Rainham Silt Lagoons

Barges at Rainham

Maintenance dredging operations are carried out in the Port of London to ensure that channel depths are maintained and to retain desired depths for shipping in dock and key river-side berths. In addition, capital dredging has occasionally been undertaken to deepen the river to meet trade requirements. Where hydrodynamic dredging techniques are not suitable, there is a need to relocate the dredgings.

The dredged material can either be relocated to sea (at a licensed marine disposal site) or to land. In general, the small scale of dredging in the Thames means that sea disposal is not a primary choice because of the cost and distance to transport the dredged material to the nearest marine site. Hence, in the late 1960s, the dredged material containment lagoons were constructed at Rainham and a pump ashore unit installed.

Historically, the disposal of dredged material to the Lagoons took place in an ad hoc manner, with no forward planning or  agreed procedural framework. To tackle this the PLA has developed an Operations Plan to provide a more structured approach to the disposal process. The Plan has been developed in consultation with key stakeholders, such at the RSPB, Natural England and the Environment Agency and aims to safeguard the operational function of the site whilst protecting its environmental features.

The Silt Lagoons, cover some 152 hectares and are located to the south of Rainham town centre, between the Rainham to Thurrock railway lines and the River. This area lies on the flood plain of the Thames and is located within a meander bend of the river channel. The Lagoons, which are raised above the surrounding ground level, are bounded to the north by the A13 and to the south by a landfill site operated by Cleanaway Limited.

Silt being discharged into the lagoons (picture courtesy of Royal Haskoning)

The operation of the Lagoons, which are presently leased from the RSPB,  include for the reception, pumping ashore as a water slurry, lagooning and dewatering of dredgings from the tidal sections and non-tidal docks, locks etc of the Rivers Thames and Medway and incorporate a bird sanctuary and wetland environment. The latter follows on from the designation of the silt lagoons by the former Nature Conservancy Council in 1986 as part of the Inner Thames Marshes SSSI.

The SSSI status of the silt lagoons was determined by a number of criteria, but particularly as a result of the wintering teal populations and rare saline tolerant fauna such as sea aster, sea couch and sea –spurry on which a number of the bird species depends for feeding. Aside from this the lagoons were also particularly important as a feeding and roosting ground for over-wintering birds.

Estimated numbers of breeding birds on the silt lagoons are shown in the attached table. This is derived from data provided by the RSPB as part of an early draft management plan for the site.

Although no figures are currently available on numbers of wintering birds on the area of the silt lagoons, there is  information on numbers of birds wintering on the whole of the Rainham, Wennington and Aveley Marshes area, which includes the lagoons. The table shows this data for key species, for which the majority of their Rainham / Wennington / Aveley populations will have been on the silt lagoons themselves (RSPB, 2001).

View from Rainham showing pipe jetty

During the period for which information is presented the silt lagoons were being used for disposal of dredgings, and consequently contained large areas of shallow water.

The closure of much of London's dock system in the 1980's led to the volume of dredgings disposed on the lagoons being greatly decreased. The result is  that they will have contained little surface water and less saline-tolerant vegetation since the 1990's.

Consequently, numbers of most, if not all, wintering waterfowl and seed-eating passerines will now be much lower than those shown in the table (RSPB, 2001). Notwithstanding this decrease in use, the lagoons are still considered a strategic resource for the Port of London and a management plan is in preparation with the RSPB.