BC Hydro Water Alerts

BC Hydro update No. 3: Puntledge River operations and forecasted storms

November 3, 2016

From BC Hydro:

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.

Previously:

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.