The issue of water attenuation is an increasingly hot topic, with more occurrences of extreme weather patterns being experienced across the UK.

This is placing drainage at the heart of construction projects, and with the sector kicking into gear following a challenging 2020, Mark Halsall, National Manager – Storm Water Control at ACO Water Management, takes a look at a critical component in drainage design: geocellular structures.

What is a geocellular structure?

Geocellular structures are a form of attenuation & infiltration system, designed to store excess water in circumstances where heavy rainfall means that the volume of water flowing from a site is too high to go immediately into sewers / off-site drainage. Water that is ‘rejected’ from the outfall flows back up the system and into the geocellular structure, where it is stored until the allowable discharge rate from site permits the storm water to join the off-site network or water body.

Geocellular structures store water underground, in a way that maintains structural integrity under the site and prevents leakage into the surrounding soil. Their versatile design allows them to be used in configurations and applications across all construction environments, as a standalone solution or as part of an integrated sustainable drainage system (SuDS) scheme. They are used across virtually all types of projects, from housing developments and car parks though to retail sites, and are vital in controlling the removal of rain water.

When selecting geocellular structures, there are a number of common misconceptions and challenges facing engineers and contractors. However, before exploring how these can be overcome, there are two key considerations that we must address:

1. Maintenance and cleaning
2. Specification and installation

Let’s take a look at both in more detail.

Maintenance and cleaning

One of the key considerations in attenuation is keeping the stored water free from contaminants. Although technology exists to ‘clean’ water as it moves through the drainage network and into the geocellular attenuation tanks, this is unlikely to be 100% effective, and as such there will still be a need to regularly maintain and clean them. A build-up of silt will reduce porosity of the structure, which essentially means the total amount of water that can be stored in the geocellular structure falls. Given that attenuation is designed to cope with worst-case scenario rainfall, it is important to ensure porosity remains as high as possible.

With that in mind, the latest geocellular structures are designed to provide straightforward access. ACO’s Stormbrixx range, for example, benefits from an ‘open structure’, which ensures easy navigation within the inside of the tank. Featuring access shafts at the top of the tank, it helps to keep the structure clean and operating effectively during heavy rainfall.

Specification and installation

Geocellular structures are likely to become more important than ever in the face of increasing rainfall and densely populated urbanised areas. This places extra importance on getting installation and specification right, with a one-size-fits-all approach likely to cause more harm than good.

In a bid to help those tasked with delivering water management solutions, ACO Water Management is running a free CPD which looks at the design, specification, and maintenance considerations associated with geocellular structures.