# Analysis of the Water Circulation Structure in the Paldang Reservoir, South Korea
## 3 Results
### Analysis of Monitoring Data
#### 3.1.2 Water Temperature  
Time-series of vertical water temperature distributions for different stations are illustrated in Figures 6-8. The water temperature gradients (DT/DZ) were normally less than 1 \({}^{\circ}\)C at all sites in the early stage of observations, from May 12 through May 22, which corresponded to the vertical mixing period when the water temperatures in all layers continued to rise. In contrast, the water temperature gradients increased at a later stage, from May 28 to June 17, which corresponded to the stratification period when the water temperature gradients greater than 1 \({}^{\circ}\)C were commonly observed. Moreover, the water temperature in the middle and lower layers remained constant while the water temperature in the surface layer steadily increased. The discharge water temperatures were compared between the CPD located in the North Han River and the IPW in the South Han River, both of which flow into the Paldang Reservoir. The results showed that the influent water temperatures at both locations were similar to each other in the early stage of observations, but the influent water temperatures of the South Han River were more than 7 \({}^{\circ}\)C higher than those of the North Han River in the later stages. At PC1 (the lower reaches of the North Han River), the average water temperatures were 21.82 and 17.76 \({}^{\circ}\)C at 1 and 8 m below the water surface, respectively; see Figure 6. The highest and lowest water temperatures at 1 m below the water surface were  
Figure 6: Profiles and time series of the water temperature, flow velocity, and Richardson number at PC1. Figure 7: Profiles and time series of the water temperature, flow velocity, and Richardson number at PC2. At PC2 (the lower reaches of the South Han River), in Figure 7, the average water temperature was 25.01 \({}^{\circ}\)C at 1 m below the water surface and 17.65 \({}^{\circ}\)C at 8 m below the water surface. The highest and lowest water temperatures were 28.47 and 21.46 \({}^{\circ}\)C at 1 m below the water surface, respectively, which amounted to a difference of 7.01 \({}^{\circ}\)C. Furthermore, the highest and lowest water temperatures were 18.59 and 16.91 \({}^{\circ}\)C, respectively, at 9 m below the water surface, which amounted to an insignificant difference of 1.68 \({}^{\circ}\)C. The highest and the average water temperatures of the surface layer at PC2 were greater than those at other stations, and the highest water temperature gradient was observed at PC2. During the vertical mixing period, the water temperatures above 20 \({}^{\circ}\)C was 26.02% at 1 m below the water surface, and the water temperatures below 17 \({}^{\circ}\)C was 0.54%. No water temperatures above 20 \({}^{\circ}\)C were observed at 8 m below the water surface, while the water temperatures below 17 \({}^{\circ}\)C was 67.98%. During the stratification period, no water temperatures below 20 \({}^{\circ}\)C were observed at 1 m below the water surface. The water temperatures above 25 \({}^{\circ}\)C was 46.14%. No water temperatures above 20 \({}^{\circ}\)C were observed at 9 m below the water surface, and all of the data were distributed across temperatures ranging from 17 to 19 \({}^{\circ}\)C, thus indicating that there was little variation in the water temperature. At PC3 (in the vicinity of the PDD), the average water temperature was 22.67 \({}^{\circ}\)C at 1 m below the water surface and 17.32 \({}^{\circ}\)C at 19 m below the water surface, while the highest and lowest water temperatures were 26.64 and 16.89 \({}^{\circ}\)C, respectively, at 1 m below the water surface, which amounted to a difference of 9.75 \({}^{\circ}\)C. The highest and lowest water temperatures at 9 m below the water surface were 18.96 and 15.02 \({}^{\circ}\)C, respectively, which amounted to a difference of 3.94 \({}^{\circ}\)C. At PC3, the rates at which the highest, average, and lowest water temperatures dropped with water depth decreased, to a great extent, to nearly 1 \({}^{\circ}\)C/10 m at 7 m below the water surface.