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Water and soil quality

Sediment and river basin quality

Sediment and river basin quality

A healthy river needs healthy sediment as a source of life. Sediment is the basis for a variety of habitats for many aquatic species. Microbial processes cause regeneration of nutrients and important functioning of nutrient cycles for the whole water body. Sediment dynamics and gradients (wet-dry and fresh-salt) form favourable conditions for a large biodiversity, from the origin of the river to the coastal zone. Sediments are thus an essential, integral and dynamic part of our river basins, which has to be noted by water managers.

Threats and adverse effects

Sediments act as a potential sink for many hazardous chemicals. These sediments still are a secondary source of pollution especially when they become eroded and transported further downstream (e.g. due to flooding, resuspension). Along the course of the river to the sea, transportation, dilution and redistribution of sediment-associated contaminants occur. These contaminants, including nutrients, heavy metals and (persistent) organic compounds, have an impact on the chemical and ecological quality status and complicate sediment management. Deltares has developed much expertise to quantify fluxes of such compounds from sediment to surface water and vice versa. This knowledge helps water managers to assess the effectiveness of possible measures.

Adverse effects include the diminishing abundance and variety of aquatic species and consequently the vitality of the food web. Furthermore, the re-use of sediments in redevelopment projects (e.g., river restorations, “building with nature”, “room for rivers”) may be restricted. Deltares works on solutions by comparing scenarios and find the best possible options for river and flood plain restoration.

Risk assessment of contaminants

Deltares has an extensive expertise in the development of methods that assess risks of pollutants, using the concept of bioavailability. In Europe, the Water Framework Directive offers the opportunity to use such methods in order to evaluate the risks as they actually occur. We develop measuring tools, models, guidelines and environmental quality standards to assist water managers in their decisions how to improve water systems, both on a regional and an international scale.

Storage of contaminated sediment in confined disposal facilities (depots) is a common management option. The conditions that warrant this as a safe practice lean heavily on the reliability of prognoses of leaching and emission of contaminants to the environment. Deltares experts have many years of experience in dynamic modelling, monitoring and risk assessment. Recently, this knowledge was implemented in a regulatory advice to the Dutch ministry, concerning the safe large-scale storage of contaminated sediments in the environment.

Europe as a (regulatory) platform

The European sediment network SedNet aims at incorporating sediment issues and knowledge into European strategies on water management. The goal is to achieve good environmental status and to develop new tools for sediment management. Experts of Deltares initiated and still play an active role in SedNet. Deltares runs the SedNet secretariat and is steer group member of the UNESCO International Sediment Initiative. Through SedNet and other international initiatives, these Deltares sediment experts help to initiate, create and unlock sediment knowledge and experience at the European scale, and beyond. In this way, they help to synchronize national legislations concerning sediment issues into a more uniform concept.