Sedimentation of Multi-Barrel Culverts

Box culverts are generally designed to handle events with a 50 year return period and, therefore, most of the time they convey considerably lower flows. In many situations, water flow through a typical multibarrel box culvert is relatively low throughout most of the year and usually concentrates in one barrel. A common adverse consequence for multi-barrel culverts when one barrel ends up carrying most of the flow during low-flow periods is that over several years of relatively low flow, some of the barrels may silt-in so as to become partially filled with sediment. Such sedimentation can reduce the capacity of culverts to handle the larger flow events and pose high-water problems upstream of culverts. This problem and the costs it incurs are compounded because many culverts are small enough in area, yet also rather long, that cleaning sediment from a partially filled culvert can be very difficult and costly. The problem is particularly severe for culverts draining small rural watersheds. There is a need for methods of prevention or reduction of the in-filling of culverts, both for existing culverts and new culverts. Existing manuals, books, and guides do not provide adequate information on sediment control at box culverts, or for multi-barrel culverts generally. The present paper focuses on ways to ensure that multi-barrel culverts do not become silted in. The paper focuses especially on methods whereby culverts may self-cleanse themselves of sediment.