PhD Thesis Emmanuel Obeng Bekoe - Cranfield University

Change in Flows (%)
40
30
20
10
-20
-30
-40
117
-50
0
-10 0 50 100 150
Change in COFRU (%)
Baseflow Streamflow
Figure 5.4. Response of cumulative baseflow and streamflow to changes in
COFRU parameter
The parameter COFRU showed no influence in cumulative simulated
streamflows (Figure 5.4) as per the objective function of this sensitivity analysis
study. However, it was noted that it affected the shape of the hydrograph
(recession section) when it is varied. This calls for examining this parameter
during calibration. Although not plotted, rainfall was found to be extremely
sensitive as envisaged where within the range of sensitivity, 40% increase in
rainfall amount gave a corresponding increase in simulated cumulative
streamflow of over 109%.
5.2.3 Sensitivities of the Apan and the Hargreaves Method
The same procedures and processes were applied to check the level of
sensitivities when the reference evaporation method was changed to
Hargreaves (1985) method. This was done to assess whether the choice of
evapotranspiration method affects the sensitivity of parameters. It was
expected that the shape of the plots would be similar, but the gradients might
differ slightly, which was confirmed by the simulation (Figure 5.5). Figure 5.5
shows a comparison using the two methods for the two most sensitive
parameters FC1 and CAY.
Emmanuel Obeng Bekoe Phd Thesis Chapter 5 Hydrological modelling of Densu