Waterwise Irrigation

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The widespread use of automated irrigation in WA is unique in Australia. No other state relies upon irrigation to sustain gardens and landscapes to the same extent. This is obviously due to our rainfall pattern which is classically Mediterranean – hot dry summers and cool wet winters. For much of the state, the wet season is very short and we have come to depend on artificial watering to establish gardens and enable many plants to survive the long dry season.

Inefficiencies in irrigation systems

can be very costly in terms of water wastage. Professional design, installation and maintenance are recommended for best results, ideally by certified Waterwise Garden irrigators who install to Irrigation Australia standards.

Design tips

Advances in irrigation technology are giving greater flexibility in design and efficiency. Landscape designers and irrigation designers are advised to work closely together to ensure maximum effect for minimal water input. Designers can contribute to an efficient irrigation plan by following these guidelines:

  • Clearly identifying the types of plants to be irrigated to avoid shadowing/blocking effects as the plants mature.
  • Employ hydrozoning – grouping plants with similar watering requirements to ensure that maximum watering efficiency can be maintained.
  • Specify type of irrigation to be used for particular areas.
  • Match the system to the watering requirements of plants eg. an advanced tree may require a larger volume of water than a sprinkler system can provide.
  • Identify the site’s soil type, topography and microclimatic influences.
  • Identify slopes on the plan to aid choices of irrigation in system design.
  • Mark other points of interest that may have a bearing on system design such as prolonged shade, high wear and tear, areas subject to mechanical damage.

Guidelines for waterwise irrigation systems

  1. Use separate stations for distinct hydrozones e.g. lawn and garden beds.
  2. Each station should use sprinklers/emitters of the same type.
  3. Design and install to minimize variations in rate of output between identical emitters in the system (system should not operate at more than 10% variation).
  4. All emitters should work at the manufacturer’s recommended operating pressure.

Sprinkler systems

  • Use sprays with coarse or heavier precipitation rates.
  • Microsprays are not recommended due to misting.
  • Sprinklers should be spaced at no more than the radius of throw specified by the manufacturer’s recommendations.
  • Part circle sprinklers should be used where appropriate to prevent wasteful overspray.
  • In garden beds, pop up heights should be suited to the planting or shrub adaptors fitted on fixed polyrisers above planting to minimize ‘shadowing’ of plants at their mature height.
  • In narrow beds less than 3m wide, irrigation maybe be installed on one side of the bed with sprinklers of a radius of throw of between 1/4 and 1/3 greater than the width of the bed providing that overspray is against a solid object or a turfed area.
  • Sprinkler spacing should be no more than the radius of throws of each sprinkler.

Sprinkler systems

  • In line dripper and row spacing should be appropriate to the soil type, for example:
    • sandy soils – 0.3m dripper spacing, 0.3m rows.
    • medium/loamy soils – 0.4m dripper spacing, 0.4m rows.
    • heavy/clay soils – 0.5m dripper spacing, 0.5m rows.
  • Use appropriate layout techniques for the planting scheme eg. grid format for dense planting and ‘lite’ layout of dripline where the line is woven throughout a planting area for more sparse planting schemes.
  • For very sparse planting low-density poly and individual drippers may be prove to be more efficient.
  • Drip systems should be protected by the installation of a minimum 120 mesh filter to prevent clogging of emitters.
  • As subsurface drip systems (under lawn) require the introduction of a rootintrusion inhibitor at approved dosages, the mains water supply must be protected at the point of connection by a reduced pressure zone backflow device by a licensed plumber. Use only Anti Siphon (AS) dripline sub surface (turf).
  • A vacuum breaker/air release valve should be installed at high point/points in the drip system to prevent ‘suck back’.
  • An automatic line flushing valve should be installed for each station on the collection manifold at the furthest point in the system.

Benefits of drip irrigation

Landscape architects, contractors, nurseries, designers and consultants recognise the benefits of using low volume drip irrigation because of its accelerated plant growth compared to overhead sprays. The combination of rapid growth and dramatic water savings are the major benefits of drip systems. They are ideal for sloping areas, minimizing run off.

Drip systems are flexible and can be added to during further stages of development as well as being easily retrofitted to an existing micro spray system. They can be applied in regular and odd- shaped areas and are discreet in high profile landscapes.

Important!

The client should be given a recommended watering schedule for peak demand with recommended seasonal reduction for shoulder and winter periods.

Drip applications are sub-surface for turf and sub-mulch for general planting. Drip is also the most efficient method of dispersing wastewater effluent (greywater) into the soil via a purple pipe specifically required for
greywater. It is possible to install drip irrigation into existing turf with minimal disturbance using purpose-designed equipment.

Drip irrigation is the only permissible form of water delivery in many states of Australia. It is the most appropriate irrigation system for our climate and strong prevailing winds. For technical specifications on drip systems and their installation, see page 15 of the WGIP Manual.

Manufacturers and suppliers of drip irrigation components can provide further training and LIAWA can be contacted for upcoming Professional Development sessions on waterwise irrigation systems.

Irrigation controller

  • Should be a minimum three station controller and be programmable to comply with watering guidelines and restrictions.
  • Must have a ‘water budgeting’ feature to enable increase/decrease of watering times to all stations according to seasonal/prevailing weather requirements.
  • Must be able to interface with a ‘Smart Approved WaterMark’ automatic rain sensor and soil moisture sensor.
  • The rain sensor should be adjusted to shut off the irrigation automatically following rainfall.
  • Where required, the controller should be fitted with a back-up battery to hold the memory in the controller in the event of power failure.
  • Must be programmed in accordance with any existing watering regulations/restrictions in force.

‘The standard drink’

The recommended ‘standard drink’ for Perth is 10mm of rainfall or 10 litres of water per m2 of watered soil. The standard drink is the same for both turf and garden areas.

Regional offices of the Water Corporation can advise the local standard drink and the watering schedules for country areas.

Refer to the Water Corporation website for current watering regulations and guidelines:
www.watercorporation.com.au