This paper presents the results of an observational study related to the behavior of drainage sewers under conditions of hydraulic overloading. Specifically, the investigation focuses on the interaction of water and trapped air in surcharging drainage and pressurized pipeline systems, by studying the air-water flow behavior in a rapidly filling horizontal pipe. Air-water interface patterns, air entrainment, and air release through an orifice at the pipe end are documented photographically.

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... ronously recorded pressure traces are also presented to illustrate the relation between the air-water phase evolution and the pressure oscillation patterns. Depending on the air release rate of the orifice, there are three types of pressure oscillation behavior, each corresponding to a particular behavior of the air-water interface in the rapidly filling horizontal pipe.