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USGS2004

Geophysical techniques in detection to river embankments - A case study: To locate sites of potential leaks using surface-wave and electrical methods

Geophysical technologies are very effective in environmental, engineering and groundwater applications. Parameters of delineating nature of near-surface materials such as compressional-wave velocity, shear-wave velocity can be obtained using shallow seismic methods. Electric methods are primary approaches for investigating groundwater and detecting leakage. Both of methods are applied to detect embankment in hope of obtaining evidences of the strength and moisture inside the body. A technological experiment has done for detecting and discovering the hidden troubles in the embankment of Yangtze River, Songzi, Hubei, China in 2003. Surface-wave and DC multi-channel array resistivity sounding techniques were used to detect hidden trouble inside and under dike like pipe-seeps. This paper discusses the exploration strategy and the effect of geological characteristics. A practical approach of combining seismic and electric resistivity measurements was applied to locate potential pipe-seeps in embankment in the experiment. The method presents a potential leak factor based on the shear-wave velocity and the resistivity of the medium to evaluate anomalies. An anomaly found in a segment of embankment detected was verified, where occurred a pipe-seep during the 98' flooding.

Conference Paper↗

USGS2022

New model of the Barry Arm landslide in Alaska reveals potential tsunami wave heights of 2 meters, values much lower than previously estimated

The retreat of Barry Glacier has contributed to the destabilization of slopes in Barry Arm, creating the possibility that a landslide could rapidly enter the fjord and trigger a tsunami. The U.S. Geological Survey (USGS) recently released a report documenting potential tsunami wave heights in the event of a large, fast-moving landslide at the Barry Arm fiord near Prince William Sound, Alaska (Barnhart and others, 2021). This new work shows that the largest plausible wave height is smaller than initial estimates published in Dai and others (2020), but waves still represent a substantial hazard to the people who live, work, and recreate in Prince William Sound. Thus, it is important that residents and visitors remain informed about this hazard and prepare accordingly.

Alaska↗

USGS1983

Sand-wave movement on Little Georges Bank

A 1-x-1.5-km area on Little Georges Bank (centered at 41?08?N., 68?04?W.) was mapped three times during a ten-month period by sidescan sonar and echo-sounding techniques to assess the morphology and mobility of sand waves on Georges Bank. Sand-wave amplitudes in the survey area ranged from 1-11 m although most were 5-7 m. Wavelengths were not constant as the crests were sinuous and in places, even bifurcated. The sand waves are asymmetrical with their steepest sides facing northwest; however, gradients of their steep sides mostly are 4?-10? which is well below the angle of repose for sand in water. Sand waves tended to have greater relief and a sharper asymmetry during the survey in September than during those in June or April. During the survey period the sand waves moved but the direction and rate of motion was variable. Even along an individual sand wave some parts moved as much as 60 m between surveys while other parts apparently remained stationary. The sand waves were asymmetrical, but movement was not consistently in the direction that the steep sides faced. Along the same sand wave, parts moved to the northwest while other parts moved to the southeast. Despite the complex pattern of sand motion, the mean displacement of the sand waves was below the resolution of the survey technique; to resolve it, a longer survey is needed.

Open-File Report↗

USGS1982

Geological interpretation of cone penetrometer tests in Norton Sound, Alaska

In situ cone-penetrometer tests at 11 stations in Norton Sound, Alaska, complement previous studies of geologic processes and provide geotechnical data for an analysis of sediment response to loading. Assessment of the penetrometer records shows that various geologic factors influence penetration resistance. On the Yukon prodelta, penetration resistance increases with the level of storm wave or ice loading. In central and eastern Norton Sound, thermogenic and biogenic gas, as well as variations in sediment texture and composition, effect a wide range of resistance to penetration. ?? 1982 A. M. Dowden, Inc.

Geo-Marine Letters↗

USGS1989

Seismicity of Alaska 1786-1987

This map displays selected epicenters for earthquakes that occurred between 1786 and 1987. Although accurate magnitude values have not been determined for many of the pre-instrumental earthquakes, it is believed that all of the earthquakes presented on this map have magnitudes of 5.0 or greater. Symbols are plotted at epicentral locations, and symbol sizes are scaled into three magnitude categories. Within each category, duplicate epicenter locations have been eliminated. There are 2,351 separate epicenter locations, representing 2,480 earthquakes shown on this map. Because of recent increases in the number of quality of seisomgraph networks, the accuracy of epicentral parameters of earthquakes occurring since the mid-1960s is greater than that of earlier earthquakes. Earthquakes occurring since 1965 are distinguished on this map from earlier events by the intensity of color of the epicentral symbol, as indicated below. An extremely violent earthquake occurred north of Prince William Sound on Good Friday, March 27, 1964. This earthquake had a surface-wave magnitude of 8.4 and a moment magnitude of 9.2. The earthquake also generated a large sea wave (tsunami) which devastated many waterfront developments. The earthquake and its accompanying tsunami caused severe damage along Prince William Sound, Cook Inlet, and on the Kenai Peninsula. On the map, the epicenter of the 1964 earthquake is labeled with the date.

Alaska↗

USGS2015

Near-surface stratigraphy and morphology, Mississippi Inner Shelf, northern Gulf of Mexico

Over the past decade, the Mississippi Barrier Islands have been the focus of a comprehensive geologic investigation by the U.S. Geological Survey (USGS), in collaboration with the U.S. Army Corps of Engineers (USACE) and the National Park Service (NPS). The islands (Dauphin, Petite Bois, Horn, East Ship, West Ship, and Cat) are part of the Gulf Islands National Seashore (GUIS), and provide a diverse ecological habitat, protect the mainland from storm waves, and help maintain estuarine conditions within Mississippi Sound. Over the past century, the islands have been in a state of decline with respect to elevation and land-area loss. In 2005, the islands were severely impacted by Hurricane Katrina, which inundated them with a storm surge of 8 meters, causing severe shoreface erosion and widening breaches in Dauphin, West Ship, and Cat Islands. To evaluate the impact and fate of the islands, understanding their evolution and resiliency became a priority for the USGS under the Northern Gulf of Mexico Ecosystem Change and Hazard Susceptibility Project. The project formed the basis for collaboration with the USACE Mississippi Coastal Improvement Project, which is intended to restore portions of coastal Mississippi and GUIS affected by storm impact. Since then, many studies have contributed to our understanding of the islands’ morphology and nearshore stratigraphy. This report expands upon the nearshore component to provide a stratigraphic and morphologic assessment offshore of Petit Bois Island. In June 2013, as part of the MsCIP project, the USGS conducted a geophysical survey consisting of about 650 line-kilometers (km), encompassing an area of approximately 212 square kilometers (km 2 ). The survey area extended from 1 to 13 km offshore of Petite Bois Island. The geophysical investigation included interferometric swath bathymetry, sidescan sonar, and chirp subbottom profiling. The intent of the survey was to provide geologic information that would assist the USACE in developing a sediment sampling strategy for identifying deposits suitable for shoreline restoration operations. The data from the geophysical survey would also further our understanding of the geologic framework along the inner shelf. Numerous seafloor and subbottom features were identified. At the surface, shoals and shelf sand sheets of various sizes and orientations are the predominant morphology. In the subsurface, Holocene- and Pleistocene-age features include marine transgressive deposits infilling older fluvia distributary systems. These interpretations from the geophysical research were integrated with sediment cores collected by the USGS and USACE to provide textural and volumetric information.

Mississippi-Alabama shelf↗

USGS2024

Dynamic modeling of coastal compound flooding hazards due to tides, extratropical storms, waves, and sea-level rise: A case study in the Salish Sea, Washington (USA)

The Puget Sound Coastal Storm Modeling System (PS-CoSMoS) is a tool designed to dynamically downscale future climate scenarios (i.e., projected changes in wind and pressure fields and temperature) to compute regional water levels, waves, and compound flooding over large geographic areas (100 s of kilometers) at high spatial resolutions (1 m) pertinent to coastal hazard assessments and planning. This research focuses on advancing robust and computationally efficient approaches to resolving the coastal compound flooding components for complex, estuary environments and their application to the Puget Sound region of Washington State (USA) and the greater Salish Sea. The modeling system provides coastal planners with projections of storm hazards and flood exposure for recurring flood events, spanning the annual to 1-percent annual chance of flooding, necessary to manage public safety and the prioritization and cost-efficient protection of critical infrastructure and valued ecosystems. The tool is applied and validated for Whatcom County, Washington, and includes a cross-shore profile model (XBeach) and overland flooding model (SFINCS) and is nested in a regional tide–surge model and wave model. Despite uncertainties in boundary conditions, hindcast simulations performed with the coupled model system accurately identified areas that were flooded during a recent storm in 2018. Flood hazards and risks are expected to increase exponentially as the sea level rises in the study area of 210 km of shoreline. With 1 m of sea-level rise, annual flood extents are projected to increase from 13 to 33 km 2 (5 and 13% of low-lying Whatcom County) and flood risk (defined in USD) is projected to increase fifteenfold (from 14 to USD 206 million). PS-CoSMoS, like its prior iteration in California (CoSMoS), provides valuable coastal hazard projections to help communities plan for the impacts of sea-level rise and storms.

Washington↗

USGS2021

The Mars Orbiter for Resources, Ices, and Environments (MORIE) science goals and instrument trades in radar, imaging, and spectroscopy

The Mars Orbiter for Resources, Ices, and Environments (MORIE) was selected as one of NASA's 2019 Planetary Mission Concept Studies. The mission builds upon recent discoveries and current knowledge gaps linked to two primary scientific questions: (1) when did elements of the cryosphere form and how are ice deposits linked to current, recent, and ancient climate, and (2) how does the crust record the evolution of surface environments and their transition through time? Addressing these questions has emerged in numerous recent reports as a high priority in investigating the evolution of Mars as a habitable world. A subsidiary goal of the mission concept is to provide information relevant to the eventual human exploration of Mars, specifically helping to locate and quantify near-surface water ice and hydrated mineral resources. The proposed instrument suite includes polarimetric synthetic aperture radar imaging, radar sounding, high-resolution visible and infrared imaging, both short-wave and thermal-infrared spectroscopy, and multichannel wide-angle imaging. MORIE would provide novel measurements of Mars expected to lead to significant new discoveries by the first radar imaging from orbit, radar sounding directly over the poles, and mineral mapping at spatial scales that will unravel geologic sequence stratigraphy through time. The final report of the mission concept provides details on the spacecraft, orbital design, technological maturity, results from systems-level integration studies, and costs. This article is intended to expand upon the science motivation for the mission, the measurement goals and objectives, and the instrument trade space that was examined in detail during the concept study.

The Planetary Science Journal↗

USGS1982

Geotechnical characteristics of bottom sediments in the northeastern Bering Sea.

Sediment of Holocene age derived from the Yukon River, consisting dominantly of silty fine sand and sandy silt, covers the bottom of central and western Norton Sound, which is a high energy environment involving extensive ice loading, high waves, and strong bottom currents. The sediment characteristics indicate that it is susceptible to liquefaction during major storms. Substantially finer grained, weak and highly compressible sediment of Holocene age covers eastern Norton Sound and the Port Clarence embayment, which are low energy environments. Pleistocene peaty deposits underlie the Holocene and late Pleistocene deposits in both Norton Sound and Chirikov Basin and are somewhat overconsolidated. The presence of gas indicates high in situ pore pressure and hence low material strength.-from Authors

Geologie en Mijnbouw↗

USGS1999

Seafloor environments in the Long Island Sound estuarine system

Four categories of modern seafloor sedimentary environments have been identified and mapped across the large, glaciated, topographically complex Long Island Sound estuary by means of an extensive regional set of sidescan sonographs, bottom samples, and video-camera observations and supplemental marine-geologic and modeled physical-oceanographic data. (1) Environments of erosion or nondeposition contain sediments which range from boulder fields to gravelly coarse-to-medium sands and appear on the sonographs either as patterns with isolated reflections (caused by outcrops of glacial drift and bedrock) or as patterns of strong backscatter (caused by coarse lag deposits). Areas of erosion or nondeposition were found across the rugged seafloor at the eastern entrance of the Sound and atop bathymetric highs and within constricted depressions in other parts of the basin. (2) Environments of bedload transport contain mostly coarse-to-fine sand with only small amounts of mud and are depicted by sonograph patterns of sand ribbons and sand waves. Areas of bedload transport were found primarily in the eastern Sound where bottom currents have sculptured the surface of a Holocene marine delta and are moving these sediments toward the WSW into the estuary. (3) Environments of sediment sorting and reworking comprise variable amounts of fine sand and mud and are characterized either by patterns of moderate backscatter or by patterns with patches of moderate-to-weak backscatter that reflect a combination of erosion and deposition. Areas of sediment sorting and reworking were found around the periphery of the zone of bedload transport in the eastern Sound and along the southern nearshore margin. They also are located atop low knolls, on the flanks of shoal complexes, and within segments of the axial depression in the western Sound. (4) Environments of deposition are blanketed by muds and muddy fine sands that produce patterns of uniformly weak backscatter. Depositional areas occupy broad areas of the basin floor in the western part of the Sound. The regional distribution of seafloor environments reflects fundamental differences in marine-geologic conditions between the eastern and western parts of the Sound. In the funnel-shaped eastern part, a gradient of strong tidal currents coupled with the net nontidal (estuarine) bottom drift produce a westward progression of environments ranging from erosion or nondeposition at the narrow entrance to the Sound, through an extensive area of bedload transport, to a peripheral zone of sediment sorting. In the generally broader western part of the Sound, a weak tidal-current regime combined with the production of particle aggregates by biologic or chemical processes, cause large areas of deposition that are locally interrupted by a patchy distribution of various other environments where the bottom currents are enhanced by and interact with the seafloor topography.

Marine Geology↗

USGS1994

Precursory swarms of long-period events at Redoubt Volcano (1989-1990), Alaska: Their origin and use as a forecasting tool

During the eruption of Redoubt Volcano from December 1989 through April 1990, the Alaska Volcano Observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long-period (LP) seismic events (dominant period of about 0.5 s). The initial eruption on December 14 occurred after 23 years of quiescence and was heralded by a 23-hour swarm of LP events that ended abruptly with the eruption. After a series of vent-clearing explosions over the next few days, dome growth began on December 21. Another swarm, with LP events similar to those of the first, began on the 26th and ended in a major tephra eruption on January 2. Eruptions continued over the next two weeks and then ceased until February 15, when a large eruption initiated a long phase of repetitive dome-building and dome-destroying episodes that continued into April. Warnings were issued before the major events on December 14 and January 2, but as the eruptive sequence continued after January 2, the energy of the swarms decreased and forecasting became more difficult. A significant but less intense swarm preceded the February 15 eruption, which was not forecast. This eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until March 4, when the first of three new stations was installed within 3 km of the active vent. From March 4 to the end of the sequence on April 21, there were eight eruptions, six of which were preceded by detectable swarms of LP events. Although weak, these swarms provided the basis for warnings issued before the eruptions on March 23 and April 6. The initial swarm on December 13 had the following features: (1) short duration (23 hours); (2) a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm, followed by a decline of activity during the 5 hours preceding the eruption; (3) a magnitude range from −0.4 to 1.6; (4) nearly identical LP signatures with a dominant period near 0.5 s; (5) dilatational first motions everywhere; and (6) a stationary source location at a depth of 1.4 km beneath the crater. This occurrence of long-period events suggests a model involving the interaction of magma with groundwater in which magmatic gases, steam and water drive a fixed conduit at a stationary point throughout the swarm. The initiation of that sequence of events is analogous to the failure of a pressure-relief valve connecting a lower, supercharged magma-dominated reservoir to a shallow hydrothermal system. A three-dimensional model of a vibrating fluid-filled crack recently developed by Chouet is found to be compatible with the seismic data and yields the following parameters for the LP source: crack length, 280–380 m; crack width, 140–190 m; crack thickness, 0.05–0.20 m; crack stiffness, 100–200; sound speed of fluid, 0.8–1.3 km/s; compressional-wave speed of rock, 5.1 km/s; density ratio of fluid to rock, ≈0.4; and ratio of bulk modulus of fluid to rigidity of rock, 0.03–0.07. The fluid-filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0.4 to 40 bar. Such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack.

Alaska↗

USGS1999

Air blasts generated by rockfall impacts: Analysis of the 1996 Happy Isles event in Yosemite National Park

The July 10, 1996, Happy Isles rockfall in Yosemite National Park, California, released 23,000 to 38,000 m 3 of granite in four separate events. The impacts of the first two events which involved a 550-m free fall, generated seismic waves and atmospheric pressure waves (air blasts). We focus on the dynamic behavior of the second air blast that downed over 1000 trees, destroyed a bridge, demolished a snack bar, and caused one fatality and several injuries. Calculated velocities for the air blast from a two-phase, finite difference model are compared to velocities estimated from tree damage. From tornadic studies of tree damage, the air blast is estimated to have traveled <108–120 m/s within 50 m from the impact and decreased to <10–20 m/s within 500 m from the impact. The numerical model simulates the two-dimensional propagation of an air blast through a dusty atmosphere with initial conditions defined by the impact velocity and pressure. The impact velocity (105–107 m/s) is estimated from the Colorado Rockfall Simulation Program that simulates rockfall trajectories. The impact pressure (0.5 MPa) is constrained by the kinetic energy of the impact (10 10 –10 12 J) estimated from the seismic energy generated by the impact. Results from the air blast simulations indicate that the second Happy Isles air blast (weak shock wave) traveled with an initial velocity above the local sound speed. The size and location of the first impact are thought to have injected <50 wt% dust into the atmosphere. This amount of dust lowered the local atmospheric sound speed to ∼220 m/s. The discrepancy between calculated velocity data and field estimated velocity data (∼220 m/s versus ∼110 m/s) is attributed to energy dissipated by the downing of trees and additional entrainment of debris into the atmosphere not included in the calculations.

Journal of Geophysical Research B: Solid Earth↗

USGS2000

Acoustic properties of a crack containing magmatic or hydrothermal fluids

We estimate the acoustic properties of a crack containing magmatic or hydrothermal fluids to quantify the source properties of long-period (LP) events observed in volcanic areas assuming that a crack-like structure is the source of LP events. The tails of synthetic waveforms obtained from a model of a fluid-driven crack are analyzed by the Sompi method to determine the complex frequencies of one of the modes of crack resonance over a wide range of the model parameters α/ a and ρ f /ρ s , where αis the P wave velocity of the rock matrix, a is the sound speed of the fluid, and ρ f and p s are the densities of the fluid and rock matrix, respectively. The quality factor due to radiation loss ( Q r ) for the selected mode almost monotonically increases with increasing α/ a , while the dimensionless frequency ( v ) of the mode decreases with increasing α/ a and ρ f /ρ s . These results are used to estimate Q and v for a crack containing various types of fluids (gas-gas mixtures, liquid-gas mixtures, and dusty and misty gases) for values of a , ρ f , and quality factor due to intrinsic losses ( Q i ) appropriate for these types of fluids, in which Q is given by Q −l = Q r −l + Q i −1 . For a crack containing such fluids, we obtain Q ranging from almost unity to several hundred, which consistently explains the wide variety of quality factors measured in LP events observed at various volcanoes. We underscore the importance of dusty and misty gases containing small-size particles with radii around 1 μm to explain long-lasting oscillations with Q significantly larger than 100. Our results may provide a basis for the interpretation of spatial and temporal variations in the observed complex frequencies of LP events in terms of fluid compositions beneath volcanoes.

Journal of Geophysical Research B: Solid Earth↗

USGS1982

Modern shallow-water graded sand layers from storm surges, Bering Shelf: a mimic of Bouma sequences and turbidite systems

A sequence of graded sand layers, interbedded with mud, extends offshore over 100 km from the Yukon Delta shoreline across the flat, shallow (<20 m depth) epicontinental shelf of the northern Bering Sea, Alaska. Proximal graded sand beds on the delta-front platform near the shoreline are coarser (2-3phi ), thicker (10 to 20 cm), and contain more complete vertical sequences of sedimentary structures than distal beds. The inshore graded vertical sequence of structures from the base to the top of individual sand layers includes plane-parallel lamination (S b ), cross lamination (S c ), plane-parallel lamination (S d ), and mud (S e ) analogous to the Bouma T (sub a-e) turbidite sequence. Structures vary between interchannel platform deposits with complete S b -S e sequences and channel-floor sands that are all trough cross-laminated. Distally, storm-sand layers change to thin (1 to 5 cm) silt beds that contain flat and ripple-drift lamination (S (sub c-e,de) ), are commonly bioturbated, and are associated with shell and pebble lags from storm-wave reworking. The sequence of graded sands appears to be related to the major storm surges that occur every several years. The major storms increase the average 10-m water depth in southern Norton Sound as much as 5 m and cause fluctuations in pore pressure from wave cyclic loading that may liquefy the upper 2 to 3 m of sediment. Storm-associated bottom currents, possibly dominated by rapidly waning ebb flow, transport the liquefied inshore sand far offshore (> 100 kin). Such shallow-water graded layers off lobate deltas may be distinguished from similar deep-water turbidites by: 1) the predominance of trough cross-lamination, perhaps resulting from wave oscillation effects, in the proximal part of the system, and 2) gradation to common shallow marine fossils, bioturbation, and storm lag layers in distal areas.

Journal of Sedimentary Petrology↗

USGS1990

Coastal retreat and shoreface profile variations in the Canadian Beaufort Sea

The coastline of the southern Canadian Beaufort Sea consists primarily of unconsolidated bluffs. Although the sea is ice-free for 3 months of the year and wave energy is restricted by pack ice, the coast is undergoing regional retreat with erosion rates as high as 10 m a −1 in some locations. Simple and multiple regression analyses were carried out to determine the degree of correlation between the mean retreat rate measured at various locations and the different parameters that may control shoreline recession. Sediment texture, ground-ice content, cliff height, wave energy and shoreface gradient revealed medium to poor correlation with erosion rates, showing that the recessive evolution of the coastline can not be explained solely by wave-induced and subaerial processes. The comparison of nearshore echo-sounding records from 1987 with bathymetry from 1971 showed substantial erosion (up to 1 m) of the submarine profile between 12 and 15 m of water. There is strong evidence that this erosion has been caused by sea ice gouging on the seafloor. From depths of 5 to 9 m, accretion has taken place, possibly induced by ice-push processes, and inshore of the 5 m isobath wave and current erosion of the shoreface has occurred. These results suggest that the erosion of the inner shelf by ice gouging drives the erosion observed inshore on the coastal bluffs and nearshore zone as the shoreface profile strives for a state of dynamic equilibrium.

Marine Geology↗

USGS2007

Seismic amplification within the Seattle Basin, Washington State: Insights from SHIPS seismic tomography experiments

Recent observations indicate that the Seattle sedimentary basin, underlying Seattle and other urban centers in the Puget Lowland, Washington, amplifies long-period (1-5 sec) weak ground motions by factors of 10 or more. We computed east-trending P- and S-wave velocity models across the Seattle basin from Seismic Hazard Investigations of Puget Sound (SHIPS) experiments to better characterize the seismic hazard the basin poses. The 3D tomographic models, which resolve features to a depth of 10 km, for the first time define the P- and S-wave velocity structure of the eastern end of the basin. The basin, which contains sedimentary rocks of Eocene to Holocene, is broadly symmetric in east-west section and reaches a maximum thickness of 6 km along our profile beneath north Seattle. A comparison of our velocity model with coincident amplification curves for weak ground motions produced by the 1999 Chi-Chi earthquake suggests that the distribution of Quaternary deposits and reduced velocity gradients in the upper part of the basement east of Seattle have significance in forecasting variations in seismic-wave amplification across the basin. Specifically, eastward increases in the amplification of 0.2- to 5-Hz energy correlate with locally thicker unconsolidated deposits and a change from Crescent Formation basement to pre-Tertiary Cascadia basement. These models define the extent of the Seattle basin, the Seattle fault, and the geometry of the basement contact, giving insight into the tectonic evolution of the Seattle basin and its influence on ground shaking.

Bulletin of the Seismological Society of America↗

USGS1992

Gravel-bed deposition and erosion by bedform migration observed ultrasonically during storm flow, North Fork Toutle River, Washington

Ultrasonic depth sounding provides useful and unexpected information about peak discharge and sediment transport when applied during storm flow in channels with erodible beds. Streambed elevation was measured with dual ultrasonic depth sounders during the rise, crest, and recession of a storm flow in the North Fork Toutle River, Washington, on 3 December 1987. The sounder transducers were held in the flow on a rigid pipe which was suspended from a boom over the channel thalweg. The 12 h episode of depth sounding detected the superposition of fine-gravel dunes on large bed waves, the depth-limited growth of mean dune heights from 13 to 25 cm, and bedform-related deposition and erosion in the channel thalweg. The streambed elevation rose 0.3 m in 2 h with increasing stream discharge. Dune heights diminished for about an hour before the peak river stage was attained. Scour of the streambed continued through the peak stage and recession, with 0.7 m of scour over 10 h. Rapid scour of the streambed produced a falling stage while discharge was still rising. Dune heights grew as flow depth increased after peak stage. Streambed elevation was lowered as large bed waves of fine gravel migrated along the thalweg with successively lower troughs leading each bed wave. Bed elevation records from the dual depth sounders were used to calculate dune celerities of 3–6 cm s −1 and bedform wavelengths of 2–11 m. The large bed waves were subtle, dune-like gravel bedforms with wavelengths of 25–30 m. The celerities and bedform dimensions yielded bedform transport weight rates between 3 and 20 kg s −1 m −1 and grain shear stresses between 40 and 100 N m −2 for the depth-sounding episode.

Journal of Hydrology↗

USGS2021

Erosion and recovery: Sound-side inundation of Cape Lookout National Seashore during Hurricane Dorian

Hurricane Dorian tracked immediately offshore of Cape Lookout National Seashore (which includes the barrier islands of North and South Core Banks) and Ocracoke Island after devastating the Bahamas in early September, 2019. Dorian briefly made landfall at Cape Hatteras as a Category 1 hurricane on September 6 before moving northeast over the Atlantic Ocean. Winds on the Outer Banks, initially more than 40 m/s (about 90 mph) from the southeast, drove ocean waves and storm surge against the islands and pushed water across Pamlico Sound, resulting in elevated water levels in the sound’s northwestern rivers and creeks.

North Carolina↗