Fluid Mud and Determining Nautical Depth - 18/01/2013

A Case Study

Jannes Kamphuis, Manager Dredging & Maintenance, Groningen Seaports, Jeroen Verwilligen Nautical researcher, Flanders Hydraulics Research, Reinder Meinsma Senior project engineer, Wiertsema & Partners

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Ships are getting larger, dredging costs for maintenance are increasing and permits for disposing harbour sludge are increasingly difficult to obtain. An objective evaluation of harbour maintenance practices is therefore justified. Siltation of harbour basins decreases the nautical depth and maintenance is required to ensure safe shipping. The present techniques usually consist of dredging or other methods for removing sediments. Scientific research over the past decades and experience in seaports in the north of the Netherlands, Belgium and Germany have shown that a different approach, based on physical characteristics of mud layers, innovative surveying tools and strategies is feasible.  This article presents an approach for determining the nautical depth for a sea harbour with fluid mud and or a muddy bottom layer which can be successfully related to a ‘Keep Sediments Navigable’ strategy of the PIANC Report 102 ‘Minimising Harbour Siltation’.

In many parts of the world fluid-mud suspensions occur above the bottom of shipping routes creating difficulties in defining the navigational depth. When lead lines were used, the depth was recorded to the fairly solid bottom and any overlying mud layer was usually not detected. By introducing echo sounders, the water-mud interface was not always clearly defined. The interface shown on the records may depend on the instrument and the frequency used. The lack of a clearly defined water-mud interface can cause unnecessary depth restriction and possibly excessive dredging.

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Last updated: 17/01/2017