What is a culvert and what type should I use?

Culverts are lateral and completely enclosed drainage structures that run under the road or part of the land. The size and type of culvert depend on the water flow, the area discharging to it, and the depth at which the culvert is installed. Some culverts can also be used as roadway surfaces, but they are always used to convey water through pipes or channels. In general, the choice and type of material will depend on comparative costs, location of the structure, availability of skilled labor, time constraints, and the proposed design.

Box Culverts

One of the most common types of culverts is the box culvert. A box culvert has a concrete (and sometimes other materials can be used) floor that allows water to flow smoothly through it. Box culverts are usually composed of reinforced concrete (RCC). Some box culverts can be constructed using composite structures, which are useful when water needs to change direction or when a large flow of water is expected. Box culverts can also be installed in such a way that the top of the culvert is also the roadway. The most challenging part of installing these types of culverts is that you usually need to have a dry surface to install the culvert on, so water will need to be dewatered or diverted to complete the installation.

Arch Culverts

Arch culverts are usually low-profile culverts. It allows them to be installed without disturbing the causeway as it will span the entire width of the drainage. They are usually made of metal, masonry or RCC. They are simple to install and you do not need to use expensive diversion structures to install them. Common shapes include semicircular arches, elliptical arches and concrete box culverts. Another benefit of this structure is that the installation process does not take much time compared to traditional box culverts.

Pipes

Pipe culverts come in different shapes such as circular, elliptical and pipe arch. While round pipes are the most common, other shapes may be used depending on site conditions and job site constraints. They are very competitively priced and they are easy to install. As with other culvert types, the choice of the culvert will depend on the hydraulic design and other factors that may affect its performance and suitability. It is the preferred choice in urbanized areas and is often used to manage storm drain systems.

Culvert Installation Selection Tips

When deciding on the right type of culvert for your project, you will need to consider the following.

Culverts need to be installed at the correct elevation and slope to avoid erosion problems.

Maintenance of enclosed culverts can be an issue and will become more challenging over time. Maintenance costs should be considered in the selection process.

Culvert entrances and exits need to be carefully designed and installed. Sloped ends are the most efficient way a culvert can be closed. The sloped end will allow proper flow and facilitate the flow process.

Flared ends at the culvert outlet will reduce or prevent scour.

It is recommended that a rock throw or similar structure be installed at the culvert outflow to prevent erosion.

If required, backfill the sides, underside and top of the culvert with the proper aggregate. The correct aggregate will prevent erosion and protect the culvert itself.

Where possible, install culverts on all roads.

Consider the amount of traffic that will travel over the culvert and the depth at which the culvert will be installed. Sometimes culverts can collapse if not designed properly.

Installation cost and available resources are always important factors to consider before making the right choice.

Other considerations when installing a culvert

Once you have decided on the type of culvert you will use, be sure to verify that all environmental permits are up to date. Also verify that all NPDES requirements are met and that the proper equipment is available to install the culvert, backfill and compact the soil according to engineering specifications.