Geoscience Reference
In-Depth Information
Fig. 5. Relation between rainfall and changes of water table at study area during
2001-2002.
Table 2.
Comparison of water budget of 2001 and 2002 at the study area (mm).
Year
Rainfall
Evaporation
Overland flow
Recharge to groundwater
2001
2074
797
165
1111
2002
1850
665
183
1002
water (which can be either positive or negative). Over a long period, ∆
S
can be negligible compared to the other terms in the equation. Then Eq. (1)
may be simplified to the static water balance equation:
P
=
E
+
Q
+
R.
(2)
Supposed the groundwater recharge is available in the period of the
water table rising, the precipitation in the other period should be considered
as evaporation which contributes nothing for the groundwater. As a result,
Eq. (2) can be used to assess groundwater recharge in the study area based
on the measurements of precipitation, overland flow. Table 2 shows the
water budget of 2001 and 2002 at the study area. In spite of difference of
annual rainfall between 2001 and 2002, 53.56% (2001) and 54.16% (2002)
of annual rainfall recharged to groundwater. The soil moisture change after
a precipitation event depends on both the amount of water precipitated
and the value of the soil moisture before the precipitation. Excluding the
heaviest cases, the experimental data presented here indicates that the soil
moisture condition before the event is more relevant than the precipitation.
Therefore, the monitoring of soil moisture at the top layer could permit to
