Blick in eine halle mit großem wasserbecken in dem ein gelbes schiffsmodell mit messgeräten schwimmt
Under water

Nautical depth: How deep is the water really?

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

schlickprobe in einem durchsichtigen plastikbecher mit Etikett
Not cocoa, but a sample of liquid silt from the harbor.

In global ports such as Rotterdam, Antwerp or Hamburg, every centimeter of water depth often counts when it comes to bringing the large ships safely to their berths. Thanks to regular soundings, the navigators always know exactly how to steer ship traffic in the port. However, the transition between the solid water bed and the 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 silt and water above the solid bottom, known as a suspension or "fluid mud", similar to very thick cocoa.

baggerschiff mit rohrleitungen und auslegern im hafen von emden
Ships have been sailing through liquid silt in the port of Emden for some time now. Instead of dredging the silt, it is repeatedly liquefied with special ships and thus made navigable. However, the port is not open to the sea, but is closed off from the Ems by locks.

Until now, the upper limit of this locally up to several meters thick suspension layer 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.

hafenszene in rotterdam mit mehreren kleinen booten auf dem wasser vor einer hafenkulisse
There is also liquid silt in some areas in the ports of Rotterdam and Antwerp. The three ports 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 them with natural measurements, the bearings can then be interpreted in such a way that grounding can still be reliably ruled out. Ground obstacles such as stones or scrap metal are also clearly detected in the layer close to the ground using this method.</p

vogelperspektive auf den betriebshafen der WSV bei wedel an der elbe in den eine schute mit schlick einbiegt
A barge is used to deliver the silt for the large-scale trial in Wedel.
zwei orangene tanklaster vor einer großen halle spülen schlick in die halle
From the port in Wedel, the silt is transported by truck to the BAW test hall in Rissen and washed in.
Blick in eine halle mit großem wasserbecken, im vordergrund fließt aus einem rohr ein schlick-wasser-gemisch ins becken
Flushing the silt into the test basin.
Blick in eine halle mit großem wasserbecken in dem mehrere menschen wasser stehen und schlick verteilen, im vordergrund eine frau mit warnweste die ein foto macht
The silt is distributed evenly by hand.
ein mann in einem labor an einem monitor neben einem gerät zur messung der scherfestigkeit
During the test, silt samples are repeatedly examined in the laboratory, here for shear strength.
Ein mann in einer versuchshalle mit neonröhren an der decke manövriert ein schiffsmodell ein einem großen wasserbecken, ein anderer mann steht mit gummistiefeln im wasser und hilft
This self-propelled and true-to-scale ship model is full of sensors that measure exactly how the ship behaves in the liquid mud.
Blick in eine halle mit großem wasserbecken, links im vordergrund ein großer monitot und wissenschaftliche geräte
All measurement data is visible in real time.
eine plastikente schwimmt einem einem becken, im wasser spiegeln sich die neonröhren von der decke
Ducks (here a model) can also swim in liquid silt.

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 meters of silt 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 Center (MTC) in Hamburg. This allows experts and pilots to assess the behavior of seagoing vessels when they sail directly over or even through layers of liquid silt close to the bottom.</p

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The "Nautical Depth" project is a genuine port 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 liquid mud, larger draughts have already been approved for resting ships. The project partners are therefore optimistic that, in some cases, the new methods will also allow more water depth to be used for moving ships than is currently the case. Dredging operations would then be less frequent and more efficient - saving costs and protecting the environment.

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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 sail safely - 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.</p

 

 

In the tidal Elbe, there is no clearly defined boundary between solid ground and water. In muddy areas, there is often a layer of silt and water (fluid mud) up to several meters thick above the actual bottom of the water. 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 silt and sediment build-up and is regularly checked by the HPA. The aim is to ensure a usable depth of around 13.50 meters for large ships in many port areas. In laydown areas, however, the depths for large ships must be even greater in some cases.

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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 liquid silt 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.

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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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