Flood Warnings and Advisories
High Streamflow Advisory – Vancouver Island
ISSUED: November 21, 2017 10:15 AM
The River Forecast Centre is issuing the High Streamflow Advisories for:
- Central Vancouver Island including Sproat River, Somass River and tributaries and areas around Port Alberni
- Eastern Vancouver Island including the Englishman River, Tsolum River, Oyster River and tributaries around Campbell River, Comox, Parksville and surrounding areas
- Southern Vancouver Island including the Chemainus River, Cowichan River, Koksilah River and surrounding areas
A storm cycle is expected to impact Vancouver Island over the Tuesday to Thursday period. Heavy rainfall is expected, particularly over the Tuesday to Wednesday period. Rainfall totals are forecasted to be in the 100-150 mm range, with the potential for higher amounts where upslope conditions occur, and lower amounts along the eastern slopes of Vancouver Island. Temperatures are expected to rise sharply through Tuesday, with freezing levels approaching 3000m. Snowmelt is expected to contribute to river runoff during this storm event.
River levels are expected to rise through Tuesday, with peak levels expected on Wednesday or potentially into Thursday. Current modelling is indicating the potential for rivers to reach up to approximately 2-year return period flows, or similar levels that were experienced last weekend. On the Somass River, flows are currently forecasted to reach up to 5-year return period levels, or higher than was experienced this past weekend (e.g. similar levels to the November 2016 event). High tides and a moderate storm surge are expected through the week, particularly on Thursday, and may exacerbate river levels at river outlets.
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.