Evaluating the Capabilities of the Second Generation PICS Settling Column Floc Camera in a Muddy Tidal Estuary, York River, Virginia, USA

Evaluating the Capabilities of the Second Generation PICS Settling Column Floc Camera in a Muddy Tidal Estuary, York River, Virginia, USAGrace M. Cartwright, S. Jarrell Smith , Carl T. Friedrichs, and Kelsey A. Fall

US Army Corps of EngineersEngineer Research and Development CenterWaterways Experiment StationVicksburg, MSIndependent verification

Acoustic Doppler Velocimeter (ADV) Method

Bulk Settling Velocity (Ws) of suspended sediment

is burst averaged concentration from calibrated ADV backscatter is burst averaged Turbulent Reynolds Flux Cbackground is the lowest concentration observed during the study period

Motivation

ADV

Concentration (mg/L)Bulk

(Dickhudt et al, 2009; Cartwright et al, 2011; Fugate and Friedrichs, 2002)An Example Set of Bursts (mm/s)(mg/L)

Bulk Settling Velocities for MUDBED Tripod DeploymentsThe motivation for this study is to find a method to independently verify the method to estimate the bulk settling velocity of suspended sediment using downward looking ADVs deployed on 1 meter tripods (seen in this picture) with the sensor height 55 cm above the bottom of the tripod. As seen in this plot, if you plot the corrected concentration of each record of a burst (x-axis) against the corresponding turbulent Reynolds flux (y-axis) the slope of the correlation will be the bulks settling velocity of the sediment in suspension during that burst. The concentration is found by calibrating the burst average backscatter with pump sample suspended solids concentrations (collected during collocated calibration cruises) and then corrected by subtracting the lowest concentration found during the deployment period. This is done because it is assumed that the sediment in suspension at this concentration is too fine to settle.2PICS Particle Imaging Camera SystemcameraLaser sourcesettling columnLaser sourceSide ViewTop ViewCurrent

1mm light sheet10 x 14 mm(Smith- INTERCOH 2012)33General overview of camera system.Left image: Point out settling column components: column, camera housing, pneumatically actuated ball valves, pneumatic actuator for rotation. Point out Side and Top view and direction of currents.Animated demonstration of operation: Sample is introduced to column with currents. Ball valves are closed, followed by rotation to vertical Column is now vertical. Wait for turbulence in column to subside (10-30 sec). Start image acquisition. At this point acquisition is complete. Valves are opened and column returned to horizontal orientation Column repositioned in water column and ready for next sample.

Upper center image. PICS mounted to side of profiling frame. Point out: 1) air lines, 2) pneumatic-actuated ball valves, 3) pneumatic rotation, 4) camera housing (inside the frame)

Upper right image: photographic arrangement. Cross-section of settling column, Acrylic viewing window for camera, Lasers produces 1mm wide light sheet. Focal plane of camera is approx 1 mm deep.

Bottom right image: Image Acquisition software permits real-time assessment of conditions in the settling column, camera control, and image logging.

Example PICS Video Sequence (1 m depth)

Fluid Velocity hinders sediment settling10/06/2012 14:06:00 (frames 001-080) collected at 8 frames/secThis video is from a sample taken higher up in the water column to show the exaggerated influence of the fluid velocity due to the boat motion. You can see how this movement hinders the settling of the particles and even reverses the direction of the smaller particles. If the movie doesnt work I will just say that if the movie was working you would see.. 4PTV/PIV method to remove fluid velocity effects

PTV: Particle Tracking Velocityindividual particles 30 m (3 pixels) PIV: Particle Image Velocitygroups of particles 20 m (2 pixels)Fluid velocities estimated for each cell from one frame to the nextPeak velocity used for each cell

Particles are tracked from frame to frameA Thread is a particle tracked for at least 5 frames(Smith and Friedrichs, 2012;Van Leussen and Cornelisse, 1993; Fennessy et al, 1994)PTV/PIV method to estimate Ws, s and mass

(Smith and Friedrichs, 2012; Oseen, 1927; Schiller and Naumann, 1933; Soulsby, 1997,)

Calculated as the net of the Particle and fluid velocity vectorsAveraged for all the frames in the trackSplit into 3 classes: Density 1. primary > 1800 kg/m32. bed aggregate 1150-1800 kg/m33. flocculants < 1150 kg/m3Particle DensityDensity calculated by rearranging Soulsbys (1997) empirical settling velocity expression

6Study Site

NSF MUltiDisiplinary Benthic Exchange Dynamics

Clay Bank area on York River Chesapeake Bay, VAMicro tidal ( 0.7 to 1 meter)Secondary Channel ~ 5 meter depth

Seabed During Neap>75% mud ~10% OrganicsSand D50 ~100 m up to 30% Pellets (~60-90 m)

Kraatz, (2010, personal comm), Rodriguez-Calderon (2010)

The study is part of the much larger NSF MUDBED project. The site is located on the York River, a microtidal estuary that flow down into the Chesapeake Bay. The location is in Claybank, a straight stretch of the of the river, in shallower secondary channel where the depths are nominally 5 meters. If you look at the inserted xrayat Neap tide, Lindsey Kraatz found the seabed to be more physically laminated and harder to erode. The seabed is typically comprised of greater than 75% mud, with up to 10% of that mud being comprised of organic matter. Rodriguez found that the mud fraction in the York River seasonally consisted of up to 30% fecal pellets 7

Study PeriodOctober 6, 2012

2 days before NeapSlack-Slack bracket Flood (~6 hrs) Each SamplePICS Turbulence dissipate 15-30 sec Collect 30 sec burst @ 8 frames/sec Collect second burst ~1 min laterADV 2 minute burst @ 10 HzLISST 2 minute burst@ 2/3 HzCTD 2 minute burst@ 1 HzPump Samples 1 sample right away 2nd sample mid CTD burst

Every Hour

Water column cast 5-6 samples (~1/m) Bottom samples every 10-15 min (Picture from Smith and Friedrichs, 2010)Two Grab Samples of Bottom Sediment

Depth 5.8 mNumber particles 400

d50,p= 54.7 md50,m = 68.1 m

ws50,p = 0.172 mm\secws50,m = 0.239 mm\sec

By particle count Flocs: 75.5 %Bed Agg: 24.5 % Primary: 0.0 %

By mass Flocs: 78.0 %Bed Agg: 22.0 % Primary: 0.0 %

20121006084703.seq08:47:03 Example PICS Results 3 classes: Density 1. primary > 1800 kg/m32. bed aggregate 1150-1800 kg/m33. flocculants < 1150 kg/m3Preliminary Results

Concentrating on bottom samples only

Water Velocity from ADV

% >60 m (by weight) from Pump Sample SPM% SPM > 60 m

50 percentile grain-size from PICSFor each sample -- 30-sec bursts approximately 1 minute apart

50 percentile settling velocity from PICSFor each sample -- 30-sec bursts approximately 1 minute apart

Bulk settling velocity from PICS and ADVFor each PICS sample -- 30-sec bursts approximately 1 minute apartFuture Work

(Figure from Smith and Friedrichs, 2010)Work up LISST data

Process the bottom sediment

Repeat Study for Spring Tide

PICS lab experiment to find Ws for isolated fecal pellets