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Sundance Springs Comm Lot 2
Water Design Report
Revised April 23, 2025
Project Background
•2 buildings
•1.31 acres
•Commercial use (mixed office, food service, retail, health gym)
•Zoning designation is B-1 (neighborhood commercial)
Design Flow
•From City of Bozeman Design and Construction Standards (COBDCS) 4.2.4 - Average Daily
Demand: “design of new water distribution system to serve non-residential areas shall be based
on an average daily flow rate for the development being constructed. Typical flow values per
unit from Circular DEQ-4 shall be used.” Occupancy levels were determined from the associated
architect plans.
•From DEQ-4 Table 3.1-1&2:
o East Building:
▪Health Gym – 39 occupants – 10 gpd/occupant = 390 gpd
▪Office 1 & 2 – 13 occupants – 13 gpd/occupant = 169 gpd
o West Building
▪Restaurant – 70 occupants (175 meals) – 3 gpd/meal = 525 gpd
▪Retail Store – 4 employees – 10 gpd/employee = 40 gpd
▪Office 1 & 2 – 8 occupants – 13 gpd/occupant = 104 gpd
o Total Daily Demand
▪390 + 169 + 525 + 40 + 104 = 1,228 gpd
▪Rounded to 1400 gpd.
o 1400 GPD is used to estimate equivalent population for domestic water demand
calculations.
•From COBDCS 4.2.6 “Peaking Factors”
o Maximum Day Demand: 2.3 * 1400 gpd = 3220 gpd
o Peak Hour Demand: 3.0 * 1400 gpd * 1/24 hr = 175 gph
•Using Peak Hour Demand:
o 175 gph = 3 gpm
•Approximately 25 gpm shall be needed for landscaping demands.
•3 gpm + 25 gpm = 28 gpm for two buildings of equivalent size and use.
•28 / 2 = 14 gpm service line demand per building
Water Main Specifications
•Main line – 8-inch diameter Ductile Iron Pipe (DIP), 325’
•Water main shall be constructed using fittings at 11.25, 22.5, and 90-degree angles.
•Water main shall be placed a minimum of 10’ from sewer main.
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COB Standard Drawings
• MPW 02660-1 Thrust Blocking for Water Main Fittings
• MPW 02660-2 Water and Sewer Main Separation
• COB 02660-3 Thrust Blocking for Water main Valves
• COB 02660-7 Typical Blowoff Valve
• COB 02660-6 Water Service Line
• COB 02660-10 Typical Valve/Tee Restraint
• COB 02660-12 Water Service Line
• COB 02660-13 Standard Fire Service Line Installation
• COB 02660-16 Water and Sewer Main and Services Location Standards
• COB 020660-17 Water Service Interior Clearances
Main Size
A line serving more than one building is designated a water main. The water main for Sundance Springs
Comm Lot 2 has water service demands of 28 GPM. Head Loss calculations indicate that 325’ of 8’’ DIP
with a C of 130 and a flow rate of 28 GPM will have an actual head loss of 0.00348 psi and a velocity of
0.197 ft/s. COB requires that the velocity in a main less than 10 inches be less than 5ft/s. COB requires
that the minimum diameter for any new main is 8 inches unless specific approval in writing is obtained
from the COB. Water main pressure at the connection point is assumed to be 40 psi based on comment
19 of the Informal Review – Review Comments Report. Working residual water pressure is assumed to
be 40 psi – 0.00348 psi = ~39 psi.
Main Extensions
The new main will be tapped from a 12” COB water main beneath Little Horse Drive. The proposed
dead-end main is approximately 325 feet in length and shall end with a 2” blow-off valve. A 6” main
extension stub exists onto the property but will be capped.
Services Lines
Each of the two buildings shall have one service line for domestic water service. An additional service
line connection will provide landscaping. Service lines are sized so as not to exceed 10 feet/sec velocity
as calculated by the fixture unit method as specific in the Uniform Plumbing Code.
Standard service lines shall be 1” type “K” copper to accommodate 14 GPM per building. The
landscaping service line shall be 1.5” type “K” copper. Backflow prevention devices will be installed as
required by the Water Superintendent.
No service line shall be extended into the buildings until an “Application for Service” has been
completed and a Plumbing Permit has been obtained from the Building Department.
Valves: One eight-inch gate valve is proposed at the connection to the existing 12-inch water main in
Little Horse Drive.
Hydrants: No hydrants are proposed on the site. Two existing hydrants on the corners of Little Horse
Drive and Ellis View Loop with South 3rd Ave provide coverage for the lot with both buildings entirely
within 400’ of one or both hydrants per IFC 2018 specifications.
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Air Relief: Air relief is provided by the 2” blowoff valve.
Pressure Reducing Valves: Pressure reduction valves are not required for these service connections.
Attachments: (1) Hazen-Williams Calculations
04-23-2025
Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!
Hazen-Williams Water Flow Formula: Head Loss, Data, Charts & Calculator
Friction head loss (ftH2O per 100 ft pipe) in water pipes can be estimated with the empirical Hazen-Williams
equation.
The Darcy-Weisbach equation with the Moody diagram is considered to be the most accurate model for estimating frictional head loss for a steady
pipe flow. Since the Darcy-Weisbach equation requires iterative calculation an alternative empirical head loss calculation like the Hazen-Williams
equation may be preferred:
h100ft = 0.2083 (100 / c)1.852 q1.852 / d4.8655 (1)
where
h100ft = friction head loss in feet of water per 100 feet of pipe (fth20 /100 ft pipe)
c = Hazen-Williams roughness constant
q = volume flow (gal/min)
d = inside diameter of pipe (inches)
Note that the Hazen-Williams formula is empirical and lacks a theoretical basis. Be aware that the roughness constants are based on "normal"
conditions with approximately 1 m/s (3 ft/sec) .
Example - Friction Head Loss in Water Pipe
200 gal/min of water flows in a 3 inch PEH pipe DR 15 with inside diameter 3.048 inches. The roughness coefficient for PEH pipe is 140 and the
length of the pipe is 30 ft. The head loss for 100 ft pipe can be calculated as
h100ft = 0.2083 (100 / 140)1.852 (200 gal/min)1.852 / (3.048 in)4.8655
4/11/25, 1:58 PM Hazen-Williams Water Flow Formula: Head Loss, Data, Charts & Calculator
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= 9 ftH2O/100 ft pipe
The head loss for 30 ft pipe can be calculated
h30ft = h100ft (30 ft) / (100 ft)
= 9 (30 ft) / (100 ft)
= 2.7 ft H2O
Related Mobile App from The Engineering ToolBox
Water Pipes Head Loss Calculator App
- free apps for offline use on mobile devices.
Online Hazens-Williams Calculator
Imperial Units
The calculators below can used to calculate the specific head loss (head loss per 1 00 ft (m) pipe) and the actual head loss for the actual length of
pipe. Default values are from the example above.
325 l - pipe or tube length (ft)
130 c - roughness coefficient determined for the type of pipe or tube
28 q - flow rate (gal/min)
8.0 d - inside diameter (inch)
Calculate!
Specific Head Loss (ft H2O / 100 ft pipe): 0.00248
Specific Head Loss (psi / 100 ft pipe): 0.00107
Actual Head Loss (ft H2O): 0.00805
Actual Head Loss (psi): 0.00348
Velocity (ft/s): 0.179
4/11/25, 1:58 PM Hazen-Williams Water Flow Formula: Head Loss, Data, Charts & Calculator
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Pipe and Tube Dimensions
Make Shortcut to this Calculator on Your Home Screen?
SI Units
9 l - pipe or tube length (m)
140 c - roughness coefficient determined for the type of pipe or tube
10 q - flow rate (liter/sec)
76 d - inside diameter (mm)
Calculate!
Hazen-Williams equation in an Excel template
The Hazen-Williams equation is not the only empirical formula available. Manning's formula is commonly used to calculate gravity driven flows in
open channels.
The flow velocity can be calculated as
v = 0.408709 q / d2 (2)
where
v = flow velocity (ft/s)
Limitations
The Hazen-Williams equation is assumed to be relatively accurate for water flow in piping systems when
the Reynolds Numbers is above 105 ( turbulent flow)
the water temperature is in the range 40 - 75 oF (5 - 25 oC) and the kinematic viscosity is approximately 1.1 cSt
For hotter water with lower kinematic viscosity (example 0.55 cSt at 130 oF (54.4 oC)) the error will be significant.
Since the Hazen-Williams method is only valid for water flow - the Darcy Weisbach method should be used for other liquids or gases.
1 ft (foot) = 0.3048 m
1 in (inch) = 25.4 mm
4/11/25, 1:58 PM Hazen-Williams Water Flow Formula: Head Loss, Data, Charts & Calculator
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1 gal (US)/min =6.30888×10-5 m3/s = 0.227 m3/h = 0.0631 dm3 (liter)/s = 2.228×10-3 ft3/s = 0.1337 ft3/min = 0.8327 Imperial gal (UK)/min
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4/11/25, 1:58 PM Hazen-Williams Water Flow Formula: Head Loss, Data, Charts & Calculator
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Reynolds number for clean cold water flow.
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