Inchbonnie Hydro Ltd is a private company with 5 shareholders one of which is Greymouth man and Coaster Paul Steegh.

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Roberta Owen
7 years ago
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1 Inchbonnie Hydro Ltd is a private company with 5 shareholders one of which is Greymouth man and Coaster Paul Steegh. This is a project like the Amethyst power station at Hari Hari that has tested the skills of all the Coasters involved. It s another brilliant step towards selfsufficiency in power generation on the Coast. Rubislaw Creek and Johnstons creek flow from catchments high up in the Hohonu range and are ideally suited for hydro power generation. The hydro is a 'run of the river' scheme where water is taken from the stream without the use of dams or storage. The water intakes are situated in the streams and the scheme is designed to have minimal impact on the ecology of the streams and the surrounding flora and fauna. Inchbonnie Hydro owns the land on which the bottom sections of the penstock and the power house will be located. The intakes and the upper sections of the penstock are on DOC land for which DOC has granted an easement. Resource consents for the scheme have been granted by the West Coast Regional Council. Image: The 2 catchments feeding the hydro scheme have a combined area of 11 sq km.

2 The scheme will divert water from both streams through High Density Polyethylene (HDPE) pipelines to the ridge between the two catchments, and then down a steel penstock to a powerhouse on the banks of the Taramakau River. The intakes are approximately 490m above sea level and the power house site is 120m above sea level giving a head of 370m. The total amount of water to be diverted from both streams combined will be up to 700 L/s. A tail race from the power house will deliver the water into the natural watercourse beneath both streams immediately above where they enter the Taramakau river. The hydro will be a Pelton wheel turbine with 2 nozzles. Up to 1700 Kw of power will be generated and will be fed to the high voltage lines nearby. Image: 1.5 MW plant with the generator on the left and the hydro turbine with the 2 inlet pipes on the right.

3 April 2015 Latest update: Six weeks up to the end of April have been spent building the Rubieslaw intake. The first 2 weeks were spent excavating the rock. We decided to move a lot more bedrock than we had originally planned. Especially in removing one big rock that would have impeded the flow off the intake. Our main tools have been a hydraulic breaker/drill and explosives. The hard part was that we had to break up every piece of rock into a size that we could physically lift and carry out of the way. I don't know how many tons of rock we have broken, picked up and carried, but quite few.

4 The weather has held reasonably well and we have only been forced out of the stream for a few days. When it does flood, there is no way we can go near the intake. On those days we worked on the foundations for the settlement tank. The intake consists of an upstream wall 1.5 meters high on average. 700mm downstream of that and 700mm lower we have the downstream wall creating a chamber in between. The coanda screens imported from the UK fit across the top of the chamber. The walls are between 300 and 500mm thick reinforced with 2 layers of 16mm rebar at 200mm centers. The rebar starters are chemset 350mm into the rock with epoxy resin from Adhesive Technologies. The form work was built with 18mm specially surfaced plywood with 100 X 50 timber framing. Once all the

5 framing was in place we backed it up with 2 or 3 rows of whalings per wall. These were connected to another row of whalings on the other side of the wall be a series of she bolts through the wall.

6 We have been very lucky to have John Pugh on the job. He is the go to man on the West Coast for concrete construction on challenging sites. We had to keep pulling the formwork out of the job whenever floods were forecast. Finally we made the big call to leave it all in place and bolt it all up ready for concrete despite a forecast of rain and rely on our diversions to keep most of the water off. The weather window had to be long enough to allow at least 48 hours for the concrete to cure before the next flood event. The intake took 8 cube of concrete lifted in 0.2 cube at a time by helicopter. The latest job has been further rock works upstream of the intake to channel at least 400 liters a second towards the intake before any water flows over the naturally formed ledges bypassing the intake.

7 March 2015 January and February were spent welding together the PE penstock and winching it up into the bush. 2km of PE pipe was delivered from Pentair during January (5 truck loads). Most of it was hauled up the hill with tractor and trailer to the staging point where we set up the welding station. We lifted one truck load up by helicopter. We built a hydraulic winch with a 5 ton pull capability. It's basically a tow truck winch powered run by a 22hp Honda motor powering hydraulics. It weighed 700kg and was lifted into place by helicopter.

8 The 12m lengths of pipe were welded together and the "string" was winched up towards the intakes 12m at a time. There were 5 strings in total. The longest was 490 meters, which had a maximum pulling load of 5 tons as it approached the Johnstons intake. We used a 20 ton tow line from the winch to the pipe guided by a series of heavy duty snatch blocks. The pipe from each intake to the junction is 400mm diameter. From the junction down to the staging point we have used 300 meters of 500mm PE pipe (there will be 750 meters of steel pipe from here down to the power house.

9 Everything was right at the limit pulling the last few meters of the 500mm pipe up. Over 25 tons of pipe requiring approximately 12 tons of pulling load. The winch was straining with a 4:1 purchase in the rope. December 2014 Work was concentrated on the lower sections of the penstock while the particularly wet spring weather was on us.

10 We tackled the very bottom sections of the penstock first as this was likely to be most problematic. This is the steepest part of the penstock with no digger access possible. We dug out the penstock foundations and removed the high points by hand. These lower 20 penstock supports are made up of a pair of steel piles set in approximately 1 cube of concrete each. It took 4 truckloads of concrete lifted into place by helicopter. On the next section up we were able to drive the piles into the ground with a 30 ton digger and a pile driver developed by Steegh Contracting from a rock breaker. This was a great success and the piles are all very solidly wedged into the boulder and glacial moraine ground. The time saving over hand dug concrete supports was considerable and we now have 40 of the 60 supports built.

11 Meanwhile the roads were all surfaced with Taramakau gravel. The lower road to the powerhouse site has been made to a very high standard. The powerhouse platform has been built. This involved removing all the vegetation and clay from the site and then benching out the glacial moraine substrate into 4 levels of solid ground before building it up with heavily compacted Taramakau gravel to a height 3m above the alluvial flats.

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