The North Otago Irrigation Company (NOIC) scheme takes water from the Waitaki River, pumps it from Borton’s Pond (at the intake of the Lower Waitaki Irrigation Scheme) into a canal, and then a second pump station lifts the water to a Head Pond. From the Head Pond, a gravity line takes water into the Waiareka and Kakanui Valleys, with the scheme extending as far south as Herbert. Across the command area water is distributed to farmers via a total of 20 branch lines and 12 booster stations. A major attraction of the scheme is that the water is delivered on demand and under pressure to the farm boundary, and in almost every case no further on-farm pumping is required.
Delivery to Farmer's Properties
A share provides 0.4 litres per second per hectare which is equivalent to 3.6 mm per day – or almost an inch per week. Water is delivered to the farmer’s property via an offtake box which is part of the scheme infrastructure. This offtake contains an isolating valve and a pressure reducing valve and flow meter which regulates the pressure and the amount of water able to be delivered to individual properties. There are currently over 200 offtakes on the scheme. The total volumetric flow taken by each offtake is measured continuously by a mechanical meter and checked each month.
Borton’s pond was created as the intake area for the Lower Waitaki Irrigation Scheme when it was built in the 1970’s. The intake gates are capable of allowing up to 27 cumecs (27,000 litres per second) into the pond. Of this, 19 cumecs are for the Lower Waitaki Irrigation Company and 8 cumecs are for NOIC. This allocation is sufficient for NOIC to issue a total of 20,000 shares, which in turn allows irrigation of up to approximately 26,000 hectares (based on an average use of 1.3 hectares per share). A 550 m long ‘Still Arm’ canal, crossing under State Highway 83 carries the water from Borton’s pond to a pump station at Black Point (Pump Station 1).
Pump Station 1
Pump Station 1 (PS1) houses four large pumps and a smaller stock water supply. The large water cooled electric motors are 3350 horse power and pull 2.5 – 2.8 megawatts each - similar to the average electricity use of around 2,000 households per pump. Each pump is capable of delivering 2 cumecs (2 tonnes) of water per second - equivalent to approximately 70 Olympic swimming pools per pump per day, up a total lift of 84 m. These pumps were reputedly the largest in the Southern hemisphere at the time of construction.
Substation at Pump Station 1
The substation located beside PS1 is fed with electricity from the national grid on the north side of the Waitaki River. A transformer converts the incoming 110 kV supply to 11 kV to operate the pumps at PS1. An 11 kV overhead line owned by NOIC then distributes electricity to Pump Station 2 and to pump stations on the Duntroon line. The operation and maintenance of the substation is a partnership between Network Waitaki Ltd and NOIC.
Water Transfer to the Head Pond
A 600 m long, 1.8 m diameter epoxy covered steel pipe carries the water from PS1 up to a second 1.9 km long canal. The canal is split by a road crossing which is also the regional boundary between Canterbury and Otago. The two canal sections are known as the Canterbury and Otago canals respectively. The Otago canal delivers water to a second pump station at Camp Hill (Pump Station 2). Pump Station 2 (PS2) contains four large 2.2 megawatt pumps. From here, a 2.8 km long pressure main, with a vertical lift of 61 m, delivers the water to a Head Pond beside the Ngapara Georgetown Road.
The Head Pond holds 90,000 cubic meters of water (90 million litres). The pond is lined with high density polyethylene (HDPE) liner. Sensors at the pond enable PS1 and PS2 to automatically fill the pond when the level drops.
Water is distributed to farmers via an underground pipe network. The distributary works include over 200 km of pipeline and associated valves and structures. Pipelines traverse privately owned land and Waitaki District Council road boundaries. Easements are generally held where pipelines traverse private property or where other permanent scheme infrastructure is located.
The pipeline network comprises 20 lines and 12 booster pump stations, as outlined below:
- The Duntroon Line – pumped
- The Duntroon Extension Line – pumped (constructed in 2010)
- The Glen Settlement Line – pumped
- The Tilverstowe Line – pumped
- The Tilverstowe Extension Line – pumped (constructed in 2012)
- The Waiareka Line – gravity
The supply for the Duntroon line and Duntroon Extension line is delivered by water pumped from the Canterbury/Otago canal via three pump stations located along the line. All other reticulation is from the Head Pond. The Glen Settlement, Tilverstowe and Tilverstowe Extension lines are pumped directly from the Head Pond. The Waiareka line takes water from the Head Pond down into the Waiareka Valley via gravity. There are four branch lines off the Waiareka Line:
- The Five Forks Line – gravity and pumped
- The Paradise Gully Line – gravity and pumped (constructed in 2009)
- The Burnside Line - gravity
- The Windsor Park Line – gravity
In 2017 an expansion project bringing water into the Kakanui Valley was completed. This involved construction of a large diameter gravity pipeline from the Head Pond into the Kakanui Valley known as the Main Spine. Five branch lines reach from the Main Spine into the surrounding areas:
- The Peaks Line - pumped
- The Dunrobin Line –pumped
- The Round Hill Line - gravity
- The Raupo Creek Line - gravity
- The Serpentine Line - gravity
There are a further four branch lines off the Serpentine Line:
- The Kauru Hill Line - pumped
- The All Day Bay Line - gravity
- The Maheno Line - gravity
- The Herbert Line - pumped
Four pump stations lift water into areas serviced by the branch lines, delivering pressurised water to 250 m above sea level.
Pressure Reducing Valves
There are two large pressure reducing valves located on the scheme designed to lower the pressure for safety, leak reduction and cost savings (reduced pipe pressure rating). The pressure reducing valve stations have a safety relief that discharges water to the environment in the event of a pressure surge, protecting the downstream network.
In addition to the piped system, water is also augmented to the Waiareka Creek for abstraction by shareholders further down the catchment, and to provide a minimum environmental enhancement flow of 100 L/s. The environmental enhancement flow is required by the resource consents held by NOIC and is intended to improve the in-stream environmental values of the creek.
NOIC has a permit to discharge up to 1 cumec of water to the creek. Water is currently discharged from the Waiareka line at a discharge structure located near Pig Island Rd. The discharge structure dissipates the water pressure before it is released to the creek. Works have been undertaken on the Waiareka Creek to accommodate the increased flows. Creek shareholders are required to order water through an established protocol to ensure that NOIC can manage flows within the creek. A flow monitoring device is located at Rocklands Rd and is linked to the Otago Regional Council via telemetry to ensure that a minimum flow of 100 L/s is maintained during the irrigation season.
All water taken from the creek is separately metered and telemetered directly to the ORC.