Abstract: In order to explore the accumulation range of debris flow, a numerical simulation of the Lamazhazi debris flow in Miyun County, Beijing was carried out by using the LAHARZ software combined with the 1:10 000 DEM map of the small drainage basin. The authors utilized the data of volume and accumulation area of debris flow in some areas of China, and obtained a new statistical model for debris flow volume and its accumulation area. The optimal river threshold was determined to be 15 000 through comparing the simulated river channel with the actual river channel; combined with the on-site survey statistical and rainfall historical data, the debris flow volume thresholds for 10, 20, 50, and 100 years under heavy rain were determined to be 56 500, 72 900, 94 200, and 113 100 m³, respectively. The corresponding accumulation area of the debris flow trench is predicted as follows:the area of the debris flow under the condition of once-in-a-century rainstorm is 48 729 m², and the longest distance is about 490 m, which has an impact on the downstream villages.

Key words: debris flow, LAHARZ, numerical simulation, accumulation area