Flood Management in a Climate Emergency
Hydrologist David Ramsbottom assesses the challenges facing flood alleviation schemes
A packed meeting heard the scheme described as “fundamentally flawed” by internationally renowned hydrological engineer and expert on the effects of climate change on flood management, David Ramsbottom of consultants HR Wallingford.
“I think there is a fundamental flaw in the scheme. The basic concept of a flood relief channel is to move water as efficiently as you can through the flood plain. They’ve designed it in such a way by lowering flood plain by removing 700 thousand tonnes of soil and gravel that the capacity and the reduction in flood level is actually quite small. And therefore, the overall flood benefit is limited. For a low-level flood, the scheme will reduce water levels by about 30 centimetres about a foot and that would be the maximum. But for a large flood then the reduction level would be about 20 centimetres and that’s about the length of my pen.”
He said that putting in a small channel and lowering the flood plain relying on covering a lot of ground was an inefficient way of moving flood water because the shallow depths mean the velocities of moving water were low. He said that the Jubilee river channel at Maidenhead was designed to carry 40% of the total flood flow, whereas the Oxford channel would only carry 15%. He also said that the flood defences, including raised banks on the Botley Road and South Hinksey may have a problem as there was a risk the water could go underneath the flood defences and cause flooding. He acknowledged some attention had been paid to this but questioned if it was enough.
David Ramsbottom said that the jury was currently out on exactly what could be achieved by doing work upstream and that had got to be part of the debate. The EA was currently looking into the feasibility of several measures.
He said that on a brighter note that regenerative farming practices to return the topsoil held out great hope because increasing ground cover and restoring the topsoil could reduce run off significantly. “There are farmers in the Thames catchment looking at different ways of managing the land including different ploughing practices, having much more ground cover, herbal lays and various other regenerative farming practices. As farming covers much greater land areas this could significantly reduce run off. From all I’ve seen this is the greatest possible hope simply because we need to go in this direction due to climate change.”