Irrigation Design by We3r4h66

VIEWS: 32 PAGES: 28

									Irrigation Design
Irrigation Design
                  Goals
•   Planning Landscape Watering Zones
•   Irrigating Low Water Landscapes
•   Methods for watering plants
•   Components of a irrigation system
•   Design
•   Installation
•   Maintenance
 Planning Landscape Water Zones
• Climate information
• Site microhabitats
• Modifying habitats
  – By adding irrigation
• Modifying topography
  – Slope ,drainage or
    adding soil
      Watering Zones and Plant
              Selection
• Water requirements
  – four categories:
    minimal water (10 inches or less),
    low water (10-15 inches),
     medium water (15-20 inches),
     and high water (over 20 inches)
• Precipitation zone
  – Four zones:
    Desert, semi-desert ,foothill, and
    mountain plant communities
            Landscape Plan

• Watering zones
  – Plant communities
    • Plant communities = water
      zones
    • Determines type of system
    • Number of irrigation valves
       Water Requirement

• Determine water requirement
  – natural precipitation +
    supplemental water = water
    requirement of plant
  – ―Top up‖ to the maximum of the
    precipitation zone to keep the
    plant looking it’s best
         Things to Remember
• Precipitation rate vary from year
  to year
  – Wild plants adapt
• Ballpark approach
• Focus
  – native plants vary widely in their
    water needs
  – natural precipitation does count
  – there is definitely such a thing as too
    much water
    Irrigating Low Water Landscapes Overview;
                   Considerations
•       Irrigation of a low water landscape
    –     non-uniform
    –     ―hourglass‖ plants
    –     Some water stress is OK
    Irrigating Low Water Landscapes Overview
•       Water use in non-uniform low water landscape
        different than turf
    –     Evapotranspiration (ETo): Estimation of plant water
          use from climatic factors, radiation, wind, air
          temperature, humidity and some implicit or assumed
          plant factors that are combined into a number that
          approximates how much water is lost from a
          hypothetical cool season turf=reference
          evapotranspiration=ETo
    –     ETo is used in irrigation scheduling, the basis of
          proper irrigation management—when and how
          much—for both drip and sprinkler
    –     ETo, the amount of water transpired and evaporated
          from a surface, is an approximate measure of how
          much water is needed
    –     Link, Link2
    Irrigating Low Water Landscapes: Design
•       Hand irrigation - permanent versus temporary
        (for subsequent non-irrigated landscape)
    –     The lower the irrigation use, the more critical plant
          selection becomes
•       Sprinkler irrigation versus low volume/drip
        irrigation?
    –     Sprinkler best suited for low growing, uniform
          surface plantings such as ground cover, low
          perennials/shrub
    –     Low volume/drip best for tall growing or widely
          spaced plants and small areas
     Irrigating Low Water Landscapes:
                   Design
• Advantages of low volume/drip irrigation
  – Low pressure, 10-30 psi versus 30-60 psi for
    sprinklers
  – Target application that does not need to wet
    entire root zone as trees can increase uptake
    in wetted zone and can utilize hydraulic
    transfer
  – No loss due to overspray and wind, can easily
    irrigate oddly shaped areas
Advantages -Low Volume (cont)
 – Does not wet entire area, discourage weed
   growth due to dry soil
 – Fewer moving parts, lower pressure, less
   breakdown from water
 – Above-ground flexible polyethylene tubing,
   sometimes below ground
 – Targeted water application that only wets
   around the root zone
 – Apply small amount of water for longer
   durations than sprinkler
    Irrigating Low Water Landscapes:
                  Design
•   Disadvantages
    –   Potentially more costly and tedious to install,
        depending on size of area to be irrigated and plant
        density
    –   Potentially more maintenance/risk from breakage
        and damage from above-ground exposed parts
    –   Even when buried, easily damaged if there is
        frequent digging; don’t use under weed fabric
    –   Needs immaculately clean water; almost always
        requires installation of a filter
Components of a Drip Irrigation
         System
        Design: Types of low volume/drip
                                  emitters
•       Point Source
    –       Water comes from a single point; wets only area large enough to
            be covered with water through capillary action 0.5-2 gallons/hour;
            quality products are pressure compensating

        •     Separate emitter point
              source: point source
              emitter is punched into
              tubing at desired
              location
        •     In-line emitter point
              source: emitter is inside
              of tubing, either ½‖
              (5/8‖) or ¼‖ tubing,
              spaced at intervals of
              either 6‖, 12‖, or 24‖.
Types emitters
    (cont)
•   Microsprinkler/sprays
    –   Water is sprayed out,
        covers an area 12-
        48‖, either in a circle
        or half circle pattern,
        1-10 gallons/hour
    –   Come in fixed output
        and adjustable output
    –   Adjustable output
        sprinklers easier to
        clean
             Types emitters (cont)

•   Others
    – Trickle tape: long, very thin plastic tubing
      with openings spaced 4‖-12‖ apart, 5-10
      gallons/100 ft; extremely thin tubing, easily
      punctured; tricky to use
    – Porous tubing: ground-up rubber that emits
      water throughout entire circumference and
      length of tubing; useless
             Design: Fittings Types

•       Kind of like a tinker toy set
    –     Compression: slide tubing into fitting which
          has a sharp lip that snags the tubing
    –     Spin-loc: slide tubing over a nipple with an
          O-ring, then is tightened down with a
          twisting nut
    –     Barbed: slide tubing over a very barbed
          nipple that grabs the inside of the tubing
                             Design
•   Fixed spacing design
    – In-line emitters (trickle tape can be used the
      same way)
      •   Set at a regular spacing (1, 1.5, 2 feet) that are laid
          out parallel at distances also 1, 1.5, 2 apart

      •   Water applied in a
          uniform grid pattern
          Allows calculation of
              depth of water
      •   Used with more
          dense plantings and
          larger trees
In-line, grid
spacing drip
  system
   Drip Design w/ In-line, Grid Spacing
• Advantages
  – Easy to envision, engineer, and
    install prior to planting, very
    difficult after planting
  – Looping piping results in even
    application rate
• Disadvantages
  – Everything gets same amount of
    water, so some plants may get
    over watered if used in mixed
    planting
  – Difficult to determine breaks if
    covered by vegetation
  Drip Design w/ In-line, Grid Spacing

• Considerations
  – Total output amount from all emitters <75% of the
    flow rate for the size of tubing
  – If ¾‖ line supplies 12 gallons/minute (720 gal/hour)
    supportable output approximately 500 gallons/hour
     • If 1 gal/hr emitters, spaced at 12‖ in-line, 12‖ between lines,
       then one valve can supply 500 ft2; if 18‖ square spacing
       using, then about 1000 ft2 covered
     • If 0.6 gal/hr emitters, with 12‖x12‖ spacing, 833 ft2; with
       18‖x18‖ spacing, 1800 ft2 can be covered
  – Not full amount because of pressure losses
        Drip Design w/ In-line, Grid Spacing
•       Use fixed spacing drip when there is high plant
        density, such as perennial beds, or for large
        trees with a large root zone that needs to be
        watered
•       Fixed spacing scheduling: treat it the same as
        a sprinkler system in terms of applying depth of
        water; two ways of scheduling irrigations:
    –     Irrigating at same interval, generally once/several
          days to once/several weeks, varying runtime
          according to conditions
    –     Irrigating at fixed runtime, varying interval between
          days (depletion method), based on amount of soil
          water available to the plant-rooting depth x amount of
          water in the root zone
        Drip Design w/ Random Spacing
•   Random spacing
    –   Snake tubing to individual plants and connect
        appropriate number of emitters
    –   Based on size of plant, scaled to all plants on the
        same irrigation zone
    Drip Design w/ Random Spacing

•   Best approach for wider-spaced plant
    material, particularly trees and shrub
•   Suitable use for low volume sprinkler;
    adjustable flow low volumes sprinklers
    ideal, as they can be adjusted upwards
    at the plant grows
•   Eg. Run 1-gallon/hour emitters to small
    shrubs, scale up with more emitters for
    larger plant sizes
      Drip Design w/ Random Spacing
•   Determine mature size
    then scale the number of
    emitters to that size
    based on size of other
    plants in that zone
•   Example, mature bigtooth
    maple =10 feet canopy
    diameter, water use up to
    18 gallons/day
•   Use four adjustable low
    volume sprinklers to
    adequately cover root
    zone; for rabbitbrush with
    a two foot diameter, use
    one
        Drip Design w/ Random Spacing

•   Space emitter according to mature size so that
    a larger area of root zone is irrigated
•   Overall Considerations
    –    In a sandy soil, irrigation frequency has to be
         increased for any type of system
    –    Assumptions for estimating plant water use are very
         coarse
    –    The more drought adapted the plant, the more
         leeway you have: if water runs short, plant very
         unlikely to die, will just grow slow
    –    Again, using low volume/drip irrigation requires very
         careful thought in designing

								
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