The following case studies exemplify some of the risks and impacts that increased sedimentation and rapid runoff have had upon a variety of infrastructure, and the costs associated with these.
Case studies 1, 2 and 4 illustrate how rapid runoff following heavy rainfall events led to accelerated river bank erosion which either damaged or placed built infrastructure at risk. The erosion of stream embankments as shown in these case studies contributes further sediment inputs to watercourses, with knock on effects as described below in relation to case study 3.
Case study 3 illustrates how significant amounts of sediment from agricultural runoff can accumulate in rivers and deposit on river beds, reducing the capacity of such watercourses (and similarly artificial drainage channels such as road drains) to convey flow. The reduced channel capacity can therefore increase flood risk, whilst the additional sediment deposited in rivers can blanket gravels damaging potential fish spawning habitats and feeding sites. In the case-study example, the sediment accumulation impairs the operation of flood defences, and helps illustrate some of the costs associated with sediment management in the water environment.
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