Resetting the river template: the potential for climate-related extreme floods to transform river geomorphology and ecology

1. Climate change is expected to alter the occurrence of extreme climatic events, including major floods. Future shifts in the frequency and intensity of extreme floods will vary by region and could modify the geomorphological character of riverine habitat.

2. The geomorphological structure of rivers determines the quality and quantity of habitat available for resident biota, and thus, changes to morphology from more extreme floods are likely to affect river ecology over and above the direct effects of the flood events themselves.

3. Extreme floods can exacerbate the effect of multiple anthropogenic stressors, with potentially dramatic effects on freshwater ecosystems. For instance, high flows mobilise nutrients, sediment and toxic chemicals, and aid dispersal of invasive species, whereas land-use change and channelisation impair flood refugia and constrain recolonisation pathways.

4. Extreme floods may also benefit riverine and riparian biota, overwhelming current anthropogenic constraints and infrastructure to increase habitat complexity and floodplain area.

5. Management to protect human life and infrastructure from severe river flooding can alter channel geomorphology, habitat quality and ecology. However, flood prevention engineering that incorporates the natural form of rivers could potentially mitigate anthropogenic flood damage, in turn restoring habitat and historical ecosystem functioning.

6. We examine potential changes in river channel and floodplain geomorphological characteristics resulting from altered extreme flooding regimes and consider likely implications for the management of the world's freshwater biota.