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Planning your irrigation network

Before installing any dripperline, calculate the optimum irrigation area based on volume of graywater, ETo value, rainfall, and plant / garden coefficient.

Step 1:

Calculate the average volume of graywater generated per person per day.

Find out the ETo value for your area.

Find out the rainfall for your area.

Discuss with your local gardening experts whether you have very low, low, medium or high water usage plants in your garden. The water requirement may vary from one garden area to another - keep in mind that capillary effects will result in water moving within the soil up to 10 feet or more.

Having a mix of low water and medium water plants in one area should not cause an issue. Capillary irrigation provides enough moisture to thirsty plants without overwatering less thristy nearby plants.

Use the calculator to determine the optimum irrigation area.

  

 

 

 

Step 2:

Measure the garden areas you want to irrigate with graywater, and compare the size of your garden areas with the calculated optimum area.

If the garden area is too small (ie too much graywater), the collection / pumping system can be connected to an automatic timer (e.g. turn on every second day).

If the garden area is too big (ie not enough graywater), either makeup water should be added, or the irrigated area reduced in size.

 

 

 

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Measure the garden irrigation area, compare with calculated optimum.

 

Step 3:

Determine how the water will be supplied to the dripperlines, using the 3/4" supply tube.

A simple installation may involve a graywater diversion device located near a side fence, in an area of very low traffic. The 3/4" LDPE supply tube can be led directly to the fence, and along the side boundary as required.
Where a graywater diversion device has been installed on a concrete driveway, or a concrete footpath at the rear of the house, other options should be considered.
 
If the floor of the house is elevated (i.e. has usable subspace), the supply line can be fed under the house - typically through sub floor vents - and emerge at the required garden location. Use of schedule 40 pipe is recommended in place of 3/4" polyethylene under a house.

Supply line can also be run overhead e.g. along the roof of a garage / carport, or over the top of a fence / gate (ensure the pump in the graywater diversion device has sufficient head pressure to lift water to these heights).

 

 

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Step 4:


Plan where the dripperlines will be installed in the garden.

Because of capillary effects, the dripperline does not need to be next to the base of the plant. The important concept to remember is:

'water the soil, not the plant'

 

 

 

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Step 5:

   
Based on the garden soil type, determine the appropriate line spacing.

Calculate the total length of dripperline required.

(Note: the irrigation calculator does this for you, based on the soil type selected.)

   
Gravel and Sands:    1.8'
Sandy Loams:   1.8'
Loams:
  2.4'
Clay Loams:
  2.7'
Light Clays:
  3.0'
Medium to Heavy Clays:   4.5'

Layout Considerations:

The maximum length of a dead end lateral dripperline is 45 feet.
 
A long straight or L shaped garden bed is best irrigated with 1 dripperline that is connected to the supply line at the start and end of the dripperline — pressure and supply will be equalized over both directions, providing even drip rates along the dripperline.
 
The maximum length of a dripperline connected at each end is 90 feet, although we recommend keeping the length down to 60 feet if possible.

If there is a substantial fall over the irrigated area, where possible try to locate dripperlines along the contour.

 
Substantial grade (greater than 10%)

A graywater diversion system with a 650w dirty water submersible pump will provide sufficient dripperline pressure for up to 20 feet differential height in the dripperlines (above the height of the pump).

However, when the pump stops, water already in the dripperlines will naturally flow towards the lowest emitter. Non-return valves may be required in uphill supply lines.

If a contour can't be followed (e.g. a long narrow garden bed running down a slope), lay supply line along the length of the garden bed, with a number of short dripperlines connected, instead of a single long dripperline.

Ornamental / Fruit trees

Trees located in a general lawn area often require more water than those located in garden beds. Cut a slot in the grass to run supply line, and then connect dripperline in a full circle under the foliage extents.

Cool / Moist areas

Some garden beds will require much less water than the majority of the garden - typically, narrow garden beds shaded by the house for most of the day. Inserting a 16mm valve into the head of the dripperline will allow the householder to vary the flow to such areas as required.


Small Gardens

If the garden is small and only requires 150' or less of dripperline, consider doubling up the dripperline.

150' of dripperline will only allow up to 5 gallons per minute to be irrigated, no matter how powerful the pump.

If graywater might be generated at 10 gallons per minute, and can only be irrigated at 5 gallons per minute, graywater could build up in the collection container and overflow to the sewer / septic.

Large Gardens / High Volume of Graywater

The maximum amount of dripperline in a single zone should be approximately 500'.

While a large family can easily generate 10,000 gallons of graywater per month, and this water would irrigate 4,500 sq ft on their property, requiring 1,500' of IrriGRAY dripperline; it will not work to have the entire irrigation area in one zone.

1,500' of dripperline can process a maximum of 100 gallons per minute - far more than any graywater generated at any one time.

Imagine a person having a shower, creating graywater at 3 gallons per minute, for a total of 10 minutes (30 gallons).

The pump will cycle on and off as it moves the water quickly, but the lines will not have time to pressurize (and therefore provide even irrigation) before the shower has been finished.


In situations such as this two options are available:

  • Create a zoned irrigation system so only 1/3 of the area is irrigated at one time, or;
  • Use a large (in this case a 400 gallon tank) and connect a timer to the pump power supply so that it can operate only once or twice per day - pumping for longer periods thus pressurizing the lines. The downside of this is that shower water can develop an odor while stored for even a few hours.


For this reason zoning is the preferred outcome.

Manual vs Automatic Zone Control

Manual zoning is easily implemented by fitting 3/4" valves to the supply line.

Automatic zone control can be established using one of two methods:

Indexing Valves

An indexing valve switches water from one zone to the next based on the volume of water that has passed through the valve.

Programmed zones with solenoid control

Good quality solenoids do work well with graywater, however care is required when choosing the irrigation controller. Unlike potable water irrigation, where the irrigation might only occur for one or two hours a day, graywater could be generated (and therefore irrigated) any time during the 24 hours of the day.

It is critical, therefore, that the controller must be able to have at least one zone open at any moment of the day. Consult your irrigation specialist to discuss controller options if this method is your preferred choice.