# Analysis of the Water Circulation Structure in the Paldang Reservoir, South Korea
## 2 Materials and Methods
### Field Surveys  
For the continuous depth-specific hydraulic surveys, the ADCP (Model WH-600, RD Instruments) was deployed to measure the flow velocity and direction. The measurements were performed at a time interval of 10 min, and the lateral spacing of the ADCP measurements was set to 0.2-0.5 m, thus allowing for a blank range of less than 1 m above the riverbed (Figure 2). The upper 20% and 50% and the lower 20% in terms of depth were defined as the surface, middle, and lower layers, respectively. The flow velocity and direction information was extracted from the raw measurement data, and during this extraction, the outliers were removed and data were calibrated to true north. The flow velocity variation and the average flow of the Paldang Reservoir were determined by examining the time-series of flow velocity and direction, flow velocity rose diagrams, vertical distributions of residual current, and velocity vector diagrams at individual stations. The bottom sediment at survey sites was examined for granularity to ensure the stable installation of the measuring instruments, and the potential risk of sinking was also investigated for the measuring instruments. By attachment to a trawl-resistant bottom mount (TRBM), ADCPs were moored on the bottom surface in such a way as to avoid the loss of a device caused by fishery activities and vessel traffic and to ensure the stability of the data collection. The TRBM was fastened to the bottom surface by an anchor to prevent the measuring instruments from being swept away by high-velocity flow. In this study, water temperature gauges for the moorings (Model TR-1050 and TR-1060, RBR Ltd.) were used to perform continuous surveys on the water temperature at different water depths. The measurement time was set to 10 s, and the water temperature gauge was attached to the mooring line with a vertical spacing of 1 m (Figure 2). The measured temperature data were inspected for quality control purposes, and the time-series and vertical distributions of water temperature, as well as preliminary analyses, were compared to each other in order to determine the spatiotemporal characteristics of the water temperature variation. Furthermore, water temperature data were averaged at 10 min intervals and interpolated by using the Kriging technique [35; 36; 37; 38] in order to perform a comprehensive analysis that also covered the ADCP data. The parameters used in the Kriging interpolation are listed in Table 1. The measuring instruments were securely fastened to mooring chains  
Figure 2: Installation of the water temperature gauge and acoustic Doppler current profiler (ADCP). The TRBM is the trawl-resistant bottom mount. and anchors to avoid being swept away by high-velocity flow. Furthermore, buoys were connected to the instruments and other markers, such as flags and night navigation lights, that were also installed to ensure navigation safety and to prevent damage to the instruments in the event of a ship collision. For local meteorological observations, an integrated meteorological sensor (Model WXT520, VAISALA) was deployed to measure wind velocity, wind direction, relative humidity, temperature, pressure, and precipitation, with the measurement time being set to 1 min. For the installation of a bottom-mount meteorological sensor, the base stand for the observation system was placed in a fixed position on the rooftop of a building located at the confluence of the South Han River and the North Han River and at the point closest to the Paldang Reservoir while being unaffected by the surrounding terrain. The observed meteorological data, including hourly wind velocity and direction, temperature, humidity, pressure, and rainfall amount, were compared with the observational data obtained from the Yangpyeong and Cheongpyeong weather stations, which are both located within the Paldang Reservoir, in order to determine spatiotemporal meteorological characteristics.