5.2. The effect of slope
As the slope increased, the initial abstraction, the infiltration and
the recession time of overland flow will deceased, which results in less
opportunity for infiltration and more surface runoff as compared with a
horizontal surface. These have been demonstrated by many researchers
(Evett and Dutt 1985; Philip, 1991; Huang, 1995; Fox et al., 1997;
Chaplot and Bissonnais, 2003). However, CN2 of standard
SCS-CN method obtained from the handbook table (SCS, 1972) corresponds
to a slope of 5%. Therefore, the slope equation (Eq.6) was developed
which incorporating the slope in the SCS-CN method for steep slope
conditions.
In this study, the effect of slope seems not reflected as the Huang et
al. (2006) preformed worse than the original SCS-CN method when
accounted for the slope factor in the method. The reason is that the
traditional SCS-CN has already over-predicted storm events of Regime 3,
the over-prediction were intensified when the slope factor was taken
account into Huang et al.(2006) because the runoff increased with slope
gradient (Fig 2). However, when the over-prediction was removed by the
proposed method, the effect of slope can be easily found and with the
slope increased the effect of slope was more intensified as the runoff
increased by slope.