# Analysis of the Water Quality Improvement in Urban Stream Using MIKE 21 FM
## 5 Model Verification and Analysis Results
### Model Verification Results  
To verify the constructed MIKE 21 FM model, observation data and simulation data were compared. Figure 9 shows the measured water quality data provided by the water environment measurement network of the Ministry of Environment in Korea. The water quality data observed between January and October 2018 and the water quality results at the same observation point by modeling simulation were compared.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Item** & **Contents** \\ \hline Model composition & Grid composition & Unstructured triangular grid system \\  & Number of grids & Number of grids for practical calculation: 905 \\  & & Gulpocheon inflow discharge: 2018 measured flow (Water \\  & Flow input data & Environment Measurement Network, 2019), Gulpop sewage treatment plant discharged water (Bucheonsi, 2019), Ozone treatment facility \\  & & reclaimed water (Incheon Environment Corporation, 2019) \\  & & Gulpocheon measured flow: 2018 Ministry of Environment Water \\  & & Environment Measurement Network data, \\  & Water quality input data & Sewage treatment discharged flow: 2018 Gulpop sewage treatment plant discharge data \\  & & Ozone treatment reclaimed water discharge flow: Ozone treatment \\  & & reclaimed water discharge flow (Incheon Environment Corporation, 2019) \\  & & BOD process: 1 st order decay (dissolved) = 0.5/d \\  & & Oxygen process: Secchi disk depth = 0.4 m, Temp. Coef. respiration = 1.08, \\  & & Half-saturation Conc. = 2 g/L \\ Simulation conditions & Main water quality constants & Nitrification: 1 st order decay rate = 0.05/d, Oxygen demand by nitrification, NH\({}_{4}\) to NO\({}_{2}\) = 3.42, Half-Sat. oxygen Conc. = 2 mg/L \\  & & Phosphorus process: Phosphorus content in dissolved BOD = 0.06, \\  & & Half-Sat. Conc. for P-uptake = 0.005 mg/L \\  & & Before supply of the reclaimed water: January to October, a total of \\  & & 300 days (2018) \\  & & After the supply of the reclaimed water: January to October, a total of \\  & & 300 days (2018) \\  & & Minimum time step = 0.01 s, Eddy coefficient = 0.28, Manning’s \\  & & roughness coefficient (river bed condition) = 1/32 \\  & & Case 1: Conditions of not discharging the ozone-treated reclaimed wastewater \\ Simulation case & & Wastewater \\ \hline \hline \end{tabular}
\end{table}
Table 2: Hydraulic and water quality simulation conditions.  
The comparison results at the same point through monthly observational water quality data and modeling simulation are shown in Figure 10.  
As shown in Figure 10, the water quality of the measured and simulated values was similar. In the case of BOD, the simulated values tended to be slightly lower than the observed values, and in the case of DO, the simulated values were generally high, but the trend was similar. Overall, TN and TP showed consistent results.  
Figure 11 shows the correlation with the R\({}^{2}\) values for the observed and simulation values as a result of the scatter graph.  
For BOD, DO, TN, and TP, the measured values and model values are expressed as R\({}^{2}\) values, respectively. Excluding DO, it was found to be more than 0.9, which was consistent with each other. In the case of DO, the R\({}^{2}\) value was about 0.8, but the overall trend of the simulated results was consistent. Using this built model, water quality change was compared according to the simulations before and after supplying ozone-treated reclaimed water in Section 5.3.  
Figure 10: Comparison of observed data and simulation results.  
Figure 9: Observation and water quality data [23].