The first sod was officially turned in April last year and by September 1 this year water from the Rakaia River was flowing in stage one of the scheme.
It’s been a huge engineering feat that’s come in on time and within the $180m budget.
Originally CPW was to have included a purpose-built storage lake in the foothills of the Southern Alps, with the aim of storing flood flows from the snow-fed Rakaia and Waimakariri Rivers.
That proposal didn’t get over its consenting hurdles and an alternative scheme was developed that uses run-of-river takes from both rivers but importantly has the ability to access water stored in Lake Coleridge thanks to an agreement with Trustpower.
Getting the rights to water from the rivers wasn’t straightforward.
The intake channels, settling ponds and headrace meant 2.8 million cubic metres of material had to be moved.
Not only did the scheme’s proponents have to battle hundreds of submissions against its consent applications, it also had to fight “water wars” with other water users in the courts.
With those tussles finally sorted out in 2012 work began in earnest on raising the capital for the infrastructure and tendering the work.
The construction has been a marvel in itself – from the huge river intake area upstream in the Rakaia River to the on-site manufacturing of 130km of pipes and construction of bridges on farms and public roads.
CPW chief executive Derek Crombie said the headrace canal was 17km long and was now being designed to service the 33,500ha balance of the scheme. The scale of the work meant the 120m lengths of high-density polyethylene (HDPE) pipe were made in a purpose-built factory in a marquee set up in a paddock near Te Pirita.
Twenty container loads or 100 tonnes a day of HDPE beads were brought on-site, heated to melt them, then extruded to create the pipes which were transported using trailers hitched together to sites across the plains.
Four major pipelines run from the headrace canal, down the plains towards State Highway 1 and each length of pipe has been fusion-welded or melted together on-site in the paddock in a kitted-out container.
Laterals run out from the pipelines to farms that hold shares.
There are 120 turnouts from those laterals, taking water to 104 farming entities in the first stage of the project.
Design work for stage two is being done now and farmers in the northern side of the command area can expect to be presented with construction share costs by the end of October.
While stage one has prompted some farmers to convert to dairy, stage two is expected to provide more in the way of reliable support operations for dairying, Crombie said.
“It will mean new water and more reliable water for existing irrigators and we expect that will mean more reliable winter crops and better cropping yields rather than conversions to dairy,” he said.
Original shareholders in the scheme paid $1750/share and needed one share per hectare when they signed up.
Each share gave them 5.18mm/ha/day.
They also have to pay an annual charge of $750/share – used to fund stage one construction and the running costs of the scheme.
Principal and interest repayments account for $560 while the operating and maintenance portion is $190.
“That $750 essentially buys them pipe capacity – the infrastructure,” he said.
On top of that they can elect to buy stored water at a cost of 8c/m3 (cumec) guaranteeing full irrigation throughout the season.
Crombie said modelling indicated total demand from the scheme including stored water would be 5000-6000m3/ha/year providing farmers with a 500-600mm top-up to their annual rainfall.
Dial up water
Farmers accessing irrigation from Central Plains Water won’t have to worry about annualised volumes and running out of irrigation water during the season.
As long as they’re prepared to pay, they can dial up water stored in Lake Coleridge any time.
CPW chief executive Derek Crombie said modelling indicated, based on the amount of water available from run-of-river, farmers would on average use about 1250m3/ha of stored water.
In a wet year that would only be 500m3/ha and in a dry year could be as much as 2000m3/ha.
At a cost of 8c/m3 that means an average cost of $120/ha and a range of $50-$180/ha depending on the season.
Shareholders would be advised about current and predicted river flow conditions, giving them the opportunity to order stored water for the following days through the scheme’s online ordering system.
On top of that they have storage costs, at an average $120/share, but it could be $50-$180 depending on the season.
Watching out for the environment
Shareholders won’t have to line up for nutrient discharge consents before 2017 like their counterparts outside irrigation schemes. CPW environmental general manager Susan Goodfellow said the scheme had been allocated a global nutrient load for new irrigators of 979 tonnes of nitrogen.
Of that 621t was from dryland farmers’ baseline discharge so existed before the scheme.
That meant only 358t of new nitrogen discharge would come from CPW’s new irrigators which equated to 6% of the total farming load in the Selwyn-Waihora catchment.
Existing Canterbury dairy farmers have consents relating to groundwater takes and effluent discharge but by 2017 they will need a new consent to farm that will include a requirement to meet their Matrix of Good Management (MGM) nitrate leaching number.
Those numbers are due out early next year.
Goodfellow said CPW would hold
the discharge consent for the scheme, which would mean existing irrigated
farms and new irrigated farms within
the scheme wouldn’t be required to
get an individual discharge consent
to farm, unlike those outside the
scheme.
The advent of CPW has allowed some farmers to convert additional areas of
their farm, and in some instances fully replace their groundwater with CPW surface water.
A few farmers have opted to retain their groundwater takes and add to them with CPW water.
CPW would also handle the consenting process for those mixed irrigation source farmers.
They’ll all be required to meet MGM numbers which will be set out in their farm environment plans.
All shareholders within the stage 1 scheme area already have a farm environment plan. They were completed, as a requirement of the scheme’s consent, by September 1.
They’ll be audited during the first quarter of next year and will be an on-going point of communication between shareholders and the scheme’s farmer liaison team which includes specialist environmental staff.
Because CPW sits within the Selwyn-Waihora catchment it’s obliged to operate under Variation one of the Land and Water Regional Plan which requires nitrogen leaching reductions in the order of 30% by dairy farmers by 2037.
Goodfellow said that as part of CPW’s discharge consent it is working through what that means for all CPW farmers within the scheme, including dairy farmers, as the overall reduction for the whole catchment is 14%.
One thing’s for sure, there won’t be any guessing about what the water quality and quantity parameters in the scheme are.
There are 20 monitoring bores within the scheme area and 12 groundwater bores in the lowland area of the scheme as well as four water testing sites within Lake Ellesmere-Te Waihora and 29 other surface water testing sites.
All are independently monitored with testing funded by CPW.
An independent ground and surface water expert review panel has been established.
It’s brief is to review the information coming from the monitoring sites and if changes occur they follow a documented process of inquiry to determine what’s going on.
If CPW is confirmed to be the cause of any problem CPW’s Environmental Management Fund has been established to fund mitigation works. The fund equates to $1.6m over 10 years. An equivalent fund has been established for Te Runanga O Ngai Tahu for mitigation and improvement works for streams, wetlands and the margins of Lake Ellesmere-Te Waihora.
