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 to 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.
To find out more go to the BRE Bookshop website for an up to date version of the soakaway design, which includes design procedure, soil infiltration rate, time of emptying soakaway, construction details and design examples.