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Hydrodynamic Timescales of Mobile Bay, Alabama and their Spatial Variability

Alabama Water Resources Conference. Hydrodynamic Timescales of Mobile Bay, Alabama and their Spatial Variability. Bret M. Webb, Ph.D. Chris Marr. Bret M. Webb, Ph.D. Department o f Civil Engineering bwebb@southalabama.edu. University of South Alabama, Department of Civil Engineering.

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Hydrodynamic Timescales of Mobile Bay, Alabama and their Spatial Variability

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  1. Alabama Water Resources Conference Hydrodynamic Timescales of Mobile Bay, Alabama and their Spatial Variability Bret M. Webb, Ph.D. Chris Marr Bret M. Webb, Ph.D. Department of Civil Engineering bwebb@southalabama.edu University of South Alabama, Department of Civil Engineering

  2. Thanks to… Acknowledgments Chris Marr (USA MSCE) Dr. Kevin White (USA) Dr. Kyeong Park (DISL) A portion of this research was made possible by a grant from BP Gulf of Mexico Research Initiative, with assistance from the Dauphin Island Sea Lab, and in part by a grant of high performance computing resources and technical support from the Alabama Supercomputer Authority.

  3. Overview • Background & Study Area • Terminology • Methods & Experiments • Simulation Results • Conclusions • Recommendations

  4. Background & Study Area • Micro-tidal • 4th largest discharge • 95% of flows from AL and Tombigbee rivers • Austin (1954) • Schroeder (1978) • Wiseman (1988) • NOAA (1989) • Pennock et al. (1994) Study Area Previous Work

  5. Terminology Residence Time Exposure Time Flushing Time

  6. Existing Methods Estimating Hydrodynamic Timescales • Tidal Prism • Freshwater Fraction • Steady-State Box Models • 1D/2D/3D Models • Tracer/Dye Studies • Drifter Studies Selected References Guo, Q., and Lordi, G.P. (2000). “Method for quantifying freshwater input and flushing time in estuaries.” Journal of Environmental Engineering, 126, 675-683. Hagy, J.D., Sanford, L.P., and Boynton, W.R. (2000). “Estimation of net physical transport and hydraulic residence times for a coastal plain estuary using box models.” Estuaries, 23(3), 328-340. Meyers, S.D., and Luther, M.E. (2008). “A Numerical Simulation of Residual Circulation in Tampa Bay. Part 2: Lagrangian Residence Time.” Estuaries and Coasts, 31, 815-827. Miller, R.L., and McPherson, B.F. (1991). “Estimating estuarine flushing and residence times in Charlotte Harbor, Florida, via salt balance and a box model.” Limnology and Oceanography, 36, 602-612. Sheldon, J.E., and Alber, M. (2006). “The Calculation of Estuarine Turnover Times Using Freshwater Fraction and Tidal Prism Models: A Critical Evaluation.” Estuaries and Coasts, 29(1), 133-146.

  7. Methods & Experiments Hydrodynamic Modeling Approach ADCIRC (2DDI) Tides River Discharge Wind and Pressure LPTM ADCIRC Velocity Output Random Walk +33,000 Particles Initial Particles Only Results

  8. Methods & Experiments Particle Animation Flood conditions Q = 6747 m3 s-1 Coloring by longitudinal initial position Black dashed line is the ship channel Thin black line is the shoreline

  9. Methods & Experiments

  10. Methods & Experiments Model Validation Water Levels (95% CI) Dauphin Island Cedar Point Mobile State Docks Meaher State Park Weeks Bay Bon Secour Bay Tidal Currents (90% CI) Mobile State Docks Container Terminal Farewell Buoy M

  11. General Results Average System Response Particle Concentration Curves

  12. Predictive Equations - System

  13. Spatial Variability – Residence Time Drought Conditions Average of yearly minimum flows for the periods 1960 – 2011 and 1975 – 2011. Q = 246 m3 s-1 ____________________________ 82.9 ± 40.5 days

  14. Spatial Variability – Residence Time Dry Season Flows Average of flows for the period June to November over 1960 – 2011 and 1975 – 2011. Q = 802 m3 s-1 ____________________________ 43.7 ± 19.5 days

  15. Spatial Variability – Residence Time Average Conditions Average of yearly mean flows for the periods 1960 – 2011 and 1975 – 2011. Q = 1715 m3 s-1 ____________________________ 19.5 ± 20.0 days

  16. Spatial Variability – Residence Time Wet Season Flows Average of flows for the period December to May over 1960 – 2011 and 1975 – 2011. Q = 2637 m3 s-1 ____________________________ 14.9 ± 19.1 days

  17. Spatial Variability – Residence Time Flood Conditions Average of yearly maximum flows for the periods 1960 – 2011 and 1975 – 2011. Q = 6747 m3 s-1 ____________________________ 8.5 ± 17.6 days

  18. Spatial Variability – Residence Time Q = 637 m3 s-1 Without Local Winds With Local Winds

  19. Synthesis – Synoptic Flushing Map

  20. Concluding Remarks • Flow Variability • Spatial Variability • Effects of Local Winds • Predictive Equations • Management Tool • Habitat Restoration • Prioritizing Needs • Emergency Response Recommended Applications

  21. Questions… For more information about the results of this study, please contact Dr. Bret Webb: bwebb@southalabama.edu

  22. General Results

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