LOW WOOD HYDROPOWER REFUIRBISHMENT, HAVERTHWAITE, CUMBRIA the likely design flow. The two aspects were interlinked, but the available flow to the turbines would clearly be dictated by the capacity of the existing mill race. To establish this, a series of cross sections were surveyed and a computer generated ISIS model built to estimate the theoretical capacity of the channel.
Client Low Wood Products Ltd Principal Contractor J N Bentley Ltd Consulting Engineers Inter Hydro Technology
Over an extended period a range of upgrade options were investigated, including pre-cast concrete lining of the channel and synthetic liners in an effort to find a cost effective means of increasing the hydraulic capacity, and ultimately design flow, to the proposed turbines. The ISIS model was central to this work, and ultimately a limited scheme of channel lining was decided upon, with some re-grading of the bed slope, and widening of the channel at the right angled bend where the historical mill race was extended in 1952 to increase the capacity to 8.0m³/s. The re-grading proposed will focus on removing high spots of gravel which have been created by fish spawning in the channel.
Architect N/A M&E Suppliers Spaans Babcock Ltd Contract Value £1,300,000 Contract Period 2011
The Low Wood hydropower refurbishment presented a number of unique challenges in the design and licensing process, and has been under consideration for approximately four years prior to construction work commencing in 2011. Much of the early work centred on selecting the most appropriate turbines or use at the site, and also establishing
Once this process had determined the available flow, a number of turbine options were investigated in order to identify the most economical solution. Francis turbines, Kaplan turbines and Hydrodynamic Screw turbines were considered, but ultimately the Hydrodynamic Screw was selected. One of the primary drivers for this was the fact that fish can pass down through these turbines without harm.
This was perceived as a particular benefit, particularly by the Environment Agency, as at present, any fish entering the mill race, and any young which hatch there, are unable to swim upstream out of the mill race and are consequently killed passing through the existing turbines. Any new Francis or Kaplan turbine installation would therefore have required elaborate and expensive screens to prevent this. Once the turbine type was identified, Spaans Babcock were selected as preferred suppliers after discussions with a number of firms, and the designs currently being implemented were developed by Inter Hydro Technology around two Spaans Babcock turbines. Believed to be the largest hydrodynamic screw turbines in Europe at 16.2m long, they are self supported, and when operational with the proposed design flow of 4.0m³/s, each turbine will exert a vertical load of 766kN (78tonnes) and a horizontal force of 250kN. To support these loadings the reinforced concrete structure is by necessity complex. A photograph of one of the hydrodynamic screws in production is included above. th
Work began on May 16 2011, and is scheduled to finish in mid November 2011. The Principal Contractor is JN Bentley Ltd of Skipton, North Yorkshire and at the time of writing works are on programme.
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