Pressure Surges Following Sudden Air Pocket Entrapment in Stormwater Tunnels

Stormwater storage tunnels may undergo rapid pipe filling conditions during extreme rain events. Such conditions are relevant as adverse conditions may develop, such as surging due to entrapment and compression of entrapped air pockets. Operational issues such as structural damage, geysering and the return of conveyed water to grade, among others, have been linked to air pocket entrapment. This chapter presents results from the experimental investigations of pres-sure surges caused by sudden air pocket entrapment. Steady flow was supplied in a pipeline in such a way that pressurized flows existed at the upstream end while the downstream end experienced free surface flow due to free discharge conditions at the downstream end. A combination of flow rates and slopes resulted in several gradually varied flow profiles at the discharge, with various volumes of atmospheric air at the discharge end. By suddenly closing the downstream discharge valve, an air pocket was en-trapped and surges were recorded. To emulate conditions in which surge relie