Mitigating Risk to Underwater Crossings to Improve Water Supply … · 2017. 10. 24. · Mitigating...
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Mitigating Risk to Underwater Crossings to Improve Water Supply Reliability: Two Case Studies 10 th CTWWA/JWWA/WRF Water System Seismic Conference Tainan, Taiwan – October 18-21, 2017 Serge Terentieff, P.E., G.E.
Transcript of Mitigating Risk to Underwater Crossings to Improve Water Supply … · 2017. 10. 24. · Mitigating...
Mitigating Risk to Underwater Crossings to Improve Water Supply Reliability:
Two Case Studies
10th CTWWA/JWWA/WRF Water System Seismic ConferenceTainan, Taiwan – October 18-21, 2017
Serge Terentieff, P.E., G.E.
Outline
• Background
• Risk Assessment
• Mitigation Strategy
• Summary
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Case Study #1Raw water supply: Aqueduct Interconnections & River Crossing Repair Concept
Case Study #2Potable water supply: Alameda estuary crossings
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EBMUD Water Supply System
Case Study #1: MokelumneAqueducts in the Delta Region
Case Study #2: Estuary crossings to Alameda
San Joaquin River Crossing
Old & Middle River Crossings
Risk-Based Approach to Assess LOF & COF and Guide Mitigation Strategy
The probability an underwater crossing will fail
The resulting magnitude of consequence if the underwater pipe breaks
LOF COF
Likelihood of FailureLow High
Con
sequ
ence
of F
ailu
reH
igh
L
ow
The probability an underwater crossing will fail
Alameda Estuary Crossings
Case Study #2MOK AQ #3
River CrossingsCase Study #1B
MOK AQ #1 & 2(interconnections)
Case Study #1A
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Case Study 1: Natural Hazards & Risks to Mok AQs in the Delta
• Natural hazards:– Flooding
– Seismic Events
– Subsidence
• Risk to AQs:– Structural failure
of AQ #1 & 2
– Damage from levee failure & flooding
– Damage to AQ #3 at a river crossing
Typical Levee Cross-Section
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CRESTEL +10.0
HIGH TIDEWSEL +6.0
EL -10.0 +/-
LEVEE FILLS
DENSE SAND [Pleistocene deposits]
LOOSE SAND [Halocene deposits]
PEAT / ORGANICS EL -20.0 +/-
EL -40.0 and deeper
Case Study 1A: Risk to MOK AQs #1 & 2: High Likelihood/Consequence
BixlerInterconnection
Stockton Interconnection
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Delta Interconnections to Mitigate Risk to MOK AQs #1/2
To increase Mokelumne Aqueduct conveyance following Delta emergency events
0 MGDMokelumne 2 - 53 MGD
Lafayette 1Mokelumne 1 - 41 MGD
Lafayette 2Mokelumne 3 - 105 MGD
Campo Seco
0 MGD
0 MGD 0 MGD
Walnut Creek
199 MGD
Bixler
41 MGD
105 MGD
Pardee
567 ft
I-5
41 MGD
105 MGD0 MGD 0 MGD
53 MGD53 MGD
42 MGDMokelumne 2 - 42 MGD
Lafayette 1Mokelumne 1 - 33 MGD
Lafayette 2Mokelumne 3 - 87 MGD
Campo Seco
43 MGD
33 MGD 34 MGD
Walnut Creek
162 MGD
Bixler
34 MGD
85 MGD
Pardee
567 ft
I-5
0 MGD
162 MGD75 MGD 77 MGD
43 MGD0 MGD
Existing Gravity Flow Capacity
= 199 MGD
Post-Disaster Gravity Flow Capacity
= 105 MGD
XX
Post-Disaster Gravity Flow Capacity
= 162 MGD
XX
Aqueducts without Delta Interconnections
Aqueducts with Delta Interconnections
Case Study 1B: Risk to MOK AQ#3 @ River Crossings
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Low Likelihood/High Consequence Event:AQ No. 3 River Crossing Repair Concept at San Joaquin River
• Conventional Repair ~ 8+ Months
• Terminal Storage ~ 6 Months
• “Float & Sink” Repair ~ 6 Months
Case Study 2: Natural Hazards & Risks to Estuary Crossings
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Case Study 2: Alameda Estuary Crossings: Overview & Purpose
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Crossing No. 1
Crossing No. 3
Crossing No. 2Proposed Crossings
• Severn underwater pipelines crossings built (1917 – 1987)
• Four crossings remain in-service today
• Three new 24” crossings & open-trench pipelines needed
• Ensure long-term reliability and redundancy
• Meet existing and future demands
• Repair and replace aging infrastructure
In-service Crossings
Selected Project: Crossing No. 1
• Install 1,780 feet of 24-inch HDD pipeline in new alignment
• Install ~5,000 feet of connecting pipeline on each side
• Estimated project cost = $14M
HDD Option: Selected Project
Summary
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• Assess risk, considering LOF and COF
• Adopt a mitigation strategy based on risk/consequence: Case Study #1A: Pre-disaster
mitigation (High LOF & High COF) Case Study #1B: Post-disaster
response (Low LOF & High COF) Case Study #2: Pre-disaster
mitigation (High LOF & High COF)
Thank you for your kind attention
Atlantic Ave
Buena Vista Ave
Lincoln Ave
Alternative Alignments for Crossing No. 1
• Alice-Webster vicinity – 5 alternatives
• Northeast corridor – 4 alternatives
• Connection to Bay Farm Island
– 2 alternatives
Microtunneling Option
Jet Grouting to Reduce Potential for Differential Settlement
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HDD 24-inch (600 mm) Diameter Water Main w/Conductor Casing
PLAN
PROFILE
