The Jiuzhaigou earthquake on 8 August 2017, led to a significant increase in the amount of loose, solid material, which has been a rich source of debris-flow activity. In this paper, a comprehensive debris-flow prevention and control system consisting of stabilization, blocking, and deposition structures is proposed based on the topographic features of the debris-flow gullies in the Jiuzhaigou Valley. Taking the Xiajijie Lake gully as a case study, the history and formation of debris-flow disasters were analysed. This study proposes the main principles of debris-flow prevention and control as well as implementation measures, consisting of lateral diversion and deposition at the outlet of the gully. In addition, several environmental mitigation measures are proposed. Galvanized wire gabions can be placed in front of trees to lessen the debris-flow impact force, and bushes can be planted in front of deposition retaining walls to increase their aesthetic value. Alternatively, steel structures can be constructed on deposition retaining walls and filled with nutrient soil, and grass can be planted in these structures for an enhanced aesthetic appeal.

On 8 August 2017, an Ms 7.0 earthquake struck Jiuzhaigou Valley, triggering abundant landslides and providing a huge source of material for potential debris flows. After the earthquake debris flows were triggered by heavy rainfall, causing traffic disruption and serious property losses. This study aims to describe the debris flow events in Zechawa Gully, calculate the peak discharges of the debris flows, characterize the debris flow disasters, propose mitigation countermeasures to control these disasters and analyse the effectiveness of countermeasures that were implemented in May 2019. The results showed the following: (1) The frequency of the debris flows in Zechawa Gully with small- and medium-scale will increase due to the influence of the Ms 7.0 Jiuzhaigou earthquake. (2) An accurate debris flow peak discharge can be obtained by comparing the calculated results of four different methods. (3) The failure of a check dam in the channel had an amplification effect on the peak discharge, resulting in a destructive debris flow event on 4 August 2016. Due to the disaster risk posed by dam failure, both blocking and deposit stopping measures should be adopted for debris flow mitigation. (4) Optimized engineering countermeasures with blocking and deposit stopping measures were proposed and implemented in May 2019 based on the debris flow disaster characteristics of Zechawa Gully, and the reconstructed engineering projects were effective in controlling a post-earthquake debris flow disaster on 21 June 2019.