Hydrodynamic and Sediment Transport Model Application for OSAT3 Guidance: Ratio of the wave- and current-induced shear stress to the critical value for oil-tar balls and sediment mobilization over a tidal cycle

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• What does this data set describe?
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  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
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What does this data set describe?

1. How might this data set be cited?
   Dalyander, P. Soupy, Long, Joseph W., Plant, Nathaniel G., and Thompson, David M., 2012, Hydrodynamic and Sediment Transport Model Application for OSAT3 Guidance: Ratio of the wave- and current-induced shear stress to the critical value for oil-tar balls and sediment mobilization over a tidal cycle: U.S. Geological Survey Open-File Report 2012-1234, U.S. Geological Survey, Coastal and Marine Geology Program, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL.

   Online Links:

   • https://pubs.usgs.gov/of/2012/1234/datafiles.html

   This is part of the following larger work.
   Plant, Nathaniel G., Long, Joseph W., Dalyander, P.Soupy, and Thompson, David M., 2012, Hydrodynamic and Sediment Transport Model Application for OSAT3 Guidance: U.S. Geological Survey Open-File Report 2012-1234, U.S. Geological Survey, Coastal and Marine Geology Program, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL.

   Online Links:

   • https://pubs.usgs.gov/of/2012/1234/

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -88.715420
   East_Bounding_Coordinate: -85.412233
   North_Bounding_Coordinate: 30.692506
   South_Bounding_Coordinate: 29.405594
   

3. What does it look like?

   model_bathymetry.jpg (JPEG)

   Graphic showing the numerical model domain over which analysis is conducted.

4. Does the data set describe conditions during a particular time period?

   Beginning_Date: 01-Apr-2010

   Ending_Date: 01-Aug-2012

   Currentness_Reference:

   ground condition

5. What is the general form of this data set?

   Geospatial_Data_Presentation_Form: vector digital data
   

6. How does the data set represent geographic features?
   1. How are geographic features stored in the data set?
      

      Indirect_Spatial_Reference: Gulf of Mexico
      

      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • G-polygon (982790)
   2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000001. Longitudes are given to the nearest 0.000001. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257224.
      

      Vertical_Coordinate_System_Definition:

      Altitude_System_Definition:

      Altitude_Datum_Name: North American Vertical Datum of 1988
      Altitude_Resolution: 0.01 m
      Altitude_Distance_Units: meters
      Altitude_Encoding_Method:

      Explicit elevation coordinate included with horizontal coordinates

7. How does the data set describe geographic features?

   Tidal_mobility_TT

   Hydrodynamic and Sediment Transport Model Application for OSAT3 Guidance: Ratio of the wave- and current-induced shear stress to the critical value for oil-tar balls and sediment mobilization at a specific time step in a tidal cycle (Source: USGS)

   FID

   Internal feature number. (Source: ESRI) Sequential unique whole numbers that are automatically generated.

   Shape

   Feature geometry. (Source: ESRI) Coordinates defining the features.

   Scenario_H

   Scenario wave height number, see wave_scenarios.txt (Source: USGS)

   Range of values
   Minimum:	1
   Maximum:	5
   Units:	non-dimensional
   Resolution:	1

   Scenario_D

   Scenario wave direction number, see wave_scenarios.txt (Source: USGS)

   Range of values
   Minimum:	1
   Maximum:	16
   Units:	non-dimensional
   Resolution:	1

   Time_Step

   Time step index into the 24 hour tidal cycle simulation (Source: USGS)

   Range of values
   Minimum:	1
   Maximum:	24
   Units:	non-dimensional
   Resolution:	1

   sediment

   Unitless ratio of the combined wave- and current-induced shear stress to the critical stress for 300 micron quartz sand calculated from the Shield's parameter. Values greater than one indicate sand is likely mobilized under the wave conditions associated with this scenario. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB1_high

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 1 (see SRB_classes.txt) calculated from the Shield's parameter. The Shield's parameter is a relatively high critical stress estimate and does not account for a reduced critical stress due to potential SRB exposure above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB1_med

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 1 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.02. This critical stress estimate is a mid-range value accounting for a reduced critical stress due to some exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB1_low

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 1 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.01. This critical stress estimate is a low value accounting for a reduced critical stress due to exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB2_high

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 2 (see SRB_classes.txt) calculated from the Shield's parameter. The Shield's parameter is a relatively high critical stress estimate and does not account for a reduced critical stress due to potential SRB exposure above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB2_med

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 2 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.02. This critical stress estimate is a mid-range value accounting for a reduced critical stress due to some exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB2_low

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 2 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.01. This critical stress estimate is a low value accounting for a reduced critical stress due to exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB3_high

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 3 (see SRB_classes.txt) calculated from the Shield's parameter. The Shield's parameter is a relatively high critical stress estimate and does not account for a reduced critical stress due to potential SRB exposure above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB3_med

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 3 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.02. This critical stress estimate is a mid-range value accounting for a reduced critical stress due to some exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB3_low

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 3 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.01. This critical stress estimate is a low value accounting for a reduced critical stress due to exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB4_high

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 4 (see SRB_classes.txt) calculated from the Shield's parameter. The Shield's parameter is a relatively high critical stress estimate and does not account for a reduced critical stress due to potential SRB exposure above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB4_med

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 4 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.02. This critical stress estimate is a mid-range value accounting for a reduced critical stress due to some exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB4_low

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 4 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.01. This critical stress estimate is a low value accounting for a reduced critical stress due to exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB5_high

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 5 (see SRB_classes.txt) calculated from the Shield's parameter. The Shield's parameter is a relatively high critical stress estimate and does not account for a reduced critical stress due to potential SRB exposure above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB5_med

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 5 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.02. This critical stress estimate is a mid-range value accounting for a reduced critical stress due to some exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB5_low

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 5 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.01. This critical stress estimate is a low value accounting for a reduced critical stress due to exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB6_high

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 6 (see SRB_classes.txt) calculated from the Shield's parameter. The Shield's parameter is a relatively high critical stress estimate and does not account for a reduced critical stress due to potential SRB exposure above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB6_med

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 6 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.02. This critical stress estimate is a mid-range value accounting for a reduced critical stress due to some exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

   SRB6_low

   Unitless ratio of the combined wave- and current-induced shear stress for this scenario to the critical stress for SRB class 6 (see SRB_classes.txt) calculated from a non-dimensional Shield's parameter of 0.01. This critical stress estimate is a low value accounting for a reduced critical stress due to exposure of the SRB above the seafloor. (Source: USGS)

   Range of values
   Minimum:	0
   Maximum:	100
   Units:	non-dimensional
   Resolution:	0.01

Who produced the data set?

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • P. Soupy Dalyander
   • Joseph W. Long
   • Nathaniel G. Plant
   • David M. Thompson
2. Who also contributed to the data set?
3. To whom should users address questions about the data?
   P. Soupy Dalyander

   U.S. Geological Survey

   Oceanographer

   384 Woods Hole Road

   Woods Hole, MA
   

   USA

   (508) 548-8700 x2290 (voice)

   (508) 457-2310 (FAX)

   sdalyander@usgs.gov

Why was the data set created?

This GIS layer contains an estimate of the ratio of combined wave- and current- induced shear stress in the shallow northern Gulf of Mexico (Alabama and portion of the Florida coast) to the critical stress of surface residual balls (SRB) of various sizes and local sediment. This layer is part of a series of data layers (naming convention Tidal_mobility_TT.xxx, where TT is an hourly time step and is also indicated in attributes within the file) demonstrating the variability with tidal fluctuations in this ratio for a fixed set of wave conditions over a 24 hour period. The wave conditions in the file correspond to waves at NOAA NDBC buoy 42040 of between 1.5-2 m, coming from between 135-157.50 degrees relative to north (corresponding to scenario H4_D7 in the included wave_scenarios.txt file). The time steps (e.g., HH in the file names) of maximum flood and maximum ebb for various inlets in the domain are indicated in the included inlet_flood_ebb_tides.txt. Values greater than one indicate the threshold for incipient motion is exceeded, and the SRB or sediment is likely mobilized. Characteristics of SRB classes and the sediment properties used may be found in the look-up table included in the GIS zip file, SRB_casses.txt. This data layer is intended to show regions of likely mobilization for intended use by individuals in SRB mitigation attempting to explain redistribution or burial of SRBs, and displays variability over a tidal cycle.

How was the data set created?

1. From what previous works were the data drawn?

   NOAA GFS (source 1 of 4)

   NOAA National Centers for Environmental Prediction (NCEP), 20110601, NOAA/NCEP Global Forecast System (GFS) Atmospheric Model: NOAA National Centers for Environmental Prediction, Camp Springs, MD.

   Online Links:

   • http://nomads.ncdc.noaa.gov/data.php

   Type_of_Source_Media: online
   Source_Contribution:

   Wind speed data at 10 m above the sea surface from the NOAA Global Forecast System (GFS) 0.5 degree model is interpolated by NOAA to the 4' Wavewatch3 grid and archived. These archived data are used to drive the numerical wave and circulation model that creates estimated of bottom shear stress.

   NOAA WW3 (source 2 of 4)

   NOAA National Centers for Environmental Prediction (NCEP, 20121001, NOAA/NWS/NCEP 4' Wavewatch III Operational Wave Forecast: NOAA National Centers for Environmental Prediction, Camp Springs, MD.

   Online Links:

   • http://polar.ncep.noaa.gov/waves/index2.shtml

   Type_of_Source_Media: online
   Source_Contribution:

   Boundary conditions for the wave model were provided by the 4' NOAA/NWS/NCEP Wavewatch III operational ocean wave forecast.

   TPXO Tides (source 3 of 4)

   Egbert, Gary, and Erofeeva, Lana, 20120801, The OSU TOPEX/Poseidon Global Inverse Solution TPXO: Oregon State University, Corvallis, OR.

   Online Links:

   • http://volkov.oce.orst.edu/tides/global.html

   Type_of_Source_Media: online
   Source_Contribution:

   The OSU TOPEX/Poseidon tidal prediction software package and associated data were used to develop a prediction of the tides at the offshore boundaries of the model domain in order to compute the phase lags between the two corners.

   Dauphin Tides (source 4 of 4)

   National Oceanic and Atmospheric Administration, 20120801, Dauphin Island, AL, Tide Gauge Data (Station 8735180): NOAA Center for Operational Oceanographic Products and Services (CO-OPS), Silver Spring, MD.

   Online Links:

   • http://tidesandcurrents.noaa.gov/data_menu.shtml?stn=8735180 Dauphin Island, AL&type=Tide Data

   Type_of_Source_Media: online
   Source_Contribution:

   Observed tides from the NOAA Dauphin Island, AL, tide gauge (station 8735180) were used to reconstruct a morphological tide used to force tidal variations in the simulation.

2. How were the data generated, processed, and modified?

   Date: 2012 (process 1 of 8)

   Analyze the water level elevation data from the NOAA tide gauge at Dauphin Island, AL, (8735180), for the period of April 1, 2010, to August 17, 2012, using T_TIDE (a Mathworks MATLAB software package described in Pawlowicz et al, 2002, , based on algorithms and FORTRAN code previously developed by Godin, 1972, and Foreman, 1977, 1978). Following the method prescribed in Lesser, 2009, develop the morphological tide, e.g., an equivalent description of the tidal variation responsible for the bulk of the morphological dynamics. A TPXO tidal prediction was then made at the two offshore points and analyzed with the T_TIDE software, and a phase lag between the M2 and C1 constituents was calculated.
   Foreman, M.G.G., 1977. Manual for tidal heights analysis and prediction. Pacific Marine Science Report 77-10, Institute of Ocean Sciences, Patricia Bay, Sidney, BC.
   Foreman, M.G.G., 1978. Manual for tidal currents analysis and prediction. Pacific Marine Science Report 78-6, Institute of Ocean Sciences, Patricia Bay, Sidney, BC.
   Godin, G., 1972. The Analysis of Tides. University of Toronto Press, Toronto.
   Lesser, G.R., 2009. An Approach to Medium-term Coastal Morphological Modelling. Dissertation. Delft University of Technology.
   Pawlowicz, R., Beardsley, B., Lentz, S., 2002. Classical tidal harmonic analysis including error estimates in MATLAB using T_TIDE. Comput. Geosci. 28, 929-937. Person who carried out this activity:
   

   David Thompson

   U.S. Geological Survey

   Oceanographer

   600 4th Street S

   St. Petersburg, FL
   

   USA

   (727) 803-8747 x3079 (voice)

   (727) 803-2032 (FAX)

   dthompson@usgs.gov

   Data sources used in this process:

   • Dauphin Tides
   • TPXO Tides

   Data sources produced in this process:

   • Morpho Tides

   Date: 2012 (process 2 of 8)

   The D-Flow and D-Waves components of the Deltares Delft3D numerical model suite (version 4.00.01) were used to estimate bottom orbital velocity, peak period, peak wave direction, and east and north components of wind and wave-driven velocity for the offshore wave conditions corresponding this scenario Hh_Dd (characteristics of which may be found in the included wave_scenarios.txt file) in each grid cell in the model domain. The wave model D-Waves, based on the Simulating WAves Nearshore (SWAN) model, is a 3rd generation phase-averaged numerical wave model which conserves wave energy subject to generation, dissipation, and transformation processes and resolves spectral energy density over a range of user-specified frequencies and directions. D-Wave was used in stationary mode. D-Flow solves the shallow water Navier Stokes equations and is run in 2-D depth-averaged mode, with linkage to D-Waves allowing the generation of wave-driven currents via wave radiation stress forcing. Default values for model parameters governing horizontal viscosity, bottom roughness, and wind drag were used. Neumann boundary conditions were used along the east, west, and south model boundaries with harmonic forcing set to zero. The southern boundary was designated as a water level boundary with harmonic forcing using the M2 and C1 constituents of the morphological tide. The morphological tide harmonics were applied to the SW corner and the harmonics plus the phase lags were applied at the SE corner.
   Significant wave height, dominant wave period, and wave direction were prescribed as D-Wave TPAR format files every 30 grid cells along the model boundary using results from the NOAA Wavewatch III 4' multi-grid model for a representative moment in time corresponding to the offshore wave conditions of the scenario, the specific time of which may be found in the included wave_scenarios.txt file. A JONSWAP (JOint NOrth Sea WAve Project) spectral shape was assumed at these boundary points. Wind forcing was provided using the archived WavewatchIII 4' winds, extracted from the NOAA GFS wind model, for this time. The D-Wave directional space covers a full circle with a resolution was 5 degrees (72 bins). The frequency range was specified as 0.05-1 Hz with logarithmic spacing. Bottom friction calculations used the JONSWAP formulation with a uniform roughness coefficient of 0.067 m2/s3. 3rd-generation physics are activated which accounts for wind wave generation, triad wave interactions and whitecapping (via the Komen et al parameterization). Depth-induced wave breaking dissipation is included using the method of Battjes and Janssen with default values for alpha (1) and gamma (0.73). Wave model outputs of bottom orbital velocity, peak period, and peak wave direction were extracted on the wave model grid, and current model outputs of east and north current velocity component were extracted and interpolated to the wave model grid (staggered points in relation to the current model grid).
   NDBC observations from station 42012 for the representative scenario time periods were used to validate the wave model results. Person who carried out this activity:
   

   Joseph W. Long

   U.S. Geological Survey

   Oceanographer

   600 4th Street S

   St. Petersburg, FL
   

   USA

   (727) 803-8747 x3024 (voice)

   (727) 803-2032 (FAX)

   jwlong@usgs.gov

   Data sources used in this process:

   • NOAA GFS
   • NOAA WW3
   • MORPHO TIDES

   Data sources produced in this process:

   • DELFT3D

   Date: 2012 (process 3 of 8)

   Use the wave model and current model results to calculate the bottom shear stress within each model grid cell using Mathworks MATLAB software (v2012A). The wave-current stress was calculating following the method of Soulsby (1995) to parameterize four methods giving good overall performance for estimating wave-current stress, based on original formulations by Grant and Madsen (1979), Fredsøe (1984), Huynh-Thanh and Temperville (1991), and Davies et al. (1998). The combined wave-current stress for the individual components of wave and current stress was calculated for hydrodynamic model output following the method prescribed in Soulsby (1997) for each of the four methods. The mean value of the four methodologies was used to estimate the combined wave-current shear stress for the hydrodynamic scenario. Wave direction, bottom orbital velocity, and period, and depth-averaged current magnitude and direction, required for this calculation, are calculated internally by the model. The roughness used is 1/12 the diameter of the SRB or sediment being analyzed, following Soulsby (1997). Stress values are saved in MATLAB .mat format.
   The same individual who completed this processing step completed all additional processing steps.
   References: Davies, A.G., Soulsby, R.L., King, H.L. (1988). A numerical model of the combined wave and current bottom boundary layer. J. Geophys. Res. 93, 491-508.
   Fredsøe, J. (1984). Turbulent boundary layer in wave-current motion. J. Hydraul. Eng. ASCE (110), 1103-1120.
   Grant, W.D., Madsen, O.S. (1979). Combined wave and current interaction with a rough bottom. J. Geophys. Res. (84), 1797-1808.
   Huynh-Thanh, S., Temperville, A. (1991). A numerical model of the rough turbulent boundary layer in combined wave and current interaction, in Sand Transport in Rivers, Estuaries, and the Sea, eds. R. L. Soulsby and R. Bettess, pp 93-100. Balkema, Rotterdam.
   Soulsby, R.L. (1995). Bed shear-stresses due to combined waves and currents, in Advances in Coastal Morphodynamics, eds. M.J.F. Stive, H.J. de Vriend, J. Fredsøe, L. Hamm, R.L. Soulsby, C. Teisson and J.C. Winterwerp, pp. 4-20 and 3-23. Delft Hydraulics, Netherlands.
   Soulsby, R.L. (1997). Dynamics of Marine Sands. Thomas Telford Publications: London, 249 pp. Person who carried out this activity:
   

   P. Soupy Dalyander

   U.S. Geological Survey

   Oceanographer

   384 Woods Hole Road

   Woods Hole, MA
   

   USA

   (508) 548-8700 x2290 (voice)

   (508) 457-2310 (FAX)

   sdalyander@usgs.gov

   Data sources used in this process:

   • DELFT3D

   Data sources produced in this process:

   • WC STRESS

   Date: 2012 (process 4 of 8)

   Estimate the critical shear stress for 300 micron quartz sediment and 6 SRB size classes and take the ratio of the combined wave-current stress to this critical value at each grid point. The specific characteristics for the sediment and SRB classes may be found in the included SRB_classes.txt file. Calculations are performed in Mathworks MATLAB (v2012A). Critical stress thresholds are calculated using the Shield's parameter following Soulsby (1997) and saved in MATLAB .mat format. In the case of SRBs, the Shield's parameter is identified as a "high" critical stress value, corresponding to instances when an SRB of the identified size is within a uniform bed of similarly sized SRBs. Exposure above the bed, such as may occur with a single SRB on a sand band, reduces the critical shear stress value for incipient motion. Based on field observations of gravel and sand mixtures, a "medium" critical stress value is calculated from a constant non-dimensional Shields parameter of 0.02, and a "low" critical stress value is calculated from a constant non-dimensional Shields parameter of 0.01 (Andrews, 1983; Bottacin-Busolin et al, 2008; Fenton and Abbott, 1977; Wiberg and Smith, 1987; Wilcock, 1998). Because the in-situ sediment is assumed to be of a relatively uniform size, a single critical stress value based on the Shields parameter is used.
   References:
   Andrews, E.D. (1983). Entrainment of gravel from naturally sorted riverbed material. Geo. Soc. Amer. Bull. (94), 1225-1231.
   Bottacin-Busolin, A., Tait, S.J., Marion, A., Chegini, A., Tregnaghi, M. (2008). Probabilistic description of grain resistance from simultaneous flow field and grain motion measurements. Water Resources Res. (44), WO9419.
   Fenton, J.D., Abbott, J.E. (1977). Initial movement of grains on a stream bed: the effect of relative protusion. Proc. R. Soc. Lond. A. (352), 523-537.
   Soulsby, R., 1997. Dynamics of Marine Sands, a Manual for Practical Applications. Thomas Telford Publications, London.
   Wibert, P.L., Smith, J.D. (1987). Calculations of the Critical Shear Stress for Motion of Uniform and Heterogenous Sediments. Water Resources Res. (23), 1471-1480.
   Wilcock, P.R. (1998). Two-Fraction Model of Initial Sediment Motion in Gravel-Bed Rivers. Science (280), 410-412. Data sources used in this process:

   • WC STRESS

   Data sources produced in this process:

   • RATIO

   Date: 2012 (process 5 of 8)

   Export the values for each grid cell from MATLAB format into an ArcGIS shapefile using the Mathworks MATLAB Mapping Toolbox (v2012A). Each of 24 hourly time steps from the tidal simulation are output to a seperate GIS layer of naming convention Tidal_mobility_TT.xxx, where TT is the hourly time step. Land grid cells are not exported to Arc. The shapefile is written with the "shapewrite" command. Because MATLAB does not assign a projection, the projection corresponding to the projection associated with the bathymetry used in the numerical models is added in ArcCatalog 9.3. The file was then quality checked in ArcMap to insure values were properly exported to the shapefile from MATLAB. Data sources used in this process:

   • RATIO

   Date: 13-Mar-2017 (process 6 of 8)

   Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: Alan O. Allwardt

   Contractor -- Information Specialist

   2885 Mission Street

   Santa Cruz, CA
   

   831-460-7551 (voice)

   831-427-4748 (FAX)

   aallwardt@usgs.gov

   Date: 03-Apr-2018 (process 7 of 8)

   Keywords section of metadata optimized by correcting variations of theme keyword thesauri and updating/adding keywords. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: Arnell S. Forde

   Geologist

   600 4th Street South

   St. Petersburg, FL
   

   727-502-8000 (voice)

   aforde@usgs.gov

   Date: 13-Oct-2020 (process 8 of 8)

   Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
   

   U.S. Geological Survey

   Attn: VeeAnn A. Cross

   Marine Geologist

   384 Woods Hole Road

   Woods Hole, MA
   

   508-548-8700 x2251 (voice)

   508-457-2310 (FAX)

   vatnipp@usgs.gov

3. What similar or related data should the user be aware of?

How reliable are the data; what problems remain in the data set?

1. How well have the observations been checked?
   The attributes in this layer are the ratio of combined wave-current shear stress to critical stress for sediment and several sized SRBs. This layer is part of a series of data layers (naming convention Tidal_mobility_HH.xxx, where HH is an hourly time step, ranging from 1 to 24, and is also indicated in attributes within the file) demonstrating the variability with tidal fluctuations in this ratio for a fixed set of wave conditions over a 24 hour period. The wave conditions in the file correspond to waves at NOAA NDBC buoy 42040 of between 1.5-2 m, coming from between 135-157.50 degrees relative to north (corresponding to scenario H4_D7 in the included wave_scenarios.txt file). SRB class and sediment properties may be found in the look-up table included in the GIS zip file, SRB_casses.txt. Statistical values will vary if a different numerical model is used for the hydrodynamics, or if a different method is used in calculating wave-current stress or critical stress.
2. How accurate are the geographic locations?
   Numerical models are used in the generation of hydrodynamic conditions used in creating this data layer. Because the overall horizontal accuracy of the data set depends on the accuracy of the model, the underlying bathymetry, forcing values used, and so forth, the spatial accuracy of this data layer cannot be meaningfully quantified.
3. How accurate are the heights or depths?
   
4. Where are the gaps in the data? What is missing?
   This statistic was calculated at all locations (wet grid cells) where model output exists. Because of differences between the scenarios, not all grid cells may be included in all scenarios. This layer is part of a series of data layers (naming convention Tidal_mobility_TT.xxx, where TT is an hourly time step, ranging from 1 to 24, and is also indicated in attributes within the file) demonstrating the variability with tidal fluctuations in this ratio for a fixed set of wave conditions over a 24 hour period. The wave conditions in the file correspond to waves at NOAA NDBC buoy 42040 of between 1.5-2 m, coming from between 135-157.50 degrees relative to north (corresponding to scenario H4_D7 in the included wave_scenarios.txt file). SRB class and sediment properties may be found in the look-up table included in the GIS zip file, SRB_casses.txt. The bottom shear stress was calculated from wave and current estimates generated with Delft3D, and would vary if different models were used or if different model inputs (such as bathymetry, forcing winds, and boundary conditions) or parameterizations were chosen. Calculated currents were depth-averaged and therefore the calculated mobility values are expected to be most valid in well-mixed regions, e.g., the surf zone. Mobility estimates would vary for different size or density objects and/or if a different formulation for calculating the critical stress value is used.
5. How consistent are the relationships among the observations, including topology?
   No duplicate features are present. All polygons are closed, and all lines intersect where intended. No undershoots or overshoots are present.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None
Use_Constraints:

Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the originator of the dataset.

1. Who distributes the data set? (Distributor 1 of 1)
   
   P. Soupy Dalyander

   U.S. Geological Survey

   Oceanographer

   384 Woods Hole Road

   Woods Hole, MA
   

   USA

   (508) 548-8700 x2290 (voice)

   (508) 457-2310 (FAX)

   sdalyander@usgs.gov
2. What's the catalog number I need to order this data set? Tidal_mobility_TT.shp: ratio of combined wave- and current-induced shear stress for hourly time-step TT in a time-series of mobility over a tidal cycle to critical stress for sediment and various size SRBs (see SRB_classes.txt). NOTE: Specific layer name indicates the time-step (TT) for the layer.
3. What legal disclaimers am I supposed to read?

   Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials.
   Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

4. How can I download or order the data?
   • Availability in digital form:

     Data format:	WinZip archive file containing the shapefile components. The WinZip file also includes FGDC compliant metadata. in format SHP (version 3.3) ESRI shapefile Size: 150
     Network links:	https://pubs.usgs.gov/of/2012/1234/datafiles.html

   • Cost to order the data: None

5. What hardware or software do I need in order to use the data set?

   These data are available in Environmental Systems Research Institute (ESRI) shapefile format. The user must have ArcGIS or ArcView 3.0 or greater software to read and process the data file. In lieu of ArcView or ArcGIS, the user may utilize another GIS application package capable of importing the data. A free data viewer, ArcExplorer, capable of displaying the data is available from ESRI at www.esri.com.

Who wrote the metadata?

Dates:

Last modified: 13-Oct-2020

Metadata author:

U.S. Geological Survey

Attn: P. Soupy Dalyander

Oceanographer

384 Woods Hole Role

Woods Hole, MA

USA

(508) 548-8700 x2290 (voice)

(508) 457-2310 (FAX)

sdalyander@usgs.gov

Metadata standard:

Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)