2020

RIWA-Maas: A Plea for Transparency in Water Use

Attention is followed by action. What needs to happen, and why? Following a journey through the river basin, Maarten van der Ploeg outlines a concrete perspective for future action:

"Water managers both at home and abroad are doing their best to make water management future-proof. However, simply hoarding freshwater is not enough to continue guaranteeing the availability of Meuse water. To ensure there is sufficient water, a broad societal debate is required. It comes down to the question: is current water management even sustainable at all?"

Transparency in Use

According to Van der Ploeg, we must also dare to look at water consumption. "After all, this factor largely determines how much water ultimately keeps flowing through the Meuse. This means we primarily need to map out water-intensive activities very precisely. How much Meuse water does industry use, and how much goes to agriculture? We also need to think about forms of 'hidden water use.' Intensive livestock farming, for instance, requires large quantities of maize, and therefore Meuse water."

In other words: transparency in use is crucial. This is why drinking water companies publish how much water they abstract from the Meuse each year. For other users, such as agriculture and industry, this overview is largely non-existent. Yet, this information is essential for dialogue: do current water-intensive activities still fit the locations where they are currently taking place? To assess whether current water management is future-proof, we will have to re-evaluate it thoroughly.

Water Balance Makes the Future Visualizable

How do we achieve this? "The international water balance (RIBASIM) that we are developing from within the drinking water sector, together with Rijkswaterstaat and Deltares, can help facilitate this dialogue. Using the model, different scenarios can be made concretely visualizable.

Imagine there is actually 40 percent less Meuse water available, on top of the low river discharges we already experienced during recent dry years: when and at which locations will water shortages then arise? And what can be done to replenish the deficit?

This also involves the awareness that low river discharges impact water quality. It is precisely during water scarcity that water quality must be up to standard. After all, there is less dilution of contaminants during such periods, which ultimately leaves even less water available for use.

Finally, because 90 to 95 percent of Dutch Meuse water originates abroad, you have to look across the border to know whether enough water will continue to flow into the Netherlands in the future. As far as RIWA-Maas is concerned, we should therefore create the water balance for the Meuse basin together with partners from the respective countries and regions. The International Meuse Commission, as a platform for solving transboundary issues, will therefore only become more important."

Meuse Water Balance

Question: How exactly is the international Meuse river basin structured?

In 2020, drinking water companies primarily focused on 'water availability.' To get a grip on this, work was carried out in 2020 on an international water balance for the Meuse (RIBASIM), and research was launched into the contribution of tributaries to the discharge of the Meuse.

In the article 'A Journey Through the Meuse Basin,' these two studies come together, but within an international context. The article addresses how the Meuse water system functions precisely. This knowledge is important for gaining insight into water availability across the international basin.

RIBASIM as a Calculation Model for an International Water Balance

To gain insight into current and future water availability, Deltares is developing a model for a Meuse water balance. The project team consists of Rijkswaterstaat South-Netherlands, WML, Dunea, Evides, and RIWA-Maas.

Knowledge institute Deltares already possessed a potentially suitable base model for this purpose: RIBASIM. Until now, this model has mainly been used internationally in regions facing severe water shortages. Applying RIBASIM in Europe and the Meuse basin is a new approach.

RIBASIM is a calculation model consisting of two components: water availability (precipitation, runoff, evaporation) is weighed against water use (groundwater and surface water). In the schematized Meuse basin, data converges at nine nodes to be calculated.

Furthermore, RIBASIM allows for extrapolations into the future, for instance, to map the impact of population growth or climate change on water availability, or the effects of changing land use.

An Instrument for Transboundary Dialogue

RIBASIM will be deployed to stimulate mutual dialogue and cooperation within the Meuse basin. This is done in two steps. On one hand, the substantive and factual baseline assumptions of RIBASIM are aligned with those of other water balance models, such as the calculation model from KU Leuven. Alignment is also sought with other scientific water models, such as Pegase/Chimere.

On the other hand, RIBASIM is used to simulate future water availability. RIWA-Maas aims to achieve this by working with experts from different parts of the Meuse basin to simulate local and regional climate forecasts within the model, allowing them to see the outcomes collectively. To this end, consultations are ongoing with the International Meuse Commission and the affiliated international partners of the Mosan Initiative for Climate Change Action (MICCA).

Contribution of Tributaries

To gain insight into the contribution of tributaries to the water discharge of the Meuse, Deltares conducted a study in 2020. This study examined the 22 tributaries of the Meuse and their water discharge over the past 28 years. Core questions included: Can a pattern be recognized in the water discharge? Do the rivers have a 'memory'? In what way do three consecutive dry summers affect water availability?

What prompted this research? Maarten van der Ploeg explains: "Two years ago, we observed that a relatively small tributary like the Rur made a significant contribution to water availability and the drinking water supply for drinking water companies Dunea and Evides in South Holland. This clearly demonstrated our international dependence on an seemingly minor tributary.

It also became clear that during low water levels, France, Germany, Belgium, and the Netherlands act on an individual basis, and that water availability remains primarily a national issue. An international framework was lacking. This insight prompted us in 2020 to look more broadly at the influence of tributaries in the Meuse basin. We commissioned Deltares to conduct this study. This action anticipates an initiative by the International Meuse Commission, which is currently working on an action plan for low water levels."

The Deltares study will be published following the release of the annual Meuse water quality report.

Insights into Tributaries

Based on literature and the available dataset, researchers divide the Meuse basin into four sections:

• Upper Reach: The upper area of the Meuse contains the basin upstream of Stenay, the Chiers, and the Bar. Due to the buffering capacity of the underground terrain, these tributaries make a relatively large contribution to the discharge of the Meuse during low water periods. During low water, their contribution is approximately 25%, which corresponds to their surface area of around 6,500 km² (about 26% of the gauged catchment area).

• Ardennes: The Ardennes region contains the tributaries Semois, Viroin, Houille, Hermeton, Lesse, Sambre, Ourthe, Amblève, and Vesdre. This area covers a surface of approximately 10,000 km² (40%). The low permeability of the subsurface in this catchment area, combined with steep gradients, contributes to rapid runoff of precipitation. Consequently, this area's contribution to high-water peaks is significant, while its contribution to low discharges is relatively minor. Nevertheless, summer discharge from this region is not negligible. Even in the summer of 2020—the fourth consecutive dry summer—this area's contribution to the Meuse discharge was still 32%. The largest contribution here comes from the Sambre, which features a large upstream reservoir that is utilized partly to support shipping during low water periods.

• Middle Reach: The middle course contains the tributaries Molignée, Bocq, Hoyoux, Mehaigne, Jeker, Geul, and Geleenbeek. These rivers are situated in a flat area with permeable soil. The region covers an area of about 1,900 km² (8%). This area's contribution to the total discharge of the Meuse is relatively low (9 to 13%), yet quite constant. As a result, these tributaries contribute relatively more during low-water periods than during high-water periods.

• Lower Reach: This area covers about 26% of the gauged Meuse catchment basin. The main tributaries are the Rur, Swalm, Niers, and Dieze. Just like in the "Middle Reach," the Rur, Swalm, and Niers contribute relatively more to the Meuse discharge during low water (collectively around 20%) than during high water (around 15%). This can be partly explained by upstream reservoirs, soil composition, and topography.

The discharge of the Dieze responds more sharply to dry spells than the other tributaries in this area. This discharge depends partly on the outflow from the Zuid-Willemsvaart canal and wastewater treatment plants (WWTPs).