What is a culvert?

Written on:

You may have heard the term culvert being tossed around when talking with contractors or your local authority during a building process, but what exactly is it?

A culvert is a large diameter drainage pipe that is normally found under a roadway. The culvert allows for water to pass through the opening without backing up on the roadway or eroding it out. Many local authorities will require you to install culverts when putting in a new driveway.

Types of Culvert Materials

When choosing a culvert material type there are a few considerations such as cost, durability, and local regulations. Before you decide on a culvert material type, you will want to check with the local authority. If you are within city limits, you will need to call the city and tell them you are replacing or installing a new culvert – they will inform you of the material type and size that needs to be installed. The same is true if you are outside of city limits – you will have to call the county to confirm material type and size. If your property is located on a highway, you will need to contact the highway department. In some instances, we have talked with customers that have been able to get the city, county, or highway department to cover the material costs or even the whole project.

The two main types of culvert materials we normally install are HDPE or CMP, but we also see RCP and sometimes PVC. Below we will break down the details and pros and cons of each material.

HDPE (High Density Polyethylene) is a dual wall plastic pipe that is easy to install because it is lightweight, very durable, and not prone to corrosion because it is plastic. HDPE is often cheaper than CMP (corrugated metal pipe) up to a certain diameter, normally about 24”, and holds up well for a residential driveway in most instances. However in our experience, most counties and municipalities do not allow this material to be used in drainage right of ways at the front of your property.

RCP (Reinforced Concrete Pipe) is another very durable option for a culvert or drainage system. This type of material is often seen in commercial drainage systems where asphalt or concrete is required over the top of it. RCP is a very heavy material to handle because it is quite literally concrete with rebar in it. This culvert often comes in shorter sections than plastic or metal pipes due to how heavy it is. At Excavation Contractors LLC, we normally recommend installing plastic (HDPE) or metal (CMP) culverts instead of RCP in residential applications because of the cost difference and they will hold up just fine with normal residential traffic.

CMP (Corrugated Metal Pipe) is a durable metal pipe great for culverts. This pipe is a little more expensive than HDPE (if you need a culvert less than about 24”). Most municipalities, counties, or highway departments will require you to put this type of pipe in your driveway crossing if it is by the drainage easement on the roadway. CMP has come a long way since it was starting to produce in the late 1800’s to early 1900’s. CMP is made of steel material that is then galvanized to resist rust. CMP will normally last anywhere from 40-80 years as long as the galvanization remains intact. You may have seen some metal pipe that has become rusted or failed over time, but galvanization techniques have improved and those pipes were more than likely installed over 30 years ago.

PVC (polyvinyl chloride) is not as common of a culvert material but can be seen in some applications. We do not recommend this material to be used for culvert installations. One reason is that to get a sizable culvert to allow water to flow under your driveway may cost you TWO arms and a leg. This is because you will need to get schedule 40 pipe or better so that it does not crush under the weight of a vehicle. If you want plastic and are not under the jurisdiction of an authority, we recommend using HDPE for a culvert.

Final Thoughts on Culverts

Once you have decided (or have been told) what type of material you will use for a culvert, you may want to consider protecting the area outside of the pipe. Some ways you can do this is by cleaning out the ditch and placing erosion mats, concrete headwalls, or placing rip rap. We will break down the benefits of each below:

Cleaning out the drainage ditch and installing erosion mats can help to make sure you don’t get a bunch of debris inside of your culvert. When sticks and loose debris get caught in your drainage ditches, they can create a dam in front of your pipe causing water to pool in your ditch or even jump the top of your driveway causing erosion. In some instances, cleaning out the ditch will be mandatory for proper installation of your culvert to ensure water efficiently flows through the pipe. If you want a grass lined drainage ditch, you will need to grade the area so that water will flow and then install erosion mats so that during heavy storms, the water doesn’t erode the dirt away causing sediment to build up in your culvert.

Another great addition to a culvert is a headwall. A headwall is a concrete or block structure that attaches to the culvert. Headwalls help to keep your driveway intact by preventing water from hitting the bank of your driveway and making a circular motion that will compromise the integrity over time. Headwalls are a great way to ensure that the end of the pipe doesn’t get bent up or crushed from cars running it over on smaller diameter culverts. You will also want to install a headwall if you plan on putting asphalt or concrete over the crossing so that water does not erode the dirt and rock from underneath.

The final option to consider adding on to your culvert is to add rip rap. Rip Rap is a rock most commonly sized anywhere from 6”-12”. This rock is mainly used to control erosion and can help with slowing water down. In most applications, this rock is used in areas that have trouble growing grass. Grass doesn’t always like to grow as efficiently in areas that are sloped very steep or is too wet and ends up killing it. Rip rap can also add an aesthetic appeal for some homeowners depending on their landscape. It is more expensive to install rip rap than erosion mats due to material costs and equipment to place it, but does just as well, if not better, to mitigate erosion.

To get a quote from Excavation Contractors LLC on your culvert project, click the “Get a Quote” button and fill out the form!

Related Blogs