Full-Scale Experimental Study on Hydraulic Efficiency of Grate Inlets under Grate and Storm Sewer Blockage Conditions

This study presents a full-scale experimental analysis of the effects of grate geometry, surface blockage ratio, and storm sewer blockage on the hydraulic efficiency of urban stormwater grate inlets. Six types of grate inlets that are currently used in Seoul were tested in a custom-built flume designed to replicate the cross-sectional and gutter flow characteristics of an urban roadway at a constant inflow rate of 0.26 m<sup>3</sup>/s. The results showed that the standard grate, with a large open area and simple geometry, had the highest hydraulic efficiency, whereas the aesthetic pattern grates with smaller and more complex openings exhibited lower efficiency. For the standard grate, the efficiency decreased almost linearly as the surface blockage ratio increased from 0 to 90%, and partial blockages in the downstream storm sewer reduced the efficiency more than surface grate blockages. This study quantitatively clarifies the relative impacts of grate inlet blockage and storm sewer blockage on urban drainage efficiency under full-scale conditions, and the findings can serve as baseline data for improving the design and maintenance guidelines of urban drainage systems in flood-prone areas.