USGS - science for a changing world

St. Petersburg Coastal and Marine Science Center

St. Petersburg Coastal and Marine Science Center > Coastal Change Hazards: Hurricanes and Extreme Storms

Coastal Change Hazards: Hurricanes and Extreme Storms

National Assessment of Hurricane-Induced Coastal Erosion Hazards

Introduction

Sandy beaches provide a natural barrier between the ocean and inland communities, ecosystems, and resources. However, these dynamic environments move and change in response to winds, waves, and currents. During a hurricane, these changes can be large and sometimes catastrophic. High waves and storm surge act together to erode beaches and inundate low-lying lands, putting inland communities at risk. A decade of USGS research on storm-driven coastal change hazards has provided the data and modeling capabilities to identify areas of our coastline that are likely to experience extreme and potentially hazardous erosion during a hurricane.

The analysis is based on a storm-impact scaling model that uses observations of beach morphology combined with sophisticated hydrodynamic models to predict how the coast will respond to the direct landfall of category 1-5 hurricanes. Hurricane-induced water levels, due to both surge and waves, are compared to beach and dune elevations to determine the probabilities of three types of coastal change (1) collision dune toe is eroded by waves and surge, (2) overwash - sand is transported landward over the beach and dune by waves and surge, and (3) inundation - beach and dune are completely and continuously submerged by surge and wave setup. As new beach morphology observations and storm predictions become available, this analysis will be updated to describe how coastal vulnerability to storms will vary in the future.

Probabilities of hurricane-induced coastal change for the Mid-Atlantic States have been updated using post-Sandy beach morphology (November 2012).

map viewer
Probabilities of Coastal Change (click to use interactive map)

Please note that Adobe Flash Player (version 11.1 or higher) is required for viewing the interactive map and can be downloaded here: http://get.adobe.com/flashplayer/.


Key Findings

Percentage of sandy beaches very likely (probability > 0.9) to experience erosion associated with collision, overwash, and inundation during category 1-5 hurricane landfall.

Hurricane Intensity Category
1 2 3 4 5*
collision (dune erosion)
US Gulf of Mexico 99 100 100 100 100
US Southeast Atlantic 89 95 96 96 96
US Mid-Atlantic 74 99 100 100 -
overwash
US Gulf of Mexico 71 85 92 97 98
US Southeast Atlantic 47 66 78 87 92
US Mid-Atlantic 25 49 78 95 -
inundation
US Gulf of Mexico 27 58 73 83 89
US Southeast Atlantic 12 36 51 64 75
US Mid-Atlantic 7 24 46 68 -

*Category 5 hurricane conditions were not simulated for the mid-Atlantic region.

Table updated using post-Sandy probabilities for the Mid-Atlantic region

In general, lower dune elevations along the Gulf of Mexico and southeast Atlantic coasts make these regions more vulnerable to erosion hazards during hurricanes. Average dune elevations along the shores of the Gulf of Mexico are just 2.4 m high, making approximately 71% of these beaches very likely to experience extreme erosion due to overwash in the direct landfall of a category 1 storm. By contrast, dunes along the mid-Atlantic coast are, on average, over 2 m higher and, therefore, less likely to overwash or inundate. In the mid-Atlantic, only 25% of the beaches are very likely to experience overwash in the direct landfall of a category 1 storm. However, this area also has the most variability in dune size and shape. This leads to a corresponding variability in the vulnerability of the beaches, placing areas highly likely to erode adjacent to more stable locations. Another regional difference is found in the relative role of waves and storms surge in increasing coastal erosion vulnerability during low category hurricanes. In the Gulf of Mexico and southeast Atlantic regions, waves play a larger role in elevating shoreline water levels than they do in the mid-Atlantic. During a category 1 hurricane in the Gulf of Mexico or southeast Atlantic, the contribution of waves to storm-induced extreme water levels is nearly twice that of surge.

Mid-Atlantic

  • Following the passage of Hurricane Sandy, 75% of dune-backed beaches along the mid-Atlantic coast are very likely to experience dune erosion for a category 1 hurricane landfall, compared to 89% pre-storm. Hurricane Sandy eroded the dune face in many places, resulting in a higher dune toe elevation and a decreased likelihood of dune erosion. In other locations, the mean beach slope decreased, resulting in lower values for wave-induced water levels.

  • For a category 4 hurricane landfall 95% of the post-Sandy mid-Atlantic beaches are very likely to experience overwash, an increase of 3% over pre-storm. The fraction of coastline very likely to experience inundation also increased from 66 to 68% following Hurricane Sandy.

Southeast Atlantic

  • For category 1 hurricane landfall conditions, 89% of dune-backed beaches along the mid-Atlantic coast are very likely (p>90%) to experience dune erosion during the collision regime, 47% are very likely to overwash, and only 12% are very likely to inundate and experience erosion hazards that may include breaching.

  • Greater extents of the southeast Atlantic coast are very likely to overwash due to the low dunes in the region. In South Carolina, which has not seen many landfalling storms in recent years, the average dune elevation is only 2.9 m, making this stretch of coast one of the most vulnerable areas along the Atlantic; 96% of the beaches are very likely to overwash in a category 1 hurricane.

  • In a category 5 hurricane landfall, 92% of the southeast Atlantic beaches are very likely to experience overwash and associated erosion, and 75% of the beaches and dunes are vulnerable to erosion due to inundation.

  • During a category 1 hurricane landfall in the southeast Atlantic, waves increase water level at the shoreline by 170% above surge alone. The predicted wave-driven component of shoreline water levels was 3.3 m, high enough to reach the mean dune toe elevation (2.3 m) even without surge.

Gulf of Mexico

  • For a category 1 hurricane landfall, 99% of sandy beaches along the U.S. Gulf of Mexico coast are very likely (P>90%) to experience dune erosion, 71% are very likely to overwash, and 27% are very likely to inundate.

  • For category 5 hurricane landfall, 98%of the U.S. Gulf of Mexico beaches are very likely to experience overwash and associated erosion, and 89% is very likely to be vulnerable to erosion due to inundation.

  • During a category 1 hurricane landfall in the Gulf of Mexico, waves increase water levels at the shoreline, on average, by 170% above surge alone. The predicted wave-driven component of shoreline water levels was 2.8 m, high enough to erode the Gulf-coast averaged dune toe elevation (1.1 m) as well as overwash the average dune crest (2.4 m), even without surge.

  • Hurricanes are not required for significant coastal change in the Gulf region. Waves and storm surge associated with tropical storms and winter cold fronts provide sufficient energy to put low-elevation beaches and dunes at risk to erosion.

Full Reports

National Assessment of Hurricane-Induced Coastal Erosion Hazards: Mid-Atlantic - Open-File Report 20131131

National Assessment of Hurricane-Induced Coastal Erosion Hazards: Southeast Atlantic - Open-File Report 20131130

National Assessment of Hurricane-Induced Coastal Erosion Hazards: Gulf of Mexico - Open-File Report 20121084

Download Data (shape files and metadata)

Metadata


Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo FirstGov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://coastal.er.usgs.gov/hurricanes/erosionhazards/index.php
Page Contact Information: Feedback
Page Last Modified: April 15, 2014 01:01 PM (JSG)