How to: Design an Irrigation Watering System

Below we're going to give you a run through of everything you'll need to know to get you started on designing a basic irrigation system for your home.

For those up for the task, any good design for an irrigation system will begin with two things:

1. A Plan - Drawn to scale with as much information as possible. For this you can use graph paper or download our Design Planner and draw out the design at a scale of 1:100. Show all garden and lawn areas, any paths or driveways, retaining walls and location of water source e.g. garden taps / water tank.

2. Your flow rate - A flow test is important as it dictates how many sprinklers you can run at once. Click here to see our formula for performing a simple "bucket flow test".

Lets start the lesson off with popup sprinklers for your lawns.

Lawn Irrigation System with Popup Sprinklers:

Head to Head" coverage - sprinklers should be installed so that one sprinkler sprays onto the adjacent sprinkler. The drawings below which show a 10m x 5m lawn area with 6 sprinkler heads (figure I.1) and one with 2 sprinklers (figure I.2).

1. The first configuration means that there are no dry spots and that due to the overlapping of each sprinklers wetted area the run time for the zone can be reduced.

2.The second has dry spots and so the area needs to be watered for excessive durations to provide water to these dry spots.

It is better to spray from the edge of lawn and garden areas into the middle. So, it is better to position your sprinklers around the edge (see figure I.1). If the area is wider than the radius of the sprinklers used then more sprinklers should be placed in the middle.

Figure I.1 - Efficient Installation	Figure 1.2 - Inefficient Installation

Your lawn and garden areas will probably not be uniform rectangles or squares. So, when you are designing a system, wherever possible, break the areas up into rectangles and squares.

Gear driven pop up sprinklers and fan popup sprinklers should not be used within one zone.

Fan sprays put down approximately 4 times the amount of water as gear drives in the same amount of time.

This means that the area that is watered by the gear drives, will not receive enough water in the time it takes to water the area with the fan sprays, or the area with the fan sprays will be over-watered by the time it takes to water the area with the gear drives.

Garden Irrigation System with Micro Sprays or Dripline:

For garden areas we recommend micro-spray sprinklers or dripline.

Micro-spray sprinklers

With some variation due to your flow rate and pressure micro-spays generally throw a 2m radius and need between 50-70L/hr for each sprinkler.

This means that they need to be installed every 2m and your flow rate in litres per hour divided by 70 will give you the maximum number of sprinklers that can be installed on each zone. Micro-sprays should also be installed 'head to head'.

Dripline

There are many different configurations of in-line drip tube. One example is a flow rate of 2L/hr at 30cm spacing. As a general rule of thumb this dripline should be spaced at 40cm.

This means that a run of dripline should be placed in your garden every 40cm. This effectively creates a grid pattern of 30x40cm rectangles with a dripper at each corner.

• Your soil type will determine the correct spacing with sandy soil requiring closer and clay soil wider spacing.
• Once the amount of dripline necessary is determined the flow rate can be worked out and the number of zones can be determined.
• Divide the area by the spacing and then multiply this by the drip rate, then divide this number by the dripper spacing to get the flow rate required for the entire system. Then divide that number by the flow rate of your tap and you will have the number of zones necessary (see the following example for your calculations).

Keep it manual, or automate my system?

Choosing between automated or manual system is entirely up to your preference. You can spend as much or as little as you like and you can set up the system at a variety of automation levels.

• Manual System - this is obviously the cheapest option and as a result it requires the most input from you on a day-to-day basis. You turn the tap on when you want to water and you turn it off when you think the area has had enough water. You will most likely need to build a manifold to allow different zones to be watered individually, if each zone is not connected to a separate tap.
• Tap Timer - these are the "egg timer" style timers that most people are quite familiar with. They are inexpensive but they will reduce the flow rate to your system and may require you to reduce the number of spray heads you can use within a zone on your system. Again you will need to build a manifold to allow multiple zones from one tap.
• Automatic system - this system will be more expensive but it allows you to water your lawns and gardens at any time of the day whether you are at home or not. It is better to water late in the evening or early in the morning and an automated system allows you to do this with ease. It also allows you to fit a rain sensor which will not allow the system to come on if it is, or has recently been, raining. An automatic system will require a controller and solenoid valves with multi-core cable joining the controller to the valves.

For more information on automating an irrigation system, see our blog "How to: Install a Multi-Station Automatic Irrigation System".