Recharge systems for protecting and enhancing groundwate

424
TOPIC 3
Modelling aspects and groundwater hydraulics
as unacceptable (Ghulam et al. 2004). The root mean square error is useful to quantify the differences between
observed data and simulated data with the optimized parameters:
O
=
n
∑
i=
1
n
Oi
⎛
N
1
⎞
2
(7) RMSE = ⎜ ∑ [ Mi
− Si()
b ] (87)
⎝ N
⎠
where Mi and Si (b) are measured and simulated values for an output variable.
i=
1
During recharge there was decrease in RMSE with the time (Table 3). RMSE decreased from 1.24 m after 1 hr of
recharge to 0.83 m after 87 hrs of recharge. Similar trends were shown by ME also. ME increased from 0.97 to 0.98
from 1 hr of recharge to 87 hrs of recharge. Initially high RMSE and low ME revealed that during the start of
recharge there was much deviation between the experimental head and simulated head. Similar trends were
observed during the recovery also i.e. from 1 hr to 34 hrs recovery, RMSE decresed from 3.57 m to 3.05 m and ME
increased from 0.85 to 0.87 (Table 4). Overall matching between observed and simulated data points was quite
satisfactory during calibration except during start of recharge and recovery in each cycle (Fig. 3). It might have
been due to the facts: 1) that hydrus 2D model does not take into account the storage coefficient in the aquifer
and /or 2) the entry points resistances of piezometers might have delayed their response to drawup and drawdown
pressure heads under actual field conditions.
Table 3. Number of observations N, RMSE and ME in drawup during calibration and validation in pressure heads
Time (h)
Calibration
N RMSE* (m) ME** N
* Root mean square error ; ** Modelling efficiency.
Validation
RMSE (m)
IInd IIIrd IVth
Mean ME
1 31 1.24 0.97 31 1.21 1.22 1.23 0.97
15 35 1.13 0.97 35 1.17 1.17 1.19 0.96
45 39 0.98 0.98 39 1.15 1.15 1.21 0.98
87 46 0.83 0.98 46 1.00 1.00 1.15 0.99
Table 4. Number of observations N, RMSE and ME in drawdown during calibration and validation in pressure heads
Time (h)
Calibration
N RMSE* (m) ME** N
Validation
RMSE (m)
IInd IIIrd IVth
Mean ME
1 34 3.57 0.87 300 3.50 3.80 3.82 0.85
16 44 3.20 0.88 300 3.10 3.37 3.51 0.86
34 47 3.05 0.89 300 2.95 3.10 3.21 0.87
Figure 3. Simulated and experimental
drawup/drawdown of piezometric head
as given by model during successive recovery
and recovery cycles
ISMAR 2005 ■ AQUIFER RECHARGE ■ 5th International Symposium ■ 10 –16 June 2005, Berlin