2.2 Raft and Shore Flux Tower
Figure 3 shows the two flux towers that were deployed on the research site: a 3 × 3-m raft (measurement height of 2.0 m) deployed from June to October each year and a permanent shore tower (measurement height fluctuating between 11 and 28 m depending on the water level) (Fournier et al., 2021; Pierre et al., 2022). At both sites, the eddy covariance technique was used to calculate turbulent heat fluxes from raw 10-Hz turbulence data.
The raft was anchored between two islands to offer protection against large waves, in a 30-m deep section of the reservoir. The raft hosted a fast-response sonic anemometer coupled with an infrared gas analyzer (IRGASON, Campbell Scientific, USA), a net radiometer (Kipp & Zonen, The Netherlands) and a temperature probe, all mounted 2 m above the water surface. Turbulence sensors were oriented eastward to capture the prevailing wind directions while minimizing flow distortion by the mast. The raft slowly oscillated along its three Euler angle axis due to wave-induced motions. To decontaminate raw wind measurements, an accelerometer (AHRS, Lord Sensing MicroStrain, USA) was attached adjacent to the anemometer to record pitch, yaw, and roll angles at a frequency of 10 Hz.
At the shore site, the flux tower was equipped with a combined sonic anemometer and infrared gas analyzer (IRGASON, Campbell Scientific, USA), installed 11 m above the maximum water level and pointing toward the reservoir in the NNW direction. A complete meteorological setup was also deployed: a TB4 tipping bucket (Hyquest Solutions, USA) for rainfall measurement, a propeller anemometer (05103, R.M.Young, USA), and a four-component net radiometer (CNR4, Kipp & Zonen, The Netherlands). The last two instruments were installed at heights of 10.3 m and 12.3 m, respectively. The radiometer measured all terms of the radiation budget, namely incoming and outgoing shortwave and longwave radiation, but since the instrument was installed on the shore, it did not report the radiation emitted/reflected by the reservoir.