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1.2.03 SEDYMO research project – effects of sediment dynamics on the quality of flowing waters

Many pollutants released by man into the environment end up in the water. The contamination directly discharged gathers together here, along with solids washed away by precipitation and floods and dissolved compounds. Some pollutants tend to bind to particles and are deposited with the sediments on the water bed. From there they can get back into the water, for example if they are stirred up by deepening of the waterways or flooding, or are re-dissolved as a result of chemical processes. A research project is tackling these important problems and working on supplying the currently lacking foundation and process knowledge.

Although the amount of contamination entering Germany’s rivers is constantly falling, the sediments they contain are still heavily loaded with environmental chemicals in many areas. These substances do not only enter the waters through wastewater; other causes of this pollution are contributions from the air, precipitation and floods, and contaminated solids from landfill sites and slag heaps. River mouths are especially affected by this, as this is where the pollutants from the entire course of the river gather.

Fine sediment is of particular interest to those researching water pollution. It contains relatively large amounts of pollution and the large particle surface makes it very reactive from a chemical and physical perspective. Pollution in this regard does not only relate to directly toxic environmental chemicals such as heavy metals and specific organic compounds; it also covers substances that can indirectly affect water quality, such as organic substances or nutrients such as nitrogen and phosphorus. The degradation processes and widespread algae growth reduce the oxygen levels in the water.

Dynamics of pollution release

Depending on the flow speed and the chemical and biological state of the water, solids and parts of dissolved substances transported by rivers are deposited on the riverbeds and flood plains. The sediments therefore also indicate the water pollution of the last few days, but their components can also be released again. If solids are present (mineral or organic particles), then either natural or artificial erosion processes are involved. Triggers include flood water, movement caused by ships or maintenance dredging to keep the waters navigable. Soluble pollutants that in the meantime have bound themselves to the sediment can be released through (micro)biological and chemical processes.

Left: Taking sediment samples at the Rhine / Right: Using an in-situ erosion tester at the Elbe

Links: Taking sediment samples at
the Rhine / Right: Using an in-situ erosion tester at the Elbe
Left: Taking sediment samples at the Rhine / Right: Using an in-situ erosion tester at the Elbe

Knowledge on the dynamics of pollutant-bearing sediments is becoming increasingly important with the implementation of the European Water Framework Directive (WFD), which focuses on measures to improve water quality across entire river basins.

Statements to date on the means of pollution entering water have predominantly referred to known sources outside the water itself. This includes diffuse sources such as agriculture and isolated sources such as landfills and industrial sites. However, this approach omits an extremely important factor: the re-release of harmful particles within the sediment on the riverbed.

The BMBF “sediment dynamics and pollutant mobility in river basins” (SEDYMO) research project was launched in May 2002 to drive forward this aspect of sediment research. The project aims to make a contribution towards the ecological optimisation of maintenance dredging within federal waterways, the sustainable management of contaminated flood sediments and the planning and execution of sediment clear-up operations to improve the structure and ecology of the water.

Interdisciplinary approach

The research project co-ordinated by the institute of environmental technology and energy economy at the Hamburg University of Technology together with 12 other partners (see TUHH project website) combines two key issues: the dynamic erosion/depositing behaviour of the fine sediment and the mobility of pollutants and loads in sediments and suspended matter. As the two aspects are closely interlinked in practice, a joint research approach between technical and natural-science disciplines is required.

Taking sediment samples at the Salzach

Taking sediment samples at the Salzach
Taking sediment samples at the Salzach

The first phase of the project saw the project team examining the erosion and transportation of fine-grained sediment using the Neckar and the Elbe as an example. The researchers used the flow channel, microcosm and turbulence column as measuring devices. The methodical work was accompanied by physical-chemical and microbiological analyses. Other sub-projects involved comparative investigations of the transportation of fine-grained sediment performed under near-natural conditions in docks and their inlets. Another sub-project investigated the mixture of fine-grain particles in the Elbe. The second phase primarily saw the scientists investigating the transportation of nutrients and pollutants. The interactions occurring in natural conditions between aggregates, pollutants, water and soil were quantified, classified as control factors of biological, sedimentological and chemical processes and consolidated into models. Six more sub-projects helped the scientists gain fundamental knowledge of the physical-chemical and biological properties of solids within water.

Broad application range

The investigations showed that the speed at which the organic pollutants are sorbed (bound) to the sediment and then desorbed (released) depends heavily on hydrodynamic conditions. Conversely, changes to the hydrochemical composition of the flowing water, e.g. due to flood events, have less influence on the binding behaviour of pollutants than previously thought.

The instruments and models developed during the course of the project to characterise and predict the erosion stability of sediments has already been put to practical use. For example, areas flooded by the severe Elbe flood in August 2002 were examined. Scientists from the research programme have also taken part in the “Iffezheim barrage” risk assessment: the shifting of 300,000 cubic metres of heavily contaminated Rhine sediment has sparked an international controversy.

The SEDYMO results are also being directly input into the work of the technical committee on managing contaminated sediments at the German Association for Water, Wastewater and Waste (DWA) and the BMBF-funded “Risk Management of Extreme Flood Events” (RIMAX) programme. They will be of particular relevance when further measures are implemented in accordance with the WFD to combat pollution sources in waterways. Reducing emissions from historically contaminated sediments will be a key task within this work.

The publication entitled “Sediment Dynamics and Pollutant Mobility in Rivers – An Interdisciplinary Approach” is the frame of reference for the interactions in both technical engineering and natural sciences of contaminated sediment in flowing waters and was compiled as part of the SEDYMO project from the contributions to the “International Symposium on Sediment Dynamics and Pollutant Mobility in River Basins”.

Hamburg University of Technology (TUHH)
Institute of environmental technology and energy economy (IUE)

Prof. (i. R.) Dr. Ulrich Förstner
Eissendorfer Straße 40
21071 Hamburg, Germany
E-mail: u.foerstner@tu-harburg.de
Stöversweg 6 a
21244 Buchholz
Tel.: +49(0) 41 81/3 67 90
Internet: www.tu-harburg.de/iue/sedymo

University of Stuttgart
Institut für Wasserbau (water engineering institute, IWS)

Prof. Dr.-Ing. habil. Bernhard Westrich
Pfaffenwaldring 61
70569 Stuttgart, Germany
Tel.: +49(0)7 11/68 56 37 76
E-mail: bernhard.westrich@iws.uni-stuttgart.de
Funding reference: 02WF0315 – 0318, 02WF0320 -0322, 02WF0467 - 02WF0470
Ressource Wasser
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