Stormwater Management Attenuation & Soakaways
Attenuation crates, Storm Cells, Soakaway Modules, Storm Crates all names for the same thing, they describe an interlocking crate system that has high strength and high void ratio: for Aquavoid Eco >95% They allow surface water to be stored in one location and gradually released back to the ground, a bit at a time, at a pace the ground can handle, rather than in one sudden deluge, as happens during a storm or downpour. In effect, the transfer of water from the surface to the ground is attenuated, is slowed down and stretched out over a longer period.
If you dump 1,000 litres of water onto a patch of ground in one go, unless you're on sand or gravel, it's unlikely the ground will be able to absorb all that water instantly: attenuation cells work by taking all the water as fast as it's delivered, returning what it can to the ground as quickly as possible, but storing the surplus until the ground is ready and able to absorb it.
Attenuation cells are specially manufactured, modular cells that provide lots of space (void space, as it's termed) within a lightweight structure that is capable of supporting quite significant loads when buried. Some cells can be placed beneath pavements and are strong enough to carry both foot and low-speed vehicular traffic – see the following oinks to our for heavy duty 400kN/m2 crate and our Eco Lite 200kN/m2 crate
Planning Law today aims to avoid inappropriate development in flood risk areas and whilst the risk of flooding cannot be prevented entirely, its effects can be reduced by good practice and the assessment of the risk that any new development poses. Sustainable measures are then included in the design to cater for the potential of flooding during periods of high rainfall.
Where the surrounding ground is insufficiently permeable to allow the volume of water to infiltrate away naturally, the insertion of a soakaway structure as part of a SUDs scheme (Aquavoid Eco with a permeable geotextile surround) will help this process dramatically by providing an underground void for temporary storage of the storm water whilst it infiltrates into the surrounding soil.
Used as a soakaway the rainwater collected through pipes from the roof and/or road can be slowly infiltrated into the soil. By infiltrating relatively clean water into the soil, the drainage system is relieved and drying out of the sub-surface can be prevented. Infiltration of rainwater is part of sustainable construction as advocated by the UK Government.
Attenuation just means to temporarily store storm water for a period of time, normally until the worst of the storm has passed, the water is then released to the sewer network. This process uses a “sealed” storage box (attenuation tank) created from our Aquavoid Eco systems with both a geotextile and geomembrane surround as part of a SUDs scheme. The storm water is collected by normal road gullies and routed to the sewer in the normal way, but is passed through a “control manhole” that only allows a controlled volume of flow through to the mains. The water then backs up in the manhole and is fed into the temporary attenuation storage system and over a period of time this stored water continues to exit the system through the control manhole at a regular rate thus preventing flooding downstream. Systems like these have often been part of a commercial SUDs scheme however more and more self and custom builders are finding that schemes are required by local authorities, through legislation and often for plots with a number of houses, if you need a SUDs compliant system and would like design guidance just give us a call on 01793 847 444
Advantages of the Aquavoid Eco crate system
- High Bearing Capacity, sufficient for pedestrian & traffic for light traffic Eco Lite 200kN/m2 and for heavy duty use the Aquavoid Eco Standard 400kN/m2
- Large Storage Capacity, 95% voids
- Economic to install & maintain
- Suitable for high and low groundwater situations
- Inlets/Outlets: 110, 160, 200, 225 & 300mm dia pipes
Have you seen how to use our Firmground to create a free draining load bearing driveway?