Flow Interception Capacity of Inclined Grate

Types C and D inlet grates have a large surface area to drain storm runoff collected along highway medians. As always, highway debris presents a clogging problem to these area grates. Under the assumption that debris would be accumulated on the water surface, an inclined angle was applied to an area grate. It is hoped that the submerged portion of the area grate will remain open to drain stormwater. The selection of inclined angle should be related to the hydraulic efficiency and the amount of floating debris in stormwater. However, there is not any quantifiable guidance as to how to choose the inclined angle for an area grate. In this study, a series of inclined angles, ranging from 0 to function as a horizontal grate to 90° to operate like a side grate, is investigated for flow interception capacity. A new set of orifice and weir formulas with an inclined angle is derived from energy principles and then tested in a $1/3$-scaled model in laboratory. The method of least-square error was used to identify the best fitted values for discharge coefficients as a function of inclined angle with or without an inlet depression. The set of new equations derived and calibrated in this study can significantly improve the current design procedures for Types C and D grates used for highway median drains.