Geology topics

David M. Thompson

Publications and source records attributed to David M. Thompson.

32 records · Page 2Linked to original sources

USGS2014

Evaluation of wave runup predictions from numerical and parametric models

Wave runup during storms is a primary driver of coastal evolution, including shoreline and dune erosion and barrier island overwash. Runup and its components, setup and swash, can be predicted from a parameterized model that was developed by comparing runup observations to offshore wave height, wave period, and local beach slope. Because observations during extreme storms are often unavailable, a numerical model is used to simulate the storm-driven runup to compare to the parameterized model and then develop an approach to improve the accuracy of the parameterization. Numerically simulated and parameterized runup were compared to observations to evaluate model accuracies. The analysis demonstrated that setup was accurately predicted by both the parameterized model and numerical simulations. Infragravity swash heights were most accurately predicted by the parameterized model. The numerical model suffered from bias and gain errors that depended on whether a one-dimensional or two-dimensional spatial domain was used. Nonetheless, all of the predictions were significantly correlated to the observations, implying that the systematic errors can be corrected. The numerical simulations did not resolve the incident-band swash motions, as expected, and the parameterized model performed best at predicting incident-band swash heights. An assimilated prediction using a weighted average of the parameterized model and the numerical simulations resulted in a reduction in prediction error variance. Finally, the numerical simulations were extended to include storm conditions that have not been previously observed. These results indicated that the parameterized predictions of setup may need modification for extreme conditions; numerical simulations can be used to extend the validity of the parameterized predictions of infragravity swash; and numerical simulations systematically underpredict incident swash, which is relatively unimportant under extreme conditions.

Coastal Engineering↗

USGS2014

Assessing mobility and redistribution patterns of sand and oil agglomerates in the surf zone

Heavier-than-water sand and oil agglomerates that formed in the surf zone following the Deepwater Horizon oil spill continued to cause beach re-oiling 3 years after initial stranding. To understand this phenomena and inform operational response now and for future spills, a numerical method to assess the mobility and alongshore movement of these “surface residual balls” (SRBs) was developed and applied to the Alabama and western Florida coasts. Alongshore flow and SRB mobility and potential flux were used to identify likely patterns of transport and deposition. Results indicate that under typical calm conditions, cm-size SRBs are unlikely to move alongshore, whereas mobility and transport is likely during storms. The greater mobility of sand compared to SRBs makes burial and exhumation of SRBs likely, and inlets were identified as probable SRB traps. Analysis of field data supports these model results.

Alabama;Florida↗

USGS2014

National assessment of hurricane-induced coastal erosion hazards: Northeast Atlantic Coast

Beaches serve as a natural buffer between the ocean and inland communities, ecosystems, and natural resources. However, these dynamic environments move and change in response to winds, waves, and currents. During extreme storms, changes to beaches can be great, and the results are sometimes catastrophic. Lives may be lost, communities destroyed, and millions of dollars spent on rebuilding. During storms, large waves may erode beaches, and high storm surge may shift the erosive force of the waves higher on the beach. In some cases, the combined effects of waves and surge may cause overwash (when waves and surge overtop the dune, transporting sand inland) or flooding. Buildings and infrastructure on or near a dune can be undermined during wave attack and subsequent erosion. Hurricanes Irene and Sandy made landfall along the Eastern United States in August 2011 and October 2012, respectively. Although these hurricanes made landfall south and west of the northeast Atlantic coast, waves from these storms caused severe erosion and undermining, destroying roads in some areas of the coast (for example Westport, Massachusetts). Waves overtopping a dune can transport water and sand inland, covering roads and blocking evacuation routes or impeding emergency relief. If storm surge inundates barrier island dunes, currents flowing across the island can create a breach, or a new inlet, completely severing evacuation routes. Extreme coastal changes caused by hurricanes may increase the vulnerability of communities both during a storm and to future storms. For example, when sand dunes are substantially eroded, inland structures are exposed to storm surge and waves. On barrier islands, absent or low dunes allow water to flow inland across the island, potentially increasing storm surge in the back bay, on the sound-side of the barrier, and on the mainland.

Connecticut, Maine, Massachusetts, New Hampshire, ↗

USGS2013

Application of a hydrodynamic and sediment transport model for guidance of response efforts related to the Deepwater Horizon oil spill in the Northern Gulf of Mexico along the coast of Alabama and Florida

U.S. Geological Survey (USGS) scientists have provided a model-based assessment of transport and deposition of residual Deepwater Horizon oil along the shoreline within the northern Gulf of Mexico in the form of mixtures of sand and weathered oil, known as surface residual balls (SRBs). The results of this USGS research, in combination with results from other components of the overall study, will inform operational decisionmaking. The results will provide guidance for response activities and data collection needs during future oil spills. In May 2012 the U.S. Coast Guard, acting as the Deepwater Horizon Federal on-scene coordinator, chartered an operational science advisory team to provide a science-based review of data collected and to conduct additional directed studies and sampling. The goal was to characterize typical shoreline profiles and morphology in the northern Gulf of Mexico to identify likely sources of residual oil and to evaluate mechanisms whereby reoiling phenomena may be occurring (for example, burial and exhumation and alongshore transport). A steering committee cochaired by British Petroleum Corporation (BP) and the National Oceanic and Atmospheric Administration (NOAA) is overseeing the project and includes State on-scene coordinators from four States (Alabama, Florida, Louisiana, and Mississippi), trustees of the U.S. Department of the Interior (DOI), and representatives from the U.S. Coast Guard. This report presents the results of hydrodynamic and sediment transport models and developed techniques for analyzing potential SRB movement and burial and exhumation along the coastline of Alabama and Florida. Results from these modeling efforts are being used to explain the complexity of reoiling in the nearshore environment and to broaden consideration of the different scenarios and difficulties that are being faced in identifying and removing residual oil. For instance, modeling results suggest that larger SRBs are not, under the most commonly observed low-energy wave conditions, likely to move very far alongshore. This finding suggests that SRBs from one source location may not (outside of storm conditions) be redistributed to other up or down coast locations. This information can guide operational response decisions. In addition, because SRBs are less mobile compared with sand, they are likely to become buried and unburied under normal sand transport processes thereby lengthening the time SRBs may take to move onshore. The rate of onshore movement was not specifically addressed by this study, yet the results resolve the cross-shore domain and cross-shore variations in alongshore transport that are relevant to achieving the primary objectives. Furthermore, during infrequent events (for example, winter storms and severe meteorological events such as Hurricane Isaac of August 2012), energy is shown to be sufficient to move a greater range of SRB sizes and potentially expose and break up submerged oil mats. When SRBs do move alongshore, the models indicate that there are regions that are more conducive to accumulation of SRB material than others. Accumulation can occur where there are reversals and decelerations in alongshore currents and where forces created by shear stress drops below critical thresholds to maintain or initiate SRB movement. In addition, flow and SRB mobility patterns around inlets indicate patterns in hydrodynamic forces that influence redistribution of SRBs and the surface oil that mixed with sediment to form oil mats in the first place.

Alabama;Florida↗

USGS2013

National assessment of hurricane-induced coastal erosion hazards: Southeast Atlantic Coast

Beaches serve as a natural barrier between the ocean and inland communities, ecosystems, and natural resources. However, these dynamic environments move and change in response to winds, waves, and currents. During extreme storms, changes to beaches can be large, and the results are sometimes catastrophic. Lives may be lost, communities destroyed, and millions of dollars spent on rebuilding. During storms, large waves may erode beaches, and high storm surge shifts the erosive force of the waves higher on the beach. In some cases, the combined effects of waves and surge may cause overwash or flooding. Building and infrastructure on or near a dune can be undermined during wave attack and subsequent erosion. During Hurricane Ivan in 2004, a five-story condominium in Orange Beach, Alabama, collapsed after the sand dune supporting the foundation eroded. The September 1999 landfall of Hurricane Dennis caused erosion and undermining that destroyed roads, foundations, and septic systems. Waves overtopping a dune can transport sand inland, covering roads and blocking evacuation routes or emergency relief. If storm surge inundates barrier island dunes, currents flowing across the island can create a breach, or new inlet, completely severing evacuation routes. Waves and surge during the 2003 landfall of Hurricane Isabel left a 200-meter (m) wide breach that cut the only road to and from the village of Hatteras, N.C. Extreme coastal changes caused by hurricanes may increase the vulnerability of communities both during a storm and to future storms. For example, when sand dunes on a barrier island are eroded substantially, inland structures are exposed to storm surge and waves. Absent or low dunes also allow water to flow inland across the island, potentially increasing storm surge in the back bay, on the soundside of the barrier, and on the mainland. During Hurricane Isabel the protective sand dunes near the breach were completely eroded, increasing vulnerability to future storms.

North Carolina;South Carolina;Georgia;Florida↗

USGS2013

National assessment of hurricane-induced coastal erosion hazards: Mid-Atlantic Coast

Beaches serve as a natural buffer between the ocean and inland communities, ecosystems, and natural resources. However, these dynamic environments move and change in response to winds, waves, and currents. During extreme storms, changes to beaches can be large, and the results are sometimes catastrophic. Lives may be lost, communities destroyed, and millions of dollars spent on rebuilding. During storms, large waves may erode beaches, and high storm surge shifts the erosive force of the waves higher on the beach. In some cases, the combined effects of waves and surge may cause overwash (when waves and surge overtop the dune, transporting sand inland) or flooding. Building and infrastructure on or near a dune can be undermined during wave attack and subsequent erosion. During Hurricane Ivan in 2004, a five-story condominium in Orange Beach, Alabama, collapsed after the sand dune supporting the foundation eroded. Hurricane Sandy, which made landfall as an extra-tropical cyclone on October 29, 2012, caused erosion and undermining that destroyed roads, boardwalks, and foundations in Seaside Heights, New Jersey. Waves overtopping a dune can transport sand inland, covering roads and blocking evacuation routes or emergency relief. If storm surge inundates barrier island dunes, currents flowing across the island can create a breach, or a new inlet, completely severing evacuation routes. Waves and surge during Hurricane Sandy, which made landfall on October 29, 2012, left a breach that cut the road and bridge to Mantoloking, N.J. Extreme coastal changes caused by hurricanes may increase the vulnerability of communities both during a storm and to future storms. For example, when sand dunes on a barrier island are eroded substantially, inland structures are exposed to storm surge and waves. Absent or low dunes also allow water to flow inland across the island, potentially increasing storm surge in the back bay, on the soundside of the barrier, and on the mainland.

New York;New Jersey;Delaware;Maryl;Virginia↗

USGS2013

Appendix D: Use of wave scenarios to assess potential submerged oil mat (SOM) formation along the coast of Florida and Alabama

During the Deepwater Horizon oil spill, oil in the surf zone mixed with sediment in the surf zone to form heavier-than-water sediment oil agglomerates of various size, ranging from small (cm-scale) pieces (surface residual balls, SRBs) to large mats (100-m scale, surface residue mats, SR mats). Once SR mats formed in the nearshore or in the intertidal zone, they may have become buried by sand moving onshore or alongshore. To assist in locating possible sites of buried oil, wave scenarios previously developed by the U.S. Geological Survey (USGS) were used to determine the depths at which surface oil had the potential to mix with suspended sediment. For sediment to mix with floating oil and form an agglomerate of sufficient density to sink to the seafloor, either the water must be very shallow (e.g., within the swash zone) or sediment must be suspended to the water surface in sufficient concentrations to create a denser-than-sea water agglomerate. The focus of this study is to analyze suspended sediment mixing with surface oil in depths beyond the swash zone, in order to define the seaward limit of mat formation. A theoretical investigation of sediment dynamics in the nearshore zone revealed that non-breaking waves do not suspend enough sediment to the surface to form sinking sand/oil agglomerates. For this study, it was assumed that the cross-shore distribution of potential agglomerate formation is associated with the primary breaker line, and the presence of plunging breakers, over the time frame of oiling. The potential locations of submerged oil mats (SOMs) are sites where (1) possible agglomerate formation occurred, where (2) sediment accreted post-oiling and buried the SOM, and where (3) the bathymetry has not subsequently eroded to re-expose any mat that may have formed at that site. To facilitate identification of these locations, the range of water level variation over the time frame of oiling was also prescribed, which combined with the wave-breaking depth analysis and pre-oiling bathymetry would identify the potential geographic locations of SOMs.

Operational Science Advisory Team Report↗

USGS2012

Modeling dune response using measured and equilibrium bathymetric profiles

Coastal engineers typically use numerical models such as SBEACH to predict coastal change due to extreme storms. SBEACH model inputs include pre-storm profiles, wave heights and periods, and water levels. This study focuses on the sensitivity of SBEACH to the details of pre-storm bathymetry. The SBEACH model is tested with two initial conditions for bathymetry, including (1) measured bathymetry from lidar, and (2) calculated equilibrium profiles. Results show that longshore variability in the predicted erosion signal is greater over measured bathymetric profiles, due to longshore variations in initial surf zone bathymetry. Additionally, patterns in predicted erosion can be partially explained by the configuration of the inner surf zone from the shoreline to the trough, with surf zone slope accounting for 67% of the variability in predicted erosion volumes.

Conference Paper↗

USGS2012

National assessment of hurricane-induced coastal erosion hazards--Gulf of Mexico

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. This report defines hurricane-induced coastal erosion hazards for sandy beaches along the U.S. Gulf of Mexico coastline. 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: collision (dune erosion), overwash, and inundation. 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.

Open-File Report↗

USGS2011

Process-based model predictions of hurricane induced morphodynamic change on low-lying barrier islands

Using Delft3D, a Chandeleur Island model was constructed to examine the sediment-transport patterns and morphodynamic change caused by Hurricane Katrina and similar storm events. The model setup included a coarse Gulf of Mexico domain and a nested finer-resolution Chandeleur Island domain. The finer-resolution domain resolved morphodynamic processes driven by storms and tides. A sensitivity analysis of the simulated morphodynamic response was performed to investigate the effects of variations in surge levels. The Chandeleur morphodynamic model reproduced several important features that matched observed morphodynamic changes. A simulation of bathymetric change driven by storm surge alone (no waves) along the central portion of the Chandeleur Islands showed (1) a general landward retreat and lowering of the island chain and (2) multiple breaches that increased the degree of island dissection. The locations of many of the breaches correspond with the low-lying or narrow sections of the initial bathymetry. The major part of the morphological change occurred prior to the peak of the surge when overtopping of the islands produced a strong water-level gradient and induced significant flow velocities.

Conference Paper↗

USGS2007

Beach morphology monitoring in the Columbia River Littoral Cell: 1997-2005

This report describes methods used, data collected, and results of the Beach Morphology Monitoring Program in the Columbia River Littoral Cell (CRLC) from 1997 to 2005. A collaborative group primarily consisting of the US Geological Survey and the Washington State Department of Ecology performed this work. Beach Monitoring efforts consisted of collecting topographic and bathymetric horizontal and vertical position data using a Real Time Kinematic Differential Global Positioning System (RTK-DGPS). Sediment size distribution data was also collected as part of this effort. The monitoring program was designed to: 1) quantify the short- to medium-term (seasonal to interannual) beach change rates and morphological variability along the CRLC and assess the processes responsible for these changes; 2) collect beach state data (i.e., grain size, beach slope, and dune/sandbar height/position) to enhance the conceptual understanding of CRLC functioning and refine predictions of future coastal change and hazards; 3) compare and contrast the scales of environmental forcing and beach morphodynamics in the CRLC to other coastlines of the world; and 4) provide beach change data in a useful format to land use managers.

Oregon, Washington↗

USGS2007

Vulnerability of National Park Service beaches to inundation during a direct hurricane landfall: Cape Lookout National Seashore

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.

North Carolina↗

USGS2007

Vulnerability of National Park Service beaches to inundation during a direct hurricane landfall: Cumberland Island National Seashore

Cumberland Island National Seashore, a barrier-island coastal park in Georgia, is vulnerable to the powerful, sand-moving forces of hurricanes. Waves and storm surge associated with these strong tropical storms are part of the natural process of barrier-island evolution and can cause extensive morphologic changes in coastal parks, leading to reduced visitor accessibility and enjoyment. 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.

Georgia↗

USGS2007

Vulnerability of National Park Service beaches to inundation during a direct hurricane landfall: Fire Island National Seashore

Waves and storm surge associated with strong tropical storms are part of the natural process of barrier-island evolution and can cause extensive morphologic changes in coastal parks, leading to reduced visitor accessibility and enjoyment. Even at Fire Island National Seashore, a barrier-island coastal park in New York where extratropical storms (northeasters) dominate storm activity, the beaches are vulnerable to the powerful, sand-moving forces of hurricanes. 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 1-4 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.

New York↗