The Thames River and estuary has provided a national gateway port since the Roman Period. Encroachment through reclamation and construction of wharfage ensured access was maintained, although by the early C19th some dredging works had commenced principally to lower shoals on the main channels and to provide a source of ballast. From 1857, when the Thames Conservators were reconstituted, dredging activity in the Thames increased to maintain and improve the main navigation, ensuring passage of new classes of commercial shipping, which were both wider and deeper draughted. Significant dredging works were undertaken between 1895 and 1900. Further works were undertaken during a second capital dredging campaign concluded by 1928, during which some 37 million cubic yards were excavated.
Since 1928, dredging in the Thames has been primarily associated with maintaining depths. The main navigation channel created by 1928 was largely self maintaining, but annual dredging returns for the River and docks for the periods 1928 to 1956 are fairly consistent, averaging 2,660,000 hopper tonnes per annum [1,860,000 m3] (extracted from An Overview of tidal Thames Estuary, HR Wallingford Report EX 4936, Rev 2.0, Table 4.1, and corroborated in The Thames Estuary Coastal Processes and Conservation, Institute of Estuarine and Coastal Studies, October 1993 – Section 6.1). Much of this material was disposed of in the outer estuary (Black Deep and Barrow Deep) located in the outer Estuary. Approximately 50% of this dredging originated in the Mud, Gravesend and other Reaches.
Following a review of the dredging requirements of the River in the 1950s, the PLA implemented a significant change of policy for the dredging objectives and disposal practice. This resulted, from 1967, in a considerable annual reduction in the dredging commitment particularly within the Mud Reaches (HR Wallingford EX 4936, Table 4.2). This included a significant reduction in maintenance dredging from Gravesend Reach/Divers Shoal from 1965 and does not appear to have impacted significantly on the navigable depth in the River. It should also be noted that in the preceding years (1962 to 1966), significant capital dredging had been undertaken including the relocation of the navigation channel in Lower Gravesend Reach (relocated 500 feet south - 1964/1965) and Knock John Channel (Deterioration of North Edinburgh Channel, new channel through Black Deep - 1966) in response to recommendations by the then Hydraulics Research Station.
Historically, arisings have been disposed at sea at sites seaward of Southend. However, two onshore disposal sites have operated at Rainham and Cliffe. Rainham was operational pre-1949 but was further developed following the Inglis and Allen dredging review of 1957. Initially comprising two large lagoons, the site was extended with the addition of seven new lagoons, commencing operations in January 1968. The original two lagoons have since been incorporated into the household waste landfill operations facility. Rainham now comprises a series of nine linked lagoons, and currently has a capacity of approximately 1.3 million m3. The site is owned by the MOD, and managed jointly by RSPB (Inner Thames Marshes SSSI) and by the PLA (disposal lagoons).
Cliffe was originally licensed to receive dredge materials (having formerly operated as clay pits) in 1960. With Rainham originally anticipated to be full by 1982, Westminster Dredging expanded their interest in the Cliffe disposal site in 1972 to provide capacity for 20 years of maintenance operations. The site received its Waste Management Licence in 1977, and this has been maintained. The site was acquired by RSPB in 2001, to provide a habitat for overwintering waders. Nevertheless, it continues to receive dredge material.
The deployment of water injection dredging (WID) equipment has alleviated much of the routine requirement for on-shore disposal capacity. The original Jetsed dredger was built in 1987, and the "Maasmond" now operates in the Thames for approximately nine berth operators, undertaking campaigns on a 3 monthly cycle (although not at all berths).