Runout Prediction of Aizi Gully Debris Flow Based on Model Calculation

On June 28, 2012, a large catastrophic debris flow occurred in Aizi gully in Baihetan hydropower station near-zone area, this debris flow event caused 40 people dead or missing, moreover debris flow in Aizi gully have serious influence on the process of construction progress of Baihetan hydropower station. After debris flow disaster, the field investigation was conducted, by means of field investigation the related parameters were acquired, which includes topographic parameters, loose solid material distribution and meteorological conditions. In addition the area where prone to debris flow also zoned. On the basis of these data, the trend of debris flow in Aizi gully was analysed, after analysis we found that the possibility of large catastrophic debris flow occurred in Aizi gully in the future is significantly high. Runout distance plays a key role in the process of disaster mitigation. Combined with the feature(topographic feature, rainfall types and loose solid material) of Aizi gully basin and the description of eye witnesses, the dynamic characteristics of Aizi gully debris flow was back-calculated, then three calculation models were introduced to calculate the runout distance respectively, by comparison the calculation results we found that the least runout distance was 315m, combined the runout distance and prone area we know that the construction camps were located within the prone area, therefore if no prevent measures adopted, the safety of construction camps and workers can not be guaranteed. Comprehensively considered the topographic feature of Aizi gully basin and the runout distance, we proposed to build three level dams and establish early warning systems in the basin, which can greatly reduce the destructive power of debris flow, and helpful to deliver warning information timely, finally the debris flow risk can be reduced significantly.