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Assessing Seismic (Cascadia Subduction Zone) Risk at Oregon Dams Keith Mills, P.E., G.E. Dam Safety Engineer Oregon Water Resources Department.

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Presentation on theme: "Assessing Seismic (Cascadia Subduction Zone) Risk at Oregon Dams Keith Mills, P.E., G.E. Dam Safety Engineer Oregon Water Resources Department."— Presentation transcript:

1 Assessing Seismic (Cascadia Subduction Zone) Risk at Oregon Dams Keith Mills, P.E., G.E. Dam Safety Engineer Oregon Water Resources Department

2 Oregon Statutory Dams 10 feet or higher 10 feet or higher Over 9.2 acre feet of water Over 9.2 acre feet of water Design review/approval Design review/approval Inspection frequency by hazard classification Inspection frequency by hazard classification High – annual inspection High – annual inspection Plus Emergency Action Plans (EAPs) Plus Emergency Action Plans (EAPs) Significant – Once every 2-3 years Significant – Once every 2-3 years Low – Once every 5-6 years Low – Once every 5-6 years Federal Agencies responsible for their dams Federal Agencies responsible for their dams Dam information in database on the web Dam information in database on the web High Hazard 61/130 Significant Hazard 152/175 Low Hazard 733/

3 OWRD Seismic Hazards Assessment 36 high hazard dams closest to Cascadia S.Z. Dams west of longitude degrees Dams west of longitude degrees 3 State regulated dams - current and satisfactory seismic analysis 3 State regulated dams - current and satisfactory seismic analysis 1 State regulated dam with analysis showing failure at 0.15 g 1 State regulated dam with analysis showing failure at 0.15 g 3 State regulated dams with indicators of liquefaction potential 3 State regulated dams with indicators of liquefaction potential 1 USBR dam - unsatisfactory seismic analysis (deformation) 1 USBR dam - unsatisfactory seismic analysis (deformation) Remaining dams unknown (to OWRD) but with no major apparent indicators of liquefiable or highly compressible foundations or with hydraulically placed embankment materials. Remaining dams unknown (to OWRD) but with no major apparent indicators of liquefiable or highly compressible foundations or with hydraulically placed embankment materials.

4 Priorities for Seismic Analysis Need for seismic stability modifications Big Creek Upper and Lower dams (Newport) Big Creek Upper and Lower dams (Newport) In progress (HDR/Cornforth) In progress (HDR/Cornforth) Bear Creek dam (Astoria) Bear Creek dam (Astoria) Re-investigation (City - OWRD scoping now) Re-investigation (City - OWRD scoping now) Lower Pony Creek dam (Coos Bay – North Bend) Lower Pony Creek dam (Coos Bay – North Bend) Proposed in dam owners next budget Proposed in dam owners next budget Northwest State Regulated High Hazard dams

5 Big Creek Dams 65 feet of sandy silt below lower dam 65 feet of sandy silt below lower dam Water treatment plant at base of dams Water treatment plant at base of dams Half of SPT’s for lower dam: N = 0 Half of SPT’s for lower dam: N = 0 N = 0 not that uncommon around coastal estuaries N = 0 not that uncommon around coastal estuaries HDR lead consultant HDR lead consultant Subsurface investigation complete Subsurface investigation complete Soil testing and analysis in progress Soil testing and analysis in progress Cornforth – seismic site characterization (just completed) Cornforth – seismic site characterization (just completed)

6 Big Creek Lower ML (sandy) with half blow counts N=0

7 Bear Creek Dam Concrete dam on fractured rock Concrete dam on fractured rock Dam above Knappa-Svensen – east of Astoria Dam above Knappa-Svensen – east of Astoria Harza analysis (soil mechanics) – failure at 0.15 g Harza analysis (soil mechanics) – failure at 0.15 g Emergency Action Plan (EAP) has Level 3 Special emergency condition Emergency Action Plan (EAP) has Level 3 Special emergency condition Self evacuate like those in Tsunami zone Self evacuate like those in Tsunami zone OWRD D.S. in discussions with City of Astoria OWRD D.S. in discussions with City of Astoria Field investigation with instrumentation – uplift pressure, rock strength, concrete strength (cracks) Field investigation with instrumentation – uplift pressure, rock strength, concrete strength (cracks)

8 Left abutment – fractured rock and leakage Foundation – fractured rock, unknown uplift pressure Concrete Gravity dam built 1912 and raised in 1953

9 Pony Creek Dam Embankment dam Embankment dam Designed in 1987 Designed in 1987 No seismic analysis apparent No seismic analysis apparent Above coastal slough Above coastal slough Foundation materials uncertain Foundation materials uncertain Seismic analysis recommended and under consideration Seismic analysis recommended and under consideration Water treatment plant at base of dam Water treatment plant at base of dam

10 Dams to current seismic standard 2 rock-fill dams Rock Foundation and abutments Very little seepage Designed to current seismic standards 1 earth-fill dam on rock - Upper Pony Creek Dam – Cascadia and crustal design Hillsboro (Barney reservoir) Dam McGuire Dam McMinnville W&L

11 Preparing for Cascadia Tsunami (rapid, no direct effects on high hazard dams) Tsunami (rapid, no direct effects on high hazard dams) Large (extremely) landslides with landslide dams (LiDAR) Large (extremely) landslides with landslide dams (LiDAR) Extreme liquefaction coastal valleys Extreme liquefaction coastal valleys Bridge failures (Bruce - ODOT) Bridge failures (Bruce - ODOT) Oregon Seismic Lifelines Identification Technical Documentation (CH2MHill for ODOT) - SECTION 3 Evaluation of Roadway Damage Risk Due To Dam Seismic Damage Likely very limited coastal access by road Likely very limited coastal access by road Inspections by helicopter (they will be in high demand) Inspections by helicopter (they will be in high demand) Engineered Dams unlikely to be highest priority emergency Engineered Dams unlikely to be highest priority emergency Mapping tool with earthquakes (1 orange dot)

12 Emergency Action Plans Oregon Template – will present at ASDSO annual meeting) Oregon Template – will present at ASDSO annual meeting) Notification short and up front Notification short and up front Emergency detection and evaluation Emergency detection and evaluation Level 3 Special – Severe shaking evacuation – no notification Level 3 Special – Severe shaking evacuation – no notification Probable modes of failure Probable modes of failure Liquefaction, crest displacement, slope instability, concrete failure, rock abutment displacement Liquefaction, crest displacement, slope instability, concrete failure, rock abutment displacement Inundation (dambreak flood) maps Inundation (dambreak flood) maps Sunny day for CSZ quake Sunny day for CSZ quake Responsibilities - emergency manager – know maps and what to do – will they have resources? Responsibilities - emergency manager – know maps and what to do – will they have resources?

13 Low hazard dam failed in 2011, in eastern Oregon near Baker City Rapid Dam Breach

14 Coordination with emergency managers Evacuation responsibilities and resources Evacuation responsibilities and resources Inspection of infrastructure Inspection of infrastructure May take a long time May take a long time EAPs for dams close to CSZ EAPs for dams close to CSZ Emergency Level 3 Special Emergency Level 3 Special Oregon Emergency Response Council Oregon Emergency Response Council Dam Safety Engineer is currently OWRD representative Dam Safety Engineer is currently OWRD representative OWRD engineers input into Oregon Cascadia Plan OWRD engineers input into Oregon Cascadia Plan Also have roles in flood and drought Also have roles in flood and drought

15 Seismic Analysis Issues Possible conservatism in FLAC and Newmark analyses (Scoggins Consultant Review Board) Possible conservatism in FLAC and Newmark analyses (Scoggins Consultant Review Board) Actual behavior of dams in Subduction Event Actual behavior of dams in Subduction Event Waiting to learn from dam performance during Tohoku great earthquake Waiting to learn from dam performance during Tohoku great earthquake ML behavior in subduction zone earthquake ML behavior in subduction zone earthquake Seismic analysis of fractured rock abutments Seismic analysis of fractured rock abutments

16 Summary Aware (too much) of CSZ and what it can do Aware (too much) of CSZ and what it can do Using available resources on high priority dams Using available resources on high priority dams EAP grants EAP grants HEC-RAS/HMS inundation analysis for hazard classification HEC-RAS/HMS inundation analysis for hazard classification Seismic analysis coastal dams Seismic analysis coastal dams Very conservative seismic analyses are unhelpful for evaluating risk at existing dams Very conservative seismic analyses are unhelpful for evaluating risk at existing dams Ground access to dams closest to Cascadia will at best be difficult after a major S.Z. earthquake Ground access to dams closest to Cascadia will at best be difficult after a major S.Z. earthquake Repair of damaged dams will be prolonged Repair of damaged dams will be prolonged


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