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AEG Annual Meeting-Boston
Mitigation Design of Geohazards Causedby Fire at Hydroelectric Facilities
• W.H. Godwin, CEG William Lettis & Associates• Don Quigley, GE MACTEC Engineering & Consulting, Inc.• C. Liu, PE, SFPUC Engineering & Design Bureau
November 1, 2006
Introduction
• Purpose• Case Study
– Early Fire– Damage Assessment– Aerial and Field Mapping– Mitigation Design– Construction
• Acknowledgements and Questions
Case Study
Kirkwood Powerhouse & Penstock Facilities
Tuolumne County, California
Early Fire
Early Fire OverviewAugust 9-14 2004
1600 acres
Early Fire
Early Fire
• Life & Property– CCSF Life & Property– Public Life & Property
• Soil & Water Quality• Special Areas
-Wild and Scenic River-Heritage Oaks
Early Fire
Cottages andFacilities
Early Fire• Conceptual Treatments for:
-Powerhouse-Residences-Roads-Penstock-Transmission Lines
• Detailed engineering assessment of drainageand structure protection by SFPUC
Early Fire
Damage Assessment
• Erosion potential• Rock fall Hazard• Penstock integrity• Drainage
improvements
Damage Assessment
Damage Assessment
Rock fall hazard
Damage Assessment
October Storm2004
Aerial and Field Mapping
View East
Aerial and Field Mapping
View West
Aerial and Field Mapping
Sawmill MtnGranodiorite(Ksm)
Aerial and Field Mapping
Granite Crk Tonalite (Jgc)
Aerial and Field Mapping
Valve house
Aerial and Field Mapping
Aerial and Field Mapping
Aerial and Field Mapping
Aerial and Field Mapping
Aerial and Field Mapping
Mitigation Design
• Rock Fall Simulation• HEC Modeling• Localized rock bolting, scaling and mesh• Culvert design• Revegetation
Mitigation Design
Input Parameters• Rock Shape• Rock size• Slope roughness• Slope length/angle
Output• Velocity• Bounce Height• Kinetic Energy
Colorado Rock Fall Simulation CRSPProgram
Mitigation DesignGeologic Hazard• Source Area• Source rocks• Slope• Critical Structures• Relative hazard
Mitigation Design
CRSP Inputs
Mitigation Design
Mitigation DesignSurface profile and Analysis Pts.
Bounce height vs. Slope length
Mitigation Design
• Design outputs for 11 fences• Energy ranges from 241kJ to 1575kJ• Bounce height (90%) range 3 ft to 24ft• Did not factor in trees as barriers• Fence Heights of 2 to 4 meters
Mitigation DesignHydrologic Analysis• 25 year return interval, 24-hour hydrologic
analysis for both pre- and post-fire conditions• 100 year return interval, 24-hour duration
hydrologic analysis for both pre- and post-fireconditions
• Calculation of parameters used in the HEC-1model followed the NRCS methodology.
Mitigation Design
Drainage Recommendations• New culvert design based on 25-yr return
period flows• Erosion Control applications• Rip rap and road crossings
Mitigation Design
Construction
December-May 2005• Rock fencing (3131LF)• Draped mesh, spot bolting• New access road and culverts• Hardened Crossings• Penstock drains and safety lines• New potable water tanks
Acknowledgments and Questions
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