Waitaha Run Of River Hydro Scheme

On 31st May 2022, Westpower filed a request for reconsideration of the Minister’s decision. The focus of the reconsideration is on the following matters:

• The interests of Poutini Ngai Tahu in relation to the project and the requirement under section 4 of the Conservation Act to give effect to the principles of the Treaty of Waitangi.
• The effects of climate change on biodiversity and public conservation land and resources, and the essential role of renewable electricity generation in meeting our emissions reduction targets and addressing the impacts of climate change on biodiversity and public conservation land and resources.
• The assessment of values including natural character, landscape and recreational values and the potential impacts of the project on those values.
• The approach to legal and planning matters.

The request for reconsideration is supported by new reports on economic viability and climate change and biodiversity, and an updated simulations image that shows the new design of intake portals, which further minimises the effects on landscape (as shown below).

The Waitaha Scheme will produce approximately 110-120 GWh per year with a peak output of up to 20 MW. This is equivalent to providing power to 12,000 households and will service about 25% of the West Coast’s energy needs.

Currently the annual peak demand in the Westpower distribution area is 40.1 MW with up to 25 MW being generated on the Coast by a number of small power stations including the Amethyst run-of-river scheme (7.2 MW). The energy delivered to customers during 2021 was 223 GWh. The load forecasting shows that by 2031 there will be a gradual increase to around 68.935 MW depending on future economic growth.

When considering decarbonisation of the New Zealand economy, three areas have special importance: process heat, transportation, and space heating/cooling. Just the electrification of process heat on the Westpower network will add approximately 50 MW of new load to the network and require 390 GWh of additional energy (this is up to and beyond 2031).

Because the Waitaha generation scheme is run-of-river and not dependent on other fuels, it will displace thermal generation. Assuming annual generation of 100 GWh, this equates to a reduction in CO2 emissions of 100,000 tonnes annually.

The Scheme will benefit economic growth in the region in many ways. During construction of the scheme there will be more obvious direct economic benefits such as employment, the need for local goods and services and the indirect benefits from this. About 20 full time workers would be required during the 3-4 year construction period.

Modern power stations are automated, so once up and running require about 1 full time worker. While an operating scheme has fewer obvious direct economic benefits, the benefits come from economic confidence and resulting development and infrastructure that may result from this. The long term benefits of reduced transmission losses and security of supply underpin the economic benefits.

The scheme will enhance security of supply in the West Coast region, in turn providing potential investors and developers with the confidence to invest in the West Coast region, assured that their energy demands can be met.

There are currently 10 hydro schemes in the Westpower region, and three of these (Amethyst, Wahapo and Fox) are able to start and run isolated during outages. During outages the Amethyst Hydro can provide power to the South Westland area on its own, and as of recently the privately owned Fox Hydro Scheme has the ability to keep on power in the Fox Glacier area. If the Waitaha Hydro Scheme goes ahead, then this locally generated power together with the Amethyst will be sufficient to run all of South Westland, Hokitika and Greymouth, as long as the lines are intact. The Waitaha and Amethyst are big enough to provide a stable source that other smaller power stations on the Coast can synchronise to. This will assist in providing security of supply within the Coast. There is a major benefit for all consumers in having local generation assisting supply should an outage occur.

As a community owned company, any profits made by Westpower are reinvested in the community in a number of ways, one of which is by discounting line charges from time to time. This is a very direct way of sharing profits, and one that we have used in recent years. In 2021 we discounted charges by $5 million.

In addition, there will be a reduction in transmission losses (and therefore delivered energy costs) to the West Coast if we can generate electricity close to its end use.

It is expected that there would only be short periods during low load when power may be exported from the region, and it is not expected to be significant.  Even when it does happen, other parts of New Zealand will benefit from the 100% renewable generation produced on the West Coast.

Like Amethyst Hydro, the Waitaha Hydro Scheme is run-of-river and will also be constructed in an environmentally sensitive manner on the Department of Conservation administered land. Although it will have greater water take and generate more electricity, the Waitaha scheme will also have a small footprint and will use a tunnel to house the penstock transferring water from the intake to the powerhouse. While the gravel settling basin at the Amethyst is on the side of the river, the Waitaha settling basins will be concealed within a tunnel chamber. A brief video that shows Amethyst Hydro can be accessed at the following link: Westpower - Join our CEO Peter Armstrong on his trip down... | Facebook

Amethyst shows how significant advantages can accrue to the local community through small scale run-of-river hydro development. Moreover, as a community owned company, any profits that are made from the scheme are ultimately directed back to the consumers in the area. Westpower expects to apply the same key success factors to the Waitaha scheme.

The Waitaha run-of-river scheme has a relatively low environmental impact, because (unlike dams) there is no storage lake and the water, after being temporarily diverted, is returned to the river and full flow restored.

Results of the field work undertaken to support the initial concession application suggest that the scheme will have very little impact on the ecological values within the area, both terrestrial and aquatic. Further studies subsequently undertaken confirmed the previous findings in relation to the blue duck, long tailed bats and birds and the aquatic ecology (periphyton, invertebrates and fish) as well as providing additional information on the vegetation, lizard habitat and insects within the hydro scheme area.

The potential effects on terrestrial flora, fauna and their habitats were assessed as mainly negligible because:

• the scheme footprint largely avoids significant faunal and floral habitat and
• the footprint size is extremely small compared to the wider environment that supports the same species, often in greater densities, compared with the scheme footprint.

The potential effects of the reduced flow in the river on the aquatic ecology and life bearing capacity of the river were also considered low because the scheme avoids the areas of major concern such as Kiwi Flat, Douglas Creek and the Stable Tributary downstream of this. The selection of an intake and a weir at Morgan Gorge affords protection for koaro which are the only fish found at Kiwi Flat and also provides a barrier to trout. This option also leaves the whio/blue duck habitat intact. Disturbance events will still dominate ecology of river with the scheme in place.

The scheme is designed to have a small footprint and to minimise visual impacts, so there will only be residual effects (once the scheme is operational) related to the presence of the scheme structures and reduced flow within the abstraction reach. While recreational activities can continue, there will be a change in the natural character in the vicinity of the scheme which will alter the experience within that area for visitors. The change in flow in the abstraction reach will reduce the opportunities to kayak the Morgan Gorge and the Boulder Garden between the gorge and the Douglas Creek.

The maximum water take will be 23 cumecs. The water take will vary depending on the flows in the river and the residual flow. When the flow in the river is low, the take will be reduced below 23 cumecs while ensuring the residual flow is maintained.

The amount of water diverted does not have to be at a constant level to run the turbines and generate electricity but there will be a minimum flow at which the turbines can operate effectively and economically.

After consideration of the habitat modelling and aquatic ecological effects as well as the economics of the scheme, a minimum residual flow of 3.5 cumecs has been proposed.

Flows at the top of Kiwi Flat, range from 3.55 to 1,200 cumecs (m3/sec). The Median Flow is 16 cumecs with the seven day Mean Annual Low Flow being about 6.0 cumecs (m3/sec). Refer to the Hydrology of the Waitaha River study: Hydrology Report

Whirling Water contributes to the flow at the top of Morgan Gorge resulting in a seven day Mean Annual Low Flow of about 7.6 cumecs (m3/sec) at this location.

There are on average 42 floods per annum greater than 30 cumecs, the mean interval between flood peaks is 8.6 days, and the average flood duration is 41 hrs.

None. The type of run-of-river scheme proposed has a relatively small construction footprint and small environmental footprint compared to a dam. Westpower is not interested in being involved in developing high environmental impact schemes. There will be no formation of a lake and no submergence of native vegetation as a consequence of this scheme. The following image shows the intake of the Amethyst Hydro as an example:

With a weir and water intake at the top of Morgan Gorge, there will be an initial backwater effect that could extend back upstream to as far as the Whirling Water confluence; this would fill up with gravel (it may only require one flood to do this) and a new equilibrium reached. After this occurrence the riverbed will look similar to what it does now. The river would continue to be subject to natural flood flows. During flood flows and as seen by the levels at which flood debris can be seen in Kiwi Flat a certain amount of backwater flow occurs naturally upstream of Morgan Gorge.

The water would be taken at the top of Morgan Gorge (at the lower end of Kiwi Flat). The full flow of the river is restored below the powerhouse. The length of the abstraction reach is approximately 2.6km. There is approximately a 100 m fall between the intake and the powerhouse.

The weir will be constructed of concrete covered with Cortel steel and span the width of the river. The headworks associated with the weir include a water diversion, and some semi-submerged intake structures. The water intake channel would be built first and would act as a water diversion while the weir is constructed. Temporary stopbanks would be required during this phase of construction.

No, there will be no access road going into Kiwi Flat. Access for construction and maintenance of the headworks will primarily be via the tunnel. Helicopters will also be used and the existing walking track relocated or upgraded. Access to the powerhouse, tunnel exit portal and for construction would be via the existing Waitaha Rd (north bank) across Macgregor Creek and along the north bank of the Waitaha. Westpower would maintain any roading access to the powerhouse after construction. Westpower is unable to provide access on sections of the road that cross private land.

Westpower previously liaised with affected parties to understand what effects the hydro scheme may have on their activities and how these effects can be minimised or mitigated both during construction and once the scheme becomes operational. There have been some specific changes proposed, for example diverting the walking track around the powerhouse, and the following has been offered to kayakers:

• Up to 4 no-take days per year for requests made more than 48 hours in advance;
• Designing a safe entry point for those wanting to run the Morgan Gorge;
• Support kayaking training via Tai Poutini Polytechnic;
• Help with planning by providing hydrological information and access to a web camera.

Westpower has commissioned preliminary geological assessments. More detailed geotechnical investigations including drilling will also be carried out to assess the risks associated with the physical environment that could impact on the proposed scheme.

The river system is naturally subjected to extreme variations in flows. Natural geological hazards include landslides, the potential for an Alpine Fault rupture, and flooding. Under both options, the primary risk of a large-scale landslide is from natural causes, and will not be exacerbated by the scheme. The proposed run-of-river scheme does not have a storage facility so there would be no risk of the weir breaching and swamping the area below the weir and below Morgan Gorge. These risks will be carefully assessed and considered in the engineering designs of the proposed scheme.

Some hydroelectric plants still in full service were built 50-100 years ago e.g. the Kaniere Forks Scheme. With regular maintenance and refurbishment of equipment every 25 years or so there is no reason why this scheme should not be working in 100 years. The river retains its natural course during the life of the scheme.

The project would take approximately 3- 4 years to build from the start of construction.

Westpower’s request for a concession reconsideration was submitted to the Minister of Conservation on 31st May 2022. No public consultation sessions are planned at this stage – Westpower will be awaiting the Minister’s decision. However, any queries regarding the project can be submitted via Westpower website at waitaha@westpower.co.nz