The Effects of Dams on Floodplain Function

In 2008, ASFPM assembled a working group of floodplain experts to address floodplain management issues related to dams. The group consisted of representatives from multiple federal agencies, academic institutions, professional societies, non-profit organizations, and consulting firms. Their final report, “A Strategy to Reduce the Risk and Impact of Dams on Floodplains”, was completed in July 2013. The purpose of this document is to help floodplain management officials and communities better understand how dams affect floodplains and impact communities. During development of the report the working group prepared a subdocument summarizing the environmental issues related to dams, which is the focus of this presentation.

Dams have a significant environmental impact on the functions of rivers and their floodplains. The impacts range from disruption of ordinary riverine processes such as sediment transport, channel changes and evolution, floodplain and coastal delta morphology, and water quantity, temperature and flow, to impacts on river ecosystems and riparian habitat and vegetation. Open riverine corridors play a significant role in the ability of many species to migrate, whether due to life cycle requirements, habitat disturbances, or changing climate. In the US it is now nearly impossible to find river systems that are not fragmented by numerous dams.