Results of pilot survey to detect navigation induced dynamics in fluid mud : 9-13 December 2013, Buitenhaven IJmuiden, The Netherlands

RWS and Deltares performed a pilot survey in the harbour of l.lrnuiden, the Netherlands, in December 2013. The goal of this pilot survey, as a first trial, was to detect the dynamics of the mud layer caused by everyday navigation with sufficient accuracy to be able to convert observations to mud properties through inverse modelling. Acoustic measurements were performed during the passage of 23 vessels; 7 of them were analysed. The swath bathymetry sonar data, acquired to monitor the water/fluid mud interface beneath and close to the passing vessel, appeared to be too noisy in the first interpretation. More advanced processing is needed to extract information on the internal wave beneath the passing vessel. Acoustic measurements beneath the survey vessel, at considerable distance from the passing vessel, showed that the internal structure of the mud changed during the passage. The observed disturbance of the mud can be a manifestation of internal waves inside the mud, mud flow and/or artefacts from horizontal movement of the survey vessel. The current data and level of processing do not allow firm conclusions on the mechanism observed. ADCP measurements suggest that the entire water column flows during passage of a vessel, which supports flow in the mud layer. The ADCP signal, however, does not penetrate the mud and provides flow velocities of the water layer only. The results of this first pilot are promising with regard to the possibilities of designing an operational system of navigability based on in situ and continuous measurements in harbours with muddy water bottoms. Recommendations are made with respect to processing, experiments and modelling for the next step in this line of research.