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Infiltration and Inflow (I/I) Modeling Using Multiple Hydrograph Components
I/I Project Area
• 34 Local Component Agencies
• Most of Seattle is Combined System
• 75% of Peak Flows in King County System is I/I
• 95% of I/I is from Local Agencies
• 50% From Private Property
I/I Program Objectives
• I/I program is part of The Regional Wastewater Services Plan (RWSP)
• Determine the Amount of I/I Received by King County from Each Local Agency
• Identify Major I/I Areas Within Local Collection Systems
• Identify Specific Types of I/I Occurring Within These Areas
• Forecast the Amount of I/I that can be Removed Cost-Effectively
• Develop a Proactive Regional Strategy for I/I Removal and Control
Why Use Computer Modeling?
• Estimate Peak I/I Using Limited Measured
Data (amplifying the data)
• Distinguish Inflow from Infiltration
• Consider Design Flow Conditions
• Evaluate Multiple Scenarios and System
Options
I/I ReductionCost
RWSP SavingsEstimates
Based on OriginalStudy Assumptions
Revised Findingsper Pilot Project
Results
Based on Experience
Industry StandardsPilot Projects
AssessmentProtocols
Ranked Basins
Targets forRehabilitation
I/IModeling
Isolates Inflowvs. Infiltration
DeterminesSeverity of I/I
Technical Process Overview
Flow & RainfallMonitoring
Overview of Supporting Data
Measured Data for Model Development
• Rainfall
• Evapotranspiration
• Measured Flow Data
• Basin Information– Sewered Area
– Dry Weather Flow Pattern
Rain Data and CALAMAR
• Service area 25 x 45 miles• Rainfall Measurement with
Gauge-adjusted NEXRAD Data
• 5 Minute Data in 1 Km2 Pixels for specific storms
• 8 Calibration Zones• Gauge Data inserted
between storms
Flow Monitoring Effort
• 804 Meters in Simultaneous Operation
• 2 Wet Seasons of Flow Data
• 150 for Initial Model Calibration
• 75 Long Term Meters for Trends Analysis
• 95% of Agency Sewers in a Mini Basin
Model and Mini-Basins
#
"8
"8
"8
"8
"8
"8
"8"8
#S
"8
"8
"8
"8
"8
"8
"8
"8"8
#S
"8
• Model Basins• Calibrated to flows
measured during 2 wet seasons
• 1,000 acres• 100,000 linear feet
• Mini-Basins• 10 weeks of measured
flow• 150 acres• 22,000 linear feet
Model Basin Definition
• 150 Model Basins
• Isolate Flow Contributions
• Evaluate System Performance
MOUSE RDII Model Development and Calibration
Components of Flow
Rainfall Event
Inflow
Ground Water Infiltration
Flow Response
Total Flow
Rainfall Dependent Infiltration Dry Weather
Flow
RDII Components
RAINFALLPOTENTIAL EVAPORATION
MODEL PARAMETERS
RDII COMPONENTSEVAPORATIONRECHARGE
Hydrologic Model Schematic
Lower Zone Storage
Soil Storage
Ground Water Storage
Surface RunoffPr
ecip
itatio
n
Evap
otra
nspSnow
Storage
Infil
trat
ion
Gro
undW
ater
Rec
harg
e
Slow Response
Fast Response(Inflow)
Rainfall Dependant Infiltration
Slow Response
Cap
illar
y Fl
uxR
oot S
uctio
n
Prec
ip
ROOT INTRUSION INTO LATERAL
FOUNDATION DRAIN
SANITARYSEWER CRACKED/BROKEN PIPE
DETERIORATED MANHOLE
STORMSEWER
Rainfall Dependent Infiltration
BROKEN HOUSE LATERAL
Rainfall Derived
Infiltration
ROOF DRAIN CONNECTION
UNCAPPED CLEANOUT STORM DRAIN
CROSS-CONNECTION
FAULTY MANHOLE COVER
SANITARYSEWER
STORMSEWER
Inflow
SUMP PUMP
Inflow
• Plot Model Results
• Plot Measured Flow Data
• Plot Rainfall
• All Flow Components
• Adjust Parameters
Calibration Process
Statistical Comparison
• Scatter Plots• Overall Season Criteria
– Volume– Correlation Coefficient
• Event Criteria– Peak Flow– Volume
• Matching Select Event Peaks– Consistent Calibration Procedure– Pre-defined Objectives
• Calibration Flow Definition– Typical Problems with Measured Flow Data– Net Flow Challenges– Dry Weather Flow
Challenges and Resolutions
Ongoing Modeling Tasks
Apportion Inflow vs Infiltration to the Mini-basins
• Initial attempts based on Data Analysis
• Modified Calibration process
• Based on Model Basin Calibrations
Pilot Projects to Assess I/I Removal Costs
• 9 projects and Adjacent Control Basins• Variety of Construction Techniques • Constructed Summer and Fall 2003 • Pre and Post Monitoring and
Calibration• Establish I/I Removal Costs
Verification of Model Basin Calibration using a Hydraulic
System Model• Set Up KC System Model
• Apportion Model Basin Inflow to the system
• Run Models and Compare with Measured Flows in the System
Flow Frequency Estimates Using Long Term Simulation
• Calibrate Models to Local Rainfall
• Simulate Using Long Term Rainfall
• Get Flow Peaks from Long Term Simulation
• Apply Probability Analysis to the Peaks
• Rank Extracted Peaks
• Plot peaks vs. Log of return period
• Best fit curve of flows 1-yr and greater
• Select return period and flow
Probability AnalysisPeak Extraction
0
2
4
6
8
10
12
9/22/9
8
10/12
/98
11/1/
98
11/21
/98
12/11
/98
12/31
/98
1/20/9
9
2/9/99
Date/Time
Flow
(cfs
)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Rai
nfal
l (in
/hr)
0
5
10
15
20
25
0.1 1 10 100Return Period (years)
Flow
(cfs
)
Best fit curve
Plotted peaks
Estimate Future Flows
• Future Conditions by Decade– Available Population Forecasting– Convert Sewered Population to
Wastewater Flow– Estimate Design Flow for Each Decade
• Revise Model Basins for Each Decade– Long term simulation– Estimate 20-year flow
Modeling Objectives
• Estimate I/I Flows for Design Flow Conditions
• Identify Needed Wastewater System
• Predict System Response to I/I Rehabilitation Scenarios
• Establish Optimum I/I Rehabilitation vs. System Expansion
Current Status and Time Line for I/I Modeling Efforts
• Calibrated System Model by end of 2003
• Mini Basin Apportionment First Quarter 2004
• Facility Impacts First Quarter 2004
• Pilot Results Second Quarter 2004
Major Milestones for the I/I Program
• Alternative Options Report to the County Executive by the end of 2004
• Final Plan by the end of 2005
Lower Zone Storage
Soil Storage
Ground Water Storage
Snow Storage
Prec
ipita
tion
Evap
otra
nsp
Infil
trat
ion
Gro
undW
ater
Rec
harg
e
Fast Response(Inflow)
Surface Runoff
Slow Response
Rainfall Dependant Infiltration
Slow Response
Cap
illar
y Fl
uxR
oot S
uctio
n
Inflow
Prec
ip
Rain Gauge Data / CALAMAR
Building the I/I Plan
Flow Monitoring Data
Model Basin Flow Quantities
Hydrologic RDII Model Calibration
Hydraulic Model Calibration
20-year Design Flow Projections
Pilot Projects
Alternatives/Options
CE Analysis
RegionalI/I
Control Plan
Dry Weather Flow Model
Lower Zone Storage
Soil Storage
Ground Water Storage
Snow Storage
Prec
ipita
tion
Evap
otra
nsp
Infil
trat
ion
Gro
undW
ater
Rec
harg
e
Fast Response(Inflow)
Surface Runoff
Slow Response
Rainfall Dependant Infiltration
Slow Response
Cap
illar
y Fl
uxR
oot S
uctio
n
Slow Response
Rainfall Derived Infiltration
Slow Response
Dry Weather Flow Model
CALAMAR Output
System Background
• 34 Local Agencies• Two Regional
Treatment Plants• 17.5 Million LF of
Separated Sewer• Service within 1100
Mile2 Area• 1000 Feet of Relief
Expected Results
• Estimated Quantity of I/I
• Likely Rehabilitation Measures
• Estimated Cost of I/I Reduction
• Estimated Savings over RWSP– Capital Savings
– Operating Savings
Overall I/I Program
Regional I/I Control Program Plan• Goals for I/I Control Program• Target I/I Removal Levels• Measures to Meet Targets• Recommended Standards• Implementation Program
Policy• Alternative Options • Construction Contracting• Regulatory Proposal• Implementation• Schedule
Financial• Cost Sharing
Alternatives• Incentive-based Cost
Sharing Program• Surcharge Program
Technical• Inventory • Monitoring • Standards• Pilot Projects• Modeling