WASTE DISPOSAL (DREDGE MATERIAL)
What, why and where?
Since the 1980s disposal at sea of radioactive wastes (stopped in 1982), industrial wastes (1992), colliery mine-stone (1995) and sewage sludge (1998) has been progressively reduced, and is now prohibited. Only the disposal of dredged material from ports, harbours and marinas is presently allowed. This activity is essential to maintain navigation in ports and harbours as well as for the development of new port facilities.
There are 66 open sites routinely used for disposal. A further 50 sites are either closed (not having been used for at least 10 years) or disused (not having been used for at least five years). Sea disposal sites are selected based on a number of criteria including their location in relation to amenities and other uses of the sea in the area, economic and operational feasibility and physical, chemical and biological characteristics.
The aim is to minimise seabed disposal and seek alternative, beneficial use by conducting a Best Practicable Environmental Option ( BPEO) assessment and considering practicable alternative options before granting a licence. Dredged material may be re-used for land reclamation or beach nourishment where it is uncontaminated and physically suitable. Biologically inert or natural materials may also be considered for disposal. Fish waste (from land based processing) is sometimes disposed but this has not occurred in the period 2005-2009.
Dredged material is assessed for contaminants before disposal to reduce environmental impacts. In general, dredged material with contaminant levels below a certain threshold can be disposed of at sea. Above this, but below a higher threshold, may require further consideration and testing before a decision can be made, whilst above the higher threshold there is a presumption against disposal at sea.
During 2009 a total of 2,901,499 tonnes was dredged and deposited of a total of 5,743,882 tonnes that could be allowed under licence. The amount of disposal has remained relatively constant over time. Most disposal occurs in the sea areas adjacent to the highest densities of human population and industry. Tonnages deposited are recorded by Marine Scotland and reported to OSPAR(1).
Grangemouth, the largest dredging operation, is licensed to dispose of 1.15M tonnes equivalent (Te) of sediment annually. The actual quantity disposed is nearer 1.05m Te, based on an average over 2005-2009.
Contribution to the economy
It is not possible to calculate the GVA and number of jobs associated with dredge spoil disposal from the ABI, as it does not separately assess this activity. However, it is clear that without dredging, supported by disposal at sea, access to ports and harbours would either be limited or face costly alternative means of disposal, which could affect the maritime transport sector's contribution to the economy. Dredged material can also save costs, when of suitable material, to replenish sand on beaches providing coastal protection and supporting recreational uses of the coastline, thus enhancing economic performance.
From 2005-2009, 112 one year licences were issued for the disposal of dredged material at sea. These were mainly for ports and generated a total licence revenue of £276,035.
Seabed within Wick sea disposal site
© Marine Scotland
Pressures and impacts on Scotland's socio-economics
- Disposal allows industries/ports to function, alternative would be higher cost land disposal, requiring additional treatment/storage prior to use
- Suitable dredged material can be used for construction projects, beach replenishment/ nourishment and enhancement of flood defences or salt marsh
- Possible obstruction on seabed for other seabed users
- Possible sediment plumes could affect users requiring high water quality
Source: Based on CP2 PSEG Feeder Report section 3.16.6 (2) and UK Marine Policy Statement (3)
Seabed within the Scrabster sea disposal site
© Marine Scotland
Pressures and impacts on the environment
Pressure theme: Climate change and physical pressures
Pressure: Hydrological changes
Impact: Possible changes to local tidal current and wave conditions (if area has limited dispersion).
Pressure theme: Pollution and other chemical pressures
Pressure: Disposed material contaminants
Impact: Dredged materials may contain a number of contaminants known to have an adverse effect on marine organisms. Dredging could lead to re-suspension of contaminants that have been sequestered through sedimentation.
Pressure theme: Habitat changes
Pressure: Introduction of waste at disposal point - changes in siltation rates
Impact: Disposed material spreads laterally and there will also be some short-term turbidity in the water column leading to changes in siltation rates at adjacent seabed locations.
Pressure: Introduction of waste at disposal point - changes to substrate and habitat type
Impact: Habitat damage and smothering causing possible burial of seabed flora and fauna.
Source: Based on CP2 PSEG Feeder Report Table 3.112 (2) and UK Marine Policy Statement (3)
Marine Scotland undertakes a regular monitoring programme of sea disposal sites (see chapter 3) and records are maintained of the material deposited.
Dredging is an essential activity to keep ports and harbours open and it is therefore economically important. Dredging and disposal will continue to be undertaken in order to maintain existing shipping channels and to improve, develop and protect the coastline. The Scottish Government's Second National Planning Framework (4) identifies future port developments at Grangemouth, Rosyth, Scapa Flow, Hunterston, Loch Ryan, Cromarty Firth and Nigg. Associated dredging may be required.
New dredging to re-open old ports or further develop existing ports could result in an increase in the amount of material dredged. As a consequence there may be a need to develop new sea disposal sites as existing sites reach capacity. However, the hydrodynamic nature of most disposal sites within Scottish waters results in the natural dispersion of finer material leaving only larger, bulkier material such as rocks and boulders. It is likely that there will be reduced contamination loads in dredge spoil because of greater control on leaching of contaminants from land-based industry and also from those using harbours.
Locations and average tonnage disposed at open sites (2005 and 2009)