Experimental estimation of the head loss coefficient at surcharged four-way junction manholes

The head loss caused by the surcharged flow from four-way junction manholes is the main cause of increased flood damage in urban areas. The flow pattern significantly varies depending on the inflow conditions of the inlet pipes and constitutes the flow conditions of a four-way junction manhole, three-way junction manholes, and middle manholes. Therefore, the head loss changes with various manhole shapes must be analyzed. In this study, physical model study apparatus was prepared. Various flow rate conditions were selected by changing the flow rate ratios of the inlet pipes at 10% intervals. The head loss coefficients were also estimated. A head loss coefficient range diagram was generated based on the results. A head loss coefficient empirical formula that considers all flow conditions for surcharged four-way junction manholes is proposed. The proposed equation should be applicable to the design and assessment of drainage systems with varying inlet pipe flow rates.