Abstract

Surges may form during rapid filling incidents in stormwater storage tunnels as the tunnel undergoes a transition between a free surface flow and a surcharged state. The current state of knowledge does not allow specification of conditions that lead to extreme surges, that would provide the basis for design of surge relief systems. A laboratory model was developed to provide insight into the geometrical and flow conditions that will develop large surges. The model was tested at a variety of slopes and for flow conditions that allow for the investigation of the influence of the hydrograph at the inflow points into the tunnel. Experimental findings indicate that the largest surges occurred when a hydraulic bore just formed as it approached the surge relief structure. The maximum surges also occurred when the tunnel slopes downwards from the surge chamber. It was also observed that in conditions where the exhaust of air is impeded from the system, the compression of air may induce motion due to the air pressure acting on the water surface. Current numerical models developed to describe the surge process have not included this effect in their formulation.

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