Future water demand from pasture irrigation in the Waikato region

TR 2005/01
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Report: TR05/01

Author: Edmund Brown, Andy Haigh

Abstract

An irrigation model was developed to identify catchments where future irrigation of dairy pasture may occur in the Waikato Region and to estimate if there is enough surface water and groundwater to meet anticipated demand. The irrigation model takes into account long-term climate data, the available water capacity of the soils, grass production in response to irrigation and economic factors such as capital and operating costs of an irrigation system. The model does not account for all the on-farm variables that may effect the modelled benefits of pasture irrigation, and many of the parameters have been simplified. Thus as also recommended by Morgan & Evans (2003), the model and the results presented should not be used by farmers or farm consultants as an irrigation decision-making tool.

There are few areas in the Waikato where rainfall is not plentiful enough to enable farming. However, farmers are striving to increase profit and this can be achieved through increased grass production and converting it to milk as efficiently as possible. Irrigation in the Waikato provides the ability to have increased and consistent grass growth, which provides more consistent income.

The model identified that most areas of the Region currently utilised for dairying would produce an increased marginal benefit if they irrigated pasture. This is based on the average milksolids payout since 1990 of $4.20.

Many surface water bodies in the Waikato Region are already highly allocated. In the near future a greater portion of the irrigation demand will need to come from groundwater. The combined use of groundwater and surface water will only meet projected demand until approximately 2020, when demand will exceed the availability based on current allocation limits.

Based on the likely spatially widespread use of irrigation, prioritising areas where future irrigation may occur is quite difficult as it is just as likely that future irrigation will occur in the Reporoa Basin as in the Hauraki Plains.

Future Water Demand from Pasture Irrigation in the Waikato Region [PDF, 790 KB]

Contents
Summary ii
1 Introduction 1
2 Irrigation Model 1
2.1 Physical Limitations to Irrigation Potential 1
2.1.1 Land Slope and Use 1
2.1.2 Soil Available Water Capacity 2
2.1.3 Irrigation Regime 3
2.1.4 Pasture Production in Response to Irrigation 4
2.2 Economic Limitations of Irrigation 5
2.2.1 Pasture Production Benefits 5
2.2.2 Irrigation System Capital and Operating Costs 6
2.2.3 Farm Working Expenses 6
2.2.4 Income 6
2.3 Financial Analysis 6
3 Areas Considered Economically Viable for Pasture Irrigation 7
3.1 Pasture Irrigation Demand in 2020 and 2050 9
3.2 Converted Forestry Areas Considered Economically Viable for Pasture Irrigation 11
3.3 Policy and Consenting Implications 14
4 Conclusions 15
5 References 17
Appendices 18
A Slope Queries 18
B Available Water Capacity 19
C Geomedia Working for Map Creation 21
D Summary of Financial Model 22