Field efficiency of border strip irrigation in Canterbury, New Zealand

Abstract

Irrigation is one of the major uses of water in New Zealand. However, there is little quantitative information about the levels of irrigation efficiency (in relation to the amount of water applied) being achieved, or capable of being achieved, for the type of systems currently used in New Zealand.

The ability to identify and understand where improvements to irrigation systems can be made to increase the levels of irrigation efficiency is critical to effectively utilise limited water resources.

The purpose of this research was to determine field efficiency for border strip irrigation under New Zealand conditions, based on existing field data. The results of this study should help irrigators improve their systems to achieve a higher level of field efficiency.

Field efficiency was determined using a validated computer model that models border strip flow and estimates application efficiency (an indicator of field efficiency). Existing border strip irrigation data collected by the Ministry of Works and Development (MWD) in the early 1980's and by Taylor (1981) were used to validate the irrigation model and determine application efficiency under New Zealand conditions.

The influences of border strip irrigation design and management parameters on application efficiency were investigated. It was concluded that irrigation design was the main factor influencing field efficiency. Unfortunately, it is difficult to change the established design of border strip irrigation systems. So management parameters were further investigated to determine their influence on field efficiency.

Irrigation inflow and watering time were identified as the simplest and most easily changed irrigation management parameters that, if adjusted correctly, increase application efficiency.

Field efficiency for border strip irrigation under New Zealand conditions was identified to be in the range of 50-56%, with a maximum realistic level of 66%. This information made it possible to establish benchmark levels for irrigators, so they are able to improve their current systems to a higher level of efficiency.