55
Figure 4.18 Simulation and observed measurement data comparison before calibration
Figure 4.19 Statistic comparisons between observed.
4.3.2 Calibration and Assessment
SWAT is distributed hydrology model and consequently many potential parameters are involved. With the result that it would be impossible to calibrate all
parameters, until reduction of the number of parameters to be estimated is done. Due to spatial variability, measurement error, incompleteness in description of both
element and process present in the system, the value of all parameters will not be exactly known. To achieve a good fit between simulated and observed data, models
need to be calibrated to match simulated and observed data by optimizing the same parameter. The calibration procedure can be done manually or automatically.
10 20
30 40
50 60
70 80
50 100
150 200
250 300
P mm
Q cms
Pcp mm
Q ‐real
sim2005
y = 0.9948x ‐ 9.2574
R² = 0.5351
20 40
60 80
100 120
140
50 100
150
Simu lat
ion
Observed
56
Table 4.9 Initial and final value of SWAT Calibration parameters for stream flow
SWAT variable name Parameter
Range Final
value SURLAG
Surface runoff coefficient 1 - 40
5 Alpha BF
Base flow alpha factor days 0 - 1
0.26 GW_Revap
Groundwater “revap” coefficient 0.02 – 0.2
0.02 REVAP_MN
Percolation to the deep aquifer to occur mmH
2
O 0 - 500
10 GWQMN
Threshold depth of water in the shallow aquifer required for return flow to occur mmH
2
O 0 - 5000
800 GW-Delay
Groundwater delay days 0 - 500
31 SHALLST
Initial deep of water in shallow aquifer mmH
2
O 0 -
1000 10
CH_N1 Manning’s value for tributary stream
0 – 0.5 0.5
CH_N2 Manning’s value for main stream
0 – 0.3 0.3
CH_K1 Effective hydraulic conductivity in tributary
stream 0-300 0.5
CH_K2 Effective hydraulic conductivity in main stream
0.5 CN2
Curve Number 0 - 100
X 0.75 SOL_AWC
Available water capacity of the soil layer 0 - 1
X 4
Based on availability of discharge data, precipitation and landuse, calibration was done during period of 2004 to 2005, and then validation is done for
2005 period. The calibration used manual method by comparison of observed and simulation data. It was obtained that simulated peak flow was higher than that of
observed data, while simulated base flow was lower than observed data. Hydrology was calibrated by comparison of observed data from an in
stream Public Works Department flow gauging station to model and to adjust the key of hydrologic parameter. Based on the fact of hydrograph comparison the
calibration focused on several solutions which are adjusted to infiltration, interflow and base flow recession parameter. Details of adjustment for calibration are shown
in Table 4.9, while result of discharge calibration in Leuwidaun river gauge is shown in Figure 4.20.
Figure 4.20 Discharge in Leuwidaun river gauge after calibration
10 20
30 40
50 60
70 80
20 40
60 80
100 120
P mm
Q c
ms
Pcp mm
Q ‐real
cal1 ‐ucca
57
Figure. 4.21 Correlation error between Observed and simulation data after calibrated
Manual calibration of several parameters resulted in correlation error R
2
of 0.64 where Q
Obs
= 0.9655.Q
Sim
– 7.6956, and NSE is 0.495, the value of R
2
and NSE value is not good enough and the error is caused by un-detailed soil
parameter, where in this model soil map used recognized map with scale 1 : 250,000. The correlation error and Nash is shown in figure 4.21.
4.4 Landuse Change Impact to Water yield and Optimizing Landuse
