Transport Characteristics and River-Blocking Possibilities of Debris Flows in Namudang Gully, Lhoka Prefecture of Tibet, China

Predicting the possibilities of river blocked by debris flow is critical for disaster prevention and mitigation. In this paper, taking Namudang gully in Sangri County, Lhoka Prefecture of Tibet as an example, we studied the characteristics and analysed the river-blocking possibilities of debris flows in the gully based on field survey and laboratory tests. Results showed the debris flow was viscose debris flow with densities of 2.0 g/cm³, 2.1 g/cm³ and 2.2 g/cm³ at 20-year, 50-year and 100-year recurrence intervals, respectively. And the corresponding debris flow discharges were 69.39 m³/s, 105.71 m³/s and 150.72 m³/s, respectively. On this basis, we used Ratio of Discharge per Unit Width to predict the possibilities of river blocked by debris flows in the gully. Calculating results showed that, at 20-year recurrence intervals, debris flow do not block the river, only resulting in contraction of channel cross-section, and however, at 50-year and 100-year recurrence intervals, debris flows will block Qusong River. The results agreed with the field survey, which meant the "Ratio of Discharge per Unit Width" is feasible for predicting the possibilities of river blocked by debris flows.