View into a hall with a large water basin in which a yellow model ship with measuring instruments floats
Under water

Nautical depth: How deep is the water really?

To ensure that ships can navigate safely in the harbour, it is essential to know how deep the water is. To this end, the water depth is regularly measured. However, if there is mud on the seabed, there is sometimes a layer of mud and water at the interface between the seabed and the water, somewhat like thick cocoa. Can ships navigate through this safely? The HPA is investigating this together with its partners from Rotterdam and Antwerp as part of the ‘Nautical Depth’ project.

Silt sample in a transparent plastic cup with label
Not cocoa, but a sample of fluid mud from the harbour.

In global harbours such as Rotterdam, Antwerp or Hamburg, every centimetre of water depth often counts when it comes to bringing large ships safely to their berths. Thanks to regular soundings, the navigators always know exactly how to steer the ship traffic in the harbour. However, the transition between solid waterbed and water is often not so clearly defined, especially in tidal waters. In muddy areas in particular, the transition is usually fluid. In some places, there is a mixture of mud and water above the solid bottom, known as a suspension or "fluid mud", similar to very thick cocoa.

dredger with pipelines and booms in the port of emden
Ships have been travelling through fluid mud in the port of Emden for some time now. Instead of dredging the mud, it is repeatedly liquefied with special ships and thus made navigable. However, the harbour is not open to the sea, but is closed off from the Ems by locks.

Until now, the upper limit of this suspension layer, which can be up to several metres thick locally, has always been sounded and released for shipping traffic. The water depths are then correspondingly shallower and dredging is required. But a ship also floats in "cocoa" - if it were possible to reliably determine the depth of the near-bottom layer that can still be navigated without any problems, less dredging would be required, at least temporarily and in certain places. A real advantage.

harbour scene in rotterdam with several small boats on the water in front of a harbour backdrop
There is also fluid mud in some areas in the ports of Rotterdam and Antwerp. The three harbours are therefore working closely together in the "Nautical Depth" project.

Together with the ports of Rotterdam and Antwerp, the Technical University in Delft and various German research institutes, the HPA is therefore investigating how to clearly and reliably determine where ships can still sail or where dredging is really necessary. To this end, new technical measurement methods must be found that navigators can always rely on. For example, different frequencies can be used to take bearings. By comparing the soundings with natural measurements, they can then be interpreted in such a way that grounding can still be safely ruled out. Ground obstacles such as stones or scrap metal are also clearly recognised with this method in the layer close to the ground.</p

bird's-eye view of the WSV's operating harbour near wedel on the elbe into which a barge with mud turns
A barge is used to deliver the mud for the large-scale trial in Wedel.
two orange tanker lorries in front of a large hall flush mud into the hall
From the harbour in Wedel, the mud is transported by lorry to the BAW test hall in Rissen and washed in.
View into a hall with a large water basin, in the foreground a silt-water mixture flows from a pipe into the basin
Flushing the mud into the experimental basin.
view into a hall with a large water basin in which several people are standing in water and spreading mud, in the foreground a woman in a warning waistcoat taking a photo
The mud is distributed evenly by hand.
a man in a laboratory at a monitor next to a device for measuring shear strength
During the test, silt samples are repeatedly analysed in the laboratory, here for shear strength.
A man in a test hall with neon tubes on the ceiling manoeuvres a model ship in a large water basin, another man stands in the water with rubber boots and helps
This self-propelled and true-to-scale ship model is full of sensors that measure exactly how the ship behaves in the fluid mud.
View into a hall with a large water basin, on the left in the foreground a large monitor and scientific equipment
All measurement data is visible in real time.
a plastic duck floats in a basin, the neon tubes on the ceiling are reflected in the water
Ducks (here a model) can also swim in fluid mud.

The researchers are also investigating how the ships can be driven and steered in the thicker layer and what forces are then at work. To this end, a large-scale test has now been launched at the Bundesanstalt für Wasserbau (BAW) near Hamburg. Around 600 cubic metres of mud from the Köhlfleet in Hamburg were pumped into a 3000 m² test basin at the BAW and filled with water. Scale models of ships then sail through the "cocoa" and sensors observe how they behave. The data is then transferred to computer models and used in the ship handling simulator at the Marine Training Centre (MTC) in Hamburg. This allows experts and pilots to assess the behaviour of seagoing vessels when they sail directly over or even through near-bottom layers of fluid mud.

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The "Nautical Depth" project is a genuine harbour cooperation, as "fluid mud" is an issue in many tidal ports. It remains to be seen how the results can be put into practice, as safety is the top priority here. For some berths in Hamburg with fluid mud, larger draughts have already been approved for ships at rest. The project partners are therefore optimistic that, in some cases, the new methods will also allow more water depth to be utilised for moving ships than is currently the case. Dredging operations would then be less frequent and more efficient - saving costs and reducing the burden on the environment.

FAQ on the "Nautical depth" project

The most important questions and answers at a glance.

 

The nautical depth describes the depth at which ships can safely navigate - regardless of whether there is a thin layer of silt on the bottom. It is therefore more relevant for shipping than the purely physically measured water depth. Precise soundings are used to determine where ships can still navigate safely without touching the bottom.

 

 

In the tidal Elbe, there is no clearly defined boundary between solid ground and water. In muddy areas, there is often a layer of mud and water (fluid mud) up to several metres thick above the actual water bottom. It is therefore necessary to take regular soundings to determine the depth that can actually be used for nautical purposes .

 

 

The actual depth depends on the measuring point, the tide, the mud and sediment build-up and is regularly checked by the HPA. The aim is to ensure a usable depth of around 13.50 metres for large ships in many port areas. In berths, however, the depths for large ships must be even greater in some cases.

 

 

 

 

Fluid mud is a mixture of water and fine sediment, similar to viscous cocoa. Tests and simulations show that, under certain conditions, ships can safely pass through this layer without touching the bottom.</p

 

 

The HPA is working together with the ports of Rotterdam and Antwerp, TU Delft and other research institutes to determine exactly how deep ships can safely sail, even when there is fluid mud on the bottom. The aim is to reliably determine when dredging is really necessary and when it is not. This could save considerable amounts of dredging and thus relieve the burden on nature.</p

 

 

Different sounding methods are being tested, such as measurements with different frequencies. By comparing the measurement results with real silt samples, the aim is to develop a method that clearly shows where ships can sail safely and where there is a risk of grounding.

 

 

The Hamburg Port Authority provides current data and tidal information online, e.g. via the Hydro-Portal.

 

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