Fine-Grained Sediment Transport in Tidally-Influenced Environments—Detection with Optic-Acoustic Devices

Alexander Bartholomae¹, Olaf Joerdel², Martina Karle², and Kerstin Schrottke^2
1 Senckenberg Institute, Wilhlemshaven, Germany
² RCOM, Bremen, Germany

The transport of fine-grained material in the tidal system is directly related to the hydrodynamic energy. Currents, waves and the physical properties of the fluid control transport, deposition and remobilisation of these sediments. In contrast to unidirectional transport systems, tidal systems show very complex sediment transport patterns which vary with every tidal cycle. Considering the complex physico-chemical nature of fine-grained material (silt and clay) in seawater it is only possible to measure their in situ behaviour with instruments having high temporal and spatial resolution levels. To detect and quantify this material in the water column, a wide spectrum of optic-acoustic devices have been developed in recent years. Results of different case studies are presented, near bed transport measurements in millimetre resolution with Acoustic backscatter system (ABS) and 3-D Acoustic velocity metre (ADV)'s which can show the biostabilisation effect on fine-grained sediment surfaces, transport and deposition of fluid mud with a multifrequency parametric sediment echosounder in decimetre resolution, and the formation of suspended particle aggregates in a tidal basin on the basis of LISST and ADCP backscatter data. The comparison of size distributions of pump samples and the in situ backscatter data show particle size variations of 200 percent over a tidal cycle. Minimum floc sizes, which are reached at a flow velocity of about 0.8 m/s, are maintained even at considerably higher velocities, suggesting the existence of a stable minimum endmember floc size class.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005