Irrigation design is a specialist job
There are two aspects of irrigation that influence the performance and efficiency of an irrigation system, and these are design and operation. This page describes some basic design concepts that may be required for an irrigation designer and provides contacts that will be able to assist with correct irrigation design.
We recommend that you use a professional irrigation designer – irrigation design is a specialist job. Irrigation Australia Limited (IAL) is the national body of irrigation professionals for both urban and rural irrigation. IAL administers an industry-owned certification scheme that recognises irrigation professionals.
Certified irrigation designers
A Certified Irrigation Designer (CID) has demonstrated the knowledge and experience required to design irrigation systems by passing a series of closed book, supervised exams. Irrigation is a large and diverse industry, covering irrigation applications from broadacre agriculture to residential gardens.
Design requirements vary widely across this range, so engage a designer who can demonstrate design skills, knowledge and experience in projects similar to the project being proposed. Irrigation designers are bound by a code of conduct, and to maintain currency of their certification, a CID must meet annual obligations to demonstrate continuing professional development, ongoing integrity, knowledge and compliance with industry standards.
Irrigation design criteria
Your certified irrigation designer willl need to know:
- any legislative requirements associated with the abstraction and application of the water being used, particularly in regard to licencing and environmental issues
- the available or potential water volume along with quality parameters
- crop details and any details of crop effective root zone depth
- size and topography of area of water source and irrigation area
- soil survey information – soil type, texture, structure and chemical analysis
- climatic conditions near the proposed irrigation area
- power availability
- cultural or on-farm practices that may affect irrigation requirements (i.e. not spray on leaves, frequent soil cultivation, deep ripping)
- plans for future expansion of operations.
The designer will use this information to assess water supply options.
Crop water requirement
A CID will calculate the seasonal water requirement based on crop stage demand and environmental conditions for the location being assessed. With a changing climate, you should expect the CID to use scenarios of hotter, drier years to calculate peak daily water requirements and a system able to deliver the right amount volume when required.
Soil structure influences the maximum infiltration rate of water into the soil, and this should determine the maximum irrigation application rate. If water is applied at a rate faster than infiltration, runoff will result.
An irrigation system also needs to be able to deliver the right amount of water in the period required. For example, if a water sensitive crop requires 12mm between 7AM to 7PM the implied application rate required is only 1mm per hour. In practice however, you may need to apply water over 1, 2, 3 or even 4 shifts to accommodate the soil’s water holding capacity in the root zone of a crop. When combined with meeting the demand for different irrigation shifts throughout the farm, a significantly different application rates may be required.
Water quality may also influence the volume and delivered type of system required. If irrigation water contains levels of salts harmful for the crop to be irrigated, extra water may be required to provide a leaching fraction. With higher levels of salts, it may also be desirable to limit spray on the leaves of plants so drip irrigation may be the preferred option.
The topography of the area will affect the hydraulic design of an irrigation system too. Increase in elevation results in pressure loss while decreased elevation results in pressure gain. A one-metre change is equal to approximately 10kPa pressure difference.
Over an irrigation system’s life, running costs are usually greater than capital expenses. Correct hydraulic design will limit the power wasted from unnecessary creation of pressure and incorrectly selected pumps.
Plans for future expansion may influence the size of pipes, the layout of the system and the capacity of the system to deliver a certain volume over a certain time. Discuss planned expansion with your designer.
There will always be the question about the cost and benefit of larger pipes and pumps. By using a CID and working through the design criteria in this document, you may be able to assess the economics between the risk of crop or yield loss, and likely frequency of that risk occurring, versus irrigation system cost over its lifetime.
A well-designed irrigation system often costs less and performs better than a poorly designed system due to lower running costs. Using a CID and designing an irrigation system that suits your crop, soil, supply capacity and climate makes good business sense.