## 3 Results and Discussion
### Effect of Spillover  
3.2.1. 15-Days Period  
Figures 8-11 show the measured and calculated concrete temperatures at three downstream gauges (TC1 and TC4 located in the upper borehole, and TC6 located in the lower borehole), with and without the effect of spillover, and at one upstream gauge (TC5), considering the water level of the reservoir, and also the measured air temperatures (or water temperatures, Figure 10) and the height of spillover during the analyzed 15-days period, from 10 May to 25 May 2014.  
It can be seen from Figures 8 and 9 that the calculated concrete temperatures at the downstream gauges TC1 and TC4, when taking into account the effect of spillover, are in very good agreement with the measured concrete temperatures during the whole period (the root mean square error (RMSE) is 1.95 at TC1 and 1.73 at TC4, whereas the mean absolute error (MAE) is 1.39 at TC1 and 1.67 at TC4).  
The measured and calculated concrete temperatures at the upstream gauge TC5 (Figure 10), during the period of spillover, or more precisely, during the period when the water level of the reservoir is above the altitude of gauge TC5, are in very good agreement (RMSE is 0.45 and MAE is 0.31).  
Figure 8: The concrete temperatures at gauge TC1 during the analyzed 15-day period.  
Figure 11: The concrete temperatures at gauge TC6 during the analyzed 15-day period.  
Figure 10: The concrete temperatures at gauge TC5 during the analyzed 15-day period.  
Figure 9: The concrete temperatures at gauge TC4 during the analyzed 15-day period.  
From Figure 11 it can also be seen that there is very good agreement between the measured and calculated concrete temperatures at gauge TC6, taking into account the effect of spillover, assuming that the height of the spillover must be at least 0.1 m, otherwise the exposed surface of the lower downstream borehole is not wetted (RMSE is 1.28 and MAE is 1.07).  
Figure 3 shows the minor amount of spillover (when the height of spillover is less than 0.1 m), where it can be seen that the exposed surface of the upper borehole, with gauges TC1 to TC4, is wetted irrespective of the height of spillover, whereas the exposed surface of the lower borehole, with gauge TC6, is not wetted at a spillover height of less than 0.1 m, since it is located outside of the central cross-section of the dam and therefore not reached by the wetted area of the downstream side of the dam.  
The maximum (or minimum) temperature at the specific point in concrete occurs later than the maximum (or minimum) air temperature. This time difference is termed the time lag and depends on the distance from the concrete surface. At a depth of 0.1 m (gauges TC1 and TC6) the time lag was fairly short (at maximum temperatures 1 to 2 h, and at minimum temperatures 3 to 4 h). At a depth of 0.2 m (gauge TC2) the time lag was slightly longer (at maximum temperatures 2 to 3 h, and at minimum temperatures 4 to 5 h). At a depth of 0.3 m (gauge TC5) the time lag at the maximum temperatures was 5 to 6 h, and 6 to 8 h at the minimum temperatures. At a depth of 0.5 m (gauge TC3) the time lag was already 10 to 12 h, and at a depth of 1.0 m (gauge TC4) the time lag was even several days.