soakaway

A soakaway is an underground structure designed to collect and temporarily store surface water from impervious areas such as roofs, driveways, and courtyards, and allow it to infiltrate into the surrounding ground. It reduces surface runoff and helps to prevent overloading of conventional drainage systems.

Water reaches a soakaway through a network of pipes or channels that feed into a pit, trench, or chamber filled with permeable material. The surrounding soil provides the infiltration capacity, so water percolates away rather than forming puddles on the surface. Common forms include soakaway pits, soakaway trenches, and modular soakaway crates or cells.

Design considerations include the soil’s percolation rate, the size of the catchment area, and the expected rainfall. The soakaway should be positioned away from building foundations, utilities, and sources of groundwater contamination. It should be sized to avoid overtopping during peak rainfall and protected against silt and debris to prevent clogging. Local regulations, climate, and groundwater levels influence design choices and compliance requirements.

Construction and maintenance involve installing a granular fill such as gravel or crushed stone, sometimes with a perforated outflow pipe, and a geotextile wrap to limit sediment ingress. Regular inspection and cleaning are important to prevent blockage. If a soakaway becomes silty or stops infiltrating effectively, rehabilitation or replacement may be required.

In many areas, soakaways are governed by building or drainage regulations and may require permits. Alternatives include infiltration trenches, rain gardens, or swales when site conditions are unsuitable for a traditional soakaway.