BC Hydro readying for runoff down Puntledge River from record-smashing snowpack

In the Comox Valley you only have to look up to see all that snow from a record-setting season at the Mount Washington Alpine Resort.

In the Comox Valley you only have to look up to see all that snow from a record-setting season at the Mount Washington Alpine Resort.

With the approach of May, BC Hydro will be closely monitoring how all that snow will melt, Stephen Watson of Hydro’s Vancouver Island community relations said Wednesday. The Upper Wolf River weather station towards Campbell River is also showing high amounts of snow, with a snowmelt-to-water equivalent of about 2,200 millimetres.

This is about 160 per cent above normal and the second-highest on record. An average snowpack year is about 1,350 mm water equivalent.

BC Hydro considers the annual snowpack along with about 50 years of inflow data to forecast potential inflows into the Puntledge River watershed.

The Water Supply Forecast, done at the beginning of the month, indicates April to September runoff volume to be about 121 per cent of normal with a variance of about 20 per cent should it turn dry or wet. This forecast will be updated around May 9 to reflect the latest basin snow conditions and it is expected to stay well above normal.

This information is important so that BC Hydro can operate to conserve water in dry-looking years, such as 2008 and 2009, or in a wet-looking forecasts like this year, run the Puntledge River Generating Station at full capacity to create more room in the reservoir to absorb the melting snow.

The snowpack historically peaks at this time of year and then begins to slowly melt until depleted around the end of July. The Comox Lake Reservoir is currently at 133.75 metres and holding steady. It is considered full at 135.3 m.

“Given the large winter storm events over the past few years, there is some community concern for the potential flood risk with the record snowpack,” Watson noted. “At this time of year there are a number of factors that are in our favour, and this includes lower high tides, a low-elevation Tsolum River watershed that should see limited snowmelt runoff, and smaller storm systems.”

In looking at BC Hydro records dating back to 1963, the water inflows into Comox Lake Reservoir have not exceeded 200 cubic metres per second (m3/s) from May to June. These are well below the flood level inflows of 400 m3/s and beyond that can take place in the winter.

BC Hydro will run the generating station at full capacity but that will not enough to control reservoir levels over the next few months, Watson said. From May onward, this will translate into a significant number of controlled spill events.

To create more storage room, this weekend, BC Hydro will increase the discharge from the Comox Dam from 32 m3/s to about 110 m3/s. This threefold increase in the Puntledge River will begin Friday night and last through Sunday before returning to normal river flows.

BC Hydro’s preliminary operational plan is to release the same amount of water on May 14 and 15, May 21 and 23, during the 2011 Puntledge River Paddle Festival on May 28 and 29, and June 4 and 5.

BC Hydro advises the public to stay away from the Puntledge River during these high water flow events.

“This proactive operating plan has a number of benefits, such as trying to stay ahead of potentially high rates of snowmelt, a consideration for fish rearing from mid-June onward, and by providing whitewater enthusiasts advance notice of ideal river conditions,” Watson stated.

BC Hydro anticipates the reservoir to be hovering at full levels through July. The spring and summer temperatures, rate of the snowmelt, and rainfall amounts are large unknowns. BC Hydro will continue to inform the community of any significant operational changes as it balances all water use interests over the next few months, he said.

The water supply forecast bodes well for power generation, river recreation, to domestic water supply. BC Hydro plans to release its Campbell River operations update on Monday.

— Bc Hydro