Ships need to have sufficient water under their keel to be able to enter the Port of Hamburg. To maintain the depth of the water, fresh deposits (sediments) must be removed constantly from the bed of the port basin and the shipping channels. This is common practice in many of the world’s ports. The sediments are flushed towards Hamburg both from the upper reaches of the River Elbe and at each high tide from the direction of the North Sea and settle here.
The HPA dredges several million cubic metres of Elbe sediment each year as part its task to maintain the water depth. Most of the dredged material, a mixture of sand and fine-grained silt from the Elbe, can be relocated to other parts of the river. However, some of the fine-grained silt contains heavy metals and organic pollutants, which reach Hamburg primarily from the upper reaches of the Elbe. If these sediments are excessively polluted they are treated by the HPA ashore and reused or dumped.
On the following pages our experts explain how sedimentation occurs, how the HPA’s sediment management functions and what Hamburg does to ensure the cleanliness of the Elbe.
The tides are clearly visible in the tidal Elbe, in the tide-dependent section of river between the weir in Geesthacht and the estuary in the North Sea. The Port of Hamburg also experiences alternating high and low tides twice a day.
But a fascinating movement also occurs beneath the water surface: the forces of ebb and flow operate like a pump in the tidal Elbe. Not only does the more powerful incoming tide push water from the North Sea into the Elbe, but fine, sandy material is also transported upriver. The weaker ebb stream only carries a certain amount of it back out. This phenomenon is known as “tidal pumping”.
In addition, fine-grained sediments are transported downriver from the upper reaches of the Elbe. The sediments settle where the speed of the current decreases, i.e. particularly in the port basin and in the low-flow areas of the river, where they may obstruct shipping traffic.
When the Elbe carries a lot of water, the force of the current can set a larger portion of the sediments in motion and flush them into the North Sea. However, the so-called freshwater flow is subject to considerable fluctuations.
The mouth of the tidal Elbe is an estuary. This kind of river mouth, widened into a funnel shape by the ebb and flow of the tide, only form on coasts with powerful tidal processes and are subject to constant change. The estuary of the tidal Elbe is a highly dynamic transition zone between the river and sea – 200,000 tons of sediment are continually on the move here. Large sections of the estuary are under special protection as habitats. Upriver an inland delta frequently forms, like the highly branched river bifurcation area between Mühlenberger Loch and Geesthacht, in which the Port of Hamburg was constructed.
Partnership and activities of HPA to the Tide Elbe:
As in most harbours in the world, the port basin and fairways in Hamburg must be regularly cleared of sediments. They are continually dredged, otherwise the ships would soon be prevented from entering the port.
Sedimentation means that suspended matter settles on the river bed in low-flow zones. The sediments in the Port of Hamburg consist of fine-grained silt and coarser-grained sand.
The HPA’s task is to ensure the required depths for shipping traffic through sophisticated sediment management and to make sure that the dredged material is handled in a safe and environmentally-friendly manner.
Most of the material is harmless and can be put back in the water at a suitable site. A small portion of the sediments from the upper reaches of the river picks up too many pollutants on its way to Hamburg and must be treated ashore and then disposed of safely.
The aim of all these measures is to ensure balanced sediment management in the Elbe cultural area, which has been managed for centuries. To this end, the diverse uses of the river and the requirements of water and nature conservation must be reconciled. In the long-term, the quantity of sediment will also be reduced through river engineering measures. The HPA conducts research and cooperates closely with its partners for this purpose.
The jointly developed results (PDF) form the basis for more sustainable handling of sediments. The aim is to ensure that less sediment is produced and that sediment pollution is further decreased. The agreement on the transfer of sediments from Hamburg into the North Sea between the states of Schleswig-Holstein and Hamburg in spring 2016 is a first step. The HPA will work intensively with the region on further measures which could lead to a sustained reduction in dredging volumes. They will be expedited in joint plans under the name “Estuary Partnership”.
Hamburg will also drive forward its commitment to cleaning up the Elbe of pollutants – with the treatment and disposal of polluted sediments ashore and the project ELSA, which is active as far as Czech Republic, in order to support the clean up of remaining pollutant deposits close to the source.
With the aim of reducing the volume of sediments transported upriver on a long-term basis, the HPA is developing measures that are designed to ensure that the incoming tide loses energy. Experts speak of “reducing the tidal energy”. This will also reduce the volume of suspended matter which is flushed towards Hamburg.
These measures may include river engineering adjustments in the Elbe estuary area or creating or reconnecting shallow water areas which were previously already subject to the influence of the tides. This once again gives the water space to spread out, so that the pressure of the incoming tide is reduced. Measures like this could also have great benefits for natural conservation, flood protection or leisure use. As the first pilot project for new tidal capacity, the HPA is currently constructing the new approximately 40-hectare Kreetsand tidal area in the east of Wilhelmsburg.
Optimising currents in port basin entry channels may also help to reduce sediment, as they prevent suspended matter from settling excessively in low flow areas or areas which are particularly critical for ship traffic.
The water depths necessary for the draught of the ships in the Hamburg port basin and fairways must be maintained on an ongoing basis to ensure that there is always “a hand width of water” beneath the keel. The HPA’s experts exploit the natural transport induced by the current for this purpose: the sediments are taken up from the riverbed where they obstruct shipping traffic and are put back in the river at a different location, where ideally they will be driven in the direction of the North Sea with the river and ebb current as a natural component of the system. The most important instrument for this is dredging the sediments on the basis of current soundings.
If the HPA Depth-sounding vessels find that at particular places in the port excessive sediment has settled and as a result shipping may be obstructed, large special ships remove surplus sand and silt from the bottom of the Elbe. This so-called “maintenance dredging” is easy to observe from the banks of the Elbe. The special ships known as hopper dredgers are immediately recognisable.
Most of the sediments are clean enough for them to be safely put back into the natural flow process of the tidal Elbe in a different place. This is shown by extensive analyses carried out prior to the dredging (available in our download centre). So-called “relocation” has priority in sediment management. As far as possible, sediments should be left in the water. Both for ecological reasons – because the sediments are a natural component of the Elbe – and also because it is more economical than bringing them ashore. The smallest fraction of the sediment which has a greater pollutant content is finally brought ashore, treated and safely dumped or reused.
The hopper dredgers, also known as trailing suction hopper dredgers, have lowerable pipes on their sides which extend to the riverbed. A centrifugal pump sucks a mixture of water and sand or silt from the riverbed and pumps it into the open hopper. Once the full capacity of up to 15,000 cubic metres has been reached, the hopper dredger makes its way to the relocation point. Once there, the load is put back in the water through bottom flaps.
In order to ensure that the Port of Hamburg remains accessible in the summer months as well, the HPA has transported fresh sediment to “Tonne E3” in the North Sea since 2005. The aim of transferring the sediment to the North Sea is to permanently remove fine sediments from the upper tidal Elbe, thus permanently relieving the system of surplus silt. It is not possible to transfer the sediments into the Hamburg area (Neßsand) in the months from April to November for reasons of water protection. In that period protected fish species are spawning there and hydrological conditions (oxygen content, currents) are generally unfavourable at that time as well.
The transfer of dredged material from Hamburg is enabled by an approval issued by the state of Schleswig-Holstein. With the new approval, valid since 2016, fresh sediments can be transferred from the most important port areas, provided they fulfil strict quality requirements. For this purpose, the sediments in Hamburg are sampled prior to dredging and analysed (for release) by certified commercial laboratories. Only when it has been proven that the sediments are sufficiently clean may they be transferred into the North Sea.
Tonne E3 lies around 25 kilometres northwest of Hamburg’s Island of Scharhörn Bird Sanctuary, in an area in which fine-grained sediments naturally occur at a depth of approximately 35 metres (silt drop zone). The conditions on site are therefore selected to ensure that there is a high degree of similarity between the natural sediments and the dredged material and that most of the dredged material remains there.
To ensure that the effects of the transfer of sediments remain within reasonable limits, the approval is tied to strict environmental requirements. Extensive monitoring is carried out to verify compliance. Samples are currently taken twice per year at a total of 148 points in and around the dumping area and examined with regard to the formation of pollutants. The quality monitoring also includes extensive examinations of numerous other organisms in the relocation zone. Additional coastal measuring points ensure that none of the transferred dredged material ends up on the coasts and beaches. This prevents the incidence of any adverse effects occur outside the immediate relocation zone.
Some of the fine-grained sediments which arrive in the Port of Hamburg with the water of the Elbe are more heavily polluted with various pollutants. This pollution originates from mining operations, industry and wastewater discharge in the entire catchment area of the river and its tributaries right up to the source in the Czech Republic. Pollution in the Elbe sediments has decreased significantly since German reunification. However, past pollution is also retained for years. The sediments act as the Elbe’s long-term memory, so to speak.
Hamburg has defined the target of reducing the pollution load of the Elbe and its sediments. In this way, the HPA makes a significant contribution to easing the burden on the Elbe and the North Sea.
To prevent new pollution, experts from the HPA pursue a strategy of cleaning up sources of pollutants (contaminated sites) directly on site along the course of the Elbe. To this end, they work with the Elbe River Zone Community (FGG), the International Commission for the Protection of the Elbe (IKSE) and the project “Elbe Sediment Pollution Clean-Up (ELSA)”.
Sediments which already contain a higher level of pollution are removed from the river system in Hamburg. For this purpose, the HPA has developed, at substantial expense and with significant scientific work, environmentally-friendly technologies for handling polluted dredged material. While most of sediments which are regularly dredged from the Port of Hamburg can be put back in the river at a different location, approx. 20% of more heavily polluted sediments are brought ashore and safely disposed of there. They are treated in the MSPS plant (mechanical separation of port sediments) and then dumped.
One river, common responsibility!
The EC-Water Framework Directive (WRRL) obliged the EU member states to the assessments of integrated river basin management. But here in Germany the cooperation between the federal states as well as with the federal government seems difficult. Therefore, effective measures to improve the quality of sediments in the Elbe still have to be found. The renowned legal experts Prof. Dr. jur. Wolfgang Köck and Dr. jur. Moritz Reese investigated how to handle pollution of relevance to the river basin according to the WRRL. They came to the conclusion that the handling of remotely controlled pollution in the present management planning and in the measures program of FGG Elbe doesn’t fulfil the duties of the WRRL and the WHG. Besides, they identified ways to improve the cooperation between federal states and the federal government demanded by the WRRL. The ‘Masterplan redevelopment of the Elbe’ also shows ten specific priority measures to realize within the catchment area of the Elbe.
Furthermore, here’s a link to the Rechtsgutachten Flussgebietsbewirtschaftung im Bundesstaat (legal opinion on river basin management in the federal state).
The HPA is responsible for removing polluted sediments from the Elbe and safely dumping them. Two landfills are currently in operation for this purpose in the Hamburg area: Francop in the west and Feldhofe in the east.
Even if the pollution load in the Elbe continues to decrease, it will still be necessary to dredge polluted sediment from the Port of Hamburg that cannot be relocated in the river, for example in the event of construction measures. The HPA needs sufficient landfill site capacity for this material. An open-ended procedure was launched to identify a possible site in Hamburg for a third dredged material landfill. The existing drainage fields in Moorburg-Mitte were found to be the most suitable site in a comparative assessment.
The Port of Hamburg can only undertake operations when the depth of the water is maintained to ensure the required nautical draught for ships. This means, as in every port, sediment is dredged from the fairway and the berthing spots on an ongoing basis.
The main share of this sediment is released back into the water. A smaller share, which is contaminated with chemicals, is taken on land, processed and safely disposed of. This is only possible when Hamburg has enough disposal capacity at all time.
There have been two disposal sites for dredged sediment to date: in Francop and in Feldhofe. The disposal site in Francop is currently being decommissioned, as it no longer has enough capacity. The disposal site in Feldhofe is being expanded to accommodate more capacity and allow for continued operations. This means the shipping capability for the Port of Hamburg is secured for the future.
Based on technical know-how gained over many years, it is possible to expand the disposal site in Feldhofe so that it can accompany significantly more material. The existing disposal capacity will therefore be increased by up to 7 million cubic metres and the disposal area raised by 18 metres to a height of 56 metres.
The disposal of contaminated dredged sediment in Hamburg can therefore be guaranteed today with just one disposal site.
Current overall capacity of the Feldhofe disposal site:
9 million cbm of sediment
An additional approx. 7 million cbm of sediment
Height planned to date:
38 meters at the highes point
Height after capacity expansion:
56 metres at the highest point
Disposal area after capacity expansion:
Unchanged at 78 hectares
In the long term, an additional disposal site may be needed, for example when the amount of dredged sediment increases or the capacity at the Feldhofe disposal site has reached its limit. In an open and unbiased process, a potential location in Hamburg was sought out for a third dredge disposal site. The existing drainage field in Moorburg-Mitte was determined to be the most suitable location compared to other sites.
At the moment, the Feldhofe disposal site alone is able to accept the current amount of sediment – however, it is essential to secure disposal capability and hold onto the Moorburg location as a third disposal site.