INTER HYDRO TECHNOLOGY

Meadowside Shap Road Kendal Cumbria LA9 6NY

Tel: (01539) 729393 Fax: (01539) 740609 Email: mail@interhydrotechnology.com

Also at: 97 King Street Lancaster LA1 1RH Tel: (01524) 32548 Fax: (01524) 843998

www. in te rhyd ro techno logy. com

Client Private

Consulting Engineers Inter Hydro Technology

M&E Consulting Engineers Inter Hydro Technology

Contract Value £1,000,000

Contract Period 24 months

Roach Bridge Mill has had connections with the same family for generations. The old mill had been sold at the turn of the century and had fallen into disrepair, but Charles and Camilla Hadcock managed to buy it back and set about revitalising the site.

Inter Hydro Technology (IHT) Associate Director Chris Brett has followed the progress of the Roach Bridge hydro project since 2004.

IHT’s parent company R G Parkins & Partners Ltd completed the civil and structural design for the powerhouse and intake.

The original intention was to re-use the old intake channel, which was in good condition. However, to comply with the Environment Agency Good Practice Guide for low head hydro projects an entirely new intake had to be designed and the old one abandoned. The need to develop a large intake led to discoveries about the previous layout of the site. Initial ground surveys, in November 2009, suggested that the banks were largely constituted of sandstone. The new intake features an overspill weir at the river bank which limits the velocity into the intake lagoon when the turbine is operating at maximum flow to around one metre per second. This allows larger fish to swim away from the area and reduces the potential for large river-borne debris to be drawn into the intake. The intake lagoon then increases in cross section, slowing the velocity and allowing suspended solids to fall out. This ensures that water entering the turbine is, as far as possible, free of suspended silts that might otherwise enter it resulting in increased wear.

The intake screens have been designed to make sure that the approach velocity is less than 0.25 metres second, as required by the Environment Agency. There is also

a large bore pipe installed just upstream of the screens to provide any fish that enter the lagoon with the opportunity to return to the main river above the weir.

NHT Engineering of Carrickfergus in Northern Ireland proposed a Kaplan turbine which was ordered once the client had taken up references.

The internal finish on the turbine spiral is very important in terms of giving the best efficiency. Achieving a very good, flat, smooth surface on concrete can be difficult. A simple solution to this was to fabricate a steel liner which effectively became a permanent shutter for the concrete. To give this steel liner an even smoother surface it was coated with an epoxy finish. The proof of this process has been demonstrated as the turbine makes its full output at lower than the design flow, this in turn means that over the course of a year the output will be greater than forecast.

The old tunnel from the turbine discharge back to the river was intact, although badly silted up. The tunnel was sealed at the river and cleared of silt using a mini digger which entered from the turbine pit at the mill. Once cleaned it was dimensionally surveyed and inspected by R G Parkins & Partners, Structural Engineers, to determine what repairs and alterations would be needed in order to make it capable of discharging the proposed turbine flows. Some minor repairs were affected along the tunnel and the river discharge opened up to allow the full turbine flow to return to the river.

ROACH BRIDGE MILL, SAMLESBURY