The increasing frequency of intense rain events will worsen the operational conditions of stormwater systems, including the frequency in which these systems experience pressurization. Unfortunately, there has been limited research on the issue, particularly the pressurization of junctions in stormwater systems that are subject to rapid filling. Past research provided valuable insights on flows in junctions operating either on pressurized or open-channel flow conditions, but did not focus on the transition between these two flow regimes. This work summarizes the results of an experimental investigation that focused on describing the pressurization processes in a junction undergoing rapid filling. The experimental program considered a total of 67 unique combinations, with variables including different slopes of the upstream and lateral pipes, as well as different inflow rates in each one of these conduits. Fast blockage of the flow led to the pressurization process, that was characterized through video-recording and pressure monitoring at selected points along in the apparatus. This innovative research identified for the first time five unique pressurization modes based on the video recordings of the pressurization. The pressurization modes were dependent on the experimental setup, including lateral and main branch flows as well as their slopes. An independent clustering-based analysis of the experimental data was used and confirmed this classification. These results are the first ones of its kind and clearly indicates potential limitations of numerical models in representing flows in the junctions when air pocket entrapment occurs due to rapid filling conditions. Future research should address the limitations of the present experimental work in terms of scale effects, including a wider range of tested flow conditions and slopes, besides different junction geometries with storage.
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