## 3 Results and Discussion
### Optimization Results for the Jinggualiao Watershed (Step by Step)  
The determination process and the verified models were applied to the Jinggualiao watershed and the case tea farm to demonstrate its application and results. The bioretention cell was used as the control facility in this study, but other control measures or combinations of several LID facilities can also be suggested in different cases. Figure 5: The tea farm site and its bioretention cell used for verification of the site-scale SWMM LID module. (**a**) The boundary of the studied tea farm, (**b**) the location of bioretention cell in the downstream of the tea farm, (**c**) the dimension of the bioretenrion cell and (**d**) the profile section of the bioretention cell. Step 1: Set the management goal  
The water quality standard for the Jinggualiao stream is classified as in Taiwan as Class A, which is used for public drinking water and requires the highest water quality. The TP concentration standard was equal to or less than 20 \(\upmu\)g/L. For reservoirs in Taiwan, phosphorous, rather than nitrogen, is the pollutant of concern [23; 24]. As one of the upstream areas of the Feitsui Reservoir, the average TP concentration of the Jinggualiao was approximately 18.44 \(\upmu\)g/L, which was higher than that of other streams. However, the average TP concentration of the Jinggualiao watershed was less than the TP standard requirement, 20 \(\upmu\)g/L. Not all data were less than the standard value. Using the achievement rate to indicate water quality, the average achievement rate was only 58.3% (Table 1). Therefore, the achievement rate is a better indicator than the average TP concentration to set as the management goal for this case study. Step 2: Apply the verified watershed model  
The verified watershed model aims to link pollution exposure from the watershed and the resulting water quality. From Step 1, the current water quality status was available, and the achievement rate was selected as the management goal indicator. However, the observed data were collected once a month, and an annual trend was hardly seen. When the results from the verified model were used, the daily water quality could be used to supplement the management goal data. The comparison of observations and simulations of water quality are summarized in Table 2. The achievement rates were quite different, 58.3% from the observations and 79.93% from the simulations. This is because one was based on monthly data while the other used daily data. Because most water quality parameters were below the standard, the percentage that achieves the requirement would increase. In the following steps, the modeling tools use this information; therefore, the management goals were set to 85% and 90% of the TP concentration achievement rate based on the simulation results. These goals were then regarded as the short-term and long-term management goals for the Jinggualiao stream. Step 3: Find the required reduction loads  
After setting the TP achievement rate to 85% and 90%, the next step was to find the required reduction loads. In this step, a trial process is needed. In the SWMM model, users \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Year**} & **TP Concentration (\(\upmu\)g/L)** & **Achievement Rate** \\  & **(\(\mathbf{n}\) = 12 per Year)** & **(\(\mathbf{n}\) = 365 per Year)** \\ \hline
2015 & 17.92 & 75.0\% \\
2016 & 21.08 & 25.0\% \\
2017 & 16.33 & 75.0\% \\ \hline Average & 18.44 & 58.3\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The average TP concentration and the achievement rate of the Jinggualiao stream from 2015 to 2017.