Subject: High Streamflow Advisory – South Coast and Vancouver Island (MAINTAINED) – UPDATED: 11:00 AM December 20, 2018
High Streamflow Advisory – South Coast and Vancouver Island (Maintained)
UPDATED: 11:00 AM December 20, 2018
The River Forecast Centre is maintaining a High Streamflow Advisory for the South Coast and Vancouver Island including:
- Metro Vancouver – including the Serpentine and Nicomekl Rivers and local streams
- Howe Sound – including the Stawamus River and tributaries along the Sea-to-Sky Highway
- Sunshine Coast – including watersheds around Gibsons and Sechelt
- North Shore – including the Seymour River and watersheds around North Vancouver and West Vancouver
- Fraser Valley (North) – including mountainous tributaries from Coquitlam to Harrison
- West Vancouver Island – including tributaries around Gold River, Zeballos, Tofino and surrounding areas
- Central Vancouver Island – including the Sproat and Somass Rivers and areas surrounding Port Alberni
- East Vancouver Island – including tributaries around Campbell River, Courtenay, Parksville, Nanaimo and surrounding areas
- Southern Vancouver Island – including the Cowichan River, Chemainus River and surrounding tributaries
A series of powerful Pacific storms has impacted British Columbia for the past week, with many weather stations recording 200-350 mm of precipitation over that period. Freezing levels have ranged between 1000 to 1500 m resulting in significant snow accumulation over higher terrain. Rivers and creeks on Vancouver Island and the South Coast have been high, but have not resulted in flood levels.
The final storm of this series is currently passing over south-west BC, bringing strong winds and moderate rainfall. Rainfall totals overnight and this morning have been in the 30-100 mm range on Vancouver Island, and 15-40 mm range in the Howe Sound and Metro Vancouver area. Rainfall rates have been easing on Vancouver Island, and are expected to ease on the South Coast later on Thursday.
River levels are expected to rise on Thursday in response to this rainfall. Cumulative rainfall amounts over the past week have made lake-fed river systems the most vulnerable to high flows. On the Sproat River and Somass River near Port Alberni, river levels later on Thursday and into Friday are expected to reach similar or slightly above levels observed this past Tuesday (eg. estimated flows up to approximately 700 m3/s, or a 2-year flow, on the Somass River). Similarly the Cowichan River near Duncan (Water Survey of Canada gauge 08HA011) are expected to rise on Thursday and into Friday up to 300-350 m3/s (between a 2-year and 5-year flow).
Drier weather on Friday will allow for general improvement in river conditions across the region into the weekend.
The River Forecast Centre will continue to monitor conditions and update this advisory as conditions warrant.
A High Streamflow Advisory means that river levels are rising or expected to rise rapidly, but that no major flooding is expected. Minor flooding in low-lying areas is possible.
A Flood Watch means that river levels are rising and will approach or may exceed bankfull. Flooding of areas adjacent to affected rivers may occur.
A Flood Warning means that river levels have exceeded bankfull or will exceed bankfull imminently, and that flooding of areas adjacent to the rivers affected will result.