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What do you need to know about attenuation tanks?

Is your property situated in a flooding hotspot? If so, you’re most likely aware of the damage it does to our lawns, property foundations and electrics, which can be incredibly dangerous.

So, what can you do to tackle flooding caused by heavy rainfall? One option is to install an attenuation tank.

But what exactly is an attenuation tank, how does it work, and are there any legal requirements when installing one?

In this blog, we explain everything you need to know about attenuation tanks.


What is an attenuation tank?

Designed to store and disperse stormwater from the surface, an attenuation tank is an underground flood management system.

The water gathered in the attenuation system is redirected and gradually discharged into a local watercourse, such as a river or reservoir.

This flood management system can last up to 120 years as it’s made from corrosion-resistant plastic.

Attenuation tanks are positioned in the ground, typically in urban areas with impermeable surfaces such as tarmac and concrete.

However, they must be installed beneath the soil so they can be accessed easily for maintenance.

How do attenuation tanks work?

Stormwater is channelled downwards from roof drainpipes into a gully or channel drain that’s connected to a filter unit installed beneath the ground.

The filtration unit removes and collects silt from the stormwater, preventing it from clogging the tank. The water then flows into the attenuation tank through inlet piping.

Once collected in the tank, the rainwater is temporarily stored and held back by a water flow-control chamber to prevent overwhelming the local watercourse.

Once ready for discharge, the flow-control chamber pumps the stormwater through an outlet pipe into a local sewer or watercourse – for example, streams or reservoirs.

Is an attenuation system the same as a soakaway?

Attenuation tanks and soakaways are both flood management systems installed beneath the surface. However, they differ in how they remove and disperse stormwater.

A soakaway consists of plastic crates wrapped in a geotextile membrane that collects rainwater from the surface and slowly disperses it back into the surrounding soil.

Conversely, an attenuation tank redirects stormwater to another area rather than releasing it into the soil.

Are there any legal requirements when installing an attenuation tank?

Under the Flood and Water Management Act 2010, those installing stormwater drainage must use sustainable flood management methods that don’t impact the local environment.

Sewers or streams will overflow in the event of excessive water volumes, meaning they’re at risk of flooding. Therefore, discharge to a waterway will require consent from the Environment Agency.

Additionally, an attenuation tank shouldn’t be installed in areas that experience excessively heavy and continuous rainfall.

Sustainable Urban Drainage (SuDS) are usually installed by developers in those areas. SuDS are an alternative to channelling stormwater to sewers and watercourses. 

An example would be housing estates, where stormwater runoff and drainage can cause issues.

Speak to trusted drainage system retailers

If you’re unsure whether an attenuation tank is the correct flood management system, get in touch with our team on 0121 351 3230 for guidance and advice.

We can assist you in selecting the correct-sized tank and stormwater drains for your project.

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