(c) Infiltration increase process (d) Total water reduction process
Figure 11. Water quantity change of different hydraulic conductivity
volume until the end of the simulation is also proportional to the size
of the hydraulic conductivity. Different from the reduced base flow, the
value of induced infiltration is inversely proportional to the size of
the hydraulic conductivity, and the time when the induced infiltration
becomes zero after pumping is stopped is also inversely proportional to
the size of the hydraulic conductivity. In general, the total water
reduction is directly proportional to the size of the hydraulic
conductivity.
Under the condition that water is pumped throughout the simulation
period, the groundwater divide between the pumping wells and the wetland
caused by groundwater exploitation in the wetland–aquifer interaction
model is quantitatively portrayed based on the water exchange between
zone 1 and zone 2, and the base flow from the piedmont plain aquifer to
the wetland is continuously reduced until it becomes zero, while the
reverse groundwater recharge from the wetland is induced to the piedmont
plain aquifer. During the full simulation period, the reduced base flow
increased rapidly in the early stage and was relatively flat in the
later stage. The reduced base flow responded to pumping immediately,
while the induced infiltration began to occur only when the groundwater
divide spread to the wetland boundary and groundwater in zone 2 flowed
to zone 1, with a certain lag. The longer the pumping time, the more
dominant the effect of induced infiltration on wetland degradation.
In the model with cessation of pumping after 3600 days, the situation
for the first 3600 days was the same as that of pumping for the entire
time. The natural recovery process of the wetland after pumping
cessation is an inverse wetland–aquifer interaction process. The
gradual reduction of induced infiltration from zone 2 to zone 1 and the
recovery of base flow from zone 1 to zone 2 characterize both the
reappearance of the groundwater divide between the wetland and the
pumping well and the disappearance of the groundwater divide with
increasing pumping time. The groundwater flow direction in the whole
simulation area resumed to flow from west to the east again. After the
cessation of exploitation, the effect of reduced base flow on wetland
degradation shows a certain lag after pumping cessation. In contrast,
the effect of induced infiltration on wetland degradation responds
instantly. At the end of the simulation, the only cause of wetland
degradation is the reduced base flow.
Numerical simulations with different hydraulic conductivities showed
that the effect of reduced base flow on wetland degradation is
proportional to the hydraulic conductivity in the process of groundwater
exploitation and natural recovery of wetlands. However, the inflection
point at which the reduced base flow decreases with increasing pumping
time is inversely proportional to the hydraulic conductivity, and the
effect of induced infiltration on wetland degradation decreases with
increasing hydraulic conductivity in this model. The total water
reduction of wetlands increases with increasing hydraulic conductivity.