© 2009 Sangdon So

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FINE SEDIMENT RESUSPENSION IN LAKE APOPKA, FLORIDA

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

UNIVERSITY OF FLORIDA

2009

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© 2009 Sangdon So

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

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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 staffs 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.

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TABLE OF CONTENTS page

ACKNOWLEDGMENT ...................................................................................................................... 4

TABLE OF CONTENTS ..................................................................................................................... 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 Parameters .................................................................................... 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

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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 Stress............................................................. 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 SUMMARY AND CONCLUSIONS ...................................................................................... 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 TABULATION OF LAKE MEASUREMENTS .................................................................... 139

LIST OF REFERENCES ................................................................................................................. 167

BIOGRAPHICAL SKETCH ........................................................................................................... 169

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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 from 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 resuspension .................................................................................... 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 (τw, τc and τcw) 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

C-1 Weekly max, mean and min currents at different elevations at UF1. ............................... 139

C-2 Weekly max, mean and min SSC from ADCP at UF1. ..................................................... 139

C-3 Weekly max, mean and min SSC from OBS-3 at UF1. .................................................... 140

C-4 Weekly max, mean and min currents at different elevations at UF2. ............................... 140

C-5 Weekly max, mean and min SSC from ADCP at UF2. ..................................................... 140

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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-rose at 18.83 m elevation during Deployment 0-3. ..................................................... 45



3-5. Salinity, temperature and water surface elevation time-series during Deployment 0-3. ........ 47

3-6. Water surface elevation and precipitation during Deployment 0-3. ........................................ 47

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3-7. Wave height and period time-series. A) During Deployment 0-3. B) For the date when the highest wave 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 along 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. Bio-fouling may have contributed to weak signals after 10/03/07............................................. 50

3-13. SSC time-series from ADCP during Deployment 0-3. ........................................................... 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. Wind-rose for Deployment 0-3. ............................................................................................... 53

4-1. Power spectral density (PSD) of all data for Deployment 0-3. For any parameter with unit θ, the unit on the ordinate is θ2 /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 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. ................................... 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

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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) significant 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 Jain 2007)................................................................................................................................ 98

4-18. An example of measured time-series of horizontal SSC gradient (kg/m4) in the lake. ........ 99

4-19. Measured vertical 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 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)............................................................................................................................... 100

4-21. Schematic drawing 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-31-08site. 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). .............................................................................. 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

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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 0-5. ......................................................... 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 Ds0 with *cwu . Mean trend and selected 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. Initial 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

B-1. Current-rose at elev. 18.51 m during Deployment 0-2. ......................................................... 115





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B-10. Current-rose at elev. 18.63 m during Deployment 0-5. ....................................................... 119












B-22. Current-rose at elev. 18.54 m during Deployment 0-10. ..................................................... 125









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B-32. Time-series of WSE at UF0 and precipitation. .................................................................... 130



B-35. Wind-rose during Deployment 0-1. ...................................................................................... 132









B-44. Wind-rose during Deployment 0-10. .................................................................................... 136




C-1. Measurements (left) and power spectral densities for Deployment 0-1. .............................. 141








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C-9. Measurements (left) and power spectral densities for Deployment 0-10. ............................ 149




C-13. Variations of wave height and period with wind speed for Deployment 0-4. .................... 153






C-19. Variations of wave height and period with wind speed for Deployment 0-10. .................. 156

C-20. Variations of current at three elevations with wind speed for Deployment 0-5................. 156


C-22. Variations of current at three elevations with wind speed for Deployment 0-10............... 157



C-25. SSC against wind speed at 18.51 m from Deployment 0-1. ................................................ 159









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C-35. SSC against wind speed at 18.54 m from Deployment 0-10. .............................................. 164





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LIST OF SYMBOLS

ADCP Acoustic Doppler Current Profiler

a b cα α α Calibration coefficients

β Calibration coefficient

C Suspended sediment concentration

C0 Initial concentration

CD Drag coefficient

χ Non-dimensional wind fetch

C1 Free-settling concentration

Ca Concentrations at elevation za

Cm Uniform concentration due to complete mixing

CUF0 Concentration at the station UF0

CUF2 Concentration at the station UF0

CTD Conductivity-Temperature-Depth

bδ Calibration coefficient

d50 50 percent volume cumulative particle diameter

Dsz Diffusion coefficient

Ds0 Diffusion coefficient of depth-mean

δ Non-dimensional water depth

E Total wave energy or variance of the wave record

EIA echo-intensity anomaly of ADCP

ε Non-dimensional wave energy

pf Frequency of spectral peak

wf Wave friction factor

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g Gravitational acceleration

H Wave height

sH Significant 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+

υ Non-dimensional wave frequency

OBS Optical Backscatter Sensor

φ Angle between the current stress vector and the wave stress vector

PSD Power spectral density

ρ wρ Water densities

aρ Air density

S Wind-induced water level setup

S Spatial gradient of setup S

σ Wave angular frequency

SSC Suspended sediment concentration

T Wave period

τ Shear stress

cτ Current-induced bed shear stress

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cwτ Combined wave-current bed shear stress

wτ Wave-induced bed shear stress

windτ Wind shear stress

yτ Yield stress

U Wind speed

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-logger

ws Settling velocity

wsf Free-settling velocity

ws0 Characteristic value of settling velocity

za Elevation of dividing line between BSL and BNL

zb Top elevation of bottom cores

0z Bottom roughness height

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Abstract of Thesis 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 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

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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.

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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.

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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 (Håkanson 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 long-term reduction in the lake’s water level and potential

increase in turbidity. Higher suspended sediment concentration (SSC) 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 Minimum 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 excessive phosphorus loading persisted until the end of

the century. Restoration efforts since 1985 have focused on reducing phosphorus loading by

cessation of farming and restoration of the aquatic system. The water quality in the lake has been

improving for over 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 organics-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 lake’s water level on

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the suspended sediment regime, especially at high wind speeds. 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 hydrographic data required to evaluate the sediment resuspension

regime of the lake, 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 be 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 Department 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 develop 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.

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CHAPTER 2 STUDY SITE, FIELD INSTRUMENTATION AND LABORATORY 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 latitude 28˚ 37.11΄N and longitude 82˚ 37.19΄W (Figure 2-1). 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 degradation of the 20,000-ha ecosystem associated with

the lake persisted for more than 50 years.

Water 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 Canal. 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 spring in the Lake Apopka basin, Apopka Spring, also

known as Gourd Neck Spring, discharges into Gourd Neck (Figure 2-3), 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

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about 0.3 and 3 m3/s (Rosenau et al. 1977). There are three other springs, Holt Lake Spring, Bear

Spring, and Wolf’s 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 (1997). Water discharge from the lake occurred via the

Apopka-Beauclair Canal at a mean annual rate of 6.81×107 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 instrument deployment was for the primary array, UF0, at the St. Johns River

Water Management District Meteorological Tower at 28˚36΄22.22˝N and longitude

81˚37΄39.99˝W (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˚35΄28.80˝N and longitude 81̊ 37΄46.44˝W, and at UF2 at 28̊ 37΄31.50 ˝N and l81˚

35΄29.82˝W (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

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Tables 2-2 and 2-3. Photographic 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.

Underway 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 transducer 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 approximately 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 Calibration

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

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 synchronous 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 determine 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. Most voltages from the field data were

less than 800 mV, so the calibration tests were limited to low voltages. 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).

5 1.5072 10C V−= × (2.1)

Calibration 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

μm) for low (< 5 kg/m3) 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 (0.000307 2.7)1 10 NcC e− += × (2.2)

28

2.3.3 ADCP Calibration

Figure 2-11 is a plot of the echo-intensity 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).

0.22 1.980.1729e EIAC −= (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 velocity (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 column 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 with No. 200 Tyler sieve (0.074 mm diameter). This process resulted in high-

concentration 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 for 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 initial concentration profile. The samples were contained in 50 ml glass bottles

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:

2 2( )

n

s m

aCwC b

=+

(2.4)

Three settling tests 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 velocity for the present case is taken as the value of the

settling velocity at C = C1, which is wsf = 6×10-5 m/s.

Numerically simulated profiles (lines) of concentration change with time as shown in

Figure 2-12. The Suspension concentration gradually decreased with 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:

30

( ) 0sw CCt z

∂∂− =

∂ ∂ (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 concentration 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 )C z t C z= (2.6)

The zero settling flux boundary condition at the water surface (z=h) is:

( ) 0s z hw C

== (2.7)

and the zero settling flux boundary condition at the bottom(z=0) is:

0( ) 0s zw C

== (2.8)

It is seen that the simulations correspond with data (circles) reasonably well. Similar plots

for initial concentrations of 1.95 and 2.88 kg/m3 are given in Appendix A.

.

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

Interval (min) Installed Elev. (m)

from NAVD88

0-1 07/25/07-08/27/07 ADCP 60 18.99 CTD 15 18.89

0-2 08/27/07-09/14/07 ADCP 90 18.99 CTD Data lost 18.89

OBS-3 30 18.66

0-3 09/14/07-10/12/07 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 12/05/07-1/16/08

ADCP 15 19.02 CTD 30 18.89

OBS-3 30 18.66 OBS-5+ 10 18.34

0-6 01/16/08-02/29/08 ADCP 10 19.02 CTD 30 18.89

OBS-3 30 18.66

0-7 02/29/08-05/02/08 ADCP 15 19.02 CTD 60 18.89

OBS-3 30 18.66

0-8 05/02/08-06/17/08 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

32

Table 2-3. Deployments at UF1


Deployment No. Duration Instrument

Sampling Interval (min)

Installed Elev. (m) from NAVD88

1-1 04/25/08-06/17/08 ADCP 10 19.20

1-2 06/17/08-07/18/08 ADCP 15.2 18.79 OBS-3 30 18.33

Table 2-4. Deployment at UF2


Deployment No. Duration Instrument

Sampling Interval (min)

Installed Elev. (m) from NAVD88

2-1 08/28/08-09/16/08 ADCP 15 19.39

33

Figure 2-1. State of Florida and general area of study.

Figure 2-2. Central Florida lakes and waterways (Courtesy of SJRWMD).

34

Figure 2-3. Lake Apopka and locations of stations UF0, UF1 and UF2.

0.5

0.5

0.5

0.50.50.5

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

111

1

1

1

1

1

11

1 1

1

1

1

1.5

1.5

1.5

1.5

1.5

1.5

1.5

1.51.5

1.5

1.5

1.51.5

1.5

1.5

1.5

1.51.5 1.5

1.51.5

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)

DIS

TAN

CE

(m)

Boatramp

UF0Tower

UF1Tower

UF2Tower

TRANSECT1

TRANSECT2

0 2000 4000 6000 8000 10000 12000 14000 160000

2000

4000

6000

8000

10000

12000

14000

16000

Figure 2-4. Lake Apopka bathymetry, locations of UF stations and underway transects.

35

Figure 2-5. UF0 station at SJRWMD meteorological tower.

Figure 2-6. UF1 station. The same platform was later moved to UF2.

36

Figure 2-7. Schematic drawing of instrumentation at UF0.

Figure 2-8. Schematic drawing of UF1/UF2 platform and instrumentation.

37

0 250 500 750 1000 1250 15000

0.25

0.5

0.75

1

1.25

1.5

Voltage(mV)

Sus

pend

ed S

edim

ent C

once

ntra

tion(

kg/m

3 )

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 Counts

Sus

pend

ed S

edim

ent C

once

ntra

tion(

kg/m

3 )

Y=1x10-7e(0.000307X+2.7)

Figure 2-10. OBS-5+ calibration plot (SSC versus output voltage).

38

-40 -30 -20 -10 0 10 200

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 ADCP

SS

C(k

g/m

3 )

Y=0.1729e(0.22X-1.98)

DATABest fit line

Figure 2-11. ADCP calibration plot (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 =

0.00150.733.30.1

Wsf = 6.0e-006 (m/s)

Sediment Concentration (kg/m3)

Settl

ing

Velo

city

(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).

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

IF I = initial profileF = final profile


Ele

vatio

n (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. Definition sketch of concentration profile.

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). For 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, water 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

OBS-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 ̊ relative to north and dominant for 8%. The westward current was modest compared

with the other two elevations. Current-rose for each deployment is given in Appendix B.

41

The time-series of salinity, temperature and water surface elevation are provided in Figure

3-5. Water temperature variation was between 26 and 32̊C and showed a diurnal va 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˚33΄44˝N and longitude 81̊ 37΄42˝W (Figure 2 -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). The 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 3-7(C).

Although the wind speed when the highest wave height was recorded was not collected, it is

believed that high wind was the cause. 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).

42

As mentioned in Chapter 2, underway data were 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 3-10

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 components 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 1-2. OBS-5+ was

installed at UF0 during Deployments 0-5 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

43

Figure 3-13 for three elevations. As observed SSC, increased with depth indicates the presence

of stable, sediment-induced density stratification.

In Figure 3-12 the time-series 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, respectively. The values were higher than those during Deployment 0-3 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 reached 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 suspension. 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 analysis. 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 wind-rose. The maximum wind speed was 12.65 m/s, and the mean was 3.82 m/s.

44

Wind direction was distributed over all sectors of the pie chart, but winds from 60˚ relative to

north were dominant and occurred for 21% of the time. Wind-roses for every deployment of are

provided in Appendix B.

45

0

5

10

15

Vel

ocity

(cm

/s) Elev. 18.83m

0

5

10

Vel

ocity

(cm

/s) Elev. 18.63m

09/15 09/20 09/25 09/30 10/05 10/100

5

10

Day of 2007

Vel

ocity

(cm

/s) Elev. 18.33m

Figure 3-1. Current velocity time-series during Deployment 0-3.

15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 55 - 99 - 13

Velocity(cm/s)

Figure 3-2. Current-rose at 18.83 m elevation during Deployment 0-3.

46

15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 55 - 99 - 13

Velocity(cm/s)


15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 55 - 99 - 13

Velocity(cm/s)


47

20

25

30

35

Tem

pera

ture

( °C)

0.18

0.19

0.2

0.21

0.22

Sal

inity

09/15 09/20 09/25 09/30 10/05 10/1019.3

19.4

19.5

Wat

er S

urfa

ce E

lev.

(m)

Day of 2007

Figure 3-5. Salinity, temperature and water surface elevation time-series during Deployment 0-3.

18

18.2

18.4

18.6

18.8

19

19.2

19.4

19.6

19.8

20

Wat

er S

urfa

ce E

lev.

(m)

Bottom Elevation from NAVD88 : 18.16m

09/15 09/20 09/25 09/30 10/05 10/100

5

10

15

20

25

30

35

40

45

Day of 2007

Pre

cipi

tatio

n(m

m)ADCP

CTDSJRWMDBottom Elev.PRCP(mm)

Figure 3-6. Water surface elevation and precipitation during Deployment 0-3.

48

00.10.20.30.4

Wav

e H

eigh

t(m)

HeightPeriod

09/15 09/20 09/25 09/30 10/05 10/100.50.60.70.80.91

Wav

e P

erio

ds(s

)

Day of 2007

A)

00.10.20.30.4

Wav

e H

eigh

t(m)

HeightPeriod

00:00 06:00 12:00 18:00 00:000.50.60.70.80.91

Wav

e P

erio

ds(s

)

September 20, 2007

B)

00:00 06:00 12:00 18:00 00:000

5

10

15

September 20, 2007

Win

d S

peed

(m/s

)

C)

Figure 3-7. Wave height and period time-series. A) During Deployment 0-3. B) For the date when the highest wave 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

Pre

ssur

e(kP

a)

Day of 2007

A)

09:25:12 09:25:55 09:26:38 09:27:22 09:28:05

106.9

106.95

Pre

ssur

e(kP

a)

September 27 in 2007

B)

Figure 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.

49

Distance along Transect1(m)

Ele

vatio

n(m

)Water Surface Elev. from NAVD88 : 19.55m

0 1000 2000 3000 4000 5000 6000 7000 8000 900017.5

18

18.5

19

19.5

Vel

ocity

(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


Vel

ocity

(cm

/s)

Figure 3-10. Current-vector data along Transect 1 at the elevation of the top acoustic bin on 11/01/07.

50


Ele

vatio

n(m

)

Water Surf ace Elev . f rom NAVD88 : 19.55m

0 1000 2000 3000 4000 5000 6000 7000 8000 900017.5

18

18.5

19

19.5

Eas

t Vel

ocity

(cm

/s)

-15

-10

-5

0

5

10


Ele

vatio

n(m

)

Water Surf ace Elev . f rom NAVD88 : 19.55m

0 1000 2000 3000 4000 5000 6000 7000 8000 900017.5

18

18.5

19

19.5

Nor

th V

eloc

ity(c

m/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 10/100

0.05

0.1

0.15

0.2

0.25

0.3

Day of 2007

SS

C(k

g/m

3 )

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.

51

0

0.2

0.4

0.6

0.8

1

SS

C(k

g/m

3 )

Elev. 18.83m

0

0.2

0.4

0.6

0.8

SS

C(k

g/m

3 )

Elev. 18.63m

09/15 09/20 09/25 09/30 10/05 10/100

0.2

0.4

0.6

0.8

Day of 2007

SS

C(k

g/m

3 )

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 01/150

0.5

1

1.5

2

Day of 2007 & 2008

SS

C(k

g/m

3 )

OBS-5+ at Elev. 18.34m

Figure 3-14. SSC time-series from OBS-5+ at 18.34 m elevation during Deployment 0-5.

52


Ele

vatio

n(m

)

Water Surface Elev. from NAVD88 : 19.55m

0 1000 2000 3000 4000 5000 6000 7000 8000 900017.5

18

18.5

19

19.5

SS

C(k

g/m

3 )

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 10/050

5

10

15

20

Win

d S

peed

(m/s

)

Speed

09/15 09/20 09/25 09/30 10/05 10/100

100

200

300

Day of 2007

Win

d D

irect

ion(°)

Direction

Figure 3-16. Wind speed and direction during Deployment 0-3.

53

20%

15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 14

Wind Speed(m/s)

20%

15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 14

Wind Speed(m/s)

Figure 3-17. Wind-rose for Deployment 0-3.

54

CHAPTER 4 RESUSPENSION 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 for 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.

Weekly 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 wave 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 instrument 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. Data for the highest elevation were not available for that week.

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 ˚C. The variation of salinity

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 those 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 (d-1) 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 d-1, 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 WSE at frequencies of 1 d-1 and 2 d-1,

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

56

higher than the diurnal. This is clear from the degree of coherence (a measure of cross-

correlation in the frequency domain) in Figures 4-6 and 4-9, which is dominant at 1 d-1 and 2 d-1.

Thus, current velocity, wave height and SSC are strongly related to wind speed.

For wind waves two 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 former 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 corresponding time-series and frequencies in the high-

frequency 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 interdependence 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 wave height and wind speed. Coherence

is observed at several frequencies including 0.25, 1, and 1.75 d-1; however, 1 d-1 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 d-1.

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 increase linearly; however the period plot shows weaker correlation (R2 =

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 between current speeds (at three elevations) and wind speed.

For all elevations a coherence peak is observed at 1 d-1, 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 2-1 increased exponentially with wind speed. Examples 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 speed 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 d-1and 2 d-1, with the highest coherence at 1 d-1, as also suggested in Figure

4-1. Note that the strong peak at 1.1 d-1 in Figure 4-10 is close to 1 d-1.

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 between 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,

58

by wind-driven current and by the combined effects 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 presented 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 bed shear stress cwτ as defined in Eq. (4.1) is

used in this study.

( )cw c wYτ τ τ= + (4.1)

where cτ is the current-induced bottom shear stress and wτ 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 )m nY aX X= + − (4.2)

c

c w

X ττ τ

=+

(4.3)

Since the multiplier Y in Eq. (4.1) is ≥ 1, the general effect of adding a wave boundary layer to a

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:

1 2 3 4( cos ) ( cos ) log( / )I Iw Da a a a a f Cφ φ= + + + (4.4a)

1 2 3 4( cos ) ( cos ) log( / )I Iw Dm m m m m f Cφ φ= + + + (4.4b)

59

1 2 3 4( cos ) ( cos ) log( / )I Iw Dn n n n n f Cφ φ= + + + (4.4c)

The quantity φ is the angle between the current stress direction and the wave stress direction.

This angle will be taken to be zero for the present purposes. The coefficients 1 4~a a , 1 4~m m ,

1 4~n n , and I are given in Table 4-8 from Soulsby et al. (1993), who derived them from three

independent sources (designated HT91, MS90 and F84).

The current-induced bottom shear stress cτ can be calculated from Eq. (4.5).

2c D cC u=τ ρ (4.5)

where ρ 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

0

0.4ln( / ) 1DC

h z

= − (4.6)

where h is the boundary layer height (taken to be equal to the water depth in the lake) and 0z is

the bottom roughness height.

The wave shear stress wτ is given by Eq. (4.7).

20.5w w bf uτ ρ= (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).

2sinhbHu

khσ

= (4.8)

60

where H is the wave height, 2 /Tσ π= is the wave angular frequency, 2 /k Lπ= is the wave

number, T is the wave period, and L is the wavelength. Given /bA u σ= , the wave friction

factor is given by (Soulsby et al., 1993) Eq. (4.9).

0.19

0.00251exp 5.21 ; 1.57ws s

A Afk k

− = >

(4.9a)

0.3 ; 1.57ws

Afk

= ≤ (4.9b)

where sk is the Nikuradse roughness, normally taken as 030z .

As an example, select 1,000ρ = kg/m3, 85.0=T s, 29.1=h m, 0002.00 =z m (based on

numerical hydrodynamic model calibration of wind-driven circulation in the lake by Dr. Earl

Hayter, personal communication), 0.3H = m, 0.007cu = m/s and 0φ = ° . These values are

based on Deployment 0-3. Using the linear wave theory, 5.57k = m-1 is obtained from the

dispersion relationship 2 tanhgk khσ = (Dean and Dalrymple 1991). Therefore, 1.13L = m is

obtained.

Equation (4.8) yields

30.3 (2 / 0.85) 1.68 102 sinh(5.57 1.29)bu π −× ×

= = ×× ×

m/s

From Eq. (4.9)

0

/ 0.037930

b

s

uAk z

σ= =

Therefore, wf = 0.3, as / sA k is less than 1.57.

From Eq. (4.7)

3 2 40.5 1000 0.3 (1.68 10 ) 4.23 10wτ− −= × × × × = × Pa

61

From Eq. (4.6)

230.4 2.65 10

ln(1.29 / 0.0002) 1DC − = = × −

From Eq. (4.5)

3 2 41000 2.65 10 (0.007) 1.3 10cτ− −= × × × = × Pa

From Eq. (4.4) and the coefficients designated HT91 in Table 4-7,

3( 0.07 1.87) ( 0.34 0.12) log(0.3 /(2.65 10 )) 0.855a −= − + + − − × × =

3(0.72 0.33) (0.08 0.34) log(0.3 /(2.65 10 )) 1.253m −= − + + × × =

3(0.78 0.23) (0.12 0.12) log(0.3 /(2.65 10 )) 0.55n −= − + − × × =

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

4 4

1.3 10 0.2351.3 10 4.23 10

X−

− −

×= =

× + ×

From Eq. (4.2)

1.253 0.551 0.855 (0.235) (1 0.235) 1.12Y = + × − =

Similarly, Y = 1.04 for MS90 and Y = 1.17 for F84 are obtained.

Finally, for HT91, from Eq. (4.1) the combined wave-current shear stress is

4 4 41.12 (1.3 10 4.23 10 ) 6.2 10cwτ − − −= × × + × = × Pa

Similarly, cwτ is 5.75×10-4 Pa for MS90 and 6.49×10-4 Pa for F84. The combined wave-current

bed shear stress cwτ values from the three methods are close to each other.

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)], non-

dimensional depth [Eq. (4.12)], and non-dimensional fetch [Eq. (4.13)] parameters.

2

4

g EU

=ε (4.10)

pf Ug

=υ (4.11)

2

ghU

=δ (4.12)

2

gxU

=χ (4.13)

where g is the gravitational acceleration, E is the total wave energy or variance of the wave

record, 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 ε and υ are obtained from the following relationships.

1.74

3 11

1

3.64 10 tanh tanhtanh

BAA

ε − = ×

(4.14)

where 0.751 0.493A δ= and 3 0.57

1 3.13 10B χ−= × .

0.37

22

2

0.133 tanh tanhtanh

BAA

υ−

=

(4.15)

where 1.012 0.331A δ= and 4 0.73

2 5.215 10B χ−= × . These relationships are based on field

observation in Lake George in Australia.

63

As an example of the use of these equations, consider 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 60̊ relative to north as seen in Figure 3-17. The mean water depth along the fetch

was 1.28 m.

From Eq. (4.12)

2

9.81 1.28 0.2567×

= =δ

From Eq. (4.13)

2

9.81 5630 1127.17

χ ×= =

Therefore, A1 = 0.1776, B1 = 0.1719, A2 = 0.0837, and B2 = 0.0881.

From Eq. (4.14)

1.74

3 40.17193.64 10 tanh(0.1776) tanh 1.0763 10tanh(0.1776)

ε − − = × = ×

From Eq. (4.15)

0.370.08810.133 tanh(0.0837) tanh 0.3647

tanh(0.0837)υ

−

= =

By substituting these values in Eqs. (4.10) and (4.11), E and pf are obtained as 2.68×10-3 m2 and

0.51 Hz, respectively. The significant wave height is defined as 4sH E= . 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

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 11

1

9.3 10 tanh tanhtanh

BAA

ε − = ×

(4.16)

0.43

22

2

0.28 tanh tanhtanh

BAA

υ−

=

(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 4-14 in which S is the wind-induced water level

setup. From force balance it can be shown that

( - ) = ( )

wind cdS Sdx g h + S

= τ τρ

(4.18)

i.e.

1

g 1

windc

cSShh

−

= +

τττ

ρ

(4.19)

where τwind is the wind stress at the water surface. Let

2g 1 S S hh h

= +

α ρ

(4.20)

Therefore

65

wind c

c c

+=

τ α ττ τ

(4.21)

Let

c

c

=+τβ

α τ (4.22)

In other words

c wind=τ βτ (4.23)

Unfortunately, this relationship does not lead to a useful approach to determine τc because β is

unknown. In order to relate τc to τwind 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 between

measured U and uc at different mean water depths 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 (4.478×10-3) based on the best-fit equations (Figure 4-15) as follows.

34.478 10cu U−= × (4.24)

Hence, τc for the Soulsby et al. formula is obtained directly from the wind speed

3 2(4.478 10 )c DC Uτ ρ −= × (4.25)

where CD is given by Eq. (4.6). Characteristic values are z0= 0.0002 m and ρ = 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

66

water current (i.e. the 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 correspond 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 probability 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 as 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

approximation of the current responsible for the generation of τc.

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 depends on the vertical structure of the

concentration profile. The vertical structure is conveniently 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

effective 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).

67

The four zones are dynamically connected by particle settling, 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 stresses 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 resettling 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

between BSL, BNL and CB that change their thickness and concentration without participation

by DSL.

Measurements in Lake Apopka suggest that there are two modes of suspended sediment

transport. Colloidal matter and particles with very low settling velocities appear 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 concentration gradient on advective transport relative to

convection. In Figure 4-18 a sample time-series of concentration gradient (CUF0-CUF2)/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 10-4 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 the vertical gradient of

concentration between the bottom-most (at 18.14 m elevation) and the top-most (at 18.54 m)

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 greater 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

s sz

C Cw C Dt z z

∂ ∂ ∂ = + ∂ ∂ ∂ (4.26)

This balance, 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 wind-

induced 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 0sD . In general, for given sediment the settling velocity

depends on the flow shear rate and concentration (Teeter 2001a, 2001b). In the low-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 representation of the settling velocity is of the form

0 ( )ns sw w f C= (4.27)

where ws0 is a characteristic value of ws and ( )nf C is a modifier of ws0 due to the presence of

sediment in suspension. As for the response of the lake sediment to wind, the main interest is in

the settling velocity on resuspension as C increases with wind speed. Since this increase is due to

69

enhanced aggregation of flocs by turbulence, the dependence of ws on C can be assumed to be

given in its general form 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<<b2, and Eq. (2.4) reduces to

0n

s sw w C= (4.28)

where 20 ,m

sw ab−= and from Eq. (4.27) ( ) .nf C C= Given a = 0.8, b = 2.7 and m = 2.8 from

Figure 4-22 yields ws0 = 3.07×10-3 m/s. Also, n = 1. The data in red asterisk and blue circle are

based on Dr. Andrew Manning’s field photography (personal communication) and the

experiments in settling column, respectively. We will assume that Eq. (4.28) is applicable to

DSL as well because of the unusually significant binding effect of the abundant mucous in the

sediment secreted by cyanobacteria and other plankton even at low concentrations (Paerl et al.

2001).

The data points in Figure 4-22 indicate that the flocculation settling range ends at a peak

concentration of about 1.26 kg/m3, corresponding to a (peak) settling velocity of about 2.23×10-3

m/s. Thus, for C = 1.26 kg/m3 and ws = 2.23×10-3 m/s one obtains ws0 = 1.77×10-3 m/s. For the

present purpose it will be considered that the relationship -31.77×10sw C= holds over the entire

concentration range in DSL and BSL. This is especially so because at high wind speeds at which

SSC prediction is important, DSL (in which ws does not vary with C) is taken over by BSL (in

which ws increases with C). Near the bottom hindered settling becomes important; however, in

the resuspension equation to be developed it will be assumed that the near-bed layer (BNL) is a

pool of dense suspended sediment which acts as a source as well as sink of sediment in BSL. The

dividing line between BSL and BNL is the 1.26 kg/m3 (i.e. order of 1 kg/m3) isopycnal contour.

Let the elevation of this concentration level relative to the bed datum, i.e. the thickness of BNL,

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 examine 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 consisting of DSL and BSL are temporally in quasi-

equilibrium over this duration. Thus Eq. (4.26) after substitutions becomes

20

00s

s

wC Cz D

∂+ =

∂ (4.29)

which can be integrated from reference concentration Ca at elevation za

02

0a a

C zsC z

s

wdC dzC D

= −∫ ∫ (4.30)

to yield Eq. (4.31).

1 1 0

0

( )sa a

s

wC C z zD

− −− = − (4.31)

i.e.

0

0 0( )s a

s a a s

D CCw C z z D

=− +

(4.32)

The elevation za may be conveniently taken as a fraction αa of the water depth h,

i.e. .a az h= α Thus Eq. (4.33) becomes

0

0 0( )s a

s a a s

D CCw C z h Dα

=− +

(4.33)

The 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, αa ≈ 0.1/1.00 = 0.1, where 1.00

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 cw yτ − τ , where yτ 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 characteristic value of yτ 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= ; =8 10 y c a cC ×τ α α (4.34)

The coefficient αc = 8×10-8 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 y cwτ = τ must be satisfied.

The following sediment entrainment equations are iteratively selected to model Ca by

considering the effect of mixing within BNL due to shear stress

1.26 ( ) ;ba b cw y cw yC δα τ τ τ τ= + − > (4.35)

where αb and δb 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 = 40 kg/m3.

Hindered settling occurs in the layer of thickness za bounded by concentrations Ca = 1.26 kg/m3

72

at the top and Cc = 40 kg/m3 at the bottom. Consolidation occurs at higher concentrations in the

bed (Winterwerp and van Kesteren 2004).

The presence of particle-reactive short-lived Beryllium 7Be (half life t½=53 d) (Figure 4-

26) suggests that mixing of sediment in BNL occurs within 4-5 half lives of the tracer (~200-250

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 will 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 between

0 and 54.26 m/s in Table 4-9 (and plotted in Figure 4-27) indicates that the probability of

occurrence of 22.8 m/s is low (1.0000-0.99946 = 0.00054, i.e. 0.054%). Speeds (1-minute

average) that are greater than 33.5 m/s are defined as hurricane winds. 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 40 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/m3. Then, taking δb = 1.5 from classical sediment transport mechanics (Julien 1995), the

coefficient αb from Eq. (4.35) is obtained as 144.96 because cwτ = 0.31 Pa at 30 m/s with water

depth 1.26 m.

73

4.5.4 Model Calibration

The wave shear stress wτ was estimated from the significant wave height and period using

Eqs. (4.16) and (4.17), and the current shear stress cτ was calculated from Eq. (4.25). The

combined wave-current bed shear stress cwτ 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 4-29(b) the

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

of wτ to cτ is given in Table 4-10 at selected water depths and wind speeds.

Measured SSC values are available at three elevations 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 Ds0 (which along with the settling velocity governs the

magnitude of C) is calculated from Eq. (4.31). Figure 4-30 shows the plot of Ds0 against the

respective critical friction velocity for resuspension, * /cw cwu τ ρ= . From the plot, the best-fit

mean relationship between Ds0 and cwτ is as follows.

2 30 * *0.6 10 ; 2.43 10s cw cwD u u− −= × < × (4.36a)

4 30 * *0.3023 6.832 10 ; 2.43 10s cw cwD u u− −= − × ≥ × (4.36b)

Using Eq. (4.36), Eq. (4.33) is written as

74

23*

*20 *

0.6 10 ; 2.43 10( ) 0.6 10

cw acw

s a a cw

u CC uw C z h uα

−−

−

×= < ×

− + × (4.37a)

3

3**3

0 *

(0.5 1.2 10 ) ; 2.43 10( ) 0.5 1.2 10

cw acw

s a a cw

u CC uw C z h uα

−−

−

− ×= ≥ ×

− + − × (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).

33*

*30 *

(0.6756 1.297 10 ) ; 1.94 10( ) 0.6756 1.297 10

cw acw

s a a cw

u CC uw C z h uα

−−

−

− ×= ≥ ×

− + − × (4.38)

43*

*40 *

(0.3419 9.675 10 ) ; 2.88 10( ) 0.3419 9.675 10

cw acw

s a a cw

u CC uw C z h uα

−−

−

− ×= ≥ ×

− + − × (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 simulated 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

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 bottom 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 within 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 uncertainty 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 (τw, τc and τcw) and SSC at the top-most

and 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

periods 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 difference of 0.01 kg/m3. At 15.8 m/s (on 01/18/08), the

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 τw, τc and τcw. For

example, during the highest wind speed (15.8 m/s) within Deployment 0-6 (water depth 1.29 m),

τw = 0.013 Pa, τc = 0.0132 Pa and τcw = 0.033 Pa. Thus τw/ τc = 0.98, which means that both shear

stresses would be about equal. At the mean wind speed of 4 m/s (which is close to the exact

value, 4.2 m/s during the study), τw = 4.41×10-8 Pa, τc = 8.5×10-4 Pa and τcw = 8.53×10-4 Pa. Thus

the effect of current is dominant. In water depth of 1.29 m, τw exceeds τc when wind speed is

greater than about 15.8 m/s (Table 4-10). At a sustained wind speed of 30 m/s τw = 0.226 Pa, τc =

0.048 Pa and τcw = 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 τw and τc 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.

77

Table 4-1. Weeks corresponding to parametric values Deployment

No. Week Dates Deployment 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 02/18/08 - 02/24/08 31 02/25/08 - 03/02/08

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 Mean 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 0.60 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

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 1.01 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


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

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 - - - - - - - - -


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 29.7 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 - - - - - - - - -

81


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


Temperature (̊ C) 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 19.40 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 19.45 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 19.45 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

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 19.30 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. Weekly maximum, mean and minimum SSC from ADCP at different elev. at UF0

UF0 Station


SSC (kg/m3) from ADCP Top Middle Bottom

Max Mean Min Max Mean Min 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 - - - - - - - - -

83


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 - - - - - - - - -


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 - - - - - - - - -


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)

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 - - - - - - - - -


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


SSC (kg/m3) from OBS-3 Depl. Parameters

Weeks

SSC (kg/m3) 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 0.02 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 0.03 0 Minimum 0.19 0.02 0 Minimum 0.1 0.01 0

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

86

Table 4-9. Cumulative density function of wind speed Wind speed (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

87

Table 4-10. Bed shear stresses (τw, τc and τcw) for selected water depths and wind speeds Shear stress (Pa)

Wind speed (m/s)

Water depth (m)

0.5 0.75 1.0 1.29 1.5 2.0

wτ

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-02 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

cτ

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


cwτ

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


w

c

ττ

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

88

Table 4-11. SSC at 18.38 m elevation for the selected water depths and wind speeds SSC (kg/m3)

at elev. 18.38 m

Wind speed (m/s)

Water depth (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

89

Table 4-12. SSC at 18.88 m elevation for the selected water depths and wind speeds SSC (kg/m3)

at elev. 18.88 m

Wind speed (m/s)

Water depth (m)

0.5 0.75 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 1.66 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

90

0

1

23

x 105

Win

d S

peed

Power Spectral Density

0

1

2x 10

5

Tem

pera

ture

0

0.5

1

Sal

inity

0

102030

Wat

er S

urfa

ce E

lev.

0

1

2x 10

4

Vel

ocity

0

50

100

Wav

e H

eigh

t

0

50

100

Wav

e P

erio

d

Elev. 18.83m

0

5000

10000

Vel

ocityElev. 18.63m

0

5000

10000

Vel

ocity Elev. 18.33m

0

10

20

SS

CADCP at Elev. 18.83m

0

102030

SS

C


0

500

SS

C

ADCP at Elev. 18.63m

0 0.5 1 1.5 2 2.50

500

Frequency (1/days)

SS

C

ADCP at Elev. 18.33m

Figure 4-1. Power spectral density (PSD) of all data for Deployment 0-3. For any parameter with unit θ, the unit on the ordinate is θ2 /Hz.

91

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.5

1

1.5

2

2.5

3

3.5

4

4.5x 10

-4

Frequency (Hz)

PS

D o

f Pre

ssur

e

Figure 4-2. PSD for wind waves. Pressure was measured in kPa.

0

0.02

0.04

0.06

0.08

Max

PS

D(m

2 /H

z)

Max PSDFrequency

0

0.2

0.4

Freq

uenc

y 0~

0.5H

z

A)

09/15 09/20 09/25 09/30 10/05 10/100

0.02

0.04

0.06

0.08

Max

PS

D(m

2 /H

z)

Day of 2007

0.5

0.8

1.1

1.4

1.7

Freq

uenc

y 0.

5~2H

z

B)

Figure 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.

92

0 0.5 1 1.5 2 2.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Frequency(1/days)

Coh

eren

ce

Figure 4-4. Coherence between wind speed and wave height.

0

0.05

0.1

0.15

0.2

0.25

0.3

Sin

gific

ant W

ave

Hei

ght(m

) A) R2=0.6274

0 2 4 6 8 10 120.6

0.7

0.8

0.9

Wind Speed(m/s)

Sin

gific

ant W

ave

Per

iod(

s) B) R2=0.2919

DATABest fit line

Figure 4-5. Variations of A) the significant 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.

93

0 0.5 1 1.5 2 2.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Frequency(1/days)

Coh

eren

ce

Elev. 18.83mElev. 18.63mElev. 18.33m

Figure 4-6. Coherence 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.

94

Figure 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.

0 0.5 1 1.5 2 2.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Frequency(1/days)

Coh

eren

ce

Figure 4-9. Coherence between wind speed and SSC from OBS-3 at 18.66 m elevation.

95

0 0.5 1 1.5 2 2.50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Frequency(1/days)

Coh

eren

ce

Elev. 18.83mElev. 18.63mElev. 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.

96

Figure 4-12. Variation of SSC at 18.33 m elevation from ADCP with wind speed.

0 2 4 6 8 10 12 14 16 18 20 220

0.050.1

0.150.2

0.250.3

0.350.4

Wind Speed(m/s)

Wav

e H

eigh

t(m)

A)Best fit lineEq. 4.14Eq. 4.16

0 2 4 6 8 10 12 14 16 18 20 220

0.5

1

1.5

2

2.5

3

Wind Speed(m/s)

Wav

e P

erio

d(s) B)

Best fit lineEq. 4.15Eq. 4.17

Figure 4-13. Relationships between A) significant wave height, B) period and wind speed; best-fit data line and equations.

97

Figure 4-14. Schematic drawing of the relationship between wind stress and current stress in the lake.

0

0.1

0.21.40 m < h Y=0.004319X

R2=0.0000

0

0.1

1.15 m < h ≤ 1.20 m Y=0.005995XR2=0.1064

0

0.1

1.10 m < h ≤ 1.15 m

Cur

rent

spe

ed, u

c(m/s

)

Y=0.003245XR2=0.2585

0 2 4 6 8 10 12 140

0.1

h ≤ 1.10 m

Wind speed, U(m/s)

Y=0.004351XR2=0.1797

Figure 4-15. Measured variation of current speed with uc with wind speed U at station UF0. R2 values indicate weak correlations.

Δx

S+ΔS S

τwind

τc

h Hydrostatic pressure

Hydrostatic pressure

Current

98

-150 -100 -50 0 50 100 1500

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)

Cum

ulat

ive

prob

abili

ty

Elev. 19.01mElev. 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 sediment concentration zones and resuspension modes (adapted from Jain 2007).

Particle 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 Hindered settling Consolidating bed (CB)

Erosion

Settling and deposition Erosion

Bed

Suspension

Particle settling and deposition on bed

99

09/04 09/05 09/06 09/07 09/08-1

-0.5

0

0.5

1x 10

-4

Hor

izon

tal S

SC

gra

dien

t(SS

C/m

) at W

ater

Dep

th 0

.35m

Day of 2008

CUF0<CUF2

CUF0>CUF2

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 2008

Ver

tical

SS

C g

radi

ent(S

SC

/m) a

t UF0

Figure 4-19. Measured vertical 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).

100

09/04 09/05 09/06 09/07 09/08-0.5

0

0.5

1

Day of 2008

Ver

tical

SS

C g

radi

ent(S

SC

/m) a

t 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. SSC refers to concentration above the elevation z = za.

CB

BNL

BSL

DSL

z = 0

z = za

Cb Ca

C(z,t)

C

z = zb

Cc

z

C

U = UL

Hindered settling

Consolidation

Top of core

Free settling

Flocculation settling Entrainment

Ca Cc Cm

U = UH

z

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 =

0.82.72.810.1

Wsf = 3.1e-004 (m/s)

Ws = aCn/(C2+b2)m


Settl

ing

Velo

city

(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 laboratory 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-31-08site. 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

102

Figure 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).

Figure 4-25. Stress versus dry density (courtesy Dr. John Jaeger).

103

Figure 4-26. Profile of Beryllium-7 radioisotope at LA-Tower-07a (courtesy Dr. John Jaeger).

.

-10 0 10 20 30 40 50 600

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

CDF

Wind 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 SJRWMD.

Nominal thickness of stirred floc layer

104

0

2.5

5x 10

-3

Wind Speed(m/s)

τ w(P

a)

Water Depth 1.26m

0

0.005

0.01

Wind Speed(m/s)

τ c(P

a)

Water Depth 1.26m

12/06 12/11 12/16 12/21 12/26 12/31 01/05 01/10 01/150

0.005

0.01

Wind Speed(m/s)

τ 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)

τ w(P

a)

A)Water Depth 2.0mWater Depth 1.0mWater Depth 0.5m

0

0.025

0.05

0.075

Wind Speed(m/s)

τ c(P

a)

B)Water Depth 2.0mWater Depth 1.0mWater Depth 0.5m

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 300

0.2

0.4

Wind Speed(m/s)

τ cw

(Pa)

C)Water Depth 2.0mWater Depth 1.0mWater 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.

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

1x 10

-3

u*cw(m/s)

Ds0

Ds0=0.6× 10-2 u*cw

Ds0=0.6756u*cw-1.297×10-3

Ds0=0.5000u*cw-1.200×10-3

Ds0=0.3419u*cw-9.675×10-4

Figure 4-30. Variation of Ds0 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 & 2008SS

C(k

g/m

3 ) a

t Ele

v. 1

8.34

m

Computed by the Upper Bound

12/06 12/11 12/16 12/21 12/26 12/31 01/05 01/10 01/150

0.5

1

1.5

Day of 2007 & 2008

Computed by the Lower Bound

Figure 4-31. Measured and simulated time-series of SSC at 18.34 m elevation during Deployment 0-5.

106

0

0.5

1

1.5

2

Day of 2008

A) By ADCPPrediction

0

0.5

1

1.5

Day of 2008SS

C(k

g/m

3 ) a

t Ele

v. 1

8.38

m

B) Upper Bound

01/18 01/23 01/28 02/02 02/07 02/12 02/17 02/22 02/270

0.5

1

1.5

Day of 2008

C) Lower Bound

Figure 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.

0

0.25

0.5

0.75

1

Day of 2008

A) By ADCPPrediction

0

0.25

0.5

0.75

Day of 2008SS

C(k

g/m

3 ) a

t Ele

v. 1

8.88

m

B) Upper Bound

01/18 01/23 01/28 02/02 02/07 02/12 02/17 02/22 02/270

0.25

0.5

0.75

Day of 2008

C) Lower Bound

Figure 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.

107

00.5

11.5

2

Day of 2008

Water Depth 0.50m

00.5

11.5

Day of 2008

Water Depth 0.75m

00.5

11.5

Day of 2008

SS

C(k

g/m

3 ) a

t Ele

v. 1

8.38

m

Water Depth 1.00m

00.5

11.5

Day of 2008

Water Depth 1.50m

01/18 01/23 01/28 02/02 02/07 02/12 02/17 02/22 02/270

0.51

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 2008

SS

C(k

g/m

3 ) a

t Ele

v. 1

8.88

m

Water 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 02/270

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.

108

CHAPTER 5 SUMMARY AND CONCLUSIONS

5.1 Summary

Water quality in many shallow aquatic systems is strongly influenced by the suspended

solids. Resuspended sediment 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 the

potential 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 analytical

model for local resuspension has been developed.

The model relies on the assumption of short-term (hourly time-scale) equilibrium between

entraining 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 account 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 above the ambient level. This limitation

must be borne in mind when assessing the significance of SSC predictions at wind speeds in

109

excess of about 20 m/s. Following calibration and validation, the model has been used to predict

the effects of high wind speeds 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. The 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 Apopka-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 probability of

occurrence of a speed of 20 m/s is only 0.055%. The dominant wind direction during the

study was from 60̊ relative to the north.

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 observed 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 resuspension 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 recorded at UF0 were 10 and 41 cm,

respectively. The significant wave period remained close to 0.7 s. A consequence of

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 enough 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-weight

(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< 40 kg/m3). The base of BNL is the surface of

the consolidating or consolidated bed (CB) (BSL; 40 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 dewatering 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

111

matter), BSL and DSL. Participation of the bed (CB) in the resuspension process appears

to be practically nil most of the time.

11. SSC increases with the combined wave-current bed shear stress τcw. The contribution

from wave-induced stress (τw) and wind-driven current-induced stress (τc) varies with

water depth and wind speed. At a recorded wind speed of 15.8 m/s (and water depth 1.3

m), τw = 0.013 Pa, τc = 0.0132 Pa and τcw = 0.033 Pa. Thus the contribution of τw and τc to

τcw 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 ≈16 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 point of water quality one

would expect that the main concern would be the peak value of SSC at the lower

elevation (18 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, lowering the depth of water (at UF0) successively from the present 1.3 m to 1 m,

0.75 m and (the extreme low) 0.5 m would increase 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

estimations 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 the order of 13.8 kg/m3. Contribution to resuspension

from waves would be 4-5 times that due to current.

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-wide 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. Investigate 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 stratification as part of an effort to assess the role of turbid fronts in lake

dynamics.

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 =

0.122.820.1

Wsf = 2.0e-005 (m/s)


Set

tling

Vel

ocity

(m/s

)

Figure A-1. Settling velocity variation with SSC. Initial 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



Ele

vatio

n (m

)

Figure A-2. Simulation of concentration change in the settling column (C0=1.95 kg/m3).

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 =

0.12.32.92.30.1

Wsf = 4.0e-006 (m/s)


Set

tling

Vel

ocity

(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



Ele

vatio

n (m

)

Figure A-4. Simulation of concentration profile change in the settling column (C0=2.88 kg/m3).

115

APPENDIX B FIELD MEASUREMENTS

8%

4%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 55 - 1010 - 1515 - 2020 - 2525 - 30

Velocity(cm/s)

Figure B-1. Current-rose at elev. 18.51 m during Deployment 0-2.

15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 55 - 1010 - 1515 - 2020 - 2525 - 30

Velocity(cm/s)


116

15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 55 - 99 - 13

Velocity(cm/s)


15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 55 - 99 - 13

Velocity(cm/s)


117

15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 55 - 99 - 13

Velocity(cm/s)


8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 88 - 1010 - 1515 - 25

Velocity(cm/s)


118

8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 88 - 1010 - 1515 - 25

Velocity(cm/s)


8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 88 - 1010 - 1515 - 25

Velocity(cm/s)


119

9%

6%

3%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 2.52.5 - 33 - 44 - 55 - 66 - 88 - 10

Velocity(cm/s)


9%

6%

3%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 2.52.5 - 33 - 44 - 55 - 66 - 88 - 10

Velocity(cm/s)


120

9%

6%

3%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 2.52.5 - 33 - 44 - 55 - 66 - 88 - 10

Velocity(cm/s)


8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 2.52.5 - 33 - 3.53.5 - 44 - 55 - 88 - 14

Velocity(cm/s)


121

8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 2.52.5 - 33 - 3.53.5 - 44 - 55 - 88 - 14

Velocity(cm/s)


8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 0.50.5 - 11 - 1.51.5 - 22 - 2.52.5 - 33 - 3.53.5 - 44 - 55 - 88 - 14

Velocity(cm/s)


122

15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 99 - 1010 - 1515 - 2020 - 25

Velocity(cm/s)


15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 99 - 1010 - 1515 - 2020 - 25

Velocity(cm/s)


123

8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 99 - 1010 - 2020 - 30

Velocity(cm/s)


8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 99 - 1010 - 2020 - 30

Velocity(cm/s)


124

8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 99 - 1010 - 2020 - 30

Velocity(cm/s)


6%

4%

2%

WEST EAST

SOUTH

NORTH

0 - 33 - 66 - 99 - 1212 - 1515 - 1818 - 2121 - 2424 - 2727 - 30


125

6%

4%

2%

WEST EAST

SOUTH

NORTH

0 - 33 - 66 - 99 - 1212 - 1515 - 1818 - 2121 - 2424 - 2727 - 30


9%

6%

3%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 88 - 1010 - 1515 - 20

Velocity(cm/s)


126

9%

6%

3%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 88 - 1010 - 1515 - 20

Velocity(cm/s)


9%

6%

3%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 88 - 1010 - 1515 - 20

Velocity(cm/s)


127

8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 99 - 1010 - 1515 - 30

Velocity(cm/s)


8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 99 - 1010 - 1515 - 30

Velocity(cm/s)


128

8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 99 - 1010 - 1515 - 30

Velocity(cm/s)


7%

5%

3%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 99 - 1010 - 1515 - 22

Velocity(cm/s)


129

18%

12%

6%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 1010 - 1515 - 22

Velocity(cm/s)


18%

12%

6%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 1010 - 1515 - 22

Velocity(cm/s)


130

18%

12%

6%

WEST EAST

SOUTH

NORTH

0 - 11 - 22 - 33 - 44 - 55 - 66 - 77 - 88 - 1010 - 1515 - 22

Velocity(cm/s)


18

18.2

18.4

18.6

18.8

19

19.2

19.4

19.6

19.8

20

Wat

er S

urfa

ce E

lev.

(m)


Jul07 Sep07 Nov07 Dec07 Feb08 Apr08 May08 Jul08 Aug080

5

10

15

20

25

30

35

40

45

Time(month)

Pre

cipi

tatio

n(m

m)

ADCPCTDSJRWMDBottom Ele.PRCP(mm)

Figure B-32. Time-series of WSE at UF0 and precipitation.

131

18

18.2

18.4

18.6

18.8

19

19.2

19.4

19.6

19.8

20

Wat

er S

urfa

ce E

lev.

(m)


05/02 05/12 05/22 06/01 06/11 06/21 07/010

5

10

15

20

25

30

35

40

45

Day of 2008

Pre

cipi

tatio

n(m

m)

ADCPSJRWMDBottom Ele.PRCP(mm)


18

18.2

18.4

18.6

18.8

19

19.2

19.4

19.6

19.8

20

Wat

er S

urfa

ce E

lev.

(m)


08/30 09/01 09/03 09/05 09/07 09/09 09/11 09/13 09/150

5

10

15

20

25

30

35

40

45

Day of 2008

Pre

cipi

tatio

n(m

m)

ADCPSJRWMDBottom Ele.PRCP(mm)


132

6%

4%

2%

WEST EAST

SOUTH

NORTH

2 - 44 - 66 - 88 - 1010 - 1212 - 14

Wind Speed(m/s)

Figure B-35. Wind-rose during Deployment 0-1.

12%

8%

4%

WEST EAST

SOUTH

NORTH

2 - 44 - 66 - 88 - 1010 - 1212 - 14

Wind Speed(m/s)


133

20%

15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 14

Wind Speed(m/s)


15%

10%

5%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 14

Wind Speed(m/s)


134

10%

7%

4%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1515 - 20

Wind Speed(m/s)


8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1515 - 20

Wind Speed(m/s)


135

8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1414 - 16

Wind Speed(m/s)


6%

3%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1515 - 2020 - 25

Wind Speed(m/s)


136

8%

4%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1515 - 2020 - 25

Wind Speed(m/s)


9%

6%

3%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1414 - 1616 - 18

Wind Speed(m/s)


137

6%

4%

2%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1515 - 2020 - 25

Wind Speed(m/s)


8%

5%

2%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1515 - 20

Wind Speed(m/s)


138

12%

8%

4%

WEST EAST

SOUTH

NORTH

0 - 22 - 44 - 66 - 88 - 1010 - 12

Wind Speed(m/s)


139

APPENDIX C TABULATION OF LAKE MEASUREMENTS

Table C-1. Weekly max, mean and min currents at different elevations at UF1. UF1 Tower

Parameters Weeks


Max Mean 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



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 - - - - - - - - -

140

Table C-3. Weekly max, mean and min SSC from OBS-3 at UF1. Parameters

Weeks SSC (kg/m3) 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



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



57 - - - - - - - - - 58 0.67 0.02 0 0.83 0.07 0 0.67 0.08 0 59 - - - - - - - - -

141

5101520

Win

dS

peed

(m/s

)Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

2

4x 10

5

Win

d S

peed


25

30

35

Tem

pera

ture

( °C)

0

1

2x 10

5

Tem

pera

ture

0.180.190.2

0.210.22

Sal

inity

0

0.1

0.2

Sal

inity

19.3

19.419.519.6

Wat

er S

urfa

ce E

lev.

(m)

0

10

20

Pre

ssur

e

0

5

1015

Vel

ocity

(cm

/s)

Elev. 18.51m

0123x 10

5

Vel

ocityElev. 18.51m

0

5

1015

Vel

ocity

(cm

/s)

Elev. 18.31m

0

5

10x 10

6

Vel

ocity Elev. 18.31m

00.20.40.60.81

SS

C(k

g/m

3 )

Elev. 18.51m

0

100

200

SS

C

Elev. 18.51m

07/26 07/31 08/05 08/10 08/15 08/20 08/250

0.20.40.60.8

1

Day of 2007

SS

C(k

g/m

3 )

Elev. 18.31m

0 0.5 1 1.5 2 2.50

5000

Frequency (1/days)S

SC Elev. 18.31m

Figure C-1. Measurements (left) and power spectral densities for Deployment 0-1.

142

5101520

Win

dS

peed

(m/s

)Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

1

23

x 105

Win

d S

peed


0

5

10

15

Vel

ocity

(cm

/s)

Elev. 18.51m

0

51015x 10

4

Vel

ocityElev. 18.51m

00.10.20.30.4

SS

C(k

g/m

3 )


0

10

20

OB

S-3 OBS-3 at Elev. 18.66m

00.20.40.60.81

SS

C(k

g/m

3 )

Elev. 18.51m

0

1000

2000

SS

C

Elev. 18.51m

08/29 09/03 09/08 09/130

0.20.40.60.8

1

Day of 2007

SS

C(k

g/m

3 )

Elev. 18.31m

0 0.5 1 1.5 2 2.50

5000

10000

Frequency (1/days)

SS

C

Elev. 18.31m


143

5101520

Win

dS

peed

(m/s

)Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

1

2x 10

5

Win

d S

peed


1015202530

Tem

pera

ture

( °C)

0

1

2x 10

5

Tem

pera

ture

0.150.175

0.20.2250.25

Sal

inity

0

0.5

Sal

inity

19.219.319.419.519.6

Wat

er S

urfa

ce E

lev.

(m)

0

102030

Pre

ssur

e

05

101520

Vel

ocity

(cm

/s)

Elev. 18.83m

0

1

2x 10

4

Vel

ocity Elev. 18.83m

05101520

Vel

ocity

(cm

/s)

Elev. 18.63m

0

1

2x 10

4

Frequency (1/day)

Vel

ocityElev. 18.63m

05

101520

Vel

ocity

(cm

/s)

Elev. 18.33m

0

2

4x 10

4

Vel

ocity Elev. 18.33m

00.10.20.30.4

Wav

e H

eigh

t(m)

0

50

100

Wav

e H

eigh

t

0.5

0.75

1

Wav

e P

erio

ds(s

ec)

0

50

100150

Wav

e P

erio

d 00.20.40.60.81

SS

C(k

g/m

3 )Elev. 18.83m

0

200

400

SS

C

Elev. 18.83m

00.020.040.060.080.1

SS

C(k

g/m

3 )


0

0.5S

SC


00.20.40.60.81

SS

C(k

g/m

3 )

Elev. 18.63m

0

50100150

SS

C

Elev. 18.63m

10/14 10/19 10/24 10/29 11/03 11/08 11/13 11/18 11/23 11/28 12/030

0.20.40.60.8

1

Day of 2007

SS

C(k

g/m

3 )

Elev. 18.33m

0 0.5 1 1.5 2 2.50

50

100

Frequency (1/days)

SS

C

Elev. 18.33m


144

10

20W

ind

Spe

ed(m

/s)

Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

1

2x 10

5

Win

d S

peed


0

10

20

Tem

pera

ture

( °C)

0

1

2x 10

5

Tem

pera

ture

0.15

0.2

0.25

Sal

inity

0

0.5

Sal

inity

19.2

19.4

19.6

Wat

er S

urfa

ce E

lev.

(m)

0

102030

Pre

ssur

e

0

5

10

15

Vel

ocity

(Cm

/s)

Elev. 18.83m

0

1

2x 10

4

Vel

ocity Elev. 18.83m

0

5

10

15

Vel

ocity

(Cm

/s)

Elev. 18.63m

0

1

2x 10

4

Frequency (1/day)

Vel

ocityElev. 18.63m

0

5

10

15

Vel

ocity

(Cm

/s)

Elev. 18.33m

0

2

4x 10

4

Vel

ocity Elev. 18.33m

00.10.20.30.4

Wav

e H

eigh

t(m)

0

50

100

Wav

e H

eigh

t

0.6

0.8

1

Wav

e P

erio

ds(s

ec)

0

50

Wav

e P

erio

d

00.511.52

SS

C(k

g/m

3 )Elev. 18.83m

0

5000

10000

SS

C

Elev. 18.83m

00.5

11.5

2

SS

C(k

g/m

3 )

Elev. 18.63m

0

5000

10000S

SC

Elev. 18.63m

00.511.52

SS

C(k

g/m

3 )


0

5

SS

C


12/06 12/11 12/16 12/21 12/26 12/31 01/05 01/10 01/150

0.51

1.52

Day of 2007 & 2008

SS

C(k

g/m

3 )

Elev. 18.33m

0 0.5 1 1.5 2 2.50

500

1000

Frequency (1/days)

SS

C

Elev. 18.33m


145

10

20W

ind

Spe

ed(m

/s)

Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

5x 10

4

Win

d S

peed


10

152025

Tem

pera

ture

( °C)

0

51015x 10

4

Tem

pera

ture

0.15

0.2

0.25

Sal

inity

0

0.5

Sal

inity

19.3

19.419.519.6

Wat

er S

urfa

ce E

lev.

(m)

0

102030

Pre

ssur

e

0

5

10

15

Vel

ocity

(Cm

/s)

Elev. 18.88m

0

100020003000

Frequency (1/day)

Vel

ocity Elev. 18.88m

0

5

10

15

Vel

ocity

(Cm

/s)

Elev. 18.68m

0

2000

4000

Frequency (1/day)

Vel

ocityElev. 18.68m

0

5

10

15

Vel

ocity

(Cm

/s)

Elev. 18.38m

0

100020003000

Vel

ocity Elev. 18.38m

00.10.20.30.4

Wav

e H

eigh

t(m)

0

50

100

Wav

e H

eigh

t

0.5

0.7

0.9

Wav

e P

erio

ds(s

ec)

0

50

100

Wav

e P

erio

d

00.5

11.5

2

SS

C(k

g/m

3 )

Elev. 18.88m

0

50100150

SS

CElev. 18.88m

00.511.52

SS

C(k

g/m

3 )

Elev. 18.68m

0

50

100

SS

C

Elev. 18.68m

01/18 01/23 01/28 02/02 02/07 02/12 02/17 02/22 02/270

0.51

1.52

Day of 2008

SS

C(k

g/m

3 )

Elev. 18.38m

0 0.5 1 1.5 2 2.50

50

100

Frequency (1/days)

SS

C

Elev. 18.38m


146

10

20W

ind

Spe

ed(m

/s)

Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

1

23

x 105

Win

d S

peed


152025

Tem

pera

ture

( °C)

0

5x 10

5

Frequency (1/days)

Tem

pera

ture

0.15

0.2

0.25

Sal

inity

0

0.5

Sal

inity

19.3

19.419.519.6

Wat

er S

urfa

ce E

lev.

(m)

0

50

Pre

ssur

e

0

10

20

Vel

ocity

(Cm

/s)

Elev. 18.43m

0

1

2x 10

5

Frequency (1/day)

Vel

ocityElev. 18.43m

0

10

20

Vel

ocity

(Cm

/s)

Elev. 18.33m

0

1

2x 10

5

Vel

ocity Elev. 18.33m

00.10.20.30.4

Wav

e H

eigh

t(m)

0

50

100

Wav

e H

eigh

t

0

0.5

1

Wav

e P

erio

ds(s

ec)

0

50

100

Wav

e P

erio

d

00.511.52

SS

C(k

g/m

3 )

Elev. 18.43m

0

1000

2000

SS

C

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 04/300

0.51

1.52

Day of 2008

SS

C(k

g/m

3 )

Elev. 18.33m

0 0.5 1 1.5 2 2.50

100020003000

Frequency (1/days)

SS

C

Elev. 18.33m


147

10

20W

ind

Spe

ed(m

/s)

Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

5

x 105

Win

d S

peed


20

30

40

Tem

pera

ture

( °C)

0

1

2x 10

6

Frequency (1/days)

Tem

pera

ture

0.20.30.4

Sal

inity

0

1

2

Sal

inity

19.1

19.219.3

Wat

er S

urfa

ce E

lev.

(m)

0

102030

Pre

ssur

e

0

10

20

Vel

ocity

(cm

/s)

Elev. 18.83m

0

1

2x 10

5

Frequency (1/day)

Vel

ocity Elev. 18.83m

0

10

20

Vel

ocity

(cm

/s)

Elev. 18.63m

0

1

2x 10

5

Vel

ocityElev. 18.63m

0

10

20

Vel

ocity

(cm

/s)

Elev. 18.33m

0

1

2x 10

5

Vel

ocity Elev. 18.33m

00.10.20.30.4

Wav

e H

eigh

t(m)

0

50

Wav

e H

eigh

t

0.5

0.7

0.9

Wav

e P

erio

ds(s

ec)

0

2

4x 10

5

Wav

e P

erio

d

00.5

11.5

2

SS

C(k

g/m

3 )

Elev. 18.83m

0

500

1000S

SC

Elev. 18.83m

00.511.52

SS

C(k

g/m

3 )

Elev. 18.63m

0

500

1000

SS

C

Elev. 18.63m

05/02 05/07 05/12 05/17 05/22 05/27 06/01 06/06 06/11 06/160

0.51

1.52

Day of 2008

SS

C(k

g/m

3 )

Elev. 18.33m

0 0.5 1 1.5 2 2.50

100020003000

Frequency (1/days)

SS

C

Elev. 18.33m


148

10

20W

ind

Spe

ed(m

/s)

Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

5x 10

5

Win

d S

peed


20

30

40

Tem

pera

ture

( °C)

0

5x 10

5

Frequency (1/days)

Tem

pera

ture

0.20.30.4

Sal

inity

0

0.5

1

Sal

inity

19.319.419.519.619.7

Wat

er S

urfa

ce E

lev.

(m)

0

102030

Pre

ssur

e

0

10

20

Vel

ocity

(cm

/s)

Elev. 18.31m

0

5

10x 10

5

Frequency (1/day)

Vel

ocity Elev. 18.31m

0

10

20

Vel

ocity

(cm

/s)

Elev. 18.11m

0

5x 10

6

Vel

ocityElev. 18.11m

00.10.20.30.4

Wav

e H

eigh

t(m)

0

10

20

Wav

e H

eigh

t

0.5

0.7

0.9

Wav

e P

erio

ds(s

ec)

0

50

100150

Wav

e P

erio

d

00.511.52

SS

C(k

g/m

3 )


0

500

SS

C


06/21 06/26 07/01 07/06 07/11 07/16 07/21 07/26 07/31 08/05 08/100

0.51

1.52

Day of 2008

SS

C(k

g/m

3 )

Elev. 18.31m

0 0.5 1 1.5 2 2.50

5000

Frequency (1/days)

SS

C

Elev. 18.31m


149

10

20W

ind

Spe

ed(m

/s)

Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

1

23

x 105

Win

d S

peed


20

30

40

Tem

pera

ture

( °C)

0

5

10x 10

4

Frequency (1/days)

Tem

pera

ture

0.20.30.4

Sal

inity

0

0.10.2

Sal

inity

19.419.619.820

Wat

er S

urfa

ce E

lev.

(m)

0

102030

Pre

ssur

e

0

10

20

Vel

ocity

(cm

/s)

Elev. 18.54m

0

5x 10

4

Frequency (1/day)

Vel

ocity Elev. 18.54m

0

10

20

Vel

ocity

(cm

/s)

Elev. 18.34m

0

5x 10

4

Frequency (1/day)

Vel

ocityElev. 18.34m

0

10

20

Vel

ocity

(cm

/s)

Elev. 18.14m

0

5x 10

4

Vel

ocity Elev. 18.14m

00.10.20.30.4

Wav

e H

eigh

t(m)

0

10

20

Wav

e H

eigh

t

0.5

1

1.5

Wav

e P

erio

ds(s

ec)

0

100

200

Wav

e P

erio

d

00.5

11.5

2

SS

C(k

g/m

3 )

Elev. 18.54m

0

50010001500

Frequency (1/day)

SS

CElev. 18.54m

00.511.52

SS

C(k

g/m

3 )

Elev. 18.34m

0

500

1000

Frequency (1/day)

SS

C

Elev. 18.34m

08/15 08/20 08/25 08/30 09/04 09/09 09/140

0.51

1.52

Day of 2008

SS

C(k

g/m

3 )

Elev. 18.14m

0 0.5 1 1.5 2 2.50

5000

Frequency (1/days)

SS

C

Elev. 18.14m


150

10

20W

ind

Spe

ed(m

/s)

Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

5

x 105

Win

d S

peed


0

10

20

30

Vel

ocity

(cm

/s)

Elev. 19.01m

0

5x 10

5

Frequency (1/day)

Vel

ocity Elev. 19.01m

0

10

20

30

Vel

ocity

(cm

/s)

Elev. 18.61m

0

5x 10

5

Frequency (1/day)

Vel

ocityElev. 18.61m

0

10

20

30

Vel

ocity

(cm

/s)

Elev. 18.31m

0

5x 10

5

Vel

ocity Elev. 18.31m

00.5

11.5

2

SS

C(k

g/m

3 )

Elev. 19.01m

0

1000

2000

SS

C

Elev. 19.01m

00.511.52

SS

C(k

g/m

3 )

Elev. 18.61m

0

5000

SS

C

Elev. 18.61m

04/27 05/02 05/07 05/12 05/17 05/22 05/27 06/01 06/06 06/11 06/160

0.51

1.52

Day of 2008

SS

C(k

g/m

3 )

Elev. 18.31m

0 0.5 1 1.5 2 2.50

1000

2000

Frequency (1/days)

SS

C

Elev. 18.31m


151

10

20W

ind

Spe

ed(m

/s)

Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

5

x 105

Win

d S

peed


0

10

20

30

Vel

ocity

(cm

/s)

Elev. 18.31m

0

5x 10

5

Vel

ocity Elev. 18.31m

00.511.52

SS

C(k

g/m

3 )


0

100

200

SS

C


06/19 06/24 06/29 07/04 07/09 07/140

0.51

1.52

Day of 2008

SS

C(k

g/m

3 )

Elev. 18.31m

0 0.5 1 1.5 2 2.50

1000

2000

Frequency (1/days)

SS

C

Elev. 18.31m


152

10

20

Win

dS

peed

(m/s

)Speed Direction

0100200300400

Win

dD

irect

ion(°)

0

1

23

x 105

Win

d S

peed


0

10

20

Vel

ocity

(cm

/s)

Elev. 19.20m

0

1

2x 10

5

Frequency (1/day)

Vel

ocity Elev. 19.20m

0

10

20

Vel

ocity

(cm

/s)

Elev. 18.70m

0

1

2x 10

5

Frequency (1/day)

Vel

ocityElev. 18.70m

0

10

20

Vel

ocity

(cm

/s)

Elev. 18.50m

0

5x 10

4

Vel

ocity Elev. 18.50m

00.5

11.5

2

SS

C(k

g/m

3 )

Elev. 19.20m

0

100

200

Frequency (1/day)

SS

C

Elev. 19.20m

00.511.52

SS

C(k

g/m

3 )

Elev. 18.70m

0100020003000

Frequency (1/day)

SS

C

Elev. 18.70m

08/30 09/04 09/09 09/140

0.51

1.52

SS

C(k

g/m

3 )

Day of 2008

Elev. 18.50m

0 0.5 1 1.5 2 2.50

5000

10000

SS

CFrequency (1/day)

Elev. 18.50m


153

0 2 4 6 8 10 12 140

0.05

0.1

0.15

0.2

0.25

0.3

Wind Speed(m/s)

Wav

e H

eigh

t(m)

0 2 4 6 8 10 12 140.5

0.6

0.7

0.8

0.9

1

Wind Speed(m/s)

Wav

e P

erio

d(s)

Figure C-13. Variations of wave height and period with wind speed for Deployment 0-4.

0 2 4 6 8 10 12 140

0.05

0.1

0.15

0.2

0.25

0.3

Wind Speed(m/s)

Wav

e H

eigh

t(m)

0 2 4 6 8 10 12 140.5

0.6

0.7

0.8

0.9

1

Wind Speed(m/s)

Wav

e P

erio

d(s)


154

0 2 4 6 8 10 12 140

0.05

0.1

0.15

0.2

0.25

0.3

Wind Speed(m/s)

Wav

e H

eigh

t(m)

0 2 4 6 8 10 12 140.5

0.6

0.7

0.8

0.9

1

Wind Speed(m/s)

Wav

e P

erio

d(s)


0 2 4 6 8 10 12 140

0.05

0.1

0.15

0.2

0.25

0.3

Wind Speed(m/s)

Wav

e H

eigh

t(m)

0 2 4 6 8 10 12 140.5

0.6

0.7

0.8

0.9

1

Wind Speed(m/s)

Wav

e P

erio

d(s)


155

0 2 4 6 8 10 12 140

0.05

0.1

0.15

0.2

0.25

0.3

Wind Speed(m/s)

Wav

e H

eigh

t(m)

0 2 4 6 8 10 12 140.5

0.6

0.7

0.8

0.9

1

Wind Speed(m/s)

Wav

e P

erio

d(s)


0 2 4 6 8 10 12 140

0.05

0.1

0.15

0.2

0.25

0.3

Wind Speed(m/s)

Wav

e H

eigh

t(m)

0 2 4 6 8 10 12 140.5

0.6

0.7

0.8

0.9

1

Wind Speed(m/s)

Wav

e P

erio

d(s)


156

0 2 4 6 8 10 12 140

0.05

0.1

0.15

0.2

0.25

0.3

Wind Speed(m/s)

Wav

e H

eigh

t(m)

0 2 4 6 8 10 12 140.5

0.6

0.7

0.8

0.9

1

Wind Speed(m/s)

Wav

e P

erio

d(s)


0

5

10

V=6e(u/23)-6

(a) Elev. 18.83m

0

5

Wat

er C

urre

nt V

eloc

ity(c

m/s

)

V=6e(u/23)-6

(b) Elev. 18.63m

0 2 4 6 8 10 12 140

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.

157

0

5

10

V=9.5e(u/23)-9.5 Elev. 18.83m

0

5

Wat

er C

urre

nt V

eloc

ity(c

m/s

)

V=9.5e(u/23)-9.5Elev. 18.63m

0 2 4 6 8 10 12 140

5

Wind Speed(m/s)

V=8e(u/26)-8Elev. 18.33m


0

5

10

V=8e(u/23)-8

Elev. 18.54m

0

5

Wat

er C

urre

nt V

eloc

ity(c

m/s

)

V=8e(u/23)-8

Elev. 18.34m

0 2 4 6 8 10 12 140

5

Wind Speed(m/s)

V=8e(u/26)-8

Elev. 18.14m


158

0

5

10

V=13e(u/23)-13

Elev. 19.01m

0

5

Wat

er C

urre

nt V

eloc

ity(c

m/s

)

V=13e(u/23)-13

Elev. 18.61m

0 2 4 6 8 10 12 140

5

Wind Speed(m/s)

V=13e(u/26)-13

Elev. 18.31m


0

5

10

V=9e(u/23)-9 Elev. 19.20m

0

5

Wat

er C

urre

nt V

eloc

ity(c

m/s

)

V=9e(u/23)-9Elev. 18.70m

0 2 4 6 8 10 12 140

5

Wind Speed(m/s)

V=8e(u/26)-8Elev. 18.50m


159

Figure C-25. SSC against wind speed at 18.51 m from Deployment 0-1.


160



161



162



163



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165



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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), 281-291.

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. O’Connor, and C.L. Schelske, eds., Lewis Publishers, Boca Raton, FL, 511-526.

Clugston, J.P., 1963. Lake Apopka, Florida, A changing lake and its vegetation. Quarterly Journal of the Florida Academy of Science, 26, 168-174.

Dean, R.G., Dalrymple, R.A., 1991. Water Wave Mechanics for Engineers and Scientists, World Scientific, Singapore.

Håkanson, 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 shallow waters. Ph.D. thesis, University of Florida, Gainesville.

Julien, 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. thesis, 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), 103-120.

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 Research, Oceans, 102(C7), 15807-15821.

Migniot, C., 1968. A study of the physical properties of different very fine sediments and their behavior under hydrodynamic action. La Houille Blanche, 7, 591-620 (in French, with abstract in English).

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Paerl, H., Fulton, 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 Survey 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 Publication, SJ97-Sp21, St. Johns River Water Management District, Palatka, FL.

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), 41-69.

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: 1990-1994. Special Publication, SJ98-SP4, St. Johns River Water Management District, Palatka, FL.

SWIM PLAN, 2003. “2003 Lake Apopka Surface 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, 157-171.

Teeter, A.M., 2001b. Clay-silt sediment modeling using multiple grain classes; part I: application to shallow-water resuspension and deposition. 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.

http://sjrwmd.com/�

http://waterdata.usgs.gov/�

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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 University 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 admitted

to the Graduate School of the University of Florida in the spring of 2007.

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© 2009 Sangdon So