Experimental Investigation on Surcharging of Flowing Sewers
The rapid filling of large diameter stormwater conduits has been associated with a number of operational problems including structural damages and the return of stormwater to grade through vertical inflow or ventilation shafts. There have been limited investigations to date related to the flow mechanisms that lead to these problems. Laboratory investigations have been previously conducted to examine various aspects of this rapid filling problem but generally are conducted to examine a particular aspect of the overall problem. It is generally not feasible to reproduce a complete system at a reasonable scale so any laboratory study necessarily is an idealization of a real system. An outstanding question is to what extent the experiments performed to date are representative of the actual flow conditions in stormwater systems undergoing rapid filling.
This investigation presents a series of exploratory experiments conducted for conditions that were designed to more closely approximate the expected flow in real stormwater systems. In particular, the objective was to examine behavior with inflow from multiple sources. These conditions were generated by creating a surcharging front at an intermediate point in a system with an initial steady state, gradually varied flow. Measurements of pressure and velocity as well as visual observations confirmed the possibility of air entrapment and pressurization, which in turn can pose limitations to the ability of typical numerical models to describe such flows. Experimental results are presented along with a description of observed flow phenomena.
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