Particle Concentrations and Size Distributions: Implications for Contaminant Transport in NYNJ Harbo

1
Particle Concentrations and Size Distributions
Implications for Contaminant Transport in NY-NJ
Harbor New York Bight
Richard Styles1, Robert Chant1, Scott Glenn1,
Kelly Rankin2, Anne Pence2, Patrick Burke2,
Thomas Herrington2, Michael Bruno2, Clinton
Haldeman III1
1Institute of Marine and Coastal Sciences,
Rutgers University, New Brunswick, NJ 08901
2Stevens Institute of Technology, Hoboken, NJ
07030
Introduction
Overview of Hydrodynamic and Sediment
Characteristics
Correlation Statistics Dependence on Particle
Size
Particle Size Distributions
A major goal of the New Jersey component of the
Contaminant Assessment and Reduction Program
(CARP) in the New York-New Jersey Harbor is to
identify the transport pathways of contaminated
sediments. Very little historical data is
available to assess the physical characteristics
of the estuary system. As a result, the initial
phase of this project has been to acquire
detailed measurements of the estuarine
circulation patterns, the density structure, and
the distribution of suspended particulate matter.
These measurements are necessary to develop a
dynamical framework in which to form a clearer
picture of the physical processes controlling the
distribution and transport of suspended material
within the New York-New Jersey Harbor. This
poster presents preliminary results of some of
the physical parameters measured as part of the
CARP study. The focus here is to provide an
overview of the suspended sediment distributions
at the three major monitoring sites and to define
the role played by the driving tidal currents in
the resuspension and transport of estuarine
particulates. An appealing aspect of this
project is the extensive utilization of a
relatively new instrument that can measure
particle size distribution as well as
concentration. This ability to separate
concentration into discrete size classes reveals
a rich and complex internal structure.
Perth Amboy (PA) Mooring
This figure shows the correlation between the
along channel current and the concentration as a
function of particle size. The results indicate
that concentrations measured at PA have the
highest correlation with the flow. This can be
understood by noting that increases in the
near-bottom current speed are accompanied by
increases in the bottom shear stress. Once the
stress exceeds the minimum required to initiate
sediment motion at the bed, particles will start
to become entrained by the flow. As the stress
(flow speed) increases more particles become
entrained and a sediment suspension forms near
the bed. However, the correlation between flow
speed and concentration is not uniform across
particle size classes. In addition, because
this analysis only relates increases in flow
speed to concentration, it provides no
directional information. The direction is
important because it can reveal any asymmetries
in particle load between flood and ebb tide. The
agreement decreases as you move up the estuary
further from the Raritan/NY bay.
The figure to the right presents the mean
concentration as a function of particle size for
the entire 5-week deployment. The largest
concentrations are associated with the largest
particles at all three sites. Concentrations at
the two southern sites have a bimodal
distribution, in which localized concentration
peaks occur at about 190 and 140 microns for PA
and KVK, respectively. Concentrations for these
size classes at NB are relatively low. These
secondary peaks were also shown to have the
highest correlations with the current speed. At
NB and PA the bottom is comprised of mud. AT KVK
the bottom is primarily bed rock. The relatively
low concentration of larger particles at KVK is
probably due to the lack of a local supply of bed
sediments.
These three figures present an overview of the
hydrodynamic and suspended sediment conditions
during mid March, 2001. Each figure denotes a
specific location (see the regional map of the
New York-New Jersey Harbor) and contains 3 plots
describing the particle concentration, current,
salinity and water elevation measurements
obtained from the moorings. The time series
represents about one-half of the total
observations during this deployment and is chosen
to include a spring-neap tidal cycle. The
current vector has been rotated into the along
channel component with positive values indicating
flood (landward flow). The negative values
correspond to ebb, or currents traveling seaward.
During the maximum spring tide, which lasts
from about day 66 until day 72, tidal current
amplitudes are increased. During the neap phase,
which starts near year day 74 and continues until
the end of the record, they are reduced. There
is also a modulation of the salinity with the
tidal cycle indicating that the system is
stratified. Concentrations at some size classes
vary with the tidal current speed particularly
during spring tide. The concentrations at PA are
maximum near 300 microns and have periodicities
that correspond with the tidal frequency. In
contrast, concentrations at KVK are maximum at
about 200 microns and are generally much lower.
At NB, concentrations near the maximum resolution
of the LISST dominate the signal and are much
greater than at the other two stations. There is
a weak modulation at about 250 microns that is
correlated with the tidal frequency, at least
during spring tide. Despite the fact that the
current magnitudes at all three locations are
similar, there are marked differences in the
particulate concentrations. Therefore,
established empirical results in which sediment
transport is proportional to flow speed do not
apply universally to this particular system.
However, concentrations that do correlate with
the flow speed are likely to have the greatest
transport. This is more fully explored in the
next few panels.
Flood
Ebb
Sediment Transport
NB1
Hudson River
Hackensack River
Manhattan
This figure shows an estimate of the sediment
transport (Q velocity x concentration)
integrated over ebb and flood tides. The ADP
current measurements were extrapolated to the
height of the LISST using techniques consistent
with boundary layer theory for open channel flow.
The solid lines denote flood tide and the dashed
lines denote ebb (absolute value) tide. At KVK
the net transport for particles smaller than
about 70 microns is down the estuary but for the
larger particles it is up the estuary. For the
other two sites the net transport is directed up
the estuary, especially at NB where it is nearly
an order of magnitude greater during flood for
most size classes. Sediment transport is a 3-D
process so that variability in the vertical and
cross-channel coordinates is not taken into
account in these calculations. Therefore, it is
not possible to make quantitative statements
regarding the sediment budget in Newark Bay.
However, the information is useful to modelers by
providing valuable calibration information.
Passaic River
New Jersey
Newark Bay
KVK
Brooklyn
Arthur Kill
Kill Van Kull
Staten Island
New York
Concentration as a function of along channel
velocity
Raritan River
ebb
Kill van Kull (KVK) Mooring
flood
Bight
Sandy Hook
Based on the above correlation results, it is
possible to examine more fully the relationship
between suspended particle concentration and
tidal flow velocity. The three figures below
show concentration associated with the
correlation peaks as a function of the along
channel velocity.
Raritan Bay
PA
Mooring
Monitoring efforts were established in three
waterways Newark Bay, The Arthur Kill and the
Kill van Kull. Moorings were placed at three
locations within this system and are noted on the
map. The northern most mooring is denoted as
NB1, the southern most mooring is denoted as PA
(Perth Amboy), and the central mooring is denoted
as KVK. Each mooring contained a small suite of
instruments to measure particle concentration,
turbidity, full water column currents, water
depth, salinity and temperature. All three
moorings were deployed from March 2nd until April
2nd, 2001 to cover a spring-neap tidal cycle.
The data from all instruments were synchronized
and averaged into 30-minute ensembles.
During both flood and ebb, concentrations at PA
generally increase with increasing current speed,
but a large variation about this trend is
obvious. In addition, even though maximum
currents are similar on flood and ebb,
concentrations are asymmetrical.
PA
Flood
Particle Surface Area Transport
A very important parameter in studying
contaminant transport by suspended solids is the
total particle surface area. Smaller particles
tend to have larger surface area in a given
volume due to their much greater abundance. By
taking the concentration and multiplying it by
the particle size a crude estimate of the
particle area per unit volume can be computed.
After applying a constant correction factor to
transform from liters to cubic microns, the
results of total surface area transport on flood
and ebb (absolute value) is shown to the right.
Total surface area at the two southern most sites
are concentrated in the smallest size classes and
are greater on flood than ebb. In contrast, the
largest particles in NB have the greatest surface
area. The differences on flood versus ebb also
suggest landward transport of fines in this
estuary system for NB and PA. AT KVK, however,
transport of fine material is directed down
estuary.
Instrumentation
Ebb
flood
ebb
Ebb
Flood
Bottom Mooring
At KVK, concentration associated with the
strongest correlated size class are generally
lower then at PA. Maximum current speeds however
are similar. There is also less of a correlation
between concentration and flow speed, yet the
highest concentrations are associated with flood
tide.
KVK
Newark Bay (NB) Mooring
Particle size distribution and concentration were
measured using a LISST-100 (Laser In Situ
Scattering and Transmissometry). The LISST
measures in water particle concentration and size
distribution in 32 log-spaced bins ranging from
2.5 to 500 microns. The LISSTs were mounted on
the moorings approximately 0.5 m above the bottom
and sampled every 10 minutes.

• Summary
• Marked differences exist in the sediment size
  distributions and transport characteristics at
  the three sampling locations.
• Tidal frequency fluctuations in the suspended
  load is seen at all sites for at least some
  particle sizes.
• The distribution of total concentration by
  particle size class is an important feature at
  all sites.
• For sites (PA) that show a particularly strong
  tidal signal in the concentration, the net
  transport is directed up estuary.
• At KVK the net particle volume and area
  transport during this time period are directed
  down estuary.
• Emerging Trends
• Despite the fact that maximum tidal current
  speeds are similar at all three locations, mass
  transport characteristics show significant
  differences. Models that take into account only
  flow velocity to compute sediment transport rates
  will be inadequate in this system. Other
  processes, in particular flow stratification,
  sediment flocculation, non-uniform bed sediment
  distributions, and topography have a strong
  influence on the transport of sediments and will
  have to be addressed in order to develop a
  realistic dynamical framework of this complex
  estuarine system.

Ebb
Flood
Flood
LISST
NB
NB showed the weakest correlation between
concentration and flow speed. This is reflected
in the scatter plot to the right in which
concentrations are much lower than at the other
two sites and are less sensitive to variations in
flow speed.
Ebb
Currents were measured using an acoustic Doppler
profiler (ADP). The ADP measures current speed
and direction in discrete vertical cells
throughout the water column. The instrument
produces current profiles in one-half meter bins
from approximately 1 m off the bottom to the
surface. The ADP was placed in the center of the
mooring at the highest point to minimize flow
interference due to the mooring structure.
ADP
Acknowledgments Support for this research is
provided by the New Jersey Department of
Environmental Protection. We would like to thank
the numerous individuals who have helped in the
field program, with special thanks to Elizabeth
Creed, Brian Fullerton and Eli Hunter.
Ebb
Flood