Real-time validation of CoVadem derived water depths at locations with a fixated riverbed

A growing fleet of about fifty vessels participating in the CoVadem initiative continuously measure, log and broadcast data with sensors that were already on board before they started participating in the project. The underkeel clearance is measured with a single beam echo sounder, vessel position with a GPS meter and vessel draught with a ship cargo meter (a calibrated system of pressure sensors). All data from all vessels processed and combined, yields a chart of the up-to-date water depth of inland waterways in a very cost-effective way. Using hydrodynamic and hydrological models, we enrich the data with a forecast of the water depth. As such, it becomes possible to optimize cargo volumes and sail more efficiently (e.g. Bons et al., 2016).

CoVadem does not aim to determine the water depth with a precision equal to that of a multibeam echo sounder, as the single beam transducers used are typically less precise. However, the strength of CoVadem is that measurements are performed continuously, so that the information about the riverbed is always up-to-date, also at locations which are very dynamic or locations that are not surveyed with multibeam equipment. Even more information about the riverbed can be obtained, when looking at the trends of the CoVadem measurements since the latest available multibeam measurement.

Millions of measurements a day are translated into water depth using a ship squat calculation. Squat is the increased draught due to the flow of water past the ship hull. The forward speed of the ship pushes the water in front ahead. This water must return at the sides and below the ship. This results in an increased speed of the water, which, due to the Bernouilli effect induces a decreased pressure underneath the ship. This results in a water level depression in which the ship sinks (sinkage). The effect is not equal over the ship length due to the local changes in the ship hull over its length. This can cause the ship to trim. Ship squat is the combination of sinkage and (dynamic) trim.

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For more information contact Anke Cotteleer.

July 13, 2018
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