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Maintenance Dredging in the Port of London

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.

The Port of London

The PLA is responsible for maintaining navigable depths in the main channels of the tidal Thames.  In practise, the PLA prefers to move channels as a solution rather than undertake frequent large scale dredging campaigns.  However, there are a number of areas where sand waves and shoals form and it is not possible to move the channel, therefore, maintenance dredging must be carried out.  Table 1 sets out the PLA’s present maintenance dredging areas, methodologies, and frequency. 

In common with other harbours with a significant degree of commercial or recreational use, the general duties and functions of the PLA are managed under statutory powers – in this case the Port of London Act 1968 (as amended). 

Dredging falls under the conservancy function and, as with other harbour authorities for major harbours, the special legislation authorises the authority to deepen, dredge, scour and improve the bed and foreshore of the harbour etc.  Clearly this is within the context of maintaining navigational channels and removal of wrecks and other obstructions to navigation.  Hence this aspect of the conservancy function relates to securing safe and convenient navigation in the harbour.

Since the PLA’s powers are included in an Act of Parliament, the need to obtain consent for navigational dredging under Section 34 of the Coast Protection Act 1949 is removed.

As with nearly all important commercial harbours, the PLA’s special legislation prohibits persons other than the harbour authority from constructing works below mean high water or dredging without first obtaining a licence from the harbour authority.

Further information on dredging can be found at the website for the Central Dredging Association (CEDA).

Table 1 - Current PLA Maintenance Dredging Areas

ID

Dredged Area

Frequency

Dredging Methodology

Sediment Type

Approximate Quantity (m3)

1

Richmond Lock

Every 10 years

 

 

Backhoe/Grab

Silty sand  with some debris

2,000

2

Saundersness Shoal

Every 12 to 18 months

 

 

Trailer Suction

Sand and gravel with some debris

Up to 15,000

3

Hookness Shoal

Annually

 

 

Trailer Suction

Sand

Up to 8,000

4

Barking Shoal

Every 3 years

 

 

Trailer Suction

Sand

3,000

5

Purfleet Shoal

Every 3 years

 

Trailer/Plough

Sand

1,000

6

Tilburyness Shoal

Every 3 years

 

 

Trailer/WID

Sand

2,000

7

Diver Shoal (multiple areas)

6 monthly

 

 

Trailer/Plough/WID

Fine sand/silt

3,000

8

Coalhouse Shoal

Every 2-3 years

 

 

Trailer Suction

Sand and gravel

3,000

9

Sea Reach

Rarely as   channels are managed.

Trailer/Plough

Sand

Variable