BC Hydro update No. 9: Puntledge River operations and storms over for now

November 14, 2016

From BC Hydro:

BC Hydro update #9: Puntledge River operations and storms over for now

"We finally have that extended weather break we were all looking for. The continuous storm activity has finally come to an end, at least for now.

Over a seven day period, as well as a 14 day period over this storm activity, we pointed out in our last update that these set new 53 year water volume records for inflows into the Comox Lake reservoir. The amount of water into the reservoir over the two week period was likely approaching a 1-in-100 year return period for storm inflows.

October precipitation was a record high (537 mm) and the record precipitation from November 1 to 13, at our Eric Creek gauge in the upper watershed, recorded about 566 mm. That’s 1.1 metres of rain.

We know there are many variables that can lead to downstream flooding, and somewhat remarkably, those variables fortunately did not line up over the weeks of record storm run-off to cause any significant downstream flooding. When the Browns and Tsolum did peak, they peaked at low tide. Or they had a rainshadow effect and received less rainfall than in the headwaters for some of the large storms. The high tides were low over the storm period at about 4.7 metres. The King Tides begin Wednesday at 5.2 metres, which is half a metre higher. It’s all about timing. The winds did not cause too much storm surge by pushing water up the estuary. And BC Hydro was able to hold back water at key times to limit downstream effects. To go through such an extremely wet period and essentially have very limited impacts from a flood risk management perspective was very fortunate.

We need to remain diligent as we are now hitting mid-November which is typically when storm season starts. The weather over the next week looks relatively benign with lower freezing levels.

Our operations should resume normal conditions this Thursday with the planned spill ending. The Comox Lake reservoir came off its high of 135.8 metres late last week and we were able to bring it down 1.3 metres to 134.4 metres by the Sunday storm. It is now at 134.65 metres and leveling off from the last storm. We are releasing a maximum water discharge below Comox dam of about 190 m3/s. The reservoir level should be below 134 metres by Wednesday or Thursday and be well positioned for future storms.

BC Hydro will maintain a high spill rate likely through Wednesday before moving down to more typical operations and no additional water spill downstream. Please stay away from the river through Wednesday with the high flow rates.

Special thanks for the coordination work with the City of Courtenay, Comox Valley Regional District, Comox Valley Emergency Program and Emergency Management BC. Daily calls and emails took place over the long weekend and those have now come to an end given the much improved situation. This is our final update on these storms.

(Correction: in notice #8 it should have said the reservoir would have filled almost three times over a 14 day period, not a seven day period.)"

Previously:
November 10, 2016

BC Hydro update #8: Puntledge River operations and forecasted storms

"These large and continuous storms are for the record books. BC Hydro’s records go back 53 years and we’ve never see as much water volumes enter the Comox Lake reservoir over a seven day period, nor a 14 day period. Incredible water volumes. Over a seven day period the reservoir storage, from 131 metres to 135.33 metres, would refill itself almost three times.

In October we had a record 537 mm of precipitation in the upper watershed and at our Eric Creek gauge 471 mm of precipitation has been measured since November 1. Over a metre of rain in about five weeks and almost half-a-metre in eight days. November is off like a rocket for rain.

The storm earlier this week hit the upper watershed hard with high inflows but the storm direction provided a bit of a rain shadow effect for the Browns and Tsolum rivers. This was good news and did not provide a downstream flood risk. The Comox Lake did come up quite a bit and peaked at just over 135.8 metres yesterday; the highest level since the storms started in October. BC Hydro continues to spill as much as we can through the two spillway gates and this has allowed the reservoir to come down to 135.35 metres, basically the level of the dam’s concrete overflow spillway. The reservoir will keep drafting until the next storm hits tonight through into early Saturday morning.

The forecast precipitation for the next storm is for upwards of 100 mm or so in the upper watershed. The next storm, on Sunday into Monday, may drop another 100 mm. Beyond that, forecast models are uncertain if more storm weather or if it turns drier and cooler. Let’s hope it’s the latter.

The downstream flood risk will be determinate by high tides, which are moving close King Tides starting Saturday into next week, some storm surge from winds, and when and by how much the Browns and Tsolum rivers peak. The good news is we have lowered the reservoir down a bit to back off each day during the high tides. The next higher potential downstream isolated flood risk appears to be later Friday night.

BC Hydro remains closely engaged with the City of Courtenay, Comox Valley Regional District, Comox Valley Emergency Program and Emergency Management BC. Daily calls will continue each day through the weekend as we try to manage through this barrage of storms.

We will provide an update on Monday."

 

November 8, 2016

BC Hydro update #7: Puntledge River operations and forecasted storms

"The current storm has been significant but given the direction it hit the overall watershed, downstream rivers like the Browns and Tsolum did not react as much as potentially anticipated. This was good news.

We had 126 mm of rain at our Eric Creek gauge since yesterday afternoon. While we are within a short reprieve now, the current storm will shift south again this and produce more rain this evening. There is a weather break and then there are additional moderate to heavy rainfall events are forecasted for Thursday to Friday, and potentially Sunday to Monday.

Most of the water run-off from the current storm is coming into the Comox Lake reservoir. The daily average looks to be around 350 m3/s. The peak hourly flow rate could reach about 500 m3/s later this afternoon if the rain hits the watershed as forecasted. The release below Comox dam was reduced to 150 m3/s for the high tide earlier today but has gone back up to about 250 m3/s.

The Comox Lake reservoir is currently at 135.6 metres, or up about 0.55 of a metres since yesterday. The reservoir continues to rise and may hit 135.7 metres by the end of the day. However, we will continue to spill maximum amounts and bring the reservoir level down Wednesday and into Thursday before the next potential storm.

We see a limited chance of downstream flood risk through Wednesday, though conditions can change. The Puntledge River will remain very high until further notice. 

The high ocean tides have been on the lower side of around 4.7 metres the past week or two, which has been very helpful for flood risk management. The tides will be increasing to 4.8 metres on Wednesday and to 5 metres on Saturday to Monday.  

BC Hydro remains closely engaged with the City of Courtenay, Comox Valley Regional District, Comox Valley Emergency Program and Emergency Management BC. The potential for downstream isolated flooding remains in place through Tuesday. So for now a bit of good news as we try to manage through this.  

We will provide an update on Thursday."

Previously:

November 7, 2016

BC Hydro update #6: Puntledge River operations and forecasted storms

"The weather forecast has taken a turn for the worse and the significant storms look to potentially continue through the week. Precipitation in the upper watershed could be upwards of 200 mm today through Tuesday, about 25 mm on Wednesday with a possible lull. There then looks to be a similar storm to this on Thursday and Friday with about 100 mm to 140 mm forecasted, followed by another potential storm on Sunday, though that is a long ways out. There seems to be no storm reprieve to speak of. Forecast can and will likely change.

About 66 mm of rain has fallen in the upper watershed from the current storm.

We were able lower the Comox Lake reservoir be about 0.60 m through Sunday from its high of 135.6 metres, to about 135 metres. The reservoir has now begun to increase and we did reduce discharges from the dam for the high tide today. The current level is at 135.10 metres and rising.

The discharge from the Comox dam will be around 250 m3/s through today.

Forecasted water inflows into the reservoir over the next five days are around 250-300 m3/s. Under the higher inflow scenario of more potential rain has daily inflow upwards of 430 m3/s on Tuesday.

With today’s forecast, and looking at being able to slightly reduce discharges for fours each day for the high tide, the reservoir may hover around 135.6 metres. The reservoir will remain high and downstream flows will be high. Water free-spills over the dam at 135.33 metres. Under the higher forecast scenario, the reservoir may reach 136.5 metres by Friday. The highest level the reservoir has hit is 136.29 metres in January 2010.

BC Hydro remains closely engaged with the City of Courtenay, Comox Valley Regional District, Comox Valley Emergency Program and Emergency Management BC. The potential for downstream isolated flooding remains in place through Tuesday.

We will provide an update tomorrow afternoon."

Previously:

November 6,2016

BC Hydro update #5: Puntledge River system

"A bit of good news for a change though it continues to be very wet. The Monday and Tuesday atmospheric river storm is shifting a bit to the north of us. More on that in a moment.

The other good news was the storm last Friday-Saturday was not too bad. About 60 mm fell in the upper watershed. The reservoir level was able to hold steady during the storm and since then, the spillway gates have been fully open as we try to the lower the reservoir level a bit in advance of the storm to hit tonight.

The Comox Lake reservoir hit a high of 135.6 metres on Friday. It is currently at 135.25 metres or just slightly below the overflow spillway level of 135.33 metres. It will lower a bit more in the coming hours. That's a bit better than we forecasted and gives us some downstream flood risk management flexibility.

The storm forecast for Sunday night through Tuesday may drop about 100 mm to 150 mm in the upper watershed. While still significant, it appears to be not as bad as it could have been. Of course things can shift when the storm arrives.

Given we had 537 mm in October, 327 mm so far in November, and when this storm is finished, we could be hitting 1,000 mm of rain in just over five weeks. Remarkable. The BC Hydro team has done our best to manage through this and will continue to try to adjust our operations for downstream flood risk while also trying to control the reservoir level.

Looking ahead we will be able to reduce discharge from Comox dam for the high tides. With the updated weather forecast and water inflows, the reservoir may not exceed the height hit on Friday, of 135.6 metres.

BC Hydro has been involved in daily preparedness calls with Emergency Management BC, with key Comox Valley emergency response representatives. That close coordination continues.

While things look a bit better, the storm conditions are still significant and can change so we remain focused 24/7 on the possibility of downstream isolated flooding on Monday, and when the storm peaks on Tuesday.

For public safety please continue to stay away from Puntledge River."

 

November 4, 2016

BC Hydro update #4: Puntledge River operations and forecasted storms

"A brief update on the status of the forecast and our operations.

The forecast hasn’t really changed with the next storm hitting tonight and all day Saturday. Rainfall amounts may be upwards of 100 mm. The next storm, the larger storm, will begin Sunday night and last into Tuesday. It may bring 150 mm or so. Forecasts can shift and create less or more rain. Freezing levels will be high.

Over a 48 hour period from November 1 to 3, we had 260 mm or 26 cm fall in the upper watershed. The reservoir has come up two metres from this last storm. 

The water release downstream of Comox dam is about 245 m3/s. Yesterday, the daily average water inflows into the Comox Lake reservoir was 433 m3/s. The hourly peak flow was about 570 m3/s. The water storage behind the dam continues to absorb quite a bit of the water inflows.

The Comox Lake reservoir is now at 135.6 metres, about 30 cm above the overflow spillway. We are fast losing ability to hold back water at key times, such as the high tide. We will continue to do so but will only be able to pull back slightly as we need to move water out the reservoir. The level we do not want to hit is 136.5 metres, because at that level, the spillway gates will likely be placed in the upright position and will not be come down until the reservoir goes below 136.5 metres. This is a level we have never hit before. BC Hydro will continue to pass as much water as possible through the days ahead so we do not lose all downstream flood risk management capabilities should the reservoir hit 136.5 metres. 

We plan to reduce the discharge slightly from the Comox dam for the Saturday morning high tide.

We continue to have close coordination and awareness with the Comox Valley Emergency Program, City of Courtenay and other Comox Valley emergency response leaders.

Please continue to stay away from the Puntledge River and the very high water flows."

 

November 3, 2016

BC Hydro update #3: Puntledge River operations and forecasted storms

"The very wet weather continues. From Tuesday noon to Wednesday at 6 pm, over a 30 hour period, 160 mm or 16 cm of rain fell in the upper Puntledge River watershed. That was a major rain event. And there’s forecast to be big storms ahead into early next week.

In response, all inflows into the reservoir and streams downstream came up in a big way.

The Browns River hit somewhere near 160 m3/s and the Tsolum River hit about 285 m3/s. The Tsolum River was pushing peak record flow rates. For the Comox Lake reservoir, the peak hourly water inflow was around 600 m3/s.

Downstream, yesterday, we reduced discharges from the Comox dam down to 45 m3/s for the two high tides. Outside of those tides, our water release was about 170 m3/s. Much more water was coming into the reservoir than what was being released downstream. In response, the reservoir level came up 1.7 metres in about 36 hours. The reservoir is now at 135.25 metres and rising. The water release downstream is 224 m3/s – the spillway gates are wide open. We are just in the process to lower the flow to 190 m3/s and down to 150 m3/s for the evening high tide.

The reservoir level begins to free-spill over the dam at 135.33 metres, and so will be free-spilling shortly. BC Hydro’s flexibility in holding back water at key times to limit downstream flooding is diminishing as the reservoir moves higher. We begin to see some minor shoreline impacts along the reservoir and cabins at about the 135.7 metre level. Should the reservoir hit 136.5 metres, we will not be able to hold back any water and the gates would be placed in the fully upright position until the reservoir level gets below that level. This is a place we do not want to get to.

We will be moving as much water as possible as we are very concerned about two large forecasted storms coming Friday and Saturday and then Monday to Wednesday. The storm for early next week would be the largest and most worrisome should we no room to hold back water. Of course forecasts can change.

We continue to have closed coordination and awareness with Comox Valley emergency response leaders. We are very concerned about the forecast and the positioning of a now full reservoir. The lower river through the City of Courtenay will remain very high and likely have some isolated flooding through today and potentially into next week.

Please stay away from the Puntledge River and the very high stream flows through next week.

We may provide an update tomorrow."

 

November 1, 2016

BC Hydro update #2: Puntledge River operations and forecasted storms

"The wet weather continues.

 Just how wet was October? We set a new precipitation record in the upper Puntledge River watershed for the month of October. Our precipitation records go back 36 years. The new record is 537 mm or almost 54 cm, breaking the previous record of 506 mm.

As well, it was the second highest total water inflows for the month of October into Comox Lake reservoir. That record goes back 49 years.

So far we have been able to manage through this very wet period quite well with the reservoir level not getting too high, but also holding back water at key times for downstream flood risk management. The reservoir is slowly moving upward after each storm though we try to move it down again between storms. Since yesterday, we have been able to pull down the reservoir level by nearly 50 cm and it continues to drop with our Comox dam spillway gates wide open. This will be harder to do this week based on what’s forecasted, with the reservoir storage filling up; this may be a concern for full flood risk management capabilities for a potential storm at the end of week.

The month of November is off to a very wet start. Storm activity begins this evening and will be peaking on Wednesday. Precipitation totals on Wednesday are forecasted to be around 80 mm. This will be the most significant storm this week.

Precipitation rates on Thursday to Saturday may be 30 to 40 mm per day. It may be hard to lower the reservoir over this period with the constant water inflows. There is the potential for another large storm hitting the area on Monday and Tuesday.

The way the storms tracked in October and are forecasted to track this week, the mid-Vancouver Island and Comox Valley area has had more than its share of rain. A bit of a bulls-eye seems to be painted on the area.    

BC Hydro will continue to release maximum water levels from Comox dam downstream for likely the next two weeks. We will once again back off on the discharges for the high tides. Discharge rates from the dam may go as high as 200 m3/s this week as the reservoir water level increases from the storms.

The Comox Lake reservoir is currently at 133.65 metres.

Please stay away from the Puntledge River through this week and next week. River flow rates may reach the highest level so far for this fall storm season, and will be very dangerous.

Through this week, there may be the potential for isolated downstream flooding on Wednesday during the high tide, which is at 4.7 metres at 8:42 am. It will depend on when and how high the Browns and Tsolum rivers peak. Winds look to be out of the southeast and may cause some storm surge. There is a low downstream flood risk from Thursday to Sunday. Monday and Tuesday next week would be the next focus."

Previously: October 27, 2016

BC Hydro update #1: Puntledge River operations and forecasted storms

"An update on the storm activity.

The Tuesday storm dropped a very high 95 mm of rain in the upper Puntledge River watershed. That provided a peak water run-off hourly flow into the Comox Lake reservoir of about 300 m/s. The releases below the Comox dam have been mostly about 170 m3/s, but we have reduced it to about 75 m3/s in consideration of high ocean tides. As the reservoir rises the amount of water released downstream also increases, with about 170 m3/s being the current maximum spill rate possible.

Total rainfall since Tuesday is about 150 mm. 

With that peak hourly water run-off into the reservoir on Tuesday, that's the equivalent of an Olympic-sized swimming pool entering the reservoir about every 8 seconds. It's the most inflows we've seen from the storms this fall.

BC Hydro's dam was able to hold back most of that water. However, the reservoir level has increased by about a metre and is now at 134.3 metres. The level is now about a metre away from free-spilling over the Comox dam spillway.

Downstream, for flood risk management considerations, the Tsolum and Browns reacted to the storms but did not reach flow rates hit from the previous storms. They also peaked away from the high tides.

Through Saturday, we will continue to release maximum water volumes from Comox dam. We will also reduce discharges around the one higher ocean tide each day, like we are doing now, to minimize downstream total river flow rates. There is currently no downstream flood risk.

On Saturday evening the flows from the Comox dam will come down to about 35 m3/s or the typical river flow rate. This is to provide the right flow rates, particularly at Stotan Falls, for successful salmon migration up the river system. It will also provide safer river conditions for chum salmon fishers. Basically recreational fishers will have a one day opportunity to fish the lower river.

Beginning early Monday morning, Puntledge River flows will again be increased to maximum discharge rates to lower and control the reservoir in preparation for next week's forecasted storms. It has been a very wet October.

Please stay away from the Puntledge River through Saturday, and then Monday through likely next week. River flow currents will be dangerous and will vary over the day."

Previously: October 24, 2016

BC Hydro update: Puntledge River operations and forecasted storms

"Another round of storms are coming with the main one being Tuesday with rainfall amounts forecasted to be around 70 mm for the Cruikshank River side of the upper Puntledge River watershed. Tonight through Thursday, precipitation totals may be around 140 mm. The freezing level will be high with this storm. The forecast looks drier past Thursday.

The reservoir was very well positioned to absorb most of the water inflows from the three storms that hit the week of October 10. The reservoir is up slightly and now sits at 133.8 metres. It has been brought down a bit and is well positioned for these storms. We will need to spill high volumes of water beginning this evening through Thursday as we initiate flood risk management operations. Discharge from Comox dam will increase to about 110 cubic metres per second (m3/s) – a three-fold increase. The spill volumes will likely fluctuate as we reduce flows to as low as 35 m3/s for the Tuesday high tide and then increase flows for the low tides. As the reservoir water level increases the spill from the dam may go as high as 150 m3/s.

The only potential sensitivity for localised downstream flooding would be the 4.8 metre high tide on Tuesday at 3:19 pm. There is the potential for ocean storm surge up the estuary from the strong southeast winds.

For public safety, please stay away from the Puntledge River system through Thursday with the high and changing river flows.

BC Hydro may provide an update later this week if needed."