A Bioretention System is a system that uses vegetation to reduce downstream flow velocities and subsequent drain sizes whilst facilitating treatment. Bio-retention systems combine various Water Sensitive Urban Design (WSUD) treatment types in one 'treatment train'. A system is designed to carry out primary and/or secondary treatment processes of stormwaters and retard flows. This retention or retardation can enable sediments to precipitate out of the water taking along with it some pollutants. The use of biological processes to 'treat' stormwater whilst facilitating conveyance and retention gives rise to the title of Bio-retention.