(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.