Underwater Sand Waves Analysis

in Offshore Wind Farm Construction

Gwo-shyh Song, Associate Professor, National Taiwan University

Macquarie Capital Limited had entrusted GlobalAqua Survey Ltd with conducting the survey of sand wave migration in the Formosa III offshore wind farm. For understanding the migration of the sand waves, the in-situ bathymetry survey with multi-beam sonar method had been used.

The In-situ investigation was begun in late September 2017 and completed by mid-January,2018 The range with water depth less than 50m was explored in this campaign. The obtained bathymetry data were correlated with the results of last survey in October, 2016 for calculating the difference of the topography. The topographyvariations were then used for assessing the migration of the sand waves, including azimuth and velocity. This report describes how to demonstrate.


Figure 2: 3D topography plot indicating underwater sand  waves developed on seabed. Click fifigure to enlarge

the survey results so that designers can easily understand how sand waves had moved for cable laying design purpose. Water depth in the survey area is in the range of -20m to -50m. Reson’s Seabat 8101 Multibeam Echo Sounder was used in this in-situ survey. Before the survey, instrument mobilisation, the installation of multibeam acoustic transducer, motion sensor, and gyro follow the standard procedure to avoid occurrence of biases. As soon as mobilisation was completed, the patch test was conducted to make sure all the biases can be corrected.

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