Air–water interactions in urban drainage systems

Storm water and combined sewer systems are subject to rapid filling during intense rainfall events. These large-sized systems require a significant amount of air to be vented during filling. Several systems have experienced operational problems such as structural damages and geyser release through ventilation shafts. Observations from one storm water conveyance tunnel and laboratory experiments suggest that entrapment of large discrete volumes of air during rapid filling can explain geyser formation as well as large system pressures associated with the compression of trapped air. Only modest system pressures are required to produce geysers. Descriptions of several air–water interactions are presented to advance the hypotheses for the occurrence of the two detrimental phenomena. Requirements for numerical models to analyse rapidly filling conduits are discussed. A review of the existing modelling frameworks is presented. Some limitations to these models are discussed along with a discussion of possible model enhancements.