Abstract: In this paper, the operation status of check dams in the midstream of Bailong River and their control effects on debris flow are examined through field investigation and experiment analysis. Results reveal that: (1) Some debris flow gullies in the study area are faced with severe situation of debris flow control. The storage capacities of some gullies are insufficient, and the check dams are severely damaged. (2) Investigation on the slope gradient of debris flow in the upstream suggest that check dam has a good silting function. An empirical formula for the silting slope gradient is established for this region: I=(0.4~0.85)I₀. (3) On the basis of obtaining the grain size of sediment of the debris flow, the ratio of average particle size and the ratio of bulk density of the sediment are established to describe the control effect on debris flow. Check dam has good sorting function for debris flow particles, but its regulating effect on the density of debris flow is unapparent, and the critical particle size is still hard to determine. In addition,some suggestions are put forward to tackle some engineering problems.

Key words: debris flow, check dam, operation status, control effect, midstream of Bailong River