Abstract:In order to understand the impact of rainfall intensity on runoff distribution and subsurface flow process in the red soil slope with embedded gravel, the artificial simulated rainfall method was used to determine the subsurface flow characteristics of generation time, runoff rate and runoff process. The red soil gentle slope (10°) and steep slope (25°) were taken as research objects with different gravel contents (0, 10%, 20%, 30%) and rainfall intensities (60, 90, 120 mm/h). The results indicated that:(1) The runoff generation time of red soil slope with different contents of embedded gravel was close 15 min under 60 mm/h rainfall intensity, and varied greatly under 90 mm/h and 120 mm/h. The increase of rainfall intensities from 60 mm/h to 120 mm/h, the runoff quantity and runoff rates decreased with varying degrees, and the runoff rates in red soil embedded gravel with 20% and 30% at slope gradient 25° deceased 86.7% and 89.0% respectively. When the rainfall intensity was 120 mm/h, the peak values of subsurface flow were only 10.7% and 10.2% respectively of the 60 mm/h. (2) The proportions of surface runoff increased 32.8%~1 009.4% with the increasing rainfall intensities on the experimental slopes of 10° and 25°. The proportions of surface runoff were 8.0%~66.3% under rainfall intensity 60 mm/h, 76.1%~93.5% under 120 mm/h. The proportions of subsurface flow decreased 46.1%~93.9% with the increasing rainfall intensities. The proportions of subsurface flow were 7.3%~30.0% under 60 mm/h rainfall intensity, 1.1%~9.6% under 120 mm/h. (3) The binary linear regression results showed all the relationships of peak flow of subsurface flow (Ip), coefficient of subsurface flow (It), subsidence rate of subsurface flow (K) with rainfall intensity and gravel content reached the significant levels (P<0.05). Rainfall intensity and gravel content played the opposite roles in the subsurface flow process at slope gradient 10°, while both roles were same at 25°.