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Abbreviations

Acknowledgements

Executive Summary

1 Introduction

2 Methodology

3 Allocations and Areas

4 Comparisons and Trends

5 Surface-water Allocation

6 Water Use

Appendix A: Database Format

Appendix B: Assumptions and Parameters

Appendix C: Consent Database Summaries

Appendix D: Regional Summaries

References

4 Comparisons and Trends

A number of related surveys and census in the past decade form a useful basis upon which to compare the current allocation levels and irrigated areas. The 1999 allocation survey was the first national survey of allocations and therefore is a good benchmark to determine trends over the past seven years. The agricultural census in 2002, along with earlier census, provides a basis to compare reported irrigated area with consented irrigated area. The national water accounts provide regional estimates of water availability and a simple basis on which to determine the proportion of total water currently allocated.

4.1 Comparison with 1999 survey

The tables below present a comparison of current allocation levels with those reported in 1999. The 1999 survey was based on information from 14 councils (West Coast and Nelson which comprise less that 2 percent of allocations in the current study were not included in the survey).

Weekly allocation

Table 4.1 shows a comparison of weekly allocation between the 1999 and the current survey. Total allocation increased by 55 percent from 429 to 665 m³/s. Much of this increase has been in storage and groundwater allocations. However, there are several differences in interpretation between the two surveys which contribute to higher estimates of allocation in 2006, in particular the interpretation of allocations for mining water rights in Otago used for irrigation (which are the equivalent of 50 m³/s). Discounting these consents, overall weekly allocation increased by approximately 50 percent in the period 1999 to 2006.

Table 4.1: Weekly allocation (m³/s) 1996 and 2006

Note 1: For comparison purposes with the 1999 survey, the weekly allocation values exclude West Coast Regional Council and Nelson City Council (11 m³/s).

Figure 4.1 shows the comparison of weekly allocation for 14 councils (excluding Canterbury and Otago). Apart from Northland, all other councils show an increase in allocations since 1999. The decline in allocations in Northland may be actual or due to differences in the way consent records were assessed and compiled.

Figure 4.2 is a separate plot for Canterbury and Otago weekly allocations. The increase in Otago allocation is due in part to the difference in accounting for mining water rights. It also shows a large increase in allocation (48 percent) in Canterbury from 250 to 370 m³/s.

Figure 4.3 looks at allocation increases in Canterbury. Groundwater and surface-water allocations increased by approximately 92 percent and 25 percent respectively. Part of the increase in surface-water allocation (43 m³/s) is attributable to the consent (17 m³/s) for the Barhill Chertsey irrigation scheme.

Consented irrigated area

The consented irrigated area in the 1999 survey was just over 600,000 hectares (for the 14 councils). The total for the 2006 survey is 972,000 hectares, an increase of 372,000 hectares (62 percent), Table 4.2. However, discounting for the difference in number of the councils between the two surveys and the difference of interpretation of the mining water right consents in Otago, the increase is closer to 310,000 hectares or an increase of 52 percent. This is an equivalent annual increase of about 7 percent, which is slightly higher than the 55 percent per decade rate (5.5 percent per annum) reported in the 1999 survey.

Table 4.2: Consented irrigated area by region (2006 data)

It should also be noted that the 2006 survey total includes 40,000 hectares for the Barhill Chertsey irrigation scheme (yet to be developed) and 25,000 hectares for reclassification of the Waimakariri stock-water race consent from stock water to irrigation use (both in Canterbury) which, in combination, account for 20 percent of the overall increase. If both of these takes are excluded, the overall increase in area between the two surveys is approximately 40 percent (245,000 hectares) which is similar to the rate (5.8 percent pa) reported in the 1999 survey.

4.2 National water accounts

A national water balance was determined as a mean annual value (Mm³/y) over the period 1995-2001 from the national water accounts. It is calculated as the outflow to the sea. In the national water accounts values are reported as annual volumes (Mm³/y). Table 4.3 lists a summary of average water balances by regional authority.

Table 4.3 presents a summary of allocations as percentage of water balance. Nationally, allocations are 4.3 percent of total water balance but range widely between councils. It is greater than 10 percent in the councils with high levels of irrigation demand (Canterbury and Otago) and high municipal demand (Greater Wellington).

Table 4.3: Annual allocation (Mm³/y) as percent of water balance

4.3 Agricultural census

The table below, Table 4.4, presents information on irrigated area from the 2002 agricultural census. The agricultural census information was obtained from the Statistics New Zealand website. The regional data was compiled from the summary of irrigated area per territorial authority (TA). While TA boundaries generally correspond to regional boundaries, there are two notable exceptions: Franklin District which is bisected by the Auckland Waikato regional boundary, and Waitaki District which is bisected by the Canterbury Otago boundary. In both cases, the reported irrigated area within each regional boundary was calculated at the current distribution of irrigated area within the district and regional boundaries.

The census total irrigated area (463,239 ha) is considerably lower than both the consented irrigated areas in the 1999 survey and current survey (600,000 and 970,000 ha respectively). The overall difference in areas between the 2002 census and the allocation surveys indicates the differences and approach in methodologies. As discussed earlier, the census is based on the reported irrigated area (as per census questionnaire). It is a simple approach which is reliant on the accuracy and completeness of information supplied by landholders. The reported area probably reflects the area of installed irrigation and regularly irrigated. The consented irrigated area is as reported on the consent application or the calculated area based on peak weekly demand (for the consent database). Often, the requested consent and irrigated area represent a potential upper gross irrigated area for a property and includes a safety factor for future development.

A best estimate is that overall actual irrigated area is probably on the order of 80 percent of consented area. On this basis, the actual total irrigated area for the 2006 survey would be approximately 780,000 hectares which is an increase of 68 percent over the 2002 census.

Table 4.4: Reported irrigated area based on 2002 census