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What Is a Catchpit

By April 6, 2023Uncategorised

Wastewater management systems, whether it’s the mainline sewers or stormwater drainage surrounding roads and parks, can be susceptible to blockages which can lead to water backing up and causing floods.

To prevent this, catchpits are used to ‘catch’ debris or silt before entering the drainage system.

What is a catchpit?

Catchpit or cesspit is a stormwater device designed to trap debris like leaves, litter, and silt from entering downstream pipes, thus preventing potential blockages.

Also known as silt traps or interceptor traps, catchpits have been shown to retain between 30 to 50 percent total solids while laboratory studies show that catchpit sumps may be effective in retaining large objects and sediment particles larger than 500 µm (micron).

A catchpit comprises a grate, a small chamber, and a sediment trap. The chamber, known as the catchpit sump, is connected to an inlet and an outlet pipe. Although catchpits are designed to capture larger heavier debris that may get in through the grate, it also collects finer sediments that settle at the bottom of the sump.

How does a catchpit work?

The catchpit has an inlet pipe through which the wastewater enters. Typically, non-floatable debris, gravel and sand will settle at the bottom of the sump, while water overflows at the top and out through an outlet pipe which sits slightly lower than the inlet pipe.

A baffle can be fitted to the outlet pipe to filter potential floating debris from entering the pipe.

For catchpits to function effectively, accumulated debris and dirt must be removed through regular maintenance and cleaning.

When is a catchpit used?

Catchpits are used in all wastewater management systems and are typically found upstream so that it can collect all the debris and dirt before the water enters the main public or private stormwater pipes.

Vital in the management of surface water, catchpits are commonly found in environments that collect large quantities of dirt and debris, such as roads, railways, parks and gardens, driveways, and car parks. They are also used for main line sewers and stormwater drainage systems.

What catchpit products does Hynds have?

You will find the following catchpit products at Hynds:

Cesspit Units

We offer a range of precast concrete cesspit units, available as flat top or back entry. We also stock optional riser units.

Silt Traps

The silt traps are made from precast concrete suitable for areas like lawns and patios. Cast iron grates are also available and 50, 65 and 100mm holes can be drilled to suit the pipes.

Kerb Blocks

Made from precast reinforced concrete, these kerb blocks are for back entry cesspits. They are suitable for standard and mountable kerbs and they easily integrate with the kerb line.


Hynds Megapit® Units are designed for installation in areas where there is a need to intercept very high volumes of stormwater (up to 800 litres/second). These two-piece units are suitable to capture high flow of stormwater and inner-city locations.

Splay Catchpit Lid

Hynds Splay Catchpit Lids are designed for use with Auckland Transport single and double splay catchpits. They increase the kerb length to 2.4m (single splay) and 3.6m (double splay).

Hynds Street Catchpit

Developed with the Auckland City Council, the Hynds Street Catchpit is designed for improved hydraulic capture of stormwater flow. The street catchpit grates and frames are pedestrian and bicycle safe and the galvanised steel edging is durable and robust against damage from vehicles.

Hynds Superpit

The Hynds Superpit is designed and positioned to increase kerb inlet capacity above that of the standard cesspit grate inlets. Located at street level, the superpit units are used for high flow or increased flow applications. They allow excessive stormwater to enter the upstream inlet prior to the gate.