More and more of our customers are being asked to provide attenuation systems onto their build projects often at relatively small scales and this brings with it one significant problem. If you need to install an attenuation system then you may struggle to find a provider if the volume is between 20m3 and 150m3.
These jobs are too small for many of the big installers and although you may be able to buy the crates at a reasonable price you then need to install to a certified and approved quality. Although all the components for an attenuation system can be purchased from a range of builder’s merchants, often minimum order quantities stymie you straightaway, for a typical 30m3 system you would need around 100m2 of 180gsm membrane – typical minimum order standard roll size is 450m2 the attenuation membrane (LLDPE) is quite a specialist product even if you can buy this you will still be looking at very large rolls, almost certainly you are going to end up with more left over than required to do the work!.
Another issue is site welding; the attenuation membrane needs faultless joints. In order to joint the membrane you will need to hire welding equipment. This can all get a bit intimidating especially if there is no warranty or certificate of conformity at the end. This is why we teamed up with our vastly experienced UK wide installation partner UK Membranes to overcome this particular problem.
It was late last year when we launched our UK wide installation service offering a simple price per cubic metre which includes
- Crates and membranes
- Installation – customer to complete site civil works
- Full membrane wrap – on site welded
- Certificate of Conformity on completion
Customers have been impressed by the no hassle approach but even more so by the price which (job / site / size dependent) can be as little as £125.00 per m3 installed.
One of our customers Mr T Sharples said “we were obliged by the planners to install a 140m3 attenuation system onto a small housing project in a village in rural Warwickshire; initially we priced this ourselves using components and our own labour, but when we looked again at all the costs and the compliance issues Ecomerchant’s installed price was highly competitive and offered the peace of mind of a certified installation, in the end it was a simple decision.”
About the Ecomerchant Aquavoid system
Attenuation 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 crates with both a geotextile and geo- membrane surround as part of a SUDs scheme.
Used as an attenuation system when the normal drainage systems cannot cope with the volume of surface water this is diverted into the attenuation system and released slowly after the storm has passed avoiding localised flooding. Buried 0.5m below the surface connections of any diameter can be made to the system. Ideal in amenity areas and even under car parks and other load bearing areas, Aquavoid-ECO is able to take normal traffic loading.
Aquavoid-ECO is an extremely strong modular water-permeable polypropylene unit with a large storage capacity.
The Aquavoid-ECO has been designed specifically to meet the needs of sustainable construction as advocated by the UK Government and provides the means for rainwater, collected from roofs and pavements, to be infiltrated into the soil. The sewage system is relieved of additional loads and drying out of the sub-surface can be prevented.
- Prevents extreme peak flows to main drainage and water purification systems
- Rainwater is “cleaned” by geotextile surround
- Decreases flooding during heavy rain falls
- Promotes the balance in the groundwater position
- Decreases environmental problems caused by development
- Flexible – can easily be expanded in all directions
- Enables rapid construction of large storage capacities (95% voids)
- Economic to install
- Choice of many diameters for incoming pipes Inlets/Outlets: 110, 160, 200, 225 & 300mm diameter pipes
- Applicable for both high and low groundwater situations
- Housing developments
- Car Parks
- Landscaped Areas
- Recreational Areas
- Amenity Areas
- Caravan Sites
Nominal Size: 0.408m (W) x 0.685m(L) x 0.45m(H), 8 units/ m3, Weight/unit: 6.34 kg (Standard), 5.75 kg (Lite), Vertical Strength: 400kN/m2 (Standard), 200kN/m2 (Lite), Lateral Strength 80kN/m2, volume: 125 litres, Void ration: 95.0%
The above data indicates typical values – comprehensive independent physical test data on the structural and hydraulic properties of the system is available on request.
Following detailed assessment of the required volume of storm water to be stored (see CIRIA C522, R156 & BRE 365). The total number of Aquavoid-ECO-ECO units can be calculated using 8/m3 (950 litres @ 95% void ratio). Decide on the best configuration for the characteristics of the site in question and create the “box” accordingly using the length and width dimensions. As a guide units require approx 0.5m of cover in landscaped areas and 0.75m cover in vehicular areas with a 75mm sharp sand base.
Aquavoid Eco 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 – our standard crate is heavy duty 400kN/m2 crate we also supply a lighter weight version in our Eco Lite 200kN/m2 crate.
Probably the most relevant regulations regarding site water management will be The Building Regulations part H3 which place emphasis on allowing the surface water to drain into the ground locally where feasible. This is in line with SUDS policy. There are other regulations listed at the end of this article.
SUDS is used as an approach to dealing with rainwater which is particularly relevant to urban areas where there are increasing amounts of hard impermeable areas which tend to send rainwater straight into the drains and thence to the rivers rather than letting the water soak into the ground and get slowly released. During very heavy rainfall this extra runoff overwhelms the drains and causes flash flooding when sewage overflows into becks and rivers. During periods of drought, tree roots can suffer. The idea of SUDS is to hold back the water locally and release it slowly. In addition to attenuation the most common options are by combining some of the following s
- Using green / living roofs – which delay the speed of runoff
- Using permeable surfaces such as drives and car parking. Several companies manufacture pervious interlocking systems from fully recycled plastic in a variety of grades depending on bearing requirements. The gravel infill can be from recycled crushed hardcore, slate chippings etc.
- Installing a soakaway
- Creating a pond or Swale
- Creating wetlands
- Using lawns – which may be allowed to partly flood
- Installing and attenuation system. These are being increasingly required for new build providing attenuation maybe part of your planning approval
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.
Aquavoid Eco as an Infiltration System - Soakaway:
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 is collected from the roof , driveway and hard surfaces fed into the soakaway and then slowly infiltrated into the soil. By infiltrating relatively clean water into the soil, at a relatively slow rate the drainage system is put under less pressure. Infiltration of rainwater is part of sustainable construction as advocated by the UK Government.
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
Don’t forget our super convenient 1m3 pre-wrapped soakaway units, for smaller domestic applications- simple and easy, just place and go!
From just £208 per cubic metre delivered!
Source control principles and techniques, also called Best Management Practices (BMPs), are already forming part of planning controls in some areas and will become increasingly incorporated within new development projects especially with the amended Building Regulations Part H3 coming into force in October this year..
The four basic principles of SUDs
- Don’t hard pave surfaces unnecessarily – make use of porous surfacing materials and grass / gravel reinforcing systems
- Soakaway where possible or attenuate if necessary – this is part of storm water management
- Improve Water Quality – avoid pollutants entering the water course
- Re- use if possible – harvest rainwater and re-use
More guidance / Legislation on SUDs
- PPS 25 – Development and Flood Risk (Issued March 2010), PPS1, PPS3, PPS9 & PPS23
- Future Water – Government water strategy for England
- CIRIA C697 – The SUDs Manual – Best Practice Guidance
- CIRIA C698 – Site handbook for the construction of SUDS
- Flood and Water Management Act 2010 – Management of flood risk by DEFRA
- Surface Water Management Plan – March 2010 giving guidance to Local Authorities
- National Standards for Sustainable Drainage – EA, LA’s & House Builders working together
- Pollution Prevention Guidelines – Controlling pollution at its source
- Building Regulations Part H3 – including 2010 amendments. This will be superseded by this updated and amended version on October the 1st
Trade and private inquiries welcome