Modeling Water Supply Reliability following a major earthquake...• GIRAFFE •Project Development...

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

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

Image Source: www.flickr.com


May 10, 2013

AWSS System Map


May 10, 2013

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


May 10, 2013

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.


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


May 10, 2013

Estimating Fire Demands

Fire Demand Formulation

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


May 10, 2013

Delineation of Fire Response Areas

1

• Based on SFFD

Response Districts

• Further refined

based on fire

density


May 10, 2013

Ignition Location Selection

2

• Red – Block with

Highest Occurrence

of Ignitions

• Blue – Top 5

Demands per FRA


May 10, 2013

Fireflow Magnitudes

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


May 10, 2013

Model Demand Locations

4

• Demand node

highlighted in blue

• Location based on

nearest network node

to locations found in

step 2


May 10, 2013

Estimating System Reliability

Hydraulic Model (SynerGEE)

AWSS Existing Condition Model

• 6,274 junctions

• 6,312 pipe segments

• 178 valves

• 10 pumps

• 5 tanks

• Model reviewed and

calibrated with flow

test data


May 10, 2013

SynerGEE Model Results

Page 19 Modeling Water System Reliability

May 10, 2013

EPANET Model (Converted from SynerGEE)


May 10, 2013

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]


May 10, 2013

GIRAFFE GUI (Windows XP)


May 10, 2013

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)


May 10, 2013

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


May 10, 2013

GIRAFFE Model Controls

– Simulation type:

• Deterministic (single)

• Monte Carlo Fixed

• Monte Carlo Unfixed

– Convergence Criteria

– Break/Leak Ratio

– Leak type probabilities

– Random seed generator


May 10, 2013

GIRAFFE Output

– Pipe break/leak list

– System damage file

– Serviceability result

– Information by time-step

for:

• Nodes

• Pipes

• Pump stations

• Valves

• Tanks

– Output summary


May 10, 2013

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


May 10, 2013

Sensitivity Analyses Performed

– Demand location and magnitudes

– Fireboat assumption

– Partial demands

– Infirm zones


May 10, 2013

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


May 10, 2013

Cisterns


May 10, 2013

Suction Connections

Page 36

- Green: existing

suction

connection

- Red: proposed

suction

connection

(Alternative C

only)


May 10, 2013

Alternate Water Sources

Page 37

Palace of Fine Arts Pond

Laguna Honda

Lake Merced

Suction Line


May 10, 2013

Reliability Scoring

Model Results Terminology

- Reliability:

• Available supply / demand requested

- Citywide reliability:

• Average of each Fire Response Area’s reliability


May 10, 2013

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


May 10, 2013

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


May 10, 2013

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


May 10, 2013

Program Alternative Scoring


May 10, 2013

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


May 10, 2013

Thank You

[email protected]

[email protected]

[email protected]

Modeling Water System

Reliability May 10, 2013

Modeling Water Supply Reliability following a major earthquake...• GIRAFFE •Project Development...

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