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| Methods of Investigation |
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Several methods were used in the study to describe the magnitude and distribution of flow
and salinity at the estuarine creeks along the northeastern coastline of Florida Bay.
Field data-collection procedures and discharge calculation techniques for instrumented and
noninstrumented sites are summarized.
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| Field Data Collection |
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Data collected at all instrumented sites (West Highway Creek, Stillwater Creek, Trout Creek,
Mud Creek, Taylor River, Upstream Taylor River and McCormick Creek) included continuous
(15-minute interval) measurements of stage, water velocity, salinity, and temperature and
periodic measurements of discharge for index velocity calibrations. More information on index
velocity techniques is provided in Hittle and others (2001) and Morlock and others (2002).
All raw data at the instrumented sites were recorded by an electronic data logger and
transmitted every 4 hours by way of the Geostationary Operational Environmental Satellite (GOES) into the database
of the USGS Center for Water and Restoration Studies in Miami, Florida. Data collection at the
noninstrumented sites (East Highway Creek, Oregon Creek and East Creek) was limited to periodic
discharge and salinity measurements. Instrumentation was installed at Stillwater Creek and
Upstream Taylor River in 1999 to acquire a better representation of streamflow in western Long
Sound and Taylor River—both sites were previously noninstrumented.
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Acoustic Doppler current profilers (ADCPs)
mounted on a boat were used to measure discharge at the Florida Bay monitoring stations. The ADCP uses the Doppler shift in returned acoustic
signals reflected by particles suspended in the water to determine the velocity of moving water
(RD Instruments, 1989). The ADCP also has the
capability to measure water depth, flow direction, and speed of the boat based on acoustic reflections
from the streambed. Discharge and flow direction are both calculated from information provided by the
ADCP and computer software. The mean water
velocity for the stream or creek section is calculated by dividing the total discharge (measured with
the ADCP) by the cross-sectional area
corresponding to the water level at the time of measurement.
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Stage data were used to determine water depth and to calculate the stage-dependent cross-sectional
area. Stage data were collected with an incremental shaft encoder equipped with a pulley, stainless-steel
tape, weight, and float inside an 8 in. polyvinyl chloride pipe stilling well.
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Acoustic velocity meter (AVM) and acoustic Doppler velocity meter (ADVM) systems were used to
measure continuous water velocity. ADVMs were
installed at Stillwater Creek and Upstream Taylor River in 1999;
AVMs were used at the other sites. The velocity measured by the
AVM and ADVM systems represents an "index"
of the mean water velocity. The index velocity is a measured velocity at the instrumented sites that
can be used to compute the mean velocity.
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Salinity was measured near the water surface and near the bottom of the water column to help
qualify the presence of freshwater flow and to examine potential effects on the acoustic
signals caused by salinity stratification. Temperature was measured to acquire physical
information on creek characteristics, and to monitor possible vertical gradients that also
could affect acoustic signals. Due to biological fouling and electronic drift of the salinity
probes, monthly cleaning and calibration was necessary to maintain accurate measurements.
During the period of record (water years 1996-2000), salinities were calibrated monthly to
ambient conditions. Ambient salinity conditions were measured with a portable reference probe
that was calibrated to a range of laboratory salinity standards.
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