Geology Reference
In-Depth Information
ANNUAL GROUNDWATER BALANCE
The annual groundwater balance was calculated from June 2001 to June
2002. The flows are easily determined using the following equation:
(7)
where
FLOW
TOT
is the total flow along the year, the term
FLOW
representing
as well
RF
,
Q
,
EVAP
,
HIN
and
HOUT
.
Assuming that the percolation takes place only during the wet season
(from June 2001 to November 2001 when the water levels are maximum):
FLOW
FLOW
FLOW
TOT
WET
DRY
(8)
INF
INF
TOT
WET
The annual balance on the whole watershed is described in Table 4.
Table 4:
Groundwater balance during one hydrological cycle
(flow terms are in mm/yr)
INF
TOT
RF
TOT
Q
TOT
EVAP
TOT
HIN
TOT
-
HOUT
TOT
BAL
h
TOT
(m)
94.5
119
231
1.7
8.4
-10.5
-1.18
Considering the uncertainty on the components of the balance, this indicates
that the balance is more or less in equilibrium. However, the total balance
is a little bit negative, in accordance with an average water level decrease
of about 1.18 metres on the watershed during this period, in spite of a
normal monsoon (603 mm of rainfall). This clearly shows that, with such an
abstraction rate on the basin, any bad monsoon as for example the monsoon
of this year (2002), will induce a significantly negative balance followed by
a depletion of water table.
Balance(mm/yr)
Figure 5.
Spatial annual balance.
