Geology Reference
In-Depth Information
Model Calibration
The calibration strategy was initially to vary the best known parameters as
little as possible, and vary the poorly known or unknown values the most to
achieve the best overall agreement between simulated and observed datasets.
Transient state model calibration was carried out to minimize the difference
between the computed and field water level conditions with the water level
data of January 2000 in 28 wells distributed over the study area. Out of all
the input parameters, the hydraulic conductivity and specific yield are the
poorly known. Based on the data, it was decided to vary hydraulic
conductivity, specific yield values up to 10% to get a good match of the
computed and observed heads (Fig. 3). Table 2 shows the initial and calibrated
hydraulic conductivity values of the simulated head. The root mean square
error and mean error were minimised through numerous trial runs. Transient-
state simulation was carried out for a period of six years from January 2000
to January 2006, with monthly stress periods and 24 hr time steps. The trial
and error process by which calibration of the transient model was achieved
included several trials until a good match was achieved between computed
and observed heads over space and time.
Figure 3.
Computed and observed head in transient state calibration.
Table 2.
Initial and calibrated hydraulic conductivity and
specific yield of the simulated head
Geology of
Hydraulic conductivity (m/day)
Specific yield
the area
Initial
Calibrated
Initial
Calibrated
Sand
75
81
0.22
0.31
Clayey sand
25
21
0.17
0.23
