Surveys of resources and habitats

Extensive deposits of sand and gravel exist beneath the sea around the United Kingdom. These were formed in river valleys, channels, deltas or beaches in the past when sea level was significantly lower than it is now. Deposits are therefore similar to river and beach deposits that occur today on land 483, 485. These sand and gravel bodies within the seabed are stable, unlike superficial deposits of more recent sand that are mobilised and carried by marine currents, storms and tides. The main areas of potentially accessible deposits have already been dredged to some extent. Others exist in areas of water that are too deep to be dredged with the vessels available at present. The present generation of marine aggregate dredgers operate in water depths of about 18 to 60 metres although world-wide there is technology to dredge beyond 120m.

Resources are evaluated using direct and indirect techniques 490 to establish the nature of the seabed and of associated marine habitats M0003, M0018. Direct techniques involve taking samples of seabed sediments. Indirect techniques include examination of the seafloor using sonar (reflection of sound waves off the sea floor) and inspection using underwater cameras or closed circuit television. Sediment samples are taken from the seabed to establish the quality of the mineral M0022. These techniques together identify suitable sand and gravel and establish the lateral extent, thickness variations and suitability as aggregate as well as the presence of any unsuitable overburden that would need to be removed from above the economic mineral. Habitats are investigated by direct examination (diving, photography) and sampling using grabs and small trawls so that the contained species and community structures can be identified 527.

Repeated surveys establish the stability of the seabed M0046 and annual and seasonal variations in species and biodiversity including spawning and migration patterns M0056, 514, 515, 526. Results of surveys are often presented as maps M0027, M0037, M0040, nowadays mainly within geographic information systems M0010, M0014, M0019.

In recent years there have been regional surveys to provide better information on the aggregates potential and possible impacts of extraction around proposed dredging areas M0033, M0034, 480, 505 as well as to more accurately establish the associations between various habitats and sediment substrates M0007, M0008.