Maintenance Dredging in the Port of London
In common with many navigable waterways in the UK, maintenance dredging is regularly carried out in the tidal Thames. Maintenance dredging is necessary to maintain safe operational water depths for navigation, and to facilitate continued access to many of the 70 plus berths, docks, wharves and jetties.
What is maintenance dredging?
The periodic removal of shoals or sediments from existing navigational channels, berths, swinging moorings etc in order to maintain an appropriate safe depth of water for navigation, construction or operational purposes.
Port of London Authority Dredging
The PLA has a conservancy obligation under the Port Marine Safety Code to maintain and improve navigation within the Thames Estuary. To achieve this, PLA consider a wide range of measures from moving navigation aids and recommended routes to maintenance and capital dredging as trading or other factors demand. The PLA carry out regular hydrographic surveys and provide charted information informing mariners of navigable depths. However, where reduced depths within navigation channels are identified, maintenance dredging can be used to restore access windows.
The PLA is responsible for maintaining navigable depths in the main channels of the tidal Thames. Maintenance dredging by the PLA is undertaken using a variety of techniques, which largely depend on the location of the dredge area (for example accessibility and water depth) and the material type requiring dredging. A summary of the potential maintenance dredging activities, including volumes, frequency and methods, that may be undertaken by PLA is provided within the Baseline Document.
Third Party Dredging in the tidal Thames
Maintenance dredging of non-harbour authority berths and approaches is the responsibility of third-party organisations under the regulation of the PLA and Marine Management Organisation (MMO). Third-party maintenance dredging is required in the Thames Estuary when sediment builds up in the dock entrances or berth boxes. Berths are generally located adjacent to a quay or jetty are deeper than the surrounding approach channels to ensure vessels have sufficient depths to load and unload cargo over low water. This type of maintenance dredging is undertaken routinely, often several times a year. Maintenance dredging may also occur when a storm or other hydrodynamic events leads to deposition of sediment which may extend into navigation channels, or in areas of lower flow velocity. Such dredging tends to be undertaken irregularly in response to specific events. Finally, maintenance dredging may also be required when vessels need access to facilities that are infrequently used; however, this dredging is undertaken on an ad hoc basis.
There are currently over 20 locations where third-party operators undertake maintenance dredging on a regular basis, each with varying frequencies throughout the year. The quantity of material removed is dependent upon the sedimentation characteristics at each location. All dredging carried out by third parties is licensed by the PLA under Section 73 of the Port of London Act (as amended). The MMO regulates development at sea under the Marine and Coastal Access Act 2009. This includes the licensing of ‘marine licensable activities’ such as construction works and all dredging activities unless relevant exemptions apply. Under the Thames Concordat, which was developed in 2016, the MMO and PLA work closely to ensure that applications received under respective legislative regimes are dealt with in a streamlined manner.
The PLA has produced a Baseline Document that aims to make the process of assessing the environmental effect of maintenance dredging in the tidal Thames more explicit by forming a basis for any future assessment of changes in operations. This document also includes records of previous maintenance dredging within the tidal Thames, including the historic and current dredge volumes at the various sites.
Page last updated: January 2022
