# Analysis of the Water Quality Improvement in Urban Stream Using MIKE 21 FM
## 4 Model Building and Data  
Building of water quality using the MIKE 21 FM model was based on the reports and observational data of 'An Implementation Plan for the Total Water Pollution Management of the Hangang Water System in Incheon Metropolitan City (Incheon Metropolitan City, 2014)', Gulpocheon Stream Maintenance Basic Plan (Incheon Metropolitan City, 2009), and Water Environment Information System [(23)]. The inflow and outflow analysis simulation conditions were established based on the hydraulic and water quality input data investigated in this study. For the application of the water quality model to the Gulpo A unit basin (Gulpocheon water system), which is the targeted water quality maintenance region, the basin was classified into a total of five reaches. Each reach was classified into 64 calculational units with a constant interval of 0.2 km, and the water quality model was designed. For the Gulpocheon topography, the cross-sectional data presented in the Gulpocheon stream maintenance basic plan was used. Among the MIKE Zero modules, boundaries were built using the Mesh Generator. A triangular grid was used considering the elevation of the Gulpocheon topography. The total number of triangular grids was 905. The shapes of the small waterways and loops at the upstream were materialized in detail. Figure 7 presents the analysis region and grid of Gulpocheon. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Statistical** \\ **Parameters** \\ \end{tabular} } & \multicolumn{4}{c}{**Upstream**} & \multicolumn{4}{c}{**Middleream**} & \multicolumn{4}{c}{**Downstream**} \\ \cline{2-13}  & \begin{tabular}{c} **DO** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **BOD** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **TN** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **TP** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **DO** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **TN** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **TP** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **DO** \\ **(mg/L)** \\ \end{tabular} & \begin{tabular}{c} **BOD** \\ **(mg/L)** \\ \end{tabular} & \
\begin{tabular}{c} **TN** \\ **(mg/L)** \\ \end{tabular} &
\begin{tabular}{c} **TP** \\ **(mg/L)** \\ \end{tabular} \\ \hline Average & 7.04 & 4.01 & 4.59 & 0.17 & 9.05 & 10.07 & 8.02 & 0.33 & 6.70 & 7.16 & 7.20 & 0.32 \\ Minimum & 2.3 & 1.2 & 1.689 & 0.017 & 2.9 & 1.7 & 3.807 & 0.109 & 1.9 & 2.6 & 3.795 & 0.139 \\ Maximum & 12.4 & 9.7 & 11.593 & 0.522 & 16.2 & 46 & 15.642 & 1.068 & 10.4 & 20.1 & 11.946 & 1.759 \\ S.D. & 2.81 & 2.39 & 2.75 & 0.12 & 3.06 & 10.56 & 2.74 & 0.25 & 2.44 & 3.54 & 2.04 & 0.26 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Statistical analysis of observed water quality. Figure 6: Observed water quality by location. The flow and water quality conditions using the MIKE 21 FM model were set up using the 2018 actual measurement data and data obtained from organizations (Bucheonsi and Public Health and Environment Research Institute). For the flow data, the conditions before and after the supply of the base flow were set to have the same boundary conditions (i.e., primary external force conditions, such as temperature and water quality), according to the schematic diagram of a water system (An Implementation Plan for the Total Water Pollution Management of the Hangang Water System in Incheon Metropolitan City, 2014). The annual water quality data was established based on the actual measurement data and information system. The data of Incheon Environment Corporation, a facility management agency, was used for evaluating the water quality concentration of the ozone-treated discharged water. The data provided by Bucheonsi was utilized for the Gulpocheon sewage discharged water data. The input water quality based on the water quality measured in 2018 is presented in Figure 8. To set up identical water quality boundaries for the ozone-treated reclaimed water discharge conditions, the 2018 water quality was applied.