Restoration of the existing culvert that will feed the turbine chamber
A key design criterion was ensuring the VETT unit was integrated into the infrastructure of the Grade II listed mill, whilst preserving the historic and leisure amenity of the site. The mill is home to a beautiful pub and restaurant called "The River Mill", so the VETT was installed under the River Mill's outside deck out of sigh.
From stakeholder discussions with the Environment Agency it became evident that any scheme would also have to be installed and operated in a way that protects the juvenile coarse fish nursery areas in the marina and mill pond and accommodate eel passage.
Previous live trials already showcased VETT’s safe fish passage credentials and careful eel passage design will open up this stretch of the catchment to migrating eels.
The River Great Ouse is a navigable stretch of river which is also prone to flooding so it was important to coordinate the management of water levels by the Environment Agency’s sluice at Eynesbury Weir with this hydro scheme.
A control system and an operating approach agreed with the Environment Agency ensures that the hydrological parameters could be real-time monitored to achieve this.
After the feasibility and detailed design phase in 2017, all regulatory consents had been received by January 2018 and Greenford Ltd was appointed to undertake the civil construction phase of the build.
One of the highlights was the installation of the actual VETT pipework. The VETT is made out of glass reinforced plastic (GRP) and is relatively lightweight. Originally it was envisaged to assemble the pipe sections in situ in a dry cofferdam, however the contractor decided to assemble the pipe on site first and then lift it into place in one long piece. 4,000 litres of water are flowing through the pipe per second.
Video: VETT installation
Once the VETT was installed and final civil works completed it was time to install the turbine with secondary pipe.
The whole system is installed underneath a decking that is now being used by customers of the adjacent pup. In order to install the turbine, a section of the decking had to be lifted out, the turbine dropped in, and the lid had to be closed again.
This video shows the true ingenuity of VETT: A hydro system that uses 4,000 l/s with a turbine that is only 400mm in diameter, completely invisible and silent.