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Dredging

All dredging and disposal activities require a marine licence unless they qualify for an exemption. You should make sure that any additional information specifically required to license the dredging activity is included with your application before applying.

You should also make sure that if the dredging is associated with another licensable activity, such as disposing of dredged material at sea or a construction activity, that details are included in your application. The Marine Management Organisation (MMO) needs to ensure that the environmental implications of the whole project are considered when deciding a marine licence application.

Certain dredging activities carried out by or on behalf of a harbour authority

Harbour authorities will not need a marine licence to dredge and deposit dredged material where the activity involves the relocation of sediments inside surface waters for the purposes of:

  • land reclamation
  • managing waters and waterways
  • mitigating the effects of floods or droughts
  • preventing floods

The activity must be authorised by a local act or harbour order and the authority must demonstrate to MMO's satisfaction that the sediments are non-hazardous. The criteria to use to decide if waste is hazardous or not is set out in Annex III of the EU Waste Framework Directive.

MMO will seek advice on whether sediments are hazardous or not on a case-by-case basis.

If you want to dispose of dredged material at sea outside of your harbour area you will need a marine licence.

See section 75 of the Marine and Coastal Access Act 2009 (as amended) for further details.

Low-volume dredging

If your dredging is for fewer than 500 cubic metres a campaign and fewer than 1,500 cubic metres a year, you will not need a marine licence if:

  • the dredging activity is carried out for the purpose of conserving, maintaining or the navigation of an area of sea
  • the specific area has been dredged at least once in the preceding 10 years
  • fewer than 1,500 cubic metres has been dredged in the previous 12 months, including that dredging activity
  • you notify MMO that you intend to perform dredging before the activity starts

Even though a marine licence is not required, you may still need to obtain other approvals before undertaking the activity.

A dredging campaign is one or a series of dredging activities to achieve a particular objective in a defined area. For navigational purposes, the objective is usually to attain a defined depth. The time a dredging campaign can take may vary from 1 or 2 days to months or even years.

Low-volume dredging that complies with local or regional conditions

MMO will decide whether maintenance dredging applications with a volume between 500 and 3,000 cubic metres a campaign, and fewer than 10,000 cubic metres a year can be processed under a new accelerated licensing process, developed to license relatively small-scale ongoing dredging activities with a limited consultation. You must be able to demonstrate the low-risk nature through complying with agreed criteria and local or regional conditions. MMO aims to decide qualifying applications within 20 working days.

Activities will be licensed through this process if:

  • dredging is ongoing and has been carried out in the same way for at least 3 years
  • campaigns are separated by at least 1 month
  • evidence on the quality of the sediment is provided
  • the project is assessed as part of a maintenance dredging baseline document or another form of assessment agreed with Natural England of likely impacts

Other criteria relating to environmental protection and interference with other legitimate uses of the sea must also be met before a dredging activity can be confirmed as appropriate for the accelerated licensing process.

You must agree to precautionary conditions appropriate at the local or regional level to protect the marine environment that have been developed in consultation with our advisors. If the activity has been assessed as part of a maintenance dredging baseline document or other assessment agreed, details should be included with the application and any conditions that form part of that assessment will be considered in the licence determination.

You can discuss the relevance of the precautionary conditions with the appropriate advisor before you apply. Any proposed changes discussed with the appropriate advisor should be included with your application so that they can be considered in the licence determination.

Should you not accept any of these options the standard licensing process will be used. Your application may also have to go through the standard licensing process if there are requests for further information

Qualifying applications will have a 10-working-day consultation.

You must provide information on the physical and chemical characteristics of the dredged material with the application for it to be considered full and complete.

You must provide 1 surface sample that is representative of the area to be dredged for activities between 500 and 1,000 cubic metres a campaign and fewer than 10,000 cubic metres a year.

You must provide 2 surface samples that are representative of the area to be dredged for activities between 1,000 and 3,000 cubic metres a campaign and fewer than 10,000 cubic metres a year.

You must analyse the sediment samples for a minimum of:

  • trace metals – cadmium, copper, mercury, zinc, chromium, lead and nickel
  • arsenic
  • tributyltin (TBT) compounds and its degradation product dibutyltin (DBT)
  • polycyclic aromatic hydrocarbons (PAHs)
  • particle size analysis (PSA)

Read more information on sampling and analysis.

Small-scale, low-risk non-navigational dredging

Applications for small-scale, low-risk non-navigational dredging must be accompanied by an assessment of risks of contamination. The dredging must not be related to establishing the presence or nature of archaeological, heritage or historic asset(s) and campaigns must be separated by at least 1 month.

The material moved must be limited to fewer than:

  • 1,500 cubic metres in the same area for any other non-navigational dredging activity in the year before the current application
  • 500 cubic metres in any single dredging campaign – one or more dredging operations to achieve the same objective in an area

Maintenance and capital dredging

All dredging activities above 3,000 cubic metres a campaign or 10,000 cubic metres a year, those that fail to meet the small-scale or low-risk criteria, and all capital dredging activities and those associated with environmental impact assessments (EIA) will be licensed through the standard marine licensing process and you must provide all appropriate information at the time of submitting your application.

You must provide information on the physical and chemical characteristics of the dredged material (if relevant to your project) with the application for it to be considered full and complete. Sampling was previously carried out after an application was submitted.

There are specific requirements that must be met for sampling and analysis and for dredging applications in the standard licensing process. You should contact MMO before you apply to establish these requirements and to plan the sampling and analysis strategy. Read more information on sampling and analysis.

Maintenance dredging

Maintenance dredging is required to ensure navigation channels, berths or construction works are maintained at their designed depths. It involves removing recent unconsolidated sediments such as mud, sand and gravel and is carried out by many ports, harbour authorities, berth operators and marinas to maintain safe navigation.

Typically, maintenance dredging is performed on a series of repeated dredging campaigns. MMO's definition of maintenance dredging is "dredging the seabed in an area:

  • where the level of the seabed to be achieved by the dredging proposed is not lower (relative to Ordnance Datum), than it has been at any time during the preceding 10 years and
  • there is evidence that dredging has previously been undertaken to that level (or lower) during that period"

Capital dredging

Capital dredging is required to create new or deepen existing facilities such as navigational channels, harbour basin and berths and for engineering purposes such as trenches for pipes, cables and immersed tube tunnels or the removal of material unsuitable for foundations. It generally involves excavating consolidated material such as rock and clay. Typically, capital dredging is performed in a single dredging campaign.

MMO considers that capital dredging covers all new dredging activities and those in an area that has not been dredged to the desired depth within the last 10 years. MMO's definition of capital dredging is "dredging the seabed, generally for construction or navigational purposes, in an area or down to a level (relative to Ordnance Datum) not previously dredged during the preceding 10 years."

If the dredging is associated with an infrastructure project, then an EIA may be required to ensure any impacts are assessed at the project level.

Information to supply with an application

MMO’s online application system is due to be updated to allow the additional information needed to properly assess dredging activities to be included in an application. Until the update we require applicants to include this additional information with their applications.

The additional information required for dredging applications is summarised below and should be uploaded to the supporting information section of the online application form. It is required to support all dredging applications (except those for aggregate dredging).

Dredging methodology

MMO requires a detailed description of the proposed dredging methodology that specifies:

  • purpose of the dredging (navigation, berthing)
  • type of dredger to be used (hydraulic, mechanical, hydrodynamic)
  • working hours
  • duration of the dredge
  • how disposing the material will be managed
  • any special measures applied to the dredging

If there is a dredge plan or zoning of the dredge area this should be described. Before dredging starts MMO also requires the details of the dredging equipment to be used and contractor name.

Pre-dredge survey

MMO requires a pre-dredge survey of the area to be dredged for all dredging applications. The survey should show the:

  • boundary of the dredge area
  • dredge depth(s)
  • existing bed levels
  • side slopes

For further information see Surveys.

Dredging history

All maintenance dredging applications should summarise the history of dredging at that site and include:

  • how long dredging has been ongoing in terms of years and frequency of campaigns, including the quantities of material dredged a year and campaign
  • how long dredging has been carried out in its current form
  • whether there have been any significant changes to the dredge area or dredge depths in the past 10 years
  • any changes to methodology since the last river basin management plan was approved

Capital dredging applications should refer to any history of dredging at that site including when the site was last dredged and for what reason. Types of information that can provide assurance that the dredging activity has been ongoing could include previous licences, dredging contracts or invoices, disposal returns and/or results of monitoring surveys.

Current or previous licences and associated conditions

MMO requires information on any current or previous licences that may have applied to the dredging including local harbour authority, Coast Protection Act 1949, consent under Environment Agency byelaws or a marine licence.

This should detail any objections to the application, previous conditions applied to the licence or consent, restrictions on the dredging, pollution incidents or ways in which the dredging is managed to avoid impacts to the environment or to other users. Also if there is raw data from the mitigation measures imposed on previous licences then this should be uploaded alongside the application.

Physical and chemical characteristics of the dredged material

MMO needs to understand the physical nature of the material to be dredged – silt, sand, gravel, stiff clay or rock and its specific gravity – as well as the presence of any pollutants (chemical quality). Sediment quality analysis information should be provided with all dredging applications. For maintenance dredging (and some capital dredging) this sampling will also establish the physical nature of the material. See information on sampling and analysis for further information.

For capital dredging, if trial pits or a site investigation have been carried out an interpretation of the results of these surveys should be provided with the application. MMO may require raw data to be provided for internal advisors to review for significant, large-scale capital dredge projects or for those associated with disposal at sea.  

Other consents

MMO requires information on progress with achieving those other consents, such as from the landowner or local harbour authority, if they are necessary.

Maintenance Dredge Protocol

If maintenance dredging has the potential to affect designated European sites – usually a special area of conservation (SAC), a special protection area (SPA) or Ramsar site – this is considered to be a plan or project for the purposes of the Habitats Directive. In such cases, applications for marine licences for maintenance dredging activities must be assessed in line with article 6(3) of the Habitats Directive. Article 6(3) requires that plans or projects with a likely significant effect upon a site must be subject to an appropriate assessment (AA) of its implications for the conservation objectives of that site.

The Maintenance Dredging Protocol for England (MDP) provides assistance to operators seeking and regulators giving approval for maintenance dredging activities which could potentially affect European sites. The MDP provides an approach that allows the effects of maintenance dredging to be assessed without burdening those commissioning or approving maintenance dredging activities. In this way, the need to make an AA under the Habitats Directive is avoided for each and every licence application or renewal.

The MDP recommends that a baseline document is produced either by an individual applicant or a group of parties with maintenance dredging requirements within the area concerned (like an estuary) to provide a consistent basis against which authorities can assess maintenance dredging activities. This will help them identify any likely significant effect in respect of future maintenance dredging applications or proposals, taking into account in-combination effects of dredging proposals. A baseline document needs to bring together all relevant, readily available current and historical data on dredging activities within the area concerned. It must also analyse the potential effects (if any) which those dredging activities could have on the features of the European sites. The suggested content of a baseline document is set out in the MDP.

Survey data

MMO requires bathymetric survey – a survey is used to measure the water depths in an area, usually a navigation channel or berth – data to be submitted with all marine licence dredging applications to check that the dredging is undertaken only to the dredge depth applied for, in the correct area and within acceptable volume limits. Generally, you will need to submit pre-dredge survey data with your application and post-dredge survey data and a difference plot (a comparison of the pre- and post-dredge survey data) as a condition of the marine licence granted by MMO.

Certain dredging activities with a volume between 500 and 1,000 cubic metres for each campaign, and using conventional dredging techniques (such as a grab dredger or small trailer dredger) will not need to undertake these surveys due to the low risk involved and the potential disproportionate cost of these surveys relative to the scale of dredging proposed.

Should dispersive dredging techniques, such as water injection and plough dredging, be proposed, or should dredging activities be proposed within or next to a European site, site of special scientific interest (SSSI) or marine conservation zone (MCZ), pre- and post-bathymetric survey data will be required, even for those dredge activities with a volume of between 500 and 1,000 cubic metres.

The type of bathymetric survey required should be proportional to the scale and risk associated with the dredging activity.

A single beam survey is required for dredging activities that use both:

  • conventional dredging techniques with sea or land disposal of the material
  • ploughing or water injection dredging (and similar dispersive techniques) that are dredging volumes of less than 3,000 cubic metres

A multi-beam survey is required for:

  • larger dredges on a case-by-case basis
  • all ploughing or water injection dredging (and similar dispersive techniques) for volumes above 3,000 cubic metres
  • dredging in environmentally sensitive areas 

You may not be able to perform a bathymetric survey due to restricted vessel access. In such cases other methods of recording depth change, such as digital photography or topographical surveys can be considered. MMO will advise on the suitability of such approaches in support of marine licence applications on a case-by-case basis. 

The pre-dredge bathymetric survey should usually have been carried out within a 3-month period prior to the proposed dredging activity. The post-dredge survey should be carried out as soon as possible after the dredging activity is completed, usually immediately or within a few hours – MMO will take account of delays caused by adverse weather conditions or lack of access to the berth. MMO may accept a longer period for water injection dredging, such as a tidal cycle or 2 days.

A survey of intertidal dredge areas may not be possible using vessel-based techniques as access will depend on the height of the tide and the availability of shallow-draught survey vessels. In these circumstances topographic survey may be appropriate or if access is not possible then digital photography with markers may be used.

MMO requires that the bathymetric survey data is provided on a chart (digitally) showing the licensed dredge area and dredge depth. Single beam or multi-beam surveys should be presented as separate pre- and post-survey charts and as a difference plot. This plot compares the surveys and shows specifically where dredging or, potentially, sedimentation has occurred. MMO also requires a volume calculation showing the difference between the pre- and post-dredge survey. The difference plot can be used to provide this.

Contact information

Marine Licensing Team
Marine Management Organisation
Lancaster House
Hampshire Court
Newcastle upon Tyne
NE4 7YH

Tel: 0300 123 1032
Fax: 0191 376 2681
Email: marine.consents@
marinemanagement.org.uk


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