<%BANNER%>

Fine Sediment Resuspension in Lake Apopka, Florida

Permanent Link: http://ufdc.ufl.edu/UFE0024787/00001

Material Information

Title: Fine Sediment Resuspension in Lake Apopka, Florida
Physical Description: 1 online resource (169 p.)
Language: english
Creator: So, Sangdon
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: bed, entrainment, fine, resuspension, settling
Civil and Coastal Engineering -- Dissertations, Academic -- UF
Genre: Coastal and Oceanographic Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Likely effects of changing water level on the wind-driven suspended fine sediment regime have been investigated for Lake Apopka in central Florida. In order to assess the spatial and temporal behaviors of the suspended sediment concentration (SSC), instruments were deployed at three stations in the lake between June 2007 and September 2008. Relying on the measured time-series of wind, waves, currents and SSC, an approximate analytic model for local resuspension has been developed. The model is based on the vertical sediment mass balance equation and relies on the assumption of short-term equilibrium between entraining and settling sediment fluxes. During the period of measurement the usual meteorological condition was one of low winds, with scattered events when SSC values recorded notable increases above the ambient level. This limitation must be borne in mind when assessing the significance of SSC predictions at wind speeds in excess of about 20 m/s. Following calibration and validation, the model is used to predict the effects of high winds and lower as well as higher than present water levels on SSC. The water column can be conveniently divided into a dilute suspension layer (DSL) at the top, a benthic suspension layer (BSL) in the middle and a benthic nepheloid layer (BNL) at the bottom. Particulate matter in these layers appears to be derived mainly from plankton, with mucopolysaccharide as the principle agent binding the particles in to macro-flocs. At the base of BNL a consolidated but soft bed occurs in which sediment was historically contributed by macrophytes. Resuspension amounts to entrainment and settling sediment mass fluxes involving BNL, which is the primary source and sink of particulate matter in BSL and DSL. Participation of the bed appears to be negligible most of the time. SSC increases with the combined wave-current bed shear stress. At the existing (during the 2007-2008 study) mean water depth (about 1.3 m at the SJRWMD platform) and the usual moderate wind speeds in the lake (where the mean speed is about 4 m/s and about 95% of time it is less than 7-8 m/s), the contribution from wave-induced stress to resuspension appears to be less than due to current, although not always negligible. The main driving force for SSC increase under moderate winds arises from wind-driven current associatedwater circulation. A 16 m/s sustained wind speed can be thought of as episodic in this lake. At that speed waves and circulation current contribute about equally to resuspension. At the lowest elevation of measurement, about 0.17 mab, an increase in the wind speed from 5 to 16 m/s increased SSC from about 0.06 to 2 kg/m3. At the highest selected episodic speed of 30 m/s, whose probability of occurrence is 0.052%, the predicted SSC value would be on the order of 13.8 kg/m3. Contribution to resuspension from waves would be 4-5 times that due to current. At the sites of data collection a critical wind speed occurred above which SSC increased with wind speed. The speed range, from 4 to 6.5 m/s, was narrow. Since the mean speed during the study was only about 4 m/s, it appears that the lake could be characteristically at the threshold of resuspension at the present depth. If so, it is conceivable that finer particles that may resuspend at lower (than 4 m/s) wind speeds are likely to have been winnowed out of the system via discharges from the Apopka-Beauclair canal. At the lowest water depth of 0.5 m considered, when part of the lake bottom would be exposed, the effect of waves would become more significant. Increase in wind speed from 5 to 16 m/s would change the ratio of wave to current shear stress from about 0.3 to 7. SSC would increase from about 0.09 to 17 kg/m3. In recognition of the substantial role of biotic factors in governing the properties and transport behavior of the suspended particles, the role of biopolymers on particle aggregation dynamics needs to be further quantified.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Sangdon So.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Mehta, Ashish J.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024787:00001

Permanent Link: http://ufdc.ufl.edu/UFE0024787/00001

Material Information

Title: Fine Sediment Resuspension in Lake Apopka, Florida
Physical Description: 1 online resource (169 p.)
Language: english
Creator: So, Sangdon
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: bed, entrainment, fine, resuspension, settling
Civil and Coastal Engineering -- Dissertations, Academic -- UF
Genre: Coastal and Oceanographic Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Likely effects of changing water level on the wind-driven suspended fine sediment regime have been investigated for Lake Apopka in central Florida. In order to assess the spatial and temporal behaviors of the suspended sediment concentration (SSC), instruments were deployed at three stations in the lake between June 2007 and September 2008. Relying on the measured time-series of wind, waves, currents and SSC, an approximate analytic model for local resuspension has been developed. The model is based on the vertical sediment mass balance equation and relies on the assumption of short-term equilibrium between entraining and settling sediment fluxes. During the period of measurement the usual meteorological condition was one of low winds, with scattered events when SSC values recorded notable increases above the ambient level. This limitation must be borne in mind when assessing the significance of SSC predictions at wind speeds in excess of about 20 m/s. Following calibration and validation, the model is used to predict the effects of high winds and lower as well as higher than present water levels on SSC. The water column can be conveniently divided into a dilute suspension layer (DSL) at the top, a benthic suspension layer (BSL) in the middle and a benthic nepheloid layer (BNL) at the bottom. Particulate matter in these layers appears to be derived mainly from plankton, with mucopolysaccharide as the principle agent binding the particles in to macro-flocs. At the base of BNL a consolidated but soft bed occurs in which sediment was historically contributed by macrophytes. Resuspension amounts to entrainment and settling sediment mass fluxes involving BNL, which is the primary source and sink of particulate matter in BSL and DSL. Participation of the bed appears to be negligible most of the time. SSC increases with the combined wave-current bed shear stress. At the existing (during the 2007-2008 study) mean water depth (about 1.3 m at the SJRWMD platform) and the usual moderate wind speeds in the lake (where the mean speed is about 4 m/s and about 95% of time it is less than 7-8 m/s), the contribution from wave-induced stress to resuspension appears to be less than due to current, although not always negligible. The main driving force for SSC increase under moderate winds arises from wind-driven current associatedwater circulation. A 16 m/s sustained wind speed can be thought of as episodic in this lake. At that speed waves and circulation current contribute about equally to resuspension. At the lowest elevation of measurement, about 0.17 mab, an increase in the wind speed from 5 to 16 m/s increased SSC from about 0.06 to 2 kg/m3. At the highest selected episodic speed of 30 m/s, whose probability of occurrence is 0.052%, the predicted SSC value would be on the order of 13.8 kg/m3. Contribution to resuspension from waves would be 4-5 times that due to current. At the sites of data collection a critical wind speed occurred above which SSC increased with wind speed. The speed range, from 4 to 6.5 m/s, was narrow. Since the mean speed during the study was only about 4 m/s, it appears that the lake could be characteristically at the threshold of resuspension at the present depth. If so, it is conceivable that finer particles that may resuspend at lower (than 4 m/s) wind speeds are likely to have been winnowed out of the system via discharges from the Apopka-Beauclair canal. At the lowest water depth of 0.5 m considered, when part of the lake bottom would be exposed, the effect of waves would become more significant. Increase in wind speed from 5 to 16 m/s would change the ratio of wave to current shear stress from about 0.3 to 7. SSC would increase from about 0.09 to 17 kg/m3. In recognition of the substantial role of biotic factors in governing the properties and transport behavior of the suspended particles, the role of biopolymers on particle aggregation dynamics needs to be further quantified.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Sangdon So.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Mehta, Ashish J.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024787:00001


This item has the following downloads:


Full Text

PAGE 1

1 FINE SEDIMENT RESUSP ENSION IN LAKE APOPKA, FLORID A By SANGDON SO A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSIT Y OF FLORIDA 2009

PAGE 2

2 2009 Sangdon So

PAGE 3

3 To my parents, wife Jin, daughter Kang and son Jungseob

PAGE 4

4 ACKNOWLEDGMENT I would like to express my deepest thanks to my advisor and supervisory committee chairman, Dr. Ashish J. Mehta, for his guidance and support throughout this study. Special thanks go to the other members of the committee including Dr. Arnoldo Valle -Levinson, Dr. John Jaeger and Dr. Mamta Jain. Thanks should also go to the sta ffs of the Coastal Engineering Laboratory, especially Vik Adams, Jimmy Joiner and Sidney Schofield for carrying out fieldwork in Lake Apopka. I wish to acknowledge the assistance provided by Coastal and Oceanographic Engineering Program students for their support and friendliness. I would like to thank my wife Jin, my daughter Kang, son Jungseob and my parents for their love and support. This research was supported by the St. Johns River Water Management District (Palatka, FL). I appreciate the assistance provided by Dr. Rolland Fulton for making available relevant and necessary data and publications.

PAGE 5

5 TABLE OF CONTENTS page ACKNOWLEDGMENT ...................................................................................................................... 4 TABLE OF CONTENT S ..................................................................................................................... 5 LIST OF TABLES ................................................................................................................................ 7 LIST OF FIGURES .............................................................................................................................. 8 LIST OF SYMBOLS .......................................................................................................................... 16 ABSTRACT ........................................................................................................................................ 19 CHAPTER 1 INTRODUCTION ....................................................................................................................... 22 1.1 Motivation and Objective ..................................................................................................... 22 1.2 Tasks ...................................................................................................................................... 23 2 STUDY SITE, FIELD INSTRUMENTATION AND LABORATORY TESTS ................... 24 2.1 Field Site ................................................................................................................................ 24 2.2 Field Instrumentation ............................................................................................................ 25 2.3 Laboratory Tests ................................................................................................................... 26 2.3.1 Scope ........................................................................................................................... 26 2.3.2 OBS Calibration ......................................................................................................... 26 2.3.3 ADCP Calibration ...................................................................................................... 28 2.3.4 Settling Velocity ......................................................................................................... 28 3 LAKE MEASUREMENTS ........................................................................................................ 40 3.1 Hydrodynamic Data .............................................................................................................. 40 3.2 Sediment Data ....................................................................................................................... 42 3.3 Data from Other Sources ...................................................................................................... 43 4 RESUSPENSION BEHAVIOR ................................................................................................. 54 4.1 Weekly Parametric Values ................................................................................................... 54 4.2 Spectral Analysis ................................................................................................................... 55 4.3 Interdependence among P arameters .................................................................................... 56 4.3.1 Wave Height and Wind Speed................................................................................... 56 4.3.2 Current and Wind Speed ............................................................................................ 57 4.3.3 SSC and Wind Speed ................................................................................................. 57 4.4 SSC Variation with Bed Shear Stress .................................................................................. 58

PAGE 6

6 4.4.1 Estimation of Wave, Current and Combined Wave Current Shear Stresses .......... 58 4.4.2 Estimation of Wave Height and Period..................................................................... 62 4.4.3 Estimation of Current Induced Shear St ress ............................................................. 64 4.5 Resuspension Dynamics ....................................................................................................... 66 4.5.1 Resuspension Modes .................................................................................................. 66 4.5.2 Concentration Profile ................................................................................................. 68 4.5.3 BNL Mixing................................................................................................................ 71 4.5.4 Model Calibration....................................................................................................... 73 4.5.5 Model Validation ........................................................................................................ 74 4.6 Effect of Water Level Change .............................................................................................. 74 5 S UMMARY AND CONCLUSION S ...................................................................................... 108 5.1 Summary.............................................................................................................................. 108 5.2 Conclusions ......................................................................................................................... 109 5.3 Recommendations for Further Work ................................................................................. 112 APPENDIX A SETTLING VELOCITY TESTS ............................................................................................. 113 B FIELD MEASUREMENTS ..................................................................................................... 115 C TABUL ATION OF LAKE MEASUREMENTS .................................................................... 139 LIST OF REFERENCES ................................................................................................................. 167 BIOGRAPHICAL SKETCH ........................................................................................................... 169

PAGE 7

7 LIST OF TABLES Table page 2 1 Instruments deployed in the lake ........................................................................................... 31 2 2 Deployments at UF0 .............................................................................................................. 31 2 3 Deployments at UF1 .............................................................................................................. 32 2 4 Deployment at UF2 ................................................................................................................ 32 4 1 Weeks corresponding to parametric values .......................................................................... 77 4 2 Weekly maximum, mean and minimum wind and waves at UF0 ...................................... 78 4 3 Weekly maximum, mean and minimum currents at different elevations at UF0 .............. 79 4 4 Weekly maximum, mean and minimum temperature, salinity and WSE at UF0 .............. 81 4 5 Weekly maximum, mean and minimum SSC fro m ADCP at different elev. at UF0 ........ 82 4 6 Weekly maximum, mean and minimum SSC from OBS at UF0 ........................................ 84 4 7 Critical wind speed for resu spension .................................................................................... 85 4 8 Coefficients a m n and I from F84, MS90 and HT91 ........................................................ 85 4 9 Cumulative density function of wind speed ......................................................................... 86 4 10 Bed shear stresses ( w, c and cw) for selected water depths and wind speeds ................... 87 4 11 SSC at 18.38 m elevation for the selected water depths and wind speeds ......................... 88 4 12 SSC at 18.88 m elevation for the selected water depths and wind speeds ......................... 89 C1 Weekly max, mean and min currents at different elevations at UF1. ............................... 139 C2 Weekly max, mean and min SSC from ADCP at UF1. ..................................................... 139 C3 Weekly max, mean and min SSC from OBS 3 at UF1. .................................................... 140 C4 Weekly max, mean and min currents at different elevations at UF2. ............................... 140 C5 Weekly max, mean and min SSC from ADCP at UF2. ..................................................... 140

PAGE 8

8 LIST OF FIGURES Figure page 2 1. State of Florida and general area of study. ................................................................................ 33 2 2. Central Florida lakes and waterways (Courtesy of SJRWMD). .............................................. 33 2 3. Lake Apopka and locations of stations UF0, UF1 and UF2. ................................................... 34 2 4. Lake Apopka bathymetry, locations of UF stations and underway transects. ........................ 34 2 5. UF0 station at SJRWMD meteorological tower. ...................................................................... 35 2 6. UF1 station. The same platform was later moved to UF2. ....................................................... 35 2 7. Schematic drawing of instrumentation at UF0. ......................................................................... 36 2 8. Schematic drawing of UF1/UF2 platform and instrumentation. .............................................. 36 2 9. OBS 3 calibration plot (SSC versus output voltage). ............................................................... 37 2 10. OBS 5+ calibration plot (SSC versus output voltage). ........................................................... 37 2 11. ADCP calibration plot (SSC versus output EIA). ................................................................... 38 2 12. Settling velocity variation with SSC (= C) for lake sediment for an initial suspension concentration of 0.91 kg/m3. The quantity wsf is the free settling velocity (below 0.1 kg/m3). The curve is based on Eq. (2.4). ............................................................................... 38 2 13. Simulated concentration profiles (lines) in and data (circles) in the settling column. Initial suspension concentration 0.91 kg/m3. ........................................................................ 39 2 14. Definition sketch of concentration profile. .............................................................................. 39 3 1. Current velocity time -series during Deployment 0 3. .............................................................. 45 3 2. Current ros e at 18.83 m elevation during Deployment 03. ..................................................... 45 3 3. Current rose at 18.63 m elevation during Deployment 03. ..................................................... 46 3 4. Current r ose at 18.33 m elevation during Deployment 03. ..................................................... 46 3 5. Salinity, temperature and water surface elevation time -series during Deployment 0 3. ........ 4 7 3 6. Water surface elevation and precipitation during Deployment 0 3. ........................................ 47

PAGE 9

9 3 7. Wave height and period time -series. A) During Deployment 0 3. B) For the date when the highest wav e height occurred. C) Wind speeds for the period same with that of B). ............................................................................................................................................ 48 3 8. Time -series of wind waves. A) During Deployment 0 3. B) A sample time -series of water level at 4 Hz frequency for 195 s. ............................................................................... 48 3 9. Current velocity distribution along Transect 1 (shown in Figure 2.3) on 11/01/07. .............. 49 3 10. Current vector data a long Transect 1 at the elevation of the top acoustic bin on 11/01/07. ................................................................................................................................. 49 3 11. Eastern and northern components of current along Transect 1 on 11/01/07. ........................ 50 3 12. SSC time -series from OBS 3 during Deployment 0 3. Gaps indicate data loss. Biofouling may have contributed to weak signals after 10/03/07. ............................................ 50 3 13. SSC time -s eries from ADCP during Deployment 03. ........................................................... 51 3 14. SSC time -series from OBS 5+ at 18.34 m elevation during Deployment 0 5. ..................... 51 3 15. SSC contours along Transect 1 on 11/01/07. .......................................................................... 52 3 16. Wind speed and direction during Deployment 0 3. ................................................................ 52 3 17. Windrose for Depl oyment 0 3. ............................................................................................... 53 4 1. Power spectral density (PSD) of all data for Deployment 0 3. For any parameter with 2 /Hz. .............................................................................. 90 4 2. PSD for wind waves. Pressure was measured in kPa. .............................................................. 91 4 3. Time -series of maximum PSD for water level. A) At the low -frequency (less than 0.5 Hz) range. B) At the high -frequency (greater than 0.5 Hz) range. ..................................... 91 4 4. Coherence between wind speed and wave height. .................................................................... 92 4 5. Variations of A) the significant wave height and B) the period with wind speed. Since the wave height a t 0 wind speed must be zero, data points corresponding to very low wind speeds (< 2 m/s) have not been included in linear regression. ................................... 92 4 6. Coherence between wind speed and current. ............................................................................ 93 4 7. Variation of current with wind speed during Deployment 0 3. A) At Elev. 18.83 m. B) At Elev. 18.63 m. C) At Elev. 18.33m. ................................................................................. 93 4 8 Variation of current with wind speed during Deployment 0 5. A) At Elev. 18.83 m. B) At Elev. 18.63 m. C) At Elev. 18.33 m. ................................................................................ 94

PAGE 10

10 4 9. Coherence between wind speed and SSC from OBS 3 at 18.66 m elevation. ........................ 94 4 10. Coherence between wind speed and SSC from the ADCP. ................................................... 95 4 11. Variation of SSC at 18.63 m elevation from ADCP with wind speed. ................................. 95 4 12. Variation of SSC at 18.33 m elevation from ADCP with wind speed. ................................. 96 4 13. Relationships between A) si gnificant wave height, B) period and wind speed; best -fit data line and equations. .......................................................................................................... 96 4 14. Schematic drawing of the relationship between wind stress and current stress in the lake. ......................................................................................................................................... 97 4 15. Measured variation of current speed with uc with wind speed U at station UF0. R2 values indicate weak correlations. ......................................................................................... 97 4 16. Cumulative distribution of the directional anomaly between wind speed and water current at two elevations. ....................................................................................................... 98 4 17. Schematic of sediment concentration zones and resuspension modes (adapted from J ain 2007). ............................................................................................................................... 98 4 18. An example of measured time -series of horizontal SSC gradient (kg/m4) in the lake. ........ 99 4 19. Measured vertica l gradient of concentration (kg/m4) at UF0. Positive gradient indicates higher concentration at the lower sensor (elevation 18.14 m) than at the upper sensor (18.54 m). ................................................................................................................................ 99 4 20. Measured verti cal gradient of concentration (kg/m4) at UF2. Positive gradient indicates higher concentration at the lower sensor (elevation 18.50 m) than at the upper sensor (19.20 m). .............................................................................................................................. 100 4 21. Schematic d rawing showing the variation of sediment concentration with depth in the lake. SSC refers to concentration above the elevation z = za. ............................................ 100 4 22. Settling velocity variation with SSC (= C) for lake sediment. Red asterisks are from the image analysis of Dr. Andrew Manning. Blue circles are from laboratory settling column tests (Chapter 3). The quantity wsf is the free settling velocity (below 0.1 kg/m3). ................................................................................................................................... 101 4 23. Sediment dry bulk density versus organic matter and biogenic silica sediment composition data for the LA 3108site. The dashed line represents the critical value used by Schelske (1997) to delineate the top floc layer (BNL) The site is shown in Figure 4.24 (courtesy Dr. John Jaeger). .............................................................................. 101 4 24. Google image of Lake Apopka showing the 1996 sampling sites occupied by Schelske (1997) and the locations of the four 2007 sampling areas (courtesy Dr. John Jaeger). ... 102

PAGE 11

11 4 25. Stress versus dry density (courtesy Dr. John Jaeger). .......................................................... 102 4 26. Profile of Beryllium 7 radioisotope at LA Tower 07a (courtesy Dr. John Jaeger). ........... 103 4 27. Cumulative distribution function plot for wind data collected from 01/22/02 to 11/06/08 at UF0 by SJRWMD. ........................................................................................... 103 4 28. Time -series of shear stresses during Deployment 05. ......................................................... 104 4 29. Variation of shear stresses with water depths between wind speeds of 2 and 30 m/s. A) Wave shear stress. B) Current shear stress. C) Combined wave -current shear stress. .... 104 4 30. Variation of Ds 0 with cwu Mean trend and select ed upper and lower bound lines. ........... 105 4 31. Measured and simulated time -series of SSC at 18.34 m elevation during Deployment 0 5. ........................................................................................................................................ 105 4 32. Time -series of SSC at 18.38 m elevation during Deployment 0 6. A) Comparison between measured and simulated SSC based on the best -fit mean relationship. B) Simulations based on the upper bound. C) Simulations based on the lower bound. ....... 106 4 33. Time -series of SSC at 18.88 m elevation during Deployment 0 6. A) Comparison between measured and simulated SSC based on the best -fit mean relationship. B) Simulations based on the upper bound. C) Simulations based on the lower bound. ....... 106 4 34. Simulated SSC variation with water depth at 18.38 m during Deployment 0 6. ................ 107 4 35. Simulated SSC variation with water depth at 18.88 m during Deployment 0 6. ................ 107 A 1. Settling velocity variation with SSC. Initial SSC ( C0) in the settling column was 1.95 kg/m3. .................................................................................................................................... 113 A 2. Simulation of concentration change in the settling column ( C0=1.95 kg/m3). ..................... 113 A 3. Settling velocity variation with SSC. In itial SSC ( C0) in the settling column was 2.88 kg/m3. .................................................................................................................................... 114 A 4. Simulation of concentration profile change in the settling column ( C0=2.88 kg/m3). ......... 114 B1. Current -rose at elev. 18.51 m during Deployment 0 2. ......................................................... 115 B2. Current -rose at elev. 18.31 m during Deployment 0 2. ......................................................... 115 B3. Current -rose at elev. 18.83 m during Deployment 0 3. ......................................................... 116 B4. Current -rose at elev. 18.63 m during Deployment 0 3. ......................................................... 116 B5. Current -rose at elev. 18.33 m during Deployment 0 3. ......................................................... 117

PAGE 12

12 B6. Current -rose at elev. 18.83 m during Deployment 0 4. ......................................................... 117 B7. Current -rose at elev. 18.63 m during Deployment 0 4. ......................................................... 118 B8. Current -rose at elev. 18.33 m during Deployment 0 4. ......................................................... 118 B9. Current -rose at elev. 18.83 m during Deployment 0 5. ......................................................... 119 B10. Current rose at elev. 18.63 m during Deployment 05. ....................................................... 119 B11. Current rose at elev. 18.33 m during Deployment 05. ....................................................... 120 B12. Current rose at elev. 18.88 m during Deployment 06. ....................................................... 120 B13. Current rose at elev. 18.68 m during Deployment 06. ....................................................... 121 B14. Current rose at elev. 18.38 m during Deployment 06. ....................................................... 121 B15. Current rose at elev. 18.43 m during Deployment 07. ....................................................... 122 B16. Current rose at elev. 18.33 m during Deployment 07. ....................................................... 122 B1 7. Current rose at elev. 18.83 m during Deployment 08. ....................................................... 123 B18. Current rose at elev. 18.63 m during Deployment 08. ....................................................... 123 B19. Current rose at elev. 18.33 m during Deployment 08. ....................................................... 124 B20. Current rose at elev. 18.31 m during Deployment 09. ....................................................... 124 B21. C urrent rose at elev. 18.11 m during Deployment 09. ....................................................... 125 B22. Current rose at elev. 18.54 m during Deployment 010. ..................................................... 125 B23. Current rose at elev. 18.34 m during Deployment 010. ..................................................... 126 B24. Current rose at elev. 18.14 m during Deployment 010. ..................................................... 126 B25. Current rose at elev. 19.01 m during Deployment 11. ....................................................... 127 B26. Current rose at elev. 18.61 m during Deployment 11. ....................................................... 127 B27. Curr ent rose at elev. 18.31 m during Deployment 11. ....................................................... 128 B28. Current rose at elev. 18.31 m during Deployment 12. ....................................................... 128 B29. Curren t rose at elev. 19.20 m during Deployment 21. ....................................................... 129 B30. Current rose at elev. 18.70 m during Deployment 21. ....................................................... 129

PAGE 13

13 B31. Current rose at elev. 18.50 m during Deployment 21. ....................................................... 130 B32. Time -series of WSE at UF0 and precipitation. .................................................................... 130 B33. Time -series of WSE at UF1 and precipitation. .................................................................... 131 B34. Time -series of WSE at UF2 and precipitation. .................................................................... 131 B35. Wind-rose during Deployment 0 1. ...................................................................................... 132 B36. Wind-rose during Deployment 0 2. ...................................................................................... 132 B37. Wind-rose during Deployment 0 3. ...................................................................................... 133 B38. Wind-rose during Deployment 0 4. ...................................................................................... 133 B39. Wind-rose during Deployment 0 5. ...................................................................................... 134 B40. Wind-rose dur ing Deployment 0 6. ...................................................................................... 134 B41. Wind-rose during Deployment 0 7. ...................................................................................... 135 B42. Wind-rose during Deployment 0 8. ...................................................................................... 135 B43. Wind-rose during Deployment 0 9. ...................................................................................... 136 B44. Wind-rose during Deployment 0 10. .................................................................................... 136 B45. Wind-rose during Deployment 1 1. ...................................................................................... 1 37 B46. Wind-rose during Deployment 1 2. ...................................................................................... 137 B47. Wind-rose during Deployment 2 1 ...................................................................................... 138 C1. Measurements (left) and power spectral densities for Deployment 01. .............................. 141 C2. Measurements (left) and power spectral densities for Deployment 02. .............................. 142 C3. Measurements (left) and power spectral densities for Deployment 04. .............................. 143 C4. Measurement s (left) and power spectral densities for Deployment 05. .............................. 144 C5. Measurements (left) and power spectral densities for Deployment 06. .............................. 145 C6. Measurements (left) and power spectral densities for Deployment 07. .............................. 146 C7. Measurements (left) and power spectral densities for Deployment 08. .............................. 147 C8. Measurements (left) and power spectral densities for Deployment 09. .............................. 148

PAGE 14

14 C9. Measurements (left) and power spectral densities for Deployment 010. ............................ 149 C10. Measurements (left) and power spectral densities for Deployment 1 1. ............................ 150 C11. Measurements (left) and power spectral densities for Deployment 1 2. ............................ 151 C12. Measurements (left) and power spectral densities for Deployment 2 1. ............................ 152 C13. Variatio ns of wave height and period with wind speed for Deployment 04. .................... 153 C14. Variations of wave height and period with wind speed for Deployment 05. .................... 153 C15. Variations of wave height and period with wind speed for Deployment 06. .................... 154 C16. Variations of wave height and period with wind speed for Deployment 07. .................... 154 C17. Variations of wave height and period with wind speed for Deployment 08. .................... 155 C18. Variations of wave height and period with wind speed for Deployment 09. .................... 155 C19. Variations of wave height and period with wind speed for Deployment 010. .................. 156 C20. Va riations of current at three elevations with wind speed for Deployment 0 5. ................ 156 C21. Variations of current at three elevations with wind speed for Deployment 0 8. ................ 157 C22. Variations of current at three elevations with wind speed for Deployment 0 10. .............. 157 C23. Variations of current at three elevations with wind speed for Deployment 1 1. ................ 158 C24. Variations of current at three elevations with wind speed for Deployment 2 1. ................ 158 C25. SSC again st wind speed at 18.51 m from Deployment 0 1. ................................................ 159 C26. SSC against wind speed at 18.51 m from Deployment 0 2. ................................................ 159 C27. SSC aga inst wind speed at 18.63 m from Deployment 0 3. ................................................ 160 C28. SSC against wind speed at 18.33 m from Deployment 0 3. ................................................ 160 C29. SSC a gainst wind speed at 18.83 m from Deployment 0 4. ................................................ 161 C30. SSC against wind speed at 18.63 m from Deployment 0 4. ................................................ 161 C31. SSC against wind speed at 18.33 m from Deployment 0 4. ................................................ 162 C32. SSC against wind speed at 18.34 m from Deployment 0 5. ................................................ 162 C33. S SC against wind speed at 18.83 m from Deployment 0 8. ................................................ 163

PAGE 15

15 C34. SSC against wind speed at 18.63 m from Deployment 0 8. ................................................ 163 C35. SSC against wind speed at 18.54 m from Deployment 0 10. .............................................. 164 C36. SSC against wind speed at 19.01 m from Deployment 1 1. ................................................ 164 C37. SSC against wind speed at 18.61 m from Deployment 1 1. ................................................ 165 C38. SSC against wind speed at 18.31 m from Deployment 1 1. ................................................ 165 C39. SSC against wind speed at 18.50 m from Deployment 2 1. ................................................ 166

PAGE 16

16 LIST OF SYMBOL S ADCP Acoustic Doppler Current Profiler abc Calibration coefficient s Calibration coefficient C Suspended sediment concentration C0 Initial concentration CD Drag coefficient Non -dimensional wind fetch C1 Free -settling concentration Ca Concentrations at elevation za Cm Uniform concentration due to co mplete mixing CUF 0 Concentration at the station UF0 CUF 2 Concentration at the station UF0 CTD Conductivity Temperature -Depth b Calibration coefficient d50 50 percent volume cumulative particle diameter Dsz Diffusion coeffici ent Ds 0 Diffusion coefficient of depth -mean Non -dimensional water depth E Total wave energy or variance of the wave record EIA echo intensity anomaly of ADCP Non -dimensional wave energy pf Frequency of spectral peak wf Wave friction factor

PAGE 17

17 g Gravitational acceleration H Wave height sH Si g nificant wave height h Water depth k Wave number sk Nikuradse roughness L Wave lengh L02 Distance between the station UF0 and UF2 NAVD88 North American Vertical Datum of 1988 Nc Counts of near -detector of OBS 5+ Non -dimensional wave frequency OBS Optical Backscatter Sen sor Angle between the current stress vector and the wave stress vector PSD Power spectral density w Water densities a Air density S Wind induce d water level setup S Spatial gradient of setup S Wave angular frequency SSC Suspended sediment concentration T Wave period Shear stress c Current induced bed shear stress

PAGE 18

18 cw Combined wave current bed shear stress w Wave induced bed shear stress wind Wind shear stress y Yield stress U Wind sp eed UH High wind speed limit UL Low wind speed limit bu Bottom orbital velocity amplitude uc Depth -mean current velocity cwu Critical friction velocity for resuspension V voltage output from data logge r ws Settling velocity wsf Free -settling velocity ws 0 Characteristic value of settling velocity za Elevation of dividing line between BSL and BNL zb Top elevation of bottom cores 0z Bottom roughness height

PAGE 19

19 Abstract of Thes is Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science FINE SEDIMENT RESUSPENSION IN LAKE APOPKA, FLORIDA By Sangdon So August 2009 Chair: Ashish J. Mehta Major: Coastal and Oceanographic Engineering Likely effects of changing water level on the wind-driven suspended fine sediment regime have been investigated for Lake Apopka in central Florida. In order to assess the spatial and temporal behaviors o f the suspended sediment concentration (SSC), instruments were deployed at three stations in the lake between June 2007 and September 2008. Relying on the measured time -series of wind, waves, currents and SSC, an approximate analytic model for local resusp ension has been developed. The model is based on the vertical sediment mass balance equation and relies on the assumption of short term equilibrium between entraining and settling sediment fluxes. During the period of measurement the usual meteorological c ondition was one of low winds, with scattered events when SSC values recorded notable increases above the ambient level. This limitation must be borne in mind when assessing the significance of SSC predictions at wind speeds in excess of about 20 m/s. Foll owing calibration and validation, the model is used to predict the effects of high winds and lower as well as higher than present water levels on SSC. The water column can be conveniently divided into a dilute suspension layer (DSL ) at the top a benthic s uspension layer (BSL) in the middle and a benthic nepheloid layer (BNL) at the bottom Particulate matter in these layers appears to be derived mainly from plankton, with

PAGE 20

20 mucopolysaccharide as the principle agent binding the particles in to macro-flocs. At the base of BNL a consolidat ed but soft bed occurs in which sediment was historically contributed by macrophytes Resuspension amounts to entrainment and settling sediment mass fluxes involving BNL, which is the primary source and sink of particulate mat ter in BSL and DSL. Participation of the bed appears to be negligible most of the time. SSC increases with the combined wave -current bed shear stress. At the existing (during the 20072008 study) mean water depth (about 1.3 m at the SJRWMD platform) and th e usual moderate wind speeds in the lake (where the mean speed is about 4 m/s and about 95% of time it is less than 7 8 m/s ), the contribution from wave -induced stress to resuspension appears to be less than due to current, although not always negligible The main driving force for SSC increase under moderate winds arises from wind -driven current associated water circulation. A 16 m/s sustained wind speed can be thought of as episodic in this lake. At that speed waves and circulation current contribute about equally to resuspension. At the lowest elevation of measurement, about 0.17 mab, an increase in the wind speed from 5 to 16 m/s increased SSC from about 0.06 to 2 kg/m3. At the highest selected episodic speed of 30 m/s, whose probability of occurrence is 0. 052%, the predicted SSC value would be on the order of 13.8 kg/m3. Contribution to resuspension from waves would be 45 times that due to current. At the sites of data collection a critical wind speed occurred above which SSC increased with wind speed. The speed range, from 4 to 6.5 m/s, was narrow. Since the mean speed during the study was only about 4 m/s, it appears that the lake could be characteristically at the threshold of resuspension at the present depth. If so, it is conceivable that finer part icles that may resuspend at lower (than 4 m/s) wind speeds are likely to have been winnowed out of the system via discharges from the Apopka Beauclair canal.

PAGE 21

21 At the lowest water depth of 0.5 m considered, when part of the lake bottom would be exposed, the effect of waves would become more significant. Increase in wind speed from 5 to 16 m/s would change the ratio of wave to current shear stress from about 0.3 to 7. SSC would increase from about 0.09 to 17 kg/m3. In recognition of the substantial role of bi otic factors in governing the properties and transport behavior of the suspended particles, the role of biopolymers on particle aggregation dynamics needs to be further quantified.

PAGE 22

22 CHAPTER 1 INTRODUCTION 1.1 Motivation and Objective Resuspension of fine sediments in shallow aquatic systems characteristically depends on wind driven fluid motion at the bottom and on the local sediment properties (Hkanson and Jansson, 1983). Sediment resuspension can play a critical role in causing a significant shift in the aquatic ecosystem. The subject of present interest is Lake Apopka in central Florida. Of particular concern for the lake is the longterm reduction in the lakes water level and potential increase in turbidity Higher suspended sediment concentration (SS C) can increase internal nutrient recycling and reduce light penetration, thereby impeding the restoration of submersed plants within the lake. This information is important to the St. Johns River Water Management District (SJRWMD) for development of Minim um Flows and Levels for the lake, as well as consideration of any management options that might change typical lake stages. Until 1946 the lake was clear and had extensive submersed plant beds. The subsequent polluted condition of the ecosystem from excess ive phosphorus loading persisted until the end of the century Restoration efforts since 1985 have focused on reducing phosphorus loading by c essation of farming and restoration of the aquatic system T he water quality in the lake has been improving for ov er a decade, as manifested in decreases in total phosphorus, chlorophyll and SSC increases in water transparency, and re appearance of native submersed plants. However, a thick layer of easily resuspended organic s rich fine -grained sediment (muck) covers the lake bottom Based on field measurements and simple sediment transport modeling principles, the objective of this study was to examine the potential effect of changing the lakes water level on

PAGE 23

23 the suspended sediment regime, especially at high wind sp eeds. Both higher and lower water levels relative to the present are considered. 1.2 Tasks As part of the study the following field tasks were carried out: 1 In order to obtain hydr o graphic data required to evaluate the sediment resuspension regime of the la ke instrumentation was deployed on an existing meteorological tower maintained by SJRWMD and on a moveable tower deployed by the University of Florida at two additional sites. For convenience of description, henceforth these instrumentation locales will b e referred to as UF0, UF1 and UF2. 2 Data collected in the lake during July 25, 2007 to September 16, 2008 have been analyzed in conjunction with a companion study on bottom coring and sediment characterization carried out by Dr. John Jaeger of the Departme nt of Geology at the University of Florida (UF). 3 Settling velocity tests on the lake sediment were conducted in the Coastal and Oceanographic Engineering Laboratory of the University of Florida (UF). 4 Based on the above tasks an effort has been made to deve lop a generic description of the vertical structure of suspended matter and its dynamics. 5 A simple analytic model has been developed relying on the assumption of short term (hourly time -scale) equilibrium between entraining and settling fluxes in the lake s water column. It is based on the sediment mass balance for the simulation of SSC at different elevations in the water column. 6 By changing (decreasing and increasing) the water level and covering a wind speed range of 2 to 30 m/s, the model has been used to predict SSC at different elevations in the water column.

PAGE 24

24 CHAPTER 2 STUDY SITE, FIELD IN STRUMENTATION AND LA BORATORY TESTS 2.1 Field Site Lake Apopka is a 12,500 ha aquatic body about 25 km northwest of the Orlando metropolitan area in Florida at latitu de 28 1). The fourth largest lake in Florida, and historically one of the most polluted ones in the State it is the headwater for the Ocklawaha chain of lakes. The lake was once bordered on the north by an extensive floodplain marsh. Presently the maximum depth of water is about 2.7m at the center of the lake, and the mean depth is about 1.65 m. Until 1946 the lake was clear and had extensive submersed plant beds in which game fish flourished (Clugston 1963). The subsequent polluted condition is believed to have resulted from excessive phosphorus loading, mainly from a large (about 8,000 ha) farming area created on the floodplain marsh (Battoe et al. 1999, Lowe et al. 1999, Schelske et al. 2000). Subsequent degra dation of the 20,000-ha ecosystem associated with the lake persisted for more than 50 years. W ater from the lake is fed by natural springs (Figure 2 3), rainfall and stormwater runoff, and the only surface outflow from the lake is the Apopka Beauclair Cana l. Water flows from the canal into Lakes Beauclair and Dora. From Lake Dora, it flows into Lake Eustis, then into Lake Griffin and finally northward into the Ocklawaha River, which flows further northward to the St. Johns River (Figure 2 2). The largest sp ring in the Lake Apopka basin, Apopka Spring, also known as Gourd Neck Spring, discharges into Gourd Neck (Figure 23), a narrow water body located in the southwest corner of the lake (SWIM plan 2003). The average discharge rate of Apopka Spring was approximately 0.85 m3/s from 1988 through 1998, with the range 0.76 to 0.9 m3/s dependent on the lake stage (Stites et al. 2001). Based the Meinzer spring discharge scheme, Apopka Spring is classified as a second-magnitude spring that discharges water at a rate between

PAGE 25

25 about 0.3 and 3 m3/s (Rosenau et al. 1977). There are three other springs, Holt Lake Spring, Bear Spring, and Wolfs Head Spring, in the basin; however, discharge information is unavailable (SWIM plan 2003). Based on observations of water level anomaly between Lake Apopka and downstream lakes the Apopka Beauclair Canal seems to have reduced the water level in Lake Apopka (Stenberg et al. 1997). At the time of the present study the lake level was about 1 m lower than the level reported by Schleske (1 997). Water discharge from the lake occurred via the Apopka Beauclair Canal at a mean annual rate of 6.81107 m3/year for the years 1959~1999 (USGS 2002). Wind is the most important driving force in the lake (e.g., Mei et al. 1997, Bachmann et al. 2000). Fluid stress at the bottom, which is the cause of sediment resuspension, is generated by wind induced waves and current. A method of calculation of the combined wave -current bed shear stress is given in Chapter 4. 2 .2 Field Instrumentation The first inst rument deployment was for the primary array UF0, at the St. Johns River Water Management District Meteorological Tower at 28 81 (Figure 2 3 ). An Acoustic Doppler Current Profiler (ADCP) two Optical Backscatter Sensors (OBS) and a Conductivity Temperature Depth (CTD) sensor were mounted Details on the deployed devices are given in Table 2 1. Secondary arrays were located at UF1 at latitude 28 28.8 and at UF2 at 28 and l81 3 (Figure 2 3 ). At both sites the main support consisted of a three legged aluminum frame platform anchored at the bottom. The array at UF0 was installed on July 25, 2007, and decommissioned on September 16, 2008. UF1 was deployed between April 25 and July 18, 2008 and UF2 between August 28 and September 16, 2008. Details on the deployments are given in

PAGE 26

26 Tables 2 2 and 2 3. P hotographic views of the two stations are given in Figures 2 5 and 2 6, and are schematically drawn in Figures 2 7 and 2 8. Und erway current velocity and SSC data were collected on November 1, 2007 along Transect 1 shown in Figure 2 4. Data were recorded by an ADCP pointing downward, mounted on an adjustable aluminum -pole which was attached to the right side of a 5.2m McKee boat. The instrument was maintained as close to the surface as possible to collect data from the maximum number of bins. Each bin was 0.2 m and sampling was at 1s interval. The tran s ducer was 0.2 m below the water surface and the first bin was at 0.46 m, so the closest bin from the water surface was 0.66 m. The mean water depth along the transect was approximately 1.30 m from ADCP records. The maximum and minimum values were 2.36 m and 0.74 m, respectively. During that period the water surface elevation was appr oximately 19.55 m (NAVD88). The fastest and average boat speeds were 1.4 m/s and 1.2 m/s, respectively. A Global Positioning System, GPSmap 182 made by Garmin, was mounted on the top of the adjustable aluminum -pole and was activated during cruising. Also, sediment concentration data were measured by OBS 3 mounted aside the McKee on February 29, 2008 along Transect 2 shown in Figure 2 4. 2.3 Laboratory Tests 2 3 .1 Scope The response function of the OBS depends on the physicochemical properties of the suspension. Accordingly, calibration of OBS is required on a site -specific basis. Calibrations of OBS 3 and OBS 5+ units used are described in this section. Results of settling velocities tests carried out in an acrylic column are also described. 2.3.2 OBS Calibr ation For the OBS, 2 liter suspended sediment samples were collected close to UF0. In the laboratory, calibration was carried out as follows. Water samples from the lake were poured in a

PAGE 27

27 plastic black tub 45 cm in length, 30 cm in width, and 20 cm in depth Black color was meant to prevent light from being reflected by the walls of the tub. The OBS was mounted inside the tub until the sensor was submerged at least 5 cm. Output voltages for OBS 3 and counts for OBS 5+ were recorded simultaneously in order to characterize sy n chronous responses of the transducers. Sediment slurry of given concentration was poured into the tub and mixed by a hand-held mixer. When the slurry became well -mixed, a sample of the suspension from the middle of the tub was contained in a 50 ml glass bottle and OBS outputs were recorded at the same levels at which the suspension was sampled. The procedure was repeated, with suitable aliquots of the slurry added to the tub to gradually increase the SSC. Gravimetric analysis was used to de termine the SSC of the sample contained in each bottle. A CR1000 data -logger (made by Campbell Scientific ) was used to acquire the voltage data from OBS 3 in the calibration test and also in the field M ost voltages from the field data were less than 800 mV, so the calibration tests were limited to low voltage s SSC (denoted by the symbol C below) is plotted against each sample voltage V from the data logger in Figure 2 9. The best -fit line is given by Eq. (2.1). 51.507210 CV (2.1) Calib ration plot for OBS 5+ is shown Figure 2 10. This device has two detectors, a near detector (ND) and a far detector (FD). ND counts are converted to SSC of fine sediment ( d50< 62 3) as well as high SSC values, and FD counts for the mid range. In the present case only ND counts were used to calibrate OBS 5+. The best -fit line between SSC and ND counts, Nc is given by Eq. (2.2). 7(0.0003072.7)110NcCe (2.2)

PAGE 28

28 2.3.3 ADCP Calibration Figure 2 11 is a plot of the echointensity anomaly ( EIA ) of the ADCP versus SSC from OBS 3 and 5+ collected at the same time in the field. EIA was converted to SSC, which increased exponentially, as given by Eq. (2.3). 0.221.980.1729eEIAC (2.3) It was observed during the tests that resuspension began around EIA = 5 and rapidly increased after around +10. 2.3.4 Settling Velocity Several methods have been developed to calculate the settling vel ocity (Heltzel and Teeter 1987). In the present study, the procedure developed by Ross (1988) was carried out. Settling tests were conducted by using a specially designed acrylic settling column which was 2 m tall and 10 cm in diameter. The column was originally designed by Lott (1987). Tap hoses with 5 mm diameter and 10 cm length were attached to the sides at nine elevations for suspension sample withdrawal. Sediment collected in 1 liter bottles from the dense suspension in the lower part of the water col umn in the vicinity of UF0 was used in the tests. Lake water as needed was used to dilute the suspension in the column. The experimental procedure was as follows: 1 Wet sieving (using lake water) of the collected suspension in the bottles was carried out wi th No. 200 Tyler sieve (0.074 mm diameter). This process resulted in highconcentration slurry free from coarse material. This slurry with adequate quantity of lake water was placed in a 20 -liter carboy. A vacuum bubbler tube was inserted into the carboy f or a few tens of minutes, in order to premix the suspension thoroughly. 2 After the above suspension was poured into the settling column, the first set of about 20 ml samples was taken from the top to the bottom taps as soon as possible to record the initia l concentration profile The sampl es were contained in 50 ml glass bottles

PAGE 29

29 which are labeled and tightly capped. Samples were then taken after 5, 15, 30, 60, 120, and 180 minutes. The height and the temperature of the suspension were noted at each sampling time. The taps were flushed just before each sample collection to assure the removal of any sediment residue. 3 Gravimetric analysis was used to determine the profile of SSC with depth at each sampling time. Details are found in Hwang (1989) for the relationship between the settling velocity and concentration C for the flocculation and the hindered settling regions of settling velocity-SSC variation for fine sediment. The equation used is expressed as: 22()n s maC w Cb (2.4) Three settling tes ts were carried out for three conditions given in Table 2 4. Based on these tests, Figure 2 12 shows the settling velocity plot for the initial concentration 0.91 kg/m3. For this case the constants a =0.0015, b =0.7, m =3, and n =3.3 are obtained. The limiting concentration C1 for free settling is 0.1 kg/m3. Fine particles or flocs in the concentration range less than 0.1 kg/m3 settle independently without mutual interference. Thus the settling velocity is independent of concentration. The free -settling velocit y for the present case is taken as the value of the settling velocity at C = C1, which is wsf = 605 m/s. Numerically simulated profiles (lines) of concentration change with time as shown in Figure 2 12. The Suspension concentration gradually decreased w ith time from 0.91 kg/m3 to approximately 0.1 kg/m3. A lutocline is observed immediately above the bed. The simulation is based on the solution of the one -dimensional conservation equation for the suspended sediment mass:

PAGE 30

30 () 0swC C tz (2 .5) where t is time and the z coordinate is directed upward with origin at the bottom, as defined in Figure 2 14. A numerical code developed by Mehta and Li (2003) was used. After obtaining the coefficients of Eq. 2.4, the time -evolution of the concentrati on profile, C(z t ), is simulated from Eq. 2.5. The initial and boundary conditions are specified as follows: The initial condition for the profile is: (,)(,0) CztCz (2.6) The zero settling flux boundary condition at the water surface ( z = h ) is: ()0s zhwC (2.7) and the zero settling flux boundary condition at the bottom( z =0) is: 0()0s zwC (2.8) It is seen that the simulations correspond with data (circles) reasonably well. Similar plots for init ial concentrations of 1.95 and 2.88 kg/m3 are given in Appendix A.

PAGE 31

31 Table 2 1 Instruments deployed in the lake Property Instrument make Model no. Sampling Frequency (Hz) Current RD Instruments ADCP Workhorse Sentinel 1 or 0.5 Wave Height Sea Bird Electronics CTD SBE 26 03 4 SBE 37 SM SSC D & A Instrument Company OBS3 1 OBS5+ 25 Table 2 2 Deployments at UF0 UF0 Latitude Longitude 28 37 30.36 "N 81 37' 28.80 "W Deployment No. Duration Instrument Sampling Inte rval (min) Installed Elev. (m) from NAVD88 0 1 07/25/0708/27/07 ADCP 60 18.99 CTD 15 18.89 0 2 08/27/0709/14/07 ADCP 90 18.99 CTD Data lost 18.89 OBS 3 30 18.66 0 3 09/14/0710/12/07 ADCP 15 19.02 CTD 30 18.89 OBS 3 30 18.66 0 4 10/12/07 12/05/07 ADCP 10 19.02 CTD 30 18.89 OBS 3 30 18.66 0 5 12/05/071/16/08 ADCP 15 19.02 CTD 30 18.89 OBS 3 30 18.66 OBS 5+ 10 18.34 0 6 01/16/0802/29/08 ADCP 10 19.02 CTD 30 18.89 OBS 3 30 18.66 0 7 02/29/0805/02/08 ADCP 15 19.0 2 CTD 60 18.89 OBS 3 30 18.66 0 8 05/02/0806/17/08 ADCP 10 19.02 CTD 60 19.05 0 9 06/17/08 07/18/08 ADCP 15 18.79 06/17/08 08/13/08 CTD 60 18.91 06/17/08 07/18/08 OBS 5+ 20 18.33 0 10 08/28/08 09/16/08 ADCP 15 19.28 08/13/08 09/16/08 CTD 60 18.85

PAGE 32

32 Table 2 3 Deployments at UF1 UF1 Latitude Longitude 28 35' 28.80"N 81 37' 46.44"W Deployment No. Duration Instrument Sampling Interval (min) Installed Elev. (m) from NAVD88 1 1 0 4/25/08 0 6/17/08 ADCP 10 19.20 1 2 0 6/17/080 7/18/08 ADC P 15.2 18.79 OBS 3 30 18.33 Table 2 4 Deployment at UF2 UF2 Latitude Longitude 28 37' 31.50"N 81 35' 29.82"W Deployment N o. Duration Instrument Sampling Interval (min) Installed Elev. (m) from NAVD88 2 1 0 8/28/08 0 9/16/08 ADCP 15 19.39

PAGE 33

33 Figure 2 1 State of Florida and general area of study. Figure 2 2 Central Florida lakes and waterways (Courtesy of SJRWMD).

PAGE 34

34 Figure 2 3 Lake Apopka and locations of stations UF0, UF1 and UF2. 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2.5 2.5 DISTANCE(m)DISTANCE(m) Boat ramp UF0 Tower UF1 Tower UF2 Tower TRANSECT1 TRANSECT2 0 2000 4000 6000 8000 10000 12000 14000 16000 0 2000 4000 6000 8000 10000 12000 14000 16000 Figure 2 4 Lake Apopka bathymetry, locations of UF stations and underway transect s

PAGE 35

35 Figure 2 5 UF0 station at SJRWMD meteorological tower. Figure 2 6 UF1 station. The same platform was later moved to UF2.

PAGE 36

36 Figure 2 7 Schematic drawing of instrumentation at UF0. Figure 2 8 Schematic drawing of UF1/UF2 platform and instrumentation.

PAGE 37

37 0 250 500 750 1000 1250 1500 0 0.25 0.5 0.75 1 1.25 1.5 Voltage(mV)Suspended Sediment Concentration(kg/m3) Y=2x10-5X1.507 Figure 2 9 OBS 3 calibration plot (SSC versus output voltage) 3.4 3.6 3.8 4 4.2 4.4 4.6 x 104 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Near Detector CountsSuspended Sediment Concentration(kg/m3) Y=1x10-7e(0.000307X+2.7) Figure 2 10. OBS 5+ calibration plot (SSC versus output voltage).

PAGE 38

38 -40 -30 -20 -10 0 10 20 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 The Anomaly of Eco-Intensity of ADCPSSC(kg/m3) Y=0.1729e(0.22X-1.98) DATA Best fit line Figure 2 11. ADCP calibration pl ot (SSC versus output EIA) 10-1 100 101 102 10-7 10-6 10-5 10-4 10-3 10-2 a = b = m = n = c1 = 0.0015 0.7 3 3.3 0.1 Wsf = 6.0e-006 (m/s) Sediment Concentration (kg/m3)Settling Velocity (m/s) Figure 2 12. Settling velocity variation with SSC (= C) for lake sediment for an initial suspension concentration of 0.91 kg/m3. The quantity wsf is the free settling velocity (below 0.1 kg/m3). The curve is based on Eq. (2.4).

PAGE 39

39 10-2 10-1 100 101 102 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 time (min) 0 5 15 30 60 120 180 I F I = initial profile F = final profile Sediment Concentration (kg/m3)Elevation (m) Figure 2 13. Simulated concentration profiles (lines) in and data (circles) in the settling column. Initial suspension concentration 0.91 kg/m3. Bottom Z C h 0 Water Surface Figure 2 14. Definiti on sketch of concentration profile

PAGE 40

40 CHAPTER 3 LAKE MEASUREMENTS 3.1 Hydrodynamic Data Data on current velocities were collected and loaded digitally. The sampling interval ranged from 10 to 90 min as given in Tables 2 2, 2 3, and 2 4. Each water depth was sub -divided into 10 to 20 acoustic bins. Bin sizes were 0.1 or 0.2 m depending on the ADCP deployed. For measuring salinity, temperature and water surface elevation with the CTD mounted at UF0, the sampling interval ranged from 15 to 60 min (Table 2 2). F or short -period variations in the water level due to wind -waves, the pressure gage in the CTD was set to collect data at 4 Hz frequency for 195 or 225 s at the beginning of every 2 or 4 h interval. For Deployment 0 3 taken as a representative deployment, w ater current velocities were collected at 1 Hz frequency for 15 min and then averaged. Time -series of the water current velocities at three elevations are plotted in Figure 3 1. The elevations 18.63 and 18.33 m were closest to 18.66 and 18.34 m at which OB S 3 and OBS 5+, respectively, had been installed. The maximum velocity was 13.6 cm/s. All values except those on 09/20/07 were less than 5 cm/s and the mean range was 0 2 cm/s. Velocity anomalies between the three levels was minor, indicating a fairly uniform vertical profile at the site. Current rose diagrams for three elevations are plotted in Figures 3 2, 3 3, and 3 4. At the elevation of 18.83 m, the current direction is dispersed over all sectors of the pie chart; however, current toward the west was dominant for about 13% of the time. The trend at 18.63 m elevation was similar, but westward current was dominant 15% of the time. At 18.33 m the current was toward 330 and dominant for 8%. T he westward current was modest compared with the other two elevations. Current -rose for each deployment is given in Appendix B.

PAGE 41

41 The time -series of salinity, temperature and water surface elevation are provided in Figure 3 5. Water temperature variation was between 26 and 32 riation. The daily mean temperature gradually decreased. Salinity varied between 0.19 and 0.22, with no significant correlation with temperature. Water surface elevation (WSE) varied between 19.33 and 19.50 m. SJRWMD measures the water level at 28 and longitude 81 3). Figure 3 6 compares WSEs from each source. SJRWMD data are daily averages while the others follow from the sampling intervals of the deployed UF instruments. From time -series measurement of the WSE and water depth at times of deployments and servicing of the instruments, the bottom elevation of each station was estimated. The NAVD88 elevation of the bottom at UF0 and UF1 was 18.16 m, and that at UF2 was 18.37 m. Figure 3 6 also includes lake precipitation (PRCP) data measured hourly by SJRWMD. During Deployment 0 3 precipitation did not seem to have had a noticeable effect on WSE. A similar plot for entire measurement period is given in Appendix B. Wave height and period recorded by CTD are plotted in Figure 3 7( A ). Th e average height and period were 0.12 m and 0.74 s, respectively. The plot for the date when the highest wave height occurred is given separately in Figure 3 7( B). The highest wave occurred around 17:30 on 09/20/07. At the time the wave height reached about 0.41 m and the wave period was 0.69 s. Wind speeds for the period same with that of Figure 3 7( B) are plotted in Figure 37( C). Although the wind speed when the highest wave height was recorded was not collected, it is believed that high wind was the cau se. The time -series for wind waves during Deployment 0 3 is shown in Figure 3 8( A ). The data were collected at 4 Hz frequency for 195 s at the beginning of each 2 -hour sampling interval. A sample time -series of water level for 195 s on 09/27/07 is shown in Figure 3 8( B).

PAGE 42

42 As mentioned in Chapter 2, underway data wer e collected on 11/01/07 to measure the vertical and horizontal velocity distributions along a major cross -section of the lake (Figure 2 4). The WSE (19.55 m) on the day of measurement is included in Figure 3 9 and 3 11. The elevation of the first bin of ADCP was about 18.90 m as the distance between the WSE and the first bin was 0.66 m. Therefore, data could not be obtained over this distance. The velocity range was between 0 and 18 cm/s and the direction changed significantly with depth and distance. As seen in Figure 2 4 a channel exists near the center of the lake, and the depth distribution in the Figure 3 9 approximately corresponds with the bathymetry. Figure 3 1 0 shows the direction for the current in the first bin. While the southwest direction was dominant in the western side of the lake, western or northern direction was dominant in the east side. Two gyres exited, with the western one being more distinct. The northern and eastern compone nts of currents in the lake are provided in Figure 3 11. The gyres were counter -clockwise at the time of measurement. 3.2 Sediment Data Suspended sediment concentrations were obtained with OBS as well as ADCP. OBS 3 was mounted at UF0 in Deployments 0 2 to 0 7 and at UF1 during Deployment 12. OBS 5+ was installed at UF0 during Deployments 05 and 0 9. SSC values were recorded by OBS 3 every 30 min and by OBS 5+ every 10 or 20 min. Further information of the deployments is given in Tables 2 2, 2 3, and 2 4. SSC values from the ADCP were estimated from the backscatter intensities. SSC time -series obtained from OBS 3 at 18.66 m elevation is shown in Figure 3 12 for Deployment 0 3. The highest and the mean SSC values were 0.175 and 0.014 kg/m3, respectively. The range of SSC was less than 0.05 kg/m3. SSC values from ADCP are plotted in

PAGE 43

43 Figure 3 13 for three elevations. As observed SSC increased with depth indicat es the presence of stable, sediment induced density stratification. In Figure 3 12 the time -serie s has gaps due to OBS 3 malfunction. In general, OBS 5+ more accurately measured the SSC (than OBS 3), as in Deployment 0 5. The results are provided in Figure 3 14. The highest, the mean and the minimum SSC values were 1.99, 0.13, and 0.04 kg/m3, respecti vely. The values were higher than those during Deployment 03 because OBS 5+ was installed closer to the lake bottom. Also, storms occurred between 12/16 and 12/18 in 2007, and between 01/01 and 01/04 in 2008. During the most significant storm the SSC reac hed about 1.99 kg/m3. At other times the values were typically less than 0.2 kg/m3. During the deployments of OBS 5+ it was found that at all times some particulate matter, presumably representing wash load of colloid size particles, persisted in suspensio n. During Deployment 0 5 the non-depositing SSC was 0.1 kg/m3 and during Deployment 0 9 it was 0.06 kg/m3. Since the present study was focused on resuspension of bottom sediment, these SSC values were subtracted from time -series representations and analysi s. ADCP data for all deployments indicated smaller values ranging between 0.01 and 0.05 kg/m3. These were subtracted only when reporting the variation of SSC with wind speed in Fig. 4.11 and other similar plots. OBS 3 data did not reveal wash load SSC. In Figure 3 15 the vertical distribution of SSC along Transect 1 is shown. The SSC varied between 0.01 to 0.35 kg/m3; however, most values were less than 0.05 kg/m3 as in Deployment 0 3. The average depth along the transect was 1.29 m and the deepest water was about 2.1 m 3.3 Data from Other Sources Wind data at UF0 were recorded by an anemometer maintained by SJRWMD. Wind speed and direction are plotted in Figure 3 16 for Deployment 0 3. Figure 3 17 shows the corresponding windrose The maximum wind spee d was 12.65 m/s, and the mean was 3.82 m/s.

PAGE 44

44 Wind direction was distributed over all sectors of the pie chart, but winds from 60 north were dominant and occurred for 21% of the time. Windroses for every deployment of are provided in Appendix B

PAGE 45

45 0 5 10 15 Velocity(cm/s) Elev. 18.83m 0 5 10 Velocity(cm/s) Elev. 18.63m 09/15 09/20 09/25 09/30 10/05 10/10 0 5 10 Day of 2007Velocity(cm/s) Elev. 18.33m Figure 3 1 Current velocity time -series during Deployment 0 3. 15% 10% 5% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 5 5 9 9 13Velocity(cm/s) Figure 3 2 Current rose at 18.83 m elevation during Deployment 0 3.

PAGE 46

46 15% 10% 5% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 5 5 9 9 13Velocity(cm/s) Figure 3 3 Current rose at 18. 6 3 m elevation during Deployment 0 3 15% 10% 5% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 5 5 9 9 13Velocity(cm/s) Figure 3 4 Current rose at 18. 3 3 m elevation during Deployment 0 3

PAGE 47

47 20 25 30 35 Temperature(C) 0.18 0.19 0.2 0.21 0.22 Salinity 09/15 09/20 09/25 09/30 10/05 10/10 19.3 19.4 19.5 Water Surface Elev.(m)Day of 2007 Figure 3 5 Salinity, temperature and water surface elevation time-series during Deploym ent 0 3. 18 18.2 18.4 18.6 18.8 19 19.2 19.4 19.6 19.8 20 Water Surface Elev.(m)Bottom Elevation from NAVD88 : 18.16m 09/15 09/20 09/25 09/30 10/05 10/10 0 5 10 15 20 25 30 35 40 45 Day of 2007Precipitation(mm) ADCP CTD SJRWMD Bottom Elev. PRCP(mm) Figure 3 6 Water surface elevation and precipitation during Deployment 0 -3.

PAGE 48

48 0 0.1 0.2 0.3 0.4 Wave Height(m)Height Period 09/15 09/20 09/25 09/30 10/05 10/10 0.5 0.6 0.7 0.8 0.9 1 Wave Periods(s)Day of 2007 A) 0 0.1 0.2 0.3 0.4 Wave Height(m)Height Period 00:00 06:00 12:00 18:00 00:00 0.5 0.6 0.7 0.8 0.9 1 Wave Periods(s)September 20, 2007 B) 00:00 06:00 12:00 18:00 00:00 0 5 10 15 September 20, 2007Wind Speed(m/s)C) Figure 3 7 Wave height and period time -series A) D uring Deployment 0 3. B) For the date when the highest wav e height occurred. C) Wind speeds for the period same with that of B). 09/15 09/20 09/25 09/30 10/05 10/10 106 107 108 Pressure(kPa)Day of 2007 A) 09:25:12 09:25:55 09:26:38 09:27:22 09:28:05 106.9 106.95 Pressure(kPa)September 27 in 2007 B) Figure 3 8 Time-series of wind waves A) D uring Deployment 0 3. B) A sample time -series of water level at 4 Hz frequency for 195 s.

PAGE 49

49 Distance along Transect1(m)Elevation(m) Water Surface Elev. from NAVD88 : 19.55m 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 17.5 18 18.5 19 19.5 Velocity(cm/s) 0 2 4 6 8 10 12 14 16 18 Figure 3 9 Current velocity distribution along Transect 1 (shown in Figure 2.3) on 11/01/07. 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 -20 -10 0 10 20 Distance along Transect1(m)Velocity(cm/s) Figure 3 10. Current -vector data along Transect 1 at the elevation of the top acoustic bin on 11/01/07.

PAGE 50

50 Distance along Transect1(m)Elevation(m) Water Surface Elev. from NAVD88 : 19.55m 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 17.5 18 18.5 19 19.5 East Velocity(cm/s) -15 -10 -5 0 5 10 Distance along Transect1(m)Elevation(m) Water Surface Elev. from NAVD88 : 19.55m 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 17.5 18 18.5 19 19.5 North Velocity(cm/s) -10 0 10 Figure 3 11. Eastern and northern components of current along Transect 1 on 11/01/07. 09/15 09/20 09/25 09/30 10/05 10/10 0 0.05 0.1 0.15 0.2 0.25 0.3 Day of 2007SSC(kg/m3) OBS-3 at Elev. 18.66m Figure 3 12. SSC time -series from OBS 3 during Deployment 0 3. Gaps indicate data loss. Bio fouling may have contributed to weak signals after 10/03/07.

PAGE 51

51 0 0.2 0.4 0.6 0.8 1 SSC(kg/m3) Elev. 18.83m 0 0.2 0.4 0.6 0.8 SSC(kg/m3) Elev. 18.63m 09/15 09/20 09/25 09/30 10/05 10/10 0 0.2 0.4 0.6 0.8 Day of 2007SSC(kg/m3) Elev. 18.33m Figure 3 13. SSC time -series from ADCP during Deployment 0 3. 12/06 12/11 12/16 12/21 12/26 12/31 01/05 01/10 01/15 0 0.5 1 1.5 2 Day of 2007 & 2008SSC(kg/m3) OBS-5+ at Elev. 18.34m Figure 3 14. SSC time -series from OBS 5+ at 18.34 m elevation during Deployment 05.

PAGE 52

52 Distance along Transect1(m)Elevation(m) Water Surface Elev. from NAVD88 : 19.55m 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 17.5 18 18.5 19 19.5 SSC(kg/m3) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Figure 3 15. SSC contours along Transect 1 on 11/01/07. 09/10 09/15 09/20 09/25 09/30 10/05 0 5 10 15 20 Wind Speed(m/s) Speed 09/15 09/20 09/25 09/30 10/05 10/10 0 100 200 300 Day of 2007Wind Direction() Direction Figure 3 16. Wind speed and direction during Deployment 0 3.

PAGE 53

53 20% 15% 10% 5% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 14Wind Speed (m/s) 20% 15% 10% 5% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 14Wind Speed (m/s) Figure 3 17. Wind rose for Deployment 0 3.

PAGE 54

54 CHAPTER 4 RESUSPENS ION BEHAVIOR 4.1 Weekly Parametric Values In order to characterize the resuspension behavior of the lake, weekly values (representing a convenient time-scale for assessments of seasonal variability) of the measured parameters are provided in this chapter f or the entire duration of data collection at UF0. The data have been dissected by week and by the maximum, mean and the minimum values during the week. Table 4 1 gives information on the weeks and dates. Values for UF1 and UF2 are provided in Appendix C. W eekly values for wind and waves are given in Table 4 2. Weekly wind speed varied from 0 to 22.8 m/s, with the highest value recorded in the 45th week. The windiest period was the 56th week when the mean speed was 7.8 m/s. In the 46th week the weakest wind was measured (2.8 m/s). In the same table the maximum, mean and minimum values of the significant wave height and significant period are included. Wave height and period ranged from 0.01 to 0.41 m and 0.51 to 1.01 s, respectively. The highest significant w ave height was 0.14 m in the 36th week; however, the corresponding wind speed is not available. Table 4 3 provides the weekly maximum, mean and minimum current speeds. As given in Table 2 2 current output interval from the ADCP ranged from every 10 to 60 min Values in Table 4 3 represent non -wave components at different elevations. The strongest currents occurred between the 48th and the 50th week, with the highest values at the bottom -most elevation. However, it is conceivable that the recording instrume nt malfunctioned during those periods because the values, ranging between 32.3 and 35.8 cm/s, seem excessive. Except for those periods the currents were the strongest in the 36th week. The highest value of 7.3 cm/s was recorded at the middle elevation. Da ta for the highest elevation were not available for that week.

PAGE 55

55 In the 36th week the highest wave height was recorded as 0.14 m. The current velocity variation was between 0 and 22.7 cm/s. Assessments for water temperature, salinity and WSE are provided in Table 4 4. During the measurement period the temperature varied between 7.0 to 39.9 was between 0.16 and 0.25, which can be considered minor. WSE changed between 19.15 m and 19.90 m, with the highest and the lowest values of 19.85 m in the 59th week and 19.20 m in the 43rd week, respectively. The estimated weekly SSC values recorded by the ADCP are given in Table 4 5. The highest SSC was in the 34th week when relatively strong wind, wave height and current also occurred. During Deployment 0 10, although SSC was collected at 18.14 m elevation, the weekly -mean SSC was relatively low, possibly due to high WSE. Table 4 6 includes SSC measured by OBS 3 and OBS 5+. As mentioned in Section 3.2, values from OBS 5+ were higher than thos e from OBS 3 due to elevation difference. SSC measured by OBS 3 ranged from 0 to 0.28 kg/m3 with the highest value of 0.09 kg/m3. SSC from OBS 5+ varied between 0 and 1.72 kg/m3, with the highest value of 0.03 kg/m3. 4.2 Spectral Analysis Frequency spectra for the time -series data given in Chapter 3 are plotted in Figure 4 1 from Deployment 0 3. Results from other deployments are given in Appendix C. Frequencies (d1) are plotted on the abscissa and the power spectral density (PSD) of each parameter on the ordinate. A peak for all parameters except wave period occurs at the frequency of 1 d1, corresponding to the solar diurnal period. Only one dominant peak is found for wind speed, water temperature, salinity and wave height. There are two event peaks in WS E at frequencies of 1 d1 and 2 d1, corresponding to the solar diurnal and semi diurnal periods, respectively. PSDs from the ADCP data on currents and SSC have several peaks; however, there is considerable noise at frequencies

PAGE 56

56 higher than the diurnal. Thi s is clear from the degree of coherence (a measure of cross correlation in the frequency domain) in Figures 46 and 49, which is dominant at 1 d1 and 2 d1. Thus, current velocity, wave height and SSC are strongly related to wind speed. For wind waves t wo dominant energy peaks are found. Figure 4 2 shows the PSD from the time -series of waves plotted in Figure 3 7 (B). The peaks occur at the frequencies of 0.016 and 1.11 Hz. In other words waves mainly had periods of 62.5 s or 0.9 s at that time. The forme r may correspond to a seiching mode in the lake. Figure 4 3( A ) shows the time -series of maximum PSD (left ordinate) for the low frequency (less than 0.5 Hz) range, and the time -series of frequencies within which the maximum PSD was recorded. The correspond ing time -series and frequencies in the highfrequency range (greater than 0.5 Hz) are plotted in Figure 4 3( B). It is seen that waves in the high -frequency range were dominant (with larger PSD). 4.3 Interdependence among Parameters In this section, the in terdependence among selected pairs of parameters is examined. Deployment 0 3 is considered for illustrative purposes. Plots for other deployments are given in Appendix C. 4.3.1 Wave Height and Wind Speed Figure 4 4 plots the coherence spectrum between wav e height and wind speed. Coherence is observed at several frequencies including 0.25, 1, and 1.75 d1; however, 1 d1 is the dominant one for which the coherence is the greatest (0.9). This is also evident from the PSDs of wind speed and wave height in Figure 4 1 in which strong peaks occur at 1 d1. In Figures 4 5( A ) and 4 5( B) the significant wave height ( Hs) and the wave period ( T ), respectively, are plotted against wind speed ( U ). In each case a best -fit line is also shown. Wave height and period incre ase linearly; however the period plot shows weaker correlation (R2 =

PAGE 57

57 0.29) compared to the height plot (R2 = 0.63). Plots of wave against wind speed for other deployments are given in Appendix C. 4.3.2 Current and Wind Speed Figure 4 6 plots coherence betw een current speeds (at three elevations) and wind speed. For all elevations a coherence peak is observed at 1 d1, although its magnitude differs. In Figures 4 7( A ), 4 7( B) and 4 7( C) current magnitudes are plotted against wind speed at the same three elevations. The plots exhibit a high degree of scatter, and it appears that wind speed and current were non uniquely related during this period. In contrast, currents from Deployments 0 5, 0 8, 0 10, 1 1, and 21 increased exponentially with wind speed. Examp les of exponential variation are seen in Figures 4 8( A ), 4 8( B) and 4 8( C ) from Deployment 0 5. Plots for other deployments are given in Appendix C. They also include equations for best -fit curves. 4.3.3 SSC and Wind Speed Coherence between SSC and wind sp eed is plotted in Figure 4 9 for data from OBS 3 and in Figure 4 10 from the ADCP. The dominant coherence peaks between SSC (from OBS 3) and wind speed are at 1 d1and 2 d1, with the highest coherence at 1 d1, as also suggested in Figure 4 1. Note that t he strong peak at 1.1 d1 in Figure 4 10 is close to 1 d1. Figures 4 11 and 4 12 show the relationship between SSC and wind speed. Data for wind speeds below about 2 m/s have not been included since no measurable resuspension is believed to occur in the lake at such low speeds. It appears that in fact resuspension began at about 4 m/s. From similar plots for all deployments in Appendix C, the critical wind speed values for resuspension are estimated in Table 4 7. They indicate a narrow range of values bet ween 4.0 and 6.5 m/s. Since the variation of SSC with wind at different water levels in the lake is the subject of further interest, a method has been used to estimate bed shear stresses induced by wind waves,

PAGE 58

58 by wind -driven current and by the combined eff ects of waves and current. This is followed by an application of a method to estimate wave height and period. These methods are then used to make an assessment of turbidity in the lake related to storm winds at selected water levels. 4.4 SSC Variation with Bed Shear Stress 4.4.1 Estimation of Wave, Current and Combined Wave -Current Shear Stresses Models are available to describe, both analytically and numerically, the dynamics of the combined wave -current boundary layer. Soulsby et al. (1993) have presente d a semi -empirical method for estimation of bed shear stresses due to waves, current and combination of waves and current, in terms of non-dimensional parameters. Due to its simplicity and known utility, this method to calculate the combined wave -current b ed shear stress cw as defined in Eq. (4.1) is used in this study. ()cwcwY (4.1) where c is the current induced bottom shear stress and w is the bed shear stress due to waves alone. The quantities Y in Eq. (4.2) and X in Eq. (4.3) are non-dimensional parameters. 1(1)mnYaXX (4.2) c cwX (4.3) Since the multiplier Y in Eq. (4.1) is current boundary layer is to increase the combined bed shear stress by more than the sum of the individual contributions. The coefficients a m and n are given by: 12 34(cos)(cos)log(/)II wDaaaaafC (4.4a) 12 34(cos)(cos)log(/)II wDmmmmmfC (4.4b)

PAGE 59

59 12 34(cos)(cos)log(/)II wDnnnnnfC (4.4c) The quantity is the angle between the current stress direction and the wave stress direction. This angle will be taken to be zero for the present p urposes. The coefficients 14~ aa 14~ mm 14~ nn and I are given in Table 4 8 from Soulsby et al. (1993), who derived them from three independent sources (designated H T91, MS90 and F84) The current induced bottom shear stress c can be calculated from Eq. (4.5). 2 cDcCu (4.5) w here is the fluid density, DC is the drag coefficient and cu is the depth-mean current velocity in the boundary layer. The drag coefficient is obtained from Eq. (4.6) based on the well known log velocity profile. 2 00.4 ln(/)1DC hz (4.6) where h is the bounda ry layer height (taken to be equal to the water depth in the lake) and 0z is the bottom roughness height. The wave shear stress w is given by Eq. (4.7). 20.5w wbfu (4.7) where wf is the wave friction factor and bu is the bottom orbital velocity amplitude. This amplitude is calculated from the linear wave theory using Eq. (4.8). 2sinhbH u kh (4.8)

PAGE 60

60 where H is the wave height, 2/ T is the wave angular frequency, 2/ kL is the wave number, T is the wave period, and L is the wavelength. Given /bAu the wave friction factor is given by (Soulsby et al., 1993) Eq. (4.9). 0.190.00251exp5.21;1.57w ssAA f kk (4.9a) 0.3;1.57w sA f k (4.9b) where sk is the Nikuradse roughness, normally taken as 030 z As an example, select 1,000 kg/m3, 85 0 T s, 29 1 h m, 0002 00 z m (based on numerical hydrodynamic model calibration of winddriven circulation in the lake by Dr. Earl Hayter, personal communication), 0.3 H m, 0.007cu m/s and 0 These values are based on Deployment 0 3. Using the linear wave theory, 5.57 k m1 is obtained from the dis persion relationship 2tanh gkkh (Dean and Dalrymple 1991). Therefore, 1.13 L m is obtained. Equation (4.8) yields 30.3(2/0.85) 1.6810 2sinh(5.571.29)bu m/s From Eq. (4.9) 0/ 0.0379 30b su A kz Therefore, wf = 0.3, as /sAk is less than 1.57. From Eq. (4.7) 32 40.510000.3(1.6810)4.2310w Pa

PAGE 61

61 From Eq. (4.6) 2 30.4 2.6510 ln(1.29/0.0002)1DC From Eq. (4.5) 32410002.6510(0.007)1.310c Pa From Eq. (4.4) and the coefficients designated HT91 in Table 4 7, 3(0.071.87)(0.340.12)log(0.3/(2.6510))0.855 a 3(0.720.33)(0.080.34)log(0.3/(2.6510))1.253 m 3(0.780.23)(0.120.12)log(0.3/(2.6510))0.55 n In the same way it can be shown that a 0.19, m 0.97, n 0.48 for MS90, and a 1.64, m 1.43, n 0.66 for F84. Continuing with HT91, From Eq. (4.3) 4 441.310 0.235 1.3104.2310 X From Eq. (4.2) 1.253 0.5510.855(0.235)(10.235)1.12 Y Similarly, Y 1.04 for M S90 and Y 1.17 for F84 are obtained. Finally, for HT91, from Eq. (4.1) the combined wave -current shear stress is 4441.12(1.3104.2310)6.210cw Pa Similarly, cw is 5.75104 Pa for MS90 and 6.49104 Pa for F84. The combined wave -current bed shear stress cw values from the three methods are close to each other.

PAGE 62

62 4.4.2 Estimation of Wave Height and Period A method developed by Young and Verhagen (1996) for lakes is now used to estimate the wave height and the period for a given water depth and wind speed. The method relies on the use of non-dimensional energy [Eq. (4.10)], non-dimensional frequency [Eq. (4.11)], nondimensional depth [Eq. (4.12)], and non-dimensional fetch [Eq. (4.13)] param eters. 2 4gE U (4.10) pfU g (4.11) 2gh U (4.12) 2 gx U (4.13) w here g is the gravitational acceleration, E is the total wave energy or variance of the wave re cord, pf is the frequency of the spectral peak, h is the water depth, x is the fetch length and U is the wind velocity. The parameters and are obtained from the following relati onships 1.74 3 1 1 13.6410tanhtanh tanh B A A (4.14) where 0.75 10.493 A and 30.57 13.1310 B 0.37 2 2 20.133tanhtanh tanh B A A (4.15) where 1.01 20.331 A and 40.73 25.21510 B These relationships are based on field observation in Lake George in Australia.

PAGE 63

63 As an example of the use of these equations, c onsider the following set of values from Deployment 0 3. Wind speed 7 m/s and fetch length 5,630 m. This is the fetch for the dominant winds from 60 as seen in Figure 3 17. The mean water depth along the fetch was 1.28 m. From Eq. (4.12) 29.811.28 0.256 7 From Eq. (4.13) 29.815630 1127.1 7 Therefore, A1 = 0.1776, B1 = 0.1719, A2 = 0.0837, and B2 = 0.0881. From Eq. (4.14) 1.74 340.1719 3.6410tanh(0.1776)tanh 1.076310 tanh(0.1776) From Eq. (4.15) 0.370.0881 0.133tanh(0.0837)tanh 0.3647 tanh(0.0837) By substituting these values in Eqs. (4.10) and (4.11), E and pf are obtained as 2.68103 m2 and 0.51 Hz, respectively. The significant wave height is defined as 4sHE Therefore, sH and T are 0.21 m and 1.96 s, respectively. The same method is next used to calculate the wave height and period in Lake Apopka over the range of wind speeds from 2 to 30 m/s. The choice of the upper value is discussed later. The plot of sH against U thus obtained is shown in Figure 4 13( A ) in which the best -fit line in Figure 4 5( A ) is also plotted. Similar comparison for the variation of T with U and the best -fit

PAGE 64

64 line in Figure 4 5( B) are given in Figure 4 13( B). These comparisons permit recalibration of Eqs. (4.14) and (4.15). The revised expressions are as given in Eqs. (4.16) and (4.17), respectively. 1.97 3 1 1 19.310tanhtanh tanh B A A (4.16) 0.43 2 2 20.28tanhtanh tanh B A A (4.17) Using these equations, plots of sH against U and T against U are also given in Figures 4 13( A ) and 4 13( B), respectively. These indicate closer comparisons of sH and T values using the modified equations of Young and Verhagen (1996) with measurements based best -fit lines. 4.4.3 Estimation of Current-Induced Shear Stress Consider the definition sketch in Figure 414 in which S is the wind -induced water level setup. From force balance it can be shown that ( ) = ()windcdS S dxgh + S (4.18) i.e. 1 g1wind c cS S h h (4.19) where wind is the wind stress at the water surface. Let 2g1 SS h hh (4.20) Therefore

PAGE 65

65 wind c cc (4.21) Let c c (4.22) In other words cwind (4.23) Unfortunately, this rel ationship does not lead to a useful approach to determine c because is unknown. In order to relate c to wind the current speed uc at 0.17 m above the bed will be empirically related to the wind speed U Figure 4 15 shows the best -fit relationship betw een measured U and uc at different mean water depth s that existed during the study at different times As seen the current speed is not related with water depth in a systematic manner. The overall relationship between wind and current speed can be obtained in terms of an average proportionality coefficient (4.478103) based on the best -fit equations (Figure 4 15) as follows. 34.47810cuU (4.24) Hence, c for the Soulsby et al. formula is obtained directly from the wind speed 32(4.47810)cDCU (4.25) where CD is given by Eq. (4.6). Characteristic values are z0= 0.0002 m and = 1,000 kg/m3. The two -dimensional schematic representation of the relationship between wind stress and current stress in Figure 4 14 requires that the two stresses act in the same (vertical) plane (with a phase lag of 180o). In Figure 4 16 the measured directional anomaly between wind speed and

PAGE 66

66 water current (i.e. t he difference between the two directions) is plotted as a cumulative frequency distribution. Positive anomaly implies that current deflection is to the right of the wind. For mean water depth of 1.10 m, the two elevations of current measurements correspon d to heights of 0.85 m and 0.15 m above the bottom. Observe that the dashed line would mean the absence of bias in the direction of current relative to wind (with a median value of 0o). This was closely the case at 0.85 m elevation, where the cumulative pr obability for the current to be deflected more than 100o was 47%. At 0.15 m elevation the cumulative probability was 66%, implying a greater bias, but one which was considerably less than 180o. It is conceivable that the current spiraled with depth and a s a result closer to the bottom the anomaly was nearer to 180o. In any event, from these results it can be inferred that uc in Figure 4 14 is essentially an c. 4.5 Resuspension Dynamics 4.5.1 Resuspension Modes In general the mode of resuspension (surface erosion of a mud bed, mass erosion of a mud bed or entrainment of fluid mud) interactively depend s on the vertical structure of the concentration profile. The vertical structure is convenient ly sub-divided into four zones (Figure 4 17). In the upper zone the suspension layer (DSL) is dilute and exhibits Newtonian flow behavior. The lower zone is occupied by the benthic nepheloid layer (BNL), which contains fluid mud. In the benthic suspension layer (BSL), the concentration is intermediate between DSL and BNL. The suspension in BSL is non-Newtonian but the concentration is not high enough for settling to be hindered. Finally, at the bottom a consolidating bed (CB) occurs. It possesses an effecti ve normal stress but is soft enough (i.e. not fully consolidated) for bed sediment to be susceptible to resuspension when the effects of wind (waves, current) are sufficiently strong (Jain 2007)

PAGE 67

67 The four zones are dynamically connected by particle settli ng, coalescence or deposition of particles in -fluid parcels, and upward entrainment of these parcels. In the absence of BNL and BSL, DSL is sustained by erosion of particles from CB. Settling particles deposit onto the bed, unless the near -bed fluid stress es are high enough to hinder or prevent deposition. These transport processes are sometimes called classical erosion and deposition associated with CB. When BNL occurs but BSL is practically absent, sediment entrainment occurs due to mixing between fluid mud and dilute suspension. Any re settling parcels containing water and sediment if and when they reach BNL, will coalesce into BNL. Similarly, coalescence causes a downward exchange of sediment between DSL and BSL. Exchange processes can also occur betwee n BSL, BNL and CB that change their thickness and concentration without participation by DSL. Measurements in L ake Apopka suggest that there are two modes of suspended sediment transport. Colloidal matter and particles with very low settling velocities app ear to be advected as dilute turbid fronts in association with wind -driven currents. Such fronts tend to stratify the water column with diurnal variability. Synchronous SSC data from UF0 and UF2 can be used to assess the role of the horizontal concentratio n gradient on advective transport relative to convection. In Figure 4 18 a sample time-series of concentration gradient ( CUF 0CUF 2)/ L02 is shown as an example. The distance L02 between the two stations is 3,228 m. Peak values are seen to be on the order of 104 kg/m4. The wind direction was generally downstream from UF2 to UF0 during this period. Unlike turbidity fronts, depositable particles tend to undergo local resuspension with a strong bias towards vertical ( convective ) fluxes The time -series of th e vertical gradient of concentration between the bottom -most (at 18.14 m elevation) and the top-most (at 18.54 m)

PAGE 68

68 sensors corresponding to Figure 4 18 is shown in Figure 4 19. Observe that the gradient is on the order of 100 kg/m4, which is 104 times great er than the corresponding horizontal gradient in Figure 4 18. Figure 4 20 shows a similar trend at UF2. 4.5.2 Concentration Profile Resuspension is simply described by the mass suspended sediment mass balance sszCC wCD tzz (4.26) This balan ce, which is an extension of Eq. (2.5), indicates that the time rate of change of the concentration C(z t ) is determined by the net effect of the vertical gradient in the settling flux due to gravity and the diffusive flux due to boundary layer turbulence. Equation (4.26) permits the simulation of C(z t ) under the combined action of windinduced waves and current (Figure 4 28). Its solution depends on the choices of szD and ws. As in Newnans Lake in north -central Florida (Jain 2007), it can be assumed that szD is reasonably approximated by its depth -mean value 0 sD In general, for given sediment the settling velocity depends on the flow shear rate and concentration (Teeter 2001a, 2001b). In the l ow -energy environment of Lake Apopka the effect of concentration can be expected to be dominant [Eq. (2.4)] and requires further consideration. In DSL the settling velocity is free from the effect of concentration which is low. In BSL the relevant represe ntation of the settling velocity is of the form 0()n sswwfC (4.27) where ws 0 is a characteristic value of ws and ()nfC is a modifier of ws 0 due to the presence of sediment in suspension. As for the response of the lake se diment to wind, the main interest is in the settling velocity on resuspension as C increases with wind speed. Since this increase is due to

PAGE 69

69 enhanced aggregation of flocs by turbulence, the dependence of ws on C can be assumed to be given in its general for m by Eq. (2.4), which accounts for the concentration range (also called flocculation settling range) in which aggregation (or flocculation) effects are important. For the present application to BSL C2<
PAGE 70

70 be za. The bed datum ( z = 0) is the surface below which the bottom material remains static over the range of wind speed used to e xamine resuspension. Since the present interest is in snap -shots of suspended sediment concentration, e.g. every hour corresponding to the frequency of data collection, it will be further assumed that entrainment and settling in the water column consist ing of DSL and BSL are temporally in quasi equilibrium over this duration. Thus Eq. (4.26) after substitutions becomes 2 0 00s sw C C zD (4.29) which can be integrated from reference concentration Ca at elevation za 0 2 0aaCz s Cz sw dC dz CD (4.30) to yield Eq. (4.31). 11 0 0()s aa sw CCzz D (4.3 1 ) i.e. 0 00()sa saasDC C wCzzD (4.32) The elevation za a of the water depth h i.e. .aazh Thus Eq. (4.33) becomes 0 00()sa saasDC C wCzhD (4.33) T he thickness of BNL (also called the floc layer), is estimated from bottom core analysis to be ~5 to~15 cm (Dr. John Jaeger personal communication). We will consider this layer to be nominally 10 cm thick based on evidence presented later. Thus, a 0.1/1.00 = 0.1, where 1.00

PAGE 71

71 is the nominal water depth, will be selected as the representative fraction relating h to za (Figure 4 21). 4.5.3 BNL Mixing The concentration Ca at the top of BNL plays a critical role in governing the supply of sediment to BSL (and therefore to DSL). In general Ca varies with the excess bed shear stress cwy where y is the bed yield stress. The yield stress was determined in rheometric tests on sediment samples taken for the core (Dr. John Jaeger, personal communication). These tests suggest that a ch aracteristic value of y may be obtained from Eq. (4.34), as observed in Figure 4 25. The exponent 4.4 is consistent with the value obtained by Migniot (1968) from tests of a large number of muds from Europe and Africa. 4.4 -8= ;=810 ycacC (4.34) The coefficient c = 808 from Figure 4 24 was reset by setting the condition that the maximum depth down to which resuspension could occur would be z =0 when the wind speed is 30 m/s, at which the condition ycw must be satisfied. The following se diment entrainment equations are iteratively selected to model Ca by considering the effect of mixing within BNL due to shear stress 1.26();ba bcwy cwyC (4.35) where b and b are calibration coefficients. Referring to Figure 4 21 we note that the elevation za at which Ca = 1.26 kg/m3 is not coincident with zb defining the top of the cores collected in the field. The concentration at that level ( zb) was on the order of Cb = 15 kg/m3. In the suspension above the top of the core the yield stress is negligible. At the bottom of BNL ( z = 0) the concentration is about Cc = 4 0 kg/m3. Hindered settling occurs in the layer of thickness za bounded by concentrations Ca = 1.26 kg/m3

PAGE 72

72 at the top and Cc = 4 0 kg/m3 at the bottom. Consolidation occurs at highe r concentrations in the bed (Winterwerp and van Kesteren 2004). The presence of particlereactive short lived Beryllium 7Be (half life t=53 d) (Figure 426) suggests that mixing of sediment in BNL occurs within 4 5 half lives of the tracer (~200250 d). The thickness of the 7Be rich sediment layer remained roughly same during the investigation, implying that the depth of sediment mixing was unchanged. The 7Be profile indicates that mixing had occurred over a thickness of about 6~8 cm (at LA Tower 07a). This observation is supportive of selecting this as the characteristic thickness of BNL given that wind higher than 22.8 m/s (which occurred on 06/02/08) was not experienced during the study, but does occur when significant storm events take place. It wi ll be assumed that at the wind speed UH = 30 m/s, the 8 cm thick BNL layer was fully mixed, while at UL = 2 m/s, Ca = 1.26 kg/m3 and Ca increases in accordance with Eq. (4.35) The cumulative distribution function of the measured (2002 2008) wind speed b etween 0 and 54.26 m/s in Table 49 (and plotted in Figure 4 2 7 ) indicates that the probability of occurrence of 22.8 m/s is low (1.00000.99946 = 0.00054, i.e. 0.054%). Speeds (1 -minute average) that are greater than 33. 5 m/s are defined as hurricane wind s. The highest recorded wind of 54.26 m/s (3 -min average) on 09/26/04 occurred during the passage of Hurricane Jeanne across the Florida peninsula Considering the concentration increase in BNL from 1.26 to 4 0 kg/m3 to be linear, the uniform concentration due to complete mixing at a wind speed of 30 m/s would be Cm = 20.63 kg/m3b = 1.5 from classical sediment transport mechanics (Julien 1995) the b from Eq. (4.3 5 ) is obtained as 144.96 because cw = 0.3 1 Pa at 30 m/s with water depth 1.26 m.

PAGE 73

73 4.5. 4 Model Calibration The wave shear stress w was estimated from the significant wave height and period using Eqs. (4.1 6) and (4.17), and the current shear stress c was calculated from Eq. ( 4. 25) T he combined wave -current bed shear stress cw was determined from Eq. (4.1) The time -series of the shear stresses during Deployment 0 5 are given in Figure 4 28. As observed, current -induced shear stress had more effect on SSC. The wave shear stress ranged from 0 to 0.07 Pa 0 to 0.3 and 0 to 0.45 at water depths of 2.0 m, 1.0 m and 0.5 m, respectively, between 2 and 30 m/s of wind speed as shown in Figure 4 29(a). At 30 m/s, in Figure 429(b) t he current shear stress is seen to have reached 0.041 Pa 0.05 Pa and 0.062 Pa at depths of 2.0 m, 1.0 m and 0.5 m, respectively. The corresponding combined wave -current bed shear stresses in Figure 4 29(c) reached 0.13, 0.38 Pa and 0.52 Pa. Thus, the higher the wind speed and lower water surface elevation, the greater the effect wave shear stress has on resuspension. The ratio ofw to c is given in Table 4 10 at selected water depth s and wind speeds Measured SSC values are available at three elevation s above the bed (Chapter 3). Using the time -series of C at the lowest elevation (18.34 m) from Deployment 0 5 the corresponding time -series of the diffusion coefficient Ds 0 (which along with the settling velocity governs the magnitude of C) is calculated from Eq. (4.31). Figure 4 30 shows the plot of Ds 0 against the respective critical friction velocity for resuspension */cwcwu From the plot, the best -fi t mean relationship between Ds 0 and cw is as follows. 23 0**0.610; 2.4310s cw cwDuu (4.36a ) 43 0* *0.30236.83210; 2.4310s cw cwDu u (4.36b) Using Eq. (4.36), Eq. (4.33) is written as

PAGE 74

74 2 3 2 0*0.610 ;2.4310 ()0.610cwa cw saa cwuC Cu wCzhu (4.37a) 3 3 3 0*(0.51.210) ;2.4310 ()0.51.210cw a cw saa cwuC Cu wCzhu (4.37b ) The following two additional relationships cover the selected upper and lower bounds in Figure 4 30. The relationships of lower cwu for both bounds are same with Eq. (4.36a). 3 3 30*(0.67561.29710) ;1.9410 ()0.67561.29710cw a cw saa cwuC Cu wCzhu (4.38) 4 3 4 0*(0.34199.67510) ;2.8810 ()0.34199.67510cw a cw saa cwuC Cu wCzhu (4.39) Measured and simulated time -series of SSC at 18.34 m elevation for Deployment 0 5 are given in Figure 4 31. Also shown are the upper and lower bound values. 4.5.5 Model Validation The SSC data from Deployment 0 6 are compared with simulated results at elevation 18.38 m for verification. During the deployment the mean water depth was 1.29 m. Figure 4 32( A ) compares measured and simulated values of SSC. In Figures 4 32( B) and 4 -32( C) simulations are based on the upper and lower bound. It is observed that the simulation in Fig. 4.32( A ) is in reasonably agreement with measurements. The corresponding plots for 18.88 m elevation are shown in Figures 4 33( A ), ( B) and ( C ). Although there is a noticeable difference between measured and simu lated SSC at the top elevation, overall the simulations are reasonable. 4.6 Effect of Water Level Change The derived set of analytic equations comprising the model was next used in the predictive mode by selecting water depths of 2.0, 1.5, 1.0, 0.75 and 0.5 m at UF0. The 2 m depth is a nominal maximum value comparable to the water depth in the lake during the 1996 core

PAGE 75

75 collection by Schelske (1997). The lowest depth of 0.5 m represents an assumed extreme low water condition at which part of the lake bo ttom will be exposed It should be pointed out that the ability of the model to predict SSC decreases when the depths are either greater than about 0.9 m or less than 1.8 m. This is so because during the entire period of deployments the depth remained with in this range. The wind speed range is selected to be 2 to 30 m/s; the latter value is based on Table 4 9. During 2002 2008 this value was exceeded only 11 times, and thus represents a reasonable upper limit. It should be pointed out that the uncertaint y of SSC prediction increases with speeds greater than about 16 m/s the maximum sustained wind speed measured during the study. The peak value was 22.8 m/s. For all five depths, values of the bed shear stresses ( w, c and cw) and SSC at the top -most an d the bottom -most elevations are given in Tables 4 10, 4 11 and 4 12, respectively, at selected wind speeds of 5, 10, 15, 15.9, 20, 25 and 30 m/s. The tables for SSC also include values based on the upper and lower bound derived from Eqs. (4.38) and (4.39) The full set of plots of SSC at 18.38 m and 18.88 m elevation are given in Figures 4 34 and 4 35, respectively. As seen, SSC becomes higher with decreasing water depth at both elevations. The highest difference between water depths of 0.75 m and 2.0 m is 1.9 kg/m3 and 1.1 kg/m3 at 18.38 m and 18.88 m, respectively. In other words, and as expected, a change in water depth induces a greater change in concentration at the lower level than at the upper one. The difference in concentration at two water depths is more noticeable during storm period s than under calm conditions. For example, at 2 m/s wind (which occurred on 01/17/08), SSC values at 18.38 m would be 0.03 kg/m3 and 0.02 kg/m3 at the assumed water depths of 0.5 m and 2.0 m, respectively, i.e. a dif ference of 0.0 1 kg/m3. At 15.8 m/s (on 01/18/08), the

PAGE 76

76 respective values would be 3.93 kg/m3 and 1.15 kg/m3. In other words the difference is 2.78 kg/m3. In general, SSC at a given water depth and elevation is dependent on the combined wave current stress in accordance with Eq. (4.37). The relative effects of waves and current on shear stress, and therefore on SSC, can be identified from the calculated values of w, c cw. For example, during the highest wind speed (15.8 m/s) within Deployment 06 (water depth 1.29 m), w = 0. 0 13 Pa, c = 0.0132 Pa and cw = 0.033 Pa. Thus w/ c = 0.98, which means that both shear stresses would be about equal At the mean w ind speed of 4 m/s (which is close to the exact value, 4.2 m/s during the study ), w = 4.41108 Pa, c = 8.5104 Pa and cw = 8.53104 Pa. Thus the effect of current is dominant. In water depth of 1.29 m, w exceeds c when wind speed is greater than ab out 15.8 m/s (Table 4 10). At a sustained wind speed of 30 m/s w = 0.226 Pa, c = 0.048 Pa and cw = 0.297 Pa, which indicates a strongly wave dominated environment. At the high water depth of 2 m the effect of waves is generally less than that of current except when the wind speed rises to 30 m/s. If the depth of water in the above case were to be hypothetically reduced to 0.5 m, the percent contributions of w and c to the combined shear stress at 10 m/s would be about equal and at 15.8 m/s would be 77% and 23%, respectively. At the mean wind speed of 4 m/s the corresponding values would be 13% and 87%. This indicates that the roles of waves and current would switch within the range of observed wind speed in the lake.

PAGE 77

77 Table 4 1 Weeks corresponding to parametric values Depl oy ment No. Week Dates Depl oy ment No. Week Dates 0 1 1 07/30/07 08/05/07 0 7 32 03/03/08 03/09/08 2 08/06/07 08/12/07 33 03/10/08 03/16/08 3 08/13/07 08/19/07 34 03/17/08 03/23/08 4 08/20/07 08/26/07 35 03/24/08 03/30/08 0 2 5 08/27/07 09/02/07 36 03/31/08 04/06/08 6 09/03/07 09/09/07 37 04/07/08 04/13/08 7 09/10/07 09/16/07 38 04/14/08 04/20/08 0 3 8 09/17/07 09/23/07 39 04/21/08 04/27/08 9 09/24/ 07 09/30/07 40 04/28/08 05/04/08 10 10/01/07 10/07/07 0 8 41 05/05/08 05/11/08 11 10/08/07 10/14/07 42 05/12/08 05/18/08 0 4 12 10/15/07 10/21/07 43 05/19/08 05/25/08 13 10/22/07 10/28/07 44 05/26/08 06/01/08 14 10/29/07 11/04/07 45 06/02/08 06/08/08 15 11/05/07 11/11/07 46 06/09/08 06/15/08 16 11/12/07 11/18/07 0 9 47 06/16/08 06/22/08 17 11/19/07 11/25/07 48 06/23/08 06/29/08 18 11/26/07 12/02/07 49 06/30/08 07/06/08 0 5 19 12/03/07 12/09 /07 50 07/07/08 07/13/08 20 12/10/07 12/16/07 51 07/14/08 07/20/08 21 12/17/07 12/23/07 52 07/21/08 07/27/08 22 12/24/07 12/30/07 53 07/28/08 08/03/08 23 12/31/07 01/06/08 54 08/04/08 08/10/08 24 01/07/08 01/13/08 55 08/ 11/08 08/17/08 0 6 25 01/14/08 01/20/08 56 08/18/08 08/24/08 26 01/21/08 01/27/08 0 10 57 08/25/08 08/31/08 27 01/28/08 02/03/08 58 09/01/08 09/07/08 28 02/04/08 02/10/08 59 09/08/08 09/14/08 29 02/11/08 02/17/08 30 0 2/18/08 02/24/08 31 02/25/08 03/02/08

PAGE 78

78 Table 4 2 Weekly maximum, mean and minimum wind and waves at UF0 UF0 Station Depl. Parameters Weeks Wind Speed (m/s) Wave Height (m) Wave Period (s) Max Mean Min Max M ean Min Max Mean Min 0 1 1 12.7 3.8 0.1 2 3 9.6 3.2 0.1 4 12.3 3.5 0.1 0 2 5 12.7 3.0 0.1 6 12.1 3.9 0.6 7 0 3 8 0.41 0.14 0.05 0.83 0.73 0.6 0 9 12.2 3.8 0.1 0.23 0.13 0.06 0.91 0.77 0.65 10 11.0 4.3 0.1 0.21 0.12 0.07 0.88 0.77 0.63 11 0 4 12 0.16 0.11 0.06 0.81 0.67 0.57 13 8.6 4.0 0 0.22 0.10 0.07 0.82 0.70 0.61 14 14.0 5.9 0.8 0.23 0.11 0.07 0.86 0.73 0.62 15 0.14 0.09 0.05 0.81 0.72 0.65 16 17 18 0 5 19 20 0.31 0.11 0.05 0.70 0.62 0.51 21 0.21 0.10 0.06 0.73 0.64 0.54 22 0.18 0.09 0.04 0.68 0.62 0 .57 23 0.39 0.13 0.05 0.83 0.70 0.59 24 0 6 25 26 0.27 0.12 0.05 0.84 0.73 0.63 27 7.2 3.3 0.2 0.28 0.11 0.06 0.81 0.73 0.64 28 0.22 0.12 0.05 0.82 0.73 0.61 29 0.29 0.11 0.05 0.80 0. 70 0.55 30 31 0 7 32 0.22 0.12 0.07 0.92 0.70 0.62 33 10.5 3.9 0.1 0.21 0.10 0.07 0.83 0.72 0.65 34 9.9 5.3 0 0.31 0.14 0.08 0.86 0.74 0.64 35 12.0 3.9 0.1 0.17 0.10 0.06 0.85 0.72 0.63 36 0.30 0 .14 0.05 0.77 0.69 0.62 37 0.20 0.11 0.07 0.75 0.69 0.62 38 11.0 4.8 0.1 0.21 0.12 0.08 0.86 0.71 0.63 39 9.0 4.1 0.3 0.19 0.12 0.07 0.68 0.63 0.59 40 0 8 41 13.1 5.2 0.1 0.10 0.06 0.95 0.77

PAGE 79

79 42 0.08 0.04 0.01 0. 96 0.72 43 44 45 22.8 3.8 0 46 11.4 2.8 0.1 0 9 47 48 14.8 3.0 0.1 0.21 0.09 0.06 0.71 0.66 0.61 49 13.2 2.9 0 0.20 0.09 0.06 0.68 0.64 0.60 50 12.2 3.2 0 0.11 0 .08 0.06 0.72 0.68 0.60 51 0.10 0.08 0.03 0.74 0.69 0.65 52 0.13 0.08 0.04 0.79 0.73 0.70 53 11.2 3.9 0 0.10 0.08 0.07 0.76 0.71 0.68 54 12.3 3.5 0.1 0.16 0.08 0.06 0.78 0.69 0.64 55 56 16.9 7.8 0.8 0.20 0.08 0.06 0.96 0.76 0.60 0 10 57 11.2 3.5 0 0.11 0.07 0.04 1.01 0.89 0.82 58 10.9 4.6 0 0.09 0.07 0.05 0.98 0.91 0.85 59 11.6 4.8 0.1 0.09 0.07 0.06 0.98 0.93 0.86 Maximum 22.8 7.8 0.8 0.41 0.14 0.08 1. 0 1 0.93 0.86 Minimum 7.2 2.8 0 0.08 0.04 0 .01 0.68 0.62 0 .51 Table 4 3 Weekly maximum, mean and minimum currents at different elevations at UF0 UF0 Station Depl. Parameters Weeks Current Velocity (cm/s) Top Middle Bottom Max Mean Min Max Mean Min Max Mean Min Elev. 18.51 (m) Elev. 18.31 (m) 0 1 1 11.9 2.2 0.2 6.2 1.4 0.1 2 12.4 2.3 0.3 3 9.6 2.5 0 4 21.0 2.9 0.3 0 2 5 6 10.8 2.4 0.1 7 Elev. 18.83 (m) Elev. 18 .63 (m) Elev. 18.33 (m) 0 3 8 9 10 11 0 4 12 7.6 2.0 0 7.6 2.0 0 6.9 1.8 0 13 8.0 1.6 0 8.6 1.6 0 7.2 1.6 0 14 15 4.5 1.2 0 4.8 1.3 0 4.3 1.3 0

PAGE 80

80 16 17 5.2 1.2 0 5.5 1.1 0 5.8 1.0 0 18 4.0 0.9 0 5.1 0.8 0 4.8 0.7 0 0 5 19 20 21 7.2 1.2 0 22 23 24 Elev. 18.88 (m) Elev. 18.68 (m) Elev. 18.38 (m) 0 6 25 26 27 28 29 30 31 Elev. 18.43 (m) Elev. 18.33 (m) 0 7 32 16.4 5.1 0.1 2 9.7 7.5 0.2 33 11.2 4.0 0.1 32.0 7.8 0.2 34 15.9 4.0 0.1 18.3 6.8 0.3 35 22.1 5.5 0.2 23.7 6.9 0.6 36 22.7 7.3 0.5 23.0 6.2 0.3 37 17.3 7.1 0 18.7 4.4 0 38 21.6 5.9 0.3 22.3 6.2 0.2 39 15.6 5.0 0.2 22 .1 6.1 0.3 40 Elev. 18.83 (m) Elev. 18.63 (m) Elev. 18.33 (m) 0 8 41 8.7 2.1 0 10.0 2.1 0 10.6 1.8 0 42 14.2 2.6 0 15.2 2.5 0 9.1 2.0 0 43 16.3 2.9 0 16.5 2.5 0 11.9 1.9 0 44 8.9 2.7 0 9.6 2.5 0 8.0 1.9 0 45 18.5 3.4 0 19. 0 3.3 0 12.3 2.1 0 46 22.6 3.1 0 21.9 2.9 0 16.0 2.1 0 Elev. 18.31(m) 0 9 47 48 32.3 6.0 0.1 49 34.8 6.2 0.2 50 35.8 11.1 0.2 51 52 53 54 55 56

PAGE 81

81 Elev. 18.54 (m) Elev. 18.34 (m) Elev. 18.14 (m) 0 10 57 58 6.3 2.1 0 5.7 2.0 0.1 6.4 2.2 0.1 59 19.1 3.1 0.2 20.7 3.0 0.1 19.9 2.7 0 Maximum 22.6 3.4 0.2 22.7 7.3 0.5 35.8 11.1 0.6 Minimum 4 0.9 0 4.8 0.8 0 4.3 0.7 0 Table 4 4 Weekly maximum, mean and minimum temperature, salinity and WSE at UF0 UF0 Station Depl. Parameters Weeks Temperature ( Salinity Water Surface Elev. (m) Max Mean Min Max Mean Min Max Mean Min 0 1 1 33.2 29.2 26.9 0.21 0.20 0.19 19.53 19.46 19.39 2 35.5 31.0 29.6 0.21 0.20 0.19 19.50 19.45 19.40 3 33.8 30.2 28.1 0.21 0.20 0.20 19.48 19.43 19.38 4 32.5 29.9 28.2 0.22 0.21 0.20 19.44 19.4 0 19.33 0 2 5 6 7 0 3 8 30.6 27.0 24.7 0.21 0.21 0.20 19.50 19.42 19.34 9 30.7 27.7 25.3 0.21 0.20 0.19 19.51 19.47 19.42 10 29.1 26.8 24.3 0.21 0.20 0.19 19.51 19.47 19.41 11 0 4 12 28.8 26.1 23.4 0.21 0.20 0.20 19.51 19.44 19.39 13 30.0 25.0 22.5 0.21 0.20 0.19 19.51 19.46 19.39 14 24.8 22.9 20.4 0.22 0.21 0.20 19.53 19.47 19.40 15 21.8 19.0 16.2 0.23 0.22 0.20 19.52 19.48 1 9.45 16 17 18 0 5 19 20 24.1 22.0 19.2 0.22 0.21 0.20 19.46 19.39 19.25 21 19.4 16.1 12.9 0.22 0.21 0.20 19.48 19.41 19.31 22 23.0 19.6 17.7 0.22 0.21 0.21 19.43 19.39 19. 35 23 22.6 13.9 7.0 0.22 0.21 0.20 19.57 19.47 19.37 24 0 6 25 26 17.7 15.0 11.6 0.22 0.21 0.20 19.55 19.48 19.42 27 21.3 16.9 13.4 0.21 0.20 0.19 19.51 19.47 19.42 28 24.0 20.7 18.1 0.20 0.20 0.18 19.51 19.4 5 19.39 29 21.0 18.0 15.4 0.20 0.20 0.19 19.51 19.44 19.32 30 31 0 7 32 22.2 19.5 16.2 0.21 0.20 0.20 19.56 19.44 19.36

PAGE 82

82 33 22.1 18.6 15.3 0.21 0.20 0.20 19.59 19.49 19.40 34 24.2 21.7 19.5 0.22 0.21 0.20 19.55 19.48 19.39 35 24.3 19.2 15.5 0.23 0.21 0.20 19.56 19.47 19.41 36 26.6 23.9 20.8 0.22 0.21 0.20 19.47 19.44 19.38 37 26.6 24.1 22.2 0.21 0.20 0.19 19.49 19.44 19.38 38 25.0 19.8 15.4 0.20 0.20 0.19 19.49 19.44 19.39 39 27.0 23.8 21.5 0.21 0.20 0.19 19.41 19.38 19.35 40 0 8 41 32.9 27.0 23.8 0.22 0.21 0.19 19.33 19.27 19.19 42 31.2 25.6 22.3 0.23 0.22 0.21 19.30 19.24 19.17 43 30.6 26.7 24.8 0.24 0.22 0.21 19.25 19.20 19.15 44 36.5 27.4 23.9 0.23 0.22 0.21 19.28 19.25 19. 22 45 39.9 29.3 24.6 0.25 0.22 0.18 19.3 0 19.25 19.20 46 39.8 29.0 23.6 19. 28 19.25 19.20 0 9 47 48 30.6 27.7 25.8 0.22 0.21 0.20 19.36 19.33 19.28 49 31.1 27.9 26.2 0.22 0.21 0.20 19.35 19.32 19.27 50 33.6 28.6 26.7 0.21 0.20 0.19 19.40 19.36 19.29 51 30.4 28. 4 27.1 0.21 0.19 0.19 19.46 19.40 19.31 52 32.1 29.6 27.8 0.20 0.19 0.19 19.46 19.43 19.37 53 30.9 28.7 26.9 0.20 0.19 0.18 19.43 19.41 19.37 54 32.5 29.8 28.3 0.20 0.19 0.19 19.44 19.39 19.32 55 56 28.9 25.9 24.0 0.20 0.19 0.17 19.78 19.53 19.34 0 10 57 31.4 28.6 26.8 0.18 0.17 0.16 19.82 19.79 19.75 58 29.8 27.9 26.3 0.18 0.17 0.16 19.86 19.81 19.72 59 30.2 28.3 27.0 0.18 0.17 0.17 19.90 19.85 19.80 Maximum 39.9 31 29.6 0.25 0.22 0.21 19.90 19.85 19.80 Minimum 17.7 13.9 7 0.18 0.17 0.16 19.25 19.20 19.15 Table 4 5 W eekly max imum mean and min imum SSC from ADCP at different elev. at UF0 UF0 Station Depl. Parameters Weeks SSC (kg/m 3 ) from ADCP Top Middle Bottom Max Mean Min Max Mean Mi n Max Mean Min Elev. 18.51 (m) Elev. 18.31 (m) 0 1 1 0.18 0 0 1.05 0.15 0.01 2 1.05 0.02 0 3 1.31 0.02 0 4 0 0 2 5 6 0.27 0.01 0 1.56 0.36 0 7

PAGE 83

83 Ele v. 18.83 (m) Elev. 18.63 (m) Elev. 18.33 (m) 0 3 8 9 1.10 0 0 10 0.24 0 0 11 0 4 12 1.41 0 0 0.13 0 0 13 1.40 0.01 0 0.58 0 0 0.30 0.01 0 14 15 0.38 0 0 0.10 0 0 0.02 0 0 16 1.75 0.02 0 1.13 0.02 0 0.73 0.02 0 17 0.19 0 0 0.30 0 0 0.24 0 0 18 0.58 0 0 0.10 0 0 0.08 0.01 0 0 5 19 20 21 0.57 0.11 0 22 23 24 Elev. 18.88 (m) Elev. 18.68 (m) Elev. 18.38 (m) 0 6 25 26 0.90 0.17 0 0.58 0.13 0 0.46 0.10 0 27 0.46 0.07 0 0.30 0.05 0 0.24 0.03 0 28 0.15 0.03 0 0.10 0.02 0 0.06 0.01 0 29 1.12 0.02 0 0.90 0.02 0 0.58 0.01 0 30 0.24 0.02 0 0.15 0.01 0 0.08 0 0 31 Elev. 18.43 (m) Elev. 18.33 (m) 0 7 32 0.81 0.50 0.01 1.01 0.66 0.02 33 0.81 0.41 0 1.01 0.59 0.01 34 0.81 0.64 0.27 1.01 0.72 0.27 35 1.01 0.60 0.17 0.81 0.49 0.22 36 0.81 0.26 0.03 0.81 0.50 0.09 37 0.14 0.05 0.01 0.65 0.37 0.11 38 0.34 0.06 0.01 0.81 0.57 0.04 39 0.09 0.02 0 0.65 0.41 0.01 40 Elev. 18.83 (m) Elev. 18.63 (m) Elev. 18.33 (m) 0 8 41 1.57 0. 04 0 1.01 0.02 0 0.34 0.01 0 42 1.57 0.04 0 1.01 0.02 0 0.65 0.11 0 43 44 0.34 0.01 0 0.14 0.01 0 0.09 0.01 0 45 46 Elev. 18.31(m)

PAGE 84

84 0 9 47 48 1.01 0.19 0.01 49 1.25 0.13 0 50 1.25 0.18 0 51 52 53 54 55 56 Elev. 18.54 (m) Elev. 18.34 (m) Elev. 18.14 (m) 0 10 57 58 0.88 0.09 0 0.37 0.06 0 1.71 0.02 0.01 59 Maximum 1.75 0.17 0 1.41 0.64 0.27 1.71 0.72 0.27 Minimum 0.15 0 0 0.09 0 0 0.02 0 0 Table 4 6 Weekly maximum, mean and minimum SSC from OBS at UF0 UF0 Station Depl. Parameters Weeks SSC (kg/m 3 ) from OBS 3 Depl. Parameters Weeks SSC (kg/m 3 ) from OBS 5+ Max Mean Min Max Mean Min 0 2 5 0 5 19 6 0.23 0.09 0.02 20 7 0.28 0.05 0 21 0.69 0.03 0 0 3 8 0.19 0.0 2 0 22 1.60 0.01 0 9 23 10 24 0.1 0.01 0 11 0 9 47 48 1.72 0.02 0 49 1.18 0.01 0 50 1.55 0.03 0 Maximum 0.28 0.09 0.02 Maximum 1.72 0.0 3 0 Minimum 0.19 0.02 0 Mini mum 0.1 0.01 0

PAGE 85

85 Table 4 7 Critical wind speed for resuspension Deployment No. Critical wind speed (m/s) for resuspension Deployment No. Critical wind speed (m/s) for resuspension 0 1 4.0 0 8 6.5 0 2 4.0 0 9 0 3 4.0 0 10 4 0 4 4.5 1 1 4 0 5 5 .5 1 2 0 6 2 1 5 0 7 Table 4 8 Coefficients a m n and I from F84 MS90 and HT91 Equation coefficients F84 MS90 HT91 1a 0.06 0.01 0.07 2a 1.70 1.84 1.87 3a 0.29 0.58 0.34 4a 0.29 0.22 0.12 1m 0.67 0.63 0.72 2m 0.29 0.09 0.33 3m 0.09 0.23 0.08 4m 0.42 0.02 0.34 1n 0.75 0.82 0.78 2n 0.27 0.30 0.23 3n 0.11 0.19 0.12 4n 0.02 0.21 0.12 I 0.80 0. 67 0.82

PAGE 86

86 Table 4 9 Cumulative density function of wind speed Wind s peed (m/s) CDF 0 0.00620 0.534 0.05117 1.094 0.12301 1.654 0.20664 2.214 0.29805 2.774 0.39743 3.334 0.49984 3.894 0.59862 4.454 0.68888 5.014 0.76635 5.574 0.82960 6.134 0.87838 6.693 0.91473 7.253 0.94161 7.813 0.96013 8.373 0.97271 8.933 0.98079 9.493 0.98663 10.053 0.99068 10.613 0.99331 15.000 0.99880 20.000 0.99945 30.000 0.99948 40.000 0.99949 54.260 0.99950

PAGE 87

87 Table 4 10. Bed shear stresses ( w, c and cw) for selected water depths and wind speeds Shear stress (Pa) Wind s peed (m/s) Water d epth (m) 0.5 0.75 1 .0 1.29 1.5 2 .0 w 2 0 0 0 0 0 0 5 0 0 0 0 0 0 10 1.13E 02 6.37E 03 2.73E 03 0 0 0 15 4.88E 02 3.45E 0 2 2.13E 02 9.85E 03 4.98E 03 0 15.8 5.80E 02 4.18E 02 2.66E 02 1.30E 02 6.84E 03 1.10E 03 20 1.27E 01 9.81E 02 7.06E 02 4.20E 02 2.62E 02 6.55E 03 25 2.55E 01 2.08E 01 1.62E 01 1.11E 01 7.80E 02 2.72E 02 30 4.41E 01 3.71E 01 3.04E 01 2.26E 01 1.72E 01 7.46E 02 c 2 2.76E 04 2.46E 04 2.27E 04 2.12E 04 2.04E 04 1.90E 04 5 1.72E 03 1.53E 03 1.42E 03 1.33E 03 1.28E 03 1.19E 03 10 6.89E 03 6.14E 03 5.68E 03 5.31E 03 5.11E 03 4.76E 03 15 1.55E 02 1.38E 02 1.28E 02 1.20E 02 1.15E 02 1.07E 02 15.8 1.72E 02 1.53E 02 1.41E 02 1.32E 02 1.27E 02 1.19E 02 20 2.76E 02 2.46E 02 2.27E 02 2.12E 02 2.04E 02 1.90E 02 25 4.31E 02 3.84E 02 3.55E 02 3.32E 02 3.19E 02 2.97E 02 30 6.20E 02 5.52E 02 5.11E 02 4.78E 02 4.60E 02 4.28E 02 cw 2 2.85E 04 2.46E 04 2.27E 04 2.12E 04 2.04E 04 1.90E 04 5 2.95E 03 1.98E 03 1.54E 03 1.35E 03 1.28E 03 1.19E 03 10 2.21E 02 1.57E 02 1.08E 02 7.45E 03 6.15E 03 4.93E 03 15 7.33E 02 5.59E 02 4.08E 02 2.75E 02 2.11E 02 1.33E 02 15.8 8.51E 02 6.55E 02 4.83E 02 3.27E 02 2.50E 02 1.54E 02 20 1.70E 01 1.36E 01 1.05E 01 7.43E 02 5.69E 02 3.25E 02 25 3.22E 01 2.66E 01 2.16E 01 1.61E 01 1.26E 01 7.07E 02 30 5.37E 01 4.54E 01 3.80E 01 2.97E 01 2.41E 01 1.39E 01 w c 2 2.36E 03 1.93E 05 6.72E 08 5.62E 11 2.72E 13 5.67E 19 5 3.19E 01 8.14E 02 1.13E 02 7.10E 04 7.87E 05 2.85E 07 10 1.64E+00 1.04E+00 4.81E 01 1.41E 01 4.88E 02 2.70E 03 15 3.15E+00 2.50E+00 1.66E+00 8.24E 01 4.33E 01 6.74E 02 15.8 3 .38E+00 2.73E+00 1.88E+00 9.80E 01 5.37E 01 9.29E 02 20 4.60E+00 4.00E+00 3.11E+00 1.98E+00 1.28E+00 3.44E 01 25 5.92E+00 5.41E+00 4.57E+00 3.33E+00 2.44E+00 9.13E 01 30 7.11E+00 6.71E+00 5.94E+00 4.72E+00 3.74E+00 1.74E+00

PAGE 88

88 Table 4 11. SSC at 18.38 m elevation for the selected water depths and wind speeds SSC (kg/m 3 ) at elev. 18.38 m Wind s peed (m/s) Water d epth (m) 0.5 0.75 1 .0 1.29 1.5 2 .0 Best -fit values 2 0.03 0.03 0.03 0.02 0.02 0.02 5 0.09 0.07 0.06 0.06 0.06 0.06 10 1.39 1.16 0.93 0.57 0.20 0.11 15 3.38 2.63 2.04 1.57 1.35 1.06 15.8 3.93 3.04 2.32 1.74 1.48 1.15 20 8.26 6.49 4.91 3.42 2.67 1.74 25 14.60 12.66 10.51 7.78 5.98 3.27 30 19.66 18.02 16.26 13.78 11.63 6.62 Upper bound values 2 0.03 0.03 0.03 0.02 0.02 0.02 5 0.09 0.07 0.06 0.06 0.06 0.06 10 1.51 1.30 1.13 0.96 0.84 0.63 15 3.59 2.79 2.16 1.68 1.47 1.23 15.8 4.17 3.22 2.46 1.86 1.60 1.29 20 8.93 6.97 5.24 3.63 2.83 1.85 25 16.02 13.85 11.45 8.40 6.41 3.46 30 21.53 19.76 17.85 15.10 12.70 7.12 Lower bound values 2 0.03 0.03 0.03 0.02 0.02 0.02 5 0.09 0.07 0.06 0.06 0.06 0.06 10 1.20 0.93 0.57 0.13 0.12 0.11 15 3.06 2.38 1.84 1.38 1.16 0.79 15.8 3.55 2.75 2.10 1.56 1.30 0.92 20 7.27 5.77 4.41 3.10 2.42 1.55 25 12.62 10.97 9.17 6.87 5.33 2.96 30 17.01 15.57 14.04 11.91 10.10 5.88

PAGE 89

89 Table 4 12. SSC at 18.88 m elevation for the selected water depths and wind speeds SSC (kg/m 3 ) at elev. 18.88 m Wind s peed (m/s) Water d epth (m) 0.5 0.7 5 1 .0 1.29 1.5 2 .0 Best -fit values 2 0.00 0.00 0.00 0.00 0.00 5 0.01 0.01 0.01 0.01 0.01 10 0.50 0.33 0.14 0.04 0.02 15 1.37 1.07 0.79 0.65 0.43 15.8 1.56 1.22 0.90 0.74 0.49 20 2.90 2.33 1.73 1.39 0.90 25 4.85 4.18 3.33 2.72 1.6 6 30 6.71 6.06 5.21 4.53 2.94 Upper bound values 2 0.00 0.00 0.00 0.00 0.00 5 0.01 0.01 0.01 0.01 0.01 10 0.71 0.54 0.38 0.28 0.17 15 1.68 1.32 1.01 0.86 0.64 15.8 1.91 1.50 1.13 0.95 0.70 20 3.60 2.88 2.12 1.70 1.13 25 6.13 5.27 4.15 3.37 2.04 30 8.46 7.66 6.59 5.71 3.66 Lower bound values 2 0.00 0.00 0.00 0.00 0.00 5 0.01 0.01 0.01 0.01 0.01 10 0.30 0.14 0.02 0.02 0.02 15 1.02 0.79 0.56 0.43 0.23 15.8 1.17 0.91 0.65 0.51 0.29 20 2.14 1.74 1.30 1.04 0.65 25 3.53 3.06 2.45 2.02 1.25 30 4.90 4.41 3.79 3.30 2.18

PAGE 90

90 0 1 2 3 x 105 Wind SpeedPower Spectral Density 0 1 2 x 105 Temperature 0 0.5 1 Salinity 0 10 20 30 Water Surface Elev. 0 1 2 x 104 Velocity 0 50 100 Wave Height 0 50 100 Wave Period Elev. 18.83m 0 5000 10000 VelocityElev. 18.63m 0 5000 10000 VelocityElev. 18.33m 0 10 20 SSCADCP at Elev. 18.83m 0 10 20 30 SSCOBS-3 at Elev. 18.66m 0 500 SSCADCP at Elev. 18.63m 0 0.5 1 1.5 2 2.5 0 500 Frequency (1/days)SSCADCP at Elev. 18.33m Figure 4 1 Power spectral density (PSD) of all data for Deployment 0 3 For any parameter with 2 /Hz.

PAGE 91

91 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 x 10-4 Frequency (Hz)PSD of Pressure Figure 4 2 PSD for wind waves. Pressure was measured in k Pa. 0 0.02 0.04 0.06 0.08 Max PSD(m2/Hz) Max PSD Frequency 0 0.2 0.4 Frequency 0~0.5HzA) 09/15 09/20 09/25 09/30 10/05 10/10 0 0.02 0.04 0.06 0.08 Max PSD(m2/Hz)Day of 2007 0.5 0.8 1.1 1.4 1.7 Frequency 0.5~2HzB) Figure 4 3 Time-series of maximum PSD for water level A) At t he low -frequency (less than 0.5 Hz) range. B) At the high -frequency (greater than 0.5 Hz) range.

PAGE 92

92 0 0.5 1 1.5 2 2.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Frequency(1/days)Coherence Figure 4 4 Coherence between wind speed and wave height. 0 0.05 0.1 0.15 0.2 0.25 0.3 Singificant Wave Height(m)A) R2=0.6274 0 2 4 6 8 10 12 0.6 0.7 0.8 0.9 Wind Speed(m/s)Singificant Wave Period(s)B) R2=0.2919 DATA Best fit line Figure 4 5 Variations of A) the signif icant wave height and B) the period with wind speed. Since the wave height at 0 wind speed must be zero, data points corresponding to very low wind speeds (< 2 m/s) have not been included in linear regression.

PAGE 93

93 0 0.5 1 1.5 2 2.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Frequency(1/days)Coherence Elev. 18.83m Elev. 18.63m Elev. 18.33m Figure 4 6 Cohe rence between wind speed and current. Figure 4 7 Variation of current with wind speed during Deployment 0 3. A) At Elev. 18.83 m. B) At Elev. 18.63 m. C) At Elev. 18.33m.

PAGE 94

94 Figure 4 8 Variation o f current with wind speed during Deployment 0 5. A) At Elev. 18.83 m. B) At Elev. 18.63 m. C) At Elev. 18.33 m. 0 0.5 1 1.5 2 2.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Frequency(1/days)Coherence Figure 4 9 Coherence between wind speed and SSC from OBS 3 at 18.66 m elevation.

PAGE 95

95 0 0.5 1 1.5 2 2.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Frequency(1/days)Coherence Elev. 18.83m Elev. 18.63m Elev. 18.33m Figure 4 10. Coherence between wind speed and SSC from the ADCP. Figure 4 11. Variation of SSC at 18.63 m elevation from ADCP with wind speed.

PAGE 96

96 Figure 4 12. Variation of SSC at 18. 3 3 m elevation from ADCP with wind speed. 0 2 4 6 8 10 12 14 16 18 20 22 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Wind Speed(m/s)Wave Height(m)A) Best fit line Eq. 4.14 Eq. 4.16 0 2 4 6 8 10 12 14 16 18 20 22 0 0.5 1 1.5 2 2.5 3 Wind Speed(m/s)Wave Period(s)B) Best fit line Eq. 4.15 Eq. 4.17 Figure 4 13. Relationships between A) significant wave height, B) period and wind speed; best fit data line and equations.

PAGE 97

97 Figure 4 14. Schem atic drawing of the relationship between wind stress and current stress in the lake. 0 0.1 0.2 1.40 m < h Y=0.004319X R2=0.0000 0 0.1 1.15 m < h 1.20 m Y=0.005995X R2=0.1064 0 0.1 1.10 m < h 1.15 mCurrent speed, uc(m/s)Y=0.003245X R2=0.2585 0 2 4 6 8 10 12 14 0 0.1 h 1.10 m Wind speed, U (m/s) Y=0.004351X R2=0.1797 Figure 4 15. Measured variation of current speed with uc with wind speed U at station UF0. R2 values indicate weak correlations. x S S S wind c h Hydrostatic pressure Hydrostatic pressure Current

PAGE 98

98 -150 -100 -50 0 50 100 150 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Directional anomaly(Current Direction-Wind Direction)Cumulative probability Elev. 19.01m Elev. 18.31m Figure 4 16. Cumulative distribution of the directional anomaly between wind speed and water current at two elevations. Figure 4 17. Schematic of s ediment concentration zones and resuspension modes (adapted from Jain 2007). Particl e settling d Dilute suspension layer (DSL ) Particle settling and coalescence with fluid mud Entrainment Erosion Benthic suspension layer (BSL) Benthic nepheloid (fluid mud) layer (BNL) Settling and coalescence Entrainment Hin dered settling Consolidating bed (CB) Erosion Settling and deposition Erosion Bed Suspension Particle settling and deposition on bed

PAGE 99

99 09/04 09/05 09/06 09/07 09/08 -1 -0.5 0 0.5 1 x 10-4 Horizontal SSC gradient(SSC/m) at Water Depth 0.35mDay of 2008 CUF0CUF2 Figure 4 18. An example of measured time -series of horizontal SSC gradient (kg/m4) in the lake. 09/04 09/05 09/06 09/07 09/08 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 Day of 2008Vertical SSC gradient(SSC/m) at UF0 Figure 4 19. Measured vertical gradient of concentration (kg/m4) at UF0. Po sitive gradient indicates higher concentration at the lower sensor (elevation 18.14 m) than at the upper sensor (18.54 m).

PAGE 100

100 09/04 09/05 09/06 09/07 09/08 -0.5 0 0.5 1 Day of 2008Vertical SSC gradient(SSC/m) at UF2 Figure 4 20. Measured vertical gradient of concentration (kg/m4) at UF2. Positive gradient indicates higher concentration at the lower sensor (elevation 18.50 m) than at the upper sensor (19.20 m). Figure 4 21. Schematic drawing showing the variation of sediment concentration with depth in the lake. S SC refers to concentration above the elevation z = za. CB BNL BSL DSL z = 0 z = z a C b C a C ( z t ) C z = z b C c z C U = U L Hindered settling Consolidation Top of core Free settling Flocculation sett ling Entrainment C a C c C m U = U H z

PAGE 101

101 10-1 100 101 102 10-8 10-7 10-6 10-5 10-4 10-3 10-2 a = b = m = n = c1 = 0.8 2.7 2.8 1 0.1 Wsf = 3.1e-004 (m/s) Ws = aCn/(C2+b2)mSediment Concentration (kg/m3)Settling Velocity (m/s) Figure 4 22. Settling velocity variation with SSC (= C) for lake sediment Red asterisks are from the image analysis of Dr. Andrew Manning. Blue circles are from laborat ory settling column tests (Chapter 3). The quantity wsf is the free settling velocity (below 0.1 kg/m3). Figure 4 23. Sediment dry bulk density versus organic matter and biogenic silica sediment composition data for the LA 3 1 08site. The dashed line represents the critical value used by Schelske (1997) to delineate the top floc layer (BNL). The site is shown in Figure 4.24 (courtesy Dr. John Jaeger). Floc dry density

PAGE 102

102 Figure 4 24. Google image of Lake Apopka showi ng the 1996 sampling sites occupied by Schelske (1997) and the locations of the four 2007 sampling areas (courtesy Dr. John Jaeger). Figure 4 25. Stress versus dry density (courtesy Dr. John Jaeger).

PAGE 103

103 Figure 4 26. Profile of Beryllium 7 radioisotope at LA Tower 07a (courtesy Dr. John Jaeger). -10 0 10 20 30 40 50 60 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 CDFWind Speed(m/s) mean(x) = 3.85046 var(x) = 4.85414 Figure 4 27. Cumulative distribution function plot for wind data collected from 01/22/02 to 11/06/08 at UF0 by SJRWM D. Nominal thickness of stirred floc layer

PAGE 104

104 0 2.5 5 x 10-3 Wind Speed(m/s)w(Pa)Water Depth 1.26m 0 0.005 0.01 Wind Speed(m/s)c(Pa)Water Depth 1.26m 12/06 12/11 12/16 12/21 12/26 12/31 01/05 01/10 01/15 0 0.005 0.01 Wind Speed(m/s)cw(Pa)Water Depth 1.26m Figure 4 28. Time -series of shear stresses during Deployment 0 5. 0 0.1 0.2 0.3 0.4 0.5 Wind Speed(m/s)w(Pa)A) Water Depth 2.0m Water Depth 1.0m Water Depth 0.5m 0 0.025 0.05 0.075 Wind Speed(m/s)c(Pa)B) Water Depth 2.0m Water Depth 1.0m Water Depth 0.5m 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 0 0.2 0.4 Wind Speed(m/s)cw(Pa)C) Water Depth 2.0m Water Depth 1.0m Water Depth 0.5m Figure 4 29. Variation of shear stresses with water depths between wind speeds of 2 and 30 m/s. A) Wave shear stress. B) Current shear stress. C) Combined wave -current shear stress.

PAGE 105

105 0 0.5 1 1.5 2 2.5 3 3.5 4 x 10-3 0 0.2 0.4 0.6 0.8 1 x 10-3 u*cw(m/s)Ds 0Ds 0=0.6 10-2 u*cwDs 0=0.6756u*cw-1.29710-3Ds 0=0.5000u*cw-1.20010-3Ds 0=0.3419u*cw-9.67510-4 Figure 4 30. Variation of Ds 0 with cwu Mean trend and selected upper and lower bound lines. 0 0.5 1 1.5 2 Day of 2007 & 2008 Data by OBS-5+ Computed by the Best fit 0 0.5 1 1.5 Day of 2007 & 2008SSC(kg/m3) at Elev. 18.34m Computed by the Upper Bound 12/06 12/11 12/16 12/21 12/26 12/31 01/05 01/10 01/15 0 0.5 1 1.5 Day of 2007 & 2008 Computed by the Lower Bound Figure 4 31. Measured a nd simulated time -series of SSC at 18.34 m elevation during Deployment 0 5.

PAGE 106

106 0 0.5 1 1.5 2 Day of 2008 A) By ADCP Prediction 0 0.5 1 1.5 Day of 2008SSC(kg/m3) at Elev. 18.38mB) Upper Bound 01/18 01/23 01/28 02/02 02/07 02/12 02/17 02/22 02/27 0 0.5 1 1.5 Day of 2008 C) Lower Bound Figure 4 32. T ime -series of SSC at 18.38 m elevation during Deployment 0 -6. A) Comparison between measured and simulated SSC based on the best -fit me an relationship. B) Simulations based on the upper bound. C) Simulations based on the lower bound. 0 0.25 0.5 0.75 1 Day of 2008 A) By ADCP Prediction 0 0.25 0.5 0.75 Day of 2008SSC(kg/m3) at Elev. 18.88mB) Upper Bound 01/18 01/23 01/28 02/02 02/07 02/12 02/17 02/22 02/27 0 0.25 0.5 0.75 Day of 2008 C) Lower Bound Figure 4 33. T ime -series of SSC at 18.88 m elevation during Deployment 0 -6. A) Comparison between measured and simulated SSC b ased on the best -fit mean relationship. B) Simulations based on the upper bound. C) Simulations based on the lower bound.

PAGE 107

107 0 0.5 1 1.5 2 Day of 2008 Water Depth 0.50m 0 0.5 1 1.5 Day of 2008 Water Depth 0.75m 0 0.5 1 1.5 Day of 2008SSC(kg/m3) at Elev. 18.38mWater Depth 1.00m 0 0.5 1 1.5 Day of 2008 Water Depth 1.50m 01/18 01/23 01/28 02/02 02/07 02/12 02/17 02/22 02/27 0 0.5 1 1.5 Day of 2008 Water Depth 2.00m Figure 4 34. Simulated SSC variation with water depth at 18.38 m during Deployment 0 6. 0 0.5 1 1.5 Day of 2008 Water Depth 0.50m 0 0.5 1 Day of 2008 Water Depth 0.75m 0 0.5 1 Day of 2008SSC(kg/m3) at Elev. 18.88mWater Depth 1.00m 0 0.5 1 Day of 2008 Water Depth 1.50m 01/18 01/23 01/28 02/02 02/07 02/12 02/17 02/22 02/27 0 0.5 1 Day of 2008 Water Depth 2.00m Figure 4 35. Simulated SSC variation with water depth at 18.88 m during Deployment 0 6.

PAGE 108

108 CHAPTER 5 SUMMARY AND CONCLUSI ONS 5.1 Summary Water quality in many shallow aquatic systems is strongly influenced by the suspended solids. Resuspended s ediment input decreases water transparency which in turn causes reductions in vegetation and fish population. In lakes wind-driven water motion and waves are major causes of sediment resuspension, which is also dependent on water level. In this study t he p otential impacts of changing water level on the suspended sediment regime have been investigated for Lake Apopka in central Florida. In order to assess the spatial and temporal behaviors of SSC, instruments were deployed at stations referred to as UF0, UF1 and UF2 in the lake. Relying on the measured time -series of wind, waves, currents and SSC a simple analytic al model for local resuspension has been developed. The model relies on the assumption of short term (hourly time -scale) equilibrium between entra ining and settling sediment fluxes and is based on the sediment mass balance equation. The strength of this approach is in its ability to identify the component physical mechanisms that underlie the resuspension behavior of the lake. The model does not acc ount for the advective flux of suspended matter which appears to be is considerably smaller than the convective (vertical) fluxes. The model is not a substitute for a robust numerical code that can more faithfully generate temporal and spatial patterns of suspended sediment transport. During the period of measurement (July 25, 2007 to September 16, 2008) the usual meteorological condition at the lake was one of low winds; there were just a few significant events when SSC values recorded notable increases a bove the ambient level. This limitation must be borne in mind when assessing the significance of SSC predictions at wind speeds in

PAGE 109

109 excess of about 20 m/s. Following calibration and validation, the model has been used to predict the effects of high wind spe eds and lower as well as higher than present water levels on SSC. 5.2 Conclusions The main observations are as follows: 1 Lake Apopka is a wind-fetch limited aquatic body in which wind, currents and SSC dominantly oscillate at the solar diurnal frequency. Th e 12,500 ha lake is shallow, with a fairly even bottom; the mean depth is about 1.5 m with 0.5 m variability over a significant fraction of lake area. Two -meter deep areas generally occur in the middle. Discharges from the lake via Apo pka Beauclair Lock and Dam are believed to have negligible effect on SSC in the main body of the lake. 2 AT UF0 the water depth varied between 0.99 and 1.74 m during the study. The mean wind speed was about 4 m/s and the maximum was 22.8 m/s. The probabilit y of occurrence of a speed of 20 m/s is only 0. 055 %. The dominant wind direction during the study was from 60 3 At UF0, UF1 and UF2, where water depths were similar (bed elevations 18.16 m 18.16 m and 18.37 m, respectively), it was o bserved that there was a critical wind speed above which SSC increased. The speed range, from 4 to 6.5 m/s, was narrow. Since the mean speed during the study was only about 4 m/s, it appears that the lake could be characteristically at the threshold of res uspension at the present depth. If so finer particles that may resuspend at lower (than 4 m/s) wind speeds are likely to have been winnowed out of the system via discharges from the Apopka Beauclair canal. 4 The mean and maximum significant wave heights rec orded at UF0 were 10 and 41 cm, respectively. The significant wave period remained close to 0.7 s. A consequence of

PAGE 110

110 practically unchanging period is that the effect of waves at the bottom does not increase rapidly with wind speed. 5 Salinity variation was narrow, between 0.16 and 0.22, suggesting that dissolved impurities remained fairly constant. The mean and the maximum current velocities near the bottom ( elevation 17 cm above bed at UF0) were 0.04 and 0.23 m/ s, respectively. The latter value is high enou gh to resuspend fine sediment at the bottom by upward mixing. 6 The mean and maximum values of SSC at the lower elevation of 17 cm above the bed were 0.2 and 1.56 kg/ m3, respectively. 7 The resuspended sediment is organics -rich (mean LOI about 62%) and light -w eight (particle density 1,690 kg/m3). 8 The water column can be conveniently sub-divided into three layers dilute suspension layer (DSL; SSC < 0.1 kg / m3), benthic suspension layer (BSL; 0.1 SSC <1 .3 kg / m3) and benthic nepheloid layer (BNL; 1 .3 SSC< 4 0 kg / m3). The base of BNL is the surface of the consolidating or consolidated bed (CB ) (BSL; 4 0 kg / m3 SSC ). Settling of sediment within the low -concentration DSL is free, i.e. the settling velocity is practically independent of SSC In DSL the settling velocity increases with SSC due to inter -particle collisions. BNL contains fluid mud in which mud settling rate is governed (hindered) by the rate of dewaterin g of the settling slurry. 9 The thicknesses of DSL, BSL and BNL vary with the wind speed. At high winds DSL practically vanishes as BSL reaches the surface, which means that particle aggregation play a role during wind episodes 10. Resuspension of the lake sediment amounts to entrainment and settling sediment mass fluxes involving BNL (which acts as the primary source as well as sink of particulate

PAGE 111

111 matter), BSL and DSL. Participation of the bed (CB) in the resuspension process appears to be practically nil mos t of the time. 11. SSC increases with the combined wave -current bed shear stress cw. The contribution from wave -induced stress ( w) and wind-driven current induced stress ( c) varies with water depth and wind speed. A t a recorded wind speed of 15.8 m/s (and water depth 1.3 m), w = 0.013 Pa, c = 0.0132 Pa and cw = 0.033 Pa. Thus the contribution of w and c to cw is approximately same. At lower winds speeds the effect of current is greater and at higher speeds the effect of waves is greater. At the mean wind speed of 4 m/s, the effect of waves is negligible. Since sustained winds uncommonly exceed m/s, current associated with wind driven circulation and waves to a lesser degree govern the transport of suspended sediment much of the time. 12. SSC is strongly influenced by water depth. From the view poin t o f water quality one would expect that the main concern would be the peak value of SSC at the lower elevation (1 8 cm above the bed within BNL) where the concentration is high. As an illustration, at the highest (but not sustained) measured wind speed of 22.8 m/s during the study, lo wering the d ep th of water ( at UF0) successivel y f rom the present 1.3 m to 1 m, 0.75 m a n d (the extr e me low) 0.5 m would increa se SSC from 6.0 kg/m3 at 1.3 m to 8.7 kg/m3 at 1 m to 11.2 kg/m3 at 0.75 m to 13.7 kg/m3 at 0.5 m. Based on the upper bound estima tions the respective high SSC values would be 6.2 9.2 11.8 and 14.5 kg/m3 and the low values would be 5.6 8.0 10. 2 and 12. 4 kg/m3. 13. At the highest selected speed of 30 m/s, whose probability of occurrence is 0.052%, the predicted SSC value would be on t he order of 13.8 kg/m3. Contribution to resuspension from waves would be 4 5 times that due to current.

PAGE 112

112 5.3 Recommendations for Further Work To better characterize the mechanisms for resuspension in the lake, the following recommendations are made: 1 Develop a lake -w ide current circulation and sediment resuspension model to determine spatial and temporal patterns of resuspension at different wind speeds and water levels and to assess the significance of local effects of outflows through the lock and dam. 2 Inve stigate the role of biopolymers on particle aggregation dynamics in the lake. 3 Measure wave growth, including the effect of bottom sediment on wave energy dissipation in the lake, by installation of a minimum of two wave gages. 4 Measure thermal stratificatio n as part of an effort to assess the role of turbid fronts in lake dynamics.

PAGE 113

113 APPENDIX A SETTLING VELOCITY TESTS 10-1 100 101 102 10-8 10-7 10-6 10-5 10-4 10-3 10-2 a = b = m = n = c1 = 0.1 2 2.8 2 0.1 Wsf = 2.0e-005 (m/s) Sediment Concentration (kg/m3)Settling Velocity (m/s) Figure A 1 Settling velocity variation with SSC. I nitial SSC (C0) in the settling column was 1.95 kg/m3. 10-2 10-1 100 101 102 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 time (min) 0 5 15 30 60 120 180 I F I = initial profile F = final profile Sediment Concentration (kg/m3)Elevation (m) Figur e A 2 Simulation of concentration change in the settling column (C0=1.95 kg/m3)

PAGE 114

114 10-1 100 101 102 10-8 10-7 10-6 10-5 10-4 10-3 10-2 a = b = m = n = c1 = 0.1 2.3 2.9 2.3 0.1 Wsf = 4.0e-006 (m/s) Sediment Concentration (kg/m3)Settling Velocity (m/s) Figure A 3 Settling velocity variation with SSC. Initial SSC ( C0) in the settling column was 2.88 kg/m3. 10-2 10-1 100 101 102 103 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 time (min) 0 5 15 30 60 120 180 I F I = initial profile F = final profile Sediment Concentration (kg/m3)Elevation (m) Figure A 4 Simulation of concentration profile chang e in the settling column ( C0=2.88 kg/m3).

PAGE 115

115 APPENDIX B FIELD MEASUREMENTS 8% 4% WEST EAST SOUTH NORTH 0 1 1 2 2 5 5 10 10 15 15 20 20 25 25 30Velocity(cm/s) Figure B 1 Current rose at elev. 18.51 m during Deployment 0 2. 15% 10% 5% WEST EAST SOUTH NORTH 0 1 1 2 2 5 5 10 10 15 15 20 20 25 25 30Velocity(cm/s) Figure B 2 Current rose at elev. 18.31 m during Deployment 0 2.

PAGE 116

116 15% 10% 5% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 5 5 9 9 13Velocity(cm/s) Figure B 3 Current rose at elev. 18.83 m during Deployment 0 3. 15% 10% 5% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 5 5 9 9 13Velocity(cm/s) Figure B 4 Current rose at elev. 18.63 m during Deployment 0 3.

PAGE 117

117 15% 10% 5% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 5 5 9 9 13Velocity(cm/s) Figure B 5 Current rose at elev. 18.33 m during Deployment 0 3. 8% 5% 2% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 8 8 10 10 15 15 25Velocity(cm/s) Figure B 6 Current rose at elev. 18.83 m during Deployment 0 4.

PAGE 118

118 8% 5% 2% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 8 8 10 10 15 15 25Velocity(cm/s) Figure B 7 Current rose at elev. 18.63 m during Deployment 0 4. 8% 5% 2% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 8 8 10 10 15 15 25Velocity(cm/s) Figure B 8 Current rose at elev. 18.33 m during Deployment 0 4.

PAGE 119

119 9% 6% 3% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 4 4 5 5 6 6 8 8 10Velocity(cm/s) Figure B 9 Current rose at elev. 18.83 m during Deployment 0 5. 9% 6% 3% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 4 4 5 5 6 6 8 8 10Velocity(cm/s) Figure B 10. Current -rose at elev. 18.63 m during Deployment 0 5.

PAGE 120

120 9% 6% 3% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 4 4 5 5 6 6 8 8 10Velocity(cm/s) Figure B 11. Current -rose at elev. 18.33 m during Deployment 0 5. 8% 5% 2% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 4 4 5 5 8 8 14Velocity(cm/s) Figure B 12. Current -rose at elev. 18.88 m during De ployment 0 6.

PAGE 121

121 8% 5% 2% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 4 4 5 5 8 8 14Velocity(cm/s) Figure B 13. Current -rose at elev. 18.68 m during Deployment 0 6. 8% 5% 2% WEST EAST SOUTH NORTH 0 0.5 0.5 1 1 1.5 1.5 2 2 2.5 2.5 3 3 3.5 3.5 4 4 5 5 8 8 14Velocity(cm/s) Figure B 14. Current -rose at elev. 18.38 m during Deployment 0 6.

PAGE 122

122 15% 10% 5% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 15 15 20 20 25Velocity(cm/s) Figure B 15. Current -rose at elev. 18.43 m during Deployment 0 7. 15% 10% 5% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 15 15 20 20 25Velocity(cm/s) Figure B 16. Current -rose at elev. 18.33 m during Deployment 0 7.

PAGE 123

123 8% 5% 2% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 20 20 30Velocity(cm/s) Figure B 17. Current -rose at elev. 18.83 m during Deployment 0 8. 8% 5% 2% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 20 20 30Velocity(cm/s) Figure B 18. Current -rose at elev. 18.63 m during Deployment 0 8.

PAGE 124

124 8% 5% 2% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 20 20 30Velocity(cm/s) Figure B 19. Current -rose at elev. 18.33 m during Deployment 0 8. 6% 4% 2% WEST EAST SOUTH NORTH 0 3 3 6 6 9 9 12 12 15 15 18 18 21 21 24 24 27 27 30 Figure B 20. Current -rose at elev. 18.31 m during D eployment 0 9.

PAGE 125

125 6% 4% 2% WEST EAST SOUTH NORTH 0 3 3 6 6 9 9 12 12 15 15 18 18 21 21 24 24 27 27 30 Figure B 21. Current -rose at elev. 18.11 m during Deployment 0 9. 9% 6% 3% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 8 8 10 10 15 15 20Velocity(cm/s) Figure B 22. Current -rose at elev. 18.54 m during Deployment 0 10.

PAGE 126

126 9% 6% 3% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 8 8 10 10 15 15 20Velocity(cm/s) Figure B 23. Curre nt -rose at elev. 18.34 m during Deployment 0 10. 9% 6% 3% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 8 8 10 10 15 15 20Velocity(cm/s) Figure B 24. Current -rose at elev. 18.14 m during Deployment 0 10.

PAGE 127

127 8% 5% 2% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 15 15 30Velocity(cm/s) Figure B 25. Current -rose at elev. 19.01 m during Deployment 1 1. 8% 5% 2% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 15 15 30Velocity(cm/s) Figure B 26. Current -rose at elev. 18.61 m during Deployment 1 1.

PAGE 128

128 8% 5% 2% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 15 15 30Velocity(cm/s) Figure B 27. Current -rose at elev. 18.31 m during Deployment 1 1. 7% 5% 3% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 15 15 22Velocity(cm/s) Figure B 28. Current -rose at elev. 18.31 m duri ng Deployment 1 2.

PAGE 129

129 18% 12% 6% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 10 10 15 15 22Velocity(cm/s) Figure B 29. Current -rose at elev. 19.20 m during Deployment 2 1. 18% 12% 6% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 10 10 15 15 22Velocity(cm/s) Figure B 30. Current -rose at elev. 18.70 m during Deployment 2 1.

PAGE 130

130 18% 12% 6% WEST EAST SOUTH NORTH 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 10 10 15 15 22Velocity(cm/s) Figure B 31. Current -rose at elev. 18.50 m during Deployment 2 1. 18 18.2 18.4 18.6 18.8 19 19.2 19.4 19.6 19.8 20 Water Surface Elev.(m)Bottom Elevation from NAVD88 : 18.16m Jul07 Sep07 Nov07 Dec07 Feb08 Apr08 May08 Jul08 Aug08 0 5 10 15 20 25 30 35 40 45 Time(month)Precipitation(mm) ADCP CTD SJRWMD Bottom Ele. PRCP(mm) Figure B 32. Time -series of WSE at UF0 and precipitation.

PAGE 131

131 18 18.2 18.4 18.6 18.8 19 19.2 19.4 19.6 19.8 20 Water Surface Elev.(m)Bottom Elevation from NAVD88 : 18.16m 05/02 05/12 05/22 06/01 06/11 06/21 07/01 0 5 10 15 20 25 30 35 40 45 Day of 2008Precipitation(mm) ADCP SJRWMD Bottom Ele. PRCP(mm) Figure B 33. Time -series of WSE at UF1 and precipitation. 18 18.2 18.4 18.6 18.8 19 19.2 19.4 19.6 19.8 20 Water Surface Elev.(m)Bottom Elevation from NAVD88 : 18.37m 08/30 09/01 09/03 09/05 09/07 09/09 09/11 09/13 09/15 0 5 10 15 20 25 30 35 40 45 Day of 2008Precipitation(mm) ADCP SJRWMD Bottom Ele. PRCP(mm) Figure B 34. Time -series of WSE at UF2 and precipitation.

PAGE 132

132 6% 4% 2% WEST EAST SOUTH NORTH 2 4 4 6 6 8 8 10 10 12 12 14Wind Speed(m/s) Figure B 35. Wind rose during Deployment 0 1. 12% 8% 4% WEST EAST SOUTH NORTH 2 4 4 6 6 8 8 10 10 12 12 14Wind Speed(m/s) Figure B 36. Wind rose during Deployment 0 2.

PAGE 133

133 20% 15% 10% 5% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 14Wind Speed(m/s) Figure B 37. Wind rose during Deployment 0 3. 15% 10% 5% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 14Wind Speed(m/s) Figure B 38. Wind rose during Deployment 0 4.

PAGE 134

134 10% 7% 4% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 15 15 20Wind Speed (m/s) Figure B 3 9 Wind rose during Deployment 0 5. 8% 5% 2% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 15 15 20Wind Speed (m/s) Figure B 40. Wind rose during Deployment 0 6.

PAGE 135

135 8% 5% 2% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 14 14 16Wind Speed(m/s) Figure B 41. Wind rose during Deployment 0 7. 6% 3% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 15 15 20 20 25Wind Speed(m/s) Figure B 42. Wind rose during Deployment 0 8.

PAGE 136

136 8% 4% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 15 15 20 20 25Wind Speed(m/s) Figure B 43. Wind rose during Deployment 0 9. 9% 6% 3% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 14 14 16 16 18Wind Speed(m/s) Figure B 44. Wind rose during Deployment 0 10.

PAGE 137

137 6% 4% 2% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 15 15 20 20 25Wind Speed(m/s) Figure B 45. Wind rose during Deployment 1 1. 8% 5% 2% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12 12 15 15 20Wind Speed(m/s) Figure B 46. Wind rose during Deployment 1 2.

PAGE 138

138 12% 8% 4% WEST EAST SOUTH NORTH 0 2 2 4 4 6 6 8 8 10 10 12Wind Speed(m/s) Figure B 47. Wind r ose during Deployment 2 1.

PAGE 139

139 APPENDIX C TABULATION OF LAKE M EASUREMENTS Table C 1 Weekly max, mean and min currents at different elevations at UF1. UF1 Tower Parameters Weeks Current Velocity (cm/s) Top Middle Bottom Max Me an Min Max Mean Min Max Mean Min Elev. 19.01 (m) Elev. 18.61 (m) Elev. 18.31 (m) 40 12.1 3.0 0 12.5 3.3 0.1 10.0 2.6 0.1 41 11.9 4.0 0.1 14.3 4.3 0.1 13.0 3.5 0.1 42 24.8 3.9 0.1 22.5 4.3 0.1 13.7 3.6 0.1 43 16.8 4.5 0.1 16.2 4.4 0.1 10.9 3.6 0 44 10.1 3.1 0.1 10.0 3.2 0 7.2 2.4 0 45 46 23.9 3.3 0.1 22.6 3.4 0.1 17.2 2.7 0 Elev. 18.31 (m) 47 48 21.3 4.3 0 49 50 Table C 2 Weekly max, mean and min SSC from ADCP at UF1. Parameters Weeks SSC (kg/m 3 ) from ADCP Top Middle Bottom Max Mean Min Max Mean Min Max Mean Min Elev. 19.01 (m) Elev. 18.61 (m) Elev. 18.31 (m) 40 1.41 0.04 0 41 1.76 0.05 0 42 1.76 0.06 0 43 44 0.91 0.01 0 0.59 0.02 0 0.24 0.02 0 45 46 Elev. 18.31 (m) 47 48 0.81 0.14 0.03 49 50

PAGE 140

140 Table C 3 Weekly max, mean and min SSC from OBS 3 at UF1. Parameters Weeks SSC (kg/m 3 ) from OBS 3 Max Mean Min 47 48 0.47 0.03 0 49 0.49 0.09 0.02 50 0.40 0.05 0.01 Table C 4 Weekly max, mean and min currents at different elevations at UF2. UF2 Tower Parameters Weeks Current Velocity (cm/s) Top Middle Bottom Max Mean Min Max Mean Min Max Mean Min Elev. 19.20 (m) Elev. 18.70 (m) Elev. 18.50 (m) 57 58 8.2 2.7 0.1 6.9 2.4 0.1 4.9 1.7 0 59 20.6 3.3 0.2 17.9 3.3 0.1 13.6 2.6 0.2 Table C 5 Weekly max, mean and min SSC from ADCP at UF2. Parameters Weeks SSC (kg/m 3 ) from ADCP Top Middle Bottom Max Mean Min Max Mean Min Max Mean Min Elev. 19.20 (m) Elev. 18.70 (m) Elev. 18.50 (m) 57 58 0.67 0.02 0 0.83 0.07 0 0.67 0.08 0 59

PAGE 141

141 5 10 15 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 2 4 x 105 Wind SpeedPower Spectral Density 25 30 35 Temperature(C) 0 1 2 x 105 Temperature 0.18 0.19 0.2 0.21 0.22 Salinity 0 0.1 0.2 Salinity 19.3 19.4 19.5 19.6 Water Surface Elev.(m) 0 10 20 Pressure 0 5 10 15 Velocity(cm/s) Elev. 18.51m 0 1 2 3 x 105 Velocity Elev. 18.51m 0 5 10 15 Velocity(cm/s) Elev. 18.31m 0 5 10 x 106 Velocity Elev. 18.31m 0 0.2 0.4 0.6 0.8 1 SSC(kg/m3) Elev. 18.51m 0 100 200 SSC Elev. 18.51m 07/26 07/31 08/05 08/10 08/15 08/20 08/25 0 0.2 0.4 0.6 0.8 1 Day of 2007SSC(kg/m3) Elev. 18.31m 0 0.5 1 1.5 2 2.5 0 5000 Frequency (1/days)SSC Elev. 18.31m Figure C 1 Measurements (left) and power spectral densities for Deployment 0 1.

PAGE 142

142 5 10 15 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 1 2 3 x 105 Wind SpeedPower Spectral Density 0 5 10 15 Velocity(cm/s) Elev. 18.51m 0 5 10 15 x 104 Velocity Elev. 18.51m 0 0.1 0.2 0.3 0.4 SSC(kg/m3) OBS-3 at Elev. 18.66m 0 10 20 OBS-3 OBS-3 at Elev. 18.66m 0 0.2 0.4 0.6 0.8 1 SSC(kg/m3) Elev. 18.51m 0 1000 2000 SSC Elev. 18.51m 08/29 09/03 09/08 09/13 0 0.2 0.4 0.6 0.8 1 Day of 2007SSC(kg/m3) Elev. 18.31m 0 0.5 1 1.5 2 2.5 0 5000 10000 Frequency (1/days)SSC Elev. 18.31m F igure C 2 Measurements (left) and power spectral densities for Deployment 0 2.

PAGE 143

143 5 10 15 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 1 2 x 105 Wind SpeedPower Spectral Density 10 15 20 25 30 Temperature(C) 0 1 2 x 105 Temperature 0.15 0.175 0.2 0.225 0.25 Salinity 0 0.5 Salinity 19.2 19.3 19.4 19.5 19.6 Water Surface Elev.(m) 0 10 20 30 Pressure 0 5 10 15 20 Velocity(cm/s) Elev. 18.83m 0 1 2 x 104 Velocity Elev. 18.83m 0 5 10 15 20 Velocity(cm/s) Elev. 18.63m 0 1 2 x 104 Frequency (1/day)Velocity Elev. 18.63m 0 5 10 15 20 Velocity(cm/s) Elev. 18.33m 0 2 4 x 104 Velocity Elev. 18.33m 0 0.1 0.2 0.3 0.4 Wave Height(m) 0 50 100 Wave Height 0.5 0.75 1 Wave Periods(sec) 0 50 100 150 Wave Period 0 0.2 0.4 0.6 0.8 1 SSC(kg/m3) Elev. 18.83m 0 200 400 SSC Elev. 18.83m 0 0.02 0.04 0.06 0.08 0.1 SSC(kg/m3) OBS-3 at Elev. 18.66m 0 0.5 SSC OBS-3 at Elev. 18.66m 0 0.2 0.4 0.6 0.8 1 SSC(kg/m3) Elev. 18.63m 0 50 100 150 SSC Elev. 18.63m 10/14 10/19 10/24 10/29 11/03 11/08 11/13 11/18 11/23 11/28 12/03 0 0.2 0.4 0.6 0.8 1 Day of 2007SSC(kg/m3) Elev. 18.33m 0 0.5 1 1.5 2 2.5 0 50 100 Frequency (1/days)SSC Elev. 18.33m Figure C 3 Measurements (left) and power spectral densities for Deployment 0 4.

PAGE 144

144 10 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 1 2 x 105 Wind SpeedPower Spectral Density 0 10 20 Temperature(C) 0 1 2 x 105 Temperature 0.15 0.2 0.25 Salinity 0 0.5 Salinity 19.2 19.4 19.6 Water Surface Elev.(m) 0 10 20 30 Pressure 0 5 10 15 Velocity(Cm/s) Elev. 18.83m 0 1 2 x 104 Velocity Elev. 18.83m 0 5 10 15 Velocity(Cm/s) Elev. 18.63m 0 1 2 x 104 Frequency (1/day)Velocity Elev. 18.63m 0 5 10 15 Velocity(Cm/s) Elev. 18.33m 0 2 4 x 104 Velocity Elev. 18.33m 0 0.1 0.2 0.3 0.4 Wave Height(m) 0 50 100 Wave Height 0.6 0.8 1 Wave Periods(sec) 0 50 Wave Period 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.83m 0 5000 10000 SSC Elev. 18.83m 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.63m 0 5000 10000 SSC Elev. 18.63m 0 0.5 1 1.5 2 SSC(kg/m3) OBS-5+ at Elev. 18.34m 0 5 SSC OBS-5+ at Elev. 18.34m 12/06 12/11 12/16 12/21 12/26 12/31 01/05 01/10 01/15 0 0.5 1 1.5 2 Day of 2007 & 2008SSC(kg/m3) Elev. 18.33m 0 0.5 1 1.5 2 2.5 0 500 1000 Frequency (1/days)SSC Elev. 18.33m Figure C 4 Measurements (left) and power spectral densities for Deployment 0 5.

PAGE 145

145 10 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 5 x 104 Wind SpeedPower Spectral Density 10 15 20 25 Temperature(C) 0 5 10 15 x 104 Temperature 0.15 0.2 0.25 Salinity 0 0.5 Salinity 19.3 19.4 19.5 19.6 Water Surface Elev.(m) 0 10 20 30 Pressure 0 5 10 15 Velocity(Cm/s) Elev. 18.88m 0 1000 2000 3000 Frequency (1/day)Velocity Elev. 18.88m 0 5 10 15 Velocity(Cm/s) Elev. 18.68m 0 2000 4000 Frequency (1/day)Velocity Elev. 18.68m 0 5 10 15 Velocity(Cm/s) Elev. 18.38m 0 1000 2000 3000 Velocity Elev. 18.38m 0 0.1 0.2 0.3 0.4 Wave Height(m) 0 50 100 Wave Height 0.5 0.7 0.9 Wave Periods(sec) 0 50 100 Wave Period 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.88m 0 50 100 150 SSC Elev. 18.88m 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.68m 0 50 100 SSC Elev. 18.68m 01/18 01/23 01/28 02/02 02/07 02/12 02/17 02/22 02/27 0 0.5 1 1.5 2 Day of 2008SSC(kg/m3) Elev. 18.38m 0 0.5 1 1.5 2 2.5 0 50 100 Frequency (1/days)SSC Elev. 18.38m Figure C 5 Measurements (left) and power spectral densities for Deployment 0 6.

PAGE 146

146 10 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 1 2 3 x 105 Wind SpeedPower Spectral Density 15 20 25 Temperature(C) 0 5 x 105 Frequency (1/days)Temperature 0.15 0.2 0.25 Salinity 0 0.5 Salinity 19.3 19.4 19.5 19.6 Water Surface Elev.(m) 0 50 Pressure 0 10 20 Velocity(Cm/s) Elev. 18.43m 0 1 2 x 105 Frequency (1/day)Velocity Elev. 18.43m 0 10 20 Velocity(Cm/s) Elev. 18.33m 0 1 2 x 105 Velocity Elev. 18.33m 0 0.1 0.2 0.3 0.4 Wave Height(m) 0 50 100 Wave Height 0 0.5 1 Wave Periods(sec) 0 50 100 Wave Period 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.43m 0 1000 2000 SSC Elev. 18.43m 03/01 03/06 03/11 03/16 03/21 03/26 03/31 04/05 04/10 04/15 04/20 04/25 04/30 0 0.5 1 1.5 2 Day of 2008SSC(kg/m3) Elev. 18.33m 0 0.5 1 1.5 2 2.5 0 1000 2000 3000 Frequency (1/days)SSC Elev. 18.33m Figure C 6 Measurements (left) and power spectral densities for Deployment 0 7.

PAGE 147

147 10 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 5 x 105 Wind SpeedPower Spectral Density 20 30 40 Temperature(C) 0 1 2 x 106 Frequency (1/days)Temperature 0.2 0.3 0.4 Salinity 0 1 2 Salinity 19.1 19.2 19.3 Water Surface Elev.(m) 0 10 20 30 Pressure 0 10 20 Velocity(cm/s) Elev. 18.83m 0 1 2 x 105 Frequency (1/day)Velocity Elev. 18.83m 0 10 20 Velocity(cm/s) Elev. 18.63m 0 1 2 x 105 Velocity Elev. 18.63m 0 10 20 Velocity(cm/s) Elev. 18.33m 0 1 2 x 105 Velocity Elev. 18.33m 0 0.1 0.2 0.3 0.4 Wave Height(m) 0 50 Wave Height 0.5 0.7 0.9 Wave Periods(sec) 0 2 4 x 105 Wave Period 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.83m 0 500 1000 SSC Elev. 18.83m 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.63m 0 500 1000 SSC Elev. 18.63m 05/02 05/07 05/12 05/17 05/22 05/27 06/01 06/06 06/11 06/16 0 0.5 1 1.5 2 Day of 2008SSC(kg/m3) Elev. 18.33m 0 0.5 1 1.5 2 2.5 0 1000 2000 3000 Frequency (1/days)SSC Elev. 18.33m Figure C 7 Measurements (left) and power spectral densities for Deployment 0 8.

PAGE 148

148 10 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 5 x 105 Wind SpeedPower Spectral Density 20 30 40 Temperature(C) 0 5 x 105 Frequency (1/days)Temperature 0.2 0.3 0.4 Salinity 0 0.5 1 Salinity 19.3 19.4 19.5 19.6 19.7 Water Surface Elev.(m) 0 10 20 30 Pressure 0 10 20 Velocity(cm/s) Elev. 18.31m 0 5 10 x 105 Frequency (1/day)Velocity Elev. 18.31m 0 10 20 Velocity(cm/s) Elev. 18.11m 0 5 x 106 Velocity Elev. 18.11m 0 0.1 0.2 0.3 0.4 Wave Height(m) 0 10 20 Wave Height 0.5 0.7 0.9 Wave Periods(sec) 0 50 100 150 Wave Period 0 0.5 1 1.5 2 SSC(kg/m3) OBS-5+ at Elev. 18.33m 0 500 SSC OBS-5+ at Elev. 18.33m 06/21 06/26 07/01 07/06 07/11 07/16 07/21 07/26 07/31 08/05 08/10 0 0.5 1 1.5 2 Day of 2008SSC(kg/m3) Elev. 18.31m 0 0.5 1 1.5 2 2.5 0 5000 Frequency (1/days)SSC Elev. 18.31m Figure C 8 Measurements (left) and power spectral densities for Deployment 0 9.

PAGE 149

149 10 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 1 2 3 x 105 Wind SpeedPower Spectral Density 20 30 40 Temperature(C) 0 5 10 x 104 Frequency (1/days)Temperature 0.2 0.3 0.4 Salinity 0 0.1 0.2 Salinity 19.4 19.6 19.8 20 Water Surface Elev.(m) 0 10 20 30 Pressure 0 10 20 Velocity(cm/s) Elev. 18.54m 0 5 x 104 Frequency (1/day)Velocity Elev. 18.54m 0 10 20 Velocity(cm/s) Elev. 18.34m 0 5 x 104 Frequency (1/day)Velocity Elev. 18.34m 0 10 20 Velocity(cm/s) Elev. 18.14m 0 5 x 104 Velocity Elev. 18.14m 0 0.1 0.2 0.3 0.4 Wave Height(m) 0 10 20 Wave Height 0.5 1 1.5 Wave Periods(sec) 0 100 200 Wave Period 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.54m 0 500 1000 1500 Frequency (1/day)SSC Elev. 18.54m 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.34m 0 500 1000 Frequency (1/day)SSC Elev. 18.34m 08/15 08/20 08/25 08/30 09/04 09/09 09/14 0 0.5 1 1.5 2 Day of 2008SSC(kg/m3) Elev. 18.14m 0 0.5 1 1.5 2 2.5 0 5000 Frequency (1/days)SSC Elev. 18.14m Figure C 9 Measurements (left) and power spectral densities for Deployment 0 10.

PAGE 150

150 10 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 5 x 105 Wind SpeedPower Spectral Density 0 10 20 30 Velocity(cm/s) Elev. 19.01m 0 5 x 105 Frequency (1/day)Velocity Elev. 19.01m 0 10 20 30 Velocity(cm/s) Elev. 18.61m 0 5 x 105 Frequency (1/day)Velocity Elev. 18.61m 0 10 20 30 Velocity(cm/s) Elev. 18.31m 0 5 x 105 Velocity Elev. 18.31m 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 19.01m 0 1000 2000 SSC Elev. 19.01m 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.61m 0 5000 SSC Elev. 18.61m 04/27 05/02 05/07 05/12 05/17 05/22 05/27 06/01 06/06 06/11 06/16 0 0.5 1 1.5 2 Day of 2008SSC(kg/m3) Elev. 18.31m 0 0.5 1 1.5 2 2.5 0 1000 2000 Frequency (1/days)SSC Elev. 18.31m Figure C 10. Measurements (left) and power spectral densities for Deployment 1 1.

PAGE 151

151 10 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 5 x 105 Wind SpeedPower Spectral Density 0 10 20 30 Velocity(cm/s) Elev. 18.31m 0 5 x 105 Velocity Elev. 18.31m 0 0.5 1 1.5 2 SSC(kg/m3) OBS-3 at Elev. 18.33m 0 100 200 SSC OBS-3 at Elev. 18.33m 06/19 06/24 06/29 07/04 07/09 07/14 0 0.5 1 1.5 2 Day of 2008SSC(kg/m3) Elev. 18.31m 0 0.5 1 1.5 2 2.5 0 1000 2000 Frequency (1/days)SSC Elev. 18.31m Figure C 11. Measurements (left) and power spectral densities for Deployment 1 2.

PAGE 152

152 10 20 Wind Speed(m/s) Speed Direction 0 100 200 300 400 Wind Direction() 0 1 2 3 x 105 Wind SpeedPower Spectral Density 0 10 20 Velocity(cm/s) Elev. 19.20m 0 1 2 x 105 Frequency (1/day)Velocity Elev. 19.20m 0 10 20 Velocity(cm/s) Elev. 18.70m 0 1 2 x 105 Frequency (1/day)Velocity Elev. 18.70m 0 10 20 Velocity(cm/s) Elev. 18.50m 0 5 x 104 Velocity Elev. 18.50m 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 19.20m 0 100 200 Frequency (1/day)SSC Elev. 19.20m 0 0.5 1 1.5 2 SSC(kg/m3) Elev. 18.70m 0 1000 2000 3000 Frequency (1/day)SSC Elev. 18.70m 08/30 09/04 09/09 09/14 0 0.5 1 1.5 2 SSC(kg/m3)Day of 2008 Elev. 18.50m 0 0.5 1 1.5 2 2.5 0 5000 10000 SSCFrequency (1/day) Elev. 18.50m Figure C 12. Measurements (left) and power spectral densities for Deployment 2 1.

PAGE 153

153 0 2 4 6 8 10 12 14 0 0.05 0.1 0.15 0.2 0.25 0.3 Wind Speed(m/s)Wave Height(m) 0 2 4 6 8 10 12 14 0.5 0.6 0.7 0.8 0.9 1 Wind Speed(m/s)Wave Period(s) Figure C 13. Variations of wave height and period with wind speed for Deployment 0 4. 0 2 4 6 8 10 12 14 0 0.05 0.1 0.15 0.2 0.25 0.3 Wind Speed(m/s)Wave Height(m) 0 2 4 6 8 10 12 14 0.5 0.6 0.7 0.8 0.9 1 Wind Speed(m/s)Wave Period(s) Figure C 14. Variations of wave height and period with wind speed for Deployment 0 5.

PAGE 154

154 0 2 4 6 8 10 12 14 0 0.05 0.1 0.15 0.2 0.25 0.3 Wind Speed(m/s)Wave Height(m) 0 2 4 6 8 10 12 14 0.5 0.6 0.7 0.8 0.9 1 Wind Speed(m/s)Wave Period(s) Figure C 15. Variations of wave height and period with wind speed for Deployment 0 6. 0 2 4 6 8 10 12 14 0 0.05 0.1 0.15 0.2 0.25 0.3 Wind Speed(m/s)Wave Height(m) 0 2 4 6 8 10 12 14 0.5 0.6 0.7 0.8 0.9 1 Wind Speed(m/s)Wave Period(s) Figure C 16. Variations of wave height and period with wind speed for Deployment 0 7.

PAGE 155

155 0 2 4 6 8 10 12 14 0 0.05 0.1 0.15 0.2 0.25 0.3 Wind Speed(m/s)Wave Height(m) 0 2 4 6 8 10 12 14 0.5 0.6 0.7 0.8 0.9 1 Wind Speed(m/s)Wave Period(s) Figure C 17. Variations of wave height and period with wind speed for Dep loyment 0 8. 0 2 4 6 8 10 12 14 0 0.05 0.1 0.15 0.2 0.25 0.3 Wind Speed(m/s)Wave Height(m) 0 2 4 6 8 10 12 14 0.5 0.6 0.7 0.8 0.9 1 Wind Speed(m/s)Wave Period(s) Figure C 18. Variations of wave height and period with wind speed for Deployment 0 9.

PAGE 156

156 0 2 4 6 8 10 12 14 0 0.05 0.1 0.15 0.2 0.25 0.3 Wind Speed(m/s)Wave Height(m) 0 2 4 6 8 10 12 14 0.5 0.6 0.7 0.8 0.9 1 Wind Speed(m/s)Wave Period(s) Figure C 19. Variations of wave height and period with wind speed for Deployment 0 10. 0 5 10 V=6e(u/23)-6 (a) Elev. 18.83m 0 5 Water Current Velocity(cm/s)V=6e(u/23)-6 (b) Elev. 18.63m 0 2 4 6 8 10 12 14 0 5 Wind Speed(m/s) V=6e(u/26)-6 (c) Elev. 18.33m Figure C 20. Variations of current at three elevations with wind speed for Deployment 0 5.

PAGE 157

157 0 5 10 V=9.5e(u/23)-9.5 Elev. 18.83m 0 5 Water Current Velocity(cm/s) V=9.5e(u/23)-9.5 Elev. 18.63m 0 2 4 6 8 10 12 14 0 5 Wind Speed(m/s) V=8e(u/26)-8 Elev. 18.33m Figure C 21. Variations of current at three elevations with wind speed for Deployment 0 8. 0 5 10 V=8e(u/23)-8 Elev. 18.54m 0 5 Water Current Velocity(cm/s)V=8e(u/23)-8 Elev. 18.34m 0 2 4 6 8 10 12 14 0 5 Wind Speed(m/s) V=8e(u/26)-8 Elev. 18.14m Figure C 22. Variations of current at three elevations with wind speed for Deployment 0 10.

PAGE 158

158 0 5 10 V=13e(u/23)-13 Elev. 19.01m 0 5 Water Current Velocity(cm/s)V=13e(u/23)-13 Elev. 18.61m 0 2 4 6 8 10 12 14 0 5 Wind Speed(m/s) V=13e(u/26)-13 Elev. 18.31m Figure C 23. Variations of current at three elevations with wind speed for Deployment 1 1. 0 5 10 V=9e(u/23)-9 Elev. 19.20m 0 5 Water Current Velocity(cm/s)V=9e(u/23)-9 Elev. 18.70m 0 2 4 6 8 10 12 14 0 5 Wind Speed(m/s) V=8e(u/26)-8 Elev. 18.50m Figure C 24. Variations of current at three elevations with wind speed for Deployment 2 1.

PAGE 159

159 Figure C 25. SSC against wind speed at 18.51 m from Deployment 0 1. Figure C 26. SSC against wind speed at 18.51 m from Deployment 0 2.

PAGE 160

160 Figure C 27. SSC against wind speed at 18.63 m from Deployment 0 3. Figure C 28. SSC against wind speed at 18.33 m from Deployment 0 3.

PAGE 161

161 Figure C 29. SSC against wind speed at 18.83 m from Deployment 0 4. Figure C 30. SSC against wind speed at 18.63 m from Deployment 0 4.

PAGE 162

162 Figure C 31. SSC against wind speed at 18.33 m from De ployment 0 4. Figure C 32. SSC against wind speed at 18.34 m from Deployment 0 5.

PAGE 163

163 Figure C 33. SSC against wind speed at 18.83 m from Deployment 0 8. Figure C 34. S SC against wind speed at 18.63 m from Deployment 0 8.

PAGE 164

164 Figure C 35. SSC against wind speed at 18.54 m from Deployment 0 10. Figure C 36. SSC against wind speed at 19.01 m from Deployment 1 1.

PAGE 165

165 Fi gure C 37. SSC against wind speed at 18.61 m from Deployment 1 1. Figure C 38. SSC against wind speed at 18.31 m from Deployment 1 1.

PAGE 166

166 Figure C 39. SSC against wind spe ed at 18.50 m from Deployment 2 1.

PAGE 167

167 LIST OF REFERENCES Bachmann, R.W., Hoyer, M.V., Canfield, D.E., Jr., 2000. The potential for wave disturbance in shallow Florida lakes Lake and Reservoir Management 16(4), 281291. Battoe, L.E., Coveney, M.F., Lowe E.F., Stites, D.L., 1999. The role of phosphorus reduction and export in the restoration of Lake Apopka, Florida. In : Phosphorus Biogeochemistry in Subtropical Ecosystems. K.R. Reddy, G.A. OConnor, and C.L. Schelske, eds., Lewis Publishers, Boca Raton, FL, 511526. Clugston, J.P., 1963. Lake Apopka, Florida, A changing lake and its vegetation. Quarterly Journal of the Florida Academy of Science, 26, 168174. Dean, R.G., Dalrymple, R.A., 1991 Water Wave Mechanics for Engineers and Scientists World Scie ntific, Singapore. Hkanson, L., Jansson, M., 1983. Principles of Lake Sedimentology, Springer -Verlag Berlin. Heltzel, S.B., Teeter, A.M., 1987. Settling of cohesive sediments. Coastal Sediments 87, ASCE Specialty Conference on Advances in Understanding of Coastal Sediment Processes, N. Kraus, ed., ASCE, New York, 63 70. Hwang, K. N., 1989. Erodibility of fine sediment in wave dominated environments M.S. thesis, University of Florida, Gainesville. Jain, M., 2007. Wave attenuation and mud entrainment in s hallow waters. Ph.D. thesis, University of Florida, Gainesville. Julie n P. Y., 1995. Erosion and Sedimentation, Cambridge University Press, New York. Lott, J.W., 1987. Laboratory study on the behavior of turbidity current in a closed -end channel. M.S. the sis, University of Florida, Gainesville Lowe, E.F., Battoe, L.E., Coveney M.F., Stites, D., 1999. Setting water quality goals for restoration of Lake Apopka: inferring past conditions. Journal of Lake and Reservoir Management, 15(2), 103120. Mehta, A.J., Li, Y., 2003. Principles and process -modeling of cohesive sediment transport. Unpublished class notes, University of Florida, Gainesville. Mei, C.C., Fan, S., Jin, K.R., 1997. Resuspension and transport of fine sediments by waves. Journal of Geophysical R esearch, Oceans, 102( C7), 1580715821. Migniot, C., 1968. A study of the physical properties of different very fine sediments and their behavior under hydrodynamic action. La Houille Blanche, 7, 591620 (in French, with abstract in English).

PAGE 168

168 Paerl, H., Fu lton, R.S., Moisander, P.H., and Dyble, J., 2001. Harmful freshwater algal blooms, with emphasis on cyanobacterial. The Scientific World, 1 76 113. Rosenau, J.C., Faulkner, G.L., Hendry, C.W., and Hull, R.W., 1977 Springs of Florida. Florida Geological S urvey Bulletin 31 (Revised). Ross, M.A., 1988. Vertical structure of estuarine fine sediment suspensions. Ph.D. thesis, University of Florida, Gainesville. Schelske, C.L., 1997. Sediment and phosphorus deposition in Lake Apopka. Final Report. Special Publ ication, SJ97 Sp21, St. Johns River W ater Management District, Palatka, F L Schelske, C.L., Coveney, M.F., Aldridge, F.J., Kenney, W.F., Cable, J.E., 2000. Wind or nutrients: Historic development of hypereutrophy in Lake Apopka, Florida. Limnology and Lake Management 2000. Arch. Hydrobiol. Spec. Issues Advanc. Limnol, 55, 543 564. Soulsby, R. L., Hamm, L., Klopman, G ., Myrhaug, D., Simons, R. R., Thomas, G. P., 1993. Wave -current interaction within and outside the bottom boundary layer. Coastal Engineering, 21(1), 4169. Stites, D.L., Coveney, M., Battoe, L., Lowe, E., Hoge, V., 2001. An external phosphorus budget for Lake Apopka. Draft Technical Memorandum, St. Johns River Water Management District, Palatka, FL. Stenberg, J., Clark, M., and Conrow, R., 1997. Development of natural and planted vegetation and wildlife use in the Lake Apopka Marsh Flow -Way Demonstration Project: 19901994. Special Publication, SJ98 SP4, St. Johns River Water Management District, Palatka, F L SWIM PLAN, 2003. 2003 Lake Apopka S urface Water Improvement and Management(SWIM) plan. Retrieved July 7, 2009, from http://sjrwmd.com Teeter, A.M., 2001a. Clay-silt sediment modeling using multiple grain classes; part I: settling and deposition. Coastal and Estuarine Fine Sediment Transport Processes, W.H. McAnally and A.J. Mehta, eds., Elsevier, Amsterdam 157171. Teeter, A.M., 2001b. Clay-silt sediment modeling using multiple grain classes; part I: application to shallow -water resuspension and deposit ion. Coastal and Estuarine Fine Sediment Transport Processes, W.H. McAnally and A.J Mehta, eds., Elsevier, Amsterdam, 173 187. U.S. Geological Survey. 2002. Daily streamflow for Apopka Beauclair Canal near Astatula. Retrieved July 7, 2009, from http://waterdata.usgs.gov Winterwerp J.G., van Kesteren, 2004. Introduction to the Physics of Cohesive Sediment in the Marine Environment Elsevier, Amsterdam. Young, I.R., and Verhagen, L.A., 1996. The growth of fetch limited waves in water of finite depth. Part 1. Total energy and peak frequency. Coastal Engineering, 29 47 78.

PAGE 169

169 BIOGRAPHICAL SKETCH Sangdon So was born as the fifth child of Junyoung So and Sun An in Jeonju, South Korea. He entered the Chonbuk National U niversity in 1993 and spent 26 months in the Korean Army from January 1994 to March 1996. After completing his military service he went back to university and received his B.S. in civil engineering in 2001. He decided to take up graduate study and obtained M.S. in civil engineering in 2003. He married Jin Kim in January 2003, who he has always loved. After graduating he worked for about 3 years as a civil engineer. The pursuit of knowledge made him take a break and continue graduate education and was admitt ed to the Graduate School of the University of Florida in the spring of 2007.