Impact often causes structural destruction and is the key element in engineering design and risk assessment. Nature of the debris flow characteristics are the front part of the flow, where big boulders accumulate, lasts only a few seconds and the following part that lasts long looks like a mud flow with gradually decreasing discharge. Besides, boulder impact force is much greater than fluid dynamic pressure. Therefore, it is necessary to make sure that the structure is affordable of boulder impact force. In this study, an attempt has been made to clarify the impact of grain size distribution on check dam and variable of check dam type with experimental methods
