A lot of collapses and landslides induced by the Wenchuan Earthquake formed a lot of barrier dams. When these dams outburst, it tends to form dam-breaking debris flow. Since it has the characteristics of fast disaster-forming and large scale, the disaster loss caused by the dam-breaking debris flow is much more serious than that caused by the normal rainstorm debris flow. This paper took the barrier lake of the Tangfang gully in the Pingtong town, Pingwu County, Sichuan province as an example the characteristics and countermeasures of dam-breaking debris flow. It analyzed the forming process, flow discharge calculation and countermeasures of dam-breaking debris flow after earthquake by means of field investigation, field measurement and sampling analysis. The dam-breaking debris flow discharge were calculated by by means of morphology investigation method and flood method. The calculating results showed that the flow discharge result calculated by the flood method was obviously smaller than the one calculated by morphology investigation method. The main reasons are that there was serious blockage in the gully, a lot of loose solid materials induced by the earthquake, as well as the decrease of critical rainfall conditions of inducing debris flow. As a result, debris flow scale increased after the earthquake. The status of debris flow prevention in Tangfang gully had a lot of problems, such as poor conveyance capacity, broken basement and no excess-height in bend of the drainage canal, no preventing projects in the watershed. Since there were enough loose solid substances in the Tangfang gully recently. Under the condition of rainfall, debris flows will occur again. It will threaten 1600 people’s life and property safety in the Pingtong town and the reconstruction work after the earthquake. According to these problems, the countermeasures of building check dam, heightening drainage canal, warning and forecasting are put forward in this paper.
