The ICPR has presented the first sediment management plan for an international watershed. This plan presents a comprehensive view of the sediment pollution in the main stream of the Rhine and in its major tributaries.
The sediment management plan for the Rhine is based on the following sediment classification:
(1) In a first step, the most important contaminants and the areas they have polluted were identified.
(2) In a second step, sedimentation areas with more than 1000 m³ of contaminated sediments were identified. These sedimentation areas are called „areas of concern“, if there is no natural or man-made risk of re-mobilisation of the contaminated sediments.
(3) In a third step it was investigated, in how far a re-mobilisation and further transport of contaminated sediments is liable to detrimentally impact the water quality of downstream reaches. For these investigations, the assessment of the risk of re-mobilisation due to floods, wind, and anthropogenic impacts (dredging, navigation) plays an important role. In cases of considerable contamination and where great amounts of sediments are liable to be re-mobilised, the area is classified as “area presenting a risk“.
18 of the 93 analysed sedimentation areas have been classified as „areas of concern“, 22 as areas presenting a risk. For areas presenting a risk, measures aimed at reducing the risk of spreading contaminated sediments will be presented while it is recommended to intensively monitor the “areas of concern“.
Sedimentation areas on the Upper Rhine are mainly contaminated by hexachlorobenzene. In the 1970s and 1980s, this toxic substance, a by-product resulting from the production of other substances, was discharged into the Rhine near Rheinfelden. After the discharge into the Rhine, hexachorobenzene accreted to sediments with which the substances was transported downstream the Rhine from Rheinfelden. Today, sediments contaminated by this substance are mainly found in the impoundments of the Upper Rhine.
For sedimentation areas along the Middle Rhine, the Lower Rhine and the Delta Rhine heavy metals such as cadmium and polychlorinated biphenyls (PCB) are relevant contamination indicators. Cadmium is a highly toxic substances used in accumulators and for corrosion control. The PCBs represent another group of substances accumulating in sediments, but also in fish. Formerly, they were used as hydraulic fluid in mines, and as insulating oil in condensers of electric devices.
Mainly, these toxic substances represent dangerous waste accumulated over the years, which means that these substances were formerly discharged into the Rhine and are still found accumulated to sediments and suspended matter. Thus, the sediments represent the long term memory of river pollution.