Hydraulic interception efficiency of gully gratings on steep roads

The hydraulic interception efficiency of a gully grating decreases with the steepness of the road on which it is installed. This can lead to a higher potential for flooding at the downstream area of a steep road. In this study, the hydraulic inception efficiency of several types of gully gratings on steep roads, including a new grating with angled bars on a parallelogram cross-section was investigated experimentally. The experimental results for all test gratings show that the hydraulic interception efficiency varies linearly with a non-dimensional parameter expressed as a product of the Froude number, water depth to grating length ratio and flow width to grating width ratio. The empirical relationship can be easily included in numerical models for the detailed study and design of storm water drainage systems. The hydraulic performance of the grating with longitudinal bars and the new grating with angled bars on a parallelogram cross-section was better than that of the existing grating. The relative increase in the efficiency increases with the flow velocity, depth and width. While gratings with longitudinal bars may induce inconvenience to cyclists, gratings with angled bars on a parallelogram cross-section may be used on steep roads to enhance the hydraulic interception efficiency of gullies.