RAISE: Integrating river-avulsion risk into floodplain management

The researchers will work with floodplain managers and county, state and Tribal governments to develop actionable solutions that incorporate avulsion risk into floodplain management. This work will focus on the Nooksack River in Washington. River avulsions, which occur when a river's water rises above its banks and carves a new path, lead to severe flooding. In some cases, an entire river rushes through an area not typically designed to handle such volume. The integration of river-avulsion risk into floodplain management is crucial to mitigate the impacts of severe flooding. While the risk of avulsion in many river systems is understood, less is known of the mechanisms that trigger them. For this reason, predicting avulsions, especially at timescales relevant to management, is currently not feasible. This work will address this predictability gap and develop actionable approaches for incorporating avulsion risk into ongoing flood management planning. This research will incorporate avulsion risk into holistic floodplain management. Researchers will study past Nooksack River responses and channel changes, as well as local community perceptions of risks. Incorporating these factors will help best inform local management under uncertainty. By studying the geological history of triggering processes and by modeling channel response to large storms at an avulsion node, this work will contribute fundamental scientific advances regarding the process of avulsion triggering. Past river responses to geologic and human disturbances will reveal information about Nooksack River avulsion dynamics and risk. The team will also investigate the relationships between channel change and flooding. This information will help predict whether climate-driven shifts in the system might trigger avulsion. Researchers will work to understand how community members perceive risks and how these perceptions can inform decision making and communication. This work provides the scientific basis for actionable solutions that incorporate avulsion risk into floodplain management. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.