Effects of Inlet Design on Hydraulic Efficiency and Sediment Cleanout of Bridge Deck Drains

Abstract

Bridge deck drainage is driven by the hydraulic efficiency of inlets, which can be affected by grate design, downspout configuration, and debris accumulation. Inadequate drainage can result in hydroplaning, which can diminish highway safety. To evaluate the controls on drainage inlet efficiency and compare currently deployed inlet design performances, 576 controlled laboratory experiments were conducted testing grate type (rectangular bar vs curved vane) and downspout configuration (square vs circular and 20 cm vs 25 cm) across a range of flow rates, cross slopes, and longitudinal slopes. Experimental results found no significant difference for hydraulic efficiency across grate design and flow rates but suggest that the design equations may not accurately estimate inlet hydraulic efficiencies due to unaccounted splashover behavior observed in grates. An additional 144 sediment transport experiments showed that curved vane grates had better debris removal than bar grates under most flow conditions. These results can be used with hydroclimatological data to improve location-specific grate design selection and reduce debris susceptibility, maintenance costs, and the risk of hydroplaning.