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Sediment Dynamics of a tidal sand bank: Middle Ground, Massachusetts

Cdbcc920e73869b6436479419b3a1841?s=47 Rich Signell
November 07, 2007

Sediment Dynamics of a tidal sand bank: Middle Ground, Massachusetts

Presentation at the 10th Estuarine and Coastal Modeling Conference, Newport, RI, Nov 7, 2007

Cdbcc920e73869b6436479419b3a1841?s=128

Rich Signell

November 07, 2007
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  1. Sediment dynamics of a tidal sand bank: Middle Ground, Massachusetts

    Rich Signell, Erin Twomey, Bill Danforth, Chuck Worley, Barry Irwin, USGS Al Plueddemann, Tess Brandon, Amy Kukula, Dick Limeburner, Rocky Geyer WHOI Garret Duffy, Geological Survey of Canada ECM10, Newport, RI, Nov 7, 2007
  2. Woods Hole Regional Bathymetry Woods Hole Middle Ground shoal 35

    m
  3. Vineyard Sound 1-sec bathy grid 35 m 25 m Middle

    Ground is a 20 m high pile of coarse sand sitting on a gravel bed in 1.5 m/s tidal flows
  4. Ikonos Image (5 m resolution) 5-June-2001 15:36 UTC Near end

    of Flood Current 1 km Middle Ground Shoal
  5. Tidal Rectification on a Sand Ridge From I.S.Robinson, 1983, “Tidally

    Induced Residual Flows”, Chapter 7, Physical Oceanography of Shelf Seas, Elsevier Not like Georges Bank!
  6. L~100 m, h~3 m, H=20 m L~50-100 m, h~2-4 m,

    H=17 m 800 m
  7. September 27, 2006, DN=-96 500 m

  8. November 7, 2006, DN=-55 500 m

  9. Average Sand Dune Migration Rate (m/month) and Sand transport based

    on Migration Rate (kg/m/s) Sep 27, 2006 – Aug 23, 2007 6.7 (.0068) 10.4 (.0053) 8.8 (.0068) 8.4 (.0043) 5.4 (.0056)
  10. Sand bedform types Rubin & McCullough (1980) (<= 5 cm

    amplitude) (up to 8 m high)
  11. Sand wave height Rubin & McCulloch (1980)

  12. Community Sediment Transport Modeling Project John Warner’s 2006 AGU Poster

  13. Grid spacing 60-250 m

  14. ADCIRC Vdatum M2 Current (Yang & Myers, NOAA)

  15. None
  16. None
  17. None
  18. … and vorticity

  19. M2 Maj (m/s) Pha (deg) ROMS A 1.09 25.6 DATA

    A 1.12 26.8 ROMS B 1.10 17.9 DATA B 0.98 18.7 A B
  20. Transport rates from Meyer-Peter Mueller bedload are 10 times more

    than the rate calculated by sand wave migration Next steps: exploring connection between patterns in modeled bedload transport vs. observed sandwave migration
  21. Sandwave migration by cross-correlation technique Duffy & Hughes-Clark JGR, 2005

  22. Net Deposition/Erosion

  23. Change in Bed Thickness after 500 days SAND_MORPH_FAC=100

  24. None
  25. Sandwave01 100x30x3 cells SAND_MORPH_FAC=100 m m

  26. Future work • Map entire Middle Ground to obtain high

    resolution bathymetry for modeling, collect sediment samples • Develop approach for strong depth gradients in morphological simulations • Explore long term evolution of shoal • Explore parameterization of sand wave roughness • Run sand wave resolving nest
  27. Conclusions • The ROMS-based CSTM model successfully produced a counterclockwise

    tidal residual circulation around the bank, consistent with sand wave migration and moored observations • Results shows convergence of sand on the bank, providing a maintenance mechanism • With a highly resolved grid (e.g. 3 m) the model can build equilibrium sand waves • The Woods Hole region is a good test bed for the sediment transport modeling!