«SECONDARY CIRCULATION IN A SINUOUS COASTAL PLAIN ESTUARY A Dissertation Presented to The Academic Faculty By Susan Anne Elston In Partial Fulfillment ...»
SECONDARY CIRCULATION IN A SINUOUS COASTAL PLAIN ESTUARY
The Academic Faculty
Susan Anne Elston
In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy in Earth and Atmospheric Sciences
Georgia Institute of Technology
Copyright © 2005 by Susan Anne Elston
SECONDARY CIRCULATION IN A SINUOUS COASTAL PLAIN ESTUARY
Dr. Jackson O. Blanton, Advisor Dr. Judith A. Curry Skidaway Institute of Oceanography School of Earth & Atmospheric Sciences University System of Georgia Georgia Institute of Technology Dr. Derek M. Cunnold Dr. Harvey E. Seim School of Earth & Atmospheric Sciences Department of Marine Sciences Georgia Institute of Technology University of North Carolina – Chapel Hill Dr. Donald R. Webster Dr. Peter J. Webster Civil and Environmental Engineering School of Earth & Atmospheric Sciences Georgia Institute of Technology Georgia Institute of Technology Dr. Kuo C. Wong College of Marine Studies Date Approved: February 18, 2005 University of Delaware All things by immortal power Near or far, hiddenly To each other linked are That thou canst not stir a flower Without troubling of a star Francis Thompson, ‘The Mistress of Vision’ This work is dedicated to the memories of all those who have gone before, wonderful teachers, inspiring mentors, dear family and friends, that I have had the honor to know.
You give my achievements meaning and purpose.
ACKNOWLEDGMENTSI would like to thank several people who made indispensable contributions to this dissertation. I am particularly indebted to my thesis advisor, Dr. Jackson Blanton, and to my committee members, Drs. Judy Curry, Harvey Seim, Derek Cunnold, Donald Webster, Peter Webster, and Kuo Wong, for their patience, guidance, support, and expert suggestions. I would like to thank Julie Amft, Guoqing Lin, Trent Moore, Cheryl Burden Ross, Mike Sharman, Joanna Garcia-Webb, and Kim Hunter for their camaraderie along with their valuable discussions and help in collecting, processing, and analyzing the data.
The able crew (Captain Jay Fripp, Raymond Sweate, Michael Richter, and Dana Ross) of the R/V BLUE FIN and R/V GANNET of the Skidaway Institute of Oceanography kept our research group well-fed and gave us dedicated enthusiasm and support in the carrying out of the numerous field experiments conducted for this research.
Special thanks go to Professors John Simpson and Francis Bretherton, Drs. Arnaldo Valle-Levinson, Robert Chant, Carol Janzen, M. Carla Curran, Tom Rippeth, and Henk Schuttelaars for giving me precious hours in discussion and encouragement. Editorial suggestions greatly improving this work go to my father and Lynette Love. Anna Boyette kindly assisted in preparing the graphical material.
I gratefully acknowledge the financial support of the Land Margin Ecosystems Research Program of the National Science Foundation (Grant No. DEB 9412089) to the University of Georgia, the State of Georgia through its Coastal Zone Management Program, a Presidential Fellowship from the Georgia Institute of Technology, a Rhodes Fellowship from the Department of Earth and Atmospheric Sciences at the
supplementary funding and hosting me during my tenure as a graduate student.
Final thanks go to my dear friends and families: the Buchdas, the Elstons, the Grahams, the Petersons, the Sinnetts, and the Woods, and to my wonderful husband Patrick N. Graham for their unending patience, encouragement, assistance, support, and love as I pursue this endeavor.
LIST OF TABLES
LIST OF FIGURES
1.1 The Importance of Secondary Circulation to Estuarine Dynamics
1.2 Lateral Mixing
1.3 Dissertation Research Questions
2. SATILLA RIVER, GEORGIA
2.1 Discharge Conditions
2.2 Salinity Variations
2.2.1 Tidal Variations in Salinity
2.2.2 Fortnightly Variations in Salinity
2.2.3 Seasonal Variations in Salinity
3. SECONDARY CIRCULATION
3.1 Mechanisms that Generate Secondary Circulation
3.2 Mixing and Flow Scaling Parameters
3.3 Analytical Models of Secondary Circulation
3.3.1 Scale Estimates of Secondary Circulation
3.3.2 Coefficient Adjustments to Scaling Formulas for Secondary Circulation....... 35 3.3.3 Seim and Gregg Curvature-Induced Overturning Model
3.3.4 Lateral Momentum Balance in Natural Coordinates
3.3.5 Lateral Momentum Balance Model for the Satilla River, Georgia.................. 40
4. MATERIALS AND METHODS
4.1.1 Acoustic Doppler Current Profilers
4.1.2 Conductivity-Temperature-Depth Sensors
4.1.3 Surface Thermosalinograph
4.2 Methods of Deployment
4.2.1 Long Term Mooring Deployments
4.2.2 Bi-monthly Synoptic Surveys
4.2.3 Seasonal Mooring Deployments
4.2.4 Anchor Stations
4.2.5 Rapid Spatial Survey System
4.3 Methods of Data Processing
4.3.1 Acoustic Doppler Current Profilers
4.3.2 Conductivity-Temperature-Depth Sensors
4.3.3 Surface Thermosalinograph
5. FORTNIGHTLY SIGNAL OF SECONDARY CIRCULATION AT A BEND........ 64
5.2 Materials and Methods
5.2.1 Experiment Site and Environmental Conditions
5.2.2 Seasonal Mooring Deployment – Spring 1997
5.3 Results and Discussion
5.3.1 Salinity and Velocity Distributions
5.3.2 Internal Froude Number Calculations
5.3.3 Seim and Gregg Curvature-Induced Overturning Model
6. COMPARISON OF SECONDARY CIRCULATION IN FOUR REACHES............ 96
6.2 Materials and Methods
6.2.1 Experiment Site and Environmental Conditions
6.2.2 Seasonal Mooring Deployments – Spring 1997 and Fall 1999
6.3 Results and Discussion
6.3.1 Tidal and Subtidal Salinity Distributions
6.3.2 Tidal Velocity Distributions
6.3.3 Subtidal Velocity Distributions
6.3.4 The Effect of River Discharge on Secondary Circulation
6.3.5 Seim and Gregg Curvature-Induced Overturning Model
6.3.6 Scale Estimates of Secondary Circulation
6.3.7 Lateral Momentum Balance Model for the Satilla River, Georgia................ 141 6.3.8 Lateral Momentum Balance Model Sensitivity Analyses and Limitations... 154
7. SECONDARY CIRCULATION SIGNATURE IN SPACE AT TWO BENDS...... 165 7.1 Introduction
7.2 Materials and Methods
7.2.1 Experiment Site and Environmental Conditions
7.2.2 Rapid Spatial Survey System – Spring 1999
7.2.3 Reduction of ADCP data to Mean Lower Low Water
7.2.4 Idealized Channel Cross-Sections and Principle Axis Determination........... 185
7.3 Results and Discussion
7.3.1 Spring and Neap Tide Salinity Distributions
126.96.36.199 Spring Tide – Maximum Ebb
188.8.131.52 Neap Tide – Maximum Ebb
7.3.2 Spring and Neap Tide Velocity Distributions
184.108.40.206 Spring Tide – Maximum Ebb
220.127.116.11 Neap Tide – Maximum Ebb
7.3.3. Secondary Circulation and the Axial Transfer of Momentum
7.3.4. Spatial Characteristics of Secondary Circulation
7.3.5 Lateral Momentum Balance Model for the Satilla River, Georgia................ 219 18.104.22.168 Spring Tide – Maximum Ebb
22.214.171.124 Spring Tide – Maximum Flood
126.96.36.199 Neap Tide – Maximum Ebb
188.8.131.52 Neap Tide – Maximum Flood
7.3.6 Lateral Momentum Balance Model Sensitivity Analyses and Limitations... 232
8. FINAL SUMMARY AND CONCLUSIONS
9. RECOMMENDATIONS AND FUTURE RESEARCH
APPENDIX A: EQUATIONS
APPENDIX B: DEFINITIONS
Table 3.1: Scale estimates for the Satilla River, Georgia.
Table 3.2: Recent estuarine experiments using the lateral momentum balance.
An X is used to indicate which terms the authors used in their formation of a lateral momentum balance. Italics indicate the lateral momentum balances investigated in this study
Table 5.1: LMER 4 mooring deployment locations.
Table 5.2: Broad Band ADCP setup specifications for the LMER 4 experiment.
............70 Table 6.1: LMER 4 mooring deployment locations.
Table 6.2: Broad Band ADCP setup specifications for the LMER 4 experiment.
..........106 Table 6.3: SAT 2 mooring deployment locations
Table 6.4: Work Horse ADCP setup specifications for the SAT 2 experiment.
.............110 Table 6.5: Summary table of river discharge contributions, minimum halting vertical density difference, and tidal straining (SIPS) conditions for the LMER 4 and SAT 2 experiments.
Table 6.6: Summary table for the overturning model results and the analytical scale formulas for LMER 4 and SAT 2 data
Table 6.7: Summary of calculated values and 95% confidence intervals for the lateral momentum balance model applied to the LMER 4 and SAT 2 mooring data.
The bold highlighted values indicate the balance of terms for a given choice of CD.
Table 7.1: SAT 1 mooring deployment locations
Table 7.2: SAT 1 Roving transect locations.
Table 7.3: Broad Band ADCP setup specifications for the SAT 1 experiment.
..............179 x Table 7.4: The buoyancy frequency, the total axial transport per unit area, the total lateral transport per unit area, and the total axial momentum for the lateral cross-sections: Domain A 4/5 – Domain B 10/11. To assess acceleration and deceleration into and out of the channel bends, read down the table from A 4/5 – B 10/11 for flood tide and read up the table from B 10/11 – A 4/5 for ebb tide.
Table 7.5: The spatial and temporal characteristics of secondary circulation during spring and neap tides
Table 7.6: Calculated values and 95% confidence intervals for the LMBM at the lateral sections: Domain A 4/5 – Domain B 10/11.
Figure 2.1: An aerial photograph of the Satilla River in southeast Georgia
Figure 2.2: A photograph of Sara’s Creek in the upper Satilla River taken by S.
Figure 2.3: U.
S. Geological Survey historical daily mean discharge data for the Satilla River at the Atkinson, Georgia, gauging station
Figure 2.4: (a) The Satilla River discharge during the 1997 LMER 4 experiment.
(b) The Satilla River discharge during the 1999 SAT 1 and SAT 2 experiments.
Gray boxes denote the period of mooring deployments for each experiment.......13 Figure 2.5: (a) The Satilla River discharge during the SAT 1 and SAT 2 experiments.
(b) The subtidal salinity measured at the moorings 3 – 7 (red, green, cyan, blue, and magenta lines, respectively) in the Satilla River during the 1999 SAT 1 and SAT 2 experiments. The black line represents the salinity field measured at the near ocean long-term mooring. Gray boxes denote the period of mooring deployments for each experiment.
Figure 2.6: (a) Synoptic survey of high water salinity in the Satilla River under moderate discharge conditions (February 1999).
(b) Synoptic survey of high water salinity in the Satilla River under low discharge conditions (December 1999).................21 Figure 3.1: Photograph of a convergent axial foam front in the Satilla River, Georgia.
This type of convergent front indicates the presence of a local secondary circulation. The photograph was taken by S. Elston at anchor during the 1997 LMER 4 experiment.
Figure 3.2: An illustration in the change of direction for the Coriolis force and the centrifugal force as a function of tidal direction (ebb or flow)
Figure 4.1: A photograph of the Skidaway Broad Band ADCP in tow off the starboard side of the R/V Gannet
Figure 4.2: A photograph of a Skidaway Work Horse ADCP.
A SeaCAT CTD is attached on the upper left leg of the mooring frame.
Figure 4.3: A photograph of a Skidaway MicroCAT CTD prior to deployment.
.............49 Figure 4.4: A photograph of the Skidaway SBE 19 profiling CTD on the starboard deck of the R/V Blue Fin
Figure 4.6: A photograph of a Skidaway MicroCAT CTD after a month-long late summer deployment.
Rapid bio-fouling occurs when the ambient water temperature exceeds 25°C
Figure 4.7: Map of Satilla River mooring deployment sites for the SAT 1 and SAT 2 experiments.
The LMER 4 mooring was approximately 1 km on either side of SAT mooring number 3.
Figure 4.8: A schematic of the SAT 1 and SAT 2 mooring deployments.
Note that the figure is not to scale.
Figure 4.9: A schematic of the rapid spatial survey system aboard the R/V Gannet.
.......59 Figure 5.1: Photograph of a local secondary circulation during late flood tide in the Satilla River. Water on the near side of the front (toward the outside of the channel bend) is about 1 PSU less than water on the far side of the front (toward the inside of the channel bend). The photograph was taken by S. Elston during the LMER 4 experiment.
Figure 5.2: Map of the Satilla River in southeast Georgia near the Florida border.