Coastal Change

Our Nation has many kinds of coastal ecosystems: from wetlands and sandy beaches to reef-lined coasts and icy permafrost cliffs. While each of these coasts are unique, they have one thing in common—they are constantly changing. The USGS studies the processes that shape our coastal systems and predicts the resulting changes and geological, ecological, and economic consequences.

One photo of coastal homes and a road before a hurricane, the other after the hurricane has wiped out homes and road. — Oblique aerial photographs of Rodanthe, North Carolina, from May 6, 2008 (top, pre-storm), and August 31, 2011 (bottom, post-storm). The yellow arrow in each image points to the same cottage. A breach was carved through the barrier island, severing North Carolina Highway 12. The storm surge was approximately 2 m high on the soundside and less on the oceanside. Flow from the sound to the ocean may have played a role in cutting the breaches between Oregon Inlet and Cape Hatteras.

What is coastal change?

Sediments are the foundation of coastal systems, and the movement of these sediments can result in the evolution of entire ecosystems. USGS measures the amount of sediment present, and how it moves in various environments, such as wetlands, estuaries, beaches, and barrier islands. Processes such as erosion—sediments being taken away from one area of coastline—and deposition—when they are moved to another place—are driven by natural forces, including waves, wind, tides, and currents. These processes can shift shorelines in various directions and change the elevation of coastal environments, therefore influencing the areas that are habitable by people, plants, and animals.

How does USGS study coastal change?

Our scientists use many methods, both through direct measurements like coastal elevation profiles and indirectly using remote sensing, to characterize the shape of our coasts and how they are shifting over time. Some methods include light detection and ranging (LiDAR); amphibious tools and vehicles (technology suited for both land and water) for nearshore seafloor mapping; and satellite imagery, as well as elevation data collected on foot.

USGS measures and monitors the position of shorelines along the entire U.S. coastline and how they have changed since the 1800s using a combination of historical and satellite imagery. These data are used to develop tools such as the Digital Shoreline Analysis System (DSAS) for users to both visualize and track these changes on their own. The Coastal National Elevation Database (CoNED) provides high-resolution digital coastal elevation data, and topobathymetric maps that are used to identify coastal features, hazard zones, changes in ecosystems and to form the foundation for developing models that simulate sediment transport and storm surge. These data help coastal managers, engineers, planners, and resource managers understand how coastal change and its associated hazards will influence our coastal habitats and communities.

Changes to the coastline can affect where and how severely flooding may occur and how this could impact biodiversity persistence. USGS experts use a host of different high-tech devices to gather scientific data before, during, and after extreme storms. This information improves flood forecasting models, is used to update nationwide flood zone maps, helps emergency managers plan for future flooding events, and is critical for managing coastal species with specific habitat requirements.

Visualizing Change

Colored lines overlaid on aerial image of an island and island breach shows how the island footprint has changed since 1985. — Fire Island shorelines from 1985 to 2018 were extracted from imagery and are plotted together with 2018 imagery to reveal how a breach in the island has evolved through time. From 1985-2011, the island was continuous at this location. The passage of Hurricane Sandy in 2012 formed a breach in the middle of the island and this breach can be observed in 2018 imagery and shorelines from 2013-2018.

Model animation showing land elevation, current speed and direction and the formation of breaches over the North Core Banks barrier islands.

An interactive mapping application in which the user can choose parameters from the menus to create a computer model of flooding — Our Coast, Our Future (OCOF) is a collaborative, user-driven project focused on providing coastal California resource managers and land use planners locally relevant, online maps and tools to help understand, visualize, and anticipate vulnerabilities to sea level rise and storms. OCOF uses the USGS Coastal Storm Modeling System (CoSMoS), the modeling approach used to estimate sea level rise and storm scenarios. CoSMoS provides some of the most accurate and detailed results available for California.

Modeling and Predicting Coastal Change

Predictive modeling techniques are used to forecast how the coast will change in response to both natural processes and anthropogenic influences, as well as how these changes may affect the availability and distribution of habitat for coastal species of concern like piping plovers and sea turtles. This information is useful for informing conservation strategies for partners such as the National Park Service and the U.S. Fish and Wildlife Service.

Some coastal change model forecasts are provided in real-time to show areas that are expected to erode, where sand washes away; overwash, where water overtops the dunes of a beach and pushes sand inland; or inundate, where the coast is completely and continuously submerged by high water levels like storm surge. These predictive models are tested and verified using remote sensing techniques including satellites, aerial imagery, and a collection of cameras that monitor coastal areas of interest.