Hydro begins to get concerned about providing sufficient downstream environmental flows.
BC Hydro has been operating the 24-megawatt generating station at 20 to 40 per cent of capacity from October onward to conserve water for downstream fish habitat. The current output is five megawatts (or a river flow of about 13 cubic metres per second) or about 20 per cent of capacity.
The low power output this year at Vancouver Island hydroelectric facilities has meant more power coming from the mainland via undersea transmission cables to meet customer electricity demand.
The Snow Survey and Water Supply Bulletin for January was issued by the Province, and for the Vancouver Island region, the snowpack was only seven per cent of normal. The February snow bulletin shows the snowpack to be 28 per cent of normal for this time of year.
The nearby Upper Wolf River snow gauge has been trending near record lows all fall/winter and is currently at about 25 per cent of normal. The snow pack normally peaks in May so there’s still time for snow accumulation.
BC Hydro has a five-day water inflow forecast that is updated daily to help guide operations. It is based on weather and hydrology forecasts.
The next week looks to be relatively wet with three to four light to moderate but cool precipitation systems crossing Vancouver Island, with water inflows into the reservoir being around 17 m3/s. This is slightly higher than the water release downstream of the dam so the reservoir level will slightly increase this week.
BC Hydro can plan months in advance through its February to September water supply forecast, and over that time period, inflows into the Comox Lake Reservoir are forecast to be 73 per cent of normal. This forecast considers snowpack, precipitation, and historical water inflows from the past 50 years. Should the weather be dry or wet, the water inflow variance can be 20 per cent.
BC Hydro has been operating in water conservation mode this past fall and so far this winter to protect downstream fish habitat and incubating salmon eggs. The eggs have or are now hatching and turning to the alevin stage.
"Our primary goal is ensure key fish habitat is covered with water into the spring season with the outmigration of salmon fry and smolts into the ocean," Watson explained.
“The dry fall and winter has resulted in favourable incubation conditions for salmon eggs and alevins due to the lack of flooding," noted Darcy Miller of Fisheries and Oceans Canada. "Should dry conditions persist, there is high probability that warm water temperatures and low river flows over the summer and early fall will cause sub-lethal environmental conditions for juvenile and returning adult salmon.
"Co-operative discussion with BC Hydro related on water reservoir operations has achieved the best possible scenario for protection of our local fish stocks,” Miller concluded.
BC Hydro has been communicating regularly and working closely with Fisheries and Oceans Canada and Ministry of Forests, Lands and Natural Resource Operations on fisheries issues as well as being in discussions with Comox Valley Regional District staff.
“Water demand within the CVRD's bulk water system is generally low in the winter and then increases in the spring and summer as the weather warms," stated the CVRD's Marc Ruttan. "The CVRD will continue to work closely with BC Hydro and DFO in monitoring lake levels and water volumes to determine if future water conservation is required. Conservation is key to the long-term reliable supply of water for domestic use."
BC Hydro will provide an operational update around mid-March.
— BC Hydro