Garnetts Mill Hydro Electric Project
Overview
Garnett’s Mill is a Hydro-electric project twin SPAANS Archimedes Screw Turbine constructed on Otley Weir in West Yorkshire. It is located on the southern bank of the River Wharfe on the site of an old paper mill weir. The Project was developed alongside a number of residential buildings, a visitor centre and café / shop which were constructed by Barratt Homes. Lowwood Products Co Ltd (“Client”) acquired the leasehold rights to the Project Co Ltd (“Client”) acquired the leasehold rights to the Project and obtained agreement with Barratt Homes to utilise the site areas and supply electricity to the development.
The turbine house holds two 3.7m diameter screw turbines and electromechanical equipment, including the gearbox, generator, control system and transformer.
The installation is connected directly to the housing development via a private grid network to supply the development and surrounding areas, subject to demand and generation levels. The scheme, which was rated at 350 kW (175 kW per screw) and provides an annual energy output of 1,011 MWh. This is sufficient to meet the average annual electrical usage of 290 UK homes, with an annual CO² saving of 450 tonnes in comparison to imported grid energy.
EWCE were contracted to construct all civil related elements of the project and interfaces with the mechanical and electrical contractor for the supply and installation of the Archimedes Screws and associated generator and electrical equipment.
The Works
The scope of the work comprised of:
- Obtaining necessary permissions for working in river including Temporary Flood Defence Consent from Environment Agency
- Creation of cofferdams to enable excavation and construction of foundations
- Construction of concrete intake and outfall structures for two Archimedes Screw Turbines (provided and installed by the Mechanical & Electrical Contractor)
- Construction of a three-stage Larinier Fish Pass that promotes upstream migration, along with a baulk fish pass located at the opposite end of this weir. This allows fish to move more quickly past the weir, which had been an impassable barrier for most species. The existing weir had provided insurmountable barriers for upstream fish migration on the River Wharfe
- Construction of Coarse Debris Screen
- Building turbine house for housing generator and associated electrical equipment (provided and installed by Mechanical & Electrical Contractor)
- Fill and finish riverbank
- Temporary works, including provisions and removal of crane support pads to install/remove screws, temporary access provisions and support of existing weir
- Installation of overhead gantry crane
- All finishes (fixtures and fittings) to the turbine house necessary to carry out the work, surface finishes and footway regeneration
Key Challenges
The Wharfe is ecologically important populated by a wide range of coarse fish, European eels and salmonids together with otters and attendant fish eating birds, so prevention of silting during construction was imperative.
The site was surrounded by a Barratt residential construction site so there was a requirement to coordinate construction activities with them and their sub-contractors.
This was a very challenging project with extreme weather conditions in the winter causing major flooding of the River Wharfe. The river levels and weather forecasts were continually monitored throughout the works.
