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Landslide Risk Management for Berkley-Riverside Escarpment Presentation to the Community

Landslide Risk Management for Berkley-Riverside Escarpment Presentation to the Community January 16, 2006 Michael Porter, M.Eng., P.Eng. Dr. Matthias Jakob, P.Geo. Dr. K. Wayne Savigny, P.Eng., P.Geo. BGC Engineering Inc. What We Know.

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Landslide Risk Management for Berkley-Riverside Escarpment Presentation to the Community

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  1. Landslide Risk Management for Berkley-Riverside Escarpment Presentation to the Community January 16, 2006 Michael Porter, M.Eng., P.Eng. Dr. Matthias Jakob, P.Geo. Dr. K. Wayne Savigny, P.Eng., P.Geo. BGC Engineering Inc.

  2. What We Know • On January 19, 2005 a landslide killed Eliza Kuttner and seriously injured her husband • At least 5 other landslides since 1972 • all triggered by heavy rainfall • Many other locations in the GVRD are subject to landslide hazards • not unique

  3. Hong Kong (1972) Po Shan Road Landslide

  4. Hong Kong Slope Safety Program • Principles of risk management and quantitative risk assessment • Manage 58,000 registered slopes • Dr. Norbert Morgenstern (U of A) on Advisory Panel • Public education program • State-of-the-art monitoring • Hong Kong is now the world-leader in LRM • Australia, California, Seattle, British Columbia • Thousands of lives have been saved!

  5. Berkley Landslide Risk Management Program

  6. Work Completed to Date • Detailed investigations in the vicinity of the January 2005 landslide: • escarpment geology • assessment of landslide cause • assessment of residual risk Fill / Retaining Walls Marine Silt and Sand Colluvium Glacial Till

  7. Work Completed to Date • Along Rest of Escarpment (Current Contract): • inventory of past landslides • evaluation of landslide-triggering storms • rainfall and piezometer monitoring • visual inspection and hand-auger drilling • quantitative risk assessment

  8. Landslide Likelihood Estimates • Subdivided crest into 75 Increments • Rank based on: • thickness of fill • drainage conditions • slope angle • evidence of past movement > 2 times Average ~ Average < ½ Average

  9. Crest of Escarpment Landslide Initiation Zone Seymour River 25o 23o 21o 19o Landslide Deposition Zone Landslide Runout Consequence a function of the angle to the crest of the escarpment

  10. Landslide Runout Moderate to high likelihood of damage to homes Low to moderate likelihood of damage to homes Damage possible; mostly sedimentation and flooding Minor flooding >25o >23o >21o >19o

  11. Landslide Risk Estimates and Evaluation • Potential for fatality at crest and base of escarpment • To be safe, a property must pass two tests: • risk to individuals must be tolerable • societal risks must be tolerable

  12. Tolerable Risks Within a range society can live with Low, but not zero Less than other risks in everyday life Reduced further if practicable Limits defined in collaboration with the affected Community

  13. Individual Risk • Risk faced by a single individual exposed to one or more landslide hazards • Hong Kong: • Existing slopes: 10-4 per year (1:10,000) • New development: 10-5 per year (1:100,000)

  14. What Does 10-4 per year Mean? 10-4 per year = 0.0001 or a 1 in 10,000 chance of fatality per year of exposure Equivalent to average Canadian’s risk from motor vehicle accidents volvocanada.com

  15. Individual Risk Estimates for Berkley-Riverside • Risk > 10-4 per year • 51 properties at base • 1 property at crest • Risk = 10-4 to 10-5 per year • additional 56 properties • Risk < 10-5 per year • rest of escarpment

  16. Societal Risk • Risk imposed upon the community by a single landslide • Hong Kong: • F-N Curves

  17. Societal Risk

  18. Societal Risk Estimates for Berkley-Riverside Assigned to the 75 source areas along escarpment crest • Unacceptable Risk • 22 source areas • ALARP Zone • 37 source areas • Broadly Acceptable • 16 source areas • (Hong Kong Criteria)

  19. Comments on Risk Estimates • They match the historical record • calibrated • They represent a snapshot in time • risk changes over time • They do not account for: • acquisition of 8 properties affected by the January 2005 landslide • improvements to the storm sewer system • increased public awareness of the hazards • rainfall and piezometer monitoring program

  20. Monitoring Program

  21. Work Plan for Risk Reduction • More investigation of top rated sites • Evaluate viable risk control options: • ongoing monitoring and inspection • drainage improvements • removal of unstable retaining walls • removal or recompaction of unstable fills • slope reinforcement (new retaining walls; soil nails) • Quantify benefit and cost of each option • Implement preferred option(s)

  22. Closing Remarks • A risk management program has been initiated • consistent with Canadian standards and international best practices • Baseline risks have been estimated • to prioritise sites for mitigation • to facilitate evaluation of risk control options • Risks are currently managed through monitoring • We have an opportunity to apply best practices, exhibit leadership, and minimise the potential for future tragedy

  23. Thank You

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