Fish passes can take many forms, including technical solutions that utilise modern construction approaches and various types of naturalised channel that attempt to mimic features that occur naturally in a watercourse. The specific solution will depend on a variety of factors, including, but not limited to, the nature of the obstruction, the range of species for which passage is required, the typical flow regime of the river, space availability and budget.
Some of the most successful fish pass designs are those that attempt to replicate natural channels, and when designed well they have been proven to have a high passage efficiency and be able to accommodate a wide range of species. Furthermore, they are often more aesthetically pleasing then technical solutions and are therefore well suited to visually sensitive sites. Although a preferred option at most sites, the relatively large footprint required for a naturalised bypass channel means that they are not always an available solution.
In recent years we have been fortunate enough to be involved in the design and construction of a number of naturalised bypass channels, including a recent project at Stony Stratford on the River Great Ouse. A series of radial sluice gates currently prevent all upstream fish migration at the site and prevent the watercourse from meeting Water Framework Directive Objectives. Working on behalf of the Environment Agency, Fishtek recently designed a natural channel that utilises an existing paleochannel adjacent to the watercourse to bypass the sluice gates. The channel will not only provide passage to the full range of fish species that frequent the site, but it will also provide valuable juvenile and spawning habitat that is currently scarce in the lower-middle reaches of the river. In time it is also expected that the channel will be colonised by a varied macroinvertebrate community and a range of terrestrial and aquatic macrophytes.
Works recently got underway to construct the channel and the contractors are currently installing the off-take structure that will control flow into the channel. This structure is necessary in order to ensure that the channel works in harmony with the pre-existing structures at the site and flow is suitably distributed between the main channel, pre-existing leat channel and the new bypass channel. The photos below show the off-take structure being lifted into position earlier this week. Whilst the channel may not look particularly naturalised at present, there is still a long way to go, so watch this space for updates on this exciting project!