Bridge drainage systems

Design principles and procedures and maintenance practices for bridge drainage systems are evaluated in this report, which also includes recommendations for improvements on current practice. Bridges should have adequate cross-slope and grade to allow the water to run quickly into drains. Where grades permit, some states carry all the water to catch basins at the ends. An inlet box may be used to collect the runoff. Some states have detailed procedures for determining drain spacing. Debris can be controlled by keeping it out of inlet boxes, accepting and storing it so it cannot go through the system, or transporting it through. Maintenance at regular intervals is the key to the success of a drainage system. Disposal of run off water can be a simple straight drop onto the land or water beneath the bridge or a pipe system to carry the water to the local sewer system. Current practices indicate that deck cross-slope and grade should be less than 2% and 0.5% respectively; that bridge drains may be holes through the deck, fabricated inlet boxes, or catch basins at the ends of the bridge; that inlet areas should be as large as possible; that pipes should have a minimum diameter of 6 in., a miminum radius of 18 in., and a minimum slope of 2%; that cleanout plugs and elbows should be easily accessible; that there should be improved communication between designers and maintenance personnel; and most importantly, that bridge drainage systems should be regularly and carefully inspected and serviced.