Calculation of the Hydraulic Capacity of Grate Inlets with Supercritical Surface Flow and Unsurcharged Drainage Flow Conditions

Abstract

According to an increasing number of heavy rainfall events, the managing of urban flooding requires new design approaches in urban drainage engineering. With bidirectional coupled numerical models the surface runoff, the underground sewer flow and the interaction processes between both systems can be calculated. Most of the numerical models use a weir equation to calculate the surface to sewer flow with unsurcharged flow conditions, but uncertainties still exist in the representation of the real flow conditions. Street inlets, existing in different types, are the connecting elements between the surface and the underground system. In the present study, an empirical formula was developed based on physical model test runs to estimate the hydraulic capacity of grate inlets with supercritical surface flow. The influencing hydraulic parameters are the water depth and flow velocity upstream of the grate and in addition different geometrical parameters are taken into account such as the grate dimensions or the orientation of the bars (transverse, longitudinal or diagonal).