Last edited 21 May 2021


Back inlet gulley.jpg

A gulley is a fitting with a chamber which is designed to collect rainwater, wastewater and groundwater, conveying it to an underground surface-water sewer. Gullies can be used to drain waste water and rainfall from buildings, large paved areas and roadsides, pedestrian areas, parking areas, pavements, roofs and so on.

Usually buried in the ground, the gulley’s configuration typically involves a chamber and a trap (sometimes referred to as a trapped gulley), while its top surface often has a grille over which a waste or rainwater pipe can discharge. Trapped gullies can also be used to take waste water from household sinks and baths. Thus, gullies can collect rainwater from roofs, impervious surfaces and waste water from buildings. When used to drain large areas, they are frequently called yard gullies or road gullies.

The gulley’s top grille is usually designed to prevent leaves, litter and large objects from blocking the system, while the trap – which can be a P-, Q- or S-type – prevents odours from escaping into the environment and can make it difficult for rats to reach the surface. Over time, the level of sediment collecting in a trap can cause blockages which may require manual removal or mechanical suction.

Traditionally, gullies were made from cast iron or vitrified clay, but these have been largely superseded by PVC which is both cheaper and lighter whilst still being durable.

When a trapped gulley features a below-ground inlet coming from another gulley or water source, it is termed a back-inlet gulley. The horizontal inlet is typically located below the top grille but above the level of the water seal. Many gulley types provide the facility to rod the system when a blockage occurs down the line.

A gulley can also be a grated opening in a road gutter; or in a hard-landscaped area to evacuate rainwater from the surface.

Gulleys can also be used internally, e.g buried in the floor in a wet room application.

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