FiveRivers worked closely with Atkins and JCTR Ltd. to deliver this ambitious habitat restoration scheme for Berks, Bucks and Oxon Wildlife Trust (BBOWT). The project was separated into different sections; the largest of which being the excavation and construction of a naturalised fish bypass channel that created connectivity for fish species to move between the main channel of the Thames and the Duxford Loop. Works also included construction of a fish easement at Duxford Ford, re-naturalisation of the Duxford Old River floodplain, and wet-woodland restoration. Furthermore, the removal of non-native invasive species such as Himalayan Balsam was a continuous process that proceeded over the course of the project.
Naturalise fish bypass
Fish easement at Duxford Ford
The existing structures in place on the Thames and Duxford Loop were deemed to not provide ample opportunities for fish passage. This is due to the Shifford Weir structure and the Duxford Ford, which at low flow, acts as a barrier to the free movement of fish. To allow fish to pass more freely, an alternative route must be created, which creates its own issues, as a way to access the land between the bypass and the river must be created.
Furthermore, the Duxford Old River area acts as a natural floodplain for the Thames, so work was incited to re-naturalise these floodplains, thus creating more natural wetland habitats for native species. There were paleo-channels in this area, however they had become dis-established in time, which needed to be corrected for optimal floodplain function.
In the state prior to the works commencing, BBOWT was unable to have control over the water levels once the floodplain contained water. The ability to control the water level would result in more effective habitat management, particularly during significant ecological periods.
Atkins created designs that would optimise fish passage, by bypassing the Shifford Weir and devised an area where fish can traverse the Duxford Ford. Furthermore, data of where water naturally remained following flooding was collated to allow designs of a more naturalised floodplain and wetland habitat. Careful consideration of plant life and vegetation was demonstrated to design further wetland habitat improvements to the area. Five Rivers worked closely with Atkins throughout the project, to deliver their designs and to effectively implement the environmental improvements they had conceived, all the while ensuring ecological sensitivity was a key focus for the works.
Five Rivers worked closely with BBOWT to deliver Atkins’ designs, with regular meetings and site walkovers to execute the plans effectively and to successfully restore the local habitat. A bypass channel, measuring approximately 450m long, was created for fish passage to avoid the Shifford Weir. A culvert was installed at the Thames end of the bypass to allow for access to the land between the bypass and the Duxford Loop. Further fish easement works were constructed to partially raise the water level at one half of the Duxford Ford, to create an area where fish can more easily ascend the ford during times of low flow.
Paleo channels were excavated to create a more naturalised floodplain, alongside wetland scrapes being commissioned to maintain water for longer following a flood, which improves the wetland habitat. Selective plant and tree translocation also occurred to produce a better habitat, whilst the removal of Himalayan Balsam and other non-native invasive species occurred during the whole course of the project. The inclusion of pipe dams connected to Wadley Stream allows for better control of the water levels during times of ecological sensitivity, allowing the habitat to be continually optimised, and any danger to be mitigated.