What Is a Culvert Pipe? 9 Things (2024) You Must Know

If you want to drain rainwater away from your property or you’re interested in constructing a stream crossing, a culvert pipe may be a good fit.

You can create a culvert in a stream or driveway.

To do this, you’ll need to follow these steps:

bulletDetermine if you need a permit

bulletUnderstand the installation process

bulletFigure out how to best implement the installation in the location

For the above, use the tips below to enhance your understanding and determine if you need a professional on board.

1. What is a culvert pipe?

A culvert pipe is a structure that channels water past an obstacle or to a subterranean waterway.

Normally, culverts are embedded so they can be surrounded by soil.

You may also hear the word used in the U.K. for a longer artificially buried watercourse.

Culverts are used as cross-drains.

They help to relieve drainage from ditches at the roadside and pass water under a road at natural drainage and stream crossings.

Culverts come in a variety of shapes and sizes — round, elliptical, flat-bottomed, open-bottomed, pear-shaped, and box-like constructions.

The shape of the culvert pipe is determined based on factors like hydraulic performance, limitations on upstream water surface elevation, and roadway embankment height.

2. What is a culvert made from?

Culverts can be made from a variety of materials.

Here are the most common:

  1. A pipe
  2. Cast-in-place or reinforced concrete (preferred)
  3. Galvanized steel
  4. Aluminum
  5. Plastic (high-density polyethylene is most common)
  6. Composite structures made of two or more materials

3. Where are culvert pipes located?

The location of culverts should be based on economy and usage.

Placing culverts under roadways or railways is an economical route.

It also helps to minimize the flooding of important pathways.

Culverts must be strong because they support heavy vehicles, and thus, constructing them under roadways allows them to be placed perpendicular to the road.

Culverts should always be designed with both water flow and wildlife of a particular location in mind.

They want to help water flow efficiently and minimize the disruption to animals in the area.

4. What are the different types of culverts?

Here are the different types of culverts used in construction:

bulletCulvert pipes

These are rounded culverts — either single or multiple.

When a single pipe is used, the culvert has a larger diameter.

If the width of the channel is greater, then multiple culvert pipes are installed.

They’re made from a variety of materials, including steel or concrete.

bulletArch culvert pipes (pipe arch culvert)

This type of culvert looks like a half-circle.

Pipe arch culverts are suitable for larger water flows.

However, to install these, the flow should be stable because the arch shape allows drainage flow easily to the outlet.

Arch culvert pipes are favored in situations that require multiple culverts or when the installer wants a more aesthetically pleasing appearance.

Another variation of this is the arch culvert which is highly similar to the pipe arch culvert.

However, in this case, an artificial floor is used below the arch.

This floor is often made of concrete like the arch.

However, steel is sometimes used (although, this is a very expensive alternative).

bulletBox culvert pipes

This culvert is a rectangular-shaped pipe that’s usually concrete.

These culvert pipes are normally used to dispose of rainwater, which makes them less useful in a dry period.

However, they can also be used to allow animals or humans to cross a roadway or railway during dry periods.

Because these culverts have sharp edges/corners, they aren’t suitable for larger velocities.

They can, however, be installed in multiple numbers where necessary.

bulletBridge culvert pipes

This type of culvert pipe is used for canals and rivers while doubling as a road bridge for vehicles.

To create this dual-purpose culvert, a foundation is laid under the ground surface and then a series of culverts are laid with the pavement on top.

Most often, bridge culverts are rectangular or box-shaped.

If they are boxed-shaped, then an artificial floor isn’t necessary.

5. How do culvert pipes work?

Culvert pipes are hydraulic conduits.

They convey water from one side of a roadway or traffic embankment to the other.

They have the dual purpose of acting as both hydraulic structures as well as load-bearing structures for cars, pedestrians, etc.

As a result, they must be made from strong materials like concrete and steel.

6. Why do you need culvert pipes?

Culvert pipes serve a variety of purposes.

Primarily, they help prevent roadway and railway flooding.

Because they carry the weight of multiple vehicles, pedestrians, or trains, they must be able to withstand weight and erosion.

Engineers use strong and long-lasting materials like concrete, steel, plastic, and aluminum to build culverts.

By installing culverts, you create structures that help water flow below roadways or railways rather than over.

Culverts also protect electrical cables that run from one side of the roadway or railway to the other.

7. What should you keep in mind when installing culvert pipes?

If you’re considering installing culverts on your land, here’s what you should know.

The following tips can help you address pipe sizing, installation, pipe material, erosion protection, maintenance, and more.

bulletUse a pipe no smaller than 18-inches in diameter with 18-inches of clean, compacted cover

You may find that a pipe smaller than 18 inches is the “right” size, but size isn’t everything when it comes to properly designing culverts.

Having at least an 18-inch pipe makes the culvert easier to clean when it inevitably becomes clogged with leaves, pinecones, pop cans, and other debris.

And if you have a 6-inch pipe, you’ll find it’s pretty hard to keep your culvert properly functioning when it’s constantly getting clogged.

bulletMeasure the cross-sectional area of the culvert crossing as well as the slope

You want to design a crossing that’ll function during spring melt and summer afternoon thunderstorms.

Measure your stream’s width and depth right at the scour mark or high-water mark.

Multiply these two numbers together and divide by four to get your projected pipe diameter.

For example, if your average stream width and depth at the high-water mark is 10′ by 2′, then your calculation looks like this:

(10 x 2)/4 = 5ft pipe diameter

Keep in mind that the pipe height cannot be taller than the stream depth, so in this case, you may have to use multiple small pipes to build the culvert.

At the same time, be sure to measure the stream slope, as this can affect your pipe capacity.

Here’s a simple way to measure: Pull a 10-foot rope taught downstream with a line-level bubble attached to obtain level and measure the feet of rise from the channel bottom to the end of the string.

Next, calculate the slope by dividing the length (10 feet) by the rise.

Generally, pipe slopes are kept to something less than 0.25 feet per foot or 2.5 percent.

The steeper the pipe, the greater its capacity since the velocity of water flow is greater.

A higher velocity also means you need more energy dissipation at your outlet.

Does all of this sound complicated?

It is!

This is why it is generally best to hire a professional to size your culvert for you.

bulletPlace multiple culverts at least one culvert diameter apart

Separating your culvert pipes to ensure that the soil can be worked into a tight bond with a compactor is important.

Otherwise, a phenomenon known as piping can occur.

This means that water enters the space between the culvert and the backfill.

It then saturates the soil and slowly washes away fine particles.

This creates a larger void and erodes the soil until a failure occurs.

A “failure” could be when a storm washes out the remaining soil and causes a blowout or when a vehicle sinks into a hole and crushes the culvert.

bulletCompact clean soil tightly in and around culverts and the cover material

One of the top failures of culvert crossings includes poor compaction and debris-laced fill.

To install a culvert properly, you’ll need to carefully place and compact a clean fill.

Install a granular backfill of pea gravel (also called pipe bedding) in the trench to a depth of 6 inches.

You should do this both under the pipe and on both sides up to the midway point.

This will help drain groundwater and seepage away from the outer walls of the pipe and also assist in preventing piping failures.

bulletUse maximum side slopes of 2:1 (H:V) and a road surface width of at least 12 feet to calculate the pipe length

Often, people try to get by with a short pipe length when designing a culvert.

However, the design must account for the road side slopes, depth of cover, and roadway width to calculate the necessary length of pipe.

Side slopes that are constructed at a 2:1 ratio are generally unstable and erode quickly in the first few years.

They’re also difficult to maintain and establish vegetation on.

Ideally, the slope should meet the bottom of the pipe and not the top.

The latter causes a very steep point over the pipe that easily is eroded.

Add twice the diameter of the pipe, twice the slope length (cover times slope), and the roadway width to determine the pipe width.

If your culvert is in a steeply sloped channel, more length is necessary.

However, this approach works for most crossings.

bulletConsult a professional when working with special-use pipes

If you’re working with arch pipe, elliptical reinforced concrete (RCP), noncorrugated steel, and PVC, you should work with a professional as they must be carefully applied.

These special-use pipes are more technically challenging to install properly.

bulletAdd riprap protection to the upstream and downstream approaches to culverts

To provide scour protection, riprap and concrete rubble are installed at the ends of the culverts.

However, it’s often placed incorrectly or is too small to provide the necessary level of protection.

Seek professional judgment for site-specific measurements as sizing riprap can be fairly complicated.

bulletCheck the condition of the crossings frequently and clear the opening of debris

A culvert cannot operate properly if it’s blocked.

Make sure you maintain your culvert pipes and check for snow, ice, twigs, leaves, or any other debris that may clog the opening.

Simply performing a routine drive-by can ensure that the opening remains free and clear.

bulletKnow your limitations

Some jobs are too big for DIY.

Don’t be afraid to reach out and get help.

You don’t want to damage downstream areas with an improperly-designed crossing.

After all, that’s your responsibility as a landowner.

In many areas, designs on live streams require federal, state, and local permits.

Asking a professional for their guidance can ensure your land remains in tip-top condition.

8. What is the process of removing culverts to restore an open-air watercourse?

Removing culverts to restore an open-air watercourse is known as “daylighting” or “deculverting” — the latter is most used in the United Kingdom.

Daylighting is the practice of removing streams from buried conditions and exposing them to the Earth’s surface to either directly or indirectly enhance the ecological, economic, and socio-cultural well-being of the region as well as its inhabitants.

9. What are the environmental impacts of culvert pipes?

Culvert pipes can be functional, but they do have some negative impacts on the environment.

Here are the most important.

bulletPoor water quality

bulletIssues for aquatic organisms (ex: Fish commonly lose their habitats because of poorly designed crossing structures)

bulletScouring and erosion when culverts are poorly designed

That said, if the culvert pipe is properly designed and best management practices are implemented, then the above are just short-term impacts.

The overall effects on aquatic biology are minimal.

Final Thoughts

So, what’s the verdict?

Do you need a culvert pipe on your land?

Will it help enhance water flow?

Don’t hesitate to reach out to a professional if you’re unsure at any point.

If you make an error during this installation, you can damage your land downstream and end up needing to redo the entire process.

Best of luck!

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Erika Gokce Capital

Disclaimer: we are not lawyers, accountants, or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.


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