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Realizing quantitative evaluation of disaster reduction benefits of debris flow retaining dams has important theoretical and practical significance for optimizing engineering design and protecting the safety of people's lives. and property. The paper uses numerical simulation methods to obtain the mud depth, flow velocity, and range of debris flow under different operating conditions, establishes two risk evaluation index systems based on the area of high risk level and the total risk degree, proposes a quantitative evaluation method for the disaster reduction benefits of retaining dams, and conducts an empirical study using the Chutougou debris flow as an example. According to the evaluation method for disaster reduction benefits of retaining dams, it is possible to analyze the disaster reduction benefits of the proposed and existing projects and their combinations, determine whether they have achieved the disaster reduction goals, and compare and quantify the importance of different projects in disaster reduction, which can provide a basis and reference for the construction and improvement of debris flow retaining dams. The disaster reduction benefits per unit height can reflect the value of risk reduction per meter of retaining dam heightening, and can be applied to the determination of optimal engineering combination scheme of debris flow retaining dams. The change rule of the total risk degree and the disaster reduction benefits of the area with high risk level is consistent, indicating that both risk assessment methods can reflect the disaster reduction benefits of the combination of retaining dams and their changes. [ABSTRACT FROM AUTHOR]

In view of the spatial scale of threat and potential risks caused by debris flow under four extreme rainfall conditions, risk assessments of debris flow hazard in Maiduo Gully, Chaya County, Tibet were carried out, using a single building as an evaluation unit. Assessments include the risk division, vulnerability analysis and risk assessment of debris flow. This paper describes a whole workflow of a refined risk assessment. Firstly, based on a three dimensional geological model acquired from UAV, the FLO⁃2D software was used to simulate the process of debris flow outbreaking in Maiduo Gully under four extreme rainfall conditions(10%,5%,2%,1%),and the risk zones were divided. Then, analyzed the vulnerability of buildings and population in the affected area according to on site data. After that, took a single building as the evaluation unit, risks and vulnerability were normalized, and to eventually get the risk zones of building and population in study area, overlay analysis was applied on ArcGIS Desktop. These evaluation results are able to provide scientific reference to the works of local geological disasters and risk control, and the evaluation workflow can be used as a reference for future refined quantitative risk assessments of debris flow hazard as well. [ABSTRACT FROM AUTHOR]