A soakaway is an underground structure designed to allow surface water collected from roofs, driveways or yards to infiltrate slowly into the surrounding soil. Traditional soakaways were simply rubble-filled pits, but modern UK designs use modular plastic crates wrapped in geotextile, sized in line with BRE Digest 365 and Building Regulations Part H3. Soakaway suitability depends on soil permeability, established by a percolation test, and the depth of the local water table. In parts of London with heavy clay subsoils, soakaways may not be feasible and an attenuation tank with controlled discharge to sewer is used instead. Soakaways are subject to clogging by silt over time, so a catchpit or silt trap upstream is generally recommended to extend the working life of the system.
Soakaway
Underground pit or crate system allowing surface water to soak slowly into the ground.
