Case study C:    Ecological resilience towards floods

Floods can be caused by natural phenomena such as rain storms, snowmelt, failure of ice-dams, or volcanic eruptions under glaciers (jökulhlaups). Human interference has changed flooding conditions – to the better or to the worse – and has also changed the magnitude of flooding impact. Deforestation and drainage of catchments have made flow regimes more irregular, impoundments and flow regulation have in most cases reduced flooding but also increased flood risks in case dams will fail, or if filled reservoirs will receive large amounts of rain. Unexpected large floods can have major ecological impacts and cause serious infrastructural damage.

Measures to deal with flooding could operate in at least two ways, either to constrain the streams and rivers by building dikes to keep the floodwater in place when floods occur, or to modify the catchment and the stream or river channel to increase retention capacity by planting trees or understory plants, making more wetlands, plugging ditches, increasing channel roughness and sinuosity. Such measures also have to accommodate current land-use activities

We are synthesizing examples from all over the world of when ecosystem restoration has been used as a measure to reduce flooding or the impact of flooding. Examples include intentional flood fighting but also cases when restoration was driven by other objectives but still had an effect on flood regimes. The objective of our study is to provide examples of available measures and discuss their applicability to conditions in the Nordic countries, in general or in specific countries. In addition, we will guide future research by identifying gaps in knowledge.

This case study is led by Dr. Christer Nilsson Umea University