Having a competent design before installation is perhaps the most critical component to a successful drip irrigation system. If purchasing materials from your local professional irrigation retailer they will be more than happy to assist you with the design of your system.
Firstly you need to gather relevant information prior to commencing the design. Most of this information would be required if you were designing a conventional irrigation system. You need to have,
- Scaled plan of the area
- Pressure and flow test recorded @ 200kpa
- Hydrozoning – an indication of where are the lawns, native gardens, exotic gardens, vegetable gardens
- Indication of the highest points per area for location of the air release valve.
- All infrastructure normally associated with conventional systems are used i.e Controller, pvc mainline, solenoid cable, solenoid valves etc. It is at the valve servicing the drip system where things differ slightly as we need to install a filter and pressure regulator prior to entering the drip system. The design for gardens and lawns is explained individually in the next two sections.
Some information you will need to know about designing a drip system,
- Soil type will affect the spacing of the dripperline laterals.
- Pressure and flow will determine how many lineal meters of dripline can be used per valve which will determine the size of each area (m2) The integral drippers are designed to operate at a minimum pressure, this way they maintain a ‘self cleaning effect’.
- Water quality will determine the dripperline and filter selected.
How many meters of dripperline do I need?
A simple calculation to work out how much dripperline is required is to divide the dripperline lateral spacing by the area in m2.If the area is 80m2 and the driplines are to be installed 0.30m apart,
80m2 / 0.30m = 266m of dripperline
How much water will this 266m of dripperline use?
Assume the flow rate at 200kpa pressure was recorded at 28 L/min.
Assume we are going to use Techline AS 13mm dripperline with 1.6 L/hour drippers @ 0.30m intervals.
If we require 266m of Techline AS and there are drippers every 0.30m, then 266m / 0.30m = 866 drippers. Each dripper irrigates at 1.6 L/hour therefore 866 drippers x 1.6 L/hour = 1385 L/hour.
To calculate this flow rate in minutes we divide the 1385 L/hour by 60 minutes = 23 L/min.
Therfore this 80m2 area will adequately irrigate of one valve.
How long do I set my controller for with drip irrigation?
The application rate of a drip system is calculated by this simple formula, Dripper flow (L/hour) / (Dripper spacing x Dripperline lateral spacing). To carry on from the exercise above the calculation goes like this, 1.6 L/hour / (0.30m x 0.30m) or 1.6 / 0.09 = 17.7mm/hour. Therefore if we were to apply a 10mm application we would need to set the controller for around 35 minutes.