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Over 240 debris flows occurred in hillslopes, gullies( indicated those with single-channel)and watersheds(indicated those with tributaries and channels) on July 10 th 2013 in the Wenchuan county,and caused 29 casualties and about 633×106 USD losses. This work aimed to analyze characteristics,hazards and causes of these events and explore mitigating measures based on field investigation and remote sensing images interpretation. The debris flows contained clay content of 0.1%~3.56%, having densities of 1.72~2.14 t/m3, velocities of 5.0~12.7 m/s,discharges of 335~2353 m3/s and sediment yields of0.10~1.26×106 m3, and also numerously occurred in large watersheds with the area over 10 km2. Large debris flows formed 3 hazard-chains in slopes, gullies,watersheds and rivers, which all evolved in dammed lakes and outburst flood, and 26 dammed lakes and10 newly ones were generated along the rivers of Min and Yuzi. The remarkable spatial difference of loose solid materials accumulation and intense rainfall,with the cumulative of about or more than 150 mm and the hourly of over 16 mm, caused debris flows in the sections from Yingxiu to Miansi and Gengda. The damages on buildings, reconstructions, highways,factories and hydro power station originated from the impacting, scouring, burying of debris flows, the submerging of dammed lake and the scouring of outburst flood, and the huge losses came from the ruinous destructions of control engineering works of debris flows as well as the irrational location and lowresistant capabilities of reconstructions. For hazards mitigating of debris flows in long term, the feasible measures for short term, including risk-reassessing of foregone and potential hazard sites, regional alarming system establishing and integrated control in disastrous sites, and middle-long term, including improving reconstruction standard, rationally disposing river channel bed rise and selecting appropriate reconstruction time and plans, were strongly suggested.
At the time there was 29 casualties and about 633 × 106 USD losses. This year they were out of hillslopes, gullies (indicated those with single-channel) and watersheds (indicated those with tributaries and channels). Work aimed to analyze characteristics, hazards and causes of these events and explore mitigating measures based on field investigation and remote sensing images interpretation. The debris flows containing clay content of 0.1% -3.56%, having densities of 1.72-2.14 t / m3, velocities of 5.0 ~ 12.7 m / s, discharges of 335 ~ 2353 m3 / s and sediment yields of 0.10 ~ 1.26 × 106 m3, and also were numerously occurred in large watersheds with the area over 10 km2. Large debris flows formed 3 hazard-chains in slopes, gullies, watersheds and rivers, which all evolved in dammed lakes and outburst flood, and 26 dammed lakes and10 newly ones were along the rivers of min and yuzi. The remarkable spatial difference of loose solid materials accumulation and inten se rainfall, with the cumulative of about or more than 150 mm and the hourly of over 16 mm, caused debris flows in the sections from Yingxiu to Miansi and Gengda. The damages on buildings, reconstructions, highways, factories and hydro power station originated from the impacting, scouring, burying of debris flows, the submerging of dammed lake and the scouring of outburst flood, and the huge losses came from the ruinous destructions of control engineering works of debris flows as well as the irrational location and lowresistant capabilities of reconstructions. For hazards mitigating of debris flows in long term, the feasible measures for short term, including risk-reassessing of foregone and potential hazard sites, regional alarming system establishing and integrated control in disastrous sites, and middle-long term, including improving reconstruction standard, rationally disposing river channel bed rise and selecting appropriate reconstruction time and plans, were strongly suggested.