Papers by Hilary Stockdon
Barrier-island response to hurricanes is driven not only by storm surge, but also by wave-induced... more Barrier-island response to hurricanes is driven not only by storm surge, but also by wave-induced runup. During extreme storms, the 2% exceedence elevation of wave runup can be of equal or greater magnitude than surge levels, making runup a major factor in storm-induced coastal topographic and bathymetric change. Empirical formulations of runup show a dependence on locally measured, shallow-water wave
As with other recent hurricanes, Hurricane Ike, which made landfall near Galveston, TX in 2008 ca... more As with other recent hurricanes, Hurricane Ike, which made landfall near Galveston, TX in 2008 caused extensive change to coastal beach and dune topography near the landfall location. Forecasts of the expected coastal response to landfalling hurricanes are required for both short-term and long-term planning associated with the management of coastal resources. These forecasts can be supported by a combination
Extreme runup occurring during storms and hurricanes is likely to be responsible for the most dra... more Extreme runup occurring during storms and hurricanes is likely to be responsible for the most dramatic erosional events, impacting both the beach and dunes and forming an important design criterion for coastal structures and set back. Yet one of the most commonly used predictive equations for runup (Holman, 1986) is based on data from a single site and has not
By clearly defining the forcing and morphologic controls of swash variance in both the incident a... more By clearly defining the forcing and morphologic controls of swash variance in both the incident and infragravity frequency bands, we are able to derive a more complete parameterization for extreme runup that may be applicable to a wide range of beach and wave conditions. It is expected that the dynamics of the incident and infragravity bands will have different dependencies
Overwash deposits are often observed along low-elevation barrier islands after significant storm ... more Overwash deposits are often observed along low-elevation barrier islands after significant storm surge and wave events. Waves overtop the peak elevation of the beach system, transporting and depositing sediment across the island in a process known as barrier island rollover. Overwash events result in millions of dollars of damage to coastal infrastructure, providing motivation to clarify the process of sediment
The potential impact of a hurricane's landfall on a barrier island beach can be predicted usi... more The potential impact of a hurricane's landfall on a barrier island beach can be predicted using a storm-impact scaling model that compares the relative elevations of foreshore dunes and storm-induced water levels, including both storm surge and wave runup. The overall accuracy of the model in predicting one of three impact regimes (swash, dune erosion, and overwash) was found to
The U.S. Geological Survey's Extreme Storm Research Group has developed a program to measure ... more The U.S. Geological Survey's Extreme Storm Research Group has developed a program to measure and forecast coastal topographic and bathymetric change associated with major hurricanes and other extreme storm events. The measurements provide a baseline data set that documents the rapid changes associated with storms. These data are being applied to quantify changes in shoreline position, dune elevation, and other
In terms of peak magnitude, Dennis was a marginal hurricane that deteriorated into a tropical sto... more In terms of peak magnitude, Dennis was a marginal hurricane that deteriorated into a tropical storm before coming ashore in North Carolina in 1999. However, its duration was remarkable, remaining off the northern Outer Banks for nearly a week generating large waves that impacted the coast. In fact at the US Army Corps of Engineers Field Research Facility at Duck,
In addition to storm surge, the elevation of wave-induced runup plays a significant role in forci... more In addition to storm surge, the elevation of wave-induced runup plays a significant role in forcing geomorphic change during extreme storms. Empirical formulations for extreme runup, defined as the 2% exceedence level, are dependent on some measure of significant offshore wave height. Accurate prediction of extreme runup, particularly during hurricanes when wave heights are large, depends on selecting the most
Hurricane Katrina caused extreme changes to the barrier islands of the central Gulf of Mexico coa... more Hurricane Katrina caused extreme changes to the barrier islands of the central Gulf of Mexico coast. Dauphin Island, Ala., migrated landward and stranded the remains of its oceanfront row homes in the sea. Chandeleur Islands, La., were completely stripped of their sand, leaving only marshy outcrops in the storm's wake.
Coastal Engineering 2000, 2001
Coastal Impacts, Adaptation, and Vulnerabilities, 2012
Eos, Transactions American Geophysical Union, 2010
Extreme storms can have a profound impact on coastal topography and thus on ecosystems and human-... more Extreme storms can have a profound impact on coastal topography and thus on ecosystems and human-built structures within coastal regions. For instance, landfalls of several recent major hurricanes have caused significant changes to the U.S. coastline, particularly along the Gulf of Mexico. Some of these hurricanes (e.g., Ivan in 2004, Katrina and Rita in 2005, and Gustav and Ike in
Coastal Impacts, Adaptation, and Vulnerabilities, 2012
Estuaries and Coasts, 2006
Four hurricanes battered the state of Florida during 2004, the most affecting any state since Tex... more Four hurricanes battered the state of Florida during 2004, the most affecting any state since Texas endured four in 1884. Each of the storms changed the coast differently. Average shoreline change within the right front quadrant of hurricane force winds varied from 1 m of shoreline advance to 20 m of retreat, whereas average sand volume change varied from 11 to 66 m 3 m 21 of net loss (erosion). These changes did not scale simply with hurricane intensity as described by the Saffir-Simpson Hurricane Scale. The strongest storm of the season, category 4 Hurricane Charley, had the least shoreline retreat. This was likely because of other factors like the storm's rapid forward speed and small size that generated a lower storm surge than expected. Two of the storms, Hurricanes Frances and Jeanne, affected nearly the same area on the Florida east coast just 3 wk apart. The first storm, Frances, although weaker than the second, caused greater shoreline retreat and sand volume erosion. As a consequence, Hurricane Frances may have stripped away protective beach and exposed dunes to direct wave attack during Jeanne, although there was significant dune erosion during both storms. The maximum shoreline change for all four hurricanes occurred during Ivan on the coasts of eastern Alabama and the Florida Panhandle. The net volume change across a barrier island within the Ivan impact zone approached zero because of massive overwash that approximately balanced erosion of the beach. These data from the 2004 hurricane season will prove useful in developing new ways to scale and predict coastal-change effects during hurricanes.
Marine Geology, 2007
The vulnerability of a beach to extreme coastal change during a hurricane can be estimated by com... more The vulnerability of a beach to extreme coastal change during a hurricane can be estimated by comparing the relative elevations of storm-induced water levels to those of the dune or berm. A simple model that defines the coastal response based on these elevations was used to hindcast the potential impact regime along a 50-km stretch of the North Carolina coast to the landfalls of Hurricane Bonnie on August 27, 1998, and Hurricane Floyd on September 16, 1999. Maximum total water levels at the shoreline were calculated as the sum of modeled storm surge, astronomical tide, and wave runup, estimated from offshore wave conditions and the local beach slope using an empirical parameterization. Storm surge and wave runup each accounted for ∼48% of the signal (the remaining 4% is attributed to astronomical tides), indicating that wave-driven process are a significant contributor to hurricane-induced water levels. Expected water levels and lidar-derived measures of pre-storm dune and berm elevation were used to predict the spatially-varying storm-impact regime: swash, collision, or overwash. Predictions were compared to the observed response quantified using a lidar topography survey collected following hurricane landfall. The storm-averaged mean accuracy of the model in predicting the observed impact regime was 55.4%, a significant improvement over the 33.3% accuracy associated with random chance. Model sensitivity varied between regimes and was highest within the overwash regime where the accuracies were 84.2% and 89.7% for Hurricanes Bonnie and Floyd, respectively.
Marine Geology, 2002
Over time scales of hundreds to thousands of years, the net longshore sand transport direction al... more Over time scales of hundreds to thousands of years, the net longshore sand transport direction along the central California coast has been driven to the south by North Pacific winter swell. In contrast, during the El Nin ‹ o winter of 1997^1998, comparisons of before and after airborne lidar surveys showed sand was transported from south to north and accumulated on the south sides of resistant headlands bordering pocket beaches. This resulted in significant beach erosion at the south ends of pocket beaches and deposition in the north ends. Coincident with the south-to-north redistribution of sand, shoreline morphology became prominently cuspate with longshore wavelengths of 400^700 m. The width and elevation of beaches were least where maximum shoreline erosion occurred, preferentially exposing cliffs to wave attack. The resulting erosional hotspots typically were located in the embayments of giant cusps in the southern end of the pocket beaches. The observed magnitude of sea cliff retreat, which reached 14 m, varied with the number of hours that extreme wave runup exceeded certain thresholds representing the protective capacity of the beach during the El Nin ‹ o winter. A threshold representing the width of the beach performed better than a threshold representing the elevation of the beach. The magnitude of cliff erosion can be scaled using a simple model based on the cross-shore distance that extreme wave runup exceeded the pre-winter cliff position. Cliff erosion appears to be a balance between terrestrial mass wasting processes, which tend to decrease the cliff slope, and wave attack, which removes debris and erodes the cliff base increasing the cliff slope. ß
Journal of Coastal Research, 2009
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Papers by Hilary Stockdon