Flow free, River Tiffey – Happy World Fish Migration Day
Friday October 23rd, 2020
Having completed Stage 1 of ‘Freeing the Tiffey’ back in March 2019 (see film here), we are hoping to complete Stage 2 ‘Becketswell Bridge, a significant part of the project, in 2021.
So what is Stage 2?
The sill of Becketswell bridge is too high for fish to get over except in extreme floods, and even then, the power of the water is too strong for many species to swim over.
In recent monitoring, only 4 species of fish were found upstream of the bridge, whereas 8 species (dace, stoneloach, stickleback, eel, perch, minnow, bullhead and gudgeon) were recorded downstream.
In partnership with the Environment Agency, the plan is to build a series of pools downstream, which will progressively raise the water level so that fish can make it up through each pool, and eventually over the bridge sill itself.
The design has been carefully modelled to ensure that raising the water level has no impacts on flood risk, or the integrity of the bridge itself. In addition, we have been working with Anglian Water to check that the work does not impact any pipes, or other services, that may be present.
An important part of the design is to enable it to function in all flows e.g. drought and flood conditions, and will require low levels of maintenance. Crucially, the solution will cater for all fish species – some fish are more mobile than others, some are stronger swimmers, and some are able to jump or climb (as part of the project, we will be installing eel tiles against the corrugated piling to allow elvers to move safely upstream too).
What do we hope to achieve?
The goal is to increase the fish species’ composition above the bridge, but also reduce the risk of genetic isolation in the fish upstream, which can result in localised extinctions. Many species need to migrate to fulfil their lifecycle requirements, and if they’re unable to do so, they will inevitably decline.
You may wonder why removing these abandoned structures is so essential – particularly when they have been in place for a couple of centuries. Sadly, the reality is that fish stocks were plentiful back then, and this is no longer the case. Consequently, we need to make every effort to support them, ensuring that they can move freely for food, shelter and spawning.