Drainage ditches along the A13 ‘Thames gateway’ causeway
Corylus Ecology Ltd.
The A13 dual carriageway, linking central and eastern London to south Essex, includes the section known as the “Thames Gateway” east of the Goresbrook Interchange at Dagenham. Part of this section includes a large causeway that carries the road over Rainham and Wennington Marshes, opened in 1999. Rainham, Wennington and the adjoining Aveley marshes make up the Inner Thames Marshes SSSI, the largest remaining area of wetland on the upper reaches of the Thames Estuary, notable as a refuge for a diverse range of breeding birds and overwintering wildfowl. The site includes extensive low-lying grazing marsh, dissected by a network of fresh to brackish drains and ditches, supporting a diverse range of wetland plants and invertebrates, many of which are nationally rare or scarce.
The “Thames Gateway” causeway is flanked on both sides by a series of both pre-existing and newly excavated drains that now receive run-off from the road in wet weather. During June 2025 a survey of the aquatic invertebrate communities within these drains was commissioned as part of the programme of post-construction monitoring of the ecological impacts from the causeway, with repeat surveys planned for 2026 onwards.
Despite overall being of low diversity and showing indications of pollution by the road run-off, the ditches harboured a surprising number of uncommon and rare species, no doubt forming outlier populations of the more diverse assemblages within the main marsh to the south. The rare aquatic beetles Graphoderus cinerreus, Hydrophilus piceus and Limnoxenus niger were of particular interest, although several other Nationally Scarce and Local species of aquatic invertebrates were also present.