Backwater Level

Published: July 31, 2018 | Last updated: July 5, 2023

What Does Backwater Level Mean?

Backwater level is the difference between the normal water level and the water surface level resulting from an obstruction to the water' s flow in a gravity flow pipe, such as a sewer.

Such obstructions can result from trenchless installation; for example, failure to fully remove debris from the pipe in a pipe ramming operation or pulling debris into a new pipe as it's pulled through a bore.

Obstructions can also occur as a result of repair materials such as pipe liners, that do not properly adhere to the interior surface of an older, damaged pipe (called a "carrier pipe") undergoing relining or slip lining.


Trenchlesspedia Explains Backwater Level

When water passing through a gravity-fed pipe, such as a sewer pipe, encounters an obstruction to its flow, the water will attempt to flow around the obstruction. Because the volume of flow does not decrease, the obstruction causes the water to back up within the sewage pipe, preventing the gravity-fed sewer from operating properly.

Backwater level is also a design issue for trenchless operations. For example, if an open storm drain flows into a pipe of insufficient size, the stormwater flow – the backwater level – will cause the storm drain, not the storm sewer, to back up.


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