15/8/2014 – Installing flow deflectors

As an urban river, the Cale has at times had its course altered to suit the needs of the town; one obvious example is the stretch between Waterside and The Batch. This section was artificially straightened out by railway engineers in the 1860s, as the rail line was built to run alongside. Of course, with the railway long gone, this is no longer a necessity, but demolishing houses and factories to send the river back into its old course is clearly not a practical option. So, the CATCH remit this evening; to artificially un-straighten it, so that it will behave in a more natural manner.

Gary, Sophie and Tom hard at work shifting rocks.

To achieve this end, we set out to install “flow deflectors;” put simply, these are artificial structures which partially block the path of the river so that the current is deflected from side to side instead of just passing along in a straight line. This variation in current creates a variety of different habitats; fast-flowing sections where the river narrows, and pools behind the deflectors where the water remains much calmer. These different habitats, in turn, create opportunities for differing types of wildlife to find their own preferred living conditions.

Creating a “pinch point” for an area of faster, deeper river flow.

In all of this work, we have been sagely counselled by the gurus of the Wild Trout Trust, who have undertaken similar projects in numerous towns throughout England. Following their advice, a series of flow deflectors has been created out of stones, rocks and rubble from the riverbed – much of it, quite possibly, the remnants of former railway buildings. Thus we were able to recycle historical rubbish into a useful structure.

Slower, stiller pools and eddies are created behind the deflectors, with a faster-flowing current in between; all adding to the variety of wildlife habitats that the river can offer.

In the space of two and a half hours the team were able to move over three tons of rocks and assorted rubble to create six structures, forming a pinch point on the corner and then deflectors at irregular intervals along the next few hundred yards. Even before we had finished work we could see that it was having an effect, creating different flow patterns and some eddying pools behind the rocks. It creates a tremendous sense of satisfaction to see that such simple – although strenuous! – work can make a rapid and significant improvement to the river’s variety and availability of wildlife habitats.

There are long-term plans in place for similar, and perhaps bigger and better, schemes along other parts of the Cale when funding becomes available, as we continue to try to restore the Cale as an asset to the humans and the natural wildlife of the town.