Experimental hydraulic parameters of drainage grate inlets with a horizontal outflow in the broad-crested weir mode

The accurate assessment of discharge coefficients for different types of water inlets is crucial for minimizing modelling errors in drainage systems thus reducing the risk of flooding in adjacent areas. This study experimentally investigated the hydraulic characteristics of gully grate inlets with water seal and horizontal outflow, with nominal outlet pipe diameters of 100 and 150 mm, using a laboratory setup that meets the requirements of a special European regulation. Transition depths from the weir to the orifice mode were determined, and it was found that the perforated grates significantly increased the hydraulic resistance compared to the bar grates, resulting in a corresponding decrease in the discharge capacity of gully inlets. Power-law relationships between the weir discharge coefficient and gauge head were obtained for both bar and perforated grate inlets, as well as between the discharge coefficient and Froude number at the perimeter of grate inlets. These findings provide important insights for optimizing the design and performance of water inlets, particularly in the weir mode, which is critical for the proper functioning of drainage systems.