## 4 Results and Discussion  
### Defining Dam Affected Periods  
The flowrate of all events from 2007 to 2012 was computed based on Equation (3) in Section 3.2 and is shown in Table 1. It is clear to see that, in 2008, 2009, and 2010, especially in the 2008 event, the flow rate computed using observation data was smaller than other years. This may be due to the water storage of Hwanggang dam in those periods. This conjecture is reliable when referring to the observed rainfall in the same period at Gunnam station, where the streamflow was influenced directly and strongly by dam operation. In some events, the periods of storing water generally took place shortly before or after the period of releasing water from the dams.  
In Figure 2, the simulations reflect the behavior of river discharge corresponding to the amount of rainfall that fell in the event and do not consider the impact of the dam. Compared to simulations, in many rainfall events, the observed discharge is underestimated and does not correspond to the rainfall amount in the event, as indicated in the figure. Referring to the flow rate computed in Table 1, such underestimation is expected due to the loss of the water volume that was stored on the dam in the period.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Flow Rate (\%)**} & \multicolumn{3}{c}{**Observation**} & \multicolumn{3}{c}{**Simulation**} \\ \cline{2-7}  & _Gunnam_ & _Jeonkok_ & _Jeogseong_ & _Gunnam_ & _Jeonkok_ & _Jeogseong_ \\ \hline
2007 & 30.39 & 25.59 & 31.51 & 19.97 & 17.17 & 19.30 \\
2008 & 15.77 & 19.83 & 19.64 & 21.61 & 20.51 & 21.30 \\
2009 & 18.05 & 27.19 & 20.69 & 20.97 & 21.13 & 21.29 \\
2010 & 17.92 & 33.32 & 23.68 & 22.10 & 21.70 & 21.80 \\
2011 & 24.38 & 26.07 & 23.83 & 22.14 & 20.86 & 21.07 \\
2012 & 19.51 & 20.66 & 19.40 & 18.95 & 16.38 & 18.39 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Flow rate (%) of 6 flood seasons from 2007 to 2012.  
The duration of release and storage of water from the dam is shown in Table 2. The duration of water storage is the time when the behavior of precipitation and streamflow at Gunnam station did not correspond. The periods are not coincident because the dam is generally storing water when not discharging.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multicolumn{2}{c}{**Water Release**} & \multicolumn{2}{c}{**Water Storage**} \\ \cline{2-5}  & _Starting Date_ & _Ending Date_ & _Starting Date_ & _Ending Date_ \\ \hline
2007 & 17 May 2007 & 18 May 2007 & - & - \\
2008 & No information & No information & 20 July 2008 & 22 July 2008 \\
2009 & 6 September 2009 & No information & 25 July 2008 & 27 July 2008 \\  & 27 June 2010 & 27 June 2010 & 12 August 2009 & 14 August 2009 \\
2010 & 18 July 2010 & 19 July 2010 & 13 August 2010 & 17 August 2010 \\  & 21 July 2010 & No information & 25 August 2010 & 27 August 2010 \\  & 4 September 2010 & No information & 10 September 2010 & 12 September 2010 \\
2011 & 27 June 2011 & 30 June 2011 & - & - \\  & 13 July 2011 & No information & 16 August 2012 & 18 August 2012 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Durations of water release and water storage in Hwanggang dam (The red letters express the durations where dam operation affected the simulation period).  
Figure 2: The simulated and observed discharges at Gunnam station in 6 flood events (2007, 2008, 2009, 2010, 2011, and 2012) without considering dam impact. The purple dotted line expresses the periods affected by the dam releasing water, and the orange dotted line expresses the suppositional periods affected by the dam storing water.