Warner John C.

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John C.

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  • Article
    Tidal asymmetry and residual circulation over linear sandbanks and their implication on sediment transport : a process-oriented numerical study
    (American Geophysical Union, 2007-12-22) Sanay, Rosario ; Voulgaris, George ; Warner, John C.
    A series of process-oriented numerical simulations is carried out in order to evaluate the relative role of locally generated residual flow and overtides on net sediment transport over linear sandbanks. The idealized bathymetry and forcing are similar to those present in the Norfolk Sandbanks, North Sea. The importance of bottom drag parameterization and bank orientation with respect to the ambient flow is examined in terms of residual flow and overtide generation, and subsequent sediment transport implications are discussed. The results show that although the magnitudes of residual flow and overtides are sensitive to bottom roughness parameterization and bank orientation, the magnitude of the generated residual flow is always larger than that of the locally generated overtides. Also, net sediment transport is always dominated by the nonlinear interaction of the residual flow and the semidiurnal tidal currents, although cross-bank sediment transport can occur even in the absence of a cross-shore residual flow. On the other hand, net sediment divergence/convergence increases as the bottom drag decreases and as bank orientation increases. The sediment erosion/deposition is not symmetric about the crest of the bank, suggesting that originally symmetric banks would have the tendency to become asymmetric.
  • Article
    Ocean–atmosphere dynamics during Hurricane Ida and Nor’Ida : an application of the coupled ocean–atmosphere–wave–sediment transport (COAWST) modeling system
    (Elsevier B.V., 2011-12-30) Olabarrieta, Maitane ; Warner, John C. ; Armstrong, Brandy ; Zambon, Joseph B. ; He, Ruoying
    The coupled ocean–atmosphere–wave–sediment transport (COAWST) modeling system was used to investigate atmosphere–ocean–wave interactions in November 2009 during Hurricane Ida and its subsequent evolution to Nor’Ida, which was one of the most costly storm systems of the past two decades. One interesting aspect of this event is that it included two unique atmospheric extreme conditions, a hurricane and a nor’easter storm, which developed in regions with different oceanographic characteristics. Our modeled results were compared with several data sources, including GOES satellite infrared data, JASON-1 and JASON-2 altimeter data, CODAR measurements, and wave and tidal information from the National Data Buoy Center (NDBC) and the National Tidal Database. By performing a series of numerical runs, we were able to isolate the effect of the interaction terms between the atmosphere (modeled with Weather Research and Forecasting, the WRF model), the ocean (modeled with Regional Ocean Modeling System (ROMS)), and the wave propagation and generation model (modeled with Simulating Waves Nearshore (SWAN)). Special attention was given to the role of the ocean surface roughness. Three different ocean roughness closure models were analyzed: DGHQ (which is based on wave age), TY2001 (which is based on wave steepness), and OOST (which considers both the effects of wave age and steepness). Including the ocean roughness in the atmospheric module improved the wind intensity estimation and therefore also the wind waves, surface currents, and storm surge amplitude. For example, during the passage of Hurricane Ida through the Gulf of Mexico, the wind speeds were reduced due to wave-induced ocean roughness, resulting in better agreement with the measured winds. During Nor’Ida, including the wave-induced surface roughness changed the form and dimension of the main low pressure cell, affecting the intensity and direction of the winds. The combined wave age- and wave steepness-based parameterization (OOST) provided the best results for wind and wave growth prediction. However, the best agreement between the measured (CODAR) and computed surface currents and storm surge values was obtained with the wave steepness-based roughness parameterization (TY2001), although the differences obtained with respect to DGHQ were not significant. The influence of sea surface temperature (SST) fields on the atmospheric boundary layer dynamics was examined; in particular, we evaluated how the SST affects wind wave generation, surface currents and storm surges. The integrated hydrograph and integrated wave height, parameters that are highly correlated with the storm damage potential, were found to be highly sensitive to the ocean surface roughness parameterization.
  • Article
    Modeling the morphodynamics of coastal responses to extreme events: what shape are we in?
    (Annual Reviews, 2021-07-27) Sherwood, Christopher R. ; van Dongeren, Ap ; Doyle, James D. ; Hegermiller, Christie A. ; Hsu, Tian-Jian ; Kalra, Tarandeep S. ; Olabarrieta, Maitane ; Penko, Allison M. ; Rafati, Yashar ; Roelvink, Dano ; van der Lugt, Marlies ; Veeramony, Jay ; Warner, John C.
    This review focuses on recent advances in process-based numerical models of the impact of extreme storms on sandy coasts. Driven by larger-scale models of meteorology and hydrodynamics, these models simulate morphodynamics across the Sallenger storm-impact scale, including swash,collision, overwash, and inundation. Models are becoming both wider (as more processes are added) and deeper (as detailed physics replaces earlier parameterizations). Algorithms for wave-induced flows and sediment transport under shoaling waves are among the recent developments. Community and open-source models have become the norm. Observations of initial conditions (topography, land cover, and sediment characteristics) have become more detailed, and improvements in tropical cyclone and wave models provide forcing (winds, waves, surge, and upland flow) that is better resolved and more accurate, yielding commensurate improvements in model skill. We foresee that future storm-impact models will increasingly resolve individual waves, apply data assimilation, and be used in ensemble modeling modes to predict uncertainties.
  • Article
    Storm-induced inner-continental shelf circulation and sediment transport : Long Bay, South Carolina
    (Elsevier B.V., 2012-05-10) Warner, John C. ; Armstrong, Brandy ; Sylvester, Charlene S. ; Voulgaris, George ; Nelson, Timothy R. ; Schwab, William C. ; Denny, Jane F.
    Long Bay is a sediment-starved, arcuate embayment located along the US East Coast connecting both South and North Carolina. In this region the rates and pathways of sediment transport are important because they determine the availability of sediments for beach nourishment, seafloor habitat, and navigation. The impact of storms on sediment transport magnitude and direction were investigated during the period October 2003–April 2004 using bottom mounted flow meters, acoustic backscatter sensors and rotary sonars deployed at eight sites offshore of Myrtle Beach, SC, to measure currents, water levels, surface waves, salinity, temperature, suspended sediment concentrations, and bedform morphology. Measurements identify that sediment mobility is caused by waves and wind driven currents from three predominant types of storm patterns that pass through this region: (1) cold fronts, (2) warm fronts and (3) low-pressure storms. The passage of a cold front is accompanied by a rapid change in wind direction from primarily northeastward to southwestward. The passage of a warm front is accompanied by an opposite change in wind direction from mainly southwestward to northeastward. Low-pressure systems passing offshore are accompanied by a change in wind direction from southwestward to southeastward as the offshore storm moves from south to north. During the passage of cold fronts more sediment is transported when winds are northeastward and directed onshore than when the winds are directed offshore, creating a net sediment flux to the north–east. Likewise, even though the warm front has an opposite wind pattern, net sediment flux is typically to the north–east due to the larger fetch when the winds are northeastward and directed onshore. During the passage of low-pressure systems strong winds, waves, and currents to the south are sustained creating a net sediment flux southwestward. During the 3-month deployment a total of 8 cold fronts, 10 warm fronts, and 10 low-pressure systems drove a net sediment flux southwestward. Analysis of a 12-year data record from a local buoy shows an average of 41 cold fronts, 32 warm fronts, and 26 low-pressure systems per year. The culmination of these events would yield a cumulative net inner-continental shelf transport to the south–west, a trend that is further verified by sediment textural analysis and bedform morphology on the inner-continental shelf.
  • Article
    Observations and 3D hydrodynamics-based modeling of decadal-scale shoreline change along the Outer Banks, North Carolina
    (Elsevier, 2016-12-10) Safak, Ilgar ; List, Jeffrey H. ; Warner, John C. ; Kumar, Nirnimesh
    Long-term decadal-scale shoreline change is an important parameter for quantifying the stability of coastal systems. The decadal-scale coastal change is controlled by processes that occur on short time scales (such as storms) and long-term processes (such as prevailing waves). The ability to predict decadal-scale shoreline change is not well established and the fundamental physical processes controlling this change are not well understood. Here we investigate the processes that create large-scale long-term shoreline change along the Outer Banks of North Carolina, an uninterrupted 60 km stretch of coastline, using both observations and a numerical modeling approach. Shoreline positions for a 24-yr period were derived from aerial photographs of the Outer Banks. Analysis of the shoreline position data showed that, although variable, the shoreline eroded an average of 1.5 m/yr throughout this period. The modeling approach uses a three-dimensional hydrodynamics-based numerical model coupled to a spectral wave model and simulates the full 24-yr time period on a spatial grid running on a short (second scale) time-step to compute the sediment transport patterns. The observations and the model results show similar magnitudes (O(105 m3/yr)) and patterns of alongshore sediment fluxes. Both the observed and the modeled alongshore sediment transport rates have more rapid changes at the north of our section due to continuously curving coastline, and possible effects of alongshore variations in shelf bathymetry. The southern section with a relatively uniform orientation, on the other hand, has less rapid transport rate changes. Alongshore gradients of the modeled sediment fluxes are translated into shoreline change rates that have agreement in some locations but vary in others. Differences between observations and model results are potentially influenced by geologic framework processes not included in the model. Both the observations and the model results show higher rates of erosion (∼−1 m/yr) averaged over the northern half of the section as compared to the southern half where the observed and modeled averaged net shoreline changes are smaller (<0.1 m/yr). The model indicates accretion in some shallow embayments, whereas observations indicate erosion in these locations. Further analysis identifies that the magnitude of net alongshore sediment transport is strongly dominated by events associated with high wave energy. However, both big- and small- wave events cause shoreline change of the same order of magnitude because it is the gradients in transport, not the magnitude, that are controlling shoreline change. Results also indicate that alongshore momentum is not a simple balance between wave breaking and bottom stress, but also includes processes of horizontal vortex force, horizontal advection and pressure gradient that contribute to long-term alongshore sediment transport. As a comparison to a more simple approach, an empirical formulation for alongshore sediment transport is used. The empirical estimates capture the effect of the breaking term in the hydrodynamics-based model, however, other processes that are accounted for in the hydrodynamics-based model improve the agreement with the observed alongshore sediment transport.
  • Article
    Tropical to extratropical : marine environmental changes associated with Superstorm Sandy prior to its landfall
    (John Wiley & Sons, 2014-12-16) Zambon, Joseph B. ; He, Ruoying ; Warner, John C.
    Superstorm Sandy was a massive storm that impacted the U.S. East Coast on 22–31 October 2012, generating large waves, record storm surges, and major damage. The Coupled Ocean-Atmosphere-Wave-Sediment Transport modeling system was applied to hindcast this storm. Sensitivity experiments with increasing complexity of air-sea-wave coupling were used to depict characteristics of this immense storm as it underwent tropical to extratropical transition. Regardless of coupling complexity, model-simulated tracks were all similar to the observations, suggesting the storm track was largely determined by large-scale synoptic atmospheric circulation, rather than by local processes resolved through model coupling. Analyses of the sea surface temperature, ocean heat content, and upper atmospheric shear parameters showed that as a result of the extratropical transition and despite the storm encountering much cooler shelf water, its intensity and strength were not significantly impacted. Ocean coupling was not as important as originally thought for Sandy.
  • Article
    Inner-shelf ocean dynamics and seafloor morphologic changes during Hurricane Sandy
    (Elsevier, 2017-02-17) Warner, John C. ; Schwab, William C. ; List, Jeffrey H. ; Safak, Ilgar ; Liste, Maria ; Baldwin, Wayne E.
    Hurricane Sandy was one of the most destructive hurricanes in US history, making landfall on the New Jersey coast on October 30, 2012. Storm impacts included several barrier island breaches, massive coastal erosion, and flooding. While changes to the subaerial landscape are relatively easily observed, storm-induced changes to the adjacent shoreface and inner continental shelf are more difficult to evaluate. These regions provide a framework for the coastal zone, are important for navigation, aggregate resources, marine ecosystems, and coastal evolution. Here we provide unprecedented perspective regarding regional inner continental shelf sediment dynamics based on both observations and numerical modeling over time scales associated with these types of large storm events. Oceanographic conditions and seafloor morphologic changes are evaluated using both a coupled atmospheric-ocean-wave-sediment numerical modeling system that covered spatial scales ranging from the entire US east coast (1000 s of km) to local domains (10 s of km). Additionally, the modeled response for the region offshore of Fire Island, NY was compared to observational analysis from a series of geologic surveys from that location. The geologic investigations conducted in 2011 and 2014 revealed lateral movement of sedimentary structures of distances up to 450 m and in water depths up to 30 m, and vertical changes in sediment thickness greater than 1 m in some locations. The modeling investigations utilize a system with grid refinement designed to simulate oceanographic conditions with progressively increasing resolutions for the entire US East Coast (5-km grid), the New York Bight (700-m grid), and offshore of Fire Island, NY (100-m grid), allowing larger scale dynamics to drive smaller scale coastal changes. Model results in the New York Bight identify maximum storm surge of up to 3 m, surface currents on the order of 2 ms−1 along the New Jersey coast, waves up to 8 m in height, and bottom stresses exceeding 10 Pa. Flow down the Hudson Shelf Valley is shown to result in convergent sediment transport and deposition along its axis. Modeled sediment redistribution along Fire Island showed erosion across the crests of inner shelf sand ridges and sedimentation in adjacent troughs, consistent with the geologic observations.
  • Article
    Flow convergence caused by a salinity minimum in a tidal channel
    (CALFED Science Program, the California Digital Library eScholarship Repository, and the University of California—Davis John Muir Institute of the Environment., 2006-12) Warner, John C. ; Schoellhamer, David H. ; Burau, Jon R. ; Schladow, S. Geoffrey
    Residence times of dissolved substances and sedimentation rates in tidal channels are affected by residual (tidally averaged) circulation patterns. One influence on these circulation patterns is the longitudinal density gradient. In most estuaries the longitudinal density gradient typically maintains a constant direction. However, a junction of tidal channels can create a local reversal (change in sign) of the density gradient. This can occur due to a difference in the phase of tidal currents in each channel. In San Francisco Bay, the phasing of the currents at the junction of Mare Island Strait and Carquinez Strait produces a local salinity minimum in Mare Island Strait. At the location of a local salinity minimum the longitudinal density gradient reverses direction. This paper presents four numerical models that were used to investigate the circulation caused by the salinity minimum: (1) A simple one-dimensional (1D) finite difference model demonstrates that a local salinity minimum is advected into Mare Island Strait from the junction with Carquinez Strait during flood tide. (2) A three-dimensional (3D) hydrodynamic finite element model is used to compute the tidally averaged circulation in a channel that contains a salinity minimum (a change in the sign of the longitudinal density gradient) and compares that to a channel that contains a longitudinal density gradient in a constant direction. The tidally averaged circulation produced by the salinity minimum is characterized by converging flow at the bed and diverging flow at the surface, whereas the circulation produced by the constant direction gradient is characterized by converging flow at the bed and downstream surface currents. These velocity fields are used to drive both a particle tracking and a sediment transport model. (3) A particle tracking model demonstrates a 30 percent increase in the residence time of neutrally buoyant particles transported through the salinity minimum, as compared to transport through a constant direction density gradient. (4) A sediment transport model demonstrates increased deposition at the near-bed null point of the salinity minimum, as compared to the constant direction gradient null point. These results are corroborated by historically noted large sedimentation rates and a local maximum of selenium accumulation in clams at the null point in Mare Island Strait.
  • Article
    Sediment dispersal in the northwestern Adriatic Sea
    (American Geophysical Union, 2008-10-29) Harris, Courtney K. ; Sherwood, Christopher R. ; Signell, Richard P. ; Bever, Aaron J. ; Warner, John C.
    Sediment dispersal in the Adriatic Sea was evaluated using coupled three-dimensional circulation and sediment transport models, representing conditions from autumn 2002 through spring 2003. The calculations accounted for fluvial sources, resuspension by waves and currents, and suspended transport. Sediment fluxes peaked during southwestward Bora wind conditions that produced energetic waves and strengthened the Western Adriatic Coastal Current. Transport along the western Adriatic continental shelf was nearly always to the south, except during brief periods when northward Sirocco winds reduced the coastal current. Much of the modeled fluvial sediment deposition was near river mouths, such as the Po subaqueous delta. Nearly all Po sediment remained in the northern Adriatic. Material from rivers that drain the Apennine Mountains traveled farther before deposition than Po sediment, because it was modeled with a lower settling velocity. Fluvial sediment delivered to areas with high average bed shear stress was more highly dispersed than material delivered to more quiescent areas. Modeled depositional patterns were similar to observed patterns that have developed over longer timescales. Specifically, modeled Po sediment accumulation was thickest near the river mouth with a very thin deposit extending to the northeast, consistent with patterns of modern sediment texture in the northern Adriatic. Sediment resuspended from the bed and delivered by Apennine Rivers was preferentially deposited on the northern side of the Gargano Peninsula, in the location of thick Holocene accumulation. Deposition here was highest during Bora winds when convergences in current velocities and off-shelf flux enhanced delivery of material to the midshelf.
  • Article
    Modeling of barrier breaching during hurricanes Sandy and Matthew
    (American Geophysical Union, 2022-01-26) Hegermiller, Christie A. ; Warner, John C. ; Olabarrieta, Maitane ; Sherwood, Christopher R. ; Kalra, Tarandeep S.
    Physical processes driving barrier island change during storms are important to understand to mitigate coastal hazards and to evaluate conceptual models for barrier evolution. Spatial variations in barrier island topography, landcover characteristics, and nearshore and back-barrier hydrodynamics can yield complex morphological change that requires models of increasing resolution and physical complexity to predict. Using the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system, we investigated two barrier island breaches that occurred on Fire Island, NY during Hurricane Sandy (2012) and at Matanzas, FL during Hurricane Matthew (2016). The model employed a recently implemented infragravity (IG) wave driver to represent the important effects of IG waves on nearshore water levels and sediment transport. The model simulated breaching and other changes with good skill at both locations, resolving differences in the processes and evolution. The breach simulated at Fire Island was 250 m west of the observed breach, whereas the breach simulated at Matanzas was within 100 m of the observed breach. Implementation of the vegetation module of COAWST to allow three-dimensional drag over dune vegetation at Fire Island improved model skill by decreasing flows across the back-barrier, as opposed to varying bottom roughness that did not positively alter model response. Analysis of breach processes at Matanzas indicated that both far-field and local hydrodynamics influenced breach creation and evolution, including remotely generated waves and surge, but also surge propagation through back-barrier waterways. This work underscores the importance of resolving the complexity of nearshore and back-barrier systems when predicting barrier island change during extreme events.
  • Article
    A wetting and drying scheme for ROMS
    (Elsevier B.V., 2013-05-24) Warner, John C. ; Defne, Zafer ; Haas, Kevin A. ; Arango, Hernan G.
    The processes of wetting and drying have many important physical and biological impacts on shallow water systems. Inundation and dewatering effects on coastal mud flats and beaches occur on various time scales ranging from storm surge, periodic rise and fall of the tide, to infragravity wave motions. To correctly simulate these physical processes with a numerical model requires the capability of the computational cells to become inundated and dewatered. In this paper, we describe a method for wetting and drying based on an approach consistent with a cell-face blocking algorithm. The method allows water to always flow into any cell, but prevents outflow from a cell when the total depth in that cell is less than a user defined critical value. We describe the method, the implementation into the three-dimensional Regional Oceanographic Modeling System (ROMS), and exhibit the new capability under three scenarios: an analytical expression for shallow water flows, a dam break test case, and a realistic application to part of a wetland area along the Georgia Coast, USA.
  • Article
    Using a composite grid approach in a complex coastal domain to estimate estuarine residence time
    (Elsevier B.V., 2010-04-18) Warner, John C. ; Geyer, W. Rockwell ; Arango, Hernan G.
    We investigate the processes that influence residence time in a partially mixed estuary using a three-dimensional circulation model. The complex geometry of the study region is not optimal for a structured grid model and so we developed a new method of grid connectivity. This involves a novel approach that allows an unlimited number of individual grids to be combined in an efficient manner to produce a composite grid. We then implemented this new method into the numerical Regional Ocean Modeling System (ROMS) and developed a composite grid of the Hudson River estuary region to investigate the residence time of a passive tracer. Results show that the residence time is a strong function of the time of release (spring vs. neap tide), the along-channel location, and the initial vertical placement. During neap tides there is a maximum in residence time near the bottom of the estuary at the mid-salt intrusion length. During spring tides the residence time is primarily a function of along-channel location and does not exhibit a strong vertical variability. This model study of residence time illustrates the utility of the grid connectivity method for circulation and dispersion studies in regions of complex geometry.
  • Article
    Inner-shelf circulation and sediment dynamics on a series of shoreface-connected ridges offshore of Fire Island, NY
    (Springer, 2014-10-24) Warner, John C. ; List, Jeffrey H. ; Schwab, William C. ; Voulgaris, George ; Armstrong, Brandy ; Marshall, Nicole
    Locations along the inner-continental shelf offshore of Fire Island, NY, are characterized by a series of shoreface-connected ridges (SFCRs). These sand ridges have approximate dimensions of 10 km in length, 3 km spacing, and up to ∼8 m ridge to trough relief and are oriented obliquely at approximately 30° clockwise from the coastline. Stability analysis from previous studies explains how sand ridges such as these could be formed and maintained by storm-driven flows directed alongshore with a key maintenance mechanism of offshore deflected flows over ridge crests and onshore in the troughs. We examine these processes both with a limited set of idealized numerical simulations and analysis of observational data. Model results confirm that alongshore flows over the SFCRs exhibit offshore veering of currents over the ridge crests and onshore-directed flows in the troughs, and demonstrate the opposite circulation pattern for a reverse wind. To further investigate these maintenance processes, oceanographic instruments were deployed at seven sites on the SFCRs offshore of Fire Island to measure water levels, ocean currents, waves, suspended sediment concentrations, and bottom stresses from January to April 2012. Data analysis reveals that during storms with winds from the northeast, the processes of offshore deflection of currents over ridge crests and onshore in the troughs were observed, and during storm events with winds from the southwest, a reverse flow pattern over the ridges occurred. Computations of suspended sediment fluxes identify periods that are consistent with SFCR maintenance mechanisms. Alongshore winds from the northeast drove fluxes offshore on the ridge crest and onshore in the trough that would tend to promote ridge maintenance. However, alongshore winds from the southwest drove opposite circulations. The wind fields are related to different storm types that occur in the region (low-pressure systems, cold fronts, and warm fronts). From the limited data set, we identify that low-pressure systems drive sediment fluxes that tend to promote stability and maintain the SFCRs while cold front type storms appear to drive circulations that are in the opposite sense and may not be a supporting mechanism for ridge maintenance.
  • Article
    Numerical modeling of an estuary : a comprehensive skill assessment
    (American Geophysical Union, 2005-05-04) Warner, John C. ; Geyer, W. Rockwell ; Lerczak, James A.
    Numerical simulations of the Hudson River estuary using a terrain-following, three-dimensional model (Regional Ocean Modeling System, ROMS) are compared with an extensive set of timeseries and spatially resolved measurements over a 43-day period with large variations in tidal forcing and river discharge. The model is particularly effective at reproducing the observed temporal variations in both the salinity and current structure, including tidal, spring-neap, and river discharge induced variability. Large observed variations in stratification between neap and spring tides are captured qualitatively and quantitatively by the model. The observed structure and variations of the longitudinal salinity gradient are also well reproduced. The most notable discrepancy between the model and the data is in the vertical salinity structure. While the surface-to-bottom salinity difference is well reproduced, the stratification in the model tends to extend all the way to the water surface, whereas the observations indicate a distinct pycnocline and a surface mixed layer. Because the southern boundary condition is located near the mouth the estuary, the salinity within the domain is particularly sensitive to the specification of salinity at the boundary. A boundary condition for the horizontal salinity gradient, based on the local value of salinity, is developed to incorporate physical processes beyond the open boundary not resolved by the model. Model results are sensitive to the specification of the bottom roughness length and vertical stability functions, insofar as they influence the intensity of vertical mixing. The results only varied slightly between different turbulence closure methods of k-ε, k-ω, and k-kl.
  • Article
    Formation of fine sediment deposit from a flash flood river in the Mediterranean Sea
    (John Wiley & Sons, 2014-09-09) Grifoll, Manel ; Gracia, Vicenc ; Aretxabaleta, Alfredo L. ; Guillen, Jorge ; Espino, Manuel ; Warner, John C.
    We identify the mechanisms controlling fine deposits on the inner-shelf in front of the Besòs River, in the northwestern Mediterranean Sea. This river is characterized by a flash flood regime discharging large amounts of water (more than 20 times the mean water discharge) and sediment in very short periods lasting from hours to few days. Numerical model output was compared with bottom sediment observations and used to characterize the multiple spatial and temporal scales involved in offshore sediment deposit formation. A high-resolution (50 m grid size) coupled hydrodynamic-wave-sediment transport model was applied to the initial stages of the sediment dispersal after a storm-related flood event. After the flood, sediment accumulation was predominantly confined to an area near the coastline as a result of preferential deposition during the final stage of the storm. Subsequent reworking occurred due to wave-induced bottom shear stress that resuspended fine materials, with seaward flow exporting them toward the midshelf. Wave characteristics, sediment availability, and shelf circulation determined the transport after the reworking and the final sediment deposition location. One year simulations of the regional area revealed a prevalent southwestward average flow with increased intensity downstream. The circulation pattern was consistent with the observed fine deposit depocenter being shifted southward from the river mouth. At the southern edge, bathymetry controlled the fine deposition by inducing near-bottom flow convergence enhancing bottom shear stress. According to the short-term and long-term analyses, a seasonal pattern in the fine deposit formation is expected.
  • Article
    Sediment transport due to extreme events : the Hudson River estuary after tropical storms Irene and Lee
    (John Wiley & Sons, 2013-10-18) Ralston, David K. ; Warner, John C. ; Geyer, W. Rockwell ; Wall, Gary R.
    Tropical Storms Irene and Lee in 2011 produced intense precipitation and flooding in the U.S. Northeast, including the Hudson River watershed. Sediment input to the Hudson River was approximately 2.7 megaton, about 5 times the long-term annual average. Rather than the common assumption that sediment is predominantly trapped in the estuary, observations and model results indicate that approximately two thirds of the new sediment remained trapped in the tidal freshwater river more than 1 month after the storms and only about one fifth of the new sediment reached the saline estuary. High sediment concentrations were observed in the estuary, but the model results suggest that this was predominantly due to remobilization of bed sediment. Spatially localized deposits of new and remobilized sediment were consistent with longer term depositional records. The results indicate that tidal rivers can intercept (at least temporarily) delivery of terrigenous sediment to the marine environment during major flow events.
  • Article
    Shoaling wave shape estimates from field observations and derived bedload sediment rates
    (MDPI, 2022-02-08) Kalra, Tarandeep S. ; Suttles, Steven E. ; Sherwood, Christopher R. ; Warner, John C. ; Aretxabaleta, Alfredo L. ; Leavitt, Gibson R.
    he shoaling transformation from generally linear deep-water waves to asymmetric shallow-water waves modifies wave shapes and causes near-bed orbital velocities to become asymmetrical, contributing to net sediment transport. In this work, we used two methods to estimate the asymmetric wave shape from data at three sites. The first method converted wave measurements made at the surface to idealized near-bottom wave-orbital velocities using a set of empirical equations: the “parameterized” waveforms. The second method involved direct measurements of velocities and pressure made near the seabed: the “direct” waveforms. Estimates from the two methods were well correlated at all three sites (Pearson’s correlation coefficient greater than 0.85). Both methods were used to drive bedload-transport calculations that accounted for asymmetric waves, and the results were compared with a traditional excess-stress formulation and field estimates of bedload transport derived from ripple migration rates based on sonar imagery. The cumulative bedload transport from the parameterized waveform was 25% greater than the direct waveform, mainly because the parameterized waveform did not account for negative skewness. Calculated transport rates were comparable to rates estimated from ripple migration except during the largest event, when calculated rates were as much as 100 times greater, which occurred during high period waves.
  • Article
    Storm-driven sediment transport in Massachusetts Bay
    (Elsevier B.V., 2007-09-22) Warner, John C. ; Butman, Bradford ; Dalyander, P. Soupy
    Massachusetts Bay is a semi-enclosed embayment in the western Gulf of Maine about 50 km wide and 100 km long. Bottom sediment resuspension is controlled predominately by storm-induced surface waves and transport by the tidal- and wind-driven circulation. Because the Bay is open to the northeast, winds from the northeast (‘Northeasters’) generate the largest surface waves and are thus the most effective in resuspending sediments. The three-dimensional oceanographic circulation model Regional Ocean Modeling System (ROMS) is used to explore the resuspension, transport, and deposition of sediment caused by Northeasters. The model transports multiple sediment classes and tracks the evolution of a multilevel sediment bed. The surficial sediment characteristics of the bed are coupled to one of several bottom-boundary layer modules that calculate enhanced bottom roughness due to wave–current interaction. The wave field is calculated from the model Simulating WAves Nearshore (SWAN). Two idealized simulations were carried out to explore the effects of Northeasters on the transport and fate of sediments. In one simulation, an initially spatially uniform bed of mixed sediments exposed to a series of Northeasters evolved to a pattern similar to the existing surficial sediment distribution. A second set of simulations explored sediment-transport pathways caused by storms with winds from the northeast quadrant by simulating release of sediment at selected locations. Storms with winds from the north cause transport southward along the western shore of Massachusetts Bay, while storms with winds from the east and southeast drive northerly nearshore flow. The simulations show that Northeasters can effectively transport sediments from Boston Harbor and the area offshore of the harbor to the southeast into Cape Cod Bay and offshore into Stellwagen Basin. This transport pattern is consistent with Boston Harbor as the source of silver found in the surficial sediments of Cape Cod Bay and Stellwagen Basin.
  • Article
    Wave-current interaction between Hurricane Matthew wave fields and the Gulf Stream
    (American Meteorological Society, 2019-11-01) Hegermiller, Christie A. ; Warner, John C. ; Olabarrieta, Maitane ; Sherwood, Christopher R.
    Hurricanes interact with the Gulf Stream in the South Atlantic Bight (SAB) through a wide variety of processes, which are crucial to understand for prediction of open-ocean and coastal hazards during storms. However, it remains unclear how waves are modified by large-scale ocean currents under storm conditions, when waves are aligned with the storm-driven circulation and tightly coupled to the overlying wind field. Hurricane Matthew (2016) impacted the U.S. Southeast coast, causing extensive coastal change due to large waves and elevated water levels. The hurricane traveled on the continental shelf parallel to the SAB coastline, with the right side of the hurricane directly over the Gulf Stream. Using the Coupled Ocean–Atmosphere–Wave–Sediment Transport modeling system, we investigate wave–current interaction between Hurricane Matthew and the Gulf Stream. The model simulates ocean currents and waves over a grid encompassing the U.S. East Coast, with varied coupling of the hydrodynamic and wave components to isolate the effect of the currents on the waves, and the effect of the Gulf Stream relative to storm-driven circulation. The Gulf Stream modifies the direction of the storm-driven currents beneath the right side of the hurricane. Waves transitioned from following currents that result in wave lengthening, through negative current gradients that result in wave steepening and dissipation. Wave–current interaction over the Gulf Stream modified maximum coastal total water levels and changed incident wave directions at the coast by up to 20°, with strong implications for the morphodynamic response and stability of the coast to the hurricane.
  • Article
    Development of a Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) Modeling System
    (Elsevier B.V., 2010-07-29) Warner, John C. ; Armstrong, Brandy ; He, Ruoying ; Zambon, Joseph B.
    Understanding the processes responsible for coastal change is important for managing our coastal resources, both natural and economic. The current scientific understanding of coastal sediment transport and geology suggests that examining coastal processes at regional scales can lead to significant insight into how the coastal zone evolves. To better identify the significant processes affecting our coastlines and how those processes create coastal change we developed a Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) Modeling System, which is comprised of the Model Coupling Toolkit to exchange data fields between the ocean model ROMS, the atmosphere model WRF, the wave model SWAN, and the sediment capabilities of the Community Sediment Transport Model. This formulation builds upon previous developments by coupling the atmospheric model to the ocean and wave models, providing one-way grid refinement in the ocean model, one-way grid refinement in the wave model, and coupling on refined levels. Herein we describe the modeling components and the data fields exchanged. The modeling system is used to identify model sensitivity by exchanging prognostic variable fields between different model components during an application to simulate Hurricane Isabel during September 2003. Results identify that hurricane intensity is extremely sensitive to sea surface temperature. Intensity is reduced when coupled to the ocean model although the coupling provides a more realistic simulation of the sea surface temperature. Coupling of the ocean to the atmosphere also results in decreased boundary layer stress and coupling of the waves to the atmosphere results in increased bottom stress. Wave results are sensitive to both ocean and atmospheric coupling due to wave–current interactions with the ocean and wave growth from the atmosphere wind stress. Sediment resuspension at regional scale during the hurricane is controlled by shelf width and wave propagation during hurricane approach.