Water Velocity and Suspended Solids Concentrations

1
 

• CONCLUSIONS
• The fact that transects 1 and 2 have hard wood
  tree cover that does not allow underwater
  vegetation to grow, appears to play a major role
  in the relatively rapid flow in areas with dense
  tree cover. In contrast, water velocities are
  relatively low inside the tree line at transect
  3, which is located at the tail of the tree
  island. In the tail the trees are sparser and do
  not significantly impede light penetration
  towards the water, thereby permitting underwater
  vegetation to flourish. This underwater
  vegetation impedes flow, thereby decreasing water
  velocities in this area.

Water Velocity and Suspended Solids
Concentrations in the Proximity of Tree Islands
in Everglades National Park
RESULTS

• METHODS
• Spatially intensive velocity data are being
  taken along 3 transects that are perpendicular to
  the main North-South axis of each island, using a
  Sontek handheld device (Picture 2). The first and
  northern-most transect is located by the islands
  tropical hardwood hammock (head), the second
  transect is located near the middle and the third
  is located close to the tail of the island. Each
  transect has its origin to the west of the tree
  island and has a station every 5 meters.
• One Sontek Argonaut ADV autonomous velocity
  meter has been installed near each tree island to
  obtain temporally intensive velocity in three
  dimensions (Picture 3).
• Suspended sediments are characterized along the
  transects. Samples are collected without
  filtration for turbidity, particle size
  distribution and number of particles per ml
  analyses. The latter two are performed with a
  Coulter Counter Particle Size Analyzer (Picture
  4). The gravimetric analysis of total suspended
  solids, volatile suspended solids and non-
  volatile suspended solids is being conducted by
  sampling with an in-line filtration system
  (Picture 1).
• Tests using dyes and tracers will be conducted
  in order to test if the acoustic Doppler systems
  are underestimating water velocity through
  vegetation, since the Doppler system requires
  that an area be cleared of vegetation between the
  sampling volume and the transducers.  

OBJECTIVES The overall goal of this study is to
determine the importance of water flow in the
formation and preservation of tree islands in the
Florida Everglades. In the process we intend to
measure suspended sediment properties and develop
methods for measuring water velocity in the
unique environments of the Everglades.
OBJECTIVES
ABSTRACT
The Acoustic Doppler Velocity Meters work by
generating a narrow beam of sound. The sound is
then reflected by particulate matter suspended in
the water. The equipment then measures the
frequency change of the received signal and
calculates the water velocity. Unfortunately the
amount of suspended solids in the Shark Valley
Slough is so low that the measurements have not
been reliable unless suspended solids are added
by stirring the bottom or by adding particulates
to the water (Figure 5).
Water velocity measurements along the transects
varied between less than 1 cm/s to more than 4
cm/s. The highest velocities occurred at those
stations where there is an opening (due to
sawgrass die-off) in transects 1 and 3.
Relatively high velocities are observed inside
the tree line in the areas closer to the head of
the island. Low velocities were recorded inside
the tree line at the tail of the island (Figure
1).

• Wind velocity and direction are highly variable.
  Water flow is shielded from wind influences
  inside the tree line at transects 1 and 2 but not
  at transect 3. Water depth was variable in all
  transects but there is a clear tendency for water
  depth to decrease as the center of the island is
  approached in transects 1 and 2. This tendency
  was not observed for transect 3. Turbidity was
  relatively low along all 3 transects with most
  values being in the 0.45 NTUs to 0.55 NTUs range
  (Figure 2).

However, it was also noted that even with
acceptable values of sound to noise ratio (SNR)
which is achieved by adding sediments to the
water, some of the high velocity magnitudes were
primarily caused by the velocity reading in the
z direction. We believe that the high Vz values
are created by the addition of sediments and the
release of gases when the bottom is stirred. All
data have been revised and, for the sake of
consistency, incorporate only the x and y
components of velocity (Figure 6).
Enlarged Area
Area of Study
Figure 2
Black Hammock
X
Satin Leaf
X
X
The particle size distribution of most samples
was exponential in nature with the largest number
of particles having a smaller average diameter.
Mean particle size was relatively constant,
varying from 2.5 to 4.0 microns (Figure 3).
Gumbo Limbo
Velocity measurements were taken with a dye and
a ruler in areas with dense sawgrass vegetation.
Our data indicate Acoustic Doppler Velocity meter
water velocities are likely being
underestimated. Further testing has to be
performed to confirm these preliminary findings.
If it is confirmed, a different method (other
than use of the Sontek Flowtracker) will have to
be developed to measure water velocity in areas
that are densely vegetated
X - Tree Islands Under Study
ABSTRACT This study quantifies water velocities
and determines suspended sediment characteristics
in the vicinity of 3 tree islands situated in the
Shark Valley Slough in Everglades National Park.
The three islands are known as Black Hammock,
Gumbo Limbo and Satin Leaf. Additionally, we plan
to develop a method to evaluate the effect of
wind on water flow and to evaluate the use of the
acoustic Doppler meters for measuring flow in the
Everglades. We expect to find important
correlations between the variables under study
that will allow us to model and understand the
relationship between water flow and the creation
and preservation of tree islands.
CONTACT
Jose Bazante M.S., M.B.A. Helena M.
Solo-Gabriele, Ph.D., P.E. University of Miami,
Dept. of Civil, Arch., and Environmental
Engineering, Coral Gables, Florida jbazante_at_bellso
uth.net hmsolo_at_miami.edu Sherry Mitchell, Ph.D.
Everglades National Park, Homestead, Florida

• Total suspended solids were measured at 7
  stations at transect 1 using an in-line
  filtration system. Total suspended solids were in
  the order of 1.0 mg/L and were relatively
  constant between stations. As expected, most of
  the total suspended solids were volatile due
  to the high organic content of suspended solids
  in a marsh environment (Figure 4).

Michael Ross, Ph.D. and Daniel L. Childers,
Ph.D. Southeast Environmental Research
Center, Florida International University, Miami,
Florida Lynn Leonard, Ph.D. University of North
Carolina at Wilmington, Department of Earth
Science and Geology, Wilmington, North Carolina


SFC CESU, Miami, Florida (June 2-3, 2003)