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The future of many coasts is tied to the delivery of land-based sediment. The natural supply of sediment to coasts from adjacent rivers and watersheds can physically build up coastal landforms, potentially mitigating the impacts of seawater flooding and erosion that will increase with ongoing sea-level rise.

Photo collage shows examples of coastal changes at the mouths of small rivers of the world resulting from contributions of new sediment.
Examples of coastal changes at the mouths of small rivers of the world resulting from contributions of new sediment.

A new paper from USGS scientists examines and summarizes the variability in terrestrial sediment supply to coasts over the decadal to century timescales important to coastal land management. 

In some cases, watershed sediment supplies may be adequate to keep pace with sea-level rise for decades or more. In other cases, insufficient sediment discharge from rivers will lead to coastal erosion and land loss. Therefore, a better understanding of the magnitude, frequency and implications of sediment supply rates is needed, the authors note in the paper titled, "Fires, floods and other extreme events – How watershed processes under climate change will shape our coastlines".

The ebb and flow of watershed sediment supply is usually characterized by long intervals with very little sediment discharge, punctuated by brief events—earthquakes, volcanic eruptions, extreme precipitation, wildfires, or a combination thereof—that deliver tremendous volumes of sediment to coasts. 

Climate change may lead to more of these high-sediment discharge events, as more frequent and intense wildfires liberate sediment, which is transported to coastal areas in increasingly frequent and intense precipitation events. 

“Understanding sediment delivery to the coast is key for assessing coastal climate change impacts,” said Helen Dow, USGS Research Geologist, Mendenhall Fellow, and a co-author of the paper. “However, the spatial and temporal variability observed in terrestrial sediment supply, exacerbated by climate change, makes this a challenging endeavor." 

Building upon this understanding under current and future conditions of climate change requires collaborative communication and research efforts across hydrologic, geomorphic and coastal research groups. The authors encourage the continued development and progress of cross-disciplinary studies of coastal landforms, especially with respect to the linkages between rivers and the coasts they drain toward. 

"Teams of scientists will be needed to monitor and predict future sediment inputs—and how different coastal systems respond to those inputs—to create a more informed picture of the impact of climate change on coasts," added Dow.

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