Soakaway Tests For Drainage Design

BRE Soakaway Digest 365

Soakaways are a natural underground drainage system that stores surface water run-off before allowing it to discharge into the ground. Soakaways are a crucial part of Sustainable Urban Drainage System (SUDS) whereby surface water runoff drain as naturally into the ground rather than ending up in the local surface water network, watercourses or Rivers, and increasing flood risk.

In 1991, the Building Research Establishment (BRE) published its guidance on soakaway design. It contains information on on soakaway design and how to calculate soil infiltration rates for the design.

For soakaways to effectively work, soakaways should discharge from full to half-volume within 24 hours.

BRE 365 Testing

To test to BRE365 involves the following:

  • Formation of a machine (JCB or similar) or hand excavated trial pit
  • The pit is then filled with water repeatedly over a 24hr period and the rate of infiltration is recorded.
  • The records are used to calculate the infiltration rate and then used in the design of the soakaway and its size.

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