## 4 Results and Discussion
### Surface Water and Groundwater Interactions
#### 4.2.4 Effects of the Artificial Recharge on the Local Water Cycle  
The flow directions of the Kaoping, Tungkang, and Linien Rivers are generally in a north-south direction to the Taiwan Strait in the downstream fan area. With the intensive developments of aquaculture and agriculture industries, the downstream fan area had faced severe problems of groundwater over-pumping and groundwater contamination [20]. An artificial recharge project was proposed recently to mitigate the impact of over-pumping near the coastal area. The artificial lake with a total area of approximately 3 km\({}^{2}\) was planned to be located in the upstream region of the Linien river (see 18 th HRU in Figure 5). This area is the same as the determined zone with the highest head differences in wet and dry seasons (see Figure 7b). The operations of the artificial lake in the model follow the designed strategies. In the GSFLOW model, the initial stage was 40 m, specified based on the averaged local altitude near the artificial lake. The operation of the lake stages varies from 34 to 51 m, depending on the river stages. Scenarios with and without the artificial lake were considered to quantify the effect of the artificial lake on the local SGIs. Note that the cases for the comparison used the full PPG for the modeling domain. In the GSFLOW model, the case without the lake did not have the 18 th HRU, while the case with the lake added the 18 th HRU in the simulation domain. The study used the lakebed hydraulic conductivity the same as the streambed hydraulic conductivity in the stream cells. Other parameters such as the precipitation in the lake area and evaporation from the lake are the same as those in the case without the artificial lake.  
Figure 14: The summary of volumetric flow rates for the water cycle components in the entire PPG, upstream fan, and downstream fan areas. Note that the blue and red colors represent the flow rates for the upstream and downstream fans.  
There are additional terms in the water cycle for the case with the artificial lake. We exported the results from the GSFLOW model and presented the water fluxes in Figure 15. Because the lake has a relatively small area as compared to the entire PPGB, the contribution of the artificial lake on the water budgets is insignificant. For the cases with and without the lake, we had fixed the simulation conditions and the associated hydrogeological parameters. The slightly different fluxes in the water cycle can be considered as the effect of the artificial lake on the regional water budgets. Simulation results show that the lake can reduce the direct infiltration, surface runoff, and interflow because the land area had been replaced by the artificial recharge lake (see Figure 15). The influence of the artificial lake on the SGIs near streams is insignificant. Such a result indicates the small impact of the artificial recharge lake on the surface water environment. In the study, the case with the lake shows that the component of the averaged groundwater recharge increases \(0.04\times 10^{6}\) m\({}^{3}\)/d, which is approximately \(1.46\times 10^{7}\) m\({}^{3}\) in a year. The result of groundwater recharge is based on the available water budget components in the PRMS. The dynamics of the interactions in the local area might need smaller scales of HRUs and the associated observations to validate the model.