An attenuation tank is an underground tank or modular crate system that temporarily stores surface water from roofs and paved areas during intense rainfall and releases it slowly to the sewer or watercourse. By limiting peak discharge it helps prevent downstream flooding and supports sustainable drainage objectives. UK design follows the Construction Industry Research and Information Association SuDS Manual, Building Regulations Part H3 and Sewers for Adoption. Flow control devices such as vortex regulators or orifice plates are used to govern the outflow rate. Attenuation tanks are commonly required by Thames Water and local planning authorities on new and redeveloped sites in Greater London, where existing sewers are at capacity. Tanks need periodic inspection, particularly of the flow control and silt trap, to maintain their designed performance.
Attenuation tank
Underground tank temporarily storing surface water to reduce peak flows into the sewer.
