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5.3.3 Navigational dredging

(including capital projects)

a.    Extent of the activity

Dredging is a fundamental requirement for most harbours and ports [124] . Within this section dredging can be defined as, the excavation of material from the seabed and the relocation of the excavated material elsewhere for disposal. In general, dredging may be undertaken for a variety of purposes including navigation, flood control and for beach nourishment purposes. In Ceredigion, dredging is carried out to improve navigation and falls into two categories:

Maintenance Dredging:

Maintenance dredging is the routine / periodic removal of material in approach channels and basins to assist safe access for vessels. This may vary from an almost continuous activity throughout the year to an infrequent activity occurring only once every few years. Generally, for the purpose of a disposal licence, if a period of 10 years has lapsed between a new and previous dredge, the operation will be treated as capital dredging where disposal at sea is involved.

Capital Dredging:

Capital dredging is the excavation of sediments for the first time so as to increase water depths in an area to accommodate vessels (excavation therefore generally takes place in ‘virgin’ material). Arising from disposal licensing requirements, capital dredging also includes the removal of material from previously dredged areas where sedimentation has since occurred and has not been disturbed by further dredging over a period of time (10 years or greater).

i.   Within the site

Maintenance dredging requirements at New Quay and Aberaeron harbours are as follows:

New Quay: Some 3000 tonnes of sand are removed annually from the main harbour and Penpolion and is deposited at Dolau for beach replenishment purposes. These operations are carried out at low tide, using shore plant.

Aberaeron: Material is removed from the harbour at intervals of approximately 4 years and has been used for sea defence. There is a need to dredge the inner Harbour (Pwll Cam). Previous dredging activity has been temporarily suspended because the methods used (tipping over the sill for the tide to carry away) were no longer acceptable to Environment Agency Wales. Any new scheme would be likely to fall within the ‘capital dredging’ category in view of the timescales involved (see above).

ii.  Adjacent to the site

Aberystwyth: The dredging of the harbour channel is carried out every 2 years whilst the inner harbour (including the marina) is dredged approximately every 4 years. Selected suitable dredged material has been used to replenish South Beach, Aberystwyth.

Cardigan: Limitations on navigation within the Teifi estuary have given rise to concern amongst boat users. Levels on the bar are similar to those of 60 yrs ago, but the channel moves around. Proper marking of the channel could limit the need for dredging. There is no dredging regime currently in place and the County Council has previously commissioned consultants to investigate options for capital and maintenance dredging within the estuary to improve navigation. This issue is to be considered as part of the process of preparing a Teifi Estuary Management Plan (to be published in June 2000), also taking account of the high conservation value of the estuary.

Fishguard & Milford Haven: Dredging is not known to have taken place in Fishguard Harbour for some time, though it is presumed there will be the occasional requirement for it. Significant dredging is required occasionally from Milford Haven waterway. Several studies to select an alternative spoil dumping ground have taken place since the early 1990’s when concerns were raised about increased sedimentation within the Skomer Marine Nature Reserve.

b.    Mechanism for effect on the feature

The potential impacts of dredging upon the bottlenose dolphin and its habitat are two-fold: firstly as a result of the dredging itself and secondly as a result of the disposal of the dredged material. These impacts can relate to activities both within and adjacent to the SAC.

i.   Habitat impacts

Direct impacts are typically in the form of removal or smothering of benthic habitats and communities. Loss of fine fractions during dredging and disposal operations (if at sea) results in settlement of fines on the sea bed, possibly some distance from the site of the operation. This distance depends on local hydrology and particle size. Removal (dredging) or accretion (disposal) of sediments may, in the long-term, affect the sediment regime locally and possibly at some distance. Impacts on the dolphins’ habitat may affect abundance and distribution of dolphin prey. See ‘Prey Depletion’.

ii.  Noise

Vessel based navigational dredging is noisy and involves the use of several vessels on a standard ‘back and forth’ route. Effects are likely to be negligible when using shore plant, as is currently the case at New Quay. See ‘Noise’.

iii.  Pollution

Pollutants bound within the dredged sediments may be remobilised either in solution or bound to fines. Pollutants may also be released from the dredger and associated shipping. These may become biologically available, be assimilated, and enter the food chain. Certain substances subject to bioaccumulation and biomagnification would be of greatest threat to top predators such as the bottlenose dolphin. See ‘Pollution’.

iv.  Collisions

Increased shipping movements will result in an increased potential for collisions between vessels and with dolphins. See ‘Shipping’ and ‘Collisions’.

c.    Management Response

i.   Rationale

Harbour activity within and adjacent to the SAC is centred on New Quay, Aberaeron and Aberystwyth. These harbours are mainly used by fishing vessels and recreational craft. The County Council, as the Harbour Authority for Ceredigion, has responsibility for navigation in these harbours and their dredging is generally required to maintain navigable depths.

Mooring facilities are also available in the Teifi estuary where local concern has been expressed that navigation is becoming progressively restricted through the silting of the estuary.

In addition to the Habitats Regulations, the following legislation can have a bearing on proposals for dredging and disposal:

  • Coast Protection Act 1949;

  • Deposits in the Sea (exemptions) Order 1985;

  • Environment Act 1995;

  • Environmental Protection Act 1990;

  • Food and Environment Protection Act (Part 2) 1985 (FEPA);

  • Harbour Act 1964

  • Harbour Works (Assessment of Environmental Effects) Regulations 1988;

  • Harbour Works (Assessment of Environmental Effects) (Amendment) 1996;

  • Landfill Tax Regulations 1996;

  • Waste Management Licensing Regulations 1994;

  • Town and Country Planning Act 1990;

  • Various local harbour powers

Consents issued for navigational dredging may, therefore, be numerous and be required from several competent authorities. Most commonly within the Bay, consents are issued by CCC (Harbour Act 1964), NAW (Food and Environment Protection Act (Part 2) 1985 (FEPA)) but undertaken by MAFF on their behalf, DETR (Coast Protection Act 1949).

There is a requirement under the Habitats Regulations to review existing consents, and any new dredging developments would certainly constitute plans and projects and be subject to the significance/appropriate assessment procedure for the purposes of the Habitats Directive (see Figure 17.). Competent authorities should therefore ensure that the potential impacts on the bottlenose dolphins and their habitat are fully addressed in such assessments.

Almost all potential effects of dredging and dumping on the bottlenose dolphins are secondary in nature. Due to the small nature of dredging events in Cardigan Bay harbours it is unlikely that any one dredging operation, if properly managed, would be large enough to have a significant impact in its own right. Proper avoidance of sensitive areas and proper analysis of sediment composition prior to choosing the most appropriate disposal methods would probably mitigate the potential for such single event impacts. However, dredging events are typically recurrent and whilst possibly not significant in their own individual right may, cumulatively, have the potential for long term impact on the dolphins either directly or through their habitat and food.

ii.  Type of Response

F1 : The activity constitutes a plan or project.

iii.  Actions, including links to other policies/plans/measures

Actions

  • Treat all navigational dredging as a plan or project.
  • Review extant maintenance dredging operations and produce Dredging Plans to provide a framework/procedure for proposals for dredging within Ceredigion.
  • Use the best practicable environmental option for the disposal of dredged material.
  • Establish a code of practice for dredging and disposal in and adjacent to the SAC.

Links: Other coastal management plans

  • Ensure that any proposals for navigational dredging are assessed in the context of the relevant Shoreline Management Plan.
  • The possibility of improving dredging in the Teifi estuary to improve navigation will be explored within the Teifi Estuary Management Plan.
  • Ensure the Teifi Estuary Management Plan is consistent with the SAC Management Plan.

[124] Further information on interactions between Port & Harbour operations and features of UK marine SACs can be found in: ‘ABP Research. 1999. Good practice guidelines for ports and harbours operating within or near UK European marine sites. English Nature, UK Marine SACs Project. pp120.’ This report is available with other related information at: http://www.english-nature.org.uk/uk-marine/