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  1. Abstract

    Transient rip currents drive cross‐shore transport of nutrients, larvae, sediment, and other particulate matter. These currents are driven by short‐crested wave breaking, which is associated with rotational wave‐breaking forces (vorticity forcing) that generate horizontal rotational motions (eddies) at small scales. Energy from small‐scale eddies is transferred to larger‐scale eddies that interact and enhance cross‐shore exchange. Previous numerical modeling work on planar beaches has shown that cross‐shore exchange increases with increasing wave directional spread, but this relationship is not established for barred beaches, and processes connecting the wavefield to cross‐shore exchange are not well constrained. We investigate surf‐zone eddy processes using numerical simulations (FUNWAVE‐TVD) and large‐scale laboratory observations of varying offshore wave directional spreads (0 to ) and peak period (1.5–2.5 s) on an alongshore uniform barred beach. We find that mean breaking crest length decreases, while crest end density (number of crest ends in a given area) increases, with increasing directional spread. In contrast, vorticity forcing, offshore low‐frequency rotational motion, and cross‐shore exchange peak at intermediate directional spreads . Distributions of the strength of vorticity forcing per crest and across the surf zone suggest that the peak in vorticity forcing at intermediate spreads results from a combination of a larger total breaking area and relatively long crests with large forcing, despite a lower total number of crests. However, low‐frequency rotational motion within the surf zone does not peak at mid‐directional spread, instead plateauing at directional spreads greater than . Results suggest that eddy‐eddy interaction, the transformation of vorticity across the surf zone, and influence of bathymetry are fruitful topics for future work.

     
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  2. Abstract

    Extreme precipitation during Hurricane Florence, which made landfall in North Carolina in September 2018, led to breaches of hog waste lagoons, coal ash pits, and wastewater facilities. In the weeks following the storm, freshwater discharge carried pollutants, sediment, organic matter, and debris to the coastal ocean, contributing to beach closures, algae blooms, hypoxia, and other ecosystem impacts. Here, the ocean pathways of land‐sourced contaminants following Hurricane Florence are investigated using the Regional Ocean Modeling System (ROMS) with a river point source with fixed water properties from a hydrologic model (WRF‐Hydro) of the Cape Fear River Basin, North Carolina's largest watershed. Patterns of contaminant transport in the coastal ocean are quantified with a finite duration tracer release based on observed flooding of agricultural and industrial facilities. A suite of synthetic events also was simulated to investigate the sensitivity of the river plume transport pathways to river discharge and wind direction. The simulated Hurricane Florence discharge event led to westward (downcoast) transport of contaminants in a coastal current, along with intermittent storage and release of material in an offshore (bulge) or eastward (upcoast) region near the river mouth, modulated by alternating upwelling and downwelling winds. The river plume patterns led to a delayed onset and long duration of contaminants affecting beaches 100 km to the west, days to weeks after the storm. Maps of the onset and duration of hypothetical water quality hazards for a range of weather conditions may provide guidance to managers on the timing of swimming/shellfishing advisories and water quality sampling.

     
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    Free, publicly-accessible full text available March 1, 2025
  3. Existing codes spanning 2009-2012 for working with Surface Wave Instrument Floats with Tracking (SWIFT) data. Codes for both telemetry and post-processed data. Buoy versions v3, v3, and microSWIFTs supported. 
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  4. Exchange of material across the nearshore region, extending from the shoreline to a few kilometers offshore, determines the concentrations of pathogens and nutrients near the coast and the transport of larvae, whose cross-shore positions influence dispersal and recruitment. Here, we describe a framework for estimating the relative importance of cross-shore exchange mechanisms, including winds, Stokes drift, rip currents, internal waves, and diurnal heating and cooling. For each mechanism, we define an exchange velocity as a function of environmental conditions. The exchange velocity applies for organisms that keep a particular depth due to swimming or buoyancy. A related exchange diffusivity quantifies horizontal spreading of particles without enough vertical swimming speed or buoyancy to counteract turbulent velocities. This framework provides a way to determinewhich processes are important for cross-shore exchange for a particular study site, time period, and particle behavior. 
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  5. null (Ed.)
  6. This archive contains COAWST model input, grids and initial conditions, and output used to produce the results in a submitted manuscript. The files are:

    model_input.zip: input files for simulations presented in this paper
      ocean_rip_current.in: ROMS ocean model input file
      swan_rip_current.in: SWAN wave model input file (example with Hs=1m)
      coupling_rip_current.in: model coupling file
      rip_current.h: model header file
      
    model_grids_forcing.zip: bathymetry and initial condition files
         hbeach_grid_isbathy_2m.nc: ROMS bathymetry input file
         hbeach_grid_isbathy_2m.bot: SWAN bathymetry input file
         hbeach_grid_isbathy_2m.grd: SWAN grid input file
         hbeach_init_isbathy_14_18_17.nc: Initial temperature, cool surf zone dT=-1C case
         hbeach_init_isbathy_14_18_19.nc: Initial temperature, warm surf zone dT=+1C case
         hbeach_init_isbathy_14_18_16.nc: Initial temperature, cool surf zone dT=-2C case
         hbeach_init_isbathy_14_18_20.nc: Initial temperature, warm surf zone dT=+2C case
         hbeach_init_isbathy_14_18_17p5.nc: Initial temperature, cool surf zone dT=-0.5C case
         hbeach_init_isbathy_14_18_18p5.nc: Initial temperature, warm surf zone dT=+0.5C case

    model_output files: model output used to produce the figures
         netcdf files, zipped
         variables included:
              x_rho (cross-shore coordinate, m)
              y_rho (alongshore coordinate, m)
              z_rho (vertical coordinate, m)
              ocean_time (time since initialization, s, output every 5 mins)
              h (bathymetry, m)
              temp (temperature, Celsius)
              dye_02 (surfzone-released dye)
              Hwave (wave height, m)
              Dissip_break (wave dissipation W/m2) 
              ubar (cross-shore depth-average velocity, m/s, interpolated to rho-points)
         Case_141817.nc: cool surf zone dT=-1C Hs=1m
         Case_141819.nc: warm surf zone dT=+1C Hs=1m
         Case_141816.nc: cool surf zone dT=-2C Hs=1m
         Case_141820.nc: warm surf zone dT=-2C Hs=1m
         Case_141817p5.nc: cool surf zone dT=-0.5C Hs=1m
         Case_141818p5.nc: warm surf zone dT=+0.5C Hs=1m
         Case_141817_Hp5.nc: cool surf zone dT=-1C Hs=0.5m
         Case_141819_Hp5.nc: warm surf zone dT=+1C Hs=0.5m
         Case_141817_Hp75.nc: cool surf zone dT=-1C Hs=0.75m
         Case_141819_Hp75.nc: warm surf zone dT=+1C Hs=0.75m

    COAWST is an open source code and can be download at https://coawstmodel-trac.sourcerepo.com/coawstmodel_COAWST/. Descriptions of the input and output files can be found in the manual distributed with the model code and in the glossary at the end of the ocean.in file.

    Corresponding author: Melissa Moulton, mmoulton@uw.edu

     
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  7. Abstract

    Low‐frequency surf zone eddies disperse material between the shoreline and the continental shelf, and velocity fluctuations with frequencies as low as a few mHz have been observed previously on several beaches. Here spectral estimates of surf zone currents are extended to an order of magnitude lower frequency, resolving an extremely low frequency peak of approximately 0.5 mHz that is observed for a range of beaches and wave conditions. The magnitude of the 0.5‐mHz peak increases with increasing wave energy and with spatial inhomogeneity of bathymetry or currents. The 0.5‐mHz peak may indicate the frequency for which nonlinear energy transfers from higher‐frequency, smaller‐scale motions are balanced by dissipative processes and thus may be the low‐frequency limit of the hypothesized 2‐D cascade of energy from breaking waves to lower frequency motions.

     
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