Sediment quality

The introduction of the sediment quality control in Wallonia results from the decree from the Walloon government of 30/11/1995 concerning the management of materials removed from river beds and banks of water courses through dredging or dragging works (AGW 1995) as well as, for navigable water courses, the obligation that the Operational Directorate General for Mobility and Waterways (DGO2) has to regularly carry out dredging, dragging and maintenance of the navigable water courses and infrastructure it manages and, generally, directive 2008/105/EC (“NQE”), which requires member states to analyse long-term trends concerning priority substances which may accumulate in sediments and/or biota.
On behalf of the Operational Directorate General of Agriculture, Natural Resources and Environment (DGO3), the ISSeP performs controls and monitoring on the evolution of the quality of sediment in non-navigable water courses (network of 90 stations) as well as analyses the evolution of the concentrations of priority substances in sediments (network of 54 stations).

Carte réseau


In terms of navigable water courses, the ISSeP, with the help of the BEAGx, carries out sampling and physico-chemical analysis of sediment samples with the aim of either achieving an initial diagnosis  before dredging/dragging or after dragging, or characterising the sediment present under the dredging and which needs to remain in place. Other samples are taken for granulometric analyses. Finally, the ISSeP carries out and updates, for DGO2, maps summarising the quality of aquatic beds.

Sediment drill for the Charleroi Brussels canal using the peat sampler

Sampling using the peat sampler in the central canal

Ecotoxicological tests

In the context of the sediment quality monitoring mission, the physico-chemical diagnosis of a series of stations is complemented by ecotoxicological characterisation to better evaluate the bioavailability of the polluting substances and the toxicity associated with the simultaneous presence of several pollutants (synergistic or antagonistic effects). The approach proposed is based on the triad, an integrative method defined by Chapman et al. (2000) which combines chemical, toxicity and biological data. This approach is used in many countries (Canada, France, Netherlands) but also routinely in Flanders.
More specifically, in 2012, 11 stations in Walloon water courses were selected from 18 “priority substance” stations and 5 additional stations within the “exotoxicity” network of the surface water quality network, based on 5 bioassays:

  • 3 on interstitial water using specific organisms from the water column: inhibition of the bioluminescence of Vibriio fisheri (bacteria), inhibition of the growth of algae pseudokirchneriella subcapitata, and inhibition of the reproduction of the Brachionus calyciflorus rotifer.
  • 2 on whole sediments using specific organisms from the sediment: mortality and inhibition of the development of Chironomus riparius (diptheran larvae) and Heterocypris incongruens (ostracod crustaceans).

The ecological state (and specifically the biological quality elements of this state) was evaluated based on characterisation files for bodies of surface water in Wallonia (DGO3, 2009).


Review of the legislation

The AGW of 1995 and the decree from the Walloon government of 14 June 2001 encouraging the recovery of certain waste regulate the management of sediment removed from water courses. However, these decrees have not allowed for the emergence of sustainable operational solutions for the recovery/elimination of this waste, which has resulted in a significant delay in the dredging and dragging of navigable and non-navigable water courses. In addition, the classification of sludge (A and B) recommended by the AGW of 1995 to define management channels no longer appears relevant compared with other regulatory provisions introduced subsequently, such as the decree of 5 December 2008 relating to soil management. Therefore, it is essential to redefine a suitable legal framework for all channels and to develop the administrative and technical tool required for the sustainable management of these matters.
This study’s main objectives are:

  • to prepare a report on the current management, in situ characterisation of the recovery/elimination of sediment;
  • to identify the recover/elimination streams;
  • to offer a new legal framework;
  • to develop new management tools (sediment management map, automatic stream monitoring form, good practices guide for sediment characterisation, etc.).

The project’s first year was dedicated to creating a bibliography of the studies dedicated to Walloon sediment and similar materials and the establishment of the quantitative and qualitative inventory of deposits. Simultaneously, the different management pathways were the subject of evaluation and a legal analysis of the regulations was carried out.
The project’s second year was mainly dedicated to preparing the new “sediment decree” thanks to the active participation of the competent administrations (DGO3, DG02, DG01, public water management company – SPGE) as well as the law firms Orban de Xivry & Cartuyvels and Bird & Bird, which received the subcontracting contract for the legal study. A study of the expected economic impacts of the implementation of the decree (in the project’s current state) has been carried out, and it shows that its application could allow greater recovery of the sediments removed from water courses and, due to this, reduce costs related to their management.
The work currently focuses on the updating of the sediment management map. Eventually, this will be a mapping application allowing for the consultation and integration of georeferenced data relating to the management of materials removed from water courses, which will facilitate the implementation of the new corresponding regulation. It will exist in two integrated versions with different accesses (see figure below). The first will aim to help with technical agents with the examination of files and the second to facilitate the administrative procedures of managers via the use of electronic maps accompanied by the map. This could eventually be linked to the electronic application forms concerning the use of soil or waste (CUD, CUS). These applications will increase the traceability of operations by forming databases updated automatically from dredging and dragging inventories, CUS and CUD and spreading zones. These tools will allow for the sustainable management of water courses in line with Walloon environmental legislation.

Thematic correspondent for sediment quality: Elodie Bouhoulle – 04 229 88 24


Prélèvement au Peat Sampler dans le canal du Centre

 Brachionus calyciflorus
Daphnia magna
 Chironomus riparius