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CASE STUDY

Esragan Hydro Scheme

The Esragan Hydro Scheme is a conventional 'run-of-river' scheme on the Esragan River, Argyll.  It was developed by Ardchattan Hydro Ltd, partnered by Gilkes Energy Ltd.

The water is abstracted at a 2m high weir and conducted via a 1.5km long penstock pipeline to a powerhouse, giving 90m of gross head.  The outlet is approximately 0.5km North of Loch Etive at Inveresragan.

A wash-over 'Coanda' screen was employed to prevent all but the smallest of sediment from entering the system.  This screen also allows no more than the design flow of 1.2 cumecs to enter the scheme.  At the intake, a fish pass and pool has been provided for the upstream migration of fish.  A secondary intake from a small catchment was utilised on the tributary to the Esragan, the Allt a'Ghlinne.

From the intake channel beneath the Coanda screen, water is conducted through a 1200mm non-pressurised pipe to a header tank.  This pipe runs above ground for about 30m through a semi-dry channel to a buried header tank.

The penstock pipeline is 800mm in diameter, and is buried along its entire length.  The pipe was originally planned to be of GRP, but ground conditions dictated that ductile iron pipe was used, due to its greater strength. Along the main pipe length, a penstock of 300mm diameter joins from the secondary intake.

Throughout its length, the main pipeline is provided with concrete thrust blocks at all significant changes in direction, both horizontally and vertically.  Access to the pipe is provided for cleaning and 'pigging', and a custom designed pig launcher was part of the project scope.

The powerhouse is below ground level in a field adjacent to Esragan River.  It was decided to bury the powerhouse to maximise the available head, minimise perceived noise problems, negate any worries about visual intrusion, and cause minimum impact on the river bank.

The powerhouse contains the turbine, generator, control panels and breaker.  A 400V/11000V transformer and switch unit are located outside.  The turbine installed is a Gilkes Turgo Impulse Twin-Jet Turbine producing approximately 900kW.

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