Abstract: Debris flows resulting from extreme precipitation exhibit extensive scale, severe erosion along their paths, and substantial sediment deposition, necessitating the implementation of cascade check dam projects in small watersheds for hazard mitigation. In the Wenchuan earthquake-affected area, we investigated 33 typical debris flow gullies and obtained characteristic parameters for 105 check dams, along with the erosion pattern changes in gullies under the influence of cascade check dams. We summarized the types of check dams and their identification criteria and proposed four combinations of solid dams and open dams, as well as two back-silting modes under different spacings of cascade dams. We further analyzed the effects of characteristic patterns of cascade dam (dam type combination mode and back-silting mode) on channel’s erosion and deposition pattern (slope reduction coefficient due to sedimentation and relative erosion depth coefficient). The results indicated that the combination of solid and permeable dams (SO mode and OS mode) significantly influenced the back-silting pattern of channel, and the interactive back-silting mode had a notable impact on deposition pattern, while the independent back-silting operation mode yielded stronger erosion effect. The research findings offer reference for the selection of check dams and the optimization of dam spacing of cascade dams in small watersheds.

Key words: cascade check dams, dam-type combination mode, dam spacing, back-silting mode, erosion and deposition pattern