HomeMy Public PortalAbout2021-11-04 Hydraulic Analysis_Pine Creek_Woodlands
300 E. Mallard Drive, Suite 350, Boise, Idaho 83706 Tel: 208-383-4140 Fax: 208-383-4156
TECHNICAL MEMORANDUM
DATE: November 4, 2021
TO: Morgan Stroud, E.I.T. – City of McCall
CC: Sabrina Sims, Nathan Stewart, P.E. – City of McCall
FROM: Michael Boeck, P.E. – SPF Water Engineering, LLC
RE: City of McCall Hydraulic Analysis – Pine Creek Ranch (Woodlands) Subdivision
Executive Summary
The City of McCall has requested an analysis of the available fire flow near the proposed Pine
Creek Ranch (previously known as Woodlands) Subdivision. The proposed subdivision is
located at the east end of Woodlands Drive, as shown in Figure 1. This memorandum
documents the hydraulic modeling results using the City of McCall’s 2018 water system
hydraulic model. Scenarios presented in this analysis were prepared based on simulated
future demand projected for 2025.
The criteria evaluated as part of this analysis included the following:
1. Static Pressures
2. Pressures During Peak Hour Demand
3. Fire Flows During Maximum Day Demand
SPF understands the proposed subdivision will be connected to the City of McCall along the
streets of Woodlands Drive, Douglas Drive, Koski Drive, Blackwell Avenue, and Brady Drive.
The subdivision proposes to connect into the existing water system within these streets and
at the 12-inch line extended from Majestic View Drive. The site plan provided by the developer
is shown in Figure 2.
Modeling results indicate simulated available fire flows ranging from 1,328 gpm to 1,624 gpm
at a residual pressure of 25 psi, which does not meet the City’s minimum available fire flow
requirement of 1,500 gpm. The minimum fire flow requirement is met if the proposed water
system uses upsized lines, additional connections, and added looped lines at various
locations as noted in Figures 6c and 6d.
These results are based on numerical modeling of simulated conditions, which while intended
to approximate field conditions, may differ from field conditions. Proposed modifications to the
City’s public drinking water system have been reviewed with respect to IDAPA 58.01.08 (Idaho
Rules for Public Drinking Water Systems), which requires static pressures be limited to less
than 100 psi. The International Plumbing Code (Section 604.8, 2015 Edition) specifies other
maximum pressure criteria which may be appropriate (80 psi).
This analysis included the demands associated with the Low Density and Median Density
Residential lots as shown in Figure 2. Demand use factors were applied to lots associated
11/04/2021
Morgan Stroud November 4, 2021
SPF Water Engineering, LLC Page 2 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
with the Low Density areas as shown in green shading. Specific lot numbers were not
provided for the Median Density (yellow shading) areas. The site plan shows the Median
Density as a “R8” zoning designation, which allows up to 8 lots per acre. A maximum lot count
was created using the gross areas provided for the Median Density areas shown as “A”, “B”,
“C”, “D”, “E”, and “F” lots. Demand use factors were then applied to these median density
areas.
It was unclear if looping of the water system was proposed for the site plan. This analysis
looked at a variety of scenarios that systematically added looping to alleviate either lower
pressures during Peak Hour Demand events and/or low fire flow availability. Upsizing of pipe
diameters were also included as part of the analysis.
Figure 1 – Project Location and Vicinity Map
City of McCall
Proposed Pine Creek
Ranch Subdivision
Woodlands Dr.
Morgan Stroud August 27, 2021
SPF Water Engineering, LLC Page 3 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
Figure 2 – Proposed Subdivision Layout
Morgan Stroud August 27, 2021
SPF Water Engineering, LLC Page 4 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
The overall system layout of the model used in this analysis with added junctions to simulate
the proposed developed is shown in Figure 3 below.
Figure 3 - Model Layout
Woodlands
Drive
Blackwell
Avenue
Koski Drive
Fox Ridge
Lane
To Majestic
View Drive
Morgan Stroud November 4, 2021
SPF Water Engineering, LLC Page 5 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
Idaho Department of Environmental Quality Requirements
The following regulations were consulted as part of this analysis:
IDAPA 58.01.08, Section 552.01.b.i. Maximum Day Demand + Fire Flow
“Any public water system shall be capable of providing sufficient water during
maximum day demand conditions, including fire flow where provided, to maintain a
minimum pressure of twenty (20) psi throughout the distribution system, at ground
level, as measured at the service connection or along the property line adjacent to the
consumer’s premises.”
IDAPA 58.01.08, Section 501.18.a Redundant Fire Flow Capacity
“Public water systems that provide fire flow shall be designed to provide maximum day
demand plus fire flow. Pumping systems supporting fire flow capacity must be
designed so that fire flow may be provided with any pump out of service.
IDAPA 58.01.08, Section 552.01.b.v.) Pressure during Peak Hour Demand
“The following public water systems or service areas of public water systems shall
maintain a minimum pressure of forty (40) psi throughout the distribution system,
during peak hour demand conditions, excluding fire flow, measured at the service
connection or along the property line adjacent to the consumer’s premises.”
Morgan Stroud November 4, 2021
SPF Water Engineering, LLC Page 6 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
Static Pressure
Static pressure is represented by the hydraulic grade line (HGL) minus ground elevation with
zero system demand. The elevation of the project area as reported in the hydraulic model is
approximately 5,163 feet. Results from the hydraulic model indicate static pressures for the
project ranging from 57 to 79 psi as shown in Figure 4.
Figure 4 - Model Results: Static Pressures
Woodlands Dr.
Blackwell Ave
Morgan Stroud November 4, 2021
SPF Water Engineering, LLC Page 7 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
Pressure During Peak Hour Demand
Several scenario iterations were performed to determine pressures available during peak hour
demand. The first scenario used 8-inch diameter pipelines within the proposed streets as
shown in the proposed site plan. Sizing and lack of looping would not allow the 40 psi
minimum requirement (minimum pressures shown in red) to be met. Peak hour demand
pressures are shown in Figure 5a.
Figure 5a - Model Results: Pressures During 2025 Peak Hour Demand (8-inch
Diameter Pipelines and Site Plan Connections
Morgan Stroud November 4, 2021
SPF Water Engineering, LLC Page 8 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
Iterations were performed that included upsizing lines and looping the proposed system at
two points in the southern area of the subdivision. Figure 5b shows that the system was not
capable of meeting pressure at peak hour demand using 10-inch diameters with proposed
redundancy. Figure 5c shows that a 12-inch diameter line with looping was capable of
supporting the project.
Figure 5b - Model Results: Pressures During 2025 Peak Hour Demand (10-inch
Diameter Pipelines and Added Connections)
Woodlands Dr.
Added
connection to
Fox Ridge Lane
Internal
looping
added
10-inch
diameter
used
Morgan Stroud November 4, 2021
SPF Water Engineering, LLC Page 9 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
Figure 5c - Model Results: Pressures During 2025 Peak Hour Demand (12-inch
Diameter Pipelines and Added Connections)
Woodlands Dr.
Added
connection
and looping
12-inch
diameter
used
10-inch
diameter
used
Existing
segment
increased to
12-inch
Morgan Stroud November 4, 2021
SPF Water Engineering, LLC Page 10 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
Maximum Day Demand + Fire Flow
The hydraulic model was run under simulated maximum day demand (MDD) conditions to
determine available fire flow. The model used MDD associated with 2025 growth projections
for these simulations. Initial results in Figure 6a show the current fire flow availability within
the system using 8-inch diameter pipelines throughout the project area and the existing City
system. This figure shows flow deficiencies with less than 1,500 gpm with 25 psi residual
pressure for both the proposed and existing system. It also shows a reduction in fire flow to
the existing school area. Current system conditions provide fire flows of 2,500 to 2,600 gpm.
Flows to the school area are reduced to around 1,408 gpm
Figure 6a - Model Results: Available Fire Flow and 2025 MDD with 25 psi residual (8-
inch diameter pipe)
Fire flow areas not
meeting 1,500 gpm
shown with cyan
dot
Woodlands Dr.
Fire flow is reduced
at the school area
with inclusion of the
project.
Morgan Stroud November 4, 2021
SPF Water Engineering, LLC Page 11 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
The scenario was re-run by increasing pipe diameters and looping in selective areas similar
to the Peak Hour Demand scenario. This provided an increase in fire flow availability to the
proposed site at the southerly boundary. Flows below 1,500 were still noted in the existing
system along Fox Ridge Lane.
Figure 6b - Model Results: Available Fire Flow and 2025 MDD with 25 psi residual (12-
inch diameter and looped sections)
Fire flows increased for the
proposed development but
did little to support the
existing system
Woodlands Dr.
Morgan Stroud November 4, 2021
SPF Water Engineering, LLC Page 12 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
A second iteration was performed by adding a looped line near the southern area of the
project. This provided fire flows to both the southern half of the project as well as the existing
residential areas along Fox Ridge Lane. Flows slightly below 1,500 were noted in the existing
system within the school area.
Figure 6c - Model Results: Available Fire Flow and 2025 MDD with 25 psi residual (12-
inch diameter and added looped sections)
Woodlands Dr.
Added
connection Added
looping
Upsized
pipelines
throughout
development
12”
12”
12”
12”
12”
12”
12”
Morgan Stroud November 4, 2021
SPF Water Engineering, LLC Page 13 City of McCall
1280.0210 Pine Creek Ranch (Woodlands)
A third iteration was performed by adding a 12-inch pipeline connection to the school’s existing
looped system to Brady Drive. This increased fire flows to approximately 1,620 gpm within
the school area.
Figure 6d - Model Results: Available Fire Flow and 2025 MDD with 25 psi residual (12-
inch diameter added to school section)
The addition of this 12-inch connection to Brady Drive increased fire flows to approximately
1,620 gpm within the school area. This scenario also reflects proposed 2025 Maximum Day
Demands along with Fire Flow. Currently, fire flows achieve upwards of 2,000 gpm in the
school area without the proposed segment. As development continues, demands will
increase reducing the available fire flow. The added segment to the school area will need to
be constructed once the low density development of the project is completed and prior to the
development of the medium density lots.
Br
a
d
y
D
r
.
Added 12” from
School loop to
Brady Drive