Analysis of Water Quality Improvement Effect of Controlled River by Multi-Functional Weir Operation

In this study, the water quality change in a stagnant controlled river containing hard management structures due to pulsed flow was simulated. The Environmental Fluid Dynamics Code (EFDC) model was used for the water quality change simulation, and the water quality improvement effect caused by pulsed flow was simulated for multiple scenarios. Based on Case 1, in which 274.2–291.8 CMS was discharged for five hours, other scenarios, in which the gate was opened by 0.5 m and 1.0 m while the discharge time was doubled, were simulated. On comparing the water level results with the observed data, a relatively positive result of R2 = 0.82 was obtained. The water quality simulation results showed that the concentrations of Chl-a, COD, and T-P were, respectively, approximately 7.7%, 4.5%, and 4.0% higher in Case 2 than in Case 1, 24 h after the start of discharge. Cases 3 and 4, on the other hand, exhibited decreased concentrations of Chl-a, COD, and T-P 24 h after the start of discharge. These results confirm that pulsed flow leads to different water quality improvement effects depending on the discharge amount and duration. Furthermore, the water quality improvement effect was recorded at close to 0% after 72 h in all scenarios. As the water quality improvement effect due to pulsed flow appears within 24 h and almost disappears after 72 h depending on the scenario, a physical solution to this problem is required.