Vulnerability of National Park Service Beaches to Inundation during 

a Direct Hurricane Landfall: Cape Lookout National Seashore

Hilary F. Stockdon and David M. Thompson

U.S. Geological Survey

FISC-St. Petersburg

600 4th Street S.

St. Petersburg, FL 33701

Abstract

Cape Lookout National Seashore, a barrier-island coastal park 

in North Carolina, is vulnerable to the powerful, sand-moving 

forces of hurricanes. Waves and storm surge associated with 

these strong tropical storms are part of a natural process in 

barrier-island evolution and can cause extensive morphologic 

changes in coastal parks, leading to road closures and reduced 

visitor accessibility. The vulnerability of park beaches to inundation, and associated extreme coastal change, during a direct 

hurricane landfall can be assessed by comparing the elevations 

of storm-induced mean-water levels (storm surge) to the elevations of the crest of the sand dune that defines the beach system. 

Maps detailing the inundation potential for Category 1-5 hurricanes can be used by park managers to determine the relative 

vulnerability of various barrier-island parks and to assess which 

areas of a particular park are more susceptible to inundation and 

extreme coastal changes.

1. Introduction

Along much of the East Coast of the United States, hurricanes 

have been responsible for some of the most dramatic changes to 

our coastal environments – from the creation of large overwash 

deposits to the opening of new inlets. Strong winds associated 

with these tropical storms bring large waves and storm surge 

that force significant changes on fragile barrier islands, where 

the balance between island stability and rising water levels is 

maintained by dynamic changes of beach morphology. On 

developed barrier islands, hurricane-induced coastal change 

makes local infrastructure more vulnerable to failure. Even in 

our national coastal parks, where development is strictly managed, hurricanes threaten to destroy infrastructure that keeps the 

parks operational (roads, communications, park buildings) as 

well as to alter dramatically the beaches and dunes that provide 

visitors with the opportunity to observe wildlife and experience 

the interaction of the land and sea.

The impact of a hurricane on a beach has been shown to be 

highly variable over both large and small stretches of coast 

(Stockdon et al., 2003) One section of beach may be largely 

unaffected by a storm, while an adjacent area experiences 

extreme coastal change associated with island overwash or 

breaching. This spatially variable response to storms is partly 

due to longshore variability of the pre-storm beach morphology combined with variability in the offshore physical forcing 

(Stockdon et al., 2007a). Using a storm-impact scaling model 

that compares the relative elevations of barrier-island morphology and storm-induced water levels, the potential vulnerability 

of a barrier island to extreme coastal change during a hurricane 

landfall can be defined (Sallenger, 2000). 

A complete and comprehensive management plan preparing 

for a hurricane landfall, as well as plans for post-hurricane 

recovery, should be based on an assessment of what areas of 

the coast are most vulnerable. In order to help several of our 

coastal National Parks prepare for a possible hurricane landfall, 

the USGS, at the request of the National Park Service (NPS), 

has prepared an analysis of the vulnerability of Cape Lookout 

National Seashore (NS) beaches to inundation during a direct 

landfall. The results can be used to assess what areas of the park 

are most susceptible to extreme coastal change during a hurricane. These findings can also be compared to those from other 

NPS coastal parks to determine, in a relative sense, which parks 

are most at risk during strong tropical storms. 

Cape Lookout NS is located in North Carolina between Beaufort Inlet to the southwest and Ocracoke Inlet to the northwest 

(Fig. 1). The 90 km of park include the uninhabited barrier 

islands of Shackleford Banks, South Core Banks, and North 

Core Banks. The open-ocean beaches of Cape Lookout face the 

Atlantic Ocean and are susceptible to the forces of approaching 

hurricanes. 

2. Methods

2.1 Storm-impact Scaling Model

A simple storm-impact scale that compares elevations of the 

most seaward sand dune to elevations of hurricane-induced 

water levels can be used to define the likely impact regime for 

an approaching hurricane (Sallenger, 2000). During a storm, 

the combined effects of 1) the astronomical tide, 2) storm surge 

(elevated water levels associated with the large winds and low 

pressures of a hurricane), and 3) wave runup (the super-elevation of the water surface at the shoreline due to waves, both the 

time-varying and time-averaged components) move the erosive 

forces of the storm higher on the beach face than during typical 

wave conditions. The total elevation of these three parameters 

defines the maximum water level (Rhigh) attained during a storm, 

while the storm-induced mean-water level (Rlow) can be defined 

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2007–1376

October 2007


Figure 1. Location map for Cape Lookout National Seashore.

by only storm surge and wave setup. These forces may reach the 

elevation of the base (Dlow) and crest (Dhigh) of the most seaward 

sand dunes that define the landward limits of the beach system 

and represent the first-line defense of a barrier island in an 

approaching storm. Using these parameters, four storm-impact 

regimes, or thresholds for coastal change, may be defined 

–swash (Rhigh < Dlow), collision (Rhigh > Dlow), overwash (Rhigh > 

Dhigh), and inundation (Rlow > Dhigh)–to provide a framework for 

examining the general types and relative magnitudes of coastal 

change that are likely to occur during hurricanes (Sallenger, 

2000; Stockdon et al., 2007a).

Here we focus on the most extreme of the four impact regimes, 

inundation, which occurs when the storm-induced mean-water 

level (Rlow) exceeds the elevation of the crest of the most seaward sand dune (Dhigh). Within this regime, the beach system 

(foredune ridge and beach) is completely submerged, and net 

landward transport of sediment is likely to occur (Sallenger, 

2000). Typically, larger magnitudes of shoreline retreat and 

beach erosion will occur when the beach is inundated due to the 

transport of sand in both the offshore and onshore directions 

(Stockdon et al., 2007a). 

The predictive accuracy of the scaling model was tested by 

hindcasting the likely impact of Hurricanes Bonnie and Floyd 

(Stockdon et al., 2007a) and of Hurricane Ivan (Stockdon et al., 

2007b). For Hurricane Ivan, the overall hindcast accuracy of the 

model in predicting one of the four regime types was 68%. The 

sensitivity of the model within the inundation regime was 51% 

(Stockdon et al., 2007b). Underprediction errors were likely 

due to profile evolution of the low-lying barriers during the 

landfall of the Category 4 storm. In order to use this model in a 

predictive mode to examine the potential for inundation during 

a future hurricane landfall, accurate estimates of both the dune 

parameters and the expected hurricane-induced mean-water 

level are needed.

2.2 Dune Elevation

The morphology of the beach and dunes at Cape Lookout NS 

was mapped based on an airborne lidar topographic survey 

collected on October 1 and 2, 2005, by the U.S. Army Corps 

of Engineers (USACE) CHARTS system. GPS-based lidar 

surveys provide an efficient method for collecting high-reso-
lution data of subaerial topography with sufficient accuracy 

(root-mean-square vertical accuracy = 15 cm) to resolve the 

spatial details of sand-dune elevation and position (Sallenger 

et al., 2003).

The elevation of the foredune crest (or, in the absence of a dune, 

the beach berm) was extracted every 20 m along the coast of 

Cape Lookout NS from cross-shore profiles of lidar topography 

(Fig. 2). An automatic algorithm was used to select the peak of 

the most seaward dune within a prescribed beach width (here, 

150 m). The results were then manually checked to ensure the 

extraction of a consistent feature defining the landward extent 

of the beach system (Fig. 3). 

2.3 Storm Surge

In this analysis, Rlow is represented only by the storm surge. 

Wave setup was not considered because predictions of wave 

conditions (height and period) for a generic hurricane of each 

category are not currently available. The predicted elevations of 

storm surge for Saffir-Simpson Category 1-5 hurricanes were 

extracted from the NOAA SLOSH (Sea, Lake, and Overland 

Surges from Hurricanes) model, a real-time forecast model for 

hurricane-induced water levels for the Gulf and Atlantic Coasts. 

The numerical model is based on linearized, depth-integrated 

equations of motion and continuity (Jarvinen and Lawrence, 

1985). Storm surge is modeled by simulating the conditions of 

each-category storm approaching the coast from different angles 

and at varying speeds. Changes in maximum surge elevations 

are forced by time-varying wind-stress and pressure-gradient forces that depend on hurricane location, minimum pressure, and size measured from the eyewall out to the location of 

maximum winds (Jarvinen and Lawrence, 1985). The maximum surge within each grid cell is defined as the Maximum 

of the Maximum Envelope of Water (MOMs) and represents 

the worst-case, localized surge that will occur for landfall in a 

given location, not what would occur along the entire coast for 

a single storm. The results are location specific, accounting for 

local water depths, proximity to bays and rivers, etc., and are 

accurate to ± 20% of the calculated value (NOAA, 2007). Errors 

in the SLOSH model can arise from differences between the 

parametric wind models, which force SLOSH, and the actual 

hurricane wind field (Houston et al., 1999) as well as discrepancies between the coarse model grid and the real topography and 

bathymetry over which the storm may travel.

For Cape Lookout NS, the maximum surge at the shoreline 

was extracted from the MOMs results for the Pamlico Sound 

model grid (Fig. 4, left). Maximum, open-coast surge values 

were extracted at the location of the October 2005 lidar-derived, 

mean-high-water (MHW; 0.36 m NAVD88 for Shackleford 

Banks, 0.26 m NAVD88 elsewhere) shoreline position (Fig. 4, 

right). The Pamlico SLOSH-model grid has an approximate 

cell size of 2.4 to 2.8 km along the shoreline of Cape Lookout 

NS. In locations where grid resolution resulted in anomalously 

low values because the barrier island was not fully resolved, the 

most nearshore grid cell representing conditions seaward of the 

barrier island was chosen.

3. Inundation Vulnerability

The potential inundation, I, of the beach system was defined 

every 20 m along Cape Lookout NS by calculating the difference between the elevations of SLOSH-modeled storm surge 

(Rlow) for each hurricane category and of lidar-measured dune 

crests (Dhigh) (Fig. 5). Negative values (blues) indicate that 

water levels are predicted to be lower than the dune crest and 

that a particular section of beach is not likely to be inundated 

during the direct landfall of a hurricane. Positive values (reds) 

signify areas where the beach is more likely to be inundated by 

storm surge. These estimates assume landfall at mean astronomical tide and do not include the effects of wave setup, which, 

during strong storms (Category 3 and above), may increase the 

storm-induced mean-water level by more than 30% above that 

due to surge alone. This would increase the beach’s vulnerability to inundation. Additionally, the maps represent the vulnerability of the beach system as it was at the time of the October 

2005 lidar survey. Major changes to beach morphology, such 

as those caused by large storms and hurricanes, may change the 

future vulnerability of this stretch of coast. 

For the direct landfall of a Category 1 storm, only 11% of the 

Cape Lookout coast is vulnerable to inundation, compared 

to over 91% during a Category 5 storm. The eastern half and 

western 2 km of Shackleford Banks are more susceptible to 

inundation: Rlow > Dhigh for these areas for Category 3 and higher 

storms. Also, areas around inlets are more vulnerable during 

hurricane landfall. The beaches extending 3.5 km to the southwest and 1.2 km to the northeast of New Drum Inlet as well as a 

6-km stretch of coast south of Ocracoke Inlet are most vulnerable to inundation during a hurricane landfall: these areas reach 

or exceed the inundation threshold for Category 2 storms and 

higher. The longshore variability observed in I is due to spatial 

variations in the height of the frontal dune. The mean elevation 

of Dhigh is 2.81 m (NAVD88) with substantial longshore variability, standard deviation, σ, = 0.95 m (Fig. 6). Additionally, modeled surge elevations were larger along Shackleford Banks (Fig. 

4), making the beach and dunes on this southwest-facing island 

more vulnerable. The spatially averaged surge for a Category 1 

Figure 2. Cross-shore profile of lidar data from Cape Lookout NS 

showing the location of the most seaward sand dune. The ocean is 

located to the right. 
Figure 3. The extracted dune crest for approximately 1.3 km of the Cape Lookout NS coast, superimposed on the lidar 

topography. The arrow refers to the location of the profile shown in Figure 2.

Figure 4. SLOSH-model results for a Category 3 hurricane for the Pamlico Sound model grid (left) shows the variability of modeled surge 

values along the coast. Maximum, open-coast surge levels for Categories 1-5 hurricanes were extracted from the SLOSH grid along the 

Atlantic shoreline of Cape Lookout NS (right). 
Figure 5. The potential inundation, I, of the beach system at Cape Lookout NS for Categories 1-5 hurricanes is defined as the difference betwe

window was applied to the data before plotting. Positive values indicate that modeled storm surge exceeds the elevation of the dune crest sumore vulnerable to inundation and the associated extreme coastal changes. A larger version of this map can be downloaded from http://coas
Figure 6. Dune elevations (Dhigh) for Cape Lookout NS were measured from a lidar topographic survey collected on October 1 and 2, 200

categories 1-5 hurricanes were extracted from the NOAA SLOSH model and represent the open-coast ‘maximum of the maximum.’ A ladownloaded from http://coastal.er.usgs.gov/nps-beaches/. 
hurricane was 1.51 m, while the average surge for a Category 5 

storm was 4.71 m. (Fig. 6)

4. Rates of Recent Shoreline Change

Detailed analysis of the historic (150-yr) rates of shoreline 

change, calculated using the horizontal position of the MHW 

shoreline from four time periods (mid- to late-1800s, 1920s1940s, 1970s-1980s, and 1997), along Cape Lookout NS show 

areas of both accretion and erosion (Morton and Miller, 2005). 

The most erosive areas are Shackleford Banks, the northern 

end of South Core Banks, and the southern end of North Core 

Banks, whereas the remaining areas of the park are accreting or 

relatively stable. Details of the calculations and specific rates of 

change for both historic and short-term (~20 yr) periods can be 

found in Miller et al. (2005). 

Rates of recent shoreline change were calculated between the 

September 1997 shoreline used in the Morton and Miller (2005) 

analysis and the modern shoreline position as defined using 

the October 2005 lidar survey that was the basis of the inundation analysis. From each lidar survey, datum-based (MHW = 

0.36 m and 0.26 m) shoreline positions were extracted every 20 

m along the coast using techniques described in Stockdon et al. 

(2002). Horizontal movement of shoreline, calculated as the 

difference in position between 2005 and 1997, was highly variable along the 90-km stretch of coast (Fig. 7). The mean change 

along the coast of the park over the 8-yr time period was -11.17 

m, and the standard deviation was 33.32 m. The largest amount 

of change was observed adjacent to inlets. Away from inlets, the 

magnitude of shoreline change ranged from 20.4 m of accretion near the Cape to 88.0 m of shoreline retreat southwest of 

Old Drum Inlet. The mean, short-term change rate over the 8-yr 

period was -1.4 m/yr (σ = 4.17 m/yr). Detailed rates of change 

and associated error bars for the length of the park can be found 

at http://coastal.er.usgs.gov/nps-beaches/. 

5. Discussion

The inundation vulnerability maps detail the worst-case surge 

scenario for each location along the coast. Maximum surge 

typically occurs to the right of landfall under the eyewall and 

decreases with distance away from the center of the storm. Consequently, the worst case for any given storm is localized and 

will not occur along the entire coast of Cape Lookout NS. The 

map shows areas that are most likely to be inundated by storm 

surge should the hurricane make landfall immediately to the 

southwest of that particular location. 

Figure 7. Short-term (8-yr) rates of shoreline change for Cape Lookout NS. Data were smoothed with a 100-m window. Negative values 

indicate erosion. The mean rate is -1.41 m/yr. The gap in the data between 15 and 30 km in the longshore is due to poor lidar coverage around 

the shoals of Cape Lookout. 
If the beach system is inundated, the dune will be overtopped 

by storm surge. Strong waves and currents may transport large 

amounts of sand landward across the island. These types of 

changes have been shown to be more long-lasting because sand 

removed from the beach face does not typically return in the 

years following storm landfall (Stockdon et al., 2007a). Under 

some conditions, the currents will create new or expose relict 

inlets, such as those on Core Banks and Hatteras Island during 

the 2003 landfall of Hurricane Isabel. 

Acknowledgments

We thank Rebecca Beavers and Mark Borrelli (NPS) for their 

assistance in the development of this project. The lidar data 

were collected by Jeff Lillycrop (USACE) and his CHARTS 

team. We also thank Betsy Boynton, Kara Doran, Kristy Guy, 

Peter Howd, Abby Sallenger, Jolene Shirley, and Charlene 

Sullivan (USGS) for their contributions to this study. John Fry, 

Tony Curtis, and Linda York (NPS) provided early reviews 

of the map products. This work was funded by National Park 

Service, Natural Resource Program Center.

References

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response to Hurricanes Bonnie and Floyd: Proceedings, 

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Clearwater Beach, FL, CD-ROM.

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For more information:

For the USGS:

Hilary F. Stockdon

David M. Thompson

U.S. Geological Survey 

Florida Integrated Science Center–St. Petersburg

600 4th Street S.

St. Petersburg, FL 33701

Tel: (727) 803-8747

Email: hstockdon@usgs.gov

For the NPS-GRD:

Mark Borrelli

National Park Service

Natural Resource Program Center

Geologic Resources Division (GRD)

P.O. Box 25287

Denver, CO 80225-0287

Tel: (303) 969-2171