Restoring waterways: a challenge for biodiversity, natural heritage and flood control.

To assist its clients with their watercourse-related projects and actively contribute to environmental and regulatory objectives, LSC360 oversees restoration projects aimed at restoring the original hydromorphology and water quality of watercourses. These initiatives are supervised by the Water Management Authority.

What is the regulatory context with regard to water in Luxembourg?

Davy Thiringer: There is a European Water Directive 2000/60/EC transposed into Luxembourg law: the amended law of 19 December 2008 on water, which requires Member States to achieve good ecological status for watercourses on their territory. In Luxembourg, the Water Management Authority (AGE), under the supervision of the Minister for the Environment, Climate and Biodiversity, is responsible for implementing measures to meet these objectives.

What is the current state of watercourses in Luxembourg?

DT: None of Luxembourg’s more than 100 watercourses are currently in good ecological condition according to the latest management plan for the Luxembourg parts of the Rhine and Meuse river basin district (2021-2027).

What is the reason for this?

DT: The ecological status of a watercourse depends on several factors:

• The hydromorphology of the watercourse, i.e. its physical characteristics, the shape of its bed and the way the water flows.
• The quality of the water and the organisms that live in it,
• And the chemical quality.

The WFD uses concrete measurements and defined thresholds to determine whether a watercourse is in poor, mediocre, average, good or very good ecological status. The aim is to make steady progress towards achieving at least good ecological status. At present, at least one of these factors is not being met.

Of these three causes, which ones do you work on?

DT: We intervene on both the physical and qualitative aspects, because one cannot exist without the other: if the hydromorphology of a watercourse is not correct, its biology cannot be either. For example, fish need a habitat and a certain water quality to live and reproduce. They will not settle in a place if the habitat is degraded (the physical aspect), even if the water quality is good, and vice versa.

What issues can river renaturation help to address?

Mélina Dubourg: As part of renaturation projects as a whole, we work on all aspects of the watercourse. But there are also projects whose primary goal is to ensure the protection of property and people in the event of flooding. We must not forget that watercourses have been modified throughout history for specific uses (industrial, for example). The repercussions today are the episodes of heavy rainfall that we are experiencing more and more often, causing flooding and therefore potentially significant damage to local residents.

In Luxembourg, the constant increase in sealed surfaces is creating new challenges in terms of both rainwater management and the ecological status of watercourses. That is why it is preferable to think on a global scale in order to be able to respond to a range of issues.

Where do we start to restore the natural environment of a watercourse?

MD: When it comes to hydromorphology, the reasoning is always the same, regardless of the issue we are focusing on. First, we need to establish the ‘identity card’ of the watercourse in order to learn about its past, understand its present and decide on its future state.

For its past situation, the AGE can provide us with historical data (maps or measurements, for example), which allow us to verify whether the watercourse has always been located in its current place and to establish a diagnosis of its physical measurements (width, water height, etc.). Once the diagnosis has been established, we can assign it a typology, i.e. place it in a family of watercourses with common characteristics. Only after this stage can proposals for measures to be implemented be considered.

DT: The same applies to ecosystems: a watercourse is not renaturalised according to a predefined model, but on the basis of an initial diagnosis that consists of determining which species originally lived in that watercourse, what can be done to enable them to settle there again, and how to ensure ecological continuity, i.e. removing dams so that all species, sediments and materials that pass through this watercourse can circulate freely.

What is the aim of your recommendations?

DT: They aim to restore the watercourse to its original functionality. A watercourse has a storage function in the event of flooding, but also during drought. When it is straight, channelled and concreted, it is forced to remain in its channel and cannot overflow its banks in the event of rain. By reshaping it, recreating sinuosities to diversify the flow velocities and banks so that it can spread out over the surrounding plains, it will be able to overflow freely into non-urbanised areas, limiting the risk of flooding in urbanised areas.

A watercourse also plays a role in water purification. By revegetating this watercourse, reintroducing both plant and animal species, the river will regain its natural self-purification capacity.

Finally, a watercourse is a reservoir of biodiversity, a place where animals develop from the larval stage to emergence, and where a whole range of flora and fauna function in a dynamic balance.

What kind of measures do you recommend, for example?

MD: There are several areas of intervention on the watercourse: the riverbed, the banks and the alluvial plain. Measures can be implemented in a specific area or across all areas.

We can work on flow diversity by placing pieces of dead wood in the watercourse to create ecological niches.

To stabilise banks subject to erosion, natural measures such as the creation of a shrub and tree layer can be implemented. This will also provide shade and encourage the spread of species that prefer cool temperatures to sunny areas.

What constraints do you encounter in your renaturation projects?

MD: Land ownership remains the primary constraint in this type of project, as they require the use of large areas of usable land, for example, if we imagine re-meandering a straight watercourse. There is therefore a whole process to be carried out with the support of the AGE and the owners of the land concerned, to ensure that they agree to cede part of their land.

DT: It is true that treating water for reinjection into a natural environment with a certain quality threshold can generate additional costs, but our role is also to harmonise customer needs with compliance with regulatory procedures.

There is also a need to raise awareness among watercourse users.

Human activities such as industrial discharges and sewage treatment plants introduce nutrients into the water that promote the proliferation of green algae and the warming of the water, which can lead to the closure of bathing areas.  It is therefore important to raise awareness that every action can have a positive or negative impact on the quality and functionality of a watercourse.

Who do you work with?

DT: A wide variety of public and private stakeholders use LSC360’s services. We are currently developing expertise in assessing the specific environmental impacts on waterways.  For example, we are working with the AGE and wastewater treatment unions to improve the impact of treatment plants (there are around a hundred in Luxembourg) and rainwater retention basins, and to ensure that the water entering watercourses is acceptable to the natural environment, i.e. that it is not saturated with certain elements and does not degrade water quality.

MD: We are also working on measures to improve the hydromorphological quality of waterways (diversification of habitats, protection of riverbanks, etc.) while addressing the issue of flooding. As a result, many local authorities and private actors are approaching us about these sometimes sensitive issues.

How does collaboration between the different departments within LSC360 work?

DT: LSC360 brings together a range of complementary expertise that enables us to guide clients through all phases of their projects: diagnosis, design, authorisation, implementation and evaluation. Take the construction of a bridge over a watercourse, for example. This project will inevitably have an impact on the aquatic environment. Our department will therefore carry out an on-site diagnosis to determine whether there are any protected species or specific hydrological constraints, before other LSC360 departments design the bridge and take charge of the technical monitoring of the works. We also have a section that is able to monitor the environmental impact of the works and verify that the recommendations made for the protection of aquatic environments are being followed. Once the project is finalised, we can carry out a second control assessment to compare the data acquired before and after the works and highlight the real impact of our intervention. The advantage is that we can consult with each other to respond to all the issues that arise and really focus on the health of the watercourse.

Article published in Neomag