Abstract: Existing risk assessment of flood/debris flow disasters is based mainly on the analysis of heavy rainfall or glacier-melt water.In some areas,especially in high and cold mountainous areas with glacial lake developing,researches on the impact of glacial lakes on proposed railways, highways and other linear projects downstream are rarely reported. In this paper, the key geometric parameters of Rongyi glacier lake in the upstream catchment of Cuopu Gully and the characteristic parameters of channel section are obtained based on the analysis of the environmental conditions of the glacial lake via remote sensing interpretation and detailed field surveys. The structure and material composition of lake dam are analyzed, and the stability of the dam structure is analyzed. Moreover, according to hydrological calculation of Cuopu Gully catchment, the impact of flash flood on proposed railway project is evaluated. Results reveal that the dam of Rongyi glacier lake is composed of hard granite with good integrity, indicating small possibility of dam failure in the absence of extreme conditions such as highly intensive earthquake. In the scenario of P=1% design frequency rainfall in association with glacier-melt water, the peak flow of mountain flood in Cuopu gully catchment is 448 m³/s, the average flow velocity at the railway bridge section is about 2.75 m/s,and the water depth is about 4.62 m. According to the railway design, the elevation difference between the bottom of railway beam and the flow surface is 53.89 m,which is considered to be safe for the proposed railway.

Key words: Rongyi glacial lake, dam stability, flood hazards, risk analysis, flow velocity, flow depth