Update: BC Hydro Puntledge River Operations

December 12, 2014

BC Hydro Update, December 12 2:00 pm

It was an extremely challenging week for everyone involved. As communicated, the daily inflow volume last Tuesday reached 1 in 50 year event, and the Tuesday and Wednesday combined inflow volume into Comox Lake Reservoir set a new two-day record, and our records go back 51 years.

Upper elevation temperatures were high this week though they are trending downward. One can only imagine what this week would have been like if we had average snowpack levels for this time of year. Total precipitation just above the Comox Lake Reservoir from Monday through Thursday was a staggering 325 mm – that’s 0.32 metres of rain.

The Comox Lake reservoir rose 3 metres over those four days and is now trending downward. There’s basically been no rain since midnight Thursday and the forecast is for dry weather into early next week. The reservoir hit a peak of 136.2 m, which essentially matches a 50 year historical reservoir high. It is currently at 135.75 m and dropping.

BC Hydro has both spillway gates at Comox dam wide open and discharging as much water as possible. The current rate of flow below the dam is 245 m3/s. BC Hydro had dropped the flow down to 150 m3/s for the high tide this morning just to be cautious for flood risk management. We will provide this operational adjustment for each high tide as necessary. The public is advised to stay away from the Puntledge River given the high river flows through Thursday.

BC Hydro will spill maximum water flow rates possible from the dam until the reservoir level reaches 135.3 metres. From there, and also in consideration of dropping water inflows over the next four days with the drying out of the watershed, discharges from the dam may be reduced slightly but will remain high and dangerous. The public is advised to stay away from the Puntledge River given the high river flows through Thursday. BC Hydro would like to bring the reservoir down to 134.4 m and below for this time for the year so that we can be prepared for future storms.

There is no risk of flooding for the next five to seven days within our short term forecast window.

BC Hydro responded well to this severe weather event and all of our staff, who 24 hours a day, monitored and reacted as best we could to balance the watershed issues and flood risks. On behalf of BC Hydro, I would like to thank the City of Courtenay, Comox Valley Regional District, Comox Valley Emergency Program, and Emergency Management BC for all the coordination and communication efforts.

This may be BC Hydro’s final update notice on this record breaking weather event.

BC Hydro Update, December 11 11:13 am

The last round of rain for the multi-day storms will be hitting this afternoon and continue into tomorrow morning. The Puntledge River watershed may see total precipitation of around 40 mm. However in terms of downstream flood impact the worst is over. There are no significant storm systems in the forecast over the next seven days.

The Comox Lake Reservoir is at 136.15 m. This is very near a 50 year historical high reservoir level. Discharges from the dam were reduced slightly for the high tide this morning, but not as much as previous days based in the much lower flows in the Browns and Tsolum rivers.

The current discharge from the Comox dam is about 250 m3/s and this will be maintained for days to lower the reservoir. The public is advised to stay away from the Puntledge River through next week so that BC Hydro can bring levels back were they should be for this time of year and to prepare for future storm systems. The annual ocean king tides, with tides at 5.3 m, take place over the Christmas holiday season.

The Comox Lake reservoir has come up about 3 metres in the past 72 hours. BC Hydro has absorbed as much of the water as possible from these storms while considering our releases downstream for flood risk management. Inflows into the reservoir have averaged over 400 m3/s over this time, peaking upwards of 1000 m3/s, while BC Hydro has only released a maximum of 250 m3/s at low tide and down to as low as 32 m3/s at high tide each morning.

BC Hydro’s aggressive lowering of the reservoir in advance of these storms, particularly on Sunday and Monday, really helped.

Given the very high reservoir conditions on the Campbell River and Puntledge River systems, BC Hydro set up a virtual emergency operations centre. Close coordination, as has been in place all week, was further expanded.

BC Hydro has a comprehensive and robust dam safety program that looks at surveillance to capital projects to maintain our dams. Procedures are in place to have staff monitor the Comox dam at elevation 136.5 m and above 24 hours a day until water levels go back down. The dam is not at risk at those levels though proper monitoring is required should the reservoir continue to rise. Measures were put in place for staffing as there is a potential of hitting 136.5 m tonight.

A final update will provided tomorrow afternoon.

BC Hydro Update, December 10 1:40 pm

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 overvflow 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, December 9 1:30 pm

"A simple word of explanation on what happened since Monday into today is that we got walloped with rain. The Puntledge River watershed has seen massive amounts of rain and subsequent run-off into the Comox Lake reservoir and downstream river systems. On Monday, 100 mm of rain fell above the Comox Lake reservoir and now into Tuesday, from 12:00 am to 10:30 am, 94 mm of rain has fallen. That’s basically 200 mm in 36 hours.

The water inflows have been massive. The Cruikshank River hit a high of 530 m3/s this morning and is coming off that peak. The peak water inflows into the reservoir hit about 1000 m3/s - that’s the equivalent of the water within an Olympic-sized swimming pool entering the reservoir every 2.5 seconds. The water inflows will be very high through today.

The Comox Lake Reservoir has risen about 1.5 metres in the past 24 hours to noon Tuesday. At the current rate of rise, we see it beginning to free spill over the dam tonight. As the reservoir level increases, BC Hydro’s downstream operational flexibility diminishes. 

BC Hydro proactively lowered the reservoir in advance of this storm. With the very high water flows downstream, as per normal protocol, BC Hydro decreased the water release from the dam from about 180 m3/s to about 32 m3/s in advance of the high tide this morning. A water survey gauge at the 5th Street Bridge reached a maximum of 4.61 m at 8:30 am around the peak tide before slowly receding. Isolated flooding can begin at 4.2 metres. As the tide moved out, BC Hydro increased water discharges from the dam to maximum to move water out of the reservoir. This was delayed by one hour in consideration of what was happening downstream, which were followed by gate operations issues that limited our ability to release planned water volumes downstream. The current rate of discharge from the dam is about 200 m3/s. The water inflows into the reservoir upstream of the dam have been four to five times that amount.

BC Hydro will reduce flows from the Comox dam during tomorrow morning’s high tide.

The Tsolum River just hit a high of 282 m3/s which is a new record, but now starting to recede, and the Browns River hit a high of about 250 m3/s and is receding – 133 m3/s as of now.

BC Hydro is in close coordination with the City of Courtenay and emergency response agencies will continue discussions as needed over the next few days. This will be a multiple day event. A new storm, with up to 70 mm of rain is forecasted to hit the area tomorrow morning."

Previously: Monday, December 8

"An update since BC Hydro’s public notice (below) on Friday about the forecasted weather systems and hydroelectric operations. Since last week, BC Hydro has been tracking the two sub-tropical storms forecasted to hit the region this week. Unfortunately the storms are now much stronger and may hit the Comox watershed hard. BC Hydro’s weather forecasting and hydrology modelling, as of today, has seen a large increase in rainfall and forecasted inflows. The Monday-Tuesday storm is the strongest. Precipitation will peak tonight at a rate of about 10 mm per hour.

With the high ocean tides taking place in the morning each day this week, there is a risk of flooding in isolated areas of Courtenay on Tuesday and potentially each morning thereafter through Thursday. BC Hydro is concerned about these storms and the potential for flooding.

We are forecasting daily water inflow averages into the reservoir to be 350 m3/s and 320 m3/s on Tuesday and Wednesday. That means hourly peaks may hit 600-700 m3/s. It also means the uncontrolled Tsolum and Browns river flows will be high. Flooding along the river can begin at around 400 m3/s but is dependent on tide and storm surge from wind. There are winds from these storms that will cause some surge up the estuary.

Since the weekend, BC Hydro is spilling water at maximum rates and that continues through today to lower the reservoir level. The reservoir has come down about half a metre the past two days. It is currently at 133.3 metres, and provides BC Hydro with about 2 metres of storage room to try to take in these forecasted water inflows. However, that storage may be taken up fast in the next few days, and with it, BC Hydro’s flexibility to back off during high ocean tides.

BC Hydro will operate the Comox dam by releasing high flows at low tide and low flows at high tide. The flow discharge from the dam may be from 30 m3/s at high tide to 200 m3/s or more at low tide. The public is advised to stay away from the Puntledge River through the week. 

We have reached out to Comox Valley Emergency Program, City of Courtenay, Comox Valley Regional District and Emergency Management BC so that we are all coordinated.

BC Hydro may provide an update tomorrow afternoon."

Previously: December 5, 2014

From BC Hydro: "A series of storms are forecasted to hit the region over the next week. As well, the ocean tides next week will be high and challenging for flood risk management operations.

There are two significant tropical storms for next Monday-Tuesday and Wednesday-Thursday with a precipitation totals of around 200 mm over those four days. Daily inflows into the Comox Lake Reservoir are forecasted on Tuesday to be around 170 m3/s, with hourly peaks up to 400 m3/s.

The high ocean tides for those four days will be around 5.0 metres. It appears there may also be some ocean storm surge from winds from these storms.

Given the Browns River and Tsolum River are forecasted to increase significantly next week over multiple days, BC Hydro will engage in an operations to decrease the discharge to low levels from Comox dam during the high tides, and increase the discharge to high rates during low tide. This means the Puntledge River may have high swings in flows. Discharges from the dam may vary from about 35 m3/s to about 200 m3/s to control the reservoir level and consider downstream flood risk.

In advance of these storms, BC Hydro will be releasing more water from the Comox dam to allow more room in the reservoir to potentially absorb the forecasted water inflows next week. Flows from Saturday through Monday may be around 110 m3/s. The reservoir is currently at 133.95 m and slowly dropping. Water begins to free-spill over the dam at 135.3 metres. The reservoir can easily go up one metre in 24 hours under high storm water inflows.

The public is advised to stay away from the Puntledge River from today through next week.

Flooding in the Courtenay River can generally begin at around 400 m3/s, but this is influenced by ocean tides and potential ocean storm surge from winds.

Weather forecasts are subject to change and BC Hydro will provide an operational update on Monday afternoon."