Geoscience Reference
In-Depth Information
Chongming island area represents the regional water flow because of rarely
exploitation, and appears remarkably different in the south of estuary. In
fact, Shanghai city was the center of heavy extraction in the study area dur-
ing 1949-1966. After limitation of pumpage and implementation of artificial
recharge in order to control land subsidence, groundwater level in the city
was rising gradually. Contrarily, more and more groundwater was pumped
in adjacent region. These induced the groundwater flow changed from con-
vergent movement to divergent, centered on the urban district of Shanghai.
It is obvious that the variety of artificial discharge/recharge intensity is
the main driving force for groundwater flow change. Even the flow field
change can result in the enlargement/shrinkage of freshwater range in
the urban.
5. Groundwater System
Summing up above contents, three groundwater systems in the study could
be divided (see Table 2): (a) shallow system. It has never been used due
to bad water quality, so groundwater evolves naturally though dilution by
rainwater by and large and by surface water in local; (b) middle system.
Chemical evolution ways include cation exchange and mixing with the water
in adjacent layers by leakage flow in local. This system was already sub-
jected to groundwater overdraft, and the flow field was disturbed to a great
extent. Groundwater evolves was droved by human activities; (c) deep sys-
tem. This system is similar to middle system about the ways of hydro-
chemical evolution but with more closed hydrodynamic condition and the
groundwater ages are older than 16 ka B.P.
10
Table 2.
Division of groundwater system in the study area.
Groundwater
Including
Chemical
system
aquifers
Hydrodynamic
evolution
Human activities
Shallow system
Phreatic
aquifer
Quick renewal of
water
Dilution by
rainwater
Irrigation
Middle system
I-III
Renewal in local
by leakage flow
cation
exchange
and
mixing*
Artificial discharge/
recharge
Deep system
IV-V
Just about logjam
cation
exchange
Artificial discharge/
recharge
*Mixing with the water in adjacent layer. The water flow direction is decided by the
difference of water table between the adjacent aquifers.
