Sand size variability inside the hopper of a trailing suction dredger for beach nourishment purposes

Abstract

Research about the variability of sand size inside the hopper of a trailing suction dredger has yet to be done, despite its importance for beach nourishment projects. In this study, several samples were taken using different methodologies during dredging for a particular case of beach nourishment on board one dredger. Sampling was carried out with a tube core and a Van Veen grab at the surface when the hopper was full of sand. The results showed problems with the Van Veen grab, the standard methodology used for sampling aboard a dredger. This method should be reconsidered in the future because surface samples were not representative of the whole hopper due to the bias of higher percentage of shell pieces. According to the results, the core tubes introduced by percussion were the only useful method in determining average sand parameters closer to the values obtained for the borrow site. Moreover, cores also showed a linear correlation between sand size and depth: D50 increased 20% from the surface to 1 m depth; this is a sixth of the hopper depth of this study case. Regrettably, the manual percussion procedure could not reach depths greater than 1 m.