Outline resource consent application for a hydro-electric development on the Gowan River

This page contains an outline resource consent application for a hydro-electric development on the east bank of the Gowan River. The resource consent application is an annex to the MAJAC Trust application to amend the the Water Conservation (Buller River) Order 2001.

Governing rules, regulations and legislation

  • Tasman Resource Management Plan
    • Part IV Rivers & Lakes (Not yet written)
  • Resource Management Act 1991
    • Section 14. Restrictions relating to water.
  • Water Conservation (Buller River) Order 2000.
    • Schedule 2. Waters to be Protected.

Reason for the need for a Resource Consent:

  • In the absence of a published Part IV of the Tasman Resource Management Plan, Section 14 of the Resource Management Act requires that a Resource Consent by obtained to divert and take energy from the water.
  • Hydroelectric generation is not a permitted activity for the zone.
  • Earthworks for the construction of the diversion canal, penstock, powerhouse and tailrace.
  • Construction within a Conservation Zone.
  • Divert water for hydro-electric purposes.
  • Works in a river bed

Proposal description

Project overview

The proposal is to construct a Run-of-River hydroelectric development on the Gowan River below Lake Rotoroa. This will involve

  • constructing an intake structure on the side of the river
  • constructing a headrace canal and head pond on terraces alongside the river
  • constructing a penstock from the head pond to the power house
  • constructing a 10m by 18m power house at the foot of a high terrace adjacent to the river
  • constructing a tailrace from the power house to the river
  • build a new HT transmission line back to join the existing 110kV line at the Lake Rotoroa outlet

A summary of the salient features of the proposal are:

  • The scheme is proposed on the east bank of the Gowan, entirely on land owned by Majac Trust.
  • When the naturally occurring instantaneous flow of the Gowan is more than 9 cumecs the scheme would divert some of the water from the Gowan into a canal which would carry the water along the east bank for a distance of 4.00km and deliver the water via a penstock through a head of 54.5m to a turbine and generator. The water would discharge via a tailrace to rejoin the Gowan.
  • The intake will be located 2.2km downstream of the road bridge which crosses the Gowan at the outlet of Lake Rotoroa.
  • The outlet will be located 3.5km upstream of the confluence with the Buller River.
  • The intake will be a side-entry design built into the right bank of the river and will involve minimal interference with the natural flow of the river.
  • The whole of the development will be designed to minimise any visual impact on the environment and will be extensively landscaped after construction. Most of the canal is on land currently planted with young pine trees which will entirely screen the canal by the time it is constructed.

Detailed description

The Buller Conservation Order provides for removal of water from the Gowan River as follows:

15% of the water may be taken from naturally occurring flow rates above 9.0 m3/s and 5% below 9m3/s. Normal river conservation practice would define the minimum flow to remain in the river rather than limit the flow that can be taken from the river. This proposal provides that no water would be taken from the Gowan for naturally occurring flow rates below 9.0 m3/s. At flow rates above 9m3/s, it is proposed to divert water for hydro purposes in accordance with the attached river management programme.

Natural River Flow
(cumecs)
Divert for Hydro
(cumecs)
Modified River Flow
(cumecs)
4.5 -- 4.5
9.0 -- 9.0
13.5 4.5 (minimum) 9.0
18.0 9.0 9.0
22.5 13.5 9.0
27.0 18.0 9.0
31.5 20.5 11.0
36.0 23.0 13.0
40.5 25.5 15.0
45.0 28.0 (maximum) 17.0
49.5 28.0 21.5
54.0 28.0 26.0
58.5 28.0 30.5
63.0 28.0 35.0
67.5 28.0 39.5
72.0 28.0 44.0
76.5 28.0 48.5
81.0 28.0 53.0

The Buller Conservation Order allows 5% of water to be taken from the lowest naturally occurring flow in the Gowan River.

A request has been made to the Minister of Environment to vary the Order in respect to the Gowan to allow flows consistent with this river management programme.

Under the existing Order the permitted minimum flow is:

Lowest recorded Natural Flow 4.60 m3/s
less 5% 0.23 m3/s
Permitted modified flow 4.37 m3/s

The proposed modified river flows provided in this proposal allows for the cycles that occur naturally and would not result in flows as low as are permitted in the existing Conservation Order.

The Gross hydraulic head proposed for the plant is 55.0m, being the difference between the head pond level at 434m and the tailrace level at 379m. Losses due to intake screen and gates, outlet losses etc are estimated at 0.50m leaving a net head available at the turbine of 54.5m. The flow rates proposed involve diverting a maximum of 28m3/sec of water from the river for hydro generation. On this basis the maximum gross power output at the turbine shaft is 14.00MW.

The efficiency of conversion of this energy to electrical energy varies according to the water flow with a maximum of 97%, giving a the maximum electrical power output at the powerhouse is 13.6MW. There will be transmission losses which will reduce this to around 13.0MW of metered power production.

Normally the plant will operate unattended. Mechanical components for the scheme include

  • Two radial gates, 3.2m wide by 1.8m high, to control flow into the canal.
  • an intake debris screen
  • Hydraulic vertical lift, wheeled penstock intake gate 4.0m wide by 4.0m high.
  • A penstock intake screen and screen cleaner.
  • Steel penstock which trifurcates to three penstocks at the Power House.
  • Three horizontal Francis Turbines with synchronous generators, each rated at 4.55 MW nominal housed in a 12.0m x 18.0m Power House building.

From an analysis of the river flow records, the cumulative output available from the scheme is approximately 60,000,000kW hr of electricity in an average year This could vary up or down by 25% in any particular year.

Assessment of environmental effects

The scheme proposed is a typical Run-of-River open diversion channel scheme which does not involve any damming of the river. No water is consumed in the process and no change is made to the quality of the water.

The proposal will cause a reduction in the flow in the 4.0 to 4.5km stretch of the river between the intake and tailrace. As such there is a need to consider any affects that this may have on the ecology of the riverbed, the geological stability of the adjacent land and existing recreational uses of the river.

We present this assessment in three parts. Part A deals with the physical aspects of the proposed scheme, Part B deals with the effects of the scheme on the Gowan River and Part C refers to the specific requirements of the Buller Water Conservation Order.

Part A - Effects from the physical aspects

Intake

The intake has been designed and positioned at a point on the river which will minimize alteration to the existing topography. The intake is a side-entry construction on the east bank of the river located at the downstream end of a deep pool on a stable bend in the river. The river bank is two metres to six metres high at this point with large boulders and rocks typically 0.2m to 1.0m in diameter.

The intake structure will be a reinforced concrete vertical wall of varying height up to 4.0m and curved in plan to a shape similar to the natural riverbank. The abutment between the wall and the bank will use the boulders set in concrete to provide a natural transition. The overall length of the wall is approximately 100m. The concrete finish on the wall facing the river will be "exposed aggregate" to blend with the naturally occurring gravels and stones which make up the river bed.

A stop bank will be constructed at the downstream end of the intake structure. This will be formed and landscaped in a similar appearance to the naturally occurring river terraces.

The intake structure will not be visible from the road. It will be visible from the opposite bank of the river and will appear as an exposed aggregate concrete surface similar in height and form to the existing river bank and terraces and blending with these at each end. The structure will be evident as a small intrusion in the scale of the landscape and the visual effect will be minor.

The scheme uses the river bed to maintain the water level in the existing deep pool at the intake. The intake wall is aligned to the natural river bank so as not to intrude into the natural flow of the river. There is no plan to change the river shape or bed but some of the boulders may be anchored in place with concrete to stabilize the bed at a uniform level. The natural course of the river will not be affected after construction and the effect of setting of these rocks will be minor.

The intake will require a temporary diversion of the river flow during the construction. This will be done at a time of seasonal low flow and will reduce the width of the river by approximately 15%. The effect of this will be short term and minor and will not impede the natural flow. Rafting will still be able to occur safely during the construction phase.

The Gowan River has a relatively uniform flow regime and a stable river bed. However movement of the river bed over time may require periodic minor rearrangement of the bed material in order to maintain the water level in the deep pool. It is anticipated that this maintenance work will be infrequent and minor and will not impede the natural flow or affect safe rafting during maintenance works.

Head race canal:

The head race canal has been designed and positioned to follow the naturally occurring river terraces. The first section follows a former river channel and will require minimal earthworks.

Earthworks will be required to varying degrees along the balance of the length of the canal and these will be shaped, trimmed and planted in a similar form to the existing landscape such that the embankments will be visually indistinguishable from their surroundings once the replanting is established. All of the earthworks will be subject to detailed geotechnical and engineering design to ensure that a safe stable construction results.

The canal structure will be a trapezoidal shape 3-4m wide constructed with an insitu reinforced concrete base and precast concrete side walls. All structure will be below finished ground level.

The majority of the canal will be constructed through an existing exotic pine plantation entirely on the applicant's land. Remaining sections will be planted after construction of the headrace canal. The trees are presently 3.0 to 6.0 metres high. During formation of the canal, some of the trees will be removed and replanting will occur following completion of construction. Once the replanting is established, the canal will not be visible except from above or from the applicant's property.

The effect of this canal when considered in the scale of the surrounding natural landscape will be minor.

Head pond, intake gate & penstock:

The Head Pond is a continuation of the head race canal and will be formed in a naturally occurring basin using an earth bund to form the pond at the required level.

The Intake Gate is below the level of the head pond bund.

The Penstock will be 4.0m diameter steel tube generally following the natural slope of the river terrace down to the Power House, mounted on reinforced concrete anchor blocks. The Penstock bifurcates into two just before the Power House. The upper section is on a raised formation and the lower section is excavated below natural ground level. The Penstock and its supporting structure will be partly visible from the road and across the valley and will be painted an earthy grey/green to merge with the landscape. As the exotic pine forest develops it will screen the penstock from view.

The effects of these structures in the scale of the natural landscape will be minor.

Power house and switchgear:

The Power House and Switchgear will be constructed at the base of the river terrace using reinforced concrete construction, largely below ground, with the limited superstructure above ground, painted an earthy grey/green to merge with the landscape.

The construction of the Power House and Switchgear will be lowered so that the water from the turbine will discharge at a level to match the river level. The excavation for this will be battered to profiles similar to the natural river terraces. This lowering of these structures will make them difficult to see from the road, particularly when the exotic pine forest has developed.

The effect of these structures in the scale of the natural landscape will be minor.

Tailrace canal:

The first section of the tailrace canal is an extension of the Power House construction and will be below ground level. The tailrace continues as a below ground cut-and-cover construction across the valley floor to within 150m of the river.

The tailrace emerges from below ground into a head wall and side wall rectangular concrete section for a further 50m. A security screen is provided at the exit point from the below ground construction.

The rectangular concrete section becomes progressively trapezoidal over a further 50m as the tailrace approaches the river, forming a more natural cross section.

The final 50m to join the river is formed using river stones embedded in concrete, with a cross section similar to the natural river bed.

The re-entry point to the river is on the inside of a bend. Any rafting is likely to be on the outside of the bend and the effect on rafters of the confluence of the tailrace with the river will be minimal.

The tailrace will be almost entirely below ground in pine plantations. It will be visible where it joins the main river flow from the opposite bank and will appear as a natural river channel.

The effect of this construction in the scale of the natural landscape will be minor.

HT power lines:

The power generated will be conducted through HT lines on pylons to the existing 110kV lines which presently pass over The Applicant's property. These lines will follow a route behind the canal entirely on The Applicant's land. They will be visible in the distance from the road in parts but will not introduce a new visual element into the landscape, as transmission lines and pylons are already visible overseeing the Applicant's property and adjacent native forest lands.

The effect of these additional power lines in the scale of the natural landscape will be minor.

In summary we consider it is necessary to view the effects of this scheme in the context of the scale of the natural landscape as it has been modified. The Gowan Valley is a U-shaped glacial valley formation with mountains rising to 500m above the valley floor which has a width of approximately 1 km. It has a mix of native bush and scrub, exotic pine plantations, farm land and farm structures, roadlines, power pylons and transmissions lines. The elements of the proposed power scheme are very small in the context of the surrounding landscape and being entirely on The Applicant's land, cannot be approached or viewed closely by the public. Whereas they will be apparent in glimpses, they will not intrude into this landscape and their effect will be minor.

Part B: Effects on the river environment

Hydrology:

Flow data for the Gowan River has been recorded consistently over the period 1934 to 1991. A summary of these records is provided in Appendix A This provides the basis on which the flow regime for the power generation has been developed. These flow recordings are no longer being kept regularly and it is intended to re-establish these recordings at the lake outlet and at the proposed intake location as soon as possible to provide reliable data and a means of planning the operation schedule for the plant and monitoring the water diversion for the scheme.

There will be no effect on the hydrology of the river for naturally occurring flows up to 9.0 cumecs as no water will be diverted in this range.

For naturally occurring flows in the range 9.0 - 45.0 cumecs there will be reductions in the flow over the 4.0 - 4.5km section of the river of between 60% and 30% and the reduced flow will be in the range 9.0 - 17.0 cumecs. These resulting reduced flows are no different from naturally occurring flows other than in their frequency and distribution throughout the year.

For naturally occurring flows in the range 45.0 - 81.0 cumecs there will be reductions in the flow over the 4.0 - 4.5km section of the river between 30% and 60% and will be in the range 17.0 - 53.0 cumecs. These resulting reduced flows are no different from naturally occurring flows other than in their frequency and distribution throughout the year except that it will have the effect of reducing peak flows, i.e. maximum flows for this section would be 53.0 cumecs, not 81.0 cumecs. This reduction is likely to lessen flood damage and lead to a more stable river bed.

There is an effect on the hydrology of the river under this proposed regime on a particular day, but it is minor on the annual cycle and hydrology of river flow.

Rafting:

The Buller River is used intermittently by commercial operators and the public for rafting. The Gowan River, as a tributary to the Buller, provides a significant component of the total flow of the Buller in the vicinity of their confluence. It was this contribution by the Gowan to the flow of the Buller which was used during the drafting of the Buller Conservation Order as the main reason to limit the taking of water from the Gowan to 15%.

Clearly this proposal has no influence at all on the flow of the Buller at its confluence with the Gowan, as the water from the proposed hydro scheme is returned to the Gowan some 3.5km upstream of the confluence.

This section of the Gowan River is also used occasionally for rafting by commercial operators. It is a difficult stretch of river for rafting and it is only used when the flow is suitable. Rafting was abandoned for a period due to the danger of willows, but we understand it has recently been recommenced on a limited basis.

The importance of this activity has been recognised through the Buller River Conservation Order which sets out to protect rafting through imposing restrictions on the taking of water to:

For naturally occurring flows up to 9.0 cumecs - 5%
For naturally occurring flows over 9.0 cumecs - 15%

This application has regard for the objectives of the Conservation Order.

Firstly, it has no impact on rafting on the Buller River.

Secondly, the proposed scheme would operate via a sophisticated monitoring and control system which would respond to the naturally occurring river flow and automatically open and close water control gates to ensure the water diverted from the river remained within the prescribed regime. This control system would function on a "fail safe" basis so that in the event of a fault, no water would be taken from the river.

This control system is capable of being activated remotely by means of a telephone signal. The Applicant will provide to all rafters the means to reduce the amount of water diverted for hydro purposes for a period of time so that the flow of water in the river can be idealised for the rafting experience if desired. This will operate as follows:

  • A notice will be displayed at the raft launching point adjacent to the outlet of Lake Rotoroa, fitted with a telephone.
  • Rafters may use the phone, which will be permanently connected, to dial the 24 hour alarm monitoring company which will receive a call at any time.
  • The monitoring company will phone the automatic hydro control centre and enter a code to initiate a controlled shutdown of the hydro plant and restore full river flow for 2 hours or longer for large parties.

By this means The Applicant has regard for the intention of the Conservation Order and is providing:

  • A better regime than the Conservation Order for up to 9.0 cumec flows
  • The opportunity to idealise flows for rafting in the mid range
  • The opportunity to raft this section of the Gowan River in higher flows than would occur under the Conservation Order

The effect of this proposal on rafting is beneficial when compared with the naturally occurring flow or the modified flow recommended by the Conservation Order.

Rapid River Rafting Ltd is currently the only known commercial rafting operator using the Gowan River and its agreement to this proposal is appended.

Fishing:

The Gowan River has been studied and reported on by Jowett et al and the Cawthron Institute in considerable detail. Copies of these reports are attached in Appendices 2 & 3.

These reports find that the section of river from the lake outlet for a distance of 800m downstream is a sensitive breeding area, but below this the river gradient steepens and the water depths and velocities are less suitable as a trout habitat. The intake for this proposal is 2,200m downstream of the lake outlet and accordingly well clear of the sensitive area.

These reports find that the minimum recommended river flow is 3.75 - 4 m3/sec and that flows up to 9 - 15m3/sec provide an ideal trout drift feeding habitat. This proposal does not affect flows up to 9.0 cumecs, but it does extend the periods of time for which the river flow is in the range 9.0 - 15.0 cumecs.

This proposal will also limit flows in the river during flooding, which will reduce damage to the trout habitat resulting from flooding.

The intake to the scheme will be screened to prevent fish from entering the canal. Fish will not be able to enter from the downstream end. The natural river will always have sufficient water flow to allow safe passage for fish.

The section of the river which is affected by this proposal is difficult to fish. The upper reaches from the lake outlet down to the intake for this scheme is the preferred section of the river for fishing.

The effect of this proposal is beneficial to fish habitat and minor to fishing in the river.

Ecology:

The ecology of the river is unaffected by this proposal for flows up to 9 cumecs. In this respect this proposal is more favourable to the ecology than the Draft Conservation Order which permits 5% to be taken from the lowest flows.

The diversion of water in the 9-45 cumec range changes the frequency and distribution of flows in the river, but does not change the flow beyond the naturally occurring flows.

The diversion of water in the 45-81 cumec range reduces the peak flows and may avoid ecological damage caused by flooding while still allowing the effects of the natural river cycle to occur.

The effect of this proposal on the ecology of the river is minor.

In summary this proposal sets out to balance and preserve the sensitive conservation interests of the Gowan River with an economically viable low impact run-of-river hydro scheme in a way which meets the objectives of the Draft Conservation Order and contributes environmentally friendly renewable energy to New Zealand's national grid.

Part C: The Buller Water Conservation Order

The Buller Conservation Order is a wide ranging Order which deals with various aspects of the flow of this river and its tributaries.

The section concerning the Gowan River states:

(i) Subject to subclauses (ii)-(iv) below, any change in flow shall not be greater than 5% of the naturally occurring instantaneous flow.

(ii) Any change in flow of that part of the Buller River mainstem between map references M29 537 350 and the confluence of the Buller and Maruia Rivers shall not be greater than 15% of the naturally occurring instantaneous flow.

(iii) Any change in flow of that part of the Buller River mainstem between the confluence of the Buller and Gowan Rivers and map reference M29 537 350 shall not be greater than 10% of the naturally occurring instantaneous flow.

(iv) Any change in flow of the Gowan River shall not be greater than 15% of the naturally occurring instantaneous flow whenever that flow is 9 cumecs or more, except than whenever that flow is less than 9 cumecs any change shall not be greater than 5% of the naturally occurring instantaneous flow.

The flow restrictions imposed on the Gowan River exist only for rafting. In this regard it is the contribution of the Gowan to the flow in the Buller which is of greatest value, as the Buller is much more popular for rafting than the Gowan. This scheme has no effect on the flow in the Buller as the diverted water is returned to the Gowan 3 - 5km upstream of the confluence with the Buller.

Variations to the detailed provisions of the Order are able to be granted by the Minister of the Environment. Application has been made requesting that the wording of the Order be changed to:

Amend Clause 8(3)(c) to read:

(c) Any change in flow permitted at the confluence of the Buller and Gowan Rivers, item 11 of Schedule 2 must not be:

(i) greater then 15% of the naturally occurring instantaneous flow whenever that flow is 9 cumecs or more; or

(ii) greater than 5% of the naturally occurring instantaneous flow whenever that flow is less than 9 cumecs

Add a new clause 8(3)(d) to read:

(d) No diversion shall occur in the Gowan River within 2km of either Lake Rotoroa or the confluence of the Buller and Gowan Rivers and otherwise diversion may only occur if:

(i) The naturally occurring instantaneous flow is 9 cumecs or more;

(ii) The full naturally occurring instantaneous flow is able to be restored by telemetry controls from time to time to protect its rafting amenity for periods of no less than one and a half hours."

The reasons for approving this variation are:

  • Altering the wording of the Water Conservation Order to provide for the proposed development will both allow a hydro-electric power scheme to be developed adjacent to the river while avoiding any material impact on rafting by giving rafters control to divert only excess flows which exceed flow rates desirable for rafting.
  • The needs of the community and of primary and secondary industries for more secure electricity supplies, particularly in the top of the South Island, are such that low impact diversions of this nature to produce electricity are in the public interest.
  • The Water Conservation (Buller River) Order 2001 protects the Gowan River only for the purposes of rafting and for no other purpose - see Clause 6(a) and Item 10 Schedule 2 of the Order.
  • This change will allow this hydro scheme to be assessed against the amended wording of the Buller Water Conservation Order.

Iwi consultation:

Full Iwi consultation will occur with the interested parties. Currently there are discussions between Ngati Apa, Ngati Rarua, Ngati Tama, Te Atiawa and Ngati Toa regarding Iwi concerns in this area and it is intended to invite all parties to a meeting in Motueka for full consultation on this scheme and any Iwi issues arising from it. This will be done after the Buller Water Conservation Order variation has been considered by the Minister and before an application is made for a Resource Consent. Ngai Tahu will also be informed of the proposal.

Obtaining the full outline resource consent application

The following material is only available as paper copies:

Resource Consent Application form

Appendix 1 Gowan River Flow Records

Appendix 2 Jowett Fishery Report

Appendix 3 Cawthron Institute Fishery Report

Appendix 4 Iwi Consultation

Appendix 5 Rapid River Rafting Letter

Appendix 6 Title Plan

Please contact Steve Merito on 03 963 3771 if you would like a complete copy of the Outline Resource Consent application.

Reviewed:
06/01/09