The traditional method of draining surface run off water from built up areas is through underground pipe systems. These systems are designed to take water quickly away from local areas and prevent flooding. During heavy or prolonged periods of rainfall, ultimately, large quantities of water end up at processing areas such as waste water treatment works, placing an unprecedented burden on the system.
Sustainable Urban Drainage Systems (SUDS) are designed to be incorporated not only into new developments, but retro fitted into existing developments, and takes measures to handle surface run off starting at source and working out to regional control measures.
There are many methods that can be applied to achieve an effective SUDS scheme and requires a coordinated approach. Generally they consist of small scale civil engineering constructions at a local level designed to handle the environmental risks resulting from urban run offs and contribute wherever possible to environment enhancement. Filter trenches provide a quiescent zone for removal of fine silts and also encourage filtration, adsorption and biodegradation processes. There will most likely not be one correct design answer to achieve on overall system, however the ultimate goal is to mitigate many of the adverse effects of storm water run off on the environment.
During the design process a SUDS project should aim to protect the environment but, at the same time minimise the use of finite natural resources and provide reasonable value to those involved in its design, construction and operation. A key factor that may be considered is the use of recycled or secondary aggregates such as Lytag® LWA. The environmental impact, taxes and transportation issues related to using natural aggregates mean that alternative sources must be considered. These more sustainable options may also produce long term cost savings.
Lytag® LWA typical properties
| Absorption |
>20% |
| Voids Ratio |
>40% |
| Hydraulic Conductivity |
>1.6x10-1 m/s |
| Aggregate Size |
>4/8mm and 4/14mm |
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Trenches
Trenches are shallow excavations, 1-2m deep, filled with Lytag® LWA to create a temporary sub surface storage for either infiltration or filtration of stormwater run off. Ideally they should receive water from an adjacent impermeable surface.
Dia 1.1 - Stormwater from road surface runing off into trench
Soakaways
Soakaways are circular or square excavations either filled with Lytag® LWA or lined with brickwork or concrete surrounded by Lytag® LWA. They can be single or grouped to form a system. Soakaways are unobtrusive, with minimal land take, providing stormwater attenuation at source and maintaining water for ground water recharge.
Dia 1.2 - Cross-Section through a traditional soakaway
Pipe bedding and tank surrounds
Lytag® LWA is a suitable material for bedding pipes with drainage systems as required in specifications such as EN 1610 and the Highways specifications. Providing a rounded, lightweight backfill material in particular for Geocellular systems that may be affected by large, angular aggregate in excavated material or, heavy, poor draining soils that will have the soakaway characteristics improved.
Green roofs
As part of the green roof system, whether they are intensive, extensive or simple intensive systems they all can add weight to a structure. By using Hortag® horticultural medium either as the drainage layer under the vegetation or as part of the soil/growing medium a reduction in overall weight can be achieved. Lytag® LWA is approximately 50% of the weight of natural aggregate. The combination of its drainage and moisture retention properties makes it an excellent choice.
Pervious pavements
Pervious pavements provide a pavement suitable for either pedestrian or vehicular traffic while allowing rain water to infiltrate through the surface to the underlying layers.
The water may be stored before infiltration into the ground or discharge into a water course or other drainage system. Pavements can be designed for many differing situations such as pedestrian walkways, car parks or highways. Lytag® LWA is suitable for some designs depending on the construction method and final use. Guidance should be sought before final design stage.
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