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Application of high resolution acoustics for determination of the physical properties of fluid sediments

Drs. C.J. Werner

 

The application of traditional low frequency echosounders in areas with fluid sediments often appears not to be reliable. The results consist of a single depth digitalization value that is not stable and does not give information about physical properties.

Validation of acquired data is also difficult.

The integration of high resolution digital seismic acquisition techniques with traditional low echosounder frequencies enables characterization of fluid sediments and provides extensive opportunities for validation of acquired data.

A case study conducted in a tidal environment with the high resolution digital Silas SBP-10 system and geophysical point measurements (RheoTune) gives insight in the potential capability of high resolution seismics to detect changes in physical properties.

The study shows that the top of the fluidized sediments is characterized by a density gradient of at least 0.4 g./l. per cm. This change was detected by the high resolution seismics (see fig.2).

Calibrated density data resulting from high resolution seismics also show close correspondence with the 1200 g./l. density level according to the geophysical point measurements.

The rheological data (RheoTune) indicate that the fluid sediments in this area are generally of a low rheological strength (low yield strength).It is shown that this has large implications for the maintenance of navigable depth.

The investigation using high resolution seismics  also gives extra input to the study of the geomorphological dynamics in the area. First results indicate a dynamic distribution of the fluid sediment, with a large mobility in the nearshore zone.