What we found
It’s bad and it could be worse
Only 1 % of river basins in Great Britain are free of artificial barriers like dams, weirs, and culverts. On top of that connected rivers (rivers with only a few barriers) only make up 3.3% of all rivers and streams in Great Britain.
But it’s difficult to estimate this fragmentation when we don’t know how many of these barriers there really are. We worked out that existing information for these barriers underestimates stream fragmentation by at least 68 %. That means that instead of 23,618 barriers there could be as many as 66,381. Also, we know for sure that small barriers like fords, culverts and bridge aprons are completely missing from existing data.
Why it is important
Artificial barriers, like dams, weirs, sluice gates and culverts, are incredibly useful. They supply drinking water, store water for crop irrigation, generate hydropower, prevent floods, allow us to cross rivers, and navigate along them and hold back tidal surges. And because they’re so useful -they’re everywhere. An unplanned result of this high number of barriers is the cutting up, or fragmentation, of rivers.
Fragmentation of rivers can have negative impacts on sediment transport, aquatic plants, fish movements and insect populations - to name a few. If we can get an understanding of the level of fragmentation caused by barriers it will be possible to estimate their cumulative negative impacts. Supporting scientists and environmental managers in making the right decisions to set our rivers free.
How we did it
We combined existing information about the location of barriers in England, Scotland, and Wales. To do this we have to create a new set of common barrier types and remove records that duplicated others. With this information we were able to work out the average length of river free of barriers.
To confirm this information we recorded the location of all artificial barriers we found on 19 different rivers. This allowed us to estimate the number of barriers missing from existing information.
What it means
If you walk along a river…
There are very few free-flowing rivers in England, Scotland, and Wales. Meaning less freedom for fish, insects, and aquatic plants to thrive than previously thought. If you walk along a river in England, Scotland, or Wales you will probably find on average at least one artificial barrier every 1.5 kilometre.
FishBites is a science communication series by the FishBEE research group.
The FishBEE team integrates the Centre for Sustainable Aquatic Research (CSAR), based at Swansea University, UK.
This post is based on the research paper authored by Dr Josh Jones and co-authors, entitled: A comprehensive assessment of stream fragmentation in Great Britain. Free access here
Jones, J., Börger, L., Tummers, J., Jones, P., Lucas, M., Kerr, J., Kemp, P., Bizzi, S., Consuegra, S., Marcello, L., Vowles, A., Belletti, B., Verspoor, E., Van de Bund, W., Gough, P., Garcia de Leaniz, C. 2019. A comprehensive assessment of stream fragmentation in Great Britain. Science of The Total Environment, 673:756-762. ISSN 0048-9697