BC Hydro crew members scrape the debris off the John Hart Dam trash racks last week.

Hydro bracing for subtropical rainstorm

BC Hydro forecasts show a potential for between 120 and 300 mm of rain over four days

BC Hydro’s forecasters are following a series of subtropical storms that will be hitting the West Coast of North America beginning Wednesday night.

Unlike a relatively narrow band of precipitation directed at the coast from the southwest with high precipitation levels, known as an atmospheric river, these systems look to have a very wide band of heavy rain that will hit the United States and Canada from the south.

For central Vancouver Island, BC Hydro forecasts show a potential for between 120 and 300 mm of rain over four days starting Thursday. Temperatures will be warm and freezing levels high, and what limited snow pack we do have will melt further and add to the water inflows into the Campbell River system and other river systems.

There is the potential that these storms could create very high river flows over those four days and beyond.

“In my 15 years of involvement on BC Hydro operations on the Campbell River system it’s hard to recall large subtropical storm systems hitting the area in February,” BC Hydro spokesperson Stephen Watson said. “The last such storm was in 2003. Typically they are in the November to January timeframe.”

The winds look to be moderate and out of the south to southeast. This may cause a bit of storm surge up the Campbell River estuary.

The ocean tides are fairly high, though certainly not King Tides, which will be helpful in limiting downstream flooding impacts, Watson said. The higher high tides are occurring in the morning at 4.2 metres over these four days.

The Upper Campbell Reservoir/Buttle Lake is in the higher range for this time of the year from a storm over a week ago and because the snow pack is low. The reservoir is currently drafting and is now at 219.1 metres. In advance of this storm, beginning this evening, BC Hydro will begin spilling water from John Hart dam down Elk Falls Canyon. The canyon flow rates will be above the base fish habitat flow of 4 m3/s and potentially up to about 110 m3/s based on current forecasts. If water inflows exceed the current forecasts, BC Hydro may increase the spill flow even higher as the storm develops.

BC Hydro is issuing a public safety advisory to stay away from the Campbell River, particularly above Elk Falls, beginning Wednesday night through to about mid-February as BC Hydro prefers to spill a smaller amount of water over a longer period of time in consideration of fish habitat. The river flows will be higher than normal and may also fluctuate as BC Hydro modifies its operations to consider the high ocean tides. BC Hydro will provide an update on Wednesday afternoon as the weather forecast becomes clearer. At this time there is no risk of downstream flooding.