BRE Digest Soakaway Design / Soil Test Discharge their stored water sufficiently quickly to provide the necessary capacity to receive run-off from a subsequent storm.
Traditionally they have been used as a way of disposing of surface water in areas remote from public sewers or watercourses. However, recently they have also been used in fully-sewered areas to limit the impact of new building works and to avoid the cost of upgrading sewers. Digest 365 describes the process for the design and construction of soakaways and explains how to calculate rainfall design values and soil infiltration rates. It also provides information about maintenance, inspection and monitoring, provides design examples and lists sources of further information.