Delta Decision for the IJsselmeer Area

It specifically addresses water level management in the IJsselmeer in relation to freshwater supplies and water discharge to the Wadden Sea.  

Water discharge in a context of sea level rise

Starting in 2026, water will be discharged from the IJsselmeer to the Wadden Sea with a combination of gravity discharge and pumping at the Afsluitdijk barrier dam. To maintain the average level of NAP -0.25 m and peaks that occur once every ten years in the future, Rijkswaterstaat is building new sluices and pumps in the Afsluitdijk at Den Oever. They are expected to be completed in 2026. Because of more rapid changes in the climate (according to the KNMI’23 climate scenarios), new pumps or sluices may be needed around 2040 or larger fluctuations in the water level will have to be accepted. The cabinet is keeping the option open of a limited rise in winter levels in line with the sea level after 2050. This policy margin is needed to respond to changing circumstances or insights. Maintaining this margin will prevent the system from being too inflexible and precluding options in the future. 

Water level management

The Water Level Decree for the IJsselmeer Area (2018) states the ideal bandwith for the water level in the IJsselmeer and Markermeer: low enough in the winter to accommodate high water discharges and high levels of precipitation; high enough in the summer to maintain an adequate freshwater buffer. In practice, it is not always possible to maintain the desired levels. Dry periods early in the year or wet periods in the autumn and winter make that difficult. For example, research from the 2020 Freshwater Delta Programme shows that the buffer capacity for dry periods may no longer be adequate to keep the probability of shortages (once every fifty years) at the agreed level. On the basis of the Steam2050 climate scenario, the buffer capacity or influx may need to be increased in the years ahead to meet increasing water demand, or water demand may have to be reduced. The Water Level Decree will be evaluated in 2025.

Fresh water

Rijkswaterstaat is using the opportunities afforded by flexible level management in the IJsselmeer and Markermeer to ensure that stocks of fresh water will be adequate. The goal is to be able to cope with droughts that may occur once every twenty years. The option will be maintained of increasing the bandwidth for the flexible water level in the IJsselmeer and Markermeer to a maximum of 50 centimetres after 2050: from NAP -0.40 m to NAP +0.10 m. For now, it has been decided to keep policy flexible in order not to block the option of making changes in the future. Climate change means that the water level may have to be adjusted earlier for the purposes of the freshwater buffer. If it is decided to go down this road, the increase will be made gradually. 

In the event of a freshwater shortage, Rijkswaterstaat, the water authorities and the provincial authorities make joint decisions about how the available water will be allocated to the IJsselmeer area.