Data collected at the Broad River, Harney River, and Shark River stations include water level, water velocity, specific conductance and temperature, total and dissolved phosphorus species, pH, and dissolved oxygen. These three stations were established in 1997.
Flow, nutrient concentrations, and nutrient load data will provide part of the basic information needed to understand the hydrologic and water-quality characteristics for a part of the southwest coast of Florida. The analysis of these measurements will help characterize the current conditions for the three sites and explain the relation between upgradient water levels and southwest coastal stream flows, and the possible interaction between southwest coastal waters and the waters of Florida Bay. The data can also be used as input to hydrodynamic and water-quality models.
10500 University Center Drive, Suite 215
Friedman, L. C.
Levesque, V. A.; Fritz, E. M.
Levesque, V. A.; Woodham, W. M.
Continuous monitoring of water-level, stream velocity, and specific conductance combined with periodic discharge measurements and collection of water-quality samples were required to compute the discharge and nutrient flux from the five estuarine river stations. Stream velocity (index-velocity) data were used to estimate the mean cross-section channel velocity (mean velocity) that was measured using a vessel-mounted acoustic Doppler discharge measurement system. Stream velocity data were used with the measured mean channel velocity to develop index-to-mean velocity relations. Each station was equipped with similar instrumentation. Data collected at each station were reviewed for accuracy and entered into the USGS NWIS database. Data for each station were then used to develop regression equations that were used to estimate water discharge and nutrient flux.
Water-Level and Velocity Measurements Water level was measured at each station using Design Analysis Associates H-310 vented-submersible pressure sensors that were mounted within 2-in. inside-diameter polyvinylchloride (PVC) pipes with end caps, which functioned as stilling wells. Quarter-inch holes were drilled around the perimeter of the PVC pipe within 6 in. of the bottom. Pressure sensors were programmed to average over an 8-second period every 15 minutes. Distances to water-level surfaces were measured from fixed reference points every 4 to 6 weeks and compared to the water levels measured by the pressure transducers. Water-surface reference measurements varied less than 0.02 ft from the pressure transducer water levels during the study.
Two types of vertically oriented acoustic Doppler velocity systems were used to measure 2-min averages of velocity through the water column every 15 minutes:
(1) SonTek ADP 1.5 and 3 MHz velocity profilers, and (2) SonTek Argonaut-XR 3 MHz depth-averaging velocity sensors.
Vertically oriented velocity profilers were used because vertical stratification of flow was possible, and because these sensors allow variations in the velocity profiles in the water column to be measured during all conditions. One drawback to using a vertically oriented index-velocity system is the limited amount of across-channel volume that is measured. In rivers and streams with variable cross-channel flow distribution, this could prove to be a problem. If water flow is relatively uniform and flow patterns are always the same across the channel, vertically oriented sensors can provide an alternative to horizontally oriented index-velocity systems.
Discharge Measurements River discharge was measured directly using a vessel-mounted acoustic discharge system (Simpson and Oltmann, 1992). An RD Instruments 1.2 MHz acoustic Doppler discharge measurement system was used to measure discharge for calibration and validation of the index-to-mean velocity relation at all stations every 4 to 6 weeks. The discharge section edges were marked with buoys and unmeasured edge section distances were measured using optical and laser range finders. Discharge values were calculated using manufacturer's software. Individual discharge measurements took between 4 to 10 minutes to complete.
Discharge measurements were collected over varying ranges of tidal level and tidal phase for about one year to develop an index-to-mean velocity relation for each station. Multiple measurements were made during 3- to 6-hour periods to better characterize variations in flow caused by variations in tide, inflow, and wind effects, and to reduce serial correlations between measurement sets. Discharge data collected after the calibration period were used to check the accuracy of the water-level/velocity/discharge relations for the duration of the study and to apply corrections or shifts to the index-to-mean velocity relations if required. Corrections to the velocity regressions were not required at four of the five stations during the study. The Harney River station index-velocity data were corrected for June 1998 because of an electronics problem that caused the index-velocity data to be biased low.
10500 University Center Drive, Suite 215
U.S. Department of the Interior, U.S. Geological Survey, Center for
Coastal Geology
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