Drainage Terminology Explained

For many people, drains are rarely thought about in detail, if at all, until they encounter an issue. The parts we can see – the pipes and the grates – might be all we ever notice about them, but drainage is a complex system with a lot of variables.

Below we break down some of the most common drainage terms that you may find useful should a drainage issue arise.


A culvert is an enclosed drainage structure that runs under a road or a part of land. It functions in a similar manner to normal drains, but on a larger scale. According to the Highways Agency, the structure must be wider than 90cm to be defined as a culvert.

Drain tracing

Drain tracing is a method of inspection used by drainage companies to locate things like blockages, collapsed drains and concealed manholes in areas that would otherwise be very difficult or even impossible to reach.

Drain tracing works by using electrical impulses to get a clear picture of the different features of a drainage system, whereupon operators using CCTV monitors can see what and where the problem is, and then decide on the best course of action.


Effluent is the name for wastewater that has been either partially treated, completely treated or in its natural state. The term is used when the water is flowing out of a pipe or treatment plant.


The process by which soil or other sedimentary material is moved or worn away by the flow of water. This can happen everywhere, from inside pipes and drains to ground surfaces.


A gully is used to allow surface water runoff to enter a sewage system. It uses a grate and a  grit trap to ensure that minimal debris enters the system with the water.


Drain interceptors are designed to stop waste materials such as chemicals and various types of oil from entering our sewage systems. The interceptors remove these contaminants from the water that passes through, allowing the unwanted materials to be collected at a later date.

Lateral drains

Lateral drains connect the drainage system of a private property to a public sewer, allowing for the waste from that property to be transported from it and moved towards sewage plants.

Root ingress

Root ingress is a problem that is commonly found in drainage systems with underground pipes. It happens when a crack in an underground pipe allows water to seep out: the roots of nearby trees will seek out the nutrients from the water, which will lead them to the crack in the pipe. They can then force their way into the pipe itself, causing further damage and blocking the drain entirely.


A soakaway is a pit designed to receive surface water which is drained from above ground. This pit is usually filled with aggregates, such as small rocks and pebbles, which are used to allow the water to drain slowly into the soil.


Wastewater is the water that has been used in our homes and businesses and is now making its way through our drainage systems. No matter where it’s been drained from in a property, it’s classed as wastewater.

Water table

The water table is the upper level of an area of saturation. This means it’s the upper level of an area of land where the soil or rocks are permanently saturated with water. This area is also known as part of an aquifer, which is the point where water can go no deeper.

The above are just a few of the terms that are used in relation to drainage systems. While technical jargon can seem complicated and overwhelming, Express Drainage Surveys aim to make it understandable.

If you have a specific enquiry about a particular drainage term or would like to know about a drainage service or technique, get in touch with the friendly team at Express Drainage Surveys today who will be more than happy to help.