Soakaways have been the traditional way to
dispose of stormwater from buildings and paved areas remote from a public sewer or watercourse. In recent years, soakaways have been used within urban, fully-sewered areas to
limit the impact on discharge of new upstream building works and to avoid costs of sewer upgrading outside a development. Soakaways are seen increasingly as a more widely applicable
option alongside other means of stormwater control and disposal.
Soakaways must store the immediate stormwater run-off and allow for its efficient infiltration into the adjacent soil. They must discharge their stored water sufficiently quickly to provide the necessary capacity to receive run-off from a subsequent storm. The time taken for discharge depends upon the soakaway shape and size, and the surrounding soil's infiltration characteristics. They can be constructed in many different forms and from a range of materials.
This Digest describes design and construction procedures, explains how to calculate rainfall
design values and soil infiltration rates, and gives design examples.

What is the problem with paving front gardens?
Serious flooding in 2007 affected the UK. This resulted in loss of life, disruption of peoples' lives and caused damage estimated at about £3bn. In many cases the flooding happened because drains could not cope with the amount of rain water flowing to them. The effects of climate change mean that this kind of heavy rainfall event (and subsequent flooding) may occur more often in the future.
The drains in most urban areas were built many years ago and were not designed to cope with increased rainfall. Paving front gardens further adds to the problem. Although paving over one or two gardens may not seem to make a difference, the combined effect of lots of
people in a street or area doing this can increase the risk of flooding.
The harm caused by paving gardens is not limited to just flooding. Hard surfaces such as
concrete and asphalt collect pollution (oil, petrol, brake dust etc) that is washed off into
the drains. Many drains carry rainwater directly to streams or rivers where the pollution
damages wildlife and the wider environment. In older areas the rainwater may go into the
foul water sewer which normally takes household waste from bathrooms and kitchens
to the sewage treatment works. These overflow into streams and rivers in heavy rainfall.
As more water runs into foul sewers from paved areas there are more frequent overflows,
passing untreated sewage into watercourses.
Replacing grass and plant beds with concrete and asphalt surfaces means that water does
not soak into the ground. This reduces the amount that reaches our natural underground
aquifers. Some water that soaks into the ground will evaporate back into the air, causing a
cooling effect around the house. This is lost if the garden is covered with hard impermeable
surfaces and can cause local temperatures to rise (often referred to as the urban heat
island effect).

Living roofs is a broad term defined by the GLA to include green roofs, roof terraces and roof gardens. The term includes roofs and structures that may be accessible by workers or residents, and that may be intensively or extensively vegetated. Living roofs comprise two main types – green roofs and recreational roofs.
• Green roofs range from intensively vegetated (intensive) to extensively vegetated (extensive).
• Recreational living roofs provide amenity benefit.