A stretch of the River Derwent downstream from Brompton Bridge is the subject of a 1.8km channel rehabilitation pilot expected to start in the next year. The Environment Agency’s collaboration with Yorkshire Rivers Trust and others will be using this project to demonstrate the feasibility of channel modifications to enhance the ecological value of embanked and canalised parts of the middle Derwent.
The idea is to make the channel less uniform in profile and create naturalistic features -berms, riffles, backwaters etc to benefit fish, aquatic mammals, plants and invertebrates. It will be monitored closely to show how flood conveyance can still be accommodated in a more naturalised channel.
If you stop by Brompton Bridge today (there is a convenient spot to pull in just on the north side) you can see the current channel morphology typical of this reach of the river which was straightened and flood embanked over two hundred years ago. The width, depth and flow characteristics are very uniform in this engineered channel. A carefully designed scheme will create a two-stage channel to handle summer and winter flows. In places material from the banks will be pushed in to form a deep central channel, adequate for normal flow levels, while shallow berms on one or both sides will overtopped to accommodate higher flood volumes when needed, usually in winter and spring. These berms in turn promote diverse aquatic marginal plants providing varied ecological niches for invertebrates, mammals, birds etc.
The key point is that this is not a full ‘re-meandering’ project – the whole of the modification works will fit well within the existing flood banks, so none of the adjacent farmers need relinquish any productive land. Its an exciting project – one to watch as it develops – if it works well on the pilot it may be possible to apply the same principles along other parts of the Straightened Derwent and indeed The Hertford.