9. Using Multibeam and Sidescan Sonar to Monitor Aggregate Dredging

Marine aggregate dredging in the UK occurs within individually licensed areas, and before dredging is allowed to begin a Government permission (Licence) to dredge is required. This is accompanied by detailed monitoring conditions based on the environmental effects and sensitive receptors present at each site. Monitoring methods typically used in the UK include multibeam bathymetric and side scan sonar surveys and this Chapter will provide a Case Study of monitoring at one particular licence area – Area 401/2. Multibeam data showed bathymetric changes resulting from aggregate extraction limited to the direct footprint of dredging; and mobile sandwaves could be seen. Sidescan sonar data showed no changes in the overall interpretation when comparing datasets from 2013 to 2009. Minor changes in the distribution of Sabellaria spinulosa were noted, but no additional areas of conservation significance were identified and no changes to the mitigation were proposed. Fifty-two archaeological anomalies were identified during the analysis of the 2013 survey data, eight of which required mitigation. The monitoring of dredging activity at Area 401/2 has shown limited impacts arising from aggregate extraction and mitigation measures have been appropriate.