WIND INDUCED WAVE RESUSPENSION AND CONSOLIDATION
OF COHESIVE SEDIMENT IN NEWNANS LAKE, FLORIDA
by
JASON E. GOWLAND
2002
WIND INDUCED WAVE RESUSPENSION AND CONSOLIDATION OF COHESIVE
SEDIMENT IN NEWNANS LAKE, FLORIDA
By
JASON E. GOWLAND
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ENGINEERING
UNIVERSITY OF FLORIDA
2002
'ARCHIVES
ACKNOWLEDGMENT
I would like to thank all those before me that have contributed to the knowledge I
have acquired throughout my studies. This includes everyone who has and passed along
his or her spirit, a piece of his or her soul, or a fundamental piece of knowledge in order
to make the world we live in a better place.
TABLE OF CONTENTS
page
ACKNOWLEDGMENT.......................................................................... ii
LIST OF TABLES ................................................................ ............. v
LIST OF FIGURES................................................................... .......vii
LIST O F SY M B O LS................................................................................ ix
ABSTRACT ....................................................xiv
CHAPTER
1 IN TR O D U CTIO N ............................................................................ .. 1
1.1 Problem Statem ent .............................................................................................. 1
1.2 Lake Characteristics ............................................................................................ 5
1.2.1 G eology ........................................................................................................ 5
1.2.2 B iology......................................................................................................... 6
1.2.3 O organic M matter ............................................................................................. 7
1.3 Objectives and Tasks .......................................................................................... 7
1.4 Thesis O outline ..................................................................................................... 8
2 SEDIMENT RESUSPENSION ...................................................... ...........
2.1 B background ......................................................................................................... 9
2.2 W ind R record ..................................................................................................... 10
2.3 Wave Height and Period Calculation.............................................................. 12
2.4 Method To Determine Suspension Concentration................................................ 13
2.4.1 Conservation of Sediment Mass ............................................... ............ 13
2.4.2 U pw ard D iffusion ................................................................................... 14
2.4.3 E erosion ....................................................................................................... 16
2.4.4 D position .................................................................................................. 17
2.4.5 C consolidation ............................................................................................ 19
3 DATA ANALYSIS......................................................................... 23
3.1 Introduction ....................................................................................................... 23
 I
3.2 B bottom Sam ples................................................................................................ 23
3.3 Sediment Parameters......................................................................................... 24
3.3.1 D ensities........................ ............................................................................ 24
3.3.2 Organic Content............................................................................................ 26
3.3.3 Grain Size..................................... .................................29
3.4 Settling V elocities............................................................................................ 31
3.5 Erosion Param eters ........................................................................................... 33
3.6 C consolidation .................................................................................................... 35
3.6.1 Selfweight Consolidation ....................................................................... 35
3.6.2 Overburden Consolidation...................................... ................................. 36
4 SEDIMENT RESUSPENSION POTENTIAL 40
4.1 Modeling Newnans Lake Resuspension........................................... ........... ... 40
4.2 Resuspension Modeling.................................................................................. 41
4.2.1 Model Calibration and Validation ............................................. ........... 41
4.2.2 Effect of Wind Speed and Location on Resuspension................................ 44
4.2.3 Effect of Dredging on Resuspension .......................................................... 57
4.3 C consolidation .................................................................................................... 60
5 CONCLUSIONS 63
5.1 Sum m ary................................................... ....................................................... 63
5.2 C onclusions.......................... ............................................................................. 63
5.3 Recommendations for Future Work............................... .............................. 64
APPENDIX CORE THICKNESSES AND BED DENSITIES...........................66
LIST OF REFERENCES........................................................................68
BIOGRAPHICAL SKETCH ...................................................................71
LIST OF TABLES
Table page
2.1 Mean wind speeds and directions at 10 m elevation (from NCDC)..................11
3.1 Sample locations coordinates...................................................................24
3.2 Unconsolidated material densities and organic content ................................27
3.3 Consolidated material densities and organic content ......................................28
3.4 Mean organic content and densities for inner, outer and exposed area ................29
3.5 Sample, d25, dso, d7s, and sorting coefficient .................................................30
3.6 Settling velocity param eters ................................. .............................. 33
3.7 Coefficients of consolidation and compressibility for overburden consolidation
.................................................... ............. .............. ....... 39
4.1 Model calibration and validation input parameters............................................42
4.2 Mean sedimentary and erosion parameters for inner, outer and exposed areas.........46
4.3 Inner open water low water input parameters .............................................47
4.4 Inner open water area middepth concentrations at 600 min; low water .............49
4.5 Inner open water high water input parameters ..............................................50
4.6 Inner open water area middepth concentrations at 600 min; high water ..............51
4.7 Outer open water high water input parameters ..........................................52
4.8 Outer open water area middepth concentrations at 600 min; high water ..............53
4.9 Exposed area model input parameters at high water .....................................54
4.10 Exposed area middepth concentrations at 600 min; high water ......................55
4.11 Consolidated bed properties..................................................................58
4.12 Dredged bottom model input parameters................. .....................................59
4.13 Dredged lake mid depth concentration at 600 min..................................... 60
4.14 Model input parameters for 100year selfweight consolidation simulation..........62
LIST OF FIGURES
Figure pge
1.1 Location of Newnans Lake in northcentral Florida.................................... 2
1.2 Topographic map of Newnans Lake floodplain, courtesy of U.S. Geological Survey..3
1.3 Fiveyear monthly stage of Newnans Lake taken from Nagid (1999) and ECT (2001)
.........................................................................................................5
2.1 Inflow into lake basin with controlled outflow ...........................................9
2.2 Wind wave resuspended sediment is transported to outflow creek during drawdown
................................................................ ...................................... 10
2.3 Satellite photo of Prairie Creek in southwest corer of Newnans Lake ................11
2.4 Schematic diagram showing the water column and suspended sediment concentration
profile ......................................................................14
2.5 Increased neutral diffusivity at the bed surface assuming no change in fluid density
with depth ........... ....................................... ...............15
2.6 Variation of waveinduced water particle horizontal velocity with depth......... ....16
2.7 Reduced Coordinate System (a) Material or Langrangian coordinate system at time,
t=0; (b) Spatial or Eulerian coordinates at time, t; (c) Reduced coordinates at time, t
........................................................................................... ............. 2 0
3.1 Approximate locations for piston core barrel sampling along with depth
contours ............................................... ........... ....... ..... .... ...........25
3.2 Settling velocity plots for lake sediment samples.........................................32
3.3 Erosion rates vs. shear stresses..............................................................34
3.4 Selfweight consolidation of sample 4cu ...............................................35
3.5 Consolidation for an overburden stress of 25 kN/m2......................................37
3.6 Consolidation for an overburden stress of 50 kN/m2 ........ .................. .........38
3.7 Determination of bed compressibility for overburden consolidation .................38
4.1 Depth contours showing inner cores inside 0.3 m contour...............................41
4.2 Calibration run, with 90 minutes to reach 4 kg/m3 field concentration shown by blue
dot. Left plot is loglinear; right is linear scale............................................. 42
4.3 Validation run, with 90 minutes to reach 2 kg/m3 field concentration shown by blue
dot. Left plot is loglinear; right is linear scale ..............................................42
4.4 Resuspension at 8 m/s wind in the inner open water area at low water .................48
4.5 Inner open water area middepth concentration evolution at different wind speeds,
low w ater ...................................................... .................... ........... ....... 48
4.6 Inner open water area suspended sediment evolution at high water. Resuspension
occurred 10 m/s wind speed only ................................................... ..........50
4.7 Outer open water area middepth concentration evolution at different wind speeds,
high w ater............................................ .... ..... ................... .............. .. 53
4.8 Exposed area middepth concentration evolution at different wind speeds, high water
................... ........................................ ........................................... 5 5
4.9 Middepth suspended sediment concentration in the three subareas at 8 m/s
w ind.............. ...................................................................................... 56
4.10 Middepth suspended sediment concentration in the three subareas at 9 m/s
w ind................................................................................... ................. 56
4.11 Middepth suspended sediment concentration in the three subareas at 10 m/s
w ind............... ................. ... .. .... ..... ...... ................... ... ........... 57
4.12 Middepth suspended sediment concentration evolution with time; dredged
bottom ..................................................... ................. ...... ........... ......... 60
4.13 Selfweight consolidation modeling: variation of density profile with time. Model
output interval is 1 hour....................................................... ............ ........61
4.14 100year selfweight consolidation of bed material with each line representing 10
years ........... .......................... .............. ............. .......................62
A.1 Core densities for unconsolidated and consolidated samples at the respective mean
elevations of the sublengths............................................................... 67
LIST OF SYMBOLS
a settling velocity parameter
a, erosion rate parameter
av bed compressibility
A constant
b settling velocity parameter
br erosion rate parameter
c celerity
Cf, cv coefficient of consolidation
C concentration
C1 limiting free settling concentration
CD conductivity
CL chlorophylla
CR cation ratio [Ca++]+[Mg++]/[Na+]+[K+]
d water depth
do wave particle orbital diameter
d25 diameter of 25 percent of sample
dso median size diameter
d75 diameter of 75 percent of material
e void ratio
ei initial void ratio
ee ultimate void ratio
E total energy (one wavelength/unit crest width)
Ek, Ep kinetic and potential energies respectively
E average wave energy per unit surface area
F, net flux
Fs settling flux
Fe erosion flux
fp peak spectral frequency
fw wave friction factor
g gravity
h height of water above bed
hb bed depth
H+ activity of hydrogen ions
H wave height
Hso height of bed at 50 % consolidation
k wave number
ko initial permeability
kh hydraulic conductivity
ks bottom roughness parameter
K diffusion coefficient
K, neutral diffusivity coefficient
L wavelength
m mass, or settling velocity parameter
M erosion rate constant
MA dry mass after ignition
MD dry mass
Mw mass of wet sample
n porosity, or settling velocity parameter
ot output time step
OC organic content
p excess pore water pressure
pw static pore water pressure
PP primary productivity
Ro beginning of consolidation
Rloo end of consolidation
Ri gradient Richardson number
So sorting coefficient
t time
tt consolidation durration
tso time at 50 % consolidation
T wave period, time period, also turbidity
TN total organic nitrogen
TP total phosphate
TSI Trophic State Index
u horizontal velocity
Um water particle horizontal velocity
U wind speed
Ua wind stress factor
V volume
Vs velocity of the solids
Vsolids volume of the solids
Vv volume of the voids
Vw water seepage velocity
ws settling velocity
Wsf free settling velocity
x fetch
xi bed density parameter
z, zi vertical elevation coordinate
Az incremental depth
ao nondimensional empirical coefficient
ae erosion rate parameter
cXw wave diffusion coefficient
8o nondimensional empirical coefficient
v constant
S nondimensional scale for depth
e erosion rate
E nondimensional wave energy
1r
V
V
rim
v
p
PB
PD
PD
Ps
Pf
Pw
rb, Tapplied
Zs
VDep
X
bed density parameter
reduced coordinates
initial volume of solids
modified bed height
kinematic viscosity of water
nondimensional frequency
spatial or Eularian coordinate
density
bulk density
dry density
average dry density
particle density
fluid density
density of water
wave frequency
effective stress
applied bed shear stress
critical bed shear stress
deposition shear stress
erosion rate parameter
nondimensional fetch
Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering
WIND INDUCED WAVE RESUSPENSION AND CONSOLIDATION OF COHESIVE
SEDIMENT IN NEWNANS LAKE, FLORIDA
By
Jason Eric Gowland
August 2002
Chairman: Ashish J. Mehta
Major Department: Civil and Coastal Engineering
Newnans Lake in northcentral Florida has been slated for restoration of water
quality and, in 20012002, drought brought the lake down to record low levels. Since
most of the material at the lake bottom is detrital organic matter, it remains lightweight
and is easily resuspended, thus raising turbidity and degrading water quality. In this
study, windwave induced resuspension of the bed material was modeled to determine the
wind speed required to increase turbidity.
Resuspension of the bed material was found to become significant at 8 m/s wind
for the low stage of summer, 2001. At the mean lake stage, 1.1 m higher than the low
level, the required speed was in excess of 10 m/s. The drought exposed some of the bed
material to sun and air, which consequently acquired a higher strength and lower erosion
rate as compared to the submerged bed in the open water area.
In order to consolidate the bed to densities found 1.5 m below the bed surface, a
model for selfweight consolidation had to be run for a duration on the order of 100
years. It was found that, as a potential measured for restoration, dredging the
unconsolidated material, about 0.3 m in the open water area, would further reduce the
likelihood of resuspension, requiring a wind of 11 m/s at the mean stage.
CHAPTER 1
INTRODUCTION
1.1 Problem Statement
Windwave induced suspended finegrained sediment, while a natural
phenomenon, can lead to potential problems associated with nutrient and contaminant
release and transport of suspended matter to contiguous water bodies, which may be
undesirable. For example, in Florida, Lake Okeechobee and Lake Apopka are two lakes
that have had problems with nutrient loading and suspended particulate matter. Baird
(1987) notes that observations of the first algal blooms in Lake Apopka occurred in the
late 1940's and early 1950's, after which rooted aquatic vegetation began to disappear
and game fish populations declined. These algal blooms are linked to heavy loadings of
nutrients, nitrogen and phosphorous from bordering muck farms, citrus groves,
wastewater treatment plants, and various other nonpoint sources. Another well
documented example of this type is Lake Onodoga, New York, considered "America's
dirtiest lake" (Effler, 1996). The cause of water quality degradation in this case has been
linked to the production of soda ash by the Solvay Process Company along the western
bank of the lake, which began in 1884.
In the present study, a straightforward, 1Dvertical modeling of waveinduced
suspended sediment has been applied to examine the potential for fine, organicrich
sediment resuspension in Newnans Lake in northcentral Florida (Fig. 1). This lake,
located about 8 km east of Gainesville, Florida, and approximately 28 km2 in size, has
received much attention in recent years due to legislation enacted as Florida Statutes
Section 373.453 related to water quality and restoration. The St. Johns River Water
Management District, Palatka, Florida and the Florida Fish and Wildlife Conservation
Commission oversee the Newnans Lake region and have been interested in the dynamics
of the system as a whole for many years. In December of 1990, the Fresh Water Fish
Commission placed Newnans Lake on the lake restoration priority list. A 1993 report by
the Game and Fresh Water Fish Commission (Holcomb, 1993) anticipated that the
Newnans Lake restoration project would cost in the range of eight to13 million dollars.
Figure 1.1 Location of Newnans Lake in northcentral Florida.
Newnans
Lake
'Ow
Geological Survey.
As seen from Fig. 1.2, Hatchet Creek and Little Hatchet Creek are two streams
that spill into Newnans Lake in the north. Prairie Creek carries water from the lake south
to Paynes Prairie. In 1966, a flow control dam was constructed at Prairie Creek near
State Road 20 to reduce seasonal water level fluctuations in the lake. In 1976,
modifications were made to the earthen dam to reintroduce limited drawdown events in
order to improve the condition of the lake with respect to algae and weed control.
In a shallow lake environment such as Newnans, nutrients stored in the sediment
may be resuspended into the water column. This resuspension can be a significant
contributing factor to high nutrient concentrations and plant biomass in the system. As
the biomass grows, and eventually decays, a biocycle develops that accumulates organic
sediment in the system. Gottgens and Montague (1987) notes that excessive growth of
aquatic plants can lead to interference with the use of the lake for domestic, recreational,
navigational, or agricultural (aquacultural) purposes. Furthermore, if drawdown
occurred after some wave induced resuspension event the organic sediment discharge
could be considerably greater than for drawdown with low suspended sediment
concentrations. Nagid (1999) surmised that at Newnans Lake there would be an
increased probability of sediment resuspension as lake stage decreased. This observation
shall be tested in the present study based on waveinduced resuspension modeling, and
knowledge of lake level variation in recent years (Fig. 1.3).
5
21.5 i
21   February 1998 El
1 Typical 19951998 level eNiuao high
E 20.5
20
S19.5
19 August 2001 low
18.5 I I I
Jan Jul Jan Jul Jan Jul Jan Jul Jan Jul Jan Jul Jan Aug
95 95 96 96 97 97 98 98 99 99 00 00 01 01
Date
Figure 1.3 Fiveyear monthly stage of Newnans Lake taken from Nagid (1999) and ECT
(2001).
1.2 Lake Characteristics
1.2.1 Geology
Holly (1976) noted that Newnans Lake is surrounded by sediments of the
Hawthorne Formation on the west, north and east, with (Eocene) Ocala Limestone
formation to the south extending into the Paynes Prairie area. The lake began some 8,000
years BP as a dry grassland due to low water table associated with a low sea level. From
then to about 5,000 years BP it was transformed into a "grass swamp" surrounded by dry
oak forest or shrub, and in the past 5,000 years has been in its present status as a shallow,
cypress fringed, eutrophic lake. Water quality in the lake can be characterized by the
ShannonBrezonik Trophic State Index (TSI) (Wanielista, 1978):
TSI = 0.18T +0.008CD+ .1TN +4.2TP+O.O1PP+0.044CL +0.39CR +0.26 (1.1)
where T = turbidity (JTU), CD = conductivity [(Q)l'/cm =iS/cm], TN = total organic
nitrogen (mg/1), TP = total phosphate (mg/1), PP = primary productivity (mgC/m2hr),
CL = chlorophylla (mg/m3) and cation ratio CR = [Ca+]+[Mg+]/[Na+]+[K+]. Shannon
and Brezonik (1972) provide the following classification based on TSI: 03 oligotrophic,
37 mesotrophic, 710 eutrophic, and >10 hypereutrophic. They reported a value of 15.3
for Newnans Lake, implying that it was hypereutrophic in the early 1970s. Brenner and
Whitmore (1998) have given more recent data on the total organic nitrogen and total
phosphate along with radioisotopes found in the cores for dating.
1.2.2 Biology
Gottgens and Montague (1987) explained data on the phytoplankton found in the
lake. The dominant forms were bluegreen algae with several green algae as
subdominants. In a seasonal study of the lake, a shift in the size distribution of the
phytoplankton was noted. Smaller forms appeared to dominate in the fall and early
winter, while larger forms were most common in the summer. Brenner and Whitmore
(1998) include a detail summary of the diatom taxa with depth in the lake.
A survey of macrophytes indicated the following species: emergents and floating
leaved, free floating, and submersed plants. Included in the survey were cattail, American
lotus, cypress, water hyacinth, pickerel weed, alligator weed, coontail, southern naiad,
and hydrilla. Midges, segmented worms and snails were also found, which can provide
valuable data on the contamination history of the lake through paleontological
investigations of their chitin body parts, which preserve well in the sediments (Gottgens
and Montague, 1987). Nagid (1999) proposed that a macrophyte coverage of 50% of the
lake area would be necessary to significantly reduce chlorophyll concentrations, which
would maintain a clearer and more stable lake and reduce sediment resuspension. The
Florida Fish and Wildlife Conservation planted maidencane and giant bulrush in efforts
to achieve reduced nutrient availability, refuge, and spawning substrate for sport fish.
1.2.3 Organic Matter
Microorganisms and meiofauna are also found in the lake at the soilwater
interface with high organic content. Within a few millimeters of the interface, oxidative
metabolism decays the organic material; however, deeper into the mud layer oxygen is
unavailable and only anaerobic metabolism occurs. Bacteria at the interface, which
secrete adhesive substances, may influence the dynamics of the system by increasing
shear strength and reducing erodibility. Meiofauna may also have the same effect by
secreting mucus that may bind the sediment.
Wetzel and Likens (2000) note that organic matter in an aquatic ecosystem ranges
from dissolved organic compounds to large aggregates of particulate organic matter and
includes both living and dead material. Most of this material is detrital organic matter
from dead organisms, while some may be unicellular algae with cell walls of hydrated
silica embedded into an organic matrix.
1.3 Objectives and Tasks
The objective of this study was to assess the potential role of windinduced waves
in causing fine sediment resuspension in the lake. Several tasks were completed in order
to achieve this objective. These include
Analyzing bottom sediment samples from the lake to determine sedimentary
parameters used in the resuspension modeling.
Laboratory testing of the samples to determine erosion rates, settling velocity
for deposition and consolidation of the deposit.
Predicting wave height and period for waveinduced resuspension based on
wind record.
Modeling the system to predict the evolution of suspended sediment
concentration as a function of wind speed.
*Conclusions based on the modeling related to the response of turbidity in the
lake to wind forcing.
1.4 Thesis Outline
Chapter 2 discusses the resuspension modeling approach and the determination of
wave height and period from wind record. Chapter 3 explains procedures for the
analyses of the sediment samples and interpretation of data for model input parameters.
Resuspension and consolidation modeling and results based on the findings are presented
in Chapter 4. Chapter 5 conclusions are outlined. References and a biographical sketch
follow.
CHAPTER 2
SEDIMENT RESUSPENSION
2.1 Background
Shallow waterbodies such as Newnans Lake may become very turbid during a
severe windinduced wave event due to resuspension at the water mud interface or bed.
When modeling resuspension in a system such as this, model calibration must be done
using events that characterize the limits relative to the degree of resuspension. One limit
is defined by the period when there is little or no wave action and most of the material
remains at the bed (Fig. 2.1).
At the opposite end there is the condition after a storm wherein high wind and
wave action resuspends a significant amount of the bed sediment. Following such an
event a drawdown could discharge material out of the system, which in turn may prove
to be harmful to the receiving waters.
Figure 2.1 Inflow into lake basin with controlled outflow.
Drainage
Drainage Calm surface
Lake water 
Soft ...
bottom'
SFlow Outfl to
Con creek
Control
In connection with the above potentialities, this chapter introduces the modeling
of resuspension during wind events, and outlines the mathematical correlation between
laboratoryderived data and what is physically occurring in the system. The schematic
diagram of Fig. 2.2 is a visualization of the resuspension process.
The following sections help in the understanding of the associated transport
phenomena relevant to Newnans Lake.
2.2 Wind Record
The National Climate Data Center (NCDC) wind data for Gainesville Region
Airport (latitude 29 41 23 longitude 820 16 19 ) for the year 2001 are summarized in
Table 2.1. These data will be used as a basis to make estimates of characteristic wave
heights and the corresponding periods. Observe that the most common direction for the
wind was in the vicinity of 2500, toward the Prairie Creek (Fig. 2.3) direction.
Figure 2.2 Wind wave resuspended sediment is transported to outflow creek during draw
down.
i ..... Wave activity
te photo of Prairie Creek in southwest corer of Newnans Lake.
Table 2.1 Mean wind speeds and directions at 10 m elevation (from NCDC).
Wind (for period) Wind (2min max.) Wind (5s max.)
Period Speed Direction Speed Direction Speed Direction
(m/s) (deg) (m/s) (deg) (m/s) (deg)
January 3.1 310 16.1 250 19.2 270
February 3.4 270 14.8 240 18.3 240
March 3.6 270 17.9 250 23.2 320
April 3.3 270 13.9 330 17.9 330
May 3.1 250 13.4 250 16.5 250
June 2.8 250 20.1 240 23.2 220
July 2.5 270 20.1 290 28.6 290
August 2.4 240 13.4 120 19.2 120
September 2.6 90 13.0 120 17.4 160
October 2.9 40 10.7 40 13.4 20
November 2.8 40 11.6 320 14.8 320
December 2.7 300 13.0 270 15.2 280
Year 3.0 270 20.1 240 28.6 290
Figure 2.3 Sate
2.3 Wave Height and Period Calculation
The wave energy transferred to the bottom suspends the bed material. The total
energy of a wave, E (in one wave length, per unit crest length), is the sum of the kinetic
energy, Ek, and the potential energy, Ep:
pwgH2L pwgH2L pwgH2L
E = E + E 16 16 (2.1)
E 16 16 8
where H is the height of the wave, pw is the density of water and L is the wavelength.
The specific energy, E is the total average wave energy per unit surface area
given by
2
E pgH
E = (2.2)
L 8
The wave celerity, c relates to the wave period T and length L by
L
c = (2.3)
T
Relating the celerity to water depth, h and wavelength, L is an iterative method involving
the following wave dispersion relationship:
c= tanh(L (2.4)
From this equation we can determine the wave number k (= 2z7/L), hence the wave length
L, for a given wave frequency, cy (= 2;r/T).
Young and Verhagen (1996) describe fetchlimited wave growth in finitedepth
water from experiments and data collected at Lake George in Australia. Non
dimensional charts for the prediction of wave energy and peak frequency from non
dimensional fetch and depth parameters can be found in that work. The equation for non
dimensional wave energy, e, is:
g2E
W= (2.5)
U4
where Uis the wind speed. The corresponding nondimensional frequency, v, is:
fU
S (2.6)
g
wherefp is the frequency of the spectral peak. The nondimensional fetch, X, is
=Ugx (2.7)
U2
with x being the fetch length. Finally, the nondimensional scaling factor for depth, 3, is
gh
1= g (2.8)
U2
From the charts an estimate of the wave energy is obtained and converted to wave
height through
H = 4E5 (2.9)
The wave period is the inverse of the frequency of the spectral peak, i.e., 1/fp.
2.4 Method To Determine Suspension Concentration
Figure 2.4 is a schematic diagram showing the water column, the suspended
sediment concentration profile C(z), bed material being eroded/deposited and the net
sediment flux.
2.4.1 Conservation of Sediment Mass
With reference to Fig. 2.4, vertical suspended sediment transport can be
mathematically expressed by the wavemean settlingdiffusion equation:
t zK a + w C (2.10)
at 8z az
which is a particular case of the general mass conservation equation for vertical sediment
transport (Mehta et al., 1984), where K is the diffusion coefficient, ws is the sediment
dC
settling velocity, and C is the suspended sediment concentration. Thus, Fe =K is the
dz
diffusive flux and Fs= wsC is the settling flux.
The boundary conditions for solving the Eq. 2.10 are: zero net sediment flux at
the water surface, z=h, and at the bottom of the water column, z=0:
K+wC _, = F, (2.11)
zC
where F, is the net resuspension flux, which is equal to the difference between the
settling and erosion fluxes at the bed.
< .. 
jh
FC F( C()
Figure 2.4 Schematic diagram showing the water column and suspended sediment
concentration profile.
2.4.2 Upward Diffusion
The diffusion coefficient, K, is modeled by the suspended sediment concentration
gradient and is expressed as:
K= K, (2.12)
(1+ aoRi,)
where K, is the neutral diffusion coefficient for nonstratified flows, ao and Po are non
dimensional empirical coefficients and Ri is the gradient Richardson number defined as
Sp (au u/ z)2
R (u(2.13)
In the above equation, u is the horizontal velocity, pf is the fluid density, and g is
gravitational acceleration.
For wave motion, the neutral diffusivity is obtained from:
K 2 sinh2 kz
K, = a,aH2 (2.14)
2sinh2 kh
where aw is a nondimensional wave diffusion coefficient and H is the wave height.
Note that the above equations are obtained from the wave coordinate system
where z is measured from the water surface and is shown in Fig. 2.5.
Z
A wave height, H
depth, h
P=Pw
Sbed surface
K,
Figure 2.5. Increased neutral diffusivity at the bed surface assuming no change in fluid
density with depth.
2.4.3 Erosion
Wave action erodes and entrains particles from the bed surface into the water
column. For fine sediment this erosion takes place when the imposed fluid shear stress
exceeds the interparticle bond strength (or shear strength) of the bed. The resistance of
the bed to erosion is sensitive to water content, pore water chemical composition,
sediment composition (i.e., clay mineralogy and organic content), and the age and the
structure of the bed and its stress history. Once the waveinduced shear stress Tb is greater
than the shear strength Ts, erosion occurs at a linear rate.
The change of concentration in the water column dC (or AC in difference form)
due to erosion can be determined from
dC = (rb s)dt (2.15)
h
where M is an empirical rate constant and dt (or At) is the timestep for the calculation.
The erosion rate constant M is used to determine the net flux in equation 2.19 and is
described further in Chapter 4 with the corresponding model input parameters.
z
amplitude, a = H/2
P=Pw water particle
horizontal
depth, h velocity, u,
bed surface
Figure 2.6 Variation of waveinduced water particle horizontal velocity with depth.
The applied shear on the bed is a function of wave friction factor fw and the
horizontal velocity amplitude of the water particle, u,, at depth h. The horizontal
velocity of the water particle can be expressed as
cosh [k(z + h)]
u = ack (2.16)
sinh(kh)
where a is the wave amplitude (= H/2).
The wave friction factor can be obtained from (Jonsson, 1966):
f 0= 0.4 2 (2.17)
(2 k,
in which the water particle orbital diameter do = umT/r, and k, is the bottom roughness
parameter. Equation 2.17 must satisfy the requirement 4< doks<40. The applied shear
stress can then be found from
2
Tb =w m (2.18)
2
2.4.4 Deposition
When material settles out of suspension it is deposited onto the bed surface. This
process may also occur during erosion, and has been observed in laboratory tests. This is
so because once material is eroded into suspension it may also settle out to redeposit on
the bed surface. The settling flux F, is determined by the concentration of suspended
sediment and the settling velocity corresponding to that concentration. Laboratory tests
show that an increase in suspension concentration increases the settling flux F, so that an
equilibrium condition (equality of erosion and deposition) may be reached at a given
applied shear stress after a sufficiently long duration.
The erosion flux Fe is determined from the applied shear at the bed surface, while
the vertical diffusion coefficient determines how much material may be vertically
transported into the water column through (turbulent) diffusive processes. The difference
between the erosion and settling flux is the net flux or the amount of material being
suspended into concentration. The net flux can be determined by the equation
wC0 1 b (b ZTDp)
F = 0 TDep < b <:s (2.19)
M (rb ,) (b > ,)
In Eq. 2.19 if the bed shear stress, Tb is less than are equal to the deposition shear stress,
TDep then the net flux would be the settling velocity multiplied by the concentration at the
bed surface, C . with a probability of deposition factor, 1 b (Krone, 1962). The
required settling velocity is obtained from
w"f C < C
w = a_ C _C, (2.20)
(C b C>C
for concentration C less than or greater than the limiting free settling (velocity
wsy)concentration, C1 = 0.1 kg/m3. Note that a, b, n and m are sedimentspecific
coefficients.
The net erosion flux should be zero when the applied shear is greater than the
deposition shear but less than the shear strength, rs. If the deposition stress is less than
the applied shear stress the net flux is determined from the empirical erosion parameter
M.
2.4.5 Consolidation
As noted, for an applied shear stress below the critical shear stress deposition of
suspended matter will occur. As sediment accumulates, the selfweight of the particles
may crush the structure of the interparticle contacts, which decreases the void volume
and increases the resistance of the bed to erosion.
For modeling consolidation, the general assumptions for the following equation
based on the conservation of water mass the equation of continuity for water are that the
bed is saturated and that the flow in the bed can be described by Darcy's Law:
(pnV)+ (pn)= O (2.20)
84 at
in which p, is water density, V, is the water seepage velocity, n is the porosity and is
the vertical coordinate. Equation 2.20 is also called the Biot Equation for water and
solids. Considering the conservation of mass of the solids and assuming the solids
incompressible, the equation of continuity for the solids is:
S[p,(1 n)V]+ [p,1(n)] =0 (2.21)
at
where p, in particle density and V, is the seepage velocity of the solids. The momentum
balance for water flow is:
khP = n(V, V,)p g (2.22)
where kh is the hydraulic conductivity and p is the excess pore water pressure.
Combining Eqs. 2.20 and 2.21 and inserting Eq. 2.22 results in:
a kh ap 1 De
S L I Q? (2.23)
8a pg aQ 1+eDt
where De/Dt is the material derivative of the void ratio, e [= n/(1n)], and can be
expressed as
De Be Be
De= e + V (2.24)
Dt at s a
Note that for selfweight consolidation the total pressure, Otot,,, is equal to the
excess pore water pressure, p, plus the static pore water pressure, pw, plus the effective
stress, o'or (o=p + pw + o'). Finally expressing Eq. 2.23 in terms of the reduced
coordinates, q, we obtain the general equation for self weight consolidation also known
as the Gibson Equation:
L[ kh da' Be] P p d ( kh )ae e (2.24)
a7 p,,(l+e) de arq p, de l+e rI at
This is valid for the coordinate system shown in Figure 2.7.
(zo, t) = o =
Zo Present Volume
z Initialbed of
A bed 8 height 877 solids
height
77
(a) (b) (c)
Figure 2.7 Reduced Coordinate System (a) Material or Langrangian coordinate system at
time, t=; (b) Spatial or Eulerian coordinates at time, t; (c) Reduced coordinates at time, t.
For selfweight consolidation, to simplify the solution of the Gibson Equation
2.24, Been and Sills (1981) apply three basic assumptions:
(1) A linear relationship between the void ratio and the effective stress.
Ca'=A (2.25)
a,
where A is a constant and the compressibility, av is also assumed constant.
(2) A linear relationship between the permeability and the void ratio.
kh = pko (1+ e) (2.26)
where ko is the initial permeability.
(3) A constant coefficient of consolidation, cy
kh do'
Cf = w(l ) = constant (2.27)
Sp, (1 + e) de
These assumptions reduce Eq. 2.24 to:
de d2e
d c d (2.28)
dt f dq 2
The boundary conditions for the solution to the above equation are at the surface
the effective stress is zero and the void ratio at the surface remains constant:
e(zo,t)= ei (2.29)
where e, is the void ratio at the surface which is therefore equal to the initial void ratio,
eo. For the bottom boundary condition, void ratio at the bottom, z = 0, can be expressed
as
de(O, t)
= av(ps p,)= ,v (2.30)
drq
where /fl is a constant. The initial condition is
e(z,0) = e, (2.31)
Using Laplace transform, the solution to Eq. 2.28 with the above boundary conditions,
Eqs. 2.29 and 2.30, and the initial condition, Eq. 2.31 one obtains
2n+1 7q
e(, t)= e, 1 2 2 exp 2 1 2 c f t (2.32)
IL n=1 2n + 1 2 77,
From experimental observations, the effective stress at the surface is found not to be zero
but instead increases with the time of consolidation. Therefore, the void ratio at the
surface must decrease with consolidation. To realistically simulate consolidation an
imaginary overburden is included and its height is considered to depend on the difference
between the initial void ratio, ei and the ultimate void ratio, ee at the surface (Been and
Sills, 1981). The modified height of the bed, ,, is the sum of the original height and the
imaginary overburden height or
.m = r, + (e ee) (2.33)
Then, using 1m. instead of r7, in Eq. 2.32, the modified solution becomes:
2n +1 ;
cos 2
e(q,t)= e, ,1 cs/ 21 2 2r ex[ (2n+1 f t2 (2.34)
7lmo ni 2n+1 2 77.
I ( 2)
CHAPTER 3
DATA ANALYSIS
3.1 Introduction
Laboratory analysis of field data was done mainly at the Department of Civil and
Coastal Engineering's Coastal and Oceanographic Engineering Laboratory and the Soils
Laboratory. From these analyses, input parameters were obtained for modeling purpose
and are given in Section 3.6.
As noted earlier, much of the field data, in the form of bottom cores and (five)
shovel samples, were collected in the summer of 2001 when the lake was at an unusually
low level due to drought. These samples were analyzed for sedimentary parameters,
settling velocity parameters, erosion parameters and consolidation parameters for
modeling purposes. Each sample location was classified as consolidated and
unconsolidated during field sampling (Appendix).
3.2 Bottom Samples
Core samples were taken with a piston core barrel at transects across the lake
open water area (ECT, 2001). Core lengths averaged 1.41 m below top of mud layer
(Appendix). Sample location coordinates are given in Table 3.1 and are shown in Fig.
3.1. Samples in the exposed area were collected with a hand shovel.
Bathymetry was obtained over the lake during the time of sampling and the
contours are an estimate from locations and depths given in ECT (2001) for the lake at
low water level. Based on these contours the lake is conveniently divided into three
distinct areas. The inner open water area is deeper than 0.3 m, the outer open water area
which is shallower than 0.3 m and the exposed area is above the water level at the time of
sampling.
Table 3.1 Sample location coordinates
Sample ID Lat Long
5A 29.662041 82.232417
5B 29.662001 82.225155
5C 29.661946 82.217213
5D 29.662360 82.209655
4A 29.652611 82.232754
4B 29.652658 82.224720
4C 29.653002 82.215039
4D 29.652733 82.206271
3A 29.641728 82.234122
3B 29.641823 82.224667
3C 29.642107 82.215023
3D 29.641954 82.205985
2A 29.630943 82.244785
2B 29.630899 82.232208
2C 29.631073 82.219799
2D 29.631156 82.212113
1A 29.622649 82.243081
1B 29.622811 82.235576
1C 29.622838 82.227713
1D 29.622891 82.221490
3.3 Sediment Parameters
3.3.1 Densities
Determination of the wet bulk density, p was done by weighing a sample of mass,
Mw, and dividing by the volume, V, of the container. Typically, Pyrex beakers were
used to give a known volume:
M
p 
V
* Openwater coring sites
* Exposed bottom
sampling sites
(3.1)
Land 4
Figure 3.1 Approximate locations for piston core barrel sampling along with depth
contours.
After drying the sample in the oven at 1050 C for 24 hours, the dry mass, MD was
taken to determine the dry bulk density pD:
P MD (3.2)
PD V
Particle or granular density ps could then be determined through mass balance
(Mehta et al.., 1994):
P = PDPW (3.3)
PD +Pw P
where pw is water density (1,000 kg/m3).
3.3.2 Organic Content
The samples were then heated to 4000 C to determine organic content, OC, as loss on
ignition:
MD M
OC= D A x100% (3.4)
MD
where MA is sample dry mass after ignition.
Tables 3.2 and 3.3 provide the densities and the organic content of (upper)
unconsolidated and (lower) consolidated samples. The upper core was placed inside a
watertight plastic canister and labeled u. The lower core (c) representing consolidated
material. Grain sizes are given in Table 3.4, and in Table 3.5 the density and organic
content values for the exposed area are given, based on the mean values of all five "land"
samples shown in Fig. 3.1.
T~h1 ~ 9I11rA11cnAirhat~rd mnitPri21 dlFnnitie~n 2nd AtrP~nic. content
.U I JI UILLUV II IU VIIII U   r 
Sample PD Ps OC
(kg/m3) (kg/m3) (kg/m3 (%)
1Au 1068 149 1827 36
1Bu 1025 58 1769 50
ICu 1040 112 1556 49
1Du 1108 218 1985 35
2Au 1041 68 2455 48
2Bu 1005 19 1316 56
2Cu 1009 66 1150 44
2Du 1016 70 1289 52
3Au 1020 54 1577 52
3Bu 1022 39 2240 52
3Cu 1021 36 2383 53
3Du 1072 123 2422 36
4Au 1048 82 2357 45
4Bu 1022 38 2400 50
4Cu 1019 32 2333 58
4Du 1072 122 2452 45
5Au 1043 75 2304 50
5Bu 1041 71 2333 51
5Cu 1022 37 2381 53
5Du 1013 23 2308 55
Minimum 1005 19 1150 35
Average 1036 75 2042 48
Maximum 1108 218 2455 58
Table 32
Table 3.3. Consolidated material densities and organic content
Sample p Po Ps OC
(kg/m3) (kg/m3) (kg/m3) (%)
1Ac 1061 113 2153 17
1Bc 1019 81 1297 50
1Cc 1082 140 2414 32
1Dc 1114 185 2597 13
2Ac 1148 257 2353 23
2Bc 1063 108 2393 35
2Cc 1062 106 2407 37
2Dc 1092 156 2430 37
3Ac 1047 117 1676 52
3Bc 1029 67 1750 42
3Cc 1018 54 1523 48
3Dc 1092 188 1964 21
4Ac 1089 152 2408 33
4Bc 1044 73 2500 50
4Cc 1011 67 1205 46
4Dc 1091 160 2308 25
5Ac 1096 158 2541 .27
5Bc 1044 75 2400 50
5Cc 1099 166 2484 42
5Dc 1072 124 2396 32
Minimum 1011 67 1205 13
Average 1069 127 2160 36
Maximum 1148 257 2597 52
Table 3.4 Mean organic content and densities for inner, outer and exposed area.
Organic Bulk Dry Particle
Content Density Density Density
Area
OC p po ps
(%) (kg/m3) (kg/m3) (kg/m3)
Inner 51 1025 53 2025
Outer 47 1048 96 2059
Exposed 30 1156 267 2296
3.3.3 Grain Size
Grain size distribution was determined by wetsieving the sample material
through a set of Tyler sieves and filtering out by vacuumsuction the residual suspension
consisting of particles finer than 74 microns the #200 sieve. The concentration (dry mass
per unit volume of suspension) was then measured gravimetrically and multiplied by the
total volume of suspension to obtain the total dry mass of material finer than 74 microns.
The sum of the total coarse grain mass retained on the sieves and the mass of the fine
grained residue yielded total mass of the sample wetsieved so that the percent passing
each sieve could be calculated.
~~
Table 3.5 Sample, d25, dso, d75, and sorting coefficient
Sample d25 dso d75s So
(mm) (mm) (mm)
1Ac 0.220 0.293 0.379 1.3
1Bc 0.009 0.030 0.128 3.7
1Cc 0.063 0.101 0.296 2.2
1Dc 0.248 0.327 0.417 1.3
1Au 0.022 0.053 0.290 3.6
IBu 0.009 0.029 0.124 3.7
1Cu 0.009 0.031 0.136 3.8
1Du 0.029 0.061 0.291 3.2
2Ac 0.168 0.227 0.310 1.4
2Bc 0.029 0.061 0.291 3.2
2Cc 0.019 0.049 0.275 3.8
2Dc 0.019 0.049 0.278 3.8
2Au 0.010 0.034 0.146 3.9
2Bu 0.008 0.017 0.072 2.9
2Cu 0.011 0.040 0.182 4.1
2Du 0.009 0.026 0.112 3.5
3Ac 0.009 0.026 0.113 3.5
3Bc 0.013 0.043 0.210 4.0
3Cc 0.010 0.033 0.142 3.9
3Dc 0.189 0.254 0.336 1.3
3Au 0.009 0.025 0.106 3.5
3Bu 0.009 0.025 0.107 3.5
3Cu 0.009 0.023 0.101 3.4
3Du 0.020 0.050 0.290 3.8
4Ac 0.052 0.089 0.294 2.4
4Bc 0.009 0.029 0.124 3.7
4Cc 0.010 0.037 0.163 4.1
4Dc 0.143 0.198 0.306 1.5
4Au 0.010 0.039 0.175 4.1
4Bu 0.009 0.028 0.123 3.7
4Cu 0.008 0.014 0.058 2.7
4Du 0.010 0.039 0.175 4.1
Table 3.5 (continued) Sample, d25, dso, d75, and sorting coefficient
Sample d25 dso d75 So
(mm) (mm) (mm)
5Ac 0.123 0.173 0.304 1.6
5Bc 0.009 0.028 0.123 3.7
5Cc 0.013 0.042 0.206 4.0
5Dc 0.067 0.107 0.296 2.1
5Au 0.009 0.030 0.128 3.7
5Bu 0.009 0.027 0.117 3.6
5Cu 0.009 0.022 0.097 3.3
5Du 0.008 0.019 0.082 3.1
3.4 Settling Velocity
The settling column for measuring the settling velocity of initially suspended
sediment was a 2 m high, 100 mm diameter cylindrical tube with outlets at 0.05, 0.15,
0.3, 0.55, 0.8, 1.05, 1.3, and 1.55 m. Water samples (10 cm3 each) were withdrawn at
these elevations over a selected set of time of intervals, usually 0, 5, 15, 30, 60, 120, and
180 minutes. The purpose of these withdrawals was to determine the suspended sediment
concentration, C, as a function of elevation and time during the settling process.
The governing equation for suspended sediment concentration is:
aC a
(w C) =0 (3.7)
at 8z
where t is time and z is the vertical elevation coordinate (Mehta and Li, 2001). The
settling velocity ws is then be obtained from the equation above given the initial
condition:
C(z,t)= C(z,0) (3.8)
along with zero sediment flux conditions at the surface (z = h, where h is the height of
water in the column) and at the bottom (z = 0). The initial condition was prescribed by
the uniform suspension concentration at the beginning of each test. A computer program
named SET1.M written in MATLAB solved Equation 3.7 to find w, (Mehta and Li,
2001). In Fig. 3.2 the data (points) are plotted along with computed curves for different
OC.
1.00E01
1.00E02
1.OOE03
S1.00E04
1.00E05
1.00E06
0
.01
Concentration (kg/m3)
Figure 3.2 Settling velocity plot for lake sediment samples.
The settling velocity curves of Fig. 3.2 are used to determine the settling velocity
parameters for model input. Ten percent organic content is the top curve and increasing
the organic content by ten for each additional curve one ends with the sixty percent
organic content at the lower end. Each curve is represented mathematically on a loglog
scale by the following equation:
aC"
w =(C2 (3.9)
(C' +b )"
where a, b, n and m where determined to be 0.7, 7.9, 2.5, and 1.4, respectively and a free
settling limiting concentration was 0.1 kg/m3 with a velocity of 9x10"7 m/s, all for the
   I I L l l ^ i i I I T I  r 1 i_ l 
E L2 l   3 i "1 r
      , L 121  L L
4
E rganc it ,
   
1 j a1m, o.
curve for 50% organic content, which is where most of the unconsolidated sample
averages fall.
Modeling was done based on the average values of organic content in the inner,
outer, and exposed areas corresponding to the curves for that organic content and
associated coefficients a, b, n and m. These are listed in Table 3.6.
Table 3.6 Settling velocity parameters.
Organic Settling Velocity Parameters
Content
(%) a b m n
10 0.7 1.6 2.5 1.4
20 0.7 2.4 2.5 1.4
30 0.7 3.7 2.5 1.4
40 0.7 5.8 2.5 1.4
50 0.7 7.9 2.5 1.4
60 0.7 10 2.5 1.4
3.5 Erosion Parameters
Sample erosion rates were obtained using the particle erosion simulator (PES)
(Tsai and Lick, 1986). The PES is essentially a 15.2 cm diameter perplex cylinder in
which suspended sediment concentration can be monitored over time. In the present tests,
samples are mixed with water from the lake inside a cylinder and allowed to settle and
then consolidate for up to 72 hours. A porous vertical grid was then oscillated at
different angular speeds (rpm), which effectively applied a shear stress on the bed. This
shear stress was obtained from the calibration relationship (Rodriguez et al., 1997):
applied =0.0005914rpm (3.9)
Two to four different shear stresses were applied to each sample to obtain the
erosion rate s. Each shear stress was applied for one hour and concentration of
suspended sediment, C was taken at 0, 5, 15, 30 and 60 minutes. The erosion rate (flux)
was then calculated according to:
dC
F =h d (3.10)
dt
where h is the water depth and dC/dt is the timerate of change of suspension
concentration. The corresponding erosion rate function is:
F, =M( ppied r) (3.11)
For each sample, the erosion rate constant, M and the shear strength, r, were
obtained as follows: First, Fe values calculated from Eq. 3.10 were plotted against the
corresponding Tappiied calculated from Eq. 3.9, and a bestfit line was drawn through the
data points. The erosion rate constant M was then taken as the slope of the line and the
intercept of the line with the Tappied axis gave the shear strength, r, (Mehta et al., 1994).
The data indicated that the erosion rate constant increased with increasing organic
content, while the shear strength decreased (Fig. 3.3).
0.3
" 0.25
0.2
S0.15
S0.1
W 0.05
0
0
0.05 0.1 0.15 0.2 0.25 0.3
Shear Stress (Pa)
Figure 3.3 Erosion rate vs. shear stress.
/ M=2.06 g/.s
60% Oganic Content /
Ts=0.12 Pa  '
 =0.062 Pa 10% Or ganic Conter
** 
35
Following Fig. 3.3, the erosion shear strength was assumed to vary linearly with
the organic content by the following equation:
r, = 0.00129(OC)+ 0.138 (3.12)
Bounds of this equation are: rs= 0.062 Pa at 60% OC and 0.12 Pa at 10% OC.
3.6 Consolidation
3.6.1 Selfweight Consolidation
In selfweight consolidation tests carried out, the fall in the bed height was
measured as a function of time. Initially, settling occurred during which the bedwater
interface fell rapidly. Consolidation was considered to begin when there was a step
decrease in the rate of fall. The results from one such test are given in Fig. 3.4. The height
Ro = 7.62 cm at the beginning of consolidation and Rloo = 4.57 cm at the end.
10000
10 100 1000
Time (min)
Figure 3.4 Selfweight consolidation of sample 4cu.
R=7.62 dmc:
RIO = 4.57 cm,:
The bulk density of the bed material after selfweight consolidation showed a
range similar to that of unconsolidated bed from core samples in Newnans Lake. As
noted, Been and Sills (1981) assumed a constant value of the coefficient of consolidation
equal to 8.2x103 mm/s. This value was used in the resent study to estimate bed
compressibility, av for selfweight consolidation with an initial uniform void ratio of e,=
65 and a final void ratio at the surface ee= 35. Note that for definitional purposes, the
void ratio e is
V, H H,
e i= V = = (3.13)
Vsolids Hs
where V, is the volume of the voids, Vso3ids is the volume of the solids, H is the bed height
and Hs is the height of the solid phase.
Bed compressibility was then assumed to obtain the bestfit curve for the data in
Fig. 3.4.
3.6.2 Overburden Consolidation
Two consolidation tests were run with overburden stresses of 25 and 50 kN/m2
(Figs. 3.5 and 3.6). The Terzaghi consolidation equation (e.g., Lambe and Whitman,
1969) is
c U aU e o, (3.14)
SaZ2 at at
and can be derived from Eqs. 2.20 and 2.21. The coefficient of consolidation is estimated
from oedometer test according to
c 0.197(H50 /2)2 (3.15)
t50
in which Hso and tso are the height and time at 50% consolidation, respectively. The time
ts0 was determined by Casagrande's log method (Lambe and Whitman, 1969).
Permeability values calculated from Eq. 3.16 (Davidson, 1998) were found to be
very low (Table 3.7):
kh = c, w (3.16)
1+ eso
In Eq. 3.16, c, is the coefficient of consolidation determined by Eq. 3.15 and av is the bed
compressibility (which was determined graphically as the slope of the line in Fig. 3.7),
eso is the void ratio at 50% consolidation and Yw is the unit weight of water. The high
deflections that occurred under overburden were probably due to high velocity of the
solids and high seepage velocity of the water.
The results from the oedometer tests are given in Fig. 3.7 in order to determine
bed compressibility for the applied stresses of 25 and 50 kN/m2. Determination of H50,
tso and es0 are shown in Fig. 3.5 and 3.6. Results are summarized in Table 3.7.
0
0.1
R o=0.16
0.2
0.3
I 0.4
0.5
R oo000.5E
0.6
0.7
0.1 1 t oo 10 100 1000 10000
t5o= 0.4 mm
Time (min)
Figure 3.5 Consolidation for an overburden stress of 25 kN/m2
Il~f,. II. rl  l llII, r.r, r
I  C C      I ( I~ CI  (l( C
..Rso, Q:38 _?I1~'~ '''
;  IIrl ~C ~ ~i~  ; 7 7~i i i I T 7 C~'''~' I~~~ ~~~ '''
0.65
R o=0.66 c]
0.75
E
0.85
Roo=0.86
0.95
t so=0.9 min
10 twoo
Time (min)
,...,.,
1000
10000
Figure 3.6 Consolidation for an overburden stress of 50 kN/m2.
18.0
16.0
14.0
12.0
10.0
8.0
6.0 0.25m F/kN
4.0
2.0
0.0
0 10 20 30 40 50 60
Pressure (kN/m2)
Figure 3.7 Determination of bed compressibility for overburden consolidation.
Table 3.7 Coefficients of consolidation and compressibility for overburden
consolidation.
t r rn rr
9 I I I I I
Rso',=20:7,61 r InI
['i i J ~ I Ill
I II I tI I rI IIl I I lI II
'''

n
The results in Table 3.7 were used to estimate input parameters for modeling selfweight
consolidation. Note that the density in the oedometer were very close to densities of the
consolidated bed material in the lake, while densities of the unconsolidated material were
closer to those of the selfweight consolidated beds in the PES. Note also that at the lake
bed, incremental material may have deposited after selfweight consolidation of the
previously deposited material was complete. Hence, this additional load amounts to an
overburden.
CHAPTER 4
SEDIMENT RESUSPENSION POTENTIAL
4.1 Modeling Newnans Lake Resuspension
This chapter examines the resuspension potential of the bed material as a function
of the location in the lake area and water level. Model input parameters are given for the
Visual Fortran and MATLAB programs developed by Mehta and Li (2001). A uniform
depth and uniform mud layer thickness are assumed throughout the lake with an
estimated limiting wave height for resuspension of 0.2 m. This wave height was chosen
based on the limiting horizontal velocity needed to erode material at the assumed depth.
The lake was divided into three distinct regions based on bathymetry data
available from ECT (2001). From Fig. 4.1 we note that the inner open water area was
assumed to be that greater depth than 0.3 m, while the outer open water area was
shallower than the 0.3 m. The third area was the exposed, and will be submerged if and
when the lake rises by 1.1 m to its estimated mean stage. In the exposed area much of the
pore water has escaped due to desiccation.
Bed consolidation was modeled to fit laboratory test results and then the site
specific parameters thus determined were used to estimate the time to reach densities of
consolidated core samples.
Land3
Openwater coring sites
Exposed bottom1.0 km
sampling sites
Exposed area
Lan
Land4
3
d5
Figure 4.1 Depth contours showing inner cores inside 0.3 m contour.
4.2 Resuspension Modeling
4.2.1 Model Calibration and Validation
The resuspension model was calibrated and then validated using data collected at
the lake as part of the study. For a 0.05 m wave height and 1 s period under a wind speed
of 3 m/s, the concentration was found to be 4 kg/m3 at a water depth of 0.25 m. These
data were used for calibration. Table 4.1 gives the model input parameter, and model
results are given in Fig. 4.2. For further details on modeling including parameter
definitions see Section 4.2.2.
The model was then validated based on data collected under the same wave
conditions at a site where the water depth of 0.3 m and where the concentration was 2
I
42
kg/m3. Table 4.1 gives the model input parameter, and model results are given in Fig.
4.3.
Table 4.1 Model calibration and validation input parameters.
Parameter Calibration Validation
h 0.25 0.3
hb 0.3 0.3
ngrids 25 30
stt 0 0
ett 300 300
dt 60 60
Ott 30 30
C1 0.1 0.1
Wsf 9x107 9x107
a 0.7 0.7
b 7.9 7.9
m 2.5 2.5
n 1.4 1.4
ao 0.5 0.5
f3o 0.33 0.33
H 0.05 0.05
T 1 1
a, 0.35 0.35
ps 2059 2059
p 1201 1201
pw 1000 1000
TDep 0.08 0.08
f 0.049 0.057
S1 1
xi 0 0
PD 96 96
0Pe 0 0
ae 0.08 0.08
f 0 0
smax 0.2 0.2
ar 18.2 18.2
b, 0.5 0.5
zi 0.1 0.1
Ci 4x103 4x10
zi 0.2 0.2
Ci 4x10 4x10
l0. 10L2 10. 10 10' 102 0 5 10 15 20 25
Suspended Sediment Cone. (kg/m3) Suspended Sediment Cone (kg/m3)
Figure 4.2. Calibration run, with 90 minutes to reach 4 kg/m3 field concentration shown
by blue dot. Left plot is loglinear; right is linear scale.
3 III0.35
0.25 .... .
0.05 ... ................................ ............... .. ...............
0.2 . . .
0.15 ..........
0.3 . .........
0 2 i .  ..  
01 ... ... I C..........
103 10 101 10i 0 10 20 30 40 50
Suspended Sediment Cone. (kg/m) Suspended Sediment Cone. (kg/m)
Figure 4.3. Validation run, with 90 minutes to reach 2 kg/m3 field concentration shown
by blue dot. Left plot is loglinear; right is linear scale.
4.2.2 Effect of Wind Speed and Location on Resuspension
Selecting a water depth of h = 1.5 m and a mud thickness hb = 0.3 m, the water
column was divided into a number of vertical grids, ngrds= 15. The starting time of
simulation was sit= 600 min and ending time et= 600 min. The time step for calculation
dt= 60 and the output time step ot= 60 min. So for 600 min the model gave the suspended
sediment concentration profile at 60 min intervals.
Settling velocity parameters were given based on the test outlined in Chapter 3,
with the limiting free settling concentration C1= 0.1 kg/m3. The corresponding limiting
free settling velocity wsf = 9.0x107 m/s. The parameters for the curve identifying median
values for organic material were found to be a= 0.7, b= 7.9, m= 2.5 and n= 1.4.
The wave diffusion constant, aw= 0.35, was determined through the model
calibration and validation. Stabilized diffusion parameters ao= 0.5 and lo= 0.33 were
used throughout the modeling process.
The wave height H= 0.202 m and period T= 1.85 s were selected for the selected
8 m/s wind speed. A wave height of 0.209 m and 1.9 s period were used for the 9 m/s
wind speed, and 0.223 m and 2 s, respectively, for the 10 m/s wind speed.
Mean values of the unconsolidated sediment parameters was used for the inner
open water area were: the granular density Ps = 2,025 kg/m3, bed bulk density p= 1,201
kg/m3 and water density pw= 1,000 kg/m3. The bottom sediment was considered as a bed
and the critical stress for deposition rDep= 0.07 Pa. The bed shear strength for erosion, r,
is modeled by the following equation:
r, = a,(D (D (4.1)
where 0 = PD / p, and ,e is the minimum value of 0. We will assume =0 and ae=
0.07 based on the laboratory results.
The wave bottom friction coefficient fw, which changes with wave height, was
determined for the conditions above to be 0.029, 0.027, and 0.023 respectively for the 8,
9 and 10 m/s wind speed. Assuming a linear bed density variation with depth, the bed
density parameters Q= 1 and xi= 0 to satisfy Eq. 4.5:
PD D hb i (4.5)
where hb is bed depth, pD is the bed average dry density and Az is the incremental depth
from the bed surface. The erosion rate constant is related to ,s according to (Li and
Mehta, 2001):
M = s.x exp(arsbr) (4.6)
Based on laboratory test results (Table 4.2), Smax=0.2, ar=17.8, and br=0.5 were selected.
The initial concentration input was based on field information; for i=1, elevation
zi = 0.25 m, concentration Ci = 4.0x103 kg/m3, and for i=2, zi= 0.1 m and Ci = 4.0x103
kg/m3, where 4.0x103 kg/m3 is wash load which does not to settle out. The model input
data are summarized in Table 4.3.
Modeling at low water (depth of 1.5 m) (Fig. 4.4) indicated that material erodes at
a wind speed of 8 m/s and higher. This wind speed is estimated to produce waves of 0.2
m and a wave period of 1.85 s. Once this speed is attained erosion may take place. In
Fig. 4.5, the middepth concentration is plotted for each wind speed as a function of time.
In each case, erosion is rapid at the beginning; however, as time progresses the effect of
settling/deposition increases and the concentration approaches a constant value as the
rates of erosion and deposition approach equality and an equilibrium condition is
established. The results are summarized in Table 4.4.
Table 4.2 Mean sedimentary and erosion parameters for inner, outer and exposed areas.
Organic Bulk Dry Particle Bed Shear Erosion
Content Density Density Density Strength Rate Constant
Core OC p pD Ps rs M
Area Nos. (%) (kg/m3) (kg/m3) (kg/m3) (Pa) (g/Ns)
Inner 5bu 51 1041 71 2333 0.071 1.81
5cu 53 1022 37 2381 0.068 1.88
4bu 50 1022 38 2400 0.072 1.77
4cu 58 1019 32 2333 0.062 2.06
3bu 52 1022 39 2240 0.07 1.85
3cu 53 1021 36 2383 0.071 1.81
3du 36 1072 123 2422 0.09 1.27
2bu 56 1005 19 1316 0.065 1.99
2cu 44 1009 66 1150 0.08 1.56
2du 52 1016 70 1289 0.07 1.85
Average 51 1025 53 2025 0.07 1.80
Outer 5au 50 1043 75 2304 0.072 1.77
5du 55 1013 23 2308 0.066 1.95
4au 45 1048 82 2357 0.079 1.59
4du 45 1072 122 2452 0.079 1.59
3au 52 1020 54 1577 0.07 1.85
2au 48 1041 68 2455 0.075 1.7
1au 36 1068 149 1827 0.09 1.27
1bu 50 1025 58 1769 0.073 1.77
1cu 49 1040 112 1556 0.079 1.74
1du 35 1108 218 1985 0.092 1.24
Average 47 1048 96 2059 0.08 1.60
Exposed Landl 22 1151 253 2469 0.108 0.77
Land2 46 1069 121 1969 0.077 1.63
Land3 34 1138 240 2227 0.093 1.2
Land4 19 1242 407 2477 0.112 0.66
Land5 27 1181 312 2339 0.102 0.95
Average 30 1156 267 2296 0.10 1.00
Table 4.3 Inner o en water low water input parameters.
Wind 8 9 10
Speed (m/s) (m/s) (m/s)
h 1.5 1.5 1.5
hb 0.3 0.3 0.3
ngrids 15 15 15
stt 0 0 0
ett 600 600 600
dt 60 60 60
Ott 60 60 60
C1 0.1 0.1 0.1
wsf 9x107 9x107 9x107
a 0.7 0.7 0.7
b 7.9 7.9 7.9
m 2.5 2.5 2.5
n 1.4 1.4 1.4
ao 0.5 0.5 0.5
flo 0.33 0.33 0.33
H 0.202 0.209 0.223
T 1.85 1.9 2
a, 0.35 0.35 0.35
ps 2025 2025 2025
p 1201 1201 1201
pw 1000 1000 1000
rDep 0.07 0.07 0.07
fw 0.029 0.027 0.023
1 1 1
xi 0 0 0
PD 53 53 53
.e 0 0 0
ae 0.07 0.07 0.07
1 0 0 0
sma 0.2 0.2 0.2
ar 17.8 17.8 17.8
br 0.5 0.5 0.5
zi 0.5 0.5 0.5
Ci 4.0x103 4.0x10 4.0x10
zi 1 1 1
Ci 4.0xl0"3 4.0xlO3 4.0x103
5 10
Suspended Sediment Cone. (kg/m3)
Figure 4.4 Resuspension at 8 m/s wind in the inner open water area at low water.
7.00E+00
6.00E+00 
a 5.00E+00 
a 4.00E+00 .. + 8 (m/s)
 .. 9 (m/s)
S3.00E+00 A 10 (m/s)
o 2.00E+00 O .
1.00E+00
O.OOE+00
0 100 200 300 400
Time (min)
500 600 700
Figure 4.5 Inner open water area middepth concentration evolution at different wind
speeds, low water.
Table 4.4 Inner open water area middepth concentrations at 600 min; low water.
Water Wave Wave Organic Concentration
Depth Height Period Content at 600 min
(m) (m) (s) (%) (kg/m3)
1.5 0.202 1.85 51 2.4
1.5 0.209 1.9 51 4.2
1.5 0.223 2 51 6
Since Newnans Lake was at a very low state in Summer 2001, a suspension
estimate for the normal stage was made to examine whether dredging efforts would be
feasible for decreasing the potential for resuspension, thus improving the water quality.
The new modeling depth was changed to 2.6 m based on stage data given in Figure 2.1.
The new depth changed the wave height and period slightly, and also affected the wave
friction factor. At this depth the number of grid points (ngrids) was taken as 26. The new
wave heights for 8, 9 and 10 m/s wind speeds were 0.236 m, 0.234 m and 0.255 m,
respectively with respective 1.99 s, 2.00 s, and 2.10 s. These conditions yielded wave
friction factors of 0.051, 0.044, and 0.038, respectively. Table 4.5 summarizes the model
input parameters.
Figure 4.6 shows that during the high water condition a 10 m/s wind speed is
needed to suspend bed material in the inner open water area because of the increase in
water depth. Lines corresponding to the 8 and 9 m/s wind speeds are not plotted because
no material was resuspended. See also Table 4.6.
Table 4.5 Inner o en water high water input parameters.
Wind 8 9 10
speed (m/s) (m/s) (m/s)
h 2.6 2.6 2.6
hb 0.3 0.3 0.3
ngrids 26 26 26
Stt 0 0 0
ett 600 600 600
dt 60 60 60
ott 60 60 60
Cl 0.1 0.1 0.1
Wsf 9x107 9x107 9x107
a 0.7 0.7 0.7
b 7.9 7.9 7.9
m 2.5 2.5 2.5
n 1.4 1.4 1.4
ao 0.5 0.5 0.5
flo 0.33 0.33 0.33
H 0.226 0.234 0.255
T 1.9 2 2.1
ao, 0.35 0.35 0.35
ps 2025 2025 2025
p 1201 1201 1201
pw 1000 1000 1000
tDep 0.07 0.07 0.07
fw 0.051 0.044 0.038
1 1 1
xi 0 0 0
PD 53 53 53
e o 0 0 0
ae 0.07 0.07 0.07
p 0 0 0
Smax 0.2 0.2 0.2
a, 17.8 17.8 17.8
b, 0.5 0.5 0.5
zi 0.5 0.5 0.5
Ci 4.0x10 4.0x103 4.0x103
zi 1 1 1
Ci 4.0x103 4.0x10' 4.0x10
1.20E01
1.00E01
8.00E02
6.00E02
4.00E02
2.00E02
0.OOE+00
A 10 (m/s)
0 100 200 300 400 500 600 700
Time (min)
Figure 4.6 Inner open water area suspended sediment evolution at high water.
Resuspension occurred 10 m/s wind speed only.
Table 4.6 Inner open water area middepth concentrations at 600 min; high water.
Water Wave Wave Organic Concentration
Depth Height Period Content at 600 min
(m) (mS)(s) (%) (kg/m3)
2.6 0.226 1.9 51 4x103
2.6 0.234 2 51 4x10
2.6 0.255 2.1 51 lx101
Model input parameters for the outer open water area are given in Table 4.7.
Note that the high water depth changed to 1.25 m, because the mean depth inside the 0.3
m contour was 0.15 m at low water. Note also that due to this very shallow low water
depth, resuspension at low water was not examined for the outer pen water area. Results
for high water are shown in Fig. 4.8.
/
A A ____ _____ _____ ____
1


Table 4.7 Outer o en water high water input parameters.
Wind 8 9 10
speed (m/s) (m/s) (m/s)
h 1.25 1.25 1.25
hb 0.3 0.3 0.3
ngrids 26 26 26
Stt 0 0 0
ett 600 600 600
dt 60 60 60
Ott 15 15 15
C1 0.1 0.1 0.1
wsf 9x107 9x 107 9x107
a 0.7 0.7 0.7
b 7.9 7.9 7.9
m 2.5 2.5 2.5
n 1.4 1.4 1.4
ao 0.5 0.5 0.5
fo 0.33 0.33 0.33
H 0.226 0.234 0.255
T 1.9 2 2.1
a. 0.35 0.35 0.35
ps 2059 2059 2059
p 1201 1201 1201
pw 1000 1000 1000
TDep 0.08 0.08 0.08
f, 0.021 0.018 0.016
S 1 1 1
xi 0 0 0
PD 96 96 96
Pe 0 0 0
ae 0.08 0.08 0.08
P 0 0 0
Sma 0.2 0.2 0.2
ar 18.2 18.2 18.2
br 0.5 0.5 0.5
zi 0.5 0.5 0.5
Ci 4.0x10 4.0x103 4.0x10
zi 1 1 1
Ci 4.0x103 4.0x10 4.0x103
1.20E+01
1.00E+01 
S8.00E+00 
S  8 (m/s)
S6.00E+00  9 (m/s)
 10(m/s)
I 4.00E+00 
2.00E+00
0.00E+00
0 100 200 300 400 500 600 700
Time (min)
Figure 4.7 Outer open water area middepth concentration evolution at different wind
speeds, high water.
Table 4.8 Outer open water area middepth concentrations at 600 min; high water.
Water Wave Wave Organic Concentration
Depth Height Period Content at 600 min
(m) (m) (s) (%) (kg/m3)
1.25 0.226 1.9 47 7
1.25 0.234 2 47 7.9
1.25 0.255 2.1 47 10
From Fig. 1.3 estimate of mean lake stage, the exposed area was assumed to have
a water depth of 1.1 m. Waves generated by the fetch (3,000 m) and mean depth for the
open water area were used. The wave bottom friction factor values were found to be
0.027, 0.022, and 0.018 for 8, 9 and 10 m/s wind, respectively. Since the exposed area
had higher dry densities due to exposure, an erosion rate constant value of M = 1.1 g/Ns
was used with a bed shear strength rs = 0.1 Pa based on the mean values listed in Table
4.2.
Table 4.9 Exposed area model input parameters at high water.
Wind 8 9 10
speed (m/s) (m/s) (m/s)
h 1.1 1.1 1.1
hb 0.3 0.3 0.3
ngrids 11 11 11
Stt 0 0 0
ett 600 600 600
dt 15 60 60
Ott 60 60 60
C1 0.1 0.1 0.1
wsf 4.0x10 4.0x105 4.0x10
a 0.7 0.7 0.7
b 3.7 3.7 3.7
m 2.5 2.5 2.5
n 1.4 1.4 1.4
ao 0.5 0.5 0.5
fo 0.33 0.33 0.33
H 0.226 0.234 0.255
T 1.9 2 2.1
a, 0.35 0.35 0.35
ps 2296 2296 2296
p 1201 1201 1201
pw 1000 1000 1000
TDep 0.1 0.1 0.1
S 0.019 0.017 0.014
S 1 1 1
xi 0 0 0
Po 267 267 267
0e 0 0 0
ae 0.1 0.1 0.1
p 0 0 0
max 0.2 0.2 0.2
ar 16.75 16.75 16.75
br 0.5 0.5 0.5
zi 0.5 0.5 0.5
Ci 4.0x103 4.0x10 4.0x10
zi 1 1 1
Ci 4.0x10'3 4.0x103 4.0x10
9.00E+00
8.00E+00
7.00E+00
S6.00E+00 
a 5.00E+00  8 (m/s)
S. 9 (m/s)
S4.OOE+00 
au JV 2.00 10 (m/s)
S3.00E+00
2.00E+00
1.00E+00
1.00E+00   
0.00E+00
0 100 200 300 400 500 600
Time (min)
Figure 4.8 Exposed area middepth concentration evolution at different wind speeds, high
water.
Table 4.10 Exposed area middepth concentrations at 600 min; high water.
Water Wave Wave Organic Concentration
Depth Height Period Content at 600 min
(m) (m) (s) (%) (kg/m3)
1.1 0.226 1.9 30 1.2
1.1 0.234 2 30 7
1.1 0.255 1 30 8.1
Conclusions can be drawn relative to the potential for sediment resuspension in
the three subareas of the lake. Figures 4.10, 4.11 and 4.12 summarize plots of the time
evolution of middepth concentration. All plots are for the high water condition. The
outer pen water area seems to have the greatest suspension concentration for the lake as a
whole at 1 kg/m3.
S1.00E+01
~ 1.00E+00
S1.00E01
1.00E02
j 1.OOE03
 Inner Area
u Outer Area
* Exposed Area
0 100 200
300 400
500 600
Time (min)
Figure 4.9 Middepth suspended sediment concentration in the three subareas at 8 m/s
wind.
1.00E+01
1.00E+00
1.00E01
1.00E02
1.00E03
z . I ; z
 li I  
  
/ l         
 Inner
Area
 Outer
Area
SExposed
Area
0 100 200 300 400 500 600
Time (min)
Figure 4.10 Middepth suspended sediment concentration in the three subareas at 9 m/s
wind.
 
     
       
""  ' 
         
 
    
1.00E+01
S 1.00E+00
1.OOE02
01.00E03
Sl.OOE03
i
x
k
      
      
 
i_ __  _ _  
0 100 200 300 400 500 600
Time (min)
Figure 4.11 Middepth suspended sediment concentration in the three subareas at 10 m/s
wind.
4.2.3 Effect of Dredging on Resuspension
To improve water quality in the lake, one proposal calls for dredging the
unconsolidated bed layer in order to decrease the resuspended sediment in the water
column. Assuming the 0.3 m unconsolidated layer has been removed a new depth of 2.9
m at high water can be used. This new depth would increase the wave height slightly; the
new input parameters are shown in Table 4.12. Since the newly exposed bed material
will then have properties associated with the consolidated layer, the mean organic content
of the consolidated samples may be used to determine the input parameters. From this
organic content the shear strength for erosion is obtained from a linear equation based on
laboratory results:
r, =0.001290C+0.138 (4.2)
The erosion rate constant can also be determined through the mean organic
content from:
Inner
Area
. Outer
Area
Expose
d Area
M = 0.0360C0.015
From these relationships, rs and M were determined to be 0.09 Pa and 1.27 g/Ns,
respectively. These gave a rDep = 0.09, ae = 0.09, and an a, =16. The mean consolidated
bed parameters are given in Table 4.11, and model input parameters in Table 4.12.
Table 4.11 Consolidated bed properties.
Sample p pD Ps Organic Content
(kg/m3) (kg/m3) (kg/m3) (%)
1Ac 1061 113 2153 17
1Bc 1019 81 1297 50
1Cc 1082 140 2414 32
1Dc 1114 185 2597 13
2Ac 1148 257 2353 23
2Bc 1063 108 2393 35
2Cc 1062 106 2407 37
2Dc 1092 156 2430 37
3Ac 1047 117 1676 52
3Bc 1029 67 1750 42
3Cc 1018 54 1523 48
3Dc 1092 188 1964 21
4Ac 1089 152 2408 33
4Bc 1044 73 2500 50
4Cc 1011 67 1205 46
4Dc 1091 160 2308 25
5Ac 1096 158 2541 27
5Bc 1044 75 2400 50
5Cc 1099 166 2484 42
5Dc 1072 124 2396 32
Minimum 1011 67 1205 13
Average 1069 127 2160 36
Maximum 1148 257 2597 52
(4.3)
Table 4.12 Dredged bottom model input parameters.
Wind 10 11 12
speed (m/s) (m/s) (m/s)
h 2.9 2.9 2.9
hb 0.3 0.3 0.3
ngrids 29 29 29
Sit 0 0 0
ett 600 600 600
dt 60 60 60
ott 60 60 60
C1 0.1 0.1 0.1
wsf 4.2x106 4.2x106 4.2x10
a 0.7 0.7 0.7
b 5.8 5.8 5.8
m 2.5 2.5 2.5
n 1.4 1.4 1.4
ao 0.5 0.5 0.5
Ao 0.33 0.33 0.33
H 0.26 0.292 0.305
T 2.17 2.34 2.45
a,, 0.35 0.35 0.35
ps 2160 2160 2160
pm 1201 1201 1201
pw 1000 1000 1000
rTep 0.09 0.09 0.09
S 0.04 0.029 0.025
1 1 1
xi 0 0 0
PD 127 127 127
,e 0 0 0
a, 0.09 0.09 0.09
p 0 0 0
smax 0.2 0.2 0.2
ar 16 16 16
br 0.5 0.5 0.5
zi 0.5 0.5 0.5
Ci 4.0x103 4.0x10 4.0x103
zi 1 1 1
Ci 4.0x10 4.0x10 4.0x10
__ __ _A_
,n
/ ,*
.,a___
3/
11 (m/s)
 12 (m/s)
0 100 200 300 400 500 600 700
Time (min)
Figure 4.12 Middepth suspended sediment concentration evolution with time; dredged
bottom.
From Fig. 4.12 and Table 4.13 we observe that dredging the lake would have a
positive affect on reducing turbidity. Larger wind speeds would be needed to acquire the
wave height necessary to significantly resuspend the bed material at the new depth.
Specifically, by taking out the 0.3 m unconsolidated bed material a wind speed of 11 m/s
would be needed to erode bed material.
Table 4.13 Dredged lake middepth concentrations at 600 min.
Water Wave Wave Organic Concentration
Depth Height Period Content at 600 min
(m) () (s) (%) (kg/m3)
2.9 0.26 2.17 36 4x103
2.9 0.292 2.34 36 0.08
2.9 0.305 2.45 36 0.16
4.3 Consolidation
For modeling consolidation (Mehta and Li, 2001), based on a series of laboratory
tests, Been and Sills (1981) recommend a mean coefficient of consolidation is 8.2x103
mm2/s as being suitable for fine sediment settlement and associated density predictions.
The initial bed height was taken as 0.076 m. The initial (uniform) void ratio ei and the
1.80E01
1.60E01
1.40E01
E
S1.20E01
1.00E01
E 8.00E02
6.00E02
0 4.00E02
2.00E02
n nnF+nn
final void ratio ee at the surface were selected as 65 and 35, respectively. The bestfit bed
compressibility av was found to be 1.0 for a 48hour consolidation duration (tt) with a
model output interval (ot) of 1 hour [see Mehta and Li (2001) for symbol definitions].
Model outputs along with data comparison are shown in Fig. 4.13.
0.08
dt = 1 (hr)
0.07
t final = 48 (hr)
0.06 I = initial density profile
F = final density profile
0.05
0.04
0.03
F
0.02
0.01
0 I I I I I I II
re .102 104 106 Se ens 108 og:1030 1032 103o 1036d i 10proie wih time.
Brenner and Whitmore (1998).
Brenner and Whitmore (1998).
62
Table 4.14 Model input parameters for 100year selfweight consolidation simulation.
Parameter Value
di 1.3
ei 25
ee 5
cf 8.00x109
a, 0.0025
ps 2025
tt 876000
ot 87600
ngrids 13
1.4
dt = 87600 (hr)
1.2 Brenner and Whitmore
(1998) t final= 876000 (hr)
I = initial density profile
1 F = final density profile
1,078 kg/m3 average bulk density o
S consolidated samples Appendix A
0,o
[0.6 
F
0.4
10 1 0
0.2 ye rs y s
0 IL I I I
1030 1040 1050 1060 1070 1080 1090
Density (kg/m3)
Figure 4.14 100year selfweight consolidation of bed material with each line
representing 10 years.
CHAPTER 5
CONCLUSIONS
5.1 Summary
Newnans Lake in northcentral Florida has been placed on the restoration priority
list for the past twelve years, and has had a hypereutrophic rating since the early 1970's.
A significant cause of this problem is believed to be resuspension of bottom "muck" in
the lake under the action of episodic wind waves. The objective of this study was to
model windwave induced resuspension of organicrich fine sediment in the lake in order
to determine the correlation between wind speed and suspended sediment load. Such an
assessment would facilitate the development of strategies for lake restoration. In order to
meet this objective, bottom sediment samples and some suspended sediment
concentration measurements in the lake were analyzed and laboratory tests on sediment
erosion, settling and consolidation were conducted in the laboratory. Results from these
studies were then used to run a 1D vertical model on waveinduced resuspension as well
as a model for selfweight consolidation in order to simulated suspended sediment load as
a function of location and water level in the lake and wind speed and bed strength. In
addition, the effect of dredging the bottom in reducing resuspension was examined.
5.2 Conclusions
The following main conclusions have been derived:
Newnans Lake bed material is highly organic (1358%) with very low bed
densities (1,0091,148 kg/m3).
A settling velocity function was developed to account for differences in the
organic content of the suspended matter. It was found that the higher the
organic content the lower the settling velocity.
Bed strength and erosion rates showed dependence on organic content. As the
organic content increased the bed shear stress needed to resuspend material
decreased.
Significant resuspension of bed material is likely when wind speed exceeds 8
m/s.
Since the inner open water area is deeper than the outer open water area,
resuspension there is less likely, especially at the "normal" lake stage than
during the low water depth as occurred in Summer 2001. A wind speed of
around 10 m/s is required to resuspend the bed material in the inner area under
a normal water level.
Dredging out the unconsolidated top layer of the bed, which is on the average
0.3 m in thickness, would reduce the likelihood of resuspension.
5.3 Recommendations For Future Work
It seems essential to install a selfrecording tower assembly in the lake with a
pressure sensor (for waves), a vertical array of optical backscatter sensors (for suspended
sediment profiling) and a wind anemometer over several (at least six) months to obtain
synoptic data required to better calibrate and validate modeling for lake turbidity.
Accurately modeling the strength of the bed will require the use of fully non
linear Gibson's equation for consolidation.
Spectroscopy may be used to determine the structure of the organic material and
sediment that remains after loss of ignition. The USGS has begun a data base on sites in
South Florida, especially in Florida Bay and other restoration projects to determine
nutrients and elements in the pore water (http://sofia.usgs.gov/).
APPENDIX
CORE THICKNESS AND BED DENSITIES
Data on core locations and associated water depth, bottom sediment thickness,
core length and sublengths of the unconsolidated and consolidated segments for each
sample is given in Table A. 1.
Table A.1 Core locations and data
Core
Water Sediment Core C
Depth Thickness Length Sunlengt Sample
Latitude Longitude (m) (m) (m)) No.
29.630943 82.244785 0.06 1.63 1.3 0.25 2AU.
1.05 2AC
29.630899 82.232208 0.28 3.34 1.74 0.22 2BU
1.52 2BC
29.631073 82.219799 0.15 4.43 1.71 0.26 2CU
1.45 2CC
29.631156 82.212113 0.10 1.45 1.05 0.23 2DU
0.82 2DC
29.641728 82.234122 0.07 1.67 1.29 0.14 3AU
1.15 3AC
29.641823 82.224667 0.22 3.28 1.66 0.37 3BU
0.99 3BC
29.642107 82.215023 0.52 3.33 1.50 0.30 3CU
1.20 3CC
29.641954 82.205985 0.05 1.44 1.12 0.16 3DU
0.96 3DC
29.622649 82.243081 0.01 1.31 1.27 1AU
1AC
29.622811 82.235576 0.08 1.54 1.15 0.40 1BU
0.75 1BC
29.622838 82.227713 0.17 1.58 1.21 0.23 1CU
0.98 1CC
29.622891 82.221490 0.29 1.38 1.22 0.24 1DU
0.98 1DC
29.662041 82.232417 0.05 1.80 1.27 0.40 5AU
0.87 5AC
Table A. 1 Core locations and data (continued)
29.662001 82.225155 0.07 3.03 1.63 0.22 5BU
1.41 5BC
29.661946 82.217213 0.14 3.64 1.76 0.29 5CU
1.47 5CC
29.662360 82.209655 0.06 1.84 1.22 0.61 5DU
0.61 5DC
29.652611 82.232754 0.05 2.75 1.50 0.22 4AU
1.28 4AC
29.652658 82.224720 0.27 4.03 1.64 0.35 4BU
1.29 4BC
29.653002 82.215039 0.46 4.44 1.59 0.38 4CU
1.21 4CC
29.652733 82.206271 0.04 1.62 1.45 0.15 4DU
__1.30 4DC
Core densities for unconsolidated and consolidated
mean elevations of the sublengths are plotted in Fig. A.1.
samples at the respective
* Core data (upper layer) U Core data (lower layer) O PES Bed Density
"____ ml
07Q n  
Pvg= 1,036 kmkg
pav = 1,078 kgn3
10.
1000
1040
1080
Bulk density (kg/m3)
1120
1160
Figure A. 1 Core densities for unconsolidated and consolidated samples at the respective
mean elevations of the sublengths.
u.
0.4
0.8
0
o 0.8
/\ f\
i
I #
LIST OF REFERENCES
Been, K., and Sills, G. C., 1981. Self weight consolidation of soft soils: an experimental
and theoretical study. Geotechnique, 31 (4), 519535.
Brenner, M., and Whitmore, T. J., 1998. Historical sediment and nutrient accumulation
rates and past water quality in Newnans Lake. Final Report, St. Johns Water
Management District, Palatka.
Burt, T. N., 1986. Field settling velocities of estuary muds. In: Estuarine Cohesive
Sediment Dynamics, A. J. Mehta ed., SpringerVerlag, Berlin, 251265.
Davidson, J. L., 1998. Soil Mechanics Laboratory Manual. Department of Civil and
Coastal Engineering, University of Florida.
Department of the Army. 1984. Shore Protection Manual. U. S. Government Printing
Office, Washington, DC.
Effler, S. W., 1996. Limnological and engineering analysis of a polluted urban lake.
SpringerVerlag, New York.
Environmental Consulting and Technology, Inc., (ECT), 2002. Bathymetry and sediment
thickness surveys of Newnans Lake, Project 99B250. Report for ECT Project No.
9907650400, Gainesville, FL..
Faure, G., 1998. Geochemistry, Prentice Hall, Englewood Cliffs, NJ.
Federico, A. C., Dickinson, K. G., Kratzer, C. R., and Davis, F. E., 1981. Lake
Okeechobee water quality studies and eutrophication assessment. Technical Publication
#812, Resource Planning Department, West Palm Beach, FL.
Ganju, N. K., 2001. Trapping organicrich fine sediment in an estuary. M. S. thesis,
University of Florida, Gainesville.
Gottgens, J. F., and Montague, C. L., 1987. Orange, Lochloosa, and Newnans Lake: A
survey and preliminary interpretation of environmental research data. Final Report,
University of Florida, Gainesville.
Holcomb, D. E., 1993. Study 6262 Newnans Lake restoration. Completion Report
Statewide Lake Restoration, Bureau of Fisheries Management.
Holly, J. B., 1976. Stratigraphy and sedimentary history of Newnans Lake. M. S. thesis,
University of Florida, Gainesville.
Jonsson, I. G., 1966. Wave boundary layer and friction factors. Proceedings of the 10h
Coastal Engineering Confrence, Vol. 1 ASCE, New York.
Jorgensen, S. E., 1980. Lake management. Pergamon Press, New York.
Krone R. B., 1962. Flume studies of the transport of sediment in estuarial shoaling
processes. Final Report, Hydraulic Engineering Laboratory and Sanitary Engineering
Research Laboratory, University of California, Berkley.
Lambe T. W. and Whitman R. V., 1969. Soil mechanics, Wiley, New York.
Mehta, A. J., Lee, S. C., Vinzon, S. B., and Abreu, M. G., 1994. Analyses of some
sedimentary properties and erodibility characteristics of bottom sediments from the
Rodman Reservoir, Florida. Report UFL/COEL/MP94/03, Coastal and Oceanographic
Engineering Department, University of Florida, Gainesville.
Mehta, A. J., and Li, Y., 2001. Principles and process modeling of fine grained sediment
transport. OCP 6297 Lectures, University of Florida, Gainesville.
Mehta, A. J., and Parchure, T. M., 2000. Surface erosion of finegrained sediment
revisited. In: Muddy Coast Dynamics and Resource Management, B. W. Flemming et al.
eds., Elsevier, Amsterdam, 5574.
Nagid, E. J., 1999. A limnological assessment of Lake Newnan, Florida, August 1997
July 1998. M S. thesis, University of Florida, Gainesville.
Parchure, T. M., and Sturdivant, C. N., 1997. Development of a portable innovative
contaminated sediment dredge. Final Report CPARCHL972, Construction Productivity
Research Program, U.S. Army Engineer Research and Development Center, Vicksburg,
MS.
Rodriguez, H. N., Jiang, J., and Mehta, A. J., 1997. Determination of selected
sedimentary properties and erodibility of bottom sediments from the Lower Kissimmee
River and Taylor CreekNubbin Slough Basins, Florida. Report UFL/COEL97/09,
Coastal and Oceanographic Engineering Department, University of Florida, Gainesville.
Tsai, C. H., and Lick, W., 1986. A portable device for measuring sediment resuspension.
Journal of Great Lakes Research, 12 (4) 314321.
Wanielista, M. P., 1978. Stormwater Management. Ann Arbor Science, Ann Arbor, MI.
69
Wetzel, R. G., and Likens, G. E., 2000. Limnological analyses. SpringerVerlag, New
York.
Young, I. R., 1997. The growth rate of finite depth windgenerated waves. Coastal
Engineering, 23, 181195.
Young, I. R., and Verhagen, L. A., 1996. The growth of fetch limited waves of finite
depth. Part 1. Total energy and peak frequency. Coastal Engineering, 29, 4777.
BIOGRAPHICAL SKETCH
Jason Eric Gowland was born in Winter Garden, Florida, husband to Monica Erin
Henry, the son of Jan and Deborah Gowland and brother to Jessica Gowland. The author
attended Vero Beach High School and was a member of two undefeated Class 6A
football teams. As a member of the Vero Beach High School track team, he earned a
spot as All Cape Coast Conference for pole vaulting. Enrolling at the University of
Central Florida as a Lead Scholar and Florida Academic Scholar he helped in Central
Florida's transition to become a Division A program for two years then transferred to the
University of Florida to pursue a degree in civil engineering. After graduating with a
Bachelor of Science in Civil Engineering from the University of Florida, the author
proceeded to continue his education in the Department of Civil and Coastal Engineering
for a master's degree. Upon completion of a master's degree the author plans to practice
as a professional in his field in hopes to admire the world's natural beauty that he has
spent a lifetime learning to understand and build upon.
