When any previously undeveloped site is built on and paved over, water run-off from the newly impermeable surface increases by up to 80%. This can place excessive pressure on existing watercourses and local drainage infrastructure. So when storms bring sudden, unusually heavy rainfall, there can be localised flooding and damage to property.
Government and the Environment Agencies are now promoting the use of Sustainable Drainage Systems (SUDS) to restrict run-off to a level equivalent to that of a natural green field site. SUDS policy aims to achieve this in two ways:
- Temporary storage of excess flows, so that immediate outflow into streams and rivers is limited
- Efficient soakaways to infiltrate stormwater into the ground
Rising rainfall levels, and increased focus on SUDS compliance, have led to a sharp increase in the use of Stormwater Infiltration Cells systems to create underground structures for infiltration or temporary storage of Stormwater.
Benefits of these systems are:
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Significantly reduced flooding risk
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Controlled, reduced-volume release of stormwater into existing sewer systems or watercourses
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Recharging of local groundwater (in an infiltration or soakaway application)
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Sustainable, cost-effective management of the water environment
There are essentially two approaches to run-off attenuation or storage:
- ATTENUATION STORAGE – this requires a tank or other impermeable retention unit to hold the run-off and discharge via a pipe directly to the existing sewer or water course.
- INFILTRATION – this requires the retention unit to act like a soakaway and to allow the run-off to be discharged directly into the surrounding ground.