Constructed wetland systems have been used extensively for the treatment of municipal, industrial and agricultural effluent, but they have only been recently developed and investigated for the treatment of urban surface runoff. Although, vegetated wet balancing ponds have been used to treat highway runoff, their performance has not previously been assessed in the UK in comparison with constructed wetland systems. The potential for combining constructed wetlands with flood storage ponds would be beneficial in terms of flood alleviation and pollution control. The Halcrow Group Ltd and the Middlesex University Urban Pollution Research Centre were commissioned by the Environment Agency (Thames Region) in 1995 to undertake a Research and Development project to
investigate the treatment of runoff by the use of vegetative treatment systems. The project comprised: a literature review; a monitoring programme and the development of an interim manual (Halcrow et al, 1996,1998).