Evaluating the Capabilities of the Second
Generation PICS Settling Column Floc
Camera in a Muddy Tidal Estuary, York
River, Virginia, USA
Grace M. Cartwright, S. Jarrell Smith ,
Carl T. Friedrichs, and Kelsey A. Fall
US Army Corps of Engineers
Engineer Research and Development Center
Waterways Experiment Station
Vicksburg, MS
Motivation
<w’C’> (mm/s)(mg/L)
An Example Set of Bursts
Independent verification
Acoustic Doppler Velocimeter (ADV) Method
Bulk Settling Velocity (Ws) of suspended sediment
< C > -Cbackground
Ws =
< w'C ' >
Concentration (mg/L)
<C>
<w’C’>
Cbackground
is burst averaged concentration from calibrated ADV backscatter
is burst averaged Turbulent Reynold’s Flux
is the lowest concentration observed during the study period
Bulk Settling Velocities for MUDBED Tripod Deployments
ADV
Bulk
(Dickhudt et al, 2009; Cartwright et al, 2011; Fugate and Friedrichs, 2002)
PICS – Particle Imaging Camera System
Side View
Laser source
settling column
camera
1mm light sheet
Laser source
10 x 14 mm
Current
Top View
(Smith- INTERCOH 2012)
Example PICS Video Sequence (1 m depth)
10/06/2012 14:06:00 (frames 001-080) collected at 8 frames/sec
Fluid Velocity hinders sediment settling
PTV/PIV method to remove fluid velocity effects
PTV: Particle Tracking Velocity
individual particles ≥ 30 μm (3 pixels)
Particles are tracked
from frame to frame
A Thread is a
particle tracked for
at least 5 frames
PIV: Particle Image Velocity
groups of particles ≤20 μm (2 pixels)
Fluid velocities
estimated for each
cell from one frame
to the next
(Smith and Friedrichs, 2012;Van Leussen and Cornelisse, 1993; Fennessy et al, 1994)
Peak velocity used
for each cell
PTV/PIV method to estimate Ws, ρs and mass
(
ws = f r , m , rs , D
)
Particle Density
rs = f ( r , m ,ws , D)
Calculated as the net of the Particle and fluid velocity vectors
Averaged for all the frames in the track
Split into 3 classes:
1. primary
2. bed aggregate
3. flocculants
(Smith and Friedrichs, 2012; Oseen, 1927; Schiller and Naumann, 1933; Soulsby, 1997,)
Density
> 1800 kg/m3
1150-1800 kg/m3
< 1150 kg/m3
Study Site
NSF MUltiDisiplinary Benthic
Exchange Dynamics
Clay Bank area on York River
Chesapeake Bay, VA
Micro tidal ( 0.7 to 1 meter)
Secondary Channel
~ 5 meter depth
Seabed During Neap
>75% mud
~10% Organics
Sand D50 ~100 µm
up to 30% Pellets (~60-90 μm)
Kraatz, (2010, personal comm), Rodriguez-Calderon (2010)
October 6, 2012
Study Period
2 days before Neap
Slack-Slack bracket Flood (~6 hrs)
Every Hour
Water column “cast”
Bottom samples
5-6 samples (~1/m)
every 10-15 min
Each Sample
PICS
Turbulence dissipate 15-30 sec
Collect 30 sec burst @ 8 frames/sec
Collect second burst ~1 min later
ADV
2 minute burst @ 10 Hz
LISST
2 minute burst@ 2/3 Hz
CTD
2 minute burst@ 1 Hz
Pump Samples
1 sample right away
2nd sample mid CTD burst
(Picture from Smith and Friedrichs, 2010)
Two Grab Samples of Bottom Sediment
20121006084703.seq
08:47:03
Example PICS Results
Depth
5.8 m
Number particles 400
d50,p= 54.7 μm
d50,m = 68.1 μm
ws50,p = 0.172 mm\sec
ws50,m = 0.239 mm\sec
By particle count
Flocs:
75.5 %
Bed Agg:
24.5 %
Primary:
0.0 %
3 classes:
1. primary
2. bed aggregate
3. flocculants
Density
> 1800 kg/m3
1150-1800 kg/m3
< 1150 kg/m3
By mass
Flocs:
Bed Agg:
Primary:
78.0 %
22.0 %
0.0 %
Preliminary Results
Concentrating on bottom samples only
Water Velocity from ADV
% SPM > 60 μm
% >60 μm (by weight) from Pump Sample SPM
50 percentile grain-size from PICS
For each sample -- 30-sec bursts approximately 1 minute apart
50 percentile settling velocity from PICS
For each sample -- 30-sec bursts approximately 1 minute apart
Bulk settling velocity from PICS and ADV
For each PICS sample -- 30-sec bursts approximately 1 minute apart
Future Work
• Work up LISST data
• Process the bottom sediment
• Repeat Study for Spring Tide
• PICS lab experiment to find
Ws for isolated fecal pellets
(Figure from Smith and Friedrichs, 2010)