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UNCW Professor Joanne Halls uses Global Positioning Systems (GPS) to create map boundaries for different wetland species as well as upland habitats on Masonboro Island, a coastal site within the National Estuarine Research Reserve System (NERRS). © Joanne Halls/UNCW

First Study of its Kind Reveals Impact of River Sediment on US Coastline

Watershed sediment cannot offset sea level rise in most US tidal wetlands

Published on December 08, 2023

As sea level continues to rise, threatening ecosystems, communities and infrastructure, experts are searching for ways to better understand how coastal environments may change in the future. A new research breakthrough published in Science reveals a novel way to study these changes by measuring how much sediment from the nation’s rivers makes it to the coastline.

Measuring, Mapping and Modeling

After testing many approaches in many different watersheds, UNCW Department of Earth and Ocean Sciences Professor Joanne Halls and co-authors Scott Ensign (Stroud Water Research Center) and Erin Peck (Northeast Climate Adaptation Science Center and USGS Woods Hole Coastal and Marine Science Center) developed a solution to measure the rate of river sediment accumulation across all watersheds of the contiguous United States.

Using her expertise in Geographic Information Science (GIS), Halls developed a new web application called Sediment Pancakes. The app uses publicly available geospatial data to create digital models and interactive maps of the entire continental U.S. coast, including 4,972 rivers and streams. This is the first continent-wide examination of its kind.

“We tend to know much more about our large rivers and very little about the amount of river sediment in the smaller creeks and tributaries, even though these smaller systems are the majority of the landscape,” Halls said. “To our knowledge, this new web application is the only tool that provides local estimates of riverine sediment for all rivers of the contiguous U.S.”

The published paper, “Watershed Sediment Cannot Offset Sea Level Rise in Most US Tidal Wetlands,” concluded that 72% of all rivers do not provide adequate sediment, on an annual basis, to keep up with current estimates of sea level rise. In other words, river-borne sediment alone is insufficient to provide the elevation gain needed to offset increasing sea levels found in tidal wetlands like marshes, swamps and bogs.

Planning for the Future

As many local government agencies are building coastal resilience plans, and researchers nationwide are designing monitoring strategies to study and protect the coastal environments, the Sediment Pancakes app is a tool they can use to inform their planning.

“The more we leverage the enormous amount of map data toward principles of ‘smart growth,’ the better we can make our local communities,” Halls said. “My goal is to deliver map tools that assist local residents and planners so that we empower people to be engaged, exchange ideas in a meaningful and equitable way, and inspire students to be creative problem-solvers.”

Environmental Reporter