Culvert

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A large stone culvert (1888-89) in Blackwater Canyon, West Virginia. The structure formerly supported a railroad.

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.

1 Types
2 Design
3 Problems
4 Minimum energy loss culverts
5 Forestry
6 See also
7 References
8 External links

[edit] Types

Culverts come in many shapes and sizes, including round, elliptical, flat-bottomed, pear-shaped, and box. They vary from the small drainage culverts found on highways and driveways to large diameter structures on significant waterways or supporting large water control works. The latter can comprise large engineering projects.

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.

[edit] Design

In the United States, the primary guidance used by engineers in the design of culverts is the AASHTO LRFD Bridge Design Specifications. In Canada, it is the Canadian Highway Bridge Design Code, or CAN/CSA S6-06.

Designing a culvert draws on the expertise in several disciplines of civil engineering. The first step of determining an adequate size draws on the hydrologic and hydraulic aspects, while determining its structural adequacy for the intended application draws on geotechnical expertise. For larger culvert sizes, open-bottom culverts, and concrete culverts, structural design becomes a factor as well.

[edit] Problems

A small culvert under a pedestrian walkway.

Culvert construction can destroy wildlife habitat and affect behavioral patterns of fauna. In the Pacific Northwest of the United States, it has been found that many culverts impede upstream migration by salmon. Research is being carried out to determine how culverts can be adapted to make it easier for salmon and other fish to pass through them against the current. In Australia, Platypuses often avoid culverts when swimming because of the uniform water flow inside of them. Instead, they climb ashore and cross the road, which has resulted in larger numbers of the species becoming roadkill.^{[citation needed]}

When used to transport water in streams or rivers, the capacity of the culvert is generally lower than the capacity of the river itself. This results in the water overflowing the road surface during heavy flow events. If this is by design, the result is referred to as a low water crossing. When this is unacceptable, the culvert-based crossing must be replaced by a more expensive system such as a bridge.

Also, debris and trash that is carried by the water may get stuck in the culvert, decreasing the flow of water even further.

Culverts are also seen as unsightly compared to a bridge.

[edit] Minimum energy loss culverts

In the coastal plains of Queensland (North-East of Australia), torrential rains during the wet season place a heavy demand on culverts. Further the natural slope of the flood plains is often very small (S_o ~ 0.001) and little fall (or head loss) is permissible in the culverts. Professors G.R. McKay and C.J. Apelt developed and patented the design procedure of minimum energy loss culverts waterways which yield small afflux. Professor C.J. Apelt presented an authoritative review of the topic (Apelt 1983) and a well-documented documentary (Apelt 1994).

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.

A culvert on an irrigation canal in southern Alberta, Canada.

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.