SUMMARY
Location: Backbarrow, Lake District National Park, Cumbria
Rating: 400kW
Turbine: 3x Ø750mm inclined propeller type, 510rpm
Average available head: 4.8m
Design flow: 3.33m3/s per turbine
Year of commissioning: 2000
OVERVIEW
The Backbarrow site is located 3km downstream of Lake Windermere in the Lake District National Park. The site has historically been used to harness hydropower. Prior to this installation, there was a grid-connected 65kW Gilkes horizontal Francis turbine.
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Forebay with head level sensor
viewed from upstream
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racks and forebay with sluicegates in background
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Powerhouse dressed in local materials,
trash flushing channel also viewable
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Control panel located in powerhouse
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The scheme utilises water from the River Leven and is in a scenic and therefore sensitive location. The river also provides considerable revenue generation through salmon fishing. Furthermore, part of this site was a Scheduled Ancient Monument, which meant that both English Heritage and the Industrial Heritage section of the Lake District Planning Board were consulted during the planning process, as well as the Environment Agency. Great consideration was given to the environmental design of the scheme and specific requirements regarding visual impact and fisheries protection were incorporated into the design.
DESIGN ASPECTS
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The existing works provided the basis of the new scheme. Some excavation was needed for the powerhouse and tailrace. Additionally, the downstream channel was made to meander and large boulders were added to create eddies and pools that would contribute to a more ecologically friendly environment.
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The design uses 3 inclined propeller turbines: one machine can operate with variable-flow, with the other two being unregulated machines. With this arrangement, the regulated turbine T1 runs continuously and T2 and T3 run when there is sufficient flow.
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Power output is controlled by a head level sensing system. This controls the operation of T1 to fine-tune the system so that the headwater always remains above a certain minimum level.
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The turbines are shut down by butterfly valves at each inlet.
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Direct coupled 500rpm generators were used to avoid the need for speed-increasing systems and their associated maintenance and costs.
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The powerhouse was located below river-bank level so as to be invisible from upstream. The building was ‘dressed’ in local materials used for similar existing structures.
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Directly upstream of the turbine intakes, three Trashclean© racks were installed each having its own cleaning rake. The site has a history of high levels of weed and other debris.
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A Bio-Acoustic Fish Fence (BAFF) was built into the existing forebay to guide approaching fish into a bywash, so ensuring that fish could bypass the turbines.
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An eel guide and escape sluice were also incorporated into the forebay, operated by a gate valve.
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The turbine draft tubes were positioned so that the exit flow would provide an attraction flow for upstream migrating fish, drawing them towards the fish-pass.
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The draft tube exits are shielded by Electroscreens©, an innovative electrical barrier which deters migrating fish from attempting to swim up the draft tubes.
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Three propeller turbines in the powerhouse
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BAFF and fish bywash can be seen in the forebay
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Turbines were installed through a removable roof opening
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Eel pass gate valve and trash racks viewed from intake
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