Sustainability Report shows benefits of water scheme
Every year the Central Plains Water Trust (the Trust) commissions an independent expert report on the environmental, social and economic performance of the Central Plains Water Scheme. This year’s report was prepared on behalf of the Trust by Liquid Earth and the full report is attached.
Stage 1 of the Scheme opened in 2015 and provides irrigation water to 23,000 hectares between the Rakaia and Selwyn rivers, incorporating a 17km long canal from the Rakaia River to 130km of underground pipes, which in turn deliver water to 125 farm turnouts. The additional 4,600 hectares Sheffield Scheme is a stand-alone project along the western margin of the Central Plains which opened in 2017 utilising water from the Kowhai and Waimakariri Rivers in combination with a large storage pond near Springfield. Stage 2 of the Scheme was commissioned in spring 2018 to provide irrigation water to 20,000 hectares between the Selwyn and Waimakariri Rivers. The total command area for the whole Scheme is therefore 47,600 hectares. The 2018 – 19 irrigation season was the first for the operation of the Scheme as a whole.
The Scheme is unique
in that its resource consents granted in 2012 are owned by
It is a charitable trust and publishes its report on the performance of the Scheme in December each year for the information and education of the people of the Canterbury Region.
Central Plains Water Limited (CPWL), owned by local farmer shareholders, was subsequently established to construct and operate the Scheme, and the Trust has contractually licenced the use of the consents to CPWL, which is also responsible for all consent compliance and reporting required by Ecan. In consideration of the licence CPWL finances the functions of the Trust which operates independently; and CPWL is also required to provide the Trust with the data necessary for its Annual Sustainability Report.
RESULTS FOR 2018-19
The 2018-19 irrigation season ran from 1 September 2018 to 29 April 2019 supplying
63.6 million m3 of irrigation water to 132 properties in Stage 1, including 26.7 million m3 of
water taken directly from the Rakaia River and 36.9 million m3 of stored water from Lake Coleridge, while 50.4 million m3 of water was supplied to 96 properties in the Stage 2 area, including 15.0 million m3 from the Rakaia River intake and 16.9 million m3 of Lake Coleridge water. The smaller Sheffield Scheme supplied 8.3 million m3 of water to 33 properties, including 5.0 million m3 from the Waimakariri River intake and 3.3 million m3 of storage pond water.
Water taken had no measurable effect:
The water taken from the two rivers totalled only 28 percent and 12 percent respectively of the
volume potentially available under resource consents held by the Trust from the Rakaia and Waimakariri Rivers The report shows that the Scheme provided reliable irrigation water to shareholders, while having no measurable effect on the natural flows of the Rivers.
Total water use for Stage 1 was the lowest since operations commenced in the 2015-16
Season; and water use in the Stage 2 and Sheffield Scheme areas during 2018-19 was also below the anticipated longer-term average.
aquifer water needed:
Due to the use of Scheme water, groundwater usage by shareholders was less than 17% of the total volume available from ground water bores under existing water permits, and groundwater levels in Ecan‘s long-term monitoring wells in the Central Plains exhibited levels well above the long-term
average during 2018-19. The report shows that shareholders have reduced their usage of groundwater by 66% across the Scheme
Scheme did not
contribute to water quality results:
Water quality monitoring results recorded for the CPW monitoring programme during the 2018-19
year indicate surface water quality, groundwater quality and lake water quality exceeded trigger
levels established for the Scheme1 at a number of monitoring sites located both in Stage 1 and Stage
2 areas, as well as down-gradient of the Scheme. However the recorded trigger level exceedances are consistent with the historical range and/or background trends observed prior to commencement of
CPW operations. The report shows that no obvious effects on water quality, groundwater levels or surface water flows are attributable to operation of the Scheme were observed during 2018-19.
solutions for lowland streams and water quality:
The Scheme forms an integral part of measures outlined in the “Solutions Package” for delivering Ecan’s Canterbury Water Management Strategy for the Selwyn Waihora Zone by providing additional recharge to the catchment from clean alpine water, plus a reduction in the volume of groundwater used for irrigation, and also provides opportunities for targeted stream augmentation by adding Scheme water directly into the Selwyn River. This is expected to result in increased volumes of
Clean water in aquifers and flows in lowland streams, as well as dilution of nitrogen concentrations in Lake Ellesmere/Te Waihora, thereby improving water quality and quantity across the wider Zone.
Farm Environmental Plans drive best practice:
All Scheme water users are required to have an FEP. These form a key component of the overall environmental compliance requirements for the Scheme, and are independently audited. Farms are assigned a grade ranging from A (all objectives met) to D (objectives for one or more management areas not met).
Of Stage 1 FEP audits undertaken in 2018-19, 1 property received an A grade, 9 properties
received a B grade and the remaining one property received a D grade.
All Stage 2 properties were audited for the first time, and of the 135 audits completed, 21 received an A-grade, 104 a B-grade, 7 a C-grade and 3 a D-grade.
The figures show a consistently low proportion of properties (<7%) assigned either C or D-grades, with the largest change being the proportion of properties receiving higher B-grades in 2018-19.
Nutrient and Nitrogen losses reduce
Ecan’s Land and Water Regional Plan establishes a limit for nitrogen losses in Selwyn Waihora zone of 5,044.4 tonnes/year by 2037. The allocation for the CPW scheme is 979 tonnes (under OverseerFM® version 6.2.3 this is equivalent to 1,983 tonnes N/year).
Calculated cumulative nutrient losses from existing irrigators in the Scheme is 27% less
than in the baseline period 2009-13, and the entire Scheme is achieving a cumulative nitrogen loss approximately 3% lower than that estimated for the baseline period.
The year-end nutrient budgets for all new irrigators are approximately 40% below the nitrogen
allocation of 1,983 tonnes N/year specified in the LWRP.
Huge increase in agricultural production and
A study carried out in November for CPWL has calculated that the Scheme has contributed a $592M per annum increase in agricultural output in the Central Plains, far exceeding expectations.
There have also been approximately 1,000 direct and indirect additional jobs in the wider Christchurch region as a result of the Scheme.
Reliable irrigation has also supported opportunities for cultivation of alternative, high value crops such as chrysanthemum, hemp, sunflower etc, as an alternative to pastoral farming.
• Noticeable growth in rural communities, school roles;
• Increased business activity and new businesses directly resulting from Scheme operations;
• Provision of supplementary/backup water supplies for the Springfield and Sheffield communities;
• Construction of 20 turnouts in the Scheme, providing high pressure fire fighting water.