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LARE Section D Irrigation
Irrigation Design
36
Architecture
Professional
08/14/2008

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Cards

Term

 

Irrigation Design 

Pipe Sizing

Definition

 

BASED ON VELOCITY OF WATER THAT WILL FLOW THROUGH IT IN FT/SEC

PIPE DIAMETER AND MATERIAL AFFECT VELOCITY

Term

 

Irrigation Design

Soil Properties

Definition

 

  • Infiltration rate (inches/hour): depth of water infiltrated after 1 hour
  • Field capacity: volume of water soil will hold after gravity drains excess.
  • Available moisture: % moisture in soil available to plants
Term

 

Irrigation Design

Infiltration Rate

Definition

 

Affected by

  • soil type: coarse grained soils, high; cohesive soils low (sand >loam>clay)
  • slope (steeper slope, less infiltration; easier for water to move along surface)
  • antecedent moisture: dry soil, high initial rate; decreases as soil approaches saturation

 

 

Term

 

Irrigation Design

Field Capacity

Definition

 

  • Water held in soil by capillary action (attraction to soil particles)
  • Fine particle soils (silts, clays) have greater surface area/volume and therefore higher field capacities
  • High field capacity: hold larger volume, deeper and less frequent watering

 

Term

 

Irrigation Design

Available Moisture

Definition

 

  • Differs from field capacity.
  • Plants must be able to suck up water.
  • High field capacity soils (e.g., clay) may hold water tightly, therefore less available
  • Expressed as % of field capacity
Term

 

Irrigation Design

Plant Characteristics

Definition

 

  • Depth of root zone
  • Evapotranspiration rate in peak growing periods
  • Water requirement for good appearance

 

 

 

Term

 

Irrigation Design

Plant Characteristics: Root Zone Depth

Definition

 

Determines depth of soil profile for water calculations

  • Ornamental turf grass ~9-18 in
  • Mown turf ~6 in
  • Shrubs assumed ~  24 in
  • Trees ~36 - 48 in

 

Term

 

Irrigation Design

Components

Definition

 

  • Water supply
  • Delivery system
  • Distribution devices
Term

 

Irrigation Design

Water Supply: Municipal

Definition

 

  • Usually requires only tapping existing line behind a water meter or connecting to main and installing new meter
  • Volume of water available depends on supply line size and water meter size
  • Commercial/institutional usually 1 inch service or larger
Term

 

Irrigation Design

Water Supply: Municipal

Definition

 

  • Pressure available at meter varies and depends on design of water distribution system.
  • Field testing necessary.
  • Test pressure more than once and at different times of day. Nighttime usually higher because lower water use period
Term

 

Irrigation Design

Water Supply: Wells

Definition

 

  • Best to have preliminary idea of volume of water expected as well as quality
  • If found at reasonable depth (500' or less), can be very cost effective
  • Requires pump and optional pressure system
Term

 

Irrigation Design

Water Supply: Wells

Definition

 

Pumps:

  • self-priming centrifugal (shallow wells, low volume & pressure requirements)
  • submersible: fit entirely into well casing; for deeper wells with higher volume & pressure req's.
  • submersible turbine: high vol & pressure demands
Term

 

Irrigation Design

Water Supply: Wells

Definition

 

System Pressurization

  • pumps (simple system)
  • gravity (elevated water tank)
  • pressurization device
Term

 

Irrigation Design

Water Distribution System

Definition

 

  • Irrigation Pipe & Fittings
  • Valves
  • Sprinkler Irrigation Heads & Drip Emitters
Term

 

Irrigation Design

Irrigation Pipe & Fittings

Definition

 

Thermoplastics

  • PVC (good all-purpose), Polyethylene (low pressure only), ABS (sprinkler bodies, nozzles, drip emitters, valve bodies)

Metals

  • Cast Iron: most durable; protective rust layer
  • Galvanized steel: deteriorates, not good for ground contact
  • Copper: flexible, strong, chemical resistant but expensive 
Term

 

Irrigation Design

Pipe Fittings

Definition

 

  • join lengths of pipe
  • threaded: galvanized steel, thick-wall PVC
  • bell & spigot: cast iron, large diameter PVC
  • mechanical joint pipe (w/flange): cast iron, large diam. PVC
  • slip fittings: copper pipe (soldering, sweating), small dia. PVC (solvent welding/chemical bond)
Term

 

Irrigation Design

Valves

Definition
  • used to control flow of water in system from supply to individual heads and to drain or maintain water in pipe
  • manual valves: allow parts of system to be isolated for maintenance or repair while rest of system can still operate
  • remote control valves: turn water on/off at specific points in system
Term

 

Irrigation Design

Manual Valves

Definition

 

  • Gate Valve: flow straight through; have machined seat that relies on tight fit to seal valve
  • Globe valve: preferred for dirty water since washer and seat can be replace; less efficient hydraulically than gate valve
Term

 

Irrigation Design

Remote Control Valves

Definition

 

  • operated hydraulically or electrically
  • available with plastic or brass bodies, with or without pressure reg devices.
  • plastic good for valves up to 2 in. and water pressure up to 100 psi
Term

 

Irrigation Design

Special Valves

Definition

 

  • Check valve: allows flow only in one direction
  • Drain valve: used to purge water from lines and pumps (often when subject to freezing temp)
  • Pressure regulating valve: reduce pressure in selected parts of system (e.g., different zones, pump systems); needed to protect drip emitters from high pressure
  • Master valve: remotely controlled, downstream of main water supply; turns supply off when irrigation system is off; also helps protect potable water supply from contamination
Term

 

Irrigation Design

Backflow Prevention

Definition

 

  • any irrigation system supplied by potable water source must be protected from contamination in the event of system pressure drop leading to backflow

 

Term

 

Irrigation Design

Controllers

Definition

 

  • consists of two systems: timer and valve operator
  • most irrigation clocks based on even 14-day watering period and 24-hour clock graduated in minutes
Term

 

Irrigation Design

Sprinkler (Spray) Heads

Definition

 

  • distribute water in uniform pattern, usually fixed as full or part of a circle
  • commonly used for small turf areas, planting beds in residential and small commercial projects
  • useful in low-pressure situations
Term

 

Irrigation Design

Types of Spray Heads

Definition

 

Pop-up:

  • installed flush with grade
  • rises above body when water pressure applied
  • bodies available with riser hts. of 2 - 18 in.
  • turf applications: 2 - 4 in
  • ground cover & shrubs: >4 in
  • usually plastic
  • facilitate maintenance
  • no safety/tripping hazard when retracted

 

Term

 

Irrigation Design

Types of Spray Heads

Definition

Shrub Spray Head:

  • spray nozzle mounted on permanent riser
  • nozzle usually fitted to normal pipe thread adapter
  • mounted high enough to prevent foliage from interfering with spray pattern
  • High rise pop up sprays recommended near walks
Term

 

Irrigation Design

Types of Spray Heads

Definition

 

Rotary sprinklers

  • distribute water from one or more rotating nozzles
  • used for large turf areas
Term

 

Irrigation Design

Drip Emitters

Definition

 

Single port: for single plants that will not increase in size

  • Multiport: for trees/other plants that will get larger or for watering several plants
  • made for installation on PVC or flexible polyethylene tubing
  • Drip system must be actuated by valves that open/close at very low flows
  • Zones must be protected against sand/small particles in water supply and high pressure
Term

 

Irrigation Design

Hydraulics

Definition

 

Pressure

  • expressed as head measured in feet (ft) or
  • pressure measured in pounds per square in (psi)
  • column of water 1 foot high exerts uniform pressure of .433 psi
  • change in elevation results in loss/gain of pressure equal to change in elevation expressed in feet of head

 

Term

 

Irrigation Design

Hydraulics: Operating Pressure

Definition

 

  • pressure selected for operation of sprinklers
  • all sprinklers have range of operating pressures with upper and lower limit

 

Term

 

Irrigation Design

Hydraulics: Radius

Definition

 

  • distance from sprinkler head to the outer rim of water distribution pattern
  • as pressure goes up within operating pressure range, radius of throw will increase
Term

 

Irrigation Design

Hydraulics: Flow Rate

Definition

 

  • amount of water discharged from nozzle in gallons per minute (gpm)
  • as pressure increases, flow rate increases
Term

 

Irrigation Design

Hydraulics: Velocity

Definition

 

  • rate of low measured in feet per second (fps)
  • critical in determining pipe size
  • as velocity increases, friction inside pipe increases, and pressure drops
  • at high velocity, water scours pipes, erodes the seats in valves, and can break pipes due to surge pressure (water column meeting resistance in line due to change in direction/obstacle/end of line)
Term

 

Irrigation Design

Pipe Sizing

Definition

 

Irrigation Mains

  • carry water from supply source to operating zone valves
  • in large systems remain under pressure at all times

Irrigation Laterals

  • runs of pipe that carry water between zone valves and heads/emitters
  • usually smaller in size than mains
  • only under pressure when zone is being operated
Term

 

Irrigation Design

Layout

Definition

 

  • Heads: uniform coverage over areas to be watered with minimal overspray onto streets & walks
  • Head-to-Head Spacing: 50% of diameter of full circle head; ensures adequate overlapping to account for loss of depth with increasing distance from head
  • Square spacing: slightly less efficient than triangular spacing with respect to uniformity of distribution but easier to control edges and overspray
  • Triangular spacing: fewer heads needed to get uniform coverage, but harder to get uniform coverage at ends of rectangular areas. Most practical use is for large turf areas
Term

 

Irrigation Design

Precipitation Rate

Definition

 

  • how fast irrigation head applies water to surface
  • goal is to match precip rate of head to infiltration rate of soil
  • measured in inches/hour
Term
Irrigation Units
Definition
  • Velocity = feet/second (fps)
  • Flow rate (volume from nozzle) = gallons/min (gpm)
  • Pressure = pounds/sq. in (psi) or feet of head
  • Infiltration rate (of soil) = inches/hour
  • Precipitation rate (rate at which irrig. head applies water to soil) = inches/hour
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