culvert

A culvert is a drainage structure that conveys water under roads, railways, or embankments. It serves as a conduit for surface runoff or streams and is designed to pass flow while preventing roadway inundation. Culverts can be enclosed tunnels or open-bottom channels and are distinguished from bridges by their primary drainage function and typical integration with the roadway rather than spanning a gap.

Common culvert types include pipe culverts (circular, elliptical, or arch-shaped), box culverts (rectangular), and arch or slab-culverts. Open-bottom designs may be preferred for ecological reasons or headwater management. Materials vary, with concrete and reinforced concrete common for durability, and steel, aluminum, or plastics (such as HDPE) used in lighter or specialized applications.

Design considerations include hydraulic capacity for the drainage area, sediment and debris transport, scour protection at inlets and outlets, and compatibility with wildlife passage where required. In environmentally sensitive areas, culverts may be sized or chosen to maintain ecological connectivity and reduce blockage risk.

Installation requires proper bedding, alignment with grade, and stable backfill. Regular maintenance involves clearing debris, inspecting joints and leaks, monitoring scour, and replacing damaged elements. Upgrades may be needed as flows change or road networks expand.

Culvert projects typically fall under road and drainage authorities and may require hydrological analysis, permits, and environmental approvals, including fish passage requirements where applicable.