Hurricanes and other extreme storms generate storm surge and large waves, eroding the beach and dune system and reshaping the coastal landscape. During the most extreme events, changes can occur across the width of an entire barrier island. Six types of coastal change observed along the coastlines of the United States are:

Beach erosion occurs when waves and currents remove sand from the beach system. The narrowing of the beach threatens coastal properties and tourism revenue in coastal counties throughout the United States.

Dune erosion occurs when waves attack the front face of the sand dune, reducing the volume and elevation of the dune. Erosion of the sand dune leaves coastal properties more vulnerable to future storms.

When waves exceed the elevation of the dune, sand is transported across island in a process known as overwash. When overwash occurs, it often results in significant damage to coastal property.

Inundation occurs when an island is completely submerged under the rising storm surge. Strong currents may carve a channel in the island in a process known as island breaching.

Marsh erosion occurs on wetland coastlines exposed to the open ocean or wide bays. Waves and currents erode the wetland soil, causing significant losses of land area.

The impact of waves and currents on coastal cliffs may cause the base of coastal cliffs to erode, eventually undermining the cliff and causing slumping. Materials eroded from the base of the cliff provide sediment for adjacent beaches.

Forecasts of sea level rise and increased hurricane activity suggest that our nation’s coastlines are becoming increasingly vulnerable to the powerful forces of the ocean. Along our coasts, rising sea levels expose higher locations not usually subjected to the power of the sea and to the erosive forces of waves and currents.

In order to address the increased vulnerability of our Nation’s coasts, the USGS has created the National Assessment of Coastal Change Hazards program. The primary objective of this program is to determine and quantify the relative vulnerabilities of U.S. coastlines to coastal change hazards. More specifically, this research includes:

The locations of our Nation’s shorelines, dunes, and coastal cliffs have been mapped with airborne lidar creating an objective baseline that can be used to determine how our coasts have changed in the past and how they might change in the future. For example, these baseline surveys have been compared to several historical shoreline measures in order to quantitatively assess past coastal change. Comparison to lidar topographic surveys collected following the landfall of a major storm allow for quantification of storm-induced changes.

Coastal change data and complementary oceanographic data sets are used to test critical hypotheses related to understanding the physical processes that control coastal hazards. For example, are wave runup models accurate enough to predict overwash and inundation of barrier islands? Can these models be used effectively, and over thousands of kilometers of coast, to assess vulnerability?

The ultimate goal is to develop a quantitative, probabilistic assessment of the vulnerability of our Nation’s coasts to change from storms, long-term shoreline erosion/accretion, sea-level rise, and sea cliff erosion. In order to create rigorous and quantitative models, the methodologies are continually being tested and improved using recent data sets.