Figure 5. Contour of groundwater level for 270 days of pumping
When the pumping time is 300 days, the base flow from zone 1 to zone 2 becomes 1313.8 m3/d; at the same time, some water flows from zone 2 to zone 1 with a volume of 41.12 m3/d, which means that the water from the wetland recharges the piedmont plain aquifer, and the process can be described as induced infiltration. The area of induced infiltration is initially distributed in the center at the junction of zones 1 and 2. This is because the pumping wells are located in the middle of the study area, and the extent of the cone of depression formed during pumping is also roughly distributed in the middle. The inversion of the hydraulic gradient in the middle of the study area causes the groundwater flow direction to change from east to west, while the edge is relatively less affected by pumping, which can be clearly observed in Figure 5. Another reason for setting the pumping wells in the middle of the study area is that the south and north boundaries of the model are no-flux boundaries, and the contour of the groundwater level is perpendicular to the south and north boundaries. If the pumping wells are located too close to the no-flux boundaries, with the increase in pumping time, the formed cone of depression will definitely affect the groundwater flow direction at the south and north boundaries, which does not match the set boundary conditions.
As the pumping process continues, the area where the hydraulic gradient is inverted becomes increasingly larger, while the infiltration volume of zone 2 flowing to zone 1 increases, and the base flow of zone 1 flowing to zone 2 decreases. The base flow from zone 1 to zone 2 is reduced to 0.69 m3/d when pumping is carried out for 1440 days. At this time, due to the reversal of the hydraulic gradient, the infiltration from zone 2 to zone 1 increased to 2661.5 m3/d, and the water level at the location of the pumping wells dropped to 5.0 m. When pumping was carried out for another 30 days and the simulation duration was 1470 days, the base flow from zone 1 to zone 2 became 0, which means that the groundwater divide formed between the wetland and the piedmont plain due to pumping had spread to the wetland boundary, as shown in Figure 6. The groundwater in