Section 4
Section 4 - Hydraulic Model
Development and Calibration
SECTION 4 HYDRAULIC MODEL DEVELOPMENT AND
CALIBRATION
This section describes the processes utilized to develop and calibrate the hydraulic model of
EVWD’s potable water system. First, the development of the model distribution network from
EVWD’s geographical information system (GIS) is described. Subsequently, the allocation of
pressure zones, ground elevations, and water demands are discussed. This section concludes with
a discussion of the model calibration process, which is performed to verify the model results with
field measurements. In preparation for model calibration, a technical memorandum (MWH,
2013) was presented to EVWD which outlined the fire hydrant testing procedures, equipment
list, and hydrant maps needed to perform hydrant tests at 20 locations throughout the system.
The technical memorandum is attached to this report as Appendix B. The calibrated model will
be used to perform system analyses of the system under existing demand conditions and future
demand conditions.
4.1 Hydraulic Model Development
The hydraulic model of the EVWD potable water system is created using Innovyze’s InfoWater
software, which is based on ESRI’s ArcGIS platform. The ArcGIS files for the distribution
system network provided by EVWD are used as a base for creating the hydraulic model for this
Water System Master Plan (WSMP). The hydraulic model contains all pipelines and facilities
(booster pumps, storage tanks, wells, and pressure reducing valves) present in the ArcGIS
geodatabase provided by EVWD.
4.1.1 Data Collection
Data used for the development of the hydraulic model is obtained from a variety of sources. Key
information includes:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
GIS database of all water mains, laterals, and water facilities
Hydraulic water system schematic
Dimensions for storage reservoirs
Pump curves and performance tests for booster pumps
Pump controls and settings of pressure regulating valves
Water production records (2009-2012)
Customer usage records (2002-2012)
Supervisory Control and Data Acquisition (SCADA) data
General Plan and land use information
Ground elevation contour lines
Street centerline data
Aerial photography coverage
Imported and emergency water connections, sizes, and capacity
Summary of projects currently under construction or scheduled for construction in near
future
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Section 4
Hydraulic Model Development and Calibration
4.1.2 Model Construction
All pipelines and facilities included in the hydraulic model are obtained from the GIS
information provided by EVWD. The spatial representation of the hydraulic model in NAD83
datum, California State Plane Zone V coordinate system is consistent with the coordinate system
in which EVWD’s GIS data are projected.
4.1.3 Pipelines
All pipelines and facilities in the model are checked for accuracy and some pipelines and
facilities are redrawn to resolve model connectivity issues. Model attributes for pipelines include
the pipe number, pipeline length, diameter, material, roughness, and pressure zone. While most
of these attributes are provided by EVWD, the roughness attribute is based on the age and
material of the pipeline as shown in Table 4-1.
Table 4-1
Pipeline Roughness
Material
Hazen Williams C-Factor
Asbestos Cement
(3)
Cast-Iron
Cement Mortar Lined Steel
(1)
130
64
125
Copper
125
(3)
Dipped and Wrapped Steel
100
Ductile Iron
130
(2)
Steel
135
Unknown
100
(1) C Factors are estimated based on the age and the material of the pipeline.
(2) Assumed to be cement lined based on the typical age of installation.
(3) Pipelines older than 40 years are assigned a low C-factor of 100.
4.1.4 Valves and Junctions
Pressure regulating valves (PRVs) are modeled with information such as valve diameter,
pressure zones, valve settings, and minor loss coefficients. Pressure settings provided by EVWD
are used for each active valve. Zone isolation valves are modeled where the geodatabase
indicates the presence of normally closed valves. The zone isolation valves are modeled with an
initial status set to “CLOSED”.
Junctions are defined as the intersections of two or more pipelines, or at the location where any
pipeline changes diameter or material. Attribute information for junctions include elevation,
demand, and pressure zone. Fire hydrants are modeled as junctions and the fire flow demands are
recorded in the model at these junctions.
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4.1.5 Storage Tanks
Section 4
Hydraulic Model Development and Calibration
Storage tanks are modeled as cylindrical tanks. Their locations and pressure zones are
determined from the system map provided by EVWD. Attributes such as elevation, diameter,
tank height, and installation year are included based on a tank summary report provided by
EVWD. For model calibration, the initial water level of each tank is set to the recorded water
depth. The initial water level represents the water depth at the beginning of a hydraulic
simulation (midnight).
Hydropneumatic tanks are also included in the model but they are not modeled as tanks. Instead,
they are represented by a pump set to the “ON” position flowing directly to a PRV. The valve is
set to the pressure level observed in the field for the zone. Pressures experienced in a hydropneumatic zone can be satisfactorily simulated by using this modeling technique.
4.1.6 Pumps and Wells
The pump database in the model is populated with a plant number and pump curve for each
pump or well in the system. Manufacturer’s pump curve information is provided by EVWD for
the following pumps:
•
•
•
•
Plant 39 booster #2
Plant 39 well
Plant 125 well
Plant 143 well
Each pump is modeled as an adjusted multi-point curve based on the manufacturer’s pump
curves in conjunction with the most recent Southern California Edison Company (SCE) test data.
Where pump curve data are not available, total dynamic head and corresponding flow
information obtained from the most recent SCE pump test results are used in the model. The
model creates design point curves, which allow the pumps to produce head up to 133 percent of
the recorded head and flow up to two times the recorded flow. It is recommended that as new
pumps are installed throughout the system, the model be updated with the manufacturer’s pump
curve adjusted for SCE test data.
Each well is modeled as a reservoir and a pump, where the reservoir represents the groundwater
aquifer and the pump represents the well pump. The reservoirs are modeled as “fixed head” (i.e.
unlimited volume of water at a specified elevation) reservoirs with a water elevation equal to the
static groundwater level minus drawdown.
4.1.7 Surface Water Treatment Plant
The surface water treatment facility at Plant 134 is modeled with its associated booster pumps
and tank supplying the Upper, Foothill, and Canal zones. The treatment facility is modeled as a
fixed head reservoir connected to a flow control valve ensuring a steady flow of water into the
system. The flow from the plant is adjusted based on the average flow observed for each
calibration period.
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4.1.8 Facility Nomenclature
Section 4
Hydraulic Model Development and Calibration
The identification scheme used in the existing system model is based on type of facility. Tanks
begin with the letter “T”, booster pumps with the letter “PMP”, well pumps with the letters
“WELL”, and pressure reducing stations with the letters “PRS”. This prefix is followed by the
number of the plant and lastly a sequential number if there are multiple facilities at the site. For
example, T_134 is the tank at Plant 134 while PMP_134_4 is pump number 4 at the same plant.
This nomenclature makes model navigation easier for the user.
4.1.9 Facility Elevation Data
Elevations for the model are derived from contour data (two feet intervals) provided by EVWD.
Using the contour data, ground elevations are extracted and assigned to all junctions and
facilities (with the exception of storage reservoirs) in the model. Elevations for storage reservoirs
are assigned based on information contained in the summary sheets provided by EVWD.
4.1.10 Water Losses
The water demands for existing conditions are based on customer usage information (billing
data) provided by EVWD. The billing data covers the water usage for nearly 22,796 accounts for
the period of November 2002 to December 2012. The data includes information on service IDs,
street addresses, and monthly consumption. The average daily demand used in the model is
based on four years of data (2009-2012) to reduce errors that may be caused by unusual
consumption patterns in a single high or low water year. Based on these four years of data, the
average water consumption for the entire water system is 12,200 gpm (17.6 MGD). Table 4-2
contains a comparison of the consumption and production data in the system over the same fouryear period. On average, EVWD loses around eight percent of the water produced through leaks,
firefighting, maintenance tasks, and other unaccounted for use, which is typical and acceptable in
potable water systems.
Table 4-2
Water Losses
Year
Produced Water
(gpm)
Billed
Consumption
(gpm)
13,100
Water Losses
(gpm)
2009
14,100
2010
12,800
11,500
1,300
10
2011
12,800
11,800
1,000
8
2012
Average
13,500
13,300
12,500
12,200
1,000
1,100
8
8
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1,000
Water Losses
(% of
production)
7
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Section 4
Hydraulic Model Development and Calibration
4.1.11 Geocoding
The process of geographically locating each billing record is known as geocoding. Each billing
record is geographically located using the street addresses in the billing data and street centerline
GIS coverage. The geocoding process electronically places the location of each service
connection on a map. The demands are then scaled up to account for the water losses in the
system.
Demands are allocated to “demand” junctions based on proximity to the geocoded consumption
data. The existing system model is comprised of nearly 21,000 pipelines and 20,000 junctions.
To incorporate the demands into the hydraulic model, demand nodes are selected that represent a
small area of multiple accounts. Demand junctions are selected based on pressure zone
boundaries and proximity to meter locations. All junctions associated with water facilities or
transmission pipes are excluded from the demand allocation process. Upon completion of the
demand allocation process, the locations of the top 25 largest customers in the service area are
manually verified, as these large customers can impact system hydraulics significantly.
Future demands are allocated geographically based on the location of vacant parcels in the
existing land use GIS coverage. Information regarding the locations of proposed developments
(described in Section 3) is considered. The total demand for each parcel (or group of parcels) is
calculated based on the size of the parcel, land use classification, and the water duty factor. Once
the future demands are determined, the demands are assigned to the closest existing demand
node in the hydraulic model.
4.1.12 Diurnal Curve
A diurnal curve represents the average hourly demand fluctuation in a water system. The diurnal
curve for EVWD’s potable distribution system is created based on hourly production and tank
level information from the Supervisory Control and Data Acquisition (SCADA) system. Where
flows at wells and booster pump stations are not recorded in SCADA, pump ON/OFF times are
used along with the flow rates obtained from the SCE test data to estimate the volume of water
produced at the pumping facilities. Total system inflow data is based on the production data
provided by EVWD.
The calculated diurnal curve is presented on Figure 4-1. This curve represents the average
hourly demand fluctuation of all pressure zones on August 9, 2012 and is representative of a hot
summer day for the year 2012. The diurnal curve is created by preparing an hourly mass balance
using well production, imported water supplies, and change in storage. As shown on Figure 4-1,
the peak hour occurs around noon, which has a demand of 1.5 times the average demand of that
day. Individual diurnal curves for each pressure zone could not be created due to data limitations
such as the lack of flow meters to record inter-zonal transfers at pressure reducing stations and
pumping stations.
The diurnal curve shows a unique demand pattern as there is little to no peaking in usage
commonly seen in the evening in most systems that are predominantly residential. This pattern
was confirmed with EVWD operations staff.
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Hydraulic Model Development and Calibration
1.60
Water Use
(hourly/average)
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour
Figure 4-1
System Wide Diurnal Curve
4.2 Model Calibration
The hydraulic model with the existing system configuration and demands is calibrated to
enhance the accuracy of the model results and provide a planning tool that can be used to
identify system deficiencies and recommend pipelines and facilities to address system
deficiencies. Model calibration is the process of comparing model results with field results and
making model modifications where appropriate to simulate the field results as closely as
possible. Typical adjustments include adjustments to system connectivity, operational controls,
facility configurations, diurnal patterns, elevations, etc. Several indicators are utilized to
determine if the model accurately simulates field conditions: water levels in storage tanks, the
run times for pumps, and static and residual pressures from the fire flow tests, and roughness
coefficients for pipelines. This also acts as the “debugging” phase for the hydraulic model where
any modeling discrepancies or data input errors are discovered and corrected.
The hydraulic model is calibrated for two scenarios:
•
Steady State Calibration: Simulating fire hydrant flow tests to match field results (May 14th
and 16th, 2013)
•
24-hour Extended Period Simulation (EPS) Calibration: Modifying the model until it mimics
the field operations on the day of calibration (August 9, 2012)
4.2.1 Steady State Calibration
The objective of the steady state calibration is to validate the assumed pipeline roughness
coefficients (C-factors) in the hydraulic model and make modifications, where appropriate. To
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Hydraulic Model Development and Calibration
facilitate this exercise, fire hydrant tests are conducted at 20 locations throughout the distribution
system. Appendix B provides a detailed description of all data gathered for the steady state and
EPS calibration efforts. Each test consists of opening a fire hydrant (indicated as flowing
hydrant) and flowing the open hydrant until the residual pressure at an adjacent hydrant
(indicated as the gauging hydrant) stabilizes at least 5 pounds per square inch (psi) lower than the
static pressure recorded at the gauging hydrant. The flow measured at the hydrant is then input to
the hydraulic model as an additional demand and the pressures at the node that represents the
gauging hydrant location with and without this fire flow demand is then compared with the field
results.
The locations of the 20 fire hydrant tests are shown in Figure 4-2. Table 4-3 presents
information on hydrant location, hydrant number, static and residual pressure, and actual flow.
The results of the fire flow test calibration are also summarized in Table 4-3. The static and
residual pressures in the field are compared with the residual and static pressures predicted with
the hydraulic model.
As shown in Table 4-3 and Figure 4-3, nearly all of the model results are within 10 feet of head
(4.5 psi) of the observed field data as promulgated by AWWA’s Computer Modeling Manual
M32. Four tests (Location Numbers 17, 18, 19, and 20) are outside the acceptable limits. Each of
these four tests is performed in zones regulated by hydropneumatic tanks. In general,
hydropneumatic zones have at least one small pump to meet demands under normal operations
and one large pump to meet fire or other emergency conditions. The large pump remains OFF
under normal operations. When running fire flow tests with a steady state model, the emergency
pumps are turned on immediately to respond to the drop in system pressures. In reality, the
emergency pumps turn on after some pressure is already lost from the system. Based on
discussions with EVWD staff, it was agreed that calibrating the model for static pressures is
sufficient for fire flow tests conducted within hydropneumatic zones.
Two locations required further evaluation during steady state calibration. A 90 psi pressure drop
was observed during the hydrant test at Location 12 in the Canal Zone. However, the hydraulic
model simulated a 21 psi drop at this location. It appeared that this could be caused by a partially
closed valve in the vicinity of the test location. This information was presented to EVWD staff
and field investigations later revealed the presence of a closed valve in the system consistent
with the model results.
The hydrant at Location 16 is located in the Highland Upper zone where flow is controlled solely
by PRVs. Based on discussions with EVWD staff, it was found that one of the valves at the
station was closed because of leaks in the system. Adjusting the pressure setting at this PRV
resolved the pressure discrepancy between the observed data and the simulated results.
4.2.2 Extended Period Simulation
A model calibrated for a steady-state scenario provides an instantaneous snapshot of a water
distribution system. As steady state modeling does not involve time-steps, the behavior of a
water distribution system over time cannot be analyzed. An extended period simulation (EPS)
model provides a better understanding of the operations of a water distribution system than a
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Hydraulic Model Development and Calibration
steady state model. The goal of the EPS calibration is to estimate the accuracy with which the
model simulates the field operations over a 24-hour period. The EPS calibration is performed for
the 24-hour period between midnight August 8, 2012 and midnight August 9, 2012,
approximating operations on a peak summer day. The total water production on this day was
calculated to be 17,700 gpm (25.5 MGD). This is equal to 1.33 times the Average Day Demand
(ADD) for the 2010-2012 time period.
The model results are compared with the field data to determine if the model reflects the actual
system operating conditions over a 24-hour period. The modeled versus field data for the storage
tanks, booster stations, and groundwater wells on calibration day are presented in Appendix C.
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Section 4
Hydraulic Model Development and Calibration
Table 4-3
Steady State Comparison Table
Location
Number
Zone
Date
(2013)
Time
Address of gaging hydrant
(direction to flowing hydrants)
1
Lower
May14
8:15 AM
Pine St./ E. 4th St. (West)
2
Lower
May14
9:04 AM
3
Intermediate
May14
4
Intermediate
5
Average
Flow Rate
Observed/
Modeled
(gpm)
Static
Pressure
Observed
(psi)
Static
Pressure
Simulated
(psi)
Change in
Static
Pressure
Over
Observed
Residual
Pressure
Observed
(psi)
Residual
Pressure
Simulated
(psi)
Change in
Residual
Pressure
Over
Observed
Observed
Pressure
Drop
Comparison
(psi)
Simulated
Pressure
Drop
Comparison
(psi)
865
85
84
1%
79
79
1%
6
6
7114 Elmwood Rd. (South)
1,450
60
58
4%
49
53
8%
11
5
11:52 AM
Hibiscus St./ Central Ave. (East)
1,058
78
79
2%
68
74
8%
10
6
May14
8:38 AM
Base Line St./ McKinley St. (South)
2,620
100
104
4%
95
97
2%
5
7
Intermediate
May14
10:00 AM
2355 Osbun Rd. (South)
1,115
72
74
2%
69
71
3%
3
3
6
Upper
May14
10:15 AM
Val Mar Dr./ Newcomb St. (South)
1,168
85
85
1%
76
74
2%
9
10
7
Upper
May14
12:10 PM
Fisher St./ Center St. (East)
908
108
102
5%
79
72
9%
29
31
8
Upper
May16
9:54 AM
Canyon Oak Dr./ Streater Ave. (East)
1,220
106
100
5%
100
98
2%
6
2
9
Foothill
May16
9:42 AM
Lochinvar Ct./ Lochinvar Rd. (North)
1,165
108
105
3%
99
100
1%
9
5
10
Foothill
May16
8:45 AM
21st St./ Rainbow Ln. (West)
1,170
108
106
2%
103
102
1%
5
4
11
Foothill
May14
10:35 AM
Edgemont Dr./ Arden Ave. (East)
1,365
132
130
1%
124
124
0%
8
7
12
Canal
May14
10:52 AM
Juniper Dr./Manzanita Dr. (Northeast)
710
134
134
0%
44
44*
0%
90
90
13
Canal
May16
7:54 AM
Lynwood Dr./ Palm Ave. (Southeast)
1,000
102
99
3%
92
89
3%
10
10
14
Canal
May16
9:30 AM
Havenwood Ln./Westwood Ln. (East)
1,000
82
82
0%
76
75
1%
6
7
15
Mountain
May16
9:20 AM
Horner Ln./ Bernard Ln. (West)
1,220
112
114
1%
103
100
3%
9
13
16
Highland Upper
May14
11:33 AM
Fisher St./ Orange St. (West)
788
84
84
1%
52
48
7%
32
36
17
Hydro 34
May14
9:36 AM
6547 Monte Vista Dr. (East and North)
865
52
52
1%
26
48
86%
26
4
18
Hydro 59
May14
11:10 AM
500
72
72
1%
52
60
14%
20
13
19
Hydro 101
May16
8:25 AM
3712 N. Hemlock Dr. (Southwest)
3074 N Small Canyon Dr (South and East
on Mountain Top Dr.)
945
84
82
3%
44
58
31%
40
24
20
Hydro 149
May16
9:02 AM
6456 Emmerton Ln. (Southwest)
1,115
80
80
1%
39
59
51%
41
21
*Original model result showed a residual pressure of 113 psi. The value in the table resembles the model after a partially closed valve was simulated. EVWD has since found the partially closed valve and opened it.
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Pressure (psi)
Pressure (psi)
0
10
20
30
40
50
60
70
80
90
100
0
20
40
60
80
100
120
140
0
20
40
60
80
100
120
140
1
1
1
DRAFT
Project Number: 1008070
Pressure (psi)
2
2
2
3
3
3
4
4
4
5
5
5
6
6
6
10
11
Hydrant Location Number
9
12
8
8
10
11
12
Hydrant Location Number
9
Pressure Drop
9
10
11
12
Hydrant Location Number
Residual Pressure
8
13
13
13
4-11
Figure 4-3
Hydrant Testing Pressure Comparisons
7
7
7
Static Pressure
14
14
14
15
15
15
16
16
16
17
17
17
19
19
18
19
Simulated
Observed
18
Simulated
Observed
18
Simulated
Observed
February 2014
20
20
20
Section 4
Hydraulic Model Development and Calibration
Section 4
Hydraulic Model Development and Calibration
In order to achieve a balanced and calibrated model, the following adjustments are made in the
model:
•
Based on the SCE test point and the standard pump curves in the model, five wells were
producing nearly two times the flow observed in the field. These wells are modeled with flow
control valves to better mimic the field conditions.
•
Adjust facility controls for pumps. For example, based on discussions with EVWD
operations staff, the reservoir levels at which certain pumps turned ON was adjusted.
•
Change many pump controls from tank level control to timer control based on discussions
with EVWD operations staff.
4.3 Calibration Conclusions
The American Water Works Association (AWWA) Manual of Water Supply Practices M32
provides guidelines for computer modeling of water distribution systems. These guidelines
include Hydraulic Grade Line (HGL) predictions and water level fluctuation predictions. HGL
predictions by the model should be within 5 to 10 feet of those recorded in the field which is
equivalent of 2.2 to 4.3 psi. The tank water level fluctuations predicted by the model should be
within 3 to 6 feet of those recorded in the field. The lower accuracy range in these guidelines can
typically be applied to models used for design and operational evaluations while the higher
accuracy guideline (4.3 psi) is typically applied to models used for long range or master
planning.
Consistent with the above mentioned guidelines, it can be concluded that the results from the
hydraulic model are satisfactory for the purposes of long term planning. While this model can be
used for long term planning, it is important to understand the inherent errors in the model are due
to the input data used to develop the model. The following list gives possible causes for the
discrepancies between the model and field data.
•
Temporal variation in demand between EPS and steady state calibration days. The diurnal
curve created for the calibration day is also used to determine demand at each hour for the
fire flow tests. However, customer demands change from day to day and hour to hour
resulting in different diurnal curves on different days.
•
Demand variance in different pressure zones. A lack of sufficient flow meter data for each
pressure zone of the system results in the use of a generalized diurnal curve for the entire
system. With individual pressure zone diurnal curves, a more accurate demand can be
captured as some zones have little to no irrigation demand and others have high irrigation
demand.
•
Inaccuracies in elevation data. Elevations used throughout the system for junctions, pump
stations, and valves are based on ground elevation.
•
Inaccuracies in observed pump flow. Because a majority of the flows calculated for the pump
stations is based on on/off times and flow rates from SCE tests, the actual flow from any of
these devices could vary.
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Section 4
Hydraulic Model Development and Calibration
•
Inaccuracies in pump curves: EVWD has limited information on pump curves and therefore,
the model creates a generic pump curve based on a single design point. This can drastically
change the flow versus head relationship for each pump station resulting in flow or head
variances from field conditions. The lack of SCADA data to record flows at pump stations
compounds these inaccuracies.
•
Unknown groundwater level: Changes in depth to groundwater are not accounted for in the
model. Groundwater levels vary throughout the year and from year to year. The groundwater
elevations used throughout the system are based on the depth of water during the most recent
SCE tests provided by EVWD. However, groundwater drawdown can vary significantly
depending on the pumping rate and the static groundwater level conditions. These factors
introduce additional inaccuracies in the model.
Based on the findings from the steady state and the EPS calibration, the following items are
recommended to improve and refine the predictive capability of the model in the future:
•
Installation flow meters at pumping stations and PRVs between zones. Flows at these meters
should be relayed to EVWD’s SCADA system.
•
Installation of pressure loggers to capture pressures at key points in the system such as the
suction and discharge pressures at pump stations. Pressures at these loggers should be
relayed to EVWD’s SCADA system.
•
Utilizing manufacturer’s pump curves adjusted for SCE test data rather than design point
curves in the hydraulic model.
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