3.1 Stream discharge and temperature
Stream discharge was manually measured bi-weekly (May-August) or monthly
(September-April) using a horizontal-axis current meter (Global Water,
FP101) and the velocity-area method (Dingman 2002, p. 609) with an
expected uncertainty of up to 9 % (Hood, Roy, & Hayashi, 2006). A
stage-discharge rating curve was developed at each of the four stream
gauging stations (GS1 to GS4; Figure 1) using at least ten measurements.
A root mean squared error below 0.015 m3s-1 was obtained at all four gauging stations with the
largest errors occurring during the baseflow period. Water levels were
measured by pressure transducers (Solinst, Levelogger). A continuous
discharge record was computed by applying the rating curves to the
transducer data.
A number of different instruments were used to measure water
temperatures to reflect the spatial and temporal scales of interest.
Manual measurements were taken with a hand-held thermocouple thermometer
(Omega engineering, HH-25TC) during three spring temperature surveys and
for verifying continuous data. Temperature sensors (Maxime Integrated,
Ibuttons DS1921Z), coated in rubber (Plasti Dip) for waterproofing, were
used to measure longitudinal stream temperature profiles (T1 to T11),
spring branch temperatures (S1 to S3), and the temperature of the
Western tributary (T12). The thin rubber coating allowed the sensors to
reach thermal equilibrium in under 5-minutes. Each temperature sensor
was tied to a nail that was hammered into the streambed. A flat rock was
rested on each nail head to shield the sensor from solar radiation. The
pressure transducers (Solinst, Levelogger) also recorded temperatures in
the lake and at the stream gauging stations. Manufacturer-specified
accuracies are ±1°C and ±0.05°C for the Ibuttons andLeveloggers respectively. The accuracy of the Ibuttons was
improved to ±0.25°C following the method outlined in Johnson et al.
(2005). Sensors were calibrated in a constant temperature bath (VWR,
1157 Polyscience Refrigerated Circulator) over the range of temperatures
observed in the field. Streambed temperature was also monitored by anIbutton , installed in P1 (Piezometer 1), 40 cm below the
streambed (Figure 1).
Snapshots of stream surface temperature were captured with a thermal
infrared camera (FLIR, E95). The manufacturer-listed accuracy is ± 2 °C
and the thermal sensitivity is 0.04 °C. A programmable emissivity of
0.96 was used along with measured relative humidity and air
temperature.