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Coastal Gradients of Flow, Salinity and Nutrients

Freshwater Flows to Northeastern FL Bay

Hydrologic Monitoring in Joe Bay

SW FL Coastal & Wetland Systems Monitoring

Several methods were used in the study to describe the magnitude and distribution of flow and salinity at the mangrove transition zone and along the southern coastline of Florida. Field data-collection procedures and discharge calculation techniques for instrumented stations are summarized below.

Field Data Collection

Water level, temperature, salinity, and discharge

Data collected at instrumented sites included continuous (15-minute or hourly) measurements of water level, water velocity, salinity/specific conductance, temperature, and periodic measurements of discharge for index velocity calibrations. More information on index velocity techniques is discussed in Hittle and others (2001) and Morlock and others (2002), and Ruhl and other (2005). Stations with transmitting data loggers send field data every 1 to 4 hours into the database of the FISC Ft. Lauderdale office by way of the Geostationary Operational Environmental Satellite (GOES). Non-transmitting sites are routinely serviced and field data is manually uploaded to the USGS database.

Boat mounted acoustic Doppler current profilers (ADCP) were used to measure discharge at the estuarine 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 (Simpson 2002 and Oberg and others 2005). 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 is calculated by dividing the total measured discharge by the cross-sectional area corresponding to the water level at the time of measurement (Sauer 2002 and Ruhl and others 2005).

Acoustic velocity meter (AVM) and acoustic Doppler velocity meter (ADVM) systems were used to measure continuous water velocity. The velocity measured by the 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 channel velocity.

Water level data are used to determine water depth and to calculate the stage-dependent cross-sectional area. Water level data were collected an incremental shaft encoder equipped with a pulley, stainless-steel tape, weight, and float inside an 8 in. polyvinyl chloride pipe stilling well (Sauer 2002), pressure sensors, or acoustic transducers. Corrections to water level data follow USGS quality assurance quality control protocols (Rantz and others 1982 and Sauer 2002).

Salinity is measured near the water surface and the bottom of the water column to help determine the presence of freshwater flow and to examine potential effects on the acoustic signals caused by salinity stratification. Continuous salinity measurements are important for describing the seasonal patterns of freshwater flow (wet/dry season) and for identifying bi-directional flow. Elevations of the continuous monitors are available upon request. Temperature is measured to acquire physical information on creek or wetland characteristics, and to monitor possible vertical gradients that also could affect acoustic signals. Due to biological fouling and electronic drift, the continuous monitor requires routine cleaning and calibration to maintain data quality. During the period of record (water years 1996-2003), continuous monitors were calibrated during site visits to ambient conditions using a reference probe (USGS National Field Manual). Ambient salinity conditions were measured with a portable reference probe that was calibrated and or verified against a range of laboratory specific conductance standards. The determination of fouling and drift errors from water year 2003 to current follow the guidelines set forth in Wagner and others (2005). Reference temperature probes are verified against a NIST thermometer prior to field trips. When in situ temperature measurements differ by more than 0.2°C when compared to the reference temperature probe, the in situ probe is replaced.

Rainfall

A remote tipping bucket style rain gauge was used to measure 15 minute liquid precipitation at Upstream North River, Card Sound Canal and West Highway Creek. Daily rainfall in inches is published by water year. Maintenance consists of routine cleaning of debris from the filter screen, and annual calibration/verification with a known rate and volume dispenser. The gage is adjusted when the calibration error is greater than 5%. Data collection, processing, storage, and publication meet USGS standards (USGS 2006).

References

Hittle, C.D., Patino, E., Zucker, M., 2001, Freshwater Flow from Estuarine Creeks into Northeastern Florida Bay: USGS Water-Resources Investigation Report 01-4164, p. 32.

Morlock, S.E., Nguyen, H.T., and Ross, J.H., 2002, Feasibility of acoustic Doppler velocity meters for the production of discharge records from U.S. Geological Survey streamflow-gaging stations: U.S. Geological Survey Water-Resources Investigations Report 01-4157.

Oberg, Kevin A.; Morlock, Scott E.; Caldwell, William Scott, 2005, Quality-assurance plan for discharge measurements using acoustic Doppler current profilers: U.S. Geological Survey SIR 2005-5183.

Rantz, S.E. and others, 1982, Measurement and Computation of Streamflow Volume 1. Measurement of Stage and Discharge: U.S. Geological Survey Water Supply Paper 2175.

Ruhl, C.A., Simpson, M. R., 2005, Computation of discharge using the index-velocity Method in tidally affected areas: U.S. Geological Survey SIR 2005-5004.

Sauer, Vernon B., 2002, Standards for the analysis and processing of surface-water data and information using electronic methods: U.S. Geological Survey Water-Resources Investigations Report 01-4044.

Simpson, Michael R., 2002, Discharge measurements using a broad-band acoustic Doppler current profiler: U.S. Geological Survey Open-File Report 2001-1.

U.S. Geological Survey Office of Surface Water Technical Memorandum No. 2006.01.

U.S. Geological Survey, variously dated, National field manual for the collection of water-quality data: U.S. Geological Survey Techniques of Water-Resources Investigations, book 9, chaps. A1-A9, available online at http://pubs.water.usgs.gov/twri9A.

Wagner, R.J., Boulger, W.R., and Smith, B.A., 2006, Revised Guidelines and standard procedures for continuous water-quality monitors: site selection, field operation, calibration, record computation, and reporting: U.S. Geological Survey Techniques and Methods, Book 9, Chapter B.