Geoscience Reference
In-Depth Information
Fig. 4.
Variations of water table and rainfall at study area during 2001-2002.
2 years, the accumulated rainfalls from the beginning of year were 720.8 mm
in 2001 and 715.8 mm in 2002 before the water table rising, respectively.
The water table kept rising and reached its peak values of 59.08 m above
the sea level on September 27, 2001. However, the water table got its peak
of 57.75 m above the sea level on October 29, 2002. Clearly, there was a
time lag between the rainy season and the rising of the water, which was
dependent on the accumulated rainfall rather than the starting date of rainy
season. The water table reached its peak at the beginning of the dry season.
Figure 5 shows the relation between rainfall and changes of water table
at study area during 2001-2002. It was found that the water table responded
to rainfall well in the period from the date beginning to rise to the end of
rainy season. As a result, this period should be considered as recharge period
for groundwater by the rainfall in the study area.
3.4.
Water balance in the study area
Precipitation falling within the study area can be stored there, return to
the atmosphere as evapotranspiration or be transported out of the study
area as runoff or recharge to groundwater. This can be expressed by the
water balance equation as the following.
P
=
E
+
Q
+
R
+∆
S
(1)
where
P
is the rainfall,
E
the evapotranspiration,
Q
the overland flow,
R
the recharge for groundwater, and ∆
S
the change in storage for soil
