Managing muddy floods: Balancing engineered and alternative approaches

Muddy runoff from agricultural fields is widespread across Europe causing damage to properties, transport, and freshwater systems. Clean‐up costs are high and include making water fit for drinking. Mitigation against muddy flooding (MF) includes standard soil conservation and flood protection measures. MF occurs during intense localised storms, for example, in Flanders, northern Belgium, but can also result from longer duration rainfall events, for example, in southern England. MF occurs in catchments with large areas of arable land, adjacent to property or freshwater systems. Early experience with mitigation measures favoured engineered approaches. On their own, these have frequently failed to achieve adequate protection or been ruled out on economic or safety grounds: a combination of engineered and land‐use approaches is necessary. We illustrate this with reference to the Molenbeek catchment in Flanders where monitoring shows a significant decline in erosion and damage to adjacent properties. Cost–benefit analysis of mitigation measures shows them to pay for themselves over short periods of time. Protecting freshwater systems from MF damage should focus on interrupting flow from field to streams, ditches and roads which act to convey muddy runoff to the main river channels.