A culvert is a conduit used to enclose a flowing body of water. It may be used to allow water to pass underneath a road, railway, or embankment for example. Culverts can be made of many different materials; steel, polyvinyl chloride (PVC) and concrete are the most common. Formerly, construction of stone culverts was common.
There are three primary materials that culverts are made out of (in order of importance): steel, concrete, and polymer (plastic). They can also be built as a hybrid between steel and concrete, for example an open-bottom corrugated steel structure on concrete footings, or a corrugated steel structure with a concrete "collar" around the ends.
A minimum energy loss culvert or waterway is a structure designed with the concept of minimum head loss. The flow in the approach channel is contracted through a streamlined inlet into the barrel where the channel width is minimum, and then it is expanded in a streamlined outlet before being finally released into the downstream natural channel. Both the inlet and outlet must be streamlined to avoid significant form losses. The barrel invert is often lowered to increase the discharge capacity.
The concept of minimum energy loss culverts was developed by Norman Cottman, shire engineer in Victoria (Australia) and by Professor Gordon McKay, University of Queensland (Brisbane, Australia) during the late 1960s. While a number of small-size structures were designed and built in Victoria, some major structures were designed, tested and built in South-East Queensland. The largest minimum energy loss waterway is the Nudgee Road MEL waterway near the Brisbane airport with a design discharge capacity of 800 m³/s. Built between 1968 and 1970, the waterway design tested in laboratory with a 1:48 scale model. Since completion, the structure passed successfully floods up to 400 m³/s. An unusual construction feature is the grass-lined channel bed. Several minimum energy loss culverts were built in Southern Brisbane during the construction of the South-East Freeway, along Norman Creek in 1974-1975. The design discharge capacity range from 200 to 250 m³/s. All the structures are still in use today.
If a culvert made of steel is not properly galvanized, the culvert can eventually collapse, again disrupting the road or railway above it. This happened at a culvert near Gosford, New South Wales in 2006, killing five.