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

2. 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

3. 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

4. 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

5. 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

6. BC Index Map – 1000 km from Victoria
Bella Coola

8. Bella Coola & Atnarko glaciers (hillshade)

9. Location Map – Major Watersheds

10. 5149 square kilometres
Geography

11. Recent forest fires 2009

12. 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

13. CBC news British Columbia

14. GOES-15 image

15. 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

16. September 2010

17. Measuring high water mark
Photo: FLNRO

18. Highway 20 washout
Photo: FLNRO

19. Bella Coola townsite

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

21. Bella Coola airport flooded
Photo: Fawn Blake

22. The 2011 event
In September 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.

24. Historic Discharge, Bella Coola River
JAN1968
NOV2004

25. Historic Discharge, Salloomt River
NOV2004

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

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

28. Water Survey of Canada – 2010 in RED, Stn destroyed

29. 2011 spot readings in RED, Stn destroyed

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

31. 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

32. 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

33. 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