Working on a future-proof river area

The strength of Room for the River is that we look at the design of our river area at system level and with an eye for the long term. The first Room for the River programme is perhaps Europe's best known Nature-based Solution: by giving space to the rivers, we increased the spatial quality and decreased flood risk in our country all in one go.

The urgency was high after two periods of high water in the 1990s, which led to evacuations. Room for the River cost over two billion euros and (including planning) twenty years to implement. Famous is the construction of the side channel along the Waal near Nijmegen, which created both recreational and nature areas as well as a city island. The Noordwaard is also a success: de-poldering has allowed the Nieuwe Merwede to discharge flood water more effectively, creating a beautiful intertidal area.

New challenges

Once again we are faced with important choices around the design of the river area. That is why the Room for the River 2.0 program was launched this spring, in which measures are being developed to prepare the Dutch rivers for future periods of high and low flow. The programme not only examines the discharge capacity and discharge distribution of rivers, but also the ongoing river bed erosion and how other functions such as nature, shipping and agriculture can be optimally accommodated. The follow-up programme takes the same approach: through a combination of system thinking and multiple objectives, a climate-proof, robust and widely supported natural design of the river region is being worked on.

Choices

Climate change increases the likelihood of extremely high and low discharges in our rivers. How can we properly store and discharge large volumes of water in the future, especially during floods? Every time the KNMI publishes new climate scenarios, we at Deltares calculate the impact on future river discharges. In 2023, our analysis showed that average winter discharges for both the Rhine and the Meuse will increase, while average summer discharges will decrease. This decrease is partly caused by less precipitation, less meltwater from glaciers and snow, and higher evaporation in the Rhine and Meuse river basins.

Room for the River 2.0 studies the impact and effect of these discharge scenarios on river bed erosion, flood risk, fresh water availability, navigability and nature. Previously at Deltares we looked at what climate change means for the position of the river bed, by outlining the impact of various measures and compare them with a reference situation.

Working hypotheses

Deltares has been cooperating in the research on short- and long-term strategy development since the start of the Delta Program Rivers in 2010. Since 2019, this has been done in the Integral River Management program, now renamed Room for the River 2.0. This year we are examining a number of so called working hypotheses, developed in the fall of 2024 at the request of the Ministry of Infrastructure and Water Management. The aim is to assess potential solutions, in preparation for decision-making. The working hypotheses were based on then available knowledge about solutions for river bed erosion and the discharge distribution during high and low flows.

With engineering firm HKV, we are now working on these studies, using the morphological and hydraulic models Delft 3D and D-Hydro developed by Deltares. We are incorporating lessons from previous impact studies to visualize the consequences of different choices. Our findings will contribute to the decisions expected to be made in 2026.

River bed erosion

To protect us against flooding and facilitate inland navigation, we have constructed dykes, locks and dams in the Netherlands and straightened our rivers wherever possible. By eliminating meanders and constructing groynes, the flow velocity in the main channel has increased, resulting in river bed erosion. River bed erosion, as much as two meters in the Waal, leads to lower ground water levels and desiccation in surrounding land. Eventually shipping will also suffer from non-eroding fixed layers and lock sills.

One solution to river bed erosion, in addition to sand replenishment, is to reduce the flow velocity by constructing a multi-channel system. Deltares is investigating for the Rhine tributaries what effects this design would have on the river and surrounding floodplains. With a secondary channel, through which about ten percent of the river water flows, the erosive power of the river can be reduced.

Freshwater resources

Decreasing the river bed erosion is one way to influence the discharge distribution of our rivers. Because the Waal is eroding faster than the other river branches, it starts 'pulling' more and more discharge. However, freshwater availability in the north of the Netherlands must not deteriorate. Even in dry times, sufficient water must continue to flow through the IJssel to fill the IJsselmeer, the 'national rain barrel'. Farmers in the north of the Netherlands obtain water for their fields from the IJsselmeer in dry periods, for example. So determining the correct discharge distribution is still quite complicated.

Feasibility

Possible solutions or strategies that Deltares is investigating for high and low flow are: for low discharge, we want to discharge 285 m3/s into the IJssel River for as long as possible when the Rhine discharge is declining - a return to the discharge distribution that existed in the 1980s.
For high discharge, the national government has determined that we will ‘spare’ the Nederrijn/Lek when discharges exceed 16,000 cubic meters per second at Lobith (the point where the Rhine enters the country). The extra discharge, the 'surplus', must then be divided between the Waal and the IJssel. We are investigating which distributions are feasible and what this means for the required discharge and storage capacity. If, for example, the IJssel receives more than 20 percent of the surplus, what will be the consequences?

DNA of the river

At Deltares, we also include the DNA, or character, of the river when assessing potential measures. After all, every river is unique. For example, side channels are better suited to the Waal than to the meanders along the IJssel.

Cross-border

It is also necessary in Room for the River 2.0 to look across borders, for example at changes in water management in our neighbouring countries. If Germany suffers more frequently from flooding, they may take measures that affect the discharge into the Netherlands. Suppose that large-scale dyke reinforcement in Germany causes more than 18,000 cubic meters per second of river water to enter our country via the Rhine at Lobith, this will require choices to be made regarding dyke reinforcement or river widening in the Netherlands. This in turn affects spatial planning behind our dykes, such as housing construction.

Last year we already evaluated the existing spatial reservations and now we are examining in a broad consortium of various consultancies whether these are indeed necessary and whether reservations should be added. Outside of the Room for the River programme, other Deltares colleagues led by Kymo Slager are looking at smaller transboundary rivers together with our neighbours in the JCAR ATRACE project. Kymo and Judith ter Maat are also studying planned interventions in the Rhine and Meuse river basins that may affect the discharge at Lobith.

Preventing lock ins

The beauty of Room for the River 2.0 is that we are also looking at the very long term, as far away as 2100 and 2200. After all, you want to avoid making decisions now that you will regret later, the so-called 'lock ins'. Deltares has a great deal of knowledge about the river area: hydraulics, morphology, ecology, flood risk, navigability and freshwater availability, and we can apply this to all the aspects mentioned above. This way we contribute to a well-founded decision on the final programme Room for the River 2.0.