# Analysis of Water Quality Improvement Effect of Controlled River by Multi-Functional Weir Operation
## 3 Results  
### Results of Scenario by Multi-Functional Weir Operation  
Numerical simulation was performed to analyze the water quality improvement effect of pulsed flow in the section between the Gangjeong-Goryeong Weir and the Dalseong Weir. Four scenarios were considered based on the gate operation method (Table 1). First, in Case 1, the actual pulsed flow at the Gangjeong-Goryeong Weir on 16 June 2015, was reproduced through numerical simulation. In Case 1, the basic discharge amount of the Gangjeong-Goryeong Weir was 274.2 m\({}^{3}\)/s, and a pulsed flow operation was performed to temporarily discharge up to 291.8 m\({}^{3}\)/s for five hours from 11:00 to 16:00. In Case 2, the pulsed flow duration was doubled to 10 h, and a maximum of 291.8 m\({}^{3}\)/s was discharged, similar to Case 1. To compare the water quality improvement effects based on the linked operations of the weirs located in the upstream and downstream areas, changes in the water quality according to the flow rate and flow velocity were compared in Cases 3 and 4 by opening the Dalseong Weir gate by 0.5 m and 1.0 m respectively, and the same pulsed flow conditions as in Case 1 were applied.  
Figure 6: Water Quality Simulation Validation (From January 2015 to December 2015).  
Figure 7 is a graph that compares water quality changes according to the weir operation scenarios in Table 1 at the Hwawon-naru water quality observatory. Each water quality concentration exhibited different variations depending on the pulsed flow scenario. In Case 1, the DO concentration increased and Chl-a, COD, T-N, and T-P showed a tendency to decrease after 11:00 when the pulsed flow was initiated. Water quality fluctuation was observed at the Hwawon-naru point in the downstream area of the Gangjeong-Goryeong Weir from the moment the pulsed flow operation began at 11:00 on 16 June 2015; flow rate and flow velocity also increased. The DO concentration increased and the concentrations of Chl-a, COD, T-N, and T-P decreased as the discharge time increased, indicating the water quality improvement effect of pulsed flow. However, the water quality fluctuation at the Goryeong point, located in the 15-km downstream area from Hwawon-naru, was smaller than that at Hwawon-naru; also, the water quality fluctuation exhibited inconsistent tendencies. Therefore, it can be concluded that the water quality improvement effect of pulsed flow at the Gangjeong-Goryeong Weir was concentrated in the upstream area and it decreased in the direction of the downtown area.  
\begin{table}
\begin{tabular}{c c c} \hline  & & **Scenario** \\ \hline Case 1 & Real Case & 16 June 2015 Pulse Discharge actual operating Weir (11:00–16:00, Discharge: 274.2 m\({}^{3}\)/s\(\sim\)291.8 m\({}^{7}\)/s) \\ Case 2 & Real Case & 16 June 2015 Pulse Discharge actual operating Weir + Discharge times, twice extended \\ Case 3 & Upstream Weir Operations & 16 June 2015 Pulse Discharge \\  & Upstream Weir Operations & + GangjeongGoryeong Weir, Dalseong Weir \\ Case 4 & Upstream Weir Operations & + GangjeongGoryeong Weir, Dalseong Weir \\  & & 1.0 m opening gate \\ \hline \end{tabular}
\end{table}
Table 1: Scenario Simulations of the Operating Weir.  
Figure 7: Scenario Comparison Results.