TrustPower’s proposed Hydroelectric Scheme on the Arnold River is designed to make the West Coast more self sufficient in terms of energy supply.

The 46 MW Scheme (equivalent to a power supply for 27,000 homes) was granted Resource Consents by the Grey district and Westland Regional Councils in November 2008. These Resource Consents have been appealed to the Envionrment Court by TrustPower (seeking clarification of conditions), one commercial tourism operator, and two landowners. The appeals are expcted to be resolved during 2009.

The scheme will divert a proportion of the flow from the Arnold River, via a canal beginning at the location of the existing dam, to a storage pond. The power station will draw water from the storage pond, generate electricity through turbines and then return the water to the Arnold River via canals and a flow regulation pond located on Killeen Island. The Scheme involves diverting up to 100 cumecs (m3/s) of the current water flowing in the Arnold River via the canal to generate electricity. At a minimum, a 12-cumec flow (m3/s) will remain in the affected reach of the Arnold River. The scheme, including canals and ponds is approximately 12 km in length.

Once the new scheme is constructed, it is proposed that the existing power station be decommissioned. However, most of the structures including the tail race canal and pipe bridge will remain, and could become features in a wider visitor attraction associated with the Arnold River Scenic Reserve and Recreational area.  

TrustPower Limited (‘TrustPower’) proposes to develop a Hydro Electric Power Scheme utilising the Arnold River, on the West Coast. The additional energy will assist the West Coast in meeting growing demand and free up power for supply elsewhere in New Zealand. The Scheme is thus of national significance, with national as well as regional benefits.

Water flowing in the Arnold River will be drawn into a canal at the location of the existing dam at the Arnold Reservoir (Volume 2 Figures & Drawings). The minimum flow remaining in the Arnold River will be 12 cumecs. The canal will convey water to a storage pond, which in turn will feed a power station, before being discharged back to the Arnold River via a regulation pond.

The principle resource consents required relate to the diversion and discharge of the Arnold River water, the earthworks required for the canal system, the construction and operation of the power station, and the damming of water for the storage pond.

Other consents are required for associated elements of the Scheme such as culverts, intake structures, structures in rivers, riverbed disturbance and changes to groundwater. (Consents List) 

Any development proposal has the potential for both positive and negative environmental, social and economic effects. TrustPower has strived to ensure that a sustainable balance will prevail in relation to its proposed Hydro Electric Power Scheme on the Arnold River. 

At the outset of project planning, TrustPower sought to establish a communication process which encouraged dialogue and robust discussion between the engineers charged with responsibility for designing the Scheme and the specialist consultants it engaged to evaluate the environmental, social and economic effects of the engineering designs. An on-going and thorough process was instigated which entailed looking at options from all perspectives, providing feedback to the designers, and generating modifications to the design proposals. 

At an early stage, TrustPower initiated communications with a wide variety of potentially interested parties; a process of consultation which continues and which has provided much useful information which TrustPower has fed back into the design process. TrustPower considers that this extensive process of design, assessment and re-evaluation has produced a design for the Scheme which will provide a major new, additional supply of sustainably generated electric power to the West Coast and the national grid. There will also be consequential employment opportunities and secondary (multiplier) economic benefits (primarily to the Coast) during the construction phase. 

The potential environmental, social and economic effects have been thoroughly evaluated in section 6 of the Assessment of Environmental Effects Report (‘AEE’) (Arnold AEE). Where the design details result in potential unavoidable impacts, TrustPowers experts have identified mitigation measures to offset these.

 Additional mitigation measures have been developed in consultation with stakeholders and interest groups. These measures have been accepted by TrustPower - which has committed to their implementation, and which will form an integral part of the construction works for, and operation of, the Scheme. 

Mitigation measures to address what have been identified as the key areas of potential environmental effect are described in Section 4.10 of the AEE (‘AEE’) (Arnold AEE). The principal measures and environmental enhancements relating to these areas of potential impact are discussed below. 

A number of potential effects of the proposed reduced flow regime on fishing and fish populations have been identified relating primarily to trout but also potentially affecting the salmon population. TrustPower has committed to the construction of spawning channels and installing fish screens to stop adult trout and eels passing through the turbines.

TrustPower will also initiate measures as proposed by their freshwater ecology specialist (Dr Greg Ryder) to provide for the release of periodic flushing flows as, and when required, and fence the Killeen Island area to reduce stock access to the Arnold River. 

As the Arnold River is used extensively for recreation purposes, particularly kayaking, it is expected the reduced flows in the Arnold River may have an impact on this recreational use. In order to mitigate potential effects of the reduction in flows so they are no more than minor on rafting and kayaking activities, TrustPower has confirmed that it will commit to the construction of a proposed white water course. TrustPower has also undertaken to modify the riverbed by placement of rocks and the formation of channels to improve kayak passage. Controlled access to the canal is proposed for schools and Kokiri Lodge to enable them to continue to undertake basic kayaking instruction in a controlled and safe moving waterway environment. 

TrustPower and its consultants, Tonkin & Taylor, are working with CMP Kokiri to mitigate any adverse effects on the CMP Kokiri meat processing works. Possible solutions which are being considered with CMP Kokiri include installing a more effective diffuser at the effluent discharge point; and constructing an extended abstraction well system, for its groundwater take. 

The existing Arnold Power Station is to be decommissioned following construction of the Scheme. Elements of the decommissioned power station will be retained as an integral part of an enhanced visitor recreational and interpretation experience. 

Associated structures, such as the existing public toilets and visitor shelter, will also be upgraded as part of the main visitor information and interpretation focus of the Arnold River Scenic Reserve and the TrustPower recreation and enhancement area. In addition:

• The existing car park would be extended and the area will be further developed as the main visitor reception area.
• Associated structures such as the existing public toilets and visitor shelter will also be upgraded as part of the main visitor information and interpretation focus of the Arnold River Scenic Reserve and the TrustPower recreation and enhancement area, which has been designed by Boffa Miskell Ltd.
• The visual and landscape effects of the canal and its associated works between the Arnold Valley Road bridge crossing to the storage pond will be minor following the implementation of landscape enhancement works, which will include additional batter moulding and planting.

Extensive planting will be carried out within this area, which has recently been harvested for timber. Works associated with the intake and canal will be extended to include and create an enhanced and more attractive landscape and recreational setting overall. 

In association with the Department of Conservation, the upgrading of existing walkways, tracks, lookouts and feature areas will be able to be undertaken along with further and appropriate developments and enhancements within the adjacent Scenic Reserve. 

Where vegetation is disturbed, tree removal will be carried out in a manner that enables further planting to be implemented along the disturbed edge in order to re-create a more ‘natural’ appearing forest edge to the remnant stands. Mitigation measures to offset the clearance of high value forest area over the part of the Scheme’s alignment downstream of the power station will include the purchase and protection of forest with equivalent value. The restoration of the canal embankments to a similar indigenous condition (especially the northern side), will also be undertaken. 

A detailed planting programme will be developed and will likely include the planting of manuka, kamahi and coprosma shrubs on the canal earth embankments and other disturbed areas on the northward edge. This will be undertaken to facilitate indigenous ground cover. Such planting will form a dry buffer edge to the existing wetland regenerating forest. 

TrustPower are currently negotiating with property owners, with the objective of mitigating potential adverse effects via a range of options (purchases of property, securing easements, providing temporary relocation during construction activities etc). 

TrustPower has been in contact with the Te Runanga o Ngai Tahu and Te Runanaga o Ngati Waewae from the initial stages of this Scheme. The principal concern of Ngati Waewae is the ‘wellbeing’ of the mauri of waters of the Arnold River. A number of alternative methods by which that might be achieved are being considered by TrustPower. 

A protocol is to be developed should waahi tapu or archaeological sites of significance to Tangata Whenua be discovered. 

TrustPower has, and will continue to, consult with all stakeholder and parties expressing an interest in, or concern related to the Scheme. Wherever possible, practical outcomes from the consultation will be taken on board as part of the Scheme design and implementation. 

The Arnold Valley Hydro Electric Power Scheme will provide a substantial, secure, sustainable source of urgently needed electrical power for the West Coast. The Scheme will bring about change to the valley. Planning and design has focussed on minimising potential adverse effects and maximising potential opportunities. Ongoing consultation will aim to extend these opportunities.