Water and soil quality

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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.