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Three fundamentals of water efficient irrigation design

 

When designing the layout of an irrigation system, no matter the size of the project, the following fundamentals will always apply: pressure, head-to-head and zoning. Once these are taken into account, the chances of installing a system that results in high levels of efficiency are dramatically increased.

 

 

When designing the layout of an irrigation system, no matter the size of the project, the following fundamentals will always apply: pressure, head-to-head and zoning. Once these are taken into account, the chances of installing a system that results in high levels of efficiency are dramatically increased.

 

Pressure


Sprinklers operating at the incorrect pressure waste water and affect the uniformity of water distribution of your irrigation system. Operating specifications for sprinklers differ. Typical sprays (or cone sprinklers) are designed to work in a range of 1 to 2.1 bar. Poor design of an irrigation system can cause sprinklers to operate outside of this recommended range and severely affect the effective use of water and damage the irrigation system. Here are some of the problems caused by sprinklers operating at pressures that are too high or low:

 

Low Pressures

 

  • Radius of sprinkler is reduced leaving gaps between sprinklers
  • Uniformity of distribution is erratic causing wet and dry patches
  • At extremely low pressures the sprinkler may not pop-up and water will just seep out

 

Low Pressure Sprinkler Distribution 3

 

High Pressures

 

  • Water droplets are extremely fine causing “misting”, affecting radius and uniformity of distribution
  • Sprinkler can leak and constant high pressure can cause seals to fail
  • Pipes and fittings can burst or leak

 

High Pressure Sprinkler Distribution 1

 

A proper design matches available pressure and flow rates with the technical specifications of the sprinkler to ensure the system operates within the correct range.

 

Head to head


The term “head to head” refers to the spacing of sprinklers at their radius. If a sprinkler has a 3 metre radius then they must be spaced at 3m apart to ensure uniform distribution. Modern sprinklers have a distribution profile which is triangular in shape. Depth of application decreases as the spray reaches the outer limits of its radius.

 

Sprinkler Distribution Profile 1

 

If sprinklers are spaced too far apart then some areas will get less water than others. The only way to solve this problem is to run your zone for longer to ensure that the dry patches are sufficiently watered. This caused some areas to be overwatered, drowning plants and wasting water. The correct spacing of sprinklers ensures uniform distribution of water and the most efficient irrigation design.

 

Head to Head Sprinkler Spacing 1

 

Zoning
Zoning is the practice of dividing your irrigation system up into discrete “stations” that can be individually controlled to optimise water distribution

 

Zoning

 

Irrigation systems are broken up into zones for two main reasons:

  1. Available pressure and flow rates restrict the number of sprinklers that can be run at any one time
  2. Run times can be individually adjusted per zone to ensure that each landscape area gets the right amount of water

 

The first is a technical limitation determined by the available water pressure, flow rate and operating specification of the sprinklers. These will govern the number of sprinklers you can run per zone. The second is a function of the watering requirements of your landscape. Proper zoning takes into account a number of critical factors:

 

  • Plant water requirements. Turf grass requires different amounts of water to shrubs. Annuals differ from perennials. Exotic plants need more water than indigenous. Each plant type has its own specific watering requirements.
  • Soil types. Sand, loam and clay soils each have different infiltration rates which needs to be taken into account when determining how long to water for. Clay, for example, needs a “run-soak” cycle which puts down small amounts of water at a time to reduce the amount of runoff.
  • Sunny / Shady. Sunny areas experience more evaporation and require more water than shady areas. Typically the South side of your house will need far less water than the North side.
  • Sprinkler application rates. Different sprinklers apply water at different rates. A typical cone sprinkler has a precipitation rate of 40mm/hr. A rotor can have a precipitation rate of 10mm/hr. If these sprinklers are placed on the same zone there will be sever under/over watering and water wastage.

 

Zoning your system according to these criteria allows you to adjust run times per zone to optimise water usage and ensure your landscape gets just the right amount of water.