The mountain was seriously broken in the earthquake area after the Wenchuan earthquake. The critical threshold for inducing geological disasters such as debris flow and landslide was low. A type of urgent-steep gully debris flow was triggered

which led to extreme destruction. This type of debris flow has a shorter outbreak duration

a large volume concentration and a large average density

showing a strong “snowball effect” and strong “fire hose effect”. The engineering measures have an important influence on FLO-2D numerical simulation of urgent-steep gully debris flows. Therefore

FLO-2D is used to simulate the runout volumes of typical urgent-steep gully debris flows under engineering measures and nonengineering measures scenarios respectively

taking Wayao gully in Wenchuan earthquake area as an example. The accuracy of numerical simulation results is 86.4%. The block dam in the circulation area can divide block debris flow into sections under the engineering measures

which makes the debris flow run out volume reduced. When the rainfall frequency is

P

=2%

under the engineering treatment measures scenario

the runout volume is 83.16%

the accumulation fan area is 75.81%

and the average accumulation depth is 30.25% less than those in the natural scenario. The research results can provide reference for disaster prevention and mitigation engineering and early warning of debris flow of urgent-steep gullies in earthquake areas.