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-measured Water Level
Water level is monitored for both surface water and groundwater. Surface-water levels are recorded every 15 minutes using shaft encoders, vented pressure sensors, or acoustic transducers. Depth to water measurements, from reference points of known elevation, are conducted to verify the accuracy of water level readings during routine field visits. If there is a difference greater than 0.02 ft. (surface water) or 0.05 ft. (groundwater), the field sensor is reset or in cases of pressure sensors or acoustic stage sensors, the sensor is re-calibrated. Pressure transducers are used to measure water level in the ground water wells. Methods describing the use of pressure transducers are discussed by Cunningham and others (2011).
Correctoberions to the water level data are performed in the USGS NWIS database following the guidelines of Sauer (2010). Station elevations have been determined by the USGS National Mapping Division using static survey techniques and Airborne Height Finder (AHF) survey (USGS FS-0121-03). All water-level information is referenced to the North American Vertical Datum of 1988 (NAVD '88). Station levels are verified every 1-3 years by performing optical surveys to verify established elevations (Kenney, 2010). All station level summaries are available in the Caribbean-Florida Water Science Center (CFWSC) Electronic Archive.
Velocity data are collected every 15 minutes using acoustic Doppler velocity meters and are calibrated using an acoustic Doppler current profiler (ADCP) for the computation of continuous discharge (Oberg and others, 2005). Discharge data are computed using continuous water level and velocity data along with established stage area and velocity ratings. Stage area ratings are typically developed using depth soundings from the ADCP and output from a USGS software program called Areacomp (http://hydroacoustics.usgs.gov/indexvelocity/software.shtml#usgs).
Index-velocity ratings are developed through simple linear regression analyses, determining relations between instrument velocity (mean index velocity) and mean measured velocity determined from ADCP discharge measurements (Hittle and others, 2001, Morlock and others, 2002, and Ruhl and others, 2005, and Levesque and others, 2012). An index-velocity rating is required because there is no simple relation between stage and discharge for tidal and wind driven streams (Rantz, 1982). Accurate measurements of water level in tidal streams are important because the relation between the mean velocity and index-velocity may change as a function of water level and in some cases can be a variable in the index velocity rating. Factors that can impact this relation include changes in the cross sectional area, bed roughness, surface winds, aquatic vegetation, and stratification (Laenen and others, 1989). The above factors usually have minimal impact on the index-velocity rating and can be verified by direct measurement or inclusion in the rating if determined a significant variable.
The use of filters for data analysis is used for both tidal and wetland environments. Traditionally, daily mean values of discharge are computed and summarized for public use. However, due to the fact that tidal cycles are slightly greater than 24-hours in duration, computation of daily means is inappropriate and can cause aliasing of these data. Therefore, mathematical methods or filters have been developed to theoretically remove the tidal effect from these data and leave the residual discharge values (East, 2005). One such mathematical filter was developed by Godin (1982). Discharge data that is collected in areas of tidal influence is processed through a USGS program called Gr_filter (USGS 2010.08). The Gr_filter program uses the low pass Godin filter to remove the tidal signal from unfiltered discharge data. The published product is the tidally filtered daily mean value of discharge.
Specific conductance, salinity, temperature, and turbidity sensors are cleaned, calibrated, and checked against laboratory standards during routine field visits. Due to biological fouling and electronic drift, the continuous monitor requires routine site visits, especially in estuarine environments. Ambient specific conductance conditions are measured with a field meter that is calibrated and or verified against a range of laboratory specific conductance standards (USGS 2008). From 2003 to current, determination of fouling and drift errors followed the guidelines set forth in Wagner and others (2006). A modified standard protocol was adopted for the operation and maintenance of continuous water quality monitors due to rapidly changing conditions near the coast. The significant change between the standard and modified approach is that measurements are made in ambient water collected in a 5-gallon bucket versus direct in situ measurement (Wagner and others, 2006). Continuous water quality monitors are calibrated in the field or in an office setting when water temperature and or specific conductance exceed calibration criteria. The guideline is applied to all in situ monitors as well as field meters used for discrete measurements. Since the water temperature sensor is only verifiable against a thermometer that meets the standards of the National Institute of Standards and Technology (NIST), the in situ monitor is typically pulled from the station and replaced with another monitor when the calibration criteria has been exceeded. No corrections are applied to the temperature sensor as part of the USGS Coastal Monitoring Network but accuracy is still properly documented and available upon request. Water temperature record is not published if the error exceeds ± 2.0 °C. Turbidity is an expression of the optical properties of a sample that causes light rays to be scatted and absorbed rather than transmitted in a straight lines through the sample (Rasmussen and others, 2009). Turbidity can be used a surrogate to estimate suspended sediment concentrations and when combined with computed discharge, estimate suspended sediment load (Rasmussen and others, 2009). Due to biological fouling and electronic drift, the continuous monitor requires routine cleaning and calibration to maintain data quality.
With regard to the specific conductance sensor, the unit is checked against 3 NIST traceable specific conductance standards covering the entire range of conditions a particular site location may experience. If the average percent difference of the 3 standards exceeds the calibration criteria, the sensor is recalibrated. The recalibrated specific conductance sensor is typically compared against the field meter in the 5 gallon bucket prior to redeployment. Specific conductance record is not published if the error exceeds ± 30%. Processing and publishing of continuous water quality data are discussed in Wagner and others (2006).
A remote tipping bucket style rain gauge was used to measure 15 minute liquid precipitation at various sites. 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).
Cunningham, W.L., and Schalk, C.W., comps., 2011, Groundwater technical procedures of the U.S. Geological Survey: U.S. Geological Survey Techniques and Methods 1-A1, 151 p. (available only online at http://pubs.usgs.gov/tm/1a1/).
East, J. W., 2005, Status Report: Stream Velocity, Discharge, and Water-Quality Parameters at the Intersection of the San Bernard River and the Gulf Intracoastal Waterway, near Rivers End, Texas, October 2003 - September 2005.
Godin, G., 1982, The Analysis of Tides, University of Toronto Press, 264 p.
Hittle, C.D., Patino, E., Zucker, M., 2001, Freshwater Flow from Estuarine Creeks into Northeastern Florida Bay: U.S. Geological Survey Water-Resources Investigations Report 01-4164, 32 p.
Kenney, T.A., 2010, Levels at gaging stations: U.S. Geological Survey Techniques and Methods 3-A19, 60 p.
Levesque, V.A., and Oberg, K.A., 2012, Computing discharge using the index velocity method: U.S. Geological Survey Techniques and Methods 3-A23, 148 p.
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 Scientific Investigations Report 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.
Rasmussen, P.P., Gray, J.R., Glysson, G.D., and Ziegler, A.C., 2009, Guidelines and procedures for computing time-series suspended-sediment concentrations and loads from in-stream turbidity-sensor and streamflow data: U.S. Geological Survey Techniques and Methods book 3, chap. C4, 53 p.
Ruhl, C.A., Simpson, M. R., 2005, Computation of discharge using the index-velocity Method in tidally affected areas: U.S. Geological Survey Scientific Investigations Report 2005-5004.
Sauer, V.B., and Turnipseed, D.P., 2010, Stage measurement at gaging stations: U.S. Geological Survey Techniques and Methods book 3, chap. A7, 45 p.
Simpson, Michael R., 2002, Discharge measurements using a broad-band acoustic Doppler current profiler: U.S. Geological Survey Open-File Report 2001-01.
U.S. Geological Survey, Measuring and Mapping the Topography of the Florida Everglades for Ecosystem Restoration: U.S. Geological Survey Fact Sheet 021-03.
U.S. Geological Survey Office of Surface Water Technical Memorandum No. 2006.01.
U.S. Geological Survey Office of Surface Water Technical Memorandum No. 2010.08.
U.S. Geological Survey, 2008, National field manual for the collection of water-quality data: U.S. Geological Survey Techniques of Water-Resources Investigations, Book 9, Chap. A6.
Wagner, R.J., Boulger, R.W., Oblinger, C.J., and Smith, B.A., 2006, Guidelines and Standard Procedures for Continuous Water-Quality Monitors: Station Operation, Record Computation, and Data Reporting: U.S. Geological Survey Techniques and Methods 1-D3, 51 p.
Everglades Land-Margin Ecosystem Hydrology Data (Subset of South Florida Hydrology Data)
Instantaneous surface and ground water level
Instantaneous surface and ground water levels were initially recorded hourly. To better characterize tidal influence, the sampling interval was increased to every 15 minutes at lower estuary gages in 2003. At freshwater marsh gages, the sampling interval was increased to every 15 minute interval after 2006. To improve water level accuracy, 10-tip float/pulley potentiometers used for surface water were replaced with float/pulley SDI shaft encoders and passive resistance tape sensors were replaced with vented pressure transducer sensors for groundwater in 2003. All water levels were measured in decimal feet and referenced to the NAVD 88 datum.
Instantaneous surface and ground water specific conductivity and salinity
Toroidal induction conductivity sensors were initially used to measure specific conductance (corrected to 25 °C) for instantaneous surface and groundwater measurements. At each gage, specific conductance was measured by pumping water through tubing from each well into a single measurement chamber. This method was problematic and discontinued in 2001, due to excessive data loss from power failure and equipment fouling. The pumping method was replaced with in situ sensors. In 2003, toroidal sensors were replaced with 2-electrode conductivity/temperature sensors or "sondes" to improve accuracy and reduce measurement drift. Specific conductance was initially done hourly on the half-hour and increased after 2003 to a 15 minute interval to coincide with water level sampling. Specific conductivity field measurements were measured in millisiemens per cm2. Specific conductance values were converted into Practical Salinity Units (PSU) afterward within the database using the 1985 UNESCO standard formula (UNESCO, 1985).
Instantaneous surface and ground water temperature
Supplemental thermistor temperature probes were added in 1999, because toroidal specific conductivity sensors did not output water temperature. Water temperature sampling for surface and groundwater toroidal/thermistors were replaced in 2003 with single 2-electrode conductivity/ temperature "sondes" for each well. Temperature was initially sampled hourly on the half-hour and increased after 2003 to a 15 minute interval to coincide with water level sampling. Water temperature data were recorded in degrees Celsius.
Instantaneous rainfall was measured only at gages free of tree canopy interference. Beginning in 1997, rainfall was only measured at gages LO4 and CH2. Additional rain gages were added at gages SH1, SH2, SH5, LO1, LO2 and BSC from 2000-2001. Rain was measured with funnel style pulse tipping buckets (0.01 inch per tip). Rainfall measurements were recorded in decimal inches and stored as hourly summed data.
Data collection, storage and retrieval
Instantaneous water data were recorded and stored on site within a data logger/controller powered with a solar photovoltaic (PV) 12 volt battery system. Logger stored data were initially transferred daily to the computer database at Everglades National Park (ENP) via a local RF radio network. After 2006, GOES satellite transmitters were used to send daily data from the loggers to GOES satellites using National Environmental Satellite Data and Information Service (NESDIS). Incoming data were transmitted via internet from NESDIS to ENP database. The data were reviewed, and validated at the project level (Anderson and Balentine, 2011).
Calibration, data review and validation (QA/QC)
Quality Assurance and Quality Control (QA/QC) of the hydrologic data was fundamental to the USGS-BRD Land-Margin Ecosystem study. Gages located on the primary network transects (Shark and Lostmans) were scheduled for routine field visits every 30-60 days. Sensors were cleaned, calibrated and logger data were manually collected during each field visit. As needed, repair or replacement of faulty equipment was done.
Secondary network transect gages (CH1, CH2, LO4) were scheduled for visits every 90-120 days. Gage visits were made more frequently in response to observed data irregularities, or evidence of equipment failure and data loss. Monitoring equipment was calibrated or replaced (if inoperable) when field measured values exceeded acceptable study tolerance ranges. Instantaneous data were transferred to the USGS South Florida Information Access (SOFIA) web portal after project data was locally reviewed for quality assurance and control (QA/QC) and validation. Data is considered furnished data to the USGS SOFIA hydrologic database (Larsen, 2008).
Anderson, G.H., and K.M. Balentine. 2011. Standard Operating Procedures for USGS-BRD Land-Margin Ecosystem Study hydrological instrument calibration and quality control of physical water parameter data collected in Everglades National Park. BRD-USGS unpublished report. Homestead, FL, 29 p.
Larsen, M.C. 2008. Water Resources Discipline Policy on Accepting Furnished Records. U.S. Geological Survey, WRD Discipline Policy Memorandum 2008.01. Reston, VA.
UNESCO. 1985. The International System of Units (SI) in Oceanography. Techn. Pap. Mar. Sci., 45: 124 p.
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 21 December, 2015 @ 08:10 AM(KP)