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Controls of Suspended Sediment Particle Size in the York River Estuary
A thesis submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Geology
from the College of William and Mary in Virginia,
by
Benjamin D. Lewis
Williamsburg, Virginia May, 2009
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Table of Contents
Abstract………………………………………………………………………………...3
Introduction……………………………………………………………………………..4
Background Information………………………………………………………………..6
Methodology…………………………………………………………………………....9
Results………………………………………………………………………………….11
Expected………………………………………………………………………..11
General………………………………………………………………………….12
Discussion……………………………………………………………………………....17
Conclusions……………………………………………………………………………..20
Acknowledgments…………………………………………………………………...….21
References Cited………………………………………………………………………..22
Figures………………………………………………………………………………24-35
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Abstract
Until recently, observations of suspended sediment particle size have been a
difficult prospect. Optical instruments now allow suspended sediment sizes to be
observed in-situ, without disturbing the delicate flocs. In this study, suspended sediment
particle size data were gathered at two sites along the York River estuary. The
Gloucester Point site is characterized by higher biologic activity while the Clay Bank site
is characterized by higher physical activity and intense sediment transport. It was found
that as water velocity and stress along the bed increased, suspended sediment particle size
decreased. This relationship was most prominent in the larger particle size classes and at
the physically dominated Clay Bank site. The smallest size particles seemed to have little
correlation with water velocity and stress, suggesting they are either much more cohesive
than the larger particles or are individual grains. Water temperature had no noticeable
effect on particle size, suggesting that it may not be an appropriate proxy for organic
activity or that increased organic activity may not lead to larger observed particles in the
York River estuary.
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Introduction
Though many of the equations for suspended sediment transport are well known,
many of their inputs and variables are not well defined (Lynch et al, 1994; Hill et al,
1998). This is due in part to the difficulty of analyzing suspended sediment. Water
samples can be gathered and analyzed but doing so disturbs the natural turbulence the
sediment is exposed to and thus may destroy some of the aggregates present in situ. The
LISST (Laser In-Situ Scattering and Transmissometry) device uses laser diffraction to
obtain particle size distributions and volume concentrations in-situ without disturbing any
of the natural variables present. Other instruments such as optical backscatterance
sensors require potentially imprecise calibrations which may skew measured data
(Ludwig and Hanes, 1990; Downing and Beach 1989).
The York River extends southeastward across the Virginia coastal plain into the
Chesapeake Bay and forms a partially mixed estuary. The upper York estuary is
dominated by physical controls, such that current velocity, turbulence and sediment
concentrations increase with distance up the estuary (Schaffner et al. 2001). These
physical controls which dominate the upper estuary are not as prominent in the lower
estuary which is more strongly influenced by biological processes (Figure 1).
The goal of this research was to analyze data gathered from the LISST
instruments which have been and currently are being deployed on tripods located in two
parts of the York River estuary. One tripod is located at a site called Clay Bank located
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in middle to upper portion of the York where physical processes often dominate. The
other tripod is in the lower estuary adjacent to the Virginia Institute of Marine Science
(VIMS) at Gloucester Point where physical processes are less dominant. The tripods are
deployed for periods of one to two months at their respective sites, during which time the
LISST and other instruments gather time data directly from the lower water column.
After a period of one to two months, the tripods are retrieved from the water and taken
back to VIMS where the instruments are removed, cleaned and the data in them are
extracted for analysis.
The process of leaving tripods in the water column for a long period of time
allows for data to be gathered under the influence of not only the daily tidal cycle, but the
monthly spring and neap tidal cycles also. Since the tripods are deployed throughout
much of the year, the data sets can be compared based on seasonal changes as well. In
addition, permanent tripod deployment allows for data from periodic storm events to be
gathered. Due to the randomness involved with large storm events, there are relatively
little data available for analysis from them; however, long term tripod deployments allow
data to be gathered from the water column during these large storm events.
The LISST is a device designed for in-situ particle size determination introduced
by Sequoia Scientific Inc. (Pottsmith and Bhogal, 1995). Using the principles of laser
diffraction, the LISST can measure particle size spectra between 1.25 and 250 microns.
Particle size spectra can be determined using video imaging as well, but video imaging
can only measure particle sizes on the scale of 100’s to 1000’s of microns (Eisma et al.
1996). The LISST emits a laser that travels through the water and is diffracted by
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suspended sediment particles. The LISST measures the angle at which the laser is
diffracted by the sediment and classifies it into one of thirty-two size categories.
One important assumption the LISST makes is that all measured particles are
perfect spheres. This makes the calculations involved in classifying sediment fairly
simple. Of course, most fine-silt and clay sized sediments are not perfectly spherical, but
a model that does not assume spherically shaped sediments would be more complicated
and is currently not available. So while the LISST data are all off by a little, it is as close
as is currently possible. Sequoia Scientific Inc is currently working to address this issue
and incorporate randomly shaped particles into their model for measuring sediment size
by laser diffraction (Agrawal et al., 2008).
Background Information
Understanding fine sediment transport is critical to better understanding coastal,
estuarine, and shallow marine environments. Fine sediment transport plays an important
role in coastal eutrophication (Boesch et al. 2001) and nutrient contamination (Lee and
Wiberg 2002). This is due to the tendency of nutrients, such as nitrogen and
phosphorous, to adsorb onto fine grained sediment. Eutrophication is an overabundance
of nutrients in an ecosystem, which leads to a very high level of primary production.
Eventual decay of high primary productivity can lead to water hypoxia, a lowering of
water quality, and can have many harmful effects on not only fish and other marine
species, but humans as well. As nutrient and waste run off from human societies are a
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primary contributor to eutrophication, a better understanding of fine grained sediment
transport will not only be of academic importance, but may also lead to a better
understanding of the process of eutrophication.
The physical and biological conditions found in the York River estuary and its
surrounding watershed are similar to many other estuaries and coastal environments
around the world. The York contains benthic biological activity and suspended particle
properties similar to many other locations around the globe. The strong gradient in the
roles of physically dominated processes and biologically dominated processes in the
York are in many other muddy shelves worldwide, including the East China Sea and
Amazon shelf (Aller 1998). Thus, results found from a detailed study of the York
River’s fine sediment transport processes can be applied to many other systems around
the United States and around the globe, not just the Chesapeake Bay.
Biology plays an important role in influencing sediment transport (Fugate and
Friedrichs 2002). All else being equal, suspended sediment in estuaries with a strong
biologic benthic community tends to be of larger size and of a lower concentration than
estuaries without a strong benthic community. This is due in part to the tendency of
organic matter to hasten flocculation of suspended sediment particles, increasing their
size in the process, and also biological pelletization. Pelletization is the process by which
estuarine organisms feed on sediment laden with organic matter and excrete said
sediment. This process compacts sediment and increases its cohesiveness which
contributes to lower sediment concentrations found in the water columns of biologically
controlled environments.
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The York River flows for 50 kilometers from the confluence of the Mattaponi and
Pamunkey rivers all the way into the Chesapeake Bay. The York’s watershed is bounded
to the north by the Rappahannock River watershed and to the south by the James River
watershed (Figure 2). The depth of the York River varies between 20 meters in the lower
estuary near Gloucester Point and 6 meters in the upper estuary near the Mattaponi and
Pamunkey. The mean width of the York River is 3.8 kilometers (Nichols et al., 1991).
The sea bed in the York can be differentiated based upon location along the York
River (Figure 3). The sea bed in the physically dominated upper estuary is characterized
by physical striations aligned with the flow of the river. This allows layering to be
preserved and for relatively little macrobenthic activity. The sea bed in the lower estuary
is characterized by an abundance of macrobenthos, and the sediment in it tends to be
reworked by the benthic organisms such that little physical layering is distinguishable
(Schaffner et al. 2001).
The York is a microtidal estuary (tidal range<2m) with a tidal range of
approximately 1 meter (Friedrichs, 2009) (Figure 4). Even though the tidal range is
relatively small, the tidal currents in the upper estuary are strong enough to cause
significant sediment suspension (Schaffner et al., 2001). The salinity of the York varies
between 6 parts per thousand (ppt) at the confluence of the Mattaponi and Pamunkey in
the upper estuary and 25 ppt in the lower estuary near Gloucester Point. For reference,
typical sea water has a salinity of 35 ppt. The water column in the lower estuary is also
more stratified than the upper estuary due to the fact that the upper estuary is shallower
and has stronger currents than the lower estuary, both of which tend to disrupt salinity
stratification.
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Most of the sediments in the York fall into the category of mud (<4 microns) and
over 80% of the material on the bed is classified as mud. The sediment concentrations in
the lower water column of the York are influenced heavily by tidal current strength. This
implies that the sediment concentrations at Clay Bank in the upper estuary should be on
average higher than the sediment concentrations at Gloucester Point in the lower estuary
because of Clay Bank’s higher tidal velocity and shallower depth. The York contains
two estuarine turbidity maximums (ETMs) (Figure 5). These are locations at which the
water is most turbid, or contains the most amount of suspended solids. The more turbid
water is, the muddier it will look. Both ETMs in the York are located in the mid to upper
estuary (Friedrichs 2009).
Methodology
The tripods from the Clay Bank and Gloucester Point sites have been deployed
intermittently for the past three years. Seven sets of usable LISST data have been
recovered during this time interval. Gloucester Point has data sets from three time
intervals, from 7/26/07 to 8/14/07 (Summer 07), from 12/05/07 to 4/05/07 (Winter 07),
and from 4/02/08 to 6/09/08 (Spring 08). Clay Bank has data sets from four time
intervals, from 8/31/07 to 10/26/07 (Fall 07), from 12/05/07 to 2/05/08 (Winter 07, 08),
from 2/08/08 to 2/10/08 (Winter 08), and from 6/23/08 to 8/22/08 (Summer 08).
However, much of the LISST data from the aforementioned sets are not usable due to
biological fouling that builds up on the instrument after a certain amount of time.
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The LISST requires a clear pathway so that its laser can be fully transmitted and
diffracted. If this pathway is blocked, the LISST will not record any data. In many of the
data sets after a period of about two weeks, the instrument becomes coated in barnacles
and other benthic epifauna such that laser transmission, and thus sediment size
classification is impossible. VIMS is currently working to solve this problem by setting
up a real time observation system that transmits data directly from the in-situ tripods to
VIMS. This would allow researchers to recognize when the LISST data are beginning to
go bad due to fouling, and react accordingly.
Once the time intervals over which the LISST data are corrupted have been
removed, then burst averages are taken to reduce “noise” associated with random data
fluctuations, cut down on the total amount of data, and for ease of analysis. The LISST
takes measurements in bursts of 100 1-Hz samples every 15 minutes. This process
reduces the amount of data needed to be analyzed by 100 times.
At this point the data from the LISST are synchronized with data gathered from
the Acoustic Doppler Velocimeter (ADV), an instrument deployed along with the LISST
on the tripods. The ADV emits sound waves that reflect off suspended sediment particles
and then detects the amount of reflected energy. The more energy returned the more
sediment there is in the water column. In addition, water velocity is determined by the
Doppler frequency shift of the reflected sound. This process allows another measurement
of sediment concentration and also water velocity. With the LISST and ADV
synchronized such that they provide information over the same time interval, suspended
sediment size and concentration gathered from the LISST can be compared with
suspended sediment concentration and water velocity gathered from the ADV.
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Synchronizing the LISST and ADV data allow for not only analysis on the size of
suspended sediment but also serves as quality control of sorts. Sediment concentration
measured optically from the LISST can be compared to sediment concentration measured
acoustically by the ADV for practical information on the nature of acoustic versus optical
measurements.
Results
Expected Results:
Knowing that the mid to-upper portion of the York River estuary is more
dominated by physical conditions and the lower portion of the estuary is more dominated
by biological conditions, it was expected that there would be clear correlations within the
data sets. It was expected that there would be a strong negative correlation between
current velocity and suspended sediment particle size at the Clay Bank site. As the
velocity of the current increases, the shear stress acting on suspended sediment clumps
increases, shearing them into smaller clumps. The correlation was expected to be weaker
in the biologically controlled portion of the estuary, and stronger in the physically
controlled mid to-upper portion of the estuary.
In addition, it was expected that there would be a strong positive correlation
between water temperature and particle size at the Gloucester Point site. As water
temperature increases, so does organic activity, and as such, more organic matter should
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favor flocculation, making particle aggregates larger. The correlation was expected to be
weaker in the physically dominated portion of the estuary and stronger in the biologically
controlled lower portion of the estuary. Along the same lines, it was expected that the
largest particles would be found in the summer months due to the higher temperatures
and more biologic activity, leading to larger sediment clumps. Conversely, it was
expected the smallest particles would be found in the winter months due to a reduction in
organic material necessary for flocculation.
General Results:
In general, there was not nearly as much data retrieved from the LISST devices as
was hoped. As mentioned above, this was largely due to biologic fouling that corrupted
the measured data. The tripod at the Clay Bank site for the August 2007 data set was
deployed from August 31st 2007 until October 26th 2007. During this time the LISST
gathered reliable data from August 31st 2007 until September 9th 2007. The tripod at the
Clay Bank site for the December 2007 data set was deployed from December 4th 2007
until February 5th 2008 and gathered reliable LISST data from December 4th 2007 until
December 22nd 2007. The tripod at the Clay Bank site for the June 2008 data gathered
was deployed from June 23rd 2008 until August 22nd 2008 and gathered reliable LISST
data from June 23rd 2008 until July 5th 2008.
The tripod at the Gloucester Point site for the July 2007 data set was deployed
from July 26th 2007 until August 14th 2007 and during this time gathered reliable LISST
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data from July 31st 2007 until August 2nd 2007. The tripod at the Gloucester Point site for
the December 2007 data set was deployed from December 5th 2007 until April 5th 2008
and gathered reliable LISST data from December 5th 2007 until December 11th 2007.
The tripod at the Gloucester Point site for the April 2008 data set was deployed from
April 2nd 2008 until June 9th 2008 and gathered reliable data from April 2nd 2008 until
April 4th 2008.
On average, the LISST gathered reliable information for a much longer period of
time at the Clay Bank site than it did at the Gloucester Point site. The high turbulence
and current velocity at the Clay Bank site may act as a shield for the LISST’s optical
sensors, preventing organic matter from accumulating on the sensitive lenses and
corrupting the data. There may also be less organic matter present in general near Clay
Bank. The biologically dominant Gloucester Point site was only able to gather reliable
data over a short time interval, perhaps because of more organic matter being present and
the lack of strong physical conditions allowing organic matter to quickly foul the
instrument.
After gathering the LISST data and synchronizing it with ADV data over the
same time interval, data from the LISST and ADV, including sediment size, sediment
concentration, water velocity, and water temperature were analyzed in order to establish
relationships on the controls of suspended sediment size.
Suspended sediment concentrations (measured in uL/L) were gathered by the
LISST and compared with water velocity measurements gathered by the ADV (Figure 6).
Suspended sediment concentrations at the Clay Bank site show a clear correlation with
water velocity. As water velocity in the York increases, so does the amount of sediment
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in suspension. This relationship stays consistent through all the data sets. The suspended
sediment concentration varies between approximately 100 and 400 uL/L, depending on
the water velocity. Suspended sediment concentrations at the Gloucester Point site show
no clear correlation with water velocity. As the water velocity increases, the
concentration varies little, if at all. This trend is consistent seasonally for the most part
and sediment concentration stays consistently near 100 uL/L.
Suspended sediment concentrations gathered by the LISST were also
compared with time (Figures 7,8,9). This allowed daily tidal effects to be observed at the
Clay Bank and Gloucester Point sites. As an optical instrument, the LISST requires a
laser to be transmitted through the water in order to measure concentration.
Figure 7 shows the suspended sediment concentration through time and the
percent transmission through time. As the percent transmission decreases the suspended
sediment concentration measurements increase, and as the percent transmission increases
the suspended sediment concentrations decrease. As suspended sediment concentrations
increase in the water column, more lasers will be blocked, and not fully transmitted. As
suspended sediment concentrations decrease in the water column, lasers will have a
clearer path, and thus transmission will increase.
Figure 8 shows the suspended sediment concentrations through time for the data
sets at the Clay Bank site. The first plot shows the concentrations for the August 2007
data set. It is clear that the daily tidal cycle has an effect on suspended sediment
concentration. The daily high value of sediment concentration averages approximately
700 uL/L with the daily low value averaging approximately 100 uL/L. The second plot
shows the concentrations for the December 2007 data set with a daily high concentration
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average value of approximately 500 uL/L and a daily low value of approximately 50
uL/L. The third plot shows the concentration values for the June 2008 data set with a
daily high concentration average value of 600 uL/L and a daily low value of
approximately 120 uL/L.
Figure 9 shows the suspended sediment concentrations through time for the data
sets at the Gloucester Point site. Due to the biological dominance at the Gloucester Point
site, the time intervals over which the LISST gathered usable data were quite short. The
instrument gathered seven days worth of good data in December, but only two to three
days worth of good data in April and July. The first plot shows the concentrations for the
July 2007 data set. The daily high value of sediment concentration was approximately
800 uL/L, and the daily low value averages approximately 50 uL/L. The second plot
shows the concentration values for the December 2007 data set. The daily high value of
sediment concentration averages approximately 100 uL/L, and the daily low value
averages approximately 50 uL/L. The third plot shows the concentrations for the April
2008 dat set. The daily high value of sediment concentration averages approximately 100
uL/L, and the daily low value averages approximately 30 uL/L.
The suspended sediment particle sizes measured in microns from the LISST were
compared with the water velocity measurements gathered by the ADV (Figure 10). The
particle sizes are split into three classifications, large (D84), median (D50), and small
(D16). Large and median sized particles at the Clay Bank site show a clear correlation
with water velocity. As the water velocity increases, the suspended sediment particle
sizes decrease. There is no apparent correlation between water velocity and sediment
size for the small particles, as velocity increases they do not change. The data sets at the
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Gloucester Point site show the same sign correlations, but the correlations themselves are
not as strong. Depending on velocity, large sediment particles range between 150 and
400 microns and median particles range between 50 and 150 microns. The smaller
particles consistently stay around 20 microns no matter the velocity.
The gathered suspended sediment particle sizes from the LISST were also
compared with water temperature (Figure 11). Again, the particles were split into large,
median, and small size classifications. At the Clay Bank site, all three particle size
classes, small, median, and large show no apparent correlation with temperature. At the
Gloucester Point site, the December 2007 and April 2008 data sets show no clear
correlation with temperature, but the largest particles in the July 2007 data set decrease in
size as the temperature increases.
Suspended sediment particle sizes were also compared with time (Figure 12). It is
clear that the daily tidal cycle plays an important role in the control of suspended
sediment particle size. All three particle size classes contain four daily size maximums
and four daily size minimums. This is consistent with the twice-daily flood and ebb tides
observed in the York River estuary.
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Discussion
Much of the data have been gathered under less than ideal conditions, with
tripods rarely being deployed at both site at the same time, and with biological fouling
accumulating rapidly on the LISST corrupting the data. This makes interpretation of
gathered data a somewhat difficult prospect. While direct comparison of data between
the Clay Bank and Gloucester Point sites is still possible, it is important to take into
account the fact that the Gloucester Point data foul much more rapidly than the Clay
Bank data. This rapid fouling makes it such that there is far less reliable data to be
analyzed at Gloucester Point and may account for some of the interpretational problems
with the data from that site.
One of the major points of interest from this research was that the observed
suspended sediment concentrations at the Clay Bank site were much higher than the
concentrations at the Gloucester Point site. Also, suspended sediment concentrations at
the Clay Bank site increased as water velocity increased, but increasing water velocity
seemed to have no effect on suspended sediment concentrations at the Gloucester Point
site. Friedrichs et al. (2008) suggests that high suspended sediment concentration is
correlated to high erodibility. High erodibility at the Clay Bank would account for the
high concentrations observed at that site. Since the bed is easily eroded, increasing water
velocity would generate increasing lift, suspending particles into the water column. A
low erodibility at the Gloucester Point site would account for the low sediment
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concentrations observed and for the fact that sediment concentrations are not increasing
with an increasing velocity. Even water moving as fast as half a meter a second is not
able to lift much sediment into suspension at Gloucester Point. The low erodibility of the
Gloucester Point site may be correlated to the benthic epiflora living along the bed. Their
coverage of the bottom and processing of the sediment may act as a buffer against
suspension, binding together sediment and preventing it from being easily resuspended.
As expected, suspended sediment particle size decreased with increasing velocity.
The largest particles (D84) decreased in size rapidly with an increasing velocity,
suggesting the forces binding them together are not very strong. The median particles
(D50) also decreased in size with increasing velocity, but not as rapidly as the largest size
particles, suggesting the forces holding them together are stronger than the forces binding
the largest sized particles. Increasing velocity had no effect on the smallest particles
(D16). Even at maximum velocity, the smallest particles stayed the same size, suggesting
that the cohesiveness of small particles (20-40 microns) is quite high. The forces binding
these particles together are probably much stronger than the forces binding the median
and large sized particles together.
The larger particles may be as large as they are due to flocculation. Flocculation
is the tendency of loose organic matter to aid in binding together sediment clumps,
increasing their size. These loosely bound clumps would easily be torn apart at higher
velocities, decreasing their size. The smallest particles would contain few, if any flocs,
and thus may not break up easily.
One of the most interesting observations from this research was that water
temperature seemed to play no detectable role in suspended sediment particle size. It was
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expected that water temperature would be a proxy for organic activity, and that higher
organic activity would lead to more flocculation and thus larger observed suspended
sediment sizes. Figure 11 shows that there was no correlation between water temperature
and particle size. In general, increasing temperature had no effect on the size of particles
at both the Clay Bank and Gloucester Point sites. The range of measured temperatures
over each data set is quite small however. Perhaps if the LISST had gathered data over a
longer time interval in each data set, then a broader temperature range would have been
observed, which may have led to a correlation developing. In the July 2007 data set at
Gloucester Point, particle size decreases with increasing temperature. This is opposite of
the expected results and observations from all other data sets, suggesting an external
factor may have led to this decrease over the July 2007 Gloucester Point data set.
In general, it was found that the particles were larger in the December 2007 data
sets than they were in all other data sets, suggesting that temperature has no positive
effect on particle size. One possible explanation for this is that the particles are torn up
during the winter and aggregate together over the spring, summer, and fall. In both data
sets, the usable LISST data end in the beginning-middle of December, and winter does
not begin until the end of December, suggesting that the observed particles in the
December data sets may be the largest particles of the year just before they begin to break
up over the winter.
The July 2007 Gloucester Point data set proved to be a bit strange as it followed
none of the trends observed in the other Gloucester Point data sets. One possible
explanation for the inconsistencies observed for this data set is that a storm event
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occurred during this time and advected sediment from upstream into Gloucester Point,
interfering with observations gathered during this time.
Conclusions
Suspended sediment concentration increased with increasing water velocity at the
Clay Bank site. This was expected due to the high erodibility characteristic of the Clay
Bank site. Velocity had no impact on sediment concentration at the Gloucester Point site,
most likely due to the low erodibility found at that site. Suspended sediment particle size
decreased with increasing water velocity at both the Claybank and Gloucester Point sites.
This relationship was strongest at the Clay Bank site due to its dominant physical
conditions and high erodibility, and weaker at the Gloucester Point site due to its
dominant biological condition and low erodibility. At both sites, water temperature had
no effect on the size of suspended sediment particle size.
Once a real time observation system that transmits data directly from the in-situ
tripods to VIMS is completed, future work will be easier and faster to do. Currently, a
LISST device is deployed for 30-60 days, but usually only gathers a few days worth of
usable data. With real time data transmission in place, observers will be able to
recognize when the LISST data begin to go bad and repair it such that reliable data can be
gathered over a much longer period of time. This will allow long term seasonal and tidal
effects to be much more readily observed.
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Acknowledgements
This work was funded by The National Science Foundation Grant OCE-0536572.
Assistance and guidance in data collection and analysis was provided by Grace
Cartwright, Pat Dickhudt, and Carl Friedrichs.
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References
CBNERRVA 2008. A site profile of the Chesapeake Bay Nation Estuarine Research Reserve in Virginia. Version September 2008. Special Scientific Report. K.A. Moore and W.G. Reay (eds.). The Virginia Institute of Marine Science, College of William and Mary. Gloucester Point, Va. 204p. Agrawal, Y. C., A. Whitmire, O. A. Mikkelsen, and H. C. Pottsmith (2008), Light scattering by random shaped particles and consequences on measuring suspended sediments by laser diffraction, J. Geophys. Res., 113, C04023. Aller, R.C., 1998. Mobile deltaic and continental shelf muds as suboxic, fluidized bed reactors. Marine Chemistry, 61: 143-155. Boesch, D.F., R.B. Brinsfield, and R.E. Magnien, 2001. Chesapeake Bay eutrophication: scientific understanding, ecosystem restoration, and challenges for agriculture. Journal of Environmental Quality, 30: 303-320 Dellapena, T.M., S.A. Kuehl and L. Pitts, 2001. Transient, longitudinal, sedimentary furrows in the York River subestuary, Chesapeake Bay: furrow evolution and effects on seabed mixing and sediment transport. Estuaries, 24: 215-227. Downing, J.P., Beach, R.A., 1989. Laboratory apparatus for calibrating optical suspended solid sensors. Mar. Geol. 86, 243-249. Eisma, D., Bale, A.J., Dearnaley, M.P., Fennesy, M.J., Van Leussen, W., Maldiney, M.-A., Pfeiffer, A., Wells, J.T., 1996 Intercomparison of in-situ suspended matter (floc) size measurements. J. Sea Res. 36 (1-2), 3-14. Friedrichs, C.T., 2009. York River physical oceanography and sediment transport. In: K.A. Moore and W.G. Reay (eds.), A Site Profile of the Chesapeake Bay National Estuarine Research Reserve, Virginia. Journal of Coastal Research, Special Issue No. 57, in press. Friedrichs, C.T., G.M. Cartwright, and P.J. Dickhut, 2008. Quantifying benthic exchange of fine sediment via continuous, non-invasive measurements of settling velocity and bed erodibility. Oceanography, 21(4): 168-172. Fugate, D.C., and C.T. Friedrichs, 2003a. Controls on suspended aggregate size in partially mixed estuaries. Estuarine Coastal and Shelf Science, 58: 389-404.
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Hill, P.S., Syvitski, J.P., Cowan, E.A., Powell, R.D., 1998. In situ observations of floc settling velocities in Glacier Bay, Alaska. Marine Geology 145, 85-94 Lee, H.J., and P.L. Wiberg, 2002. Character, fate, and biological effects of contaminated, effluentaffected sediment on the Palos Verdes margin, southern California: an overview, Continental Shelf Research, 22 (6-7), 835-840. Ludwig, K.A., Hanes, D.M., 1990. A laboratory evaluation of optical backscatterance suspended solids sensors exposed to sand-mud mixtures. Mar. Geol. 94, 173-179 Lynch, J.F., Irish, J.D., Sherwood, C.R., Agrawal, Y.C., 1994. Determining suspended sediment particle size information from acoustical and optical backscatter measurements. Continental Shelf Research 14 (10-11), 1139-1164 Pottsmith, H.C., Bhogal, V.K., 1995. In situ particle size distribution in the aquatic environment. Paper presented at 14th World Dredging Congress, November 1995, Amsterdam, The Netherlands. Schaffner, L.C., T.M. Dellapenna, E.K. Hinchey, C.T. Friedrichs, M. Thompson Neubauer, M.E. Smith and S.A. Kuehl, 2001. Physical energy regimes, sea-bed dynamics and organism-sediment interactions along an estuarine gradient. In J.Y. Aller, S.A. Woodin and R.C. Aller (eds), Organism-Sediment Interactions. University of South Carolina Press, Columbia, SC. Pp. 161-182
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FIGURE 1
Observed floc size as a function of the Komogorov microscale, which is the size of the smallest energetic eddies. In the upper York River estuary, increased turbulence
(indicated by a smaller sized energetic eddies) reduces floc size, presumably be ripping them apart. The opposite pattern is seen in the lower Chesapeake Bay where turbulence
presumably does not effectively rip apart flocs. (Fugate and Friedrichs, 2003)
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FIGURE 2 -York River watershed highlighting county borders.
(Figure 1.4 from CBNERRVA)
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FIGURE 3
-Side scan and profile camera images collected in the York River estuary (Dellapenna et al. 2001 and Schaffner et al. 2001)
27
FIGURE 4
-Comparison of tidal range along the York, Pamunkey, and Mattapoini (Figure 3.2 of CBNERRVA)
28
FIGURE 5 -Mean salinity map of York River and general locations of primary and secondary ETM
(Figure 4.2 of CBNERRVA)
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30
FIGURE 7
-Figure showing sediment concentration through time and LISST percent transmission through time for Clay Bank December 2007
31
FIGURE 8 -Figure showing sediment concentrations through time at the Clay Bank site for August
2007, December 2007, and June 2008 data sets
32
FIGURE 9
-Figure showing sediment concentrations through time at the Gloucester Point site for July 2007, December 2007, and April 2008
33
34
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