Our friends at the Wild Trout Trust have made this video (its less than 3 minutes long) that explains the unintended effects of dredging. Nature abhors a vacuum and removing accumulated material from a river channel can have far-reaching and unintended consequences. The first principle effect is to increase the demand for eroded river-bed and river-bank material from upstream. This can dramatically increase the rate of erosion in upstream reaches. The second major effect is the interruption of the transport of sediment downstream of the dredged reach. Whilst the bed material is being re-accumulated in the dredged area, there is far less material being supplied downstream. That cutting off of the sediment supply causes a net increase in the erosion downstream of the dredged reach as well. This is due to stopping the supply of material that would otherwise patch up and fill in eroded areas to produce a more stable dynamic equilibrium state. How many people who undertake dredging understand these processes? Is the move to fast track UK-landowners ability to dredge their own streams with a much lower requirement for external assessment likely to create more problem than it solves? https://youtube/watch?v=OAZ_BuyM41s
Posted on: Wed, 15 Oct 2014 08:11:42 +0000