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

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

Transcript

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)
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
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!