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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. 

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

 

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.