Abstract:Contour ridge system is an effectively agricultural practice used throughout the world. Due to microtopography, rainwater from side slopes flows into furrows and ponds in lower areas of furrows, and thus induces seepage to occur more readily. In addition, the ponding results in that raindrop impact enhances or weakens the capacity of soil detachment and transport. Therefore, the interactive influence of raindrop impact and seepage on soil erosion process is more complicated relative to traditional slope systems. Runoff and sediment yielding process were analyzed under two soil surface hydrological conditions (free drainage, FD and seepage, SP) and two soil surface conditions (with and without raindrop impact, RI and WRI) through simulated rainfalls. Results showed that: (1) Runoff ranked in the order of SP+WRI > SP+RI > FD+RI > FD+WRI. Raindrop impact and seepage contributed -47.09% ~ 54.37% and 41.96% ~ 85.62% to the runoff, respectively. (2) Soil loss decreased in the sequence of SP+RI, SP+WRI, FD+RI, and FD+WRI. Raindrop impact and seepage made contributions of 12.92% ~ 94.94% and 25.83% ~ 97.28% to soil loss, respectively. (3) Raindrop impact showed a slightly influence on runoff process under FD condition. However, raindrop impact and seepage induced the temporal variation of runoff rate and sediment concentration more fluctuated when soil was saturated. (4) With or without raindrop impact, a power function relation was found between runoff rate and soil loss under FD condition, while exponential function could describe their relation under SP condition. These findings were helpful to understand soil erosion process within contour ridge systems, and supply guidance for soil and water comprehensive conservation for implementing contour ridge systems.