This section contains an overview of the final proposed design. For full information readers are encouraged to download the full design report
Concept sketch – cross-section looking towards Hexham Bridge, south bank:
The scheme would be situated on the south bank of the River Tyne immediately downstream of Hexham Bridge. The sketch above is a view from downstream at river level, looking upstream (broadly west); the two arches of Hexham Bridge shown are the two southernmost arches.
The scheme would capture flows from the Tyne that flow into the three southernmost arches of Hexham Bridge. The original apron that controls the flow would be retained in its existing form. A new weir at the same level as the upstream edge of the original apron would be constructed across the southern three arches, immediately downstream of the bridge, to capture the flow and channel it to the fish passes and Archimedes screw turbine. When the flow captured through the three arches exceeds the capacity of the turbine and fish pass it would flow over the new weir. This is expected to be approximately 50% of the time.
Concept Sketch – view from Hexham Bridge, showing control building (on bank) linked to ‘in river’ viewing platform
The circular nature of the Archimedes screw and the curved arches of the adjacent bridge (which are reflected in the water to complete the circle), together with the flow of the river into the Archimedes screw, and the route of the pathway on the river bank have been the design inspiration. This has generated a curved circular geometry for the new building which will house the control equipment, the platform on top of the generator housing and the link between these two elements.
The control building is generated out of a cylindrical shape cut at an angle to create a sinuous flowing curved wall tipped towards the bridge. (The pedestrian view of the installation from the bridge is a key view.) The control equipment is housed in one segment of the circular plan and is defined by the flow of the pedestrian path through the building. The remaining area within the circular plan provides a space for interpretation of the hydro scheme. Slots have been cut into the circular wall to provide framed views of the Listed bridge and the Archimedes screw equipment. Both areas are to be covered with a roof contained within the circular form of the building. This roof will provide a covered, sheltered area for interpretation.
Concept Sketch – new views of Hexham Bridge and the River Tyne
Access to the circular viewing platform from the control building is via a path and raised walkway, which mirrors the flow of water into the Archimedes screw (see above). The walkway initially orientates the viewer towards the bridge, and then curves toward the Archimedes screw itself.
The viewing platform is circular and overhangs the generator building and associated sluice gates below. It provides a view of all the key components of the installation, the screw mechanism, the inlet and the fish pass together with views of the bridge and river.
Key elements of the scheme
The key elements of the scheme are as follows:
- Fish passes for game fish, coarse fish, eel & lamprey
- Archimedes screw turbine generating electricity from water power
- Control building on the embankment to the south
- Viewing platform on top of the housing for the Archimedes screw turbine
- Public walkway between the control building and viewing platform
- Pedestrian access through the underpass from Tyne Green
- Access road from Tyne Mills industrial estate for maintenance access only
Concept Sketch – aerial view at low flows
The installation of equipment within the river is predominantly of a robust concrete construction designed to withstand the rigours imposed by the continuously flowing river throughout the year, including times of flood. The other elements include open grids and metal mesh, to protect the inlet and screw mechanism.
The use of the modern functional materials present in the engineering elements of the project to create a contemporary design solution is a similar approach to that used when the listed bridge was constructed in 1793. It employed the use of substantial solid stone masonry to create a functional yet elegant design, (which ensured that it remained stable following the failure of previous bridges into Hexham). The design for this project takes its inspiration from the new technology of the Archimedes screw mechanism to create a contemporary design solution. The design does not seek to imitate the bridge, but reflects the solidity of the masonry bridge and the geometry of the nine arches spanning across the river. The proposed installation is of a very modest scale therefore limiting any visual impact on the setting of the listed bridge.
Hexham River Hydro, an energyshare project made possible by British Gas and supported by Carbon Leapfrog, Cooperative Enterprise Hub, Vattenfall and The Naturesave Trust