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The effects of trapped air on flow oscillations and pressure surges in a model trunk sewer–manhole system subject to rapid filling are investigated. The study reveals the detrimental impacts of entrapped air during severe storm events under which pipelines are likely overloaded. The results of the investigation indicated huge peak pressures and severe pressure oscillations inside the system.Key words: trapped air, flow transient, rapid filling, sewers.

A huge slide involving 68 × 106 m3 of soils occurred along the right bank of Yalong River in Sichuan Province, China. The sliding materials blocked the river and formed a dam-like structure having a height of 175 m and creating a reservoir with a capacity of approximately 680 × 106 m3. The dam breach which was caused by overtopping lasted 13 h and resulted in an estimated maximum flood discharge of 53 000 m3/s. Based on the hydrograph created by measuring the flows downstream of the dam, the process of dam breach was roughly estimated. Key words: landslide dam, cohesionless material, overtopping, breach, flood, hydrograph, failure process.

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