Teviot Scheme

The Teviot Scheme cascades down from Lake Onslow through a number of storage structures and hydro power stations, following the Teviot River to eventually rejoin the Clutha near Roxburgh.

Scheme Overview

Lake Onslow Dam

Commissioned: 1984

Storage Capacity: 46 million cubic metres

Dam Type: Concrete Arch Dam with a crest height of 15m and length of 66m.

The water to power the Teviot River stations originates from Lake Onslow, which is high in the Lammerlaw Ranges, 38 km from Roxburgh. The Onslow Dam is the main storage dam for the Teviot Scheme. The original stone dam at Lake Onslow was built in the 1890s. In 1981 a new concrete arch dam was built at Lake Onslow, which raised the level of the lake by 5 metres and drowned the original dam. At the same time the Marslin Intake Dam was constructed further down the Teviot River to control the intake to the new power stations (Michelle and Ellis) constructed during this period. In 1984 a 2kVA rated output machine was installed at Lake Onslow to provide power for control equipment and servicing of the Lake Onslow Dam.

Pioneer controls the storage and outflows of water, while the dam is above the level of the original storage dam, as long as it provides a supply of water for irrigation and frost fighting (up to 1.57 cumecs during the summer months). Once the storage level falls below the level of the original dam, outflow control reverts to the Teviot Irrigation Company (TIC) Weir. Since 1981 this has happened rarely and a collaborative approach to outflow control has prevailed in these rare situations.

The Onslow Dam is surrounded by privately owned land.

Horseshoe Bend

Commissioned: 1999

Flow through Station: 2,000 litres per second

Annual Generation: 33 GWh

Horseshoe Bend is a 4.3MW hydro station on the Teviot River, approximately 15km east of Roxburgh. Horseshoe Bend was Pioneer’s fifth station to be built on the Teviot River. The site is approximately 600m above sea level, and subject to severe weather conditions. Water is supplied from the Horseshoe Bend Dam. The dam is of unique construction, being the first roller compacted concrete dam in New Zealand. It incorporates a stepped spillway on the downstream face. A 180m long tunnel was excavated through schist rock. This tunnel feeds the pipeline to the powerhouse with water from the dam. Most of the 480m of pipeline, bringing water to the penstock and powerhouse, is buried, with the penstock supported above ground on concrete pedestals.

The powerhouse is a steel-framed structure on a reinforced concrete foundation, that includes support for the turbine and generating plant. The turbine is a horizontal axis turbine running at 600rpm. The generator, weighing 40 tonnes, was built by ABB in South Africa and generates at 6.6kV. The energy generated is transformed to 33kV prior to being fed into the local distribution networks via Aurora’s Teviot substation. In 2010, a new larger generator transformer was installed to accommodate the additional generation from Horseshoe Bend Wind Farm.

The control system allows the station to run unattended and be operated remotely. This was designed and built by Marlborough Electric Ltd.

Five kilometres of new road were constructed to the site and six kilometres of existing road upgraded, including construction of culverts and cattle stops. The dam won a Caltex Construction Award and was nominated for judgement before ACENZ and the NZ Concrete Society.

Horseshoe Bend Dam with Horseshoe Bend Wind Farm in the background

Marslin Dam

Commissioned: 1981

Storage Capacity: 122,000 cubic metres

Dam Type: Concrete Arch Dam with a crest height of 16m and overall length of 32m.

Downstream, and fed, from the Onslow Dam, the Marslin Dam is the third reservoir on the Teviot Scheme. During normal operation, water is supplied by the dam to the Michelle Station via a pipeline. In winter or other times of high-energy use, extra water from the Marslin Dam is fed to the lower Ellis Station, via a tunnel, which bypasses the Michelle Station.

Completed in 1981, Pioneer engineers undertook the design work for the 17 m high arch dam. A new construction technique was employed that involved the use of flat-plate hydraulic jacks being built into the central vertical construction joint, in the dam sections. After the concrete had cured, 1,200 tonnes of pressure was applied by the jacks, to force the two sections apart and into the rock walls of the valley. The gap produced was then grouted to hold the dam in this position. This method produced a safer design, which used less concrete than a conventional arch dam.

The Marslin Power Station consists of the Marslin Dam, pipeline and single horizontal Francis hydro turbine and generator with a maximum output of 1.6 MW. The turbine and generator are in the powerhouse which is of concrete block construction. The power station and Marslin Dam were constructed in 1981. The station is designed to run automatically in an unattended mode. Access to Marslin Dam and power station is over private farmland.

Michelle Hydro Station

Commissioned: 1982

Flow through Station: 2,730 litres per second

Annual Generation: 12 GWh

The Michelle Station operates with one induction type machine of 1.6MW output, driven by a Francis turbine manufactured in 1981. Michelle Station has a static head of 74m. Michelle’s water supply is brought from the Marslin Dam via 670m of steel and 2,600m of concrete pipeline. The station has an overflow pipeline alongside the main penstock, which enables water to continue flowing to the lower stations when the Michelle Station is offline. Discharge and overflow water from the Michelle Power Station moves via a 740m long tailrace to the Ellis Station head pond, which is the Scheme’s fourth reservoir, and day storage area, for the lower Teviot stations. This tailrace also supplies water for irrigation.

Basic remote control of the station was implemented in early 2017 and it is designed to run unattended with the SCADA system continuously monitoring the condition and output of the plant.

Kowhai Hydro Station

Kowhai Power Station with the TIC Weir in the foreground.

Commissioned: 2010

Flow through Station: 3,400 litres per second

Annual Generation: 7.5 GWh

In 2009, Pioneer constructed this hydroelectric power station on the Teviot River. The site is approximately 3.5km east of Roxburgh adjacent to the Teviot Irrigation Company (TIC) intake weir on the Teviot River.

The pipeline and penstock associated with the power station runs from the Marslin Dam some 1.5km upstream. The pipeline follows the route, and is laid parallel, to the one supplying water to the Michelle Power Station from the Marslin Dam. At the downstream end of the penstock there is a butterfly main inlet valve between the end of the penstock and the turbine inlet. The main inlet valve is ‘fail safe’ being hydraulically held in the open position and closed by counterweight when the hydraulic pressure is released.

After flowing through the turbine, the water is discharged back into the Teviot River immediately above the TIC Weir.

The turbine and generator are in the powerhouse which is of a precast tilt slab construction designed to withstand flooding of the Teviot River. The powerhouse has a removable timber roof to allow crane access to the turbine and generator. The 690V and 33kV switchgear is inside the powerhouse.

George Hydro Station

Commissioned: 1924

Flow through Station: 1,700 litres per second

Annual Generation: 3.5 GWh

This was the first station built on the Teviot River. It was commissioned in 1924, originally operating with two generators, each of 125kW output and driven by Francis turbines. In 1926 a third machine of 500kW output was added to the scheme, also driven by a Francis turbine. In 1966 the two original machines were replaced by a single machine with a capacity of 500kW, driven by a Gilkes Impulse Turgo turbine. The station was extensively refurbished in 2002 when the two 500kW machines were replaced with a single machine of 1000kW capacity. During refurbishment all electrical equipment at the station was also replaced.

The station consists of a pipeline from the head pond, penstock, power station and substation. Water from the head pond to George Power Station, not used for high pressure irrigation, is used to generate electricity. Water used to generate electricity, but not subsequently used for low pressure irrigation, is taken via pipeline to Bridge Power Station. During the irrigation season, water for irrigation purposes takes precedence over water for generation purposes.

The station is designed to run automatically in an unattended mode.

The George Power Station is accessed via a steep, unformed track off Teviot Valley Road, near the Clutha River Bridge. This road passes over land owned by Pioneer and privately-owned. The power station is located on Pioneer-owned land.

Bridge Hydro Station

Commissioned: 1972

Flow through Station: 1,600 litres per second

Annual Generation: 1.5 GWh

The scheme was proposed in 1967 but due to long delays in obtaining approvals and other commitments at the time, development did not begin until June 1970, when tenders were called. The station is directly adjacent to the Teviot Ellis Power Station. The station consists of a pipeline and penstock from the George Power Station, the Bridge Power Station and the substation on the opposite side of the river.

The penstock comprises steel pipes gradually reducing from 915mm to 760mm in diameter, with an overall length of 457m. The water supply originates from the spill at George Station, on the hillside above.

This outflow is taken through a vertical slide gate to the penstock. Provision has been made for an overflow outlet pipe at the George Station when the Teviot Bridge Station is offline.

Water, supplied from the George Power Station, is subject to availability due to irrigation supply arrangements with the Teviot Irrigation Company.

Ellis Hydro Station

Commissioned: 1981

Flow through Station: 3,680 litres per second

Annual Generation: 38 GWh

The Ellis Power Station is accessed from the Teviot Valley Road where the road crosses the Teviot River. The Power Station consists of an intake weir (known as the Teviot Irrigation Company Weir), tunnel, water race, head pond, pipeline, penstock, power station and substation. TIC owns the weir, the tunnel, and the water race up to the connection at the Ewings Race.

Tunnel

Water from behind the TIC Weir (constructed in 1936) enters a concrete-lined horse-shoe cross section 1,550m long tunnel, constructed in 1936. The tunnel has a nominal design capacity of 2,832l/s.

Water Race

The water from the tunnel flows along a 170 m long water race which then joins the Michelle water race upstream from the head pond. The water from both the Michelle station and TIC Weir then flows approximately 650 m to the head pond.

Pipeline and Penstock

The water supply is brought from the head pond via a single 1km long, 1m diameter steel pipeline and penstock. The penstock bifurcates, at the back of the powerhouse, to provide separate feeds to each turbine. At the downstream end of each penstock there is a water-operated main inlet valve between the end of the penstock and the turbine inlet.

After flowing through the turbine, the water is discharged back into the Teviot River.

A waterpower licence was obtained for this station in May 1978, enabling the project to proceed. The station powerhouse is alongside the Teviot Bridge generating station. Installed in the station is refurbished plant purchased from the Dunedin City Council (ex. Waipori Falls Power Station). Originally built in 1942, it was commissioned at Ellis in 1981.

The Ellis Power Station is designed to run unattended with the control system continuously monitoring the condition and output of the plant. Access to the power station is via a steel bridge over the Teviot River, built in 1981.