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.