13. West Coast Region
13.1 Catchment #14: Grey
This catchment has:
- an existing hydro-electric power station (Arnold),
- no controlled lake storage.
Table 24: Hydropower Opportunities in the Grey Catchment with High to Medium Confidence of Proceeding in the Next 20 Years.| Name | MW | Average Energy Production (GWh p.a.) | Public Reference |
| Rough River | 11 | 49 | RSML 1985-2 |
| Upper Grey (a) | 7 | 31 | RSML 1985-2 |
| Upper Grey (b) | 10 | 44 | RSML 1985-2 |
| Upper Grey (c) | 35 | 153 | RSML 1985-2 |
| Upper Grey (d) | 18 | 79 | RSML 1985-2 |
| Lower Grey | 210 | 920 | NHRA 7 |
| Dobson | 60 | 270 | TPL 2003-2 |
13.1.1 Rough River
The 30km long Rough River lies on the eastern side of the Paparoa Ranges joining the Grey River about 3km below Ikamatua. Its long narrow valley was shaped by glacial action but is now clad in bush up to 1000m.
A small hydro scheme could be constructed with an intake immediately below Mirfin Creek and 10km above the Atarau Road bridge. A race would run approximately 8km from here through outwash gravels on the true right to gain 65m head above a powerhouse site on the river flats 2km above the bridge. The first section of race is an easy sidle onto a wide terrace where some short term storage could be provided.
The mean flow from the 124km² catchment is estimated to be 15.8m³/s. This would lead to an installed capacity 11MW, giving approximately 49GWh p.a. (50% plant factor).
13.1.2 The Upper Grey
The schemes on the Upper Grey include three river intake and race sites and a dam site.
The first intake site lies 2km below the confluence of the Blue Grey and the Upper Grey about 20km south-west of Springs Junction.
From the intake site a race about 6km long would follow the contour on the true left bank to a point above the Grey where it swings north-west.
The estimated mean flow at the intake is 12.9m³/s from the 192km² catchment. The mean flow is 17m³/s. The installed capacity would be 7MW, giving approximately 31GWh p.a. (50% plant factor).
The second intake site would be on the section of the Grey between the Tass River and the Gentle Annie Gorge.
This scheme is similar to the first scheme with a race running about 6km along the toe of the hill on the true right to a point just short of Snow Creek where 30 m head is obtainable.
The estimated mean flow at the intake site is 28.9m³/s from the 402km² catchment. The installed capacity would be 10MW, giving approximately 44GWh p.a. (50% plant factor).
The third site on the Grey lies at the lower end of the Waipuna Gorge where the high granite walls would enable a dam of around 75m height to be constructed creating a reservoir back through the gorge and over the lower end of the river flats above to approximately the 250m level.
The estimated mean flow at the dam site is 38.3m³/s from the 540km² catchment. An installed capacity of 35MW would give approximately 153GWh p.a. (50% plant factor).
The fourth and lower of the schemes on the Upper Grey is a further river intake site in a small granite outcrop through which the river passes about 6km downstream of the Waipuna Gorge. From here a race would follow the 150m contour 9km along the terraces and terrace faces on the true left to gain 30m head at the confluence of the Grey and Waipuna Rivers just south of the Ikamatua.
The mean flow at the intake site is estimated to be 48.6m³/s from the 642km² catchment. The installed capacity would be 18MW, giving approximately 79GWh p.a. (50% plant factor).
13.1.3 Lower Grey
A large scale scheme of around 210MW (approximately 920GWh p.a. at plant factor of 50%) appears feasible at the head of the Brunner Gorge near the settlement of Stillwater. This scheme could consist of a large dam impounding water to a height of 50m. This opportunity has been recognised for many years although no significant investigations have been undertaken. Such a dam would have significant flood mitigation effects8. The output of this allows for diversion of the Arnold as proposed by the Dobson scheme.
For this scheme, a dam would be located upstream of Brunner connected to a powerhouse on the left bank near Dobson by a short length of forebay canal and penstocks.
13.1.4 Dobson
Flow from the Arnold River would be diverted at the existing Arnold Dam through a canal to a storage lake in the Stillwater Creek catchment of the Kaiata Range behind Dobson. Water will be conveyed from the storage lake through the Kaiata Range via a tunnel and penstocks to a new power station at Dobson.
The estimated 60MW peaking station would generate about 270GWh electricity annually (plant factor about 50%). It would not only give the West Coast self-reliance in electricity but also allow the export of surplus power to Nelson and Marlborough.
Possible Interest - TrustPower (owner of Arnold Power Station)
13.2 Other Opportunities in this Region
From a hydro-electric perspective, with a high rainfall and hilly terrain with little coastal plain, the West Coast has flows and head suitable for electricity generation.
However, catchments are very "flashy" meaning that the ability to gain a high level of reliable generation is likely to be very expensive and there is limited opportunity for storage.
At least two of the existing power stations utilise the storage available in lakes in the area. They are the Arnold, on the Arnold River that flows from Lake Brunner (Moana) and Dillmans that uses the flow from Lake Kaniere.
Along with other opportunities that are restricted by the Buller River Water Conservation Order (WCO) (but not so in the case of the Grey River WCO) there are a significant number of catchments where opportunities have been identified, but the uptake is limited because of the cost etc of building transmission lines to connect them to the grid. Some of those opportunities are more suited to local community supply but are listed here for information.
However, there is also the issue of the limited transmission capacity from the Canterbury and Nelson regions to the West Coast. Transpower has identified this as a key issue [AMP 2000/01] and identified that one option is to increase the generation in the area.
13.2.1 Prohibited
#6 Buller catchment (Water Conservation (Buller River) Order 2001)
Upper Buller
Nardoo Creek - 5MW
Fyfe River - 6MW
Lake Matiri / Matiri - 20MW
Stony River - 7MW
Gowan River - 15MW
The National Water Conservation (Grey River) Order 1991 is not considered to affect opportunities.
13.2.2 Undefined
#64 Haast - Zeilian Creek - 9MW
#145 - Moeraki - Moeraki River - 9MW
#155 - Wanganui - Amethyst River - 8MW
#168 - Waitoto - Te Naihi River - 9MW
#261 Taramakau - Taipo - 33MW
#320 Matatahi River - 9MW
#671 Lake Rochfort - 6MW
#261 Waiho / Tartare River - 6MW
#552 Waimangaroa - 22MW
With the high flow in Westland rivers there are opportunities for micro hydros in many locations. This is a tradition of the area that could be re-established through the use of modern control technologies.
Back to Top