Hydraulics, Modeling and Fire Flows

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Hydraulics, Modeling and Fire Flows
MWWCA Annual Fall Convention September 20, 2007
Scott Minor, P.E., Asst. Superintendent,
Kennebunk, Kennebunkport Wells Water
Districtand Kristen Berger, P.E., Project
EngineerEarth Tech, Inc.
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Presentation Outline

• Hydrant Flushing and Flow Testing
• Hydrant Maintenance
• Collaboration between Water Utilities and Fire
  Departments
• Water System Hydraulics
• Hydraulic Modeling

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Hydrant Flushing

• Helps remove build up in water mains
• Maintains water quality
• Verifies operation of hydrants
• Flushing velocities (2.5 ft/sec min.)

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Hydrant Flow Testing

• Identifies deficiencies in distribution system
• Compare actual flow to needed flow
• Needed Fire Flows (NFF) recommended by ISO

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ISO Needed Fire Flows

• ISO Insurance Services Office
• Rate of flow necessary to control major fire in a
  specific building
• NFF based on
• Type of building construction
• Materials of construction
• Size of building
• Building uses
• Proximity to adjacent structures
• Use of sprinkler systems

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ISO Guidelines

• Flows range 500 to 12,000 gpm
• Typical Fire Flow Duration
• 2 hours for flows up to 2,500 gpm
• 3 hours for flows 3,000 to 3,500 gpm
• Number of Engine Ladder Companies based on fire
  flow

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State Guidelines

• Based on Ten States Standards
• Maintain residual pressures
• Hydrant spacing 350 to 600 feet
• Guidelines for materials and installation

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Performing Flow Tests

• Each test requires at least 1 flowing hydrant and
  1 residual hydrant
• Prefer to have residual hydrant upstream of flow
  hydrant for single direction flow test
• Ideally turn off pumps to obtain gravity flow
  from water storage tanks only (worst case
  scenario)

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Performing Flow Tests cont.

• Flush hydrants before attaching pressure gauges
• Obtain static pressures at flowing and residual
  hydrants
• Keep pressure gauge on flowing and residual
  hydrants during test
• Flow either 2.5 or 4.5 openings based on
  anticipated available flows

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Measuring Flow

• Measure flow with pitot gauge
• Record pressure at hydrants
• Calculate available residual flow
• Qresidual 29.82 x D2 x Cd x P1/2
• Qresidual Flow (gpm)
• D diameter of opening (inches)
• Cd hydrant entrance coefficient
• P pitot pressure (velocity head) (psi)

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Hydrant Entrance Coeff.

• Cd 0.7 projecting entrance
• Cd 0.8 sharp-edge entrance
• Cd 0.9 rounded entrance
• (NFPA 291 Figure 4.7.1)

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Correction Factors

• If flowing large diameter hydrant opening
  multiply calculated flow by correction factor
  (NFPA 291 Table 4.8.2)

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Sample Flow Test Spreadsheets
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Flow Available at 20 psi

• 20 psi minimum recommended pressure during fire
  flow
• Q20psi Qresid x ((Pstatic 20psi)/(Pstatic
  Presid))0.54

Qresid 2000gpm
Pstatic 58psi
Presid 50psi
Q20psi 4640gpm
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Hydrant Maintenance

• Exercise hydrants and valves
• Flag hydrants in winter
• Replace/repair damaged hydrants
• Color code hydrants
• Maintain hydrant cards, inspection repair
  reports include in GIS data

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Class AA gt1499 gpm Light Blue
Class A 1000-1499 gpm Green
Class B 500-999 gpm Orange
Class C lt500 gpm Red
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Fire Water Collaboration

• Fire Dept. should report all hydrant use for
  water systems to track water consumption,
  follow-up maint., etc.
• Fire Dept. should call water system during any
  major fire event.
• Water system to turn on pumps
• Water system to initiate emergency connections
  and system isolation, etc.

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Water Fire Collaboration

• Instruction on proper use of hydrants
• Avoid rusty water
• Avoid water hammer
• Communicate hydrant color codes
• Communicate when flow is diminished or
  unavailable due to system work, main breaks, etc.
• Communicate when hydrants are taking out and
  placed back in service

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Water System Hydraulics

• Basic system components
• Water sources
• Pumps
• Water storage
• Transmission distribution mains
• Domestic FireDemands (Existing Future)

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Distribution Methods

• Gravity System
• Surface water elevated
• Pumps not required
• Pumps Elevated Storage
• Source water pumped intosystem
• Storage tank located on hill or elevated style
  tank

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Regulations Design Standards

• Ten States Standards
• Followed by most states
• General guidelines for sizing and designing
• Size sufficient to meet domestic and fire demands
• Size to prevent water quality deterioration
• American Water Works Association (AWWA)
• Additional guidelines for designing and
  maintaining water systems

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Source Waters

• Flow to produce maximum day demand with largest
  source out of service
• Surface water and Groundwater
• Redundancy
• Multiple pumps at treatment facilities
• Emergency generators

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Water Storage Requirements

• Equalization Storage
• Volume of water required to meet the peak hour
  water demands during the maximum day demand
  period
• Fire Storage
• Volume of water required to fight a fire
• Emergency Storage
• Volume of water required during a short term
  emergency, such as a pump failure or a water
  main break

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Calculating Storage

• Equalization Storage
• 15 of Maximum Day Demand
• Fire Storage
• 3 hrs for 3,500 gpm 630,000 gal
• Emergency Storage
• 20 of Equalization and Fire Storage

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Elevation of Usable Storage

• Equalization Storage
• Maintain system pressure of 35 psi during
  domestic demand
• Minimum water level must be at least 81 ft above
  maximum service elevation
• Fire Emergency Storage
• Maintain system pressure of20 psi during fire
  emergency demand
• Minimum water level must be at least 46.5 ft
  above maximum service elevation

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Location of Storage Tank

• Opposite side of system from major source
• Allows water to flow from more than one direction
  to fire
• Increases redundancy and security in system
• May help keep water main diameters smaller
• Hill to Provide Needed Elevation
• Close to Areas with Highest Fire Flow (headlosses
  increase through system)
• Available Land
• Type of Storage Tank

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Distribution System

• Size diameter of water mains for needed fire
  flows
• Redundant water mains
• Water main looping
• C-Values effected by pipe material, age and water
  quality (40 to 140)

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Hydrant Location

• Hydrant location and spacing for Fire department
  convenience
• Available flow limited by spacing
• Maximum spacing 350 to 600 feet
• Preferred to have hydrants located on 8-inch or
  greater diameter mains
• Locate for flushing of system

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Hydraulic Computer Model

• Simulation of Distribution System
• Typically based on Hazen Williams formula
  V 0.55 x C x D0.63 x S0.54
• Used to identify system deficiencies
• Goal to maintain water pressures (20 psi) during
  fire flow demand and maximum day or peak hour
  demand
• Extended time scenarios used to observe changing
  demands/supplies

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Creating Model

• Use base map of system as background to trace
  system
• Import GIS data of water system
• Basic model input includes
• Nodes Elevation demand
• Pipes Diameter, length, material, C-value (40
  to 140)
• Tanks Diameter, water levels, elevation
• Sources/pumps Pump curves

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Calibration of Model

• Utilize results of fire flow field tests to
  calibrate
• C-flow field tests may also be used
• Turn system pumps off during tests
• Record water level in tanks
• Adjust C-values of water mains to calibrate
• Ideally model should be within 5 psi of field
  tests

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Extended Time Scenarios

• Diurnal demand curves
• Develop for individual systems
• Based on pump rates and tank level
• Observe the effects of fire flows in combination
  with different demands
• Use data to develop graphs

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Summary

• Confirm system design for existing and future
  demands
• Conduct fire flow tests
• Maintain records
• Exercise hydrants
• Use hydraulic model as tool to identify system
  deficiencies and test various improvements

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Questions?