G. M. Cartwright, C. T. Friedrichs, and L. P. Sanford

IN SITU CHARACTERIZATION OF ESTUARINE SUSPENDED SEDIMENT

IN THE PRESENCE OF MUDDY FLOCS AND PELLETS

Management Implications of Fine Sediment Transport

• Transport of pollutants

• Sediment supply to marshes

• Light limitation in SAV beds

Mud Flocculants FecalPellets

SandD~ 5 – 10 µmWs< to <<0.1 mm/sec

D ~ O(λ)Microflocs < 160 µmMacroflocs >160 µmWs

D~ 10s – 100s µm Ws

Ws ~0.1–10 mm/s

D= 63 – 500 µmWs = 2.3–60 mm/s

Ws α D λ Turbulence

λλ% Organic

Settling Velocity

Fugate and Friedrichs (2003)

Sherwood (2007)Anderson (2001), Sanford et al (2005) Taghon et al (1984), Wheatcroft et al (2005)

STUDY SITE Claybank area on York River Chesapeake Bay, VA

Micro tidal ( 0.7 to 1 meter)Secondary Channel ~ 5 meter depth

Seabed > 75% mud

LISSTADV

CTDS2E

Real-time Communication

Cables

RIPScam

15 18 21 00 03 06 09 12 15 18 210

50

100

150

200

Conc

entra

tion

from

ADV

(mg/

L)

15 18 21 00 03 06 09 12 15 180

200

400

600

800

Date (July 28, 2009 (17:00 EST) - July 29, 2009 (18:00 EST) )

Volu

me

Conc

entra

tion

(ul/L

)

LISST Total volume concLISST Volume Conc > 60 micronsRIPScam Volume Conc/10

B

A

15 18 21 00 03 06 09 12 15 18 210

20

40

60

Salin

ity (P

SU)

Velo

city

(cm

/s)

VelocitySalinity

18 21 00 03 06 09 12 15 180

0.1

0.2

0.3

0.4

Date (July 28, 2009 (17:00 EST) - July 29, 2009 (18:00 EST) )

Stre

ss (P

asca

ls)

EBB FLOOD C

D

FLOODEBB A

B

C

D

slack EBB slack Flood slack Ebb slack Flood slack

0 0.5 1 1.5 2 2.5 3 3.5 4 4.50

20

40

60

80

100LISST D16 = 21 µmLISST D50 = 85 µmLISST D84 = 218 µmLISST Peak = 104 µm RIPScam D16 = 117 µmRIPScam D50 = 197 µmRIPScam Peak = 201 µm

LISST time = 28-Jul-2009 19:55:12 EST Camera time = 100 GMT

(Log10) Particle Size (µm)

Volu

me

Conc

entra

tion

(µl/L

)

LISST 100XRIPSCAM./10

Slack after Ebb

Increasing Stress toward Ebb

20 40 60 80 100 120 140 1600

5

10

15

< C > (mg/L)

< C'

w' >

(m

g/L)

(cm

/sec

)

y = 0.0924*x - 3.41

15 18 21 00 03 06 09 12 15 18 210

1

2

3

Date (July 28, 2009 (17:00 EST) - July 29, 2009 (18:00 EST) )

Fall V

eloc

ity (m

m/s

ec)

ratio calc methodslope calc method

A

B15 18 21 00 03 06 09 12 15 18

0

10

20

30

40

50

60

Date (July 28, 2009 (17:00 EST) - July 29, 2009 (18:00 EST) )

Vol

ume

Con

c (u

l/L)

87.9 µm280 µm

15 18 21 00 03 06 09 12 15 180

20

40

60

Date (July 28, 2009 (17:00 EST) - July 29, 2009 (18:00 EST) )

Volu

me

Conc

(ul/L

)

87.9 µm280 µm

C

slack EBB slack Flood slack Ebb slack Flood slack

• The LISST can be used to identify different suspended sediment populations• Peak grainsize or D84 during maximum stress is the dominant

resilient grainsize • Peak grainsize or D50 during slack periods is the dominant flocculent size

(larger will occur but at levels that are averaged out during burst averaging)

• D50 during maximum stress represents the dominant minimum flocculent size

• Calibrations, with the Total Suspended Solids broken into resilient and non resilient portions, needs to be done to convert volume concentration to mass concentration so the density of the dominant particles can be determined

• Time averaged burst statistics can be used to determine the effective fall velocity of the sediment in suspension

Once the mass concentration of the dominant particles are identified further work can be done to calculate effective fall velocity of these size classes.

Conclusions and Future Work