Risk Assessment of Debris Flows in Small Watersheds on the Northeast Margin of Qinghai-Tibet Plateau—A Case Study of Zhujiagou Watershed

Zhanlin Qiu,Weimin Yang,Jihuan Wu,Feipeng Wan,Xuan Zha,Chenyang Liu,Yonghui Wu

doi:10.2113/2022/2123272

Abstract

Abstract In the Qinghai-Tibet Plateau, fractures and fault zones have developed in this area, where earthquakes and extreme rainfall frequently induce debris flow disasters, which seriously threaten the safety of the people and properties. In this study, Zhujiagou, Minxian County, Gansu Province in China, has a typical debris flow channel in a small watershed on the northeastern edge of the Qinghai-Tibet Plateau, which has been used as the case study for risk assessment. A debris flow-risk assessment method has been developed in this study. The fusion algorithm of entropy weight and coefficient of variation has been used to evaluate the susceptibility of debris flow in each tributary channel in the watershed. Further, numerical simulation of the debris flow events at the main channel and at the high-prone debris flow tributary channel has been carried out. The “7.18” Zhujiagou debris flow event has been used to verify that the accuracy of the numerical simulation is higher than 74.12%. This method has been applied to design the Zhujiagou debris flow-risk zoning under extreme rainfall conditions, aimed at forming a set of debris flow-risk evaluation system suitable for this type of small watershed. The results show that the peak single-width clear water flow at the mouth of the channel, the length of the channel, and the shallow surface rock formation are the main factors influencing the susceptibility of debris flow. The main tributaries of the watershed are Hagu channel, Zhuling channel, Songshu channel, and Langjia channel which are all high-prone debris flow channels. The Zhujiagou debris flow accumulation fan under the designed 1% rainfall frequency will block the Taohe, which will threaten the safety of the residents and properties near the channel, at the mouth of the channel and in the urban area on the opposite bank of the Taohe. Compared with Hagugou, Zhulinggou, and Songshugou, the low-risk area is Langjiagou. The research results of this study can be used for evaluation methods and as a basis for preventing debris flow disasters on the northeastern edge of the Qinghai-Tibet Plateau.

Highlights

The northeastern margin of the Qinghai-Tibet Plateau is located in the west extension of the West Qinling tectonic belt in China [1]
(1) Through the evaluation of debris flow susceptibility based on the fusion algorithm of entropy weight and coefficient of variation in the study area, it is concluded that the susceptibility of debris flow in each tributary channel in the study area is mainly affected by the peak single-width clear water flow at the mouth of the channel, the length of the main channel, and the controlled conditions, such as the shallow surface rock formations
(2) The results of the Zhujiagou debris flow-risk assessment under severe rainfall conditions (P = 1%) once in a century show that the Zhujiagou debris flow-risk area is about 500,625 m2, which is generally a highrisk area of debris flow

Summary

Introduction

The northeastern margin of the Qinghai-Tibet Plateau is located in the west extension of the West Qinling tectonic belt in China [1]. There are a total of 12 evaluation factors for the peak clear water flow per unit width, source distribution, relative height difference, average slope of the basin, vegetation coverage, and shallow engineering rock formations.

Results

Conclusion