EFFECT OF ORGANIC MATTER ON WAVE-

INDUCED RESUSPENSION OF FINE SEDIMENT

Newnans Lake

Fine sediment aggregate constituents

Clay mineral

Non-clay mineral

Wood fragmentWorm tube

Biopolymer

Pore water

Diatom

N

0 100 kmGulf of Mexico

AtlanticOcean

Cedar/Ortega Rivers

Rodman Reservoir

Newnans Lake

Lower Kissimmee River Basin

Lake Okeechobee

Lake Bonnet

Loxahatchee River

Florida

Extended Agricultural Area

Variation of wet bulk density with organic content

Organic content, OC (%)

Bu

lk d

ensi

ty,

(kg

m-

3)

100 20 30 40 50 60 70 80 901000

1500

2000

2500

= 1136exp(-0.32OC)-0.9OC+1110

Rodman Reservoir (Mehta et al., 1994)Lower Kissimmee River (Rodriguez et al., 1997)Loxahatchee River (Ganju, 2001)Cedar/Ortega River (Mehta et al., 2000; Gowland, 2002a)Lake Bonnet (Gowland, 2001)Newnans Lake (Gowland, 2002b)

Variation of dry density with organic

content; data from six sites

Organic content, OC (%)

Dry

den

sity

, D (

kg m

-

3)

100 20 30 40 50 60 70 80 90

500

1000

1500

2000

0

Rodman ReservoirLower Kissimmee RiverLoxahatchee RiverCedar/Ortega RiverLake BonnetNewnans Lake

D = 1900exp(-0.156OC) + 80

Variation of free settling velocity with organic content

Organic content, OC (%)

Sett

ling

vel

ocit

y, w

0 (m

/s)

10 20 30 40 50 60 70 80 90010-7

10-6

10-5

10-4

Wind Induced Wave Sediment Re-suspension

NEWNANS LAKE

Shannon-Brezonik Trophic State Index (TSI): 

T = turbidity (JTU), CD = conductivity [(μΩ)-1/cm =μS/cm], TN = total organic nitrogen (mg/l), TP = total phosphate (mg/l), PP = primary productivity (mg-C/m2-hr), CL = chlorophyll-a (mg/m3) cation ratio CR = [Ca++]+[Mg++]/[Na+]+[K+].  TSI: 0-3 oligotrophic, 3-7 mesotrophic, 7-10 eutrophic, 10 hypereutrophic Newnans Lake = 15.3 

0.18 0.008 1.1 4.2 0.01 0.044 0.39 0.26TSI T CD TN TP PP CL CR

Newnans Lake zones based on bathymetry. Suspended sediment concentration was

measured at Sites A and B

Outer open water area

Inner open water area

Exposed area

1 km N

-1.5 m

-0.5 m

-0.3 m

0.0 m

Site B

Site A

Stage variation in Newnans Lake, 1995-2001

Date (y)

Stag

e (m

NG

VD

)

February 1998El Niño high

Typical 1995-98 level

August 2001 low

1.1 m

1995 1996 1997 1998 1999 2000 2001

19

20

21

Wind Record Maximum 2-minute Maximum 5-second

Mean Speed Direction Speed Direction Speed Direction(m/s) (degrees) (m/s) (degrees) (m/s) (degrees)

Jan 3.1 310 16.1 250 19.2 270Feb 3.4 270 14.8 240 18.3 240Mar 3.6 270 17.9 250 23.2 320Apr 3.3 270 13.9 330 17.9 330May 3.1 250 13.4 250 16.5 250Jun 2.8 250 20.1 240 23.2 220Jul 2.5 270 20.1 290 28.6 290

Aug 2.4 240 13.4 120 19.2 120Sep 2.6 90 13.0 120 17.4 160Oct 2.9 40 10.7 40 13.4 20Nov 2.8 40 11.6 320 14.8 320Dec 2.7 300 13.0 270 15.2 280

Yearly 3.0 270 20.1 240 28.6 290

Wind speed(m/s)

Wave amplitude, a

(m)

Wave period, T(s)

Peak wave-induced velocity,

um(m/s)

8 0.10 1.85 0.11

9 0.10 1.90 0.12

10 0.11 2.00 0.14

Bulk density, (kg m-3)

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

Dep

th b

elow

bed

sur

face

(m

)

1030 1040 1050 1060 1070 1080

10 y

20 y30 y

40 y50 y

60 y70 y

80 y

Initial Densityprofile

Brenner and Whitmore (1998)

Gowland (2002)

Bed surface

Bed density variation due to consolidation and data from Newnans Lake

Erosion flux versus bed shear stress with lines of constant OC; data from Newnans

Lake

Shear stress, b (Pa)

0

0.1

0.2

0.3

0 0.05 0.1 0.15 0.2 0.25 0.3

OC (%) 60 50 40 30 20 10

Ero

sion

flu

x,

(kg

m-2

s-1)

Settling velocity variation with

concentration for Newnans Lake sediment

Concentration, c (kg m-3)

Sett

ling

vel

ocit

y, w

s (m

s-1)

10-1

10-2

10-3

10-4

10-5

10-6

10-2 10-1 100 101 102

OC = 10%; b = 1.6

20%; 2.4

30%; 3.7

40%; 5.8

50%; 7.9 60%; 10

10%≤OC≤30%30%<OC≤60%

Concentration Profiles at Sites A in Newnans Lake

0.05

0.10

0.15

0.20

0.25

0.000 0.5 1.0 1.5

Ele

vati

on, z

(m

)

Lutocline

30 min

60 min

90 min

Data

Concentration, c (kg m-3)

Concentration profiles at Sites B in

Newnans Lake

Lutocline

0.05

0.10

0.15

0.20

0.000 1 2 3

Ele

vati

on, z

(m

)

Concentration, c (kg m-3)

30 min60 min90 min

Data

4

120 min

0.25

0.30

Wind-induced re-suspension simulation

in Newnans Lake

0200 4000

2

1

3

100 300Time, t (min)

Con

cen

trat

ion

, cm (

kg m

-3)

8 m s-1

9 m s-1

7 m s-1

Accelerometer

Pore pressure sensor