Central Coast Flood Events Bella Coola Valley during 2010 & 2011 Ted Fuller Ministry of Energy & Mines Thompson Rivers University OL

Presentation Highlights Introduction Geography – Coast Mountains, storms from Pacific Meteorology – the precipitation events Hydrology – river response in September 2010 & 2011 Flooding – realm of 100-year to 200-year return period Impacts Acknowledgements Conclusions

Background Bella Coola Valley Public Safety Technical Expertise – Coast Mountains, isolated community, small population, very active channel migration Public Safety – Emergency Management BC Technical Expertise – Ministry of Forests, Lands & Resource Operations – Ministry of Transportation & Infrastructure

Problem Repeated high rainfall events in the last decade Recent forest fires (2009) with hydrophobic soils (Nuxalk Fire 368 ha, Heckman Fire 3086 ha) Recent deglaciation exposing new sediment sources Existing flood protection based on 1968 flood Multiple dike failures, flooding highway and airport Emergency management

Information base and synthesis Prediction, Planning and Protection River Forecast Centre issues High Streamflow Advisories, Flood Watches and Flood Warnings based on Environment Canada weather BC Government Ministries monitor the weather, river levels, stream gauge networks Local Emergency Management

BC Index Map – 1000 km from Victoria Bella Coola

Bella Coola & Atnarko glaciers (hillshade)

Location Map – Major Watersheds

5149 square kilometres Geography

Recent forest fires 2009

The 2010 event In September 2010 - 330 mm of rainfall over four days Landslides and severe flooding One highway bridge destroyed and 8 bridge approaches destroyed and 7 forestry bridges destroyed Dike breach at Bella Coola Airport Four highway 2o sections destroyed and seven sections flooded Highest recorded flow for Bella Coola River & Atnarko River in 45 years (since 1968) Possibly 200-year event

CBC news British Columbia

GOES-15 image

5-Day Precipitation 2011 event STATION PRECIPITATION (mm) MoT BELLA COOLA 317.5 MoT HECKMAN PASS 130.3 MoF HAGENSBORG 204.2 MoF TALCHAKO 230.2

September 2010

Measuring high water mark Photo: FLNRO

Highway 20 washout Photo: FLNRO

Bella Coola townsite

Bridge approach washout Photo: Ministry of Forests, Lands & Natural Resource

Bella Coola airport flooded Photo: Fawn Blake

The 2011 event In September 2011 - 229 mm of rainfall over four days – peak at September 23. Landslides and severe flooding Highway 20 impacted Dike breach at Renewed erosion of 2010 event sites The 2011 event was measured at lower peak levels possibly 150-year flood than the 2010 event.

Historic Discharge, Bella Coola River JAN1968 NOV2004

Historic Discharge, Salloomt River NOV2004

Stage Discharge Curve, Bella Coola River Source: River Forecast Centre, Victoria

Water Survey of Canada – 2010 in RED, max in GREEN

Water Survey of Canada – 2010 in RED, Stn destroyed

2011 spot readings in RED, Stn destroyed

Emergency Repairs Highway 20 bridges and roadworks Repairs to failed diking Relocation of Water Survey of Canada stream gauge

Value of Bedload Removal Restores channel capacity Improves dike safety Dike width increased (spoiled on landward side) Measurement of before & after gives bedload inflow rate for future work Population feels more secure

Conclusions Treat alluvial fans like floodplains Carry water & sediment & debris Restrict development where high bedload is expected Build setback dikes NOT river bank dikes Bedload removal is sometimes necessary Confer with Fisheries, other Ministries, locals Remember 3 things about dikes Dikes fail, Dikes fail, Dikes fail

Acknowledgements Ministry of Justice – Emergency Management BC Ministry of Forests, Lands & Natural Resource Operations (Jeptha Ball, David Campbell) Central Coast Regional District (Steve Waugh) Ministry of Transportation & Infrastructure