Cheekye Fan Current Development Application...Debris Flow Volume 35 100,000 1,000,000 10,000,000 10...
Transcript of Cheekye Fan Current Development Application...Debris Flow Volume 35 100,000 1,000,000 10,000,000 10...
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Cheekye Fan Current Development Application
District of Squamish Presentation at Public Information Meeting
Nov 24, 2014
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Outline
Hazard Policies
Next Steps
Background
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Background
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• Sediment deposits from upper parts of the basin (Mount Garibaldi)
• Recognized debris flow / flood hazard
The Cheekye Fan
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• 2011: Squamish Nation may apply, with or without partner, to the Crown for ownership of ~200 acres of CheekyeFan lands
Intergovernmental Cooperation Accord
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Official Community Plan: Hazard Policies
• Development in hazard zones 3 and 4 requires:
– Debris Flow Mgt. Plan
– Area-wide mitigation measures.
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Development Application
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OCP Land Use Designations Zoning
Development Application:BMS Cheekeye One Partnership
Resource
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Hazard Policies
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Hazard and RiskHazard: Debris flow volume and frequencyRisk: Probability X Consequences
Almost certain
Very Unlikely
Incidental CatastrophicConsequences
Pro
bab
ility
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History
1993
ThurberTerrain Hazard
and Land Use
Study
2008
BGC
Numerous Studies
How big / how often?
Where will it go?
What are the consequences?
2013
Application
2014
Expert Panel
30+ years of Study
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Expert Panel
• How Big?: volume of 5.5M m3
• How frequent?: 1:10,000 yr. return period or 0.01% chance each year
• Climate change likely to increase frequency of small events and to a lesser extent, large events.
• Risks to existing development should be mitigated whether or not there is future development.
• All forms of mitigation should be considered and carefully evaluated.
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Expert Panel Recommendations
Current ApplicationReview
Review OCP Policies and Hazard Zones
Mitigation Strategy
OCP and Rezoning
Hazard Policies
Hazard and Risk
Risk mitigation options
Development Regs
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• Debris flow mitigation works– DoS staff and 3rd party reviewer:
• design standards, risk reduction, environmental impacts, operations and maintenance
– Province: • Dike Maintenance Act (DMA), Water Act, etc.
– DoS Council: • (DMA) Agree to “diking authority” ownership, mtn., operation and rehabilitation.
• Concurrent review of OCP and zoning – Council readings including a Public Hearing
Current Application Review
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OCP/Rezoning Application
Review
District/ Peer Review
Staff Review
Public Meeting
Intro to Council
Council
InputsEnviron-mental Review
Operations and
Maintenance
Design Concept
Mitigation Strategy
Provincial Review
Current Application Review
We Are Here
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Next Steps
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• Continued review
• Begin to update policies
• Council update
• Further public comment
Next Steps
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THANK YOU
http://www.squamish.ca/showcase
Development and Project Showcase – New Development Applications
District of Squamish Development [email protected]
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D R . M A T T H I A S J A K O B , P . G E O . B G C E N G I N E E R I N G I N C .
Cheekeye River Fan and its proposed residential development:
Public Meeting, Squamish November 24, 2014
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Objectives
• Establish a reliable frequency-magnitude relationship of debris flows• Estimate/model the hazard intensity on the fan• Estimate the existing risk for loss of life on the fan• Can portions of the fan be safely occupied? If so, what type and scale of
mitigation is needed?• What can be done to improve current resident’s safety and reduce hazard of
future development to tolerable levels?• In absence of legislated levels of risk tolerance, what levels are deemed
reasonable by the DoS/the province?
21
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Current Elements at Risk
First Nations ReservesDon Ross Secondary School
Brackendale Elementary SchoolBrackendale Residential
Highway 99 UsersCheekeye Bridge
BC RailwaySquamish Airport
DOS InfrastructureBC Hydro Substation
Ross RoadSaw Mill
Squamish Valley RoadCheekeye Development
22
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23
Brakendale
Airport
Elements at Risk
Hwy. 99
Cheekeye
Subdivision
Schools
BC Hydro
Transmission
Line
First Nation
IRs
First Nation
IR
BC Rail Possible Development Area
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24
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The July 2010 rock avalanche and debris
flow at Capricorn Creek, Mount Meager
25
Photos: courtesy Prof. John Clague
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26
Cat Lake
SQUAMISHLower fan
Cheekeye Ridge Linears
Upper fan
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27
Highschool
Primary School
B R A C K E N D A L EApprox. fan boundary
SQUAMISH
Squamish River
You are here
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Not completed
The Steps
Steps completed to date:
Hazard Recognition
Frequency-Magnitude Analysis
Hazard Intensity Mapping
Consequence Determination
Risk Calculations
Risk Evaluation
Risk Reduction
Development
28
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Glacial History
29 S O U R C E : F R I E L E
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Fan Evolution
30
12,000 - 10,200 yrs 10,200 - 6,900 yrs 6,900 yrs
6,000 to 2,000 yrs present
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Dendrochronolgy
• ~60 wedges, cores, discs sampled along channel
• Cross-sections reconstituted along confined reaches
• Discharge back-calculated
31
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Test Trenching Program
32
Objectives:
• Determine size of Garbage Dump debris flow
• Update frequency-magnitude analysis
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Test Trenching Program
33
5 m
FluvialGravels
Southern part of airport Northern part of airport
Garbage Dump event
1 m
FluvialGravels
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34
Garbage Dump Debris Flow ~ 900 years ago
Airport
Hwy. 99
BC HydroSub
Cheakamus R.
2.1 M m3 = 175,000 dump truck loads
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Debris Flow Volume
35
100,000
1,000,000
10,000,000
10 100 1,000 10,000 100,000
Return Period (years)
To
tal D
eb
ris F
low
Vo
lum
e (
m3 )
10,000 yr 2.8 Mm3
2500 yr 2.4 Mm3
500 yr 1.4 Mm3
20 yr = 0.2 Mm3
100 yr = 0.6 Mm3
500,000
200 yr = 0.8 Mm3
5,000,000
50 yr = 0.4 Mm3
2500 yr 2.8 Mm3
10,000 yr 5.5 Mm3
Design return period, debris flows Austria
Design return period, debris flows Switzerland
Former design return Period, geohazards, Canada
National Building Code,Seismic Design, Canada
Upper Design Return Period, Cheekeye
Best Estimate
Worst Estimate
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What does 5.5 Mm3 debris mean?
36
5.5 million cubic metres is roughly twice the volume of BC Place Stadium
Images from www.bcplacestadium.com
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Rock Avalanche Modeling
37
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38
20-year return period event, unmitigated
Brackendale
BC HydroSub
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39
100-year return period event, unmitigated
Brackendale
BC HydroSub
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40
2500-year return period event, unmitigated
Brackendale
BC HydroSub
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41 10,000-year return period event, unmitigated
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42 Preliminary mitigation concepts
~ 35 m high barrier
Sedimentation basin
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Safety Risk
43
• In Safety Risk one differentiates between Individual Risk Safety and Group Risk Safety
• Individual Risk: Unacceptable for current development• Group Risk: Unacceptable for current development• Highway Users: Unacceptable Group Riskgiven risk tolerance standards practiced, for example, by the District of North Vancouver.
Therefore, mitigation required irrespective of new development (expert panel). New development does require higher mitigation standard than existing developments.
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Safety Target Risk Criteria
• New development individual residual risk: 1 in 100,000 (10-5).
• Existing development individual residual risk: 1 in 10,000 (10-4).
• Total group residual risk: “ALARP” zone which means “As Low As Reasonably Practical”
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Barrier Design
• Barrier to retain an “extreme” debris flow event – 5.5 Mm3
• Barrier to have a outlet to pass the Cheekeye River while maintaining the existing channel shape and sediment load downstream
• After an event, the outlet will maintain an outlet for the Cheekeye River and provide practical access for cleanout from the top
• Events that pass through the outlet are to be managed by risk reduction measures that could include earthworks on the banks of the Cheekeye River as well as debris basin upstream of Hwy 99.
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Main Barrier (preliminary design concept)
46
Downstream view
Squamish River
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Main Barrier (preliminary design concept)
47
Upstream view
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Main Barrier (preliminary design concept)
48
Upstream view
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49Vision of Post-Mitigation Design
Brackendale
BC HydroSub
5.5 Mm3 debris
Sedimentation basin
Principal retention basin
I.R. 11
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Site Investigation
• 5 boreholes have been completed at the Barrier site, 1 in the basin.
• Bedrock depth is variable. 5 to >80 m at the barrier
• The rock is overlain by sand, gravel and cobbles from previous debris events
• 15 Test pits have been dug to characterize the near-surface (<5m) soils
• Geophysics is being done to interpolate the characterization between boreholes
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Conclusions
51
• Safety risk is currently unacceptable compared to, for example, DNV standards and mitigation is recommended irrespective of future developments
• Moderate and large sized debris flows, if unmitigated, would also result in significant economic loss
• The expert review panel recommended the structure(s) be designed for a 10,000-year return period event with a volume of 5.5 Mm3
• The topography allows mitigation works to be technically feasible and would protect, amongst other elements at risk, the current and future development and the people of the Squamish Nation.
• Preliminary mitigation concept is to provide one primary barrier structures with auxiliary risk reduction measures and monitoring
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Questions?
52
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1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1 10 100 1000 10000
N (Number of Fatalities)
Fre
qu
en
cy o
f N
or
mo
re f
ata
liti
es (
F)
____
UNACCEPTABLE
ALARP
ACCEPTABLE
Pre-Barrier (All Buildings)
Post-Barrier
(All Buildings)
Post-Barrier
(Future Buildings)
Pre-Barrier (Existing Buildings)
Post-Barrier
(Existing Buildings)
Pre-Barrier (Future Buildings)
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Risk Reduction Benefits
54
• The community of Brackendale (northern portions)• The Cheekeye subdivision within Squamish• I.R. 11• The Cheekeye Substation (BC Hydro). Existing risk is already low due to a natural shelter by a
large bedrock bluff and an existing perimeter berm• Lower transmission towers (BC Hydro)• Squamish Airport• Squamish Garbage Dump• CN Rail. Risk to track washout or bridge loss over Cheekeye River will be significantly reduced.• Brackendale high school and primary school• Users of Government Road and Squamish Valley Road• Users of Highway 99• Resort Municipality of Whistler and Village of Pemberton. Economic losses due to highway
closure caused by bridge loss or highway erosion or sediment deposition will be significantly reduced
• Fortis Gas. Risk of pipeline exposure by erosion will be significantly reduced• Aquatic habitat Cheekeye, Brohm, Cheakamus Rivers. The likelihood of extreme events
destroying fish or spawning habitat will be signficiantly reduced• District of Squamish. Rates of fluvial sediment transport and aggradation in the Squamish River
floodplain near Squamish will be reduced
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Stump Lake Sediment Coring
55
Cheekeye River
Stump Lake
~ 6900 yrs BP
~ 11,600 yrs BP
A
A’
V = 15-30 m/s
Debris flow deposits
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Proposed CheekeyeDevelopmentPUBLIC INFORMATION MEETINGMonday November 24th
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RequestAmendments to the District of Squamish’s official community plan and zoning bylaw to permit a new single family neighbourhood, educational/community uses, parks, greenways and trails.
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Background1970’s-80’s 241 manufactured home strata plan was registered on the property (still exists) and
site servicing completed (existing paved road layout remains) Project halted due to the threat of a debris flow originating from the Cheekeye River Crown retained ownership of the lands
1993 Identified in the Thurber/Golder Cheekye River Terrain Hazard and Land Use Study.
Subsequently incorporated into the Squamish Official Community Plan.
2008 Umbrella Agreement between Squamish Nation and District of Squamish recognizes
further development potential of these lands
2011 Accord between the Squamish Nation and the District of Squamish recognizing
future development potential of the lands
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Development ProposalComplement Brackendale’s existing community by introducing affordable housing options close to existing schools, services while also extending the park and greenway system, trails and constructing the needed hazard debris barrier.
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Single Family LotsSingle Family
Lots
# Approx. Size
(sq. ft)
Approx.
Frontage (ft)
% of
Lots
Small Lots 79 2850 30 11
Medium Lots 591 4500 45 79
Large Lots 78 6000 60 10
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Parks and Open Spaces 57 acres of parkland and greenways
51 acre community park (home of Brackendale Fall Fair)
6 acres of parkways including park improvements
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Community/Educational Uses
Proposed Education Facility (i.e. independent school, continuing education, etc.)
Daycare Facility
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Trails Retain, enhance and expand Ray Peters Trail by a
further 1.3 km
Introduce enhanced “through” and “connecting trails” by 1.6 km
Net gain of trails by 2.2 km
Opportunities to design unique, multi-ability trails for neighbourhood and community
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Debris Barrier
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Timing and Phasing
Subject to development approval process and local real estate conditions
Intent to develop in two phases, south to north due to efficiencies with servicing installation
20 year timeframe for build out (approximately 40 lots per year)
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Geotechnical Engineering (Debris Flow Mitigation)
Environmental Review (wildlife, terrestrial, and riparian)
Site Servicing (conceptual civil design for utilities and roads)
Traffic Study
Technical Studies
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Community Questions and Comments
Public Information Meeting is the initial step in the development approval process