(c) Infiltration increase process (d) Total water reduction process
Figure 9. Water quantity change when pumping water all the time
where Q1 is the base flow, Q2 is the reduced base flow, Q3 is the induced infiltration, and Q4 is the total water reduction.
To simulate the natural recovery of the wetland when groundwater pumping is stopped after groundwater exploitation, we made some changes based on the original model. The simulation duration of the model is still 7200 days, and the pumping duration is 3600 days. When the simulation is carried out for 3600 days, the five pumping wells are closed until the end of the full simulation. After pumping is stopped, the water exchange between the wetland and the piedmont plain aquifer is similar to the inverse of the three wetland–aquifer interaction processes during the pumping period.
When pumping was stopped at 3600 days, the base flow from zone 1 to zone 2 was 0, the infiltration from zone 2 to zone 1 was 4480.1 m3/d, and the water level at the location of the pumping wells was 4.0 m. When pumping was stopped, the induced infiltration gradually decreased, and after 840 days of pumping cessation, the infiltration from zone 2 to zone 1 became 104.75 m3/d. At this time, the base flow from zone 1 to zone 2 changes from 0 to 6.45 m3/d, which means that the groundwater cone of depression formed due to pumping is gradually recovering and the water level is gradually rising. The base flow also increases slowly from 0. When pumping was stopped for 930 days, the induced infiltration became 0, and the base flow became 130.11 m3/d. Until the end of the simulation, the base flow slowly recovered to 1960 m3/d.
Similarly, in the numerical model for the cessation of pumping after 3600 days, we plotted the curves of base flow, reduced base flow, induced infiltration and total water reduction with time, as shown in Figure 10. It is possible to observe when the base flow and infiltration appear and disappear, which could quantitatively describe the base flow and infiltration.
To investigate the effects of different hydraulic conductivities on the reduced base flow, induced infiltration and total water reduction in this quasi-ideal model, different hydraulic conductivities K=15, 20, and 25 m/d were used in the original model, and the pumping duration was also set to 3600 days. Pumping was stopped after 3600 days to observe the changes in the reduced base flow, induced infiltration and total water reduction under different conditions.