Hazard assessment of debris flow by using FLO-2D and hazard matrix: a case study of Qingshui Gully in the southern Gansu Province, China

Debris flow frequently occurs in high mountains, particularly in dry hot river valleys, and cause severe loss of life and property. The Qingshui Gully of Gansu Province, China was selected as study area. Remote sensing interpretation technology, field investigation, matrix method, and FLO-2D model were applied to obtain distribution of landslides and model parameters, and simulate debris flow depth, velocity, and impact force under different rainfall return periods, and then divide debris flow intensity and hazard. The results indicated an increase in landslides with increasing human activities. The flow depth generally increased from the middle-up stream to downstream when the rainfall return periods ranged from 10 to 100 years, along with a decrease in velocity and impact force from the middle-up stream to downstream. The simulation resulted in a threatened range generally consistent with the actual result of the debris-flow history disaster. The spatial distribution of intensity classes was similar rainfall return periods was ranging from 10 to 100 years. Furthermore, the high-medium intensity area was primarily distributed in the middle-up stream of the study area, whereas the low-intensity area was located downstream. Additionally, the middle-up watershed channel area mostly belonged to the high hazard class, and it existed in the Beiyu River and around the residential area. The low-hazard area was situated downstream of the channel. The medium hazard class was located between the high and low classes. These proportions of low, medium, and high hazard areas were 28.99%, 35.48%, and 35.53% of the total area, respectively. Therefore, the present study provides a reference for fine risk management and disaster warning in dry hot river valleys.