Stockton Plateau Hydro Project

Hydro Developments Ltd (HDL) is seeking resource consents and landowner approvals to build the Stockton Plateau Hydro Project on the tributaries of the Ngakawau River. The river flows to the Tasman Sea at Ngakawau, 31 km north of Westport within the Buller District of the South Island of New Zealand.

The core components of the project are:

• Mt William reservoir will be formed below the confluence of the Plover and Fly Streams on the St Patrick Stream to the east of Mt William. The storage reservoir will inundate an area of approximately 50 hectares.

• Fives streams will be captured and diverted into the Mt William storage reservoir being: T31, Fly, Plover, St Patrick and Darcy streams.

• Weka reservoir will be formed below the confluence of Weka and Sandy Creeks near Tin Town corner and will inundate an area of approximately 28 hectares.

• Five streams will be captured and diverted into the Weka storage reservoir being: Weka, Sandy, Upper Mine, Mangatini and A.J. streams.

• The Stockton tunnel, approximately 3850m long, will connect the Mt William reservoir and the Weka storage reservoir. The Weka Power station will be built at the outlet to this tunnel.

• The Granity tunnel, approximately 4900m long, will connect the Weka reservoir to the ocean outfall at Granity. The Granity Power station will be built just inside the tunnel outlet, located in the hill-side just above and to the north of the Granity Museum. The Granity tunnel will be driven through granite, over 250m beneath the historic Millerton and Old Dip mines.

• An ocean outfall “microtunnel” will be driven beneath the sea bed to intersect a diffuser sunk into the sea bed beyond the wave break zone approximately 600m offshore. The microtunnel will be driven from a pit below Granity Tunnel outlet to the diffuser, passing beneath the railway, state highway, bare land immediately north of Lyric Theatre, road reserve, foreshore and seabed.

Overview

The Stockton Plateau Hydro Project will generate electricity by diverting drainage from the Stockton Plateau through a series of reservoirs, tunnels and power stations to an ocean outfall. The outfall will consist of a submarine tunnel connected to a diffuser built into the sea bed. The point of diffusion will be outside the wave break zone, approximately 600m offshore from the Lyric Theatre and south of Granity Stream mouth. At this point the diffusion will have no significant effect on the marine environment.

The project works will be located between the Ngakawau Ecological Area and the parts of the Stockton Plateau which have historically been the focus of mining activities. Two reservoirs and a number of diversion weirs and tunnels will be built to collect runoff from these areas. The reservoirs will be connected by tunnels driven deep underground. Power generation will occur in two power stations built at the outlets to the tunnels.

Access to the land is under negotiation. The reservoirs, power stations and diversion tunnels will be located on land currently in DOC stewardship. The outlet tunnels will pass beneath land owned by Solid Energy New Zealand Limited (SENZ), the Crown (railway, state highway and foreshore), Northern Buller Communities Society Inc (beside the Lyric Theatre), and Buller District Council (road reserve).

In terms of environmental effects, the reservoirs are the most significant components of the project. These are located beyond public view on areas modified by previous settlement and mining. The diversion tunnels and outfall tunnel will be buried over their entire length and will have minimal environmental effect.

The project is unusual for a hydro scheme in that it is built on the tributaries, not the main course of the Ngakawau River and will result in significant improvements to the Ngakawau River. The project has the potential to intercept 95% of the tributaries of the Ngakawau River affected by mining. This will result in a 17% reduction of the mean flow of the Ngakawau River at the river mouth; however, the reduction in mean flow is unlikely to be discernible. The most obvious change will be a dramatic improvement in water clarity and estuarine ecology. The visitor experience of the Charming Creek walkway which follows the river will be greatly enhanced. Flows over the Mangatini Falls will be reduced in volume but the quality will be significantly improved.

The project will generate in the order of 240 GWhr of renewable energy per year. The drop of more than 555m between the highest reservoir and ocean outfall means that large amounts of electricity can be generated from the relatively small volumes of water that will be diverted from the main river system (4 - 9 cubic metres per second). Harnessing this renewable energy will more than meet the needs of the Buller District and ensure that the West Coast region is less reliant on remote electricity generation.

When fully commissioned, the Project is expected to provide a continuous (24/7) base load in the order of 25MW. Stockton Mine may consume around 8MW. The remainder will be transmitted north to Karamea and south to Westport and beyond.

The Project has the potential to double the baseload output to around 50MW for short periods during and following heavy rainfall.

Resource Consent Applications

Consent applications for the Stockton Plateau Hydro Project were lodged with the West Coast Regional Council and the Buller District Council on the 12 November 2008. Public notification of the consent applications occured on the 12 and 13 December 2008, with the submission period closing on the 30 January 2009.