Methodology
A brief description of data-recording frequencies, instrument accuracies, and data-processing methods are presented below. Complete data-processing methods for the data presented in this report are documented in USGS Open-File Reports by Riscassi and Schaffranek (2002, 2003, 2004), available in the Publications section.
Velocity Measurements
Flow velocities were measured bi-hourly at a fixed location in the water column using 10 MHz acoustic Doppler velocity (ADV) meters. The ADV meter measures flow velocity to a resolution of 0.1 mm/s with an accuracy of 1 percent of measured velocity (SonTek, 2001). Velocities were measured at 10 Hz in a 1-minute burst yielding 600 samples. Velocity samples were filtered and edited according to criteria suggested by the instrument manufacturer and developed in processing and concurrent analysis of the flow data. Both quantitative filters and qualitative editing methods were used to quality check and verify data accuracy. A minimum statistical correlation of 70 percent and a minimum of 200 valid samples were used as quantitative filters. A minimum acoustic signal quality of 5 decibels (dB) was considered in qualitative analysis and data editing. Data that did not pass the filtering and editing criteria are not presented in this report.
Conductivity and Temperature Measurements
Conductivities and temperatures were measured bi-hourly at a fixed location near the plant litter layer using MicroCAT model SBE 37-SI meters. The MicroCAT meter measures conductivity to a resolution of 0.1 µS/cm with an accuracy of 3.0 µS/cm and temperature to a resolution of 0.0001 °C with an accuracy of 0.002 °C (Sea-Bird Electronics, 1999). Measured conductivity was converted to specific conductance for reporting purposes according to methods documented in Riscassi and Schaffranek (2002).
Temperature-Profile Measurements
Temperatures were measured at 5-, 15-, or 30-minute intervals at 5- or 10-cm depth increments throughout the water column, on the water surface, and in the air immediately above the water surface using glass-encapsulated thermistors manufactured by Yellow Springs Instruments (YSI). The YSI thermistor measures temperature to an accuracy of 0.1 °C over a 0 to 70 °C range (Yellow Springs Instruments, 1998). Thermistor readings were converted to temperatures according to methods documented in Riscassi and Schaffranek (2002).
Water-Depth Measurements
Continuous water depths at the monitoring stations were determined by correlating local water depths measured during intermittent site visits to stages continuously recorded at nearby USGS and NPS hydrologic-monitoring stations. Negative values indicate water levels below ground surface.
U.S. Department of the Interior, U.S. Geological Survey, Reston, VA, USAContact: Raymond W. Schaffranek