2013 Alabama Water Resources Conference | Coastal Issues
Hydrodynamic Timescales of Mobile Bay, Alabama and their
Spatial Variability
Alabama Water Resources Conference
Bret M. Webb, Ph.D.Chris Marr
University of South Alabama, Department of Civil Engineering
Bret M. Webb, Ph.D.Department of Civil [email protected]
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Acknowledgments
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.
Thanks to…
Chris Marr (USA MSCE)Dr. Kevin White (USA)Dr. Kyeong Park (DISL)
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• Background & Study Area• Terminology• Methods & Experiments• Simulation Results• Conclusions• Recommendations
Overview
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• 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)
Background & Study Area
Study Area
Previous Work
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Terminology
Residence Time
Exposure Time
Flushing Time
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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.
Existing Methods
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Hydrodynamic Modeling Approach
ADCIRC (2DDI)• Tides• River Discharge• Wind and Pressure
LPTM• ADCIRC Velocity Output• Random Walk• +33,000 Particles• Initial Particles Only
Methods & Experiments
Results
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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
Methods & Experiments
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Methods & Experiments
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Model ValidationWater Levels (95% CI)1. Dauphin Island2. Cedar Point3. Mobile State Docks4. Meaher State Park5. Weeks Bay6. Bon Secour Bay
Tidal Currents (90% CI)7. Mobile State Docks8. Container Terminal9. Farewell Buoy M
Methods & Experiments
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General Results
Average System Response Particle Concentration Curves
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Predictive Equations - System
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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
Spatial Variability – Residence Time
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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
Spatial Variability – Residence Time
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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
Spatial Variability – Residence Time
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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
Spatial Variability – Residence Time
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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
Spatial Variability – Residence Time
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With Local Winds Without Local Winds
Spatial Variability – Residence Time
Q = 637 m3 s-1
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Synthesis – Synoptic Flushing Map
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• Flow Variability• Spatial Variability• Effects of Local
Winds• Predictive
Equations
• Management Tool• Habitat
Restoration• Prioritizing Needs• Emergency
Response
Concluding Remarks
Recommended Applications
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Questions…For more information about the results of this study, please contact Dr. Bret Webb: [email protected]
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General Results
