5 An Assessment of the Feasibility of Designing Efficient and Effective Irrigation Systems for NZ Conditions
This section seeks to address two questions with respect to the feasibility of designing efficient and effective irrigation application systems in New Zealand. They are:
- Is the information available?
- Can the information be gained?
The assessment is structured around the critical design decisions presented in the previous section. It is based on experience and knowledge gained through continuing involvement in irrigation design and development in New Zealand, and a review of historical data from the Ministry of Works and Development concerning border-strip
Effectiveness
- There are no established criteria (minimum performance standards) for effectiveness.
- While effectiveness could be quantified in non-financial terms at present the most meaningful performance standards must be related to financial and economic outcomes. A team involving farm business management expertise and irrigation expertise would be required to resolve this. Expertise is available in both areas, but not in the one organisation.
Adequacy
- There are no established criteria (minimum performance standards) for adequacy.
- Resolution of this issue will require a combination of plant science, crop yield modelling and irrigation expertise. Expertise is available, but not in the one organisation.
Efficiency
- There are no established criteria or historical performance data on efficiency.
- Technology and expertise exists to obtain the information required.
Mode of operation
- Although there is sufficient understanding to identify the most appropriate mode of operation, achieving change where necessary probably involves significant reinvestment and education.
Uniformity
- There is good understanding of the design of sprinkler systems to achieve a given level of uniformity under still air conditions, and tools to assist with this are available. Achieving this depends on sprinkler manufacturers supplying the necessary data. Some information on the uniformity of application depth under travelling irrigators is available, but newer irrigators (since 1985) have not been tested. Expertise exists to do this.
- There is very little information on the uniformity of infiltrated depth of water for both sprinkler and border-strip irrigation. The most feasible method for the latter is to computer simulate border-strip irrigation. Suitable models exist but the data available for validating such models (ex MWD) is incomplete. Field work needed to provide the data required for improving understanding of uniformity, and hence efficiency and adequacy. Technology and expertise exists to do this.
Application rate
- There is insufficient data on the hydraulic properties of New Zealand soils for sound design of irrigation systems, and for water allocation purposes.
- Technology and expertise is available to meet this need, from a number of organisations.
Application depth range
- Information is not available on the benefits and costs of different application depth ranges.
- Technology and expertise is available to address this issue, but it would require performance standards for effectiveness, adequacy and efficiency.
Wetted footprint
- This is dependent on data on the hydraulic properties of soils. See application rate section above. It also requires more information than is currently available on the effects on uniformity of sprinkler characteristics, infiltrability, wetted footprint and engineering options.
- This is a significant research issue. Expertise is available to do this.
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