Marine Aggregates

Marine aggregate is sand or gravel, used principally as a raw material by the construction industry. In the UK, the majority of aggregate (including crushed rock) comes from land-based sources but since the 1960s, developers have been increasingly reliant on marine sources to supplement demand and meet construction needs1.

The Severn Estuary contains extensive areas of sandbanks. It is estimated that the sand bank system between Newport and Chepstow, known as the Middle Grounds, contain quantities in excess of 1700 million cubic metres2 alone. These sandbanks were not formed by modern processes, but are derived from periods of glaciation and major changes in sea level that ended approximately 4,500 years ago2. Though there appears to be no major modern source of sand3, it is considered likely that limited inputs from the Bristol Channel occur under certain oceanographic conditions.

The pattern of supply of sand for construction purposes around the Severn Estuary, particularly in South East Wales, is unique in the UK because of its current and historic dependence on marine dredged resources4. (Around 80-90% of the demand for natural sand in South Wales is met by marine sources5, compared to about 21% for the whole of England and Wales1). These marine resources are of significant commercial interest as the sand dredged is of high quality, with well sorted grain-sizes and virtually no wastage. There are also significant manufacturing and production benefits5, further supplemented by the industry’s ability to land large tonnages by sea, close to urban areas6.

Licensed Dredged Areas

The Severn Estuary

Aggregate extraction from the Severn Estuary is exclusively of sand; the resource consists of well sorted fine to medium grained sand mainly used as building sand. The sandbanks generally contain thick deposits but they mainly exist in shallow water or inter-tidal settings that restrict access to dredgers at some sites during low water5.

Dredging ceased at Denny Shoal on in October 2012 and on 30th April 2014 the licence at West Middle Grounds expired and was not renewed by the permission holder.

 

The Inner Bristol Channel

Dredging has occurred at Holm Sands since the mid-20th century and has long been the main contributor of sand and gravel, with a maximum extraction of over 1.5 million tonnes achieved in 1996 and an average since 1991 of 720,000 tonnes. The dredging operators were granted a new 15 month licence from the 1st February 2013 to extract a maximum of just over 422,000 tonnes. The licence expired on 30th April 2014 and was not renewed.

Culver Sands is currently the potential largest production area with a licensed maximum annual extraction rate of 1m tonnes. It is an isolated sandbank of well-sorted medium grained sands suitable for both building and concreting uses.

 

Dredging in 2014

Landed Tonnage

With the cessation of dredging at both Holm Sands and West Middle Grounds in April 2014, the combined maximum licensed annual extraction rate decreased from 2,238,000 tonnes to 1,650,000 tonnes. The total volume of aggregate landed in 2014 from the study area sites was 1,064,108 tonnes, approximately 64% of the combined permitted volume.

Area Dredged

With the cessation of dredging at both Holm Sands and West Middle Grounds in April 2014, the total area licensed for dredging reduced from 33.88km2 to 22.41km2. The combined area actively dredged during 2014 (excluding Bedwyn Sands) was 4.57km2 before April and 3.34km2 from May.

Regulation

The Crown Estate owns the mineral rights for much of the UK seabed and issues commercial licences for both prospecting and the extraction of aggregates1. However, the planning and consenting process is the responsibility of the regulator; the Marine Management Organisation in England and the Welsh Government administered on its behalf by Natural Resources Wales who, through a consultation process, determine whether an area can be used for aggregate extraction. The exception in the Severn Estuary is the Bedwyn Sand reserve. This area of sand bank is owned by the Swangrove Estate and permission to dredge has been granted by the Mineral Planning Authority, Monmouthshire County Council.

 

References
  1. The Crown Estate. Marine Aggregates
  2. Velegrakis, A.F., et al. 2001. Morphological development and sediment dynamics of the Middle Grounds Bank (Severn Estuary)
  3. Dyer, K.R. 1984. Sedimentation Processes in the Bristol Channel/Severn Estuary
  4. Welsh Assembly Government Strategy – Sand and gravel supply for South East Wales – position statement. Dec. 2002
  5. Severn Tidal Power SEA Topic Paper ‘Other Sea Uses’. DECC 2010
  6. Dr Andrew Bellamy, Tarmac Marine Dredging Ltd. (pers. comm. August 2011)
  7. Royal Haskoning DHV (Pers. Comm. 14 May 2015)
For more information see the following links:

Last Updated Summer 2015

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