Discharge coefficients to be used in inlet hydraulics

Urban pluvial floods can be produced or exacerbated by insufficient inlets density or by their poor hydraulic efficiency. A proper regard on inlet hydraulic performance is essential to guarantee the correct functioning of urban drainage systems during heavy storm events. The recent advances in computation analysis in the field of hydrodynamics modelling allow to use the well-known concept of dual drainage for design and planning purposes simulating flow transfers between surface layer (street) and underground layer (sewer) through a proper hydraulic characterization of inlet efficiency. Currently, powerful commercial software packages allow the simulation of flow transferring including different approaches and formulas. Many of these approaches include the possibility to treat sewer inlets as an orifice. In this context, this paper presents a methodology to obtain orifice discharge coefficients for three inlets previously tested at the Hydraulic Laboratory of the Technical University of Catalonia. Obtained results show discharge coefficient values between 0,18 and 0,58 with a Froude number between 1.12 and 4.4, quite far from usual recommended values. The procedure can be applied even to non-tested grates.