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Modeling Water Supply Reliability following a major earthquake
Anne Symonds, PE AECOM
David Myerson, PE SFPUC
AECOM – AGS, A Joint Venture
PNWS AWWA May 10,
2013
Agenda
• AWSS and Background
• Level Of Service (LOS) Goals
• Modeling
• Ignitions and Demands
• SynerGEE
• GIRAFFE
• Project Development and Assessment
• Program Recommended to SFPUC
• Next Steps
Modeling Water System Reliability
May 10, 2013 Page 2
AWSS and Background
San Francisco
Following the
1906
Earthquake
and Fires
AWSS Overview
• Separate high pressure water system originally
constructed in 1910 -1913
• 77 Miles of 10 inch and larger Cast Iron Pipe
• Two Salt Water Pump Stations
• Three gravity storage facilities fed by domestic system
• Total system consists of high pressure pipe, cisterns,
suction connections, saltwater pumps, fireboats, reservoir
and storage tanks
• Pipe construction with extra thick walls
• Double lead and restrained joints
• Limited connections
Page 4
Image Source: www.flickr.com
Modeling Water System Reliability
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AWSS System Map
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AWSS Operations
• Over time has been extended to cover more of the City,
now 135 miles, 80% cast iron pipe
• Used by the San Francisco Fire Department (SFFD) and
owned and maintained by the SFPUC City Distribution
Division (CDD)
• Normally operates in three pressure zones
• Designed to allow one pressure zone with pressures up to
340 psi
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Modeling Process
AWSS Capital Planning Study (CS-199)
• Goal:
• To maximize the likelihood that the AWSS will effectively provide
required fire fighting capabilities after a major seismic event.
• Recommended LOS Objectives:
• “AWSS will reliably provide water to supply the “probable
fire demands” after a M7.8 San Andreas earthquake”
• Each fire response area will be XX% reliable in supplying probable
demands.
• AWSS will be YY% reliable in supplying probable demands City-
wide.
Page 8
Modeling Water System Reliability
May 10, 2013
Modeling Overview
- Modeling objective:
• To determine the amount of water the AWSS can deliver given a set
of demands
- Hydraulic and reliability modeling to determine project
hydraulic benefits
- Tools used:
• SynerGEE
• GIRAFFE (Cornell University)
• EPANET
• ArcGIS
• R script
Page 9 Modeling Water System Reliability
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Estimating Fire Demands
Fire Demand Formulation
Page 11
Fire Flow Data
by Block
(Scawthorn)
Group Blocks by
Fire Response
Area (FRA)
Delineation of
FRAs
Result: Representative
Fire Demand per FRA.
Input into hydraulic and
reliability modeling at
closest hydrant location
Modeling
Monte
Carlo
Select Likely Ignition
Location for Each
FRA (review most
likely and largest fire
locations)
Calculate Magnitude of
Fire Flows for each FRA
1
2
3
4 5
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Delineation of Fire Response Areas
Page 12
1
• Based on SFFD
Response Districts
• Further refined
based on fire
density
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Ignition Location Selection
Page 13
2
• Red – Block with
Highest Occurrence
of Ignitions
• Blue – Top 5
Demands per FRA
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Fireflow Magnitudes
Page 14
3
• Stochastic set of
ignitions (1000
iterations)
• 60-minute 3rd quintile
selected as
representative
demand set
• “Suppression”
accounted for by
removing all fires at
first minute
1 2 3 4 5
Av
era
ge T
ota
l D
em
an
d
Quintile
Average Total Demand per Quintile
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Model Demand Locations
Page 15
4
• Demand node
highlighted in blue
• Location based on
nearest network node
to locations found in
step 2
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Estimating System Reliability
Hydraulic Model (SynerGEE)
AWSS Existing Condition Model
Page 17
• 6,274 junctions
• 6,312 pipe segments
• 178 valves
• 10 pumps
• 5 tanks
• Model reviewed and
calibrated with flow
test data
Modeling Water System Reliability
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SynerGEE Model Results
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EPANET Model (Converted from SynerGEE)
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Graphical Iterative Response Analysis for Flow Following Earthquakes (GIRAFFE)
GIRAFFE Overview
– Developed at Cornell University by Tom O’Rourke and
colleagues
– Uses open source EPANET engine
– Deterministic and probabilistic simulations
– 5 modules:
• System Definition [Input]
• Seismic Damage [Input]
• Earthquake Demand Simulation [Module]
• Hydraulic Network Analysis [Computation]
• Results Compilation [Output]
Page 23 Modeling Water System Reliability
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GIRAFFE GUI (Windows XP)
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GIRAFFE Model Inputs
– Pipeline Fragilities
• Based on PGV values by block
• PGV estimated from regressions between block centroid distance to
San Andreas fault and grouped by shear wave velocity (Vs30)
– System Information File (EPANET file)
Page 25 Modeling Water System Reliability
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GIRAFFE Process Flow
Page 26
Read System
Input and Repair
Rate Files
Generates
random pipe
breaks and leaks
Solves hydraulic
network
Identifies nodes
with negative
pressures
Removes node
with highest
negative
pressure
Computes
serviceability
Reconfigures
system network
Multiple Iterations
1 2
3
4
5
6 7
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GIRAFFE Model Controls
– Simulation type:
• Deterministic (single)
• Monte Carlo Fixed
• Monte Carlo Unfixed
– Convergence Criteria
– Break/Leak Ratio
– Leak type probabilities
– Random seed generator
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GIRAFFE Output
– Pipe break/leak list
– System damage file
– Serviceability result
– Information by time-step
for:
• Nodes
• Pipes
• Pump stations
• Valves
• Tanks
– Output summary
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Solution to Output Limitation
Page 31
Take damage file
from each
damage scenario
Determine
demand nodes
with negative
pressures
Systematically decrease
demands with negative
pressures until no negative
pressures on demand nodes
are left
Determine
remaining system
negative pressures
Systematically decrease ALL
demands until minimal
negative pressure remain
Determine amount
of water system
can provide
1 2
3 4
5 6
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Sensitivity Analyses Performed
– Demand location and magnitudes
– Fireboat assumption
– Partial demands
– Infirm zones
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Cistern, Suction Connection, Alternate Water Modules
Modeling Summary
Page 34
5
Stochastic Set of Fire Demands
Aggregated Demands by Fire
Response Area
High Pressure System Reliability
(GIRAFFE)
Cisterns, Suction Connections, and
Alternative Water Source Reliability
(Computational Modules)
FRA Reliability Score
Citywide Reliability Score
Modeling Water System Reliability
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Cisterns
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Suction Connections
Page 36
- Green: existing
suction
connection
- Red: proposed
suction
connection
(Alternative C
only)
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Alternate Water Sources
Page 37
Palace of Fine Arts Pond
Laguna Honda
Lake Merced
Suction Line
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Reliability Scoring
Model Results Terminology
- Reliability:
• Available supply / demand requested
- Citywide reliability:
• Average of each Fire Response Area’s reliability
Page 40 Modeling Water System Reliability
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Reliability Score Calculation
– Example FRA
– FRA demand: 5,000 gpm
– Total water available: 4,170
• HPS contribution: 3,850 gpm (average from 15 iterations)
• Cistern contribution: 320 gpm (average over 1000 sets)
• Suction connection contribution: 0 gpm
• Alternative water contribution: 0 gpm
– FRA reliability: 83% (4,170/5,000)
Page 41
Modeling Water System Reliability
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Reliability Score Context
– System tested at 3rd quintile demands with 46
simultaneous ignitions
– Considers initial fire department response but doesn’t
model response or resources required
– HPS evaluated with an aggregated demand for each FRA
while other water sources are evaluated by block
– Reliability index scores are a relative representation of
system performance
Page 42 Modeling Water System Reliability
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Alternative Programs and Assessment
Alternative Program Development
– Developed 3 Program Alternatives each composed of
multiple projects
- Alternatives A & B: new pipe extensions and water supply and some
cisterns
- Alternative C: all cisterns
– Performed Pairwise comparison of the Alternatives
– Recommended Preferred Alternative for further
consideration
Page 44 Modeling Water System Reliability
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Program Alternative Scoring
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Alternative Ranking
1 2 3
Ev
alu
atio
n C
rite
ria
Delivery
Reliability B A C
Firefighting
Capability A/B tie C
Cost B A C
Schedule A/B tie C
Operations and
Maintenance B A C
Insurance
Premiums A/B/C tie
Environmental
/ Community
Impacts
B A C
Final Ranking B A C
Next Steps
Next Steps for AWSS
– Evaluation of other potential combinations of systems to
meet potential fire demands
• Improvements to Potable Water system
• Construction of Multiuse or hybrid pipes
– Evaluation of relative risk of event
– Construction of projects funded by 2010 ESER bond
– Recommendations for future bond election
Page 47 Modeling Water System Reliability
May 10, 2013
Thank You
Modeling Water System
Reliability May 10, 2013