BC Hydro Update: Puntledge River High Flows and Flood Risk Management

January 23, 2015

From BC Hydro:

The forecast now looks drier than yesterday. There are still some uncertainties though this is a good trend. Rain amounts looked to have dropped by about a third and most of the rain will take place in the upper elevations. The west side of Vancouver Island will get the brunt of this storm.

The higher elevation temperatures are just now beginning to set in and will cause some snowmelt. The southeast winds look to be generally unchanged and may cause some storm surge into the estuary.

BC Hydro’s operations will be modified to a lower discharge rate from Comox Dam though the high and dangerous Puntledge River flows may be in place into early next week. The public should stay away from the Puntledge River as flows will be high and fluctuating as we consider the ocean tides.

Weather conditions can be highly variable and while this looks to be good news, and less risk for some isolated downstream flooding, an eye on the river flow conditions during the high tide tomorrow may be wise. 

This may be BC Hydro’s final update on this storm system.

 

Previously:

BC Hydro Update: Puntledge River High Flows and Flood Risk Management

Wednesday, January 21, 2015

BC Hydro’s updated weather forecast and subsequent potential water inflows into the Comox Lake Reservoir has slightly worsened. There is about a 20% increase in the forecasted rain totals. In addition, the rain should be more constant on Friday and Saturday and the water inflows into the reservoir may be high Friday through Sunday.

It is a narrow band of high precipitation, known as an atmospheric river, that is tracking towards the region. A 50 km shift in the storms heading to the north or south can make a significant difference in rain amounts. Even a day before this storm hits, significant uncertainties remain.

BC Hydro will increase discharges from Comox dam beginning at 6:00 pm today and target up to maximum discharges down the Puntledge River. Flow rates from the dam may go above 150 m3/s during low tides and down to only about 35 m3/s during the high tides each morning. With the high river flows and the changes in flow rates depending on the ocean tides, for public safety, BC Hydro advises the public to stay away from the Puntledge River beginning this evening through Wednesday next week.

The freezing levels continue to look to be high and will lead to melting snow.

The winds out of the southeast remain, though they look to be down to about 40 km/h.

BC Hydro remains concerned about the potential for some isolated flooding along the Courtenay River during the King Tides on Saturday and Sunday mornings. It will be dependent on the timing of the peak flows out of the Browns and Tsolum rivers. As a heads up, BC Hydro reached out to key Comox Valley emergency response agencies yesterday and communications continue.

BC Hydro will provide an update on Friday afternoon.

 

BC Hydro Update: High River Flows in Puntledge Due to Approaching Storms

Wednesday, January 21, 2015

BC Hydro is closely monitoring some subtropical weather systems that look to hit the area beginning Thursday evening through Sunday morning. In addition, the Comox Lake Reservoir has increased this past week with the moderate storm activity to date.

Beginning as early as Thursday evening, BC Hydro will increase the water discharge from the Comox Dam to the 100 m3/s to 125 m3/s range. The current rate of discharge is about 32 m3/s. The high river flow rate may be in place through Wednesday. BC Hydro will adjust river flow discharges based on actual inflow conditions and ocean tides. Forecasts can change.

For public safety, BC Hydro advises the public to stay away from the Puntledge River beginning Friday through Wednesday next week.

Precipitation over the three days starting Thursday evening may amount to up to 100 mm.  Friday and Saturday appears to be the heaviest aspect of the storm. In addition, temperatures will be quite warm reaching up to 13 degrees, with the freezing level reaching up to 2500-3000 metres. There may be significant snowmelt from this system.

The ocean tides are very high on Friday through and Sunday at 5.3 metres – about 0.4 of a metre higher than the early December 2014 storms. These tides are known as the King Tides and are the highest of the year. 

Storm ocean surge may also be a consideration as the winds are forecast to come out of the southeast and be up to 60 km/h on Friday.

BC Hydro will reduce the discharge from the Comox Dam to as low as possible during the high tides on Friday and Saturday.

The Comox Lake Reservoir is currently at 134.15 metres and has leveled off. There is over 1.2 metres of available reservoir storage to absorb this storm system.

While these storms look to be significantly weaker than the storms in early December, there will be more snowmelt in this case and that element of water inflow amounts into the river systems are more uncertain. Because of the timing of these highest ocean tides of the year, BC Hydro is a bit concerned about the Friday morning and Saturday morning tides. Should the natural flowing Browns and Tsolum rivers peak at the wrong time, there may be a risk for some isolated downstream flooding.

BC Hydro may provide an operational update later this week. Beyond Sunday, the weather looks to dry out.