Culverts are devices used to allow flow of water beneath roads and access points were passage is necessary. They are often used to dispose of runoff from roadway ditches and to preserve road beds, ditches, and banks. Strategic placement will help alleviate flooding of roadways, reduce erosion, and reduce overall maintenance problems.
There are two main types of culverts:
- stream-crossing culverts
- runoff management culverts
Stream-crossing culverts are placed where roads meet water channels. The culvert averts the water underneath it. Runoff management culverts are placed to manage runoff away from roadways. These types of culverts are commonly used to transport upland runoff and the runoff accumulation in ditches and sides of roadways, away for disposal.
Culverts can be made from many different materials but steel, concrete, and polyvinyl chloride (PVC) are the most common. A hybrid of steel and concrete may also be used. Other materials used for culverts include structural steel plate (SSP), corrugated steel pipe (CSP), and aluminum. Material selection should be based on cost, span, topography, soil chemistry, discharge, climate, and state policy.
When selecting a culvert, there are different shapes to choose from. Culverts are available in circular shapes, box, pipe arch, horizontal ellipse, metal box, and open bottom arch. Culverts can range in size from small drainage culverts for driveways and highways, to larger structures or significant waterways or water control applications.
Also, the structural adequacy for the application is determined by geotechnical expertise. When designing larger culverts, structural design becomes a key factor as well. Minimally, culverts should be able to withstand an HS-20 loading in accordance with design procedures defined by the American Association of State Highway and Transportation Officials.
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