Experimental investigation to estimate the discharge coefficient of a grate inlet under surcharge conditions

Pressure pipe flow conditions appear in sewer systems when flow exceeds the hydraulic capacity of the conduit, causing some outflow to be produced. In these cases, water exits through manholes and inlets causing surface flooding. According to some recent studies, the flow leaving the pressured sewer can be estimated assuming orifice flow conditions although it requires the use of proper values of the discharge coefficient in order to obtain realistic results. In this paper, an experimental approach to calculate discharge coefficients through an inlet for surcharged pipe conditions is presented. Tests were carried out using a real laboratory platform simulating a road lane. Different surcharged flows through the inlet from 10 to 50 l/s were considered. The range of the obtained discharge coefficient has been between 0.13 and 0.41 for surcharged flow from 10 l/s to 50 l/s. Sensitivity analysis demonstrated that discharge coefficients can be considered constant for any street longitudinal slope.