projects > freshwater flows into northeastern florida bay> 2001 Proposal
Project Proposal for 2001
Continuing Project Work Plan - FY 2001
Scope and Objectives: Two of the many unknowns along the northeastern coast of Florida Bay have been the amount of freshwater flowing into the bay and the effect that years of man-made changes in water deliveries have had, and will have, on the ecosystem.
Flow and salinity data along the mangrove zone is collected to help evaluate water management practices and the quality of Florida Bay. Hydrodynamic models of the Everglades (mainland) and Florida Bay use these data to calibrate and verify models describing flow through the mangrove zone, and circulation patterns within the bay. The main objectives of this project are to determine water discharge along the northeastern coast of Florida Bay, to evaluate the flow and salinity distribution patterns of shallow streams and provide hydrodynamic models with boundary and calibration information at selected locations along the mangrove zone.
Methodology: The following sections describe the methods and techniques used for collection and analysis of all field data in order to qualify and quantify discharge along the Florida Bay northeastern coastline. Data collection at all instrumented sites includes continuous (15-minute interval) measurements of water level, water velocity, salinity, temperature, periodic nutrient sampling, and calibration measurements of discharge. Data collection at noninstrumented sites is limited to periodic discharge measurements. All continuous data are recorded and transmitted every 4 hours by way of Geostationary Operational Environmental Satellite (GOES) into the database of the USGS Miami Subdistrict office.
Water-level data are recorded to determine water depth and to calculate stage-dependent cross-sectional area. Data are collected with an incremental shaft encoder equipped with a pulley, stainless-steel tape, weight, and float inside an 8 in. (inch) polyvinyl chloride pipe stilling well. All water-level data are referenced to the NAVD 88 datum for mean sea level.
Acoustic velocity meter (AVM) systems are used to measure continuous water velocity and have proven to be accurate and reliable instruments capable of measuring near zero velocities in open channels. These AVM systems measure the velocity of flowing water by means of an acoustic signal that travels faster with the flow than against it. The line velocity measured by the AVM systems represents an averaged value across the stream from point a to point b at a fixed depth and is considered to be an index of the mean water velocity. With the exception of Taylor River, all other sites required only one index velocity at a fixed depth in order to determine mean water velocity. At the Taylor River station, water velocity is measured at three depths to describe unusual velocity profiles.
Boat-mounted Acoustic Doppler Current Profilers (ADCPs) are used to measure water velocities in three dimensions and to calculate total discharge along a transect across a channel or stream. The ADCP uses the Doppler shift in reflected acoustic signals to determine the velocity of moving water. The ADCP also measures water depth and the speed and direction of boat movement using acoustic reflections from the streambed. Discharge and flow direction are both calculated from information collected with the ADCP and factory-provided software. The mean 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. The cross-sectional area is computed by using the site-specific stage-area ratings as described in the subsequent sections.
Salinity is measured at up to three depths to: (1) quantify the vertical salinity (density) stratification present at each site, which can be detrimental to the acoustic signals; and (2) assist in quantifying the presence of freshwater. It was determined that even though stratification of salinity in the water column did occur at these sites, the frequency and duration of these conditions rendered the events insignificant.
Temperature was collected to monitor possible vertical temperature gradients that could be as detrimental to acoustic signals as salinity gradients and as a necessary parameter to calculate salinity from conductivity readings. It was determined from data that no significant temperature stratification occurs.
Restoration Benefits: Information from this study provides knowledge of freshwater flow from Everglades National Park (ENP) to northeastern Florida Bay that has not been previously available to natural resource managers. Such information is critical for quantitatively determining the freshwater flows throughout the southern part of ENP. The flow data is used in conjunction with data from many other ongoing studies to help determine the effects of changes in water deliveries to ENP, and into Florida Bay. Flow into Florida Bay is closely related to sediment transport, salinity, and chemical characteristics of the bay, which in turn, have great influence on the biology of the bay. Additionally, freshwater flow is being and will continue to be used as input to hydrodynamic models of Florida Bay, for calibration of hydrologic models of the mainland, and for water-budget determinations for south Florida. Such models and computations are substantially more dependable and reliable because of the availability of flow and salinity data from this project. In turn, decisions regarding restoration activities based on scenario testing from such models and computations are also more reliable. As the restoration process proceeds, it will be critical to continue monitoring flow patterns in order to understand the effects of changing water supply quantity and source into the wetlands of ENP.
Collaborators, clients: Discharge and salinity data obtained through this study are currently being used by the following agencies/universities:
Urgency of Study: Ongoing research from organizations listed above, require data collected from this project on a monthly to quarterly basis. New findings in areas such as Joe Bay, Upstream Taylor River, Trout Creek, and McCormick Creek have supplied researchers with flow and salinity data previously unavailable. Although the project is currently active, the need for results and basic data are considered very urgent and critical to other projects successes.
Project Effectiveness: Freshwater flows into Florida Bay has been extremely effective for identifying the major freshwater contributors to Florida Bay and also showing discharge and salinity variations between the wet and dry seasons and storms.
WORK PLAN for FY 2001
Activities, Deliverables and Products:
|U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology
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Last updated: 15 January, 2013 @ 12:43 PM (KP)