Heavy weekend rainfall raised the level of Comox Lake by a metre, forcing BC Hydro to release extra water from its reservoir beginning Monday evening.
At Hydro’s Cruikshank River gauge, over about a 36-hour period from Saturday to midnight Sunday, about 120 mm of precipitation was recorded, Stephen Watson of Hydro said Monday in a news release.
Water inflows into the Comox Lake reservoir peaked at an hourly flow of 330 cubic metres per second (m3/s) at midnight Sunday night. The daily water inflow average into the reservoir Sunday and Monday is about 150 m3/s.
All through the weekend the discharge from Comox Dam was only about 26 m3/s. The Browns River hit a high of 112 m3/s, which is quite high for this river system, whereas the Tsolum River, a larger river system, only got up to about 87 m3/s, Watson elaborated.
The brunt of the storm, for wind and rainfall on Vancouver Island, went through this watershed and the Comox Valley.
The week ahead looks somewhat unsettled with a moderate storm potentially hitting the area this weekend. This means the daily inflow average of 150 m3/s into the reservoir will drop to about 45 m3/s by Thursday.
The Browns and Tsolum rivers are down significantly from the peak river flows.
The Comox Lake Reservoir rose one metre over the past two days and was at 134.1 metres and rising early Monday afternoon. That level was just over a metre shy of free-spilling over the Comox Dam.
“BC Hydro needs to consider reservoir shoreline impacts above 135.3 metres and downstream flood risk management,” Watson said. “The reservoir was well-positioned to absorb this storm event but we now have less storage room for future events.”
BC Hydro has regulated fish migration and spawning flows on Wednesday and Thursday this week in the Puntledge River, so river flows at Stotan Falls are to be around 17 m3/s.
The chum salmon fishery has fishers on the river through into early November. Weekend river access for fishers is deemed valuable, stated Watson.
Beginning Monday (Sept. 30) at 8 p.m., BC Hydro will increase the Puntledge River flow by about fourfold to 110 m3/s and hold at that level throughout the day Tuesday. BC Hydro will then lower the discharge down to about 40 m3/s for Wednesday and hold at that level through the weekend.
Should the weather forecast be accurate and in consideration of forecast water inflows into the reservoir, BC Hydro sees the reservoir level being around 134.4 metres by Sunday.
BC Hydro reviews operations and the weather forecast daily and will adjust operations as needed.
The public is advised to stay away from the Puntledge River on Tuesday due to the high and dangerous water flow conditions.
Watson said there is no risk of flooding downriver.
— BC Hydro