BC Hydro, Puntledge River update #5: flood risk management operation
November 24, 2017
From BC Hydro:
"The storm activity continues as does the maximum water spill from our Comox dam down the Puntledge River. We continue to try to control the reservoir while also considering downstream flood risk management. The safety advisory for people to stay away from the Puntledge River has been extended through to Sunday, December 3.
The precipitation rate the past few days has been moderate but the snowmelt has been considerable from the warm tropical-based storm that passed through the area mostly on Wednesday. The hourly peak water inflow into the reservoir hit about 400 m3/s on Wednesday evening. The lower precipitation and less influenced by snowmelt Browns and Tsolum rivers only slightly increased in flow rates.
We have continued a maximum spill release from Comox dam of about 140-170 m3/s since Sunday evening, with the discharge rate depending on the reservoir level. The reservoir went up to 134.4 metres on Thursday and is currently at 134.3 metres – about one metre from the level where water free-spills over the dam.
With up to about 100 mm or so forecast for the watershed on Saturday evening through Sunday, and with it also tapping into subtropical systems, we see a high water spill up to the maximum being in place through early next week. With modest wet weather next week, the extra water spill from the dam will likely stay in place, though eventually at a lower rate, through to December 3. This will depend on the weather.
There is very low risk of isolated downstream flooding at this time. The ocean tides continue to be a helpful by being a bit on the low side for this time of year. The King tides, which are about half-a-metre higher than current, are December 5-10."
November 22, 2017
BC Hydro, Puntledge River update #4: flood risk management operation
"The forecast today has again changed for the better with less precipitation. This is good news, and while there will be significant snowmelt from the warmer temperatures, we see a much reduced potential downstream risk of isolated flooding this week. The weather also looks to be better next week.
We have been releasing the maximum water spill from Comox dam since Sunday evening. The current water discharge below the Comox dam is about 147 m3/s. On Monday morning after the Comox Lake reservoir hit a high of 134.25 metres, or about a metre from free-spilling over the dam, the level has trended down to 133.85 metres as of noon today. At this time of year we generally try to keep the reservoir level at or below 134 metres for water storage and flood risk management considerations. There is the potential for the reservoir level to go up a bit from the snowmelt this afternoon and into tomorrow.
BC Hydro will reduce the discharge from the Comox dam for the high ocean tides each morning as needed.
At this time the Browns and Tsolum rivers are not really reacting to the storm activity though they will increase in flow. The scheduled high ocean tides are slightly drifting lower towards the weekend, which is favourable.
Sometime tomorrow or Friday we may reduce the water release from our dam down the Puntledge River and then step down again to about 70 to 100 m3/s over the weekend to control the reservoir level as needed. We will adjust operations based on actual water inflows into the reservoir. Given the high river flow conditions BC Hydro continues to advise people to stay away from the Puntledge River through Monday.
The weather forecast calls for the wet weather to continue through the weekend. However, the river flows from these storms should not be too significant. There is currently warm temperatures and a high freezing level causing some significant snowmelt, though the freezing level is expected to drop again Thursday onward.
This may be our final operational update unless there is a significant change in the weather forecast over the next few days."
BC Hydro, Puntledge River update #3: flood risk management operation
November 21, 2017
"We have a bit of silver lining in the storm forecast for Tuesday through Thursday morning. There has been a slight shift and while the storm will hit the area, the amount of forecasted rainfall will be slightly less, particularly on Wednesday. BC Hydro will continue the high rate of water release from the Comox dam to control the Comox Lake reservoir level.
We continue to leave the two spillway gates at the Comox dam wide open and move as much water as we can out of the reservoir. The current water release below the dam is about 150 m3/s. Since the peak level of about 134.25 metres yesterday, the reservoir level has slowly drafted down to 134 metres at noon today. It will continue to slowly draft or stabilize until tomorrow where level changes will depend on rainfall and the amount of snowmelt.
There is good water storage in the reservoir to significantly reduce flows downstream for the high tides tomorrow, if needed, for flood risk management.
We continue to engage with the Comox Valley Regional District and the City of Courtenay. While the potential for isolated downstream flooding has lessened, the weather scenarios of when the downstream rivers peak in correlation with the high tides and storm surge from winds are always an uncertain variable. Forecasts can change quickly on Vancouver Island so while things are looking better today compared to yesterday, we will be closely watching weather patterns and the actual water inflows and adjust our operations as needed.
This storm system looks to end on Thursday morning and in looking ahead, there are some forecasted storms on the weekend though they are less intense and the freezing level is lower. They appear to be typical storms for this time of year. However, water flows are expected to be fairly high through the week.
We expect to be releasing up to maximum water flows from Comox dam through the week and advise the community, for public safety, to stay away from the Puntledge River. "
BC Hydro, Puntledge River update #2: flood risk management operation
November 20, 2017
"This past weekend provided water inflows into the Comox Lake reservoir that were double the forecast. Looking ahead, we are focused on our flood risk management operations and closely watching a large tropical-based storm that looks to hit the area Tuesday through Thursday morning.
Over Saturday and Sunday, about 150 mm of precipitation fell in the upper Puntledge River watershed, with about 100 mm over just 14 hours on Sunday. While there was snow from this storm in the upper elevations, a good amount of the precipitation fell as rain and led to an increase into the Comox Lake reservoir level. The Sunday daily average of water inflows into the reservoir was 227 m3/s, while our Friday inflow forecast was for around 110 m3/s. The reservoir level increased from 133.6 metres on Sunday to 134.25 metres this morning.
BC Hydro began to spill extra water on Friday night with water flows that were just below our public safety notification threshold, and then on Saturday night, we increased the discharge from the Comox dam to more than double the typical flow rate of 32 m3/s. However, after the lower high tide on Sunday evening, given the amount of water entering the reservoir and the upcoming forecasted storm, we initiated a maximum spill level from Comox dam with both spillway gates fully raised. The current water release from the dam is about 160 m3/s, or about five times the typical Puntledge River flow rate.
Going through today and tomorrow morning we will try to lower the reservoir level as much as possible. As the storm hits, we will monitor downstream rivers and tides, and reduce the discharge as needed during the high tides for flood risk management.
BC Hydro continues to advise the public to stay away from the Puntledge River through the weekend.
On Sunday, BC Hydro reached out to the Comox Valley Regional District and the City of Courtenay out of concern for the potential for isolated downstream flooding on Wednesday and Thursday. There will now be information sharing multiple times per day as we move through this week. The tropical based storm system continues to track towards the area, and it is a wide band, not a narrow band like a typical atmospheric river. It is forecast to hit over three days with the two main waves being Tuesday afternoon and Wednesday afternoon/evening. The concern is that these storms will come from the south and hit the north side of the watershed, so the Browns and Tsolum rivers will react more than from this past weekend storm. As well, there will be winds from these storms that will cause some ocean storm surge up the estuary. And the much warmer temperatures will cause snowmelt with freezing levels around 2500 metres. It will depend on when the natural rivers peak and how that fits into the high tide schedules, and what the storm surge may be.
BC Hydro will provide a forecast and operational update on Tuesday."