MONITORING AND DREDGING TECHNOLOGY IN MUDDY LAYERS

摘要

Development of strategies in order to minimise costs in maintenance dredging means decreasing of dredging expenditure and quantities to be dredged. It's in no case sufficient to determine the navigable depth by means of echosounding only because echo sounding devices are working mainly with high frequencies (beginning with 100 kHz) and therefore they detect soft or very soft layers as the highest sediment horizon. An echo sounding device can never give an answer to the question if these layers can be passed by a vessel with out any problems. The only proof of navigability is represented by a vertical scan of the consistency of the material throughout the water column.Up to now the most common proof for navigability was the density of the muddy water layers. This approach never gave an answer to the question if the sediment starts to flow after contacted by a ships hull. The definition of fluidability requires an additional measurement of rheological properties, e.g. yield stress, shear rate or viscosity (Wurpts, 2005). Measurement devices for these purpose should:rn1. deliver at least one out of these parameters, whichrn2. can be controlled without any postprocessing procedures directly from a moving survey vessel andrn3. the measurement technique should be practical in practice.