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