After the flood
I think I’m going to have to stop claiming that this blog is weekly, because it’s clearly not. I’m still going to aim for weekly updates, but the precise timing looks like it's going to be fairly variable, with things continually cropping up and interfering with my plans. Last week, I was flat out trying to finish editing a report for the Environment Agency and just didn’t have time to write the blog. But fortunately (for both me and the blog) the report was on a fairly interesting topic.
As anyone who’s looked around the rest of this site will know, I regularly edit scientific reports for the Environment Agency, in order to make them more readable and accessible to the general public. Now this is something that I really enjoy doing. Editing requires different skills from writing and so getting my teeth into a nice, juicy report often makes a welcome change. Furthermore, the reports tend to be on really interesting topics that I don’t usually write about, such as preventing landfill fires, digitising old land maps from the 1930s and assessing the risk of steroid oestrogens from sewage works.
This report that I’ve just finished editing is no exception, as it detailed the results of a project looking at the movement and behaviour of coarse fish in lowland rivers and floodplains. The impetus for this project comes from the fact that an increasing number of lowland rivers in England and Wales are being physically separated from their floodplains by artificial structures such as levees (which are essentially very high river banks). This is done so that the floodplain land can be utilised, often to build houses on.
Now the problem with building houses on floodplains becomes plain to see almost every year, when heavy rains cause rivers to rise so much that they breach the levees and flood all the houses built on the floodplain. But it’s not just homeowners who suffer from living on floodplains: it turns out the separating rivers from their floodplains is also bad news for fish.
This is because, without the floodplains, any fast flowing water in the river tends to stay in the river, rather than spreading out onto the floodplain. As a result, conditions in the river tend to become fairly severe, with unfortunate consequences for the fish living there. There is also nowhere for the fish to escape to, as they can no longer hide in the calmer floodplains. Finally, if the river becomes so high that it breaches the levees, the fish get carried along with the flood water. After the flood water recedes, they are left high and dry behind the levees as they have now way to get back to the river.
This project aimed to find ways of mitigating these effects by exploring in detail how coarse fish actually utilise floodplain waterbodies, both natural and man-made. This involved researchers from the Hull International Fisheries Institute, part of Hull University, conducting five experimental studies on three English rivers: the River Ouse in Yorkshire; the River Trent near Nottingham; and the River Roding in Essex.
Now, I’m not going to go into any real detail about the five studies, because the report (together with a wonderfully written science summary) should soon be available on the Environment Agency web site for anyone interested. But the main result was that although coarse fish are surprisingly hardy in the face of floods, fish populations and general river biodiversity are greatly enhanced by having rivers connected to their floodplains or to artificial floodplain waterbodies, such as flooded quarries.
The researchers made a number of explicit recommendations for how to improve the connectivity between rivers and floodplain waterbodies, but the main implicit recommendation appeared to be not to build on floodplains. Especially as climate change is expected to cause floods in England and Wales to become more frequent and more severe.
Ironically, however, just as this report is published, building on floodplains may no longer be too much of a problem, at least for the next few years. With the credit crunch causing major house-builders to shed staff and smaller house-builders to go out of business, the number of new houses being built anywhere has dropped substantially. Bad news for prospective homeowners, but good news for fish.
