Hurricane Irene - Assessment of Potential Coastal-Change Impacts Completed
The probability of coastal change associated with processes of collision, overwash, and inundation was assessed for areas located within the region expected to be affected by landfall of Hurricane Irene.
Hurricane Irene made landfall just west of Cape Lookout, NC, on 27 August 2011 as a Category 1 hurricane. A second landfall occurred in the early morning of 28 August near Little Egg Inlet, NJ, as a Category 1 hurricane. The U.S. Geological Survey (USGS) Hurricanes and Extreme Storms Group investigates coastal change caused by major storms and responded to this event by acquiring new observations and updating an analysis of coastal changes.
Aerial photography and laser altimetry were collected to document beach morphology and the response to this storm. Comparisons of pre- and post-storm data were used to show the nature, magnitude, and spatial variability of coastal changes such as beach erosion, overwash deposition, and island breaching. These data were also used to further refine predictive models of coastal impacts from severe storms.
Assessment of Potential Coastal-Change Impacts
Hurricane landfall and associated elevated water levels, waves, and currents can lead to severe coastal change through erosion and re-deposition of sediment. The potential for coastal change due to hurricanes is predicted using a USGS-developed storm-impact scale that compares predicted elevations of hurricane-induced water levels (storm surge and wave runup) to known elevations of coastal topography to define four coastal change regimes. These regimes describe the dominant interactions between beach morphology and storm processes and the resulting modes of coastal change along beaches that serve as the "first line of defense" for many regions exposed to hurricanes.
The regimes include collision, which is when waves attack the base of dunes and cause dune-front erosion. Under higher surge or wave runup, waves can overtop dunes leading to overwash, dune erosion, landward dune migration, and overwash deposition on low, narrow islands. The most extreme coastal change regime is associated with inundation, where the elevation of storm surge exceeds the elevation of the primary dune or beach berm. Under these conditions the beach and dune can be severely eroded and low, narrow islands may breach.
The probability of coastal change associated with processes of collision, overwash, and inundation was assessed for areas located within the region expected to be affected by landfall of Hurricane Irene.
Initial Assessment, Generalized Storm Scenarios (08-25-2011)
This initial assessment describes coastal change probability based on estimating the likelihood that the beach system would experience erosion and deposition patterns consistent with collision, overwash, or inundation regimes. The probabilities were estimated by calculating the difference between modeled total water levels (including storm surge and wave runup) and lidar-derived dune or berm elevations. The storm surge elevations were obtained from the National Oceanic and Atmospheric Administration (NOAA) storm surge model (SLOSH), which simulated the surge resulting from numerous hypothetical hurricane landfall scenarios (Category 1-5) . Predicted maximum wave heights obtained from the NOAA WaveWatch3 model 7-day forecast were used to compute wave runup elevations.
In the maps below, red colors indicate high probability and white indicates low probability. The probabilities can be interpreted as indicating that the specified coastal change regime was very likely (probability >90%), likely (>66%), about as likely as not (33% to 66%), unlikely (<33%), and very unlikely (<10%) given each hypothetical storm scenario.
This analysis assumes a hypothetical hurricane landfall scenario such that each location on the map would experience the most severe impacts that would be associated with the right front quadrant of the hurricane.
Updated Assessment, Irene-Specific Conditions (updated 08-26-2011)
This assessment describes coastal change probability based on estimating the likelihood that the beach system would experience erosion and deposition patterns consistent with collision, overwash, or inundation regimes. The probabilities were estimated by calculating the difference between modeled total water levels (including storm surge and wave runup) and lidar-derived dune or berm elevations. The storm surge elevations along the open coast were obtained from the National Oceanic and Atmospheric Administration's (NOAA) probabilistic surge forecast (psurge), which is based on conditions specific to the landfalling storm. Errors in hurricane forecasts are included in order to identify probable surge levels. Rather than including the full range of storm surge probabilities, we selected the 50% exceedance surge level to represent the best-estimate scenario. Maximum wave heights obtained from the NOAA WaveWatch3 model 7-day forecast were used to compute runup elevations.
In the maps below, red colors indicate high probability and white indicates low probability. The probabilities can be interpreted as indicating that the specified coastal change regime was very likely (probability >90%), likely (>66%), about as likely as not (33% to 66%), unlikely (<33%), and very unlikely (<10%) given the present storm forecasts.
Note that the computations assumed landfall at mean astronomical tide. Landfall at high tide would lead to higher coastal change probabilities.
Disclaimer: This experimental product is based on research results of the USGS National Assessment of Coastal Change Hazards Project and is intended to indicate the potential for coastal change caused by storm surge and wave runup. This product is based on an analysis that simplifies the problem to include some of the most important aspects (estimated dune elevations and predicted total water levels). This product does not directly consider potential property damage or the impacts of high wind speeds and heavy rainfall. This product applies to open coast environments and does not consider potential coastal change along bays, passes, or inland lakes. The actual changes that occur during extreme storms are complex functions of a number of processes and variables including ocean waves, currents, and tides. The public should not base evacuation decisions on this product. Citizens should always heed the evacuation advice of local emergency management authorities.
The probability of coastal change associated with processes of collision, overwash, and inundation was assessed for areas located within the region expected to be affected by landfall of Hurricane Irene.
Hurricane Irene made landfall just west of Cape Lookout, NC, on 27 August 2011 as a Category 1 hurricane. A second landfall occurred in the early morning of 28 August near Little Egg Inlet, NJ, as a Category 1 hurricane. The U.S. Geological Survey (USGS) Hurricanes and Extreme Storms Group investigates coastal change caused by major storms and responded to this event by acquiring new observations and updating an analysis of coastal changes.
Aerial photography and laser altimetry were collected to document beach morphology and the response to this storm. Comparisons of pre- and post-storm data were used to show the nature, magnitude, and spatial variability of coastal changes such as beach erosion, overwash deposition, and island breaching. These data were also used to further refine predictive models of coastal impacts from severe storms.
Assessment of Potential Coastal-Change Impacts
Hurricane landfall and associated elevated water levels, waves, and currents can lead to severe coastal change through erosion and re-deposition of sediment. The potential for coastal change due to hurricanes is predicted using a USGS-developed storm-impact scale that compares predicted elevations of hurricane-induced water levels (storm surge and wave runup) to known elevations of coastal topography to define four coastal change regimes. These regimes describe the dominant interactions between beach morphology and storm processes and the resulting modes of coastal change along beaches that serve as the "first line of defense" for many regions exposed to hurricanes.
The regimes include collision, which is when waves attack the base of dunes and cause dune-front erosion. Under higher surge or wave runup, waves can overtop dunes leading to overwash, dune erosion, landward dune migration, and overwash deposition on low, narrow islands. The most extreme coastal change regime is associated with inundation, where the elevation of storm surge exceeds the elevation of the primary dune or beach berm. Under these conditions the beach and dune can be severely eroded and low, narrow islands may breach.
The probability of coastal change associated with processes of collision, overwash, and inundation was assessed for areas located within the region expected to be affected by landfall of Hurricane Irene.
Initial Assessment, Generalized Storm Scenarios (08-25-2011)
This initial assessment describes coastal change probability based on estimating the likelihood that the beach system would experience erosion and deposition patterns consistent with collision, overwash, or inundation regimes. The probabilities were estimated by calculating the difference between modeled total water levels (including storm surge and wave runup) and lidar-derived dune or berm elevations. The storm surge elevations were obtained from the National Oceanic and Atmospheric Administration (NOAA) storm surge model (SLOSH), which simulated the surge resulting from numerous hypothetical hurricane landfall scenarios (Category 1-5) . Predicted maximum wave heights obtained from the NOAA WaveWatch3 model 7-day forecast were used to compute wave runup elevations.
In the maps below, red colors indicate high probability and white indicates low probability. The probabilities can be interpreted as indicating that the specified coastal change regime was very likely (probability >90%), likely (>66%), about as likely as not (33% to 66%), unlikely (<33%), and very unlikely (<10%) given each hypothetical storm scenario.
This analysis assumes a hypothetical hurricane landfall scenario such that each location on the map would experience the most severe impacts that would be associated with the right front quadrant of the hurricane.
Updated Assessment, Irene-Specific Conditions (updated 08-26-2011)
This assessment describes coastal change probability based on estimating the likelihood that the beach system would experience erosion and deposition patterns consistent with collision, overwash, or inundation regimes. The probabilities were estimated by calculating the difference between modeled total water levels (including storm surge and wave runup) and lidar-derived dune or berm elevations. The storm surge elevations along the open coast were obtained from the National Oceanic and Atmospheric Administration's (NOAA) probabilistic surge forecast (psurge), which is based on conditions specific to the landfalling storm. Errors in hurricane forecasts are included in order to identify probable surge levels. Rather than including the full range of storm surge probabilities, we selected the 50% exceedance surge level to represent the best-estimate scenario. Maximum wave heights obtained from the NOAA WaveWatch3 model 7-day forecast were used to compute runup elevations.
In the maps below, red colors indicate high probability and white indicates low probability. The probabilities can be interpreted as indicating that the specified coastal change regime was very likely (probability >90%), likely (>66%), about as likely as not (33% to 66%), unlikely (<33%), and very unlikely (<10%) given the present storm forecasts.
Note that the computations assumed landfall at mean astronomical tide. Landfall at high tide would lead to higher coastal change probabilities.
Disclaimer: This experimental product is based on research results of the USGS National Assessment of Coastal Change Hazards Project and is intended to indicate the potential for coastal change caused by storm surge and wave runup. This product is based on an analysis that simplifies the problem to include some of the most important aspects (estimated dune elevations and predicted total water levels). This product does not directly consider potential property damage or the impacts of high wind speeds and heavy rainfall. This product applies to open coast environments and does not consider potential coastal change along bays, passes, or inland lakes. The actual changes that occur during extreme storms are complex functions of a number of processes and variables including ocean waves, currents, and tides. The public should not base evacuation decisions on this product. Citizens should always heed the evacuation advice of local emergency management authorities.