Expansion of water storage

De Onlanden is a nature reserve that also helps to collect water. When there is heavy rainfall in the Kop van Drenthe region, the water flows to De Onlanden. Climate change has led to more frequent and heavier rainfall. This means that more space is needed to store water.

De Onlanden can now hold 7.5 million cubic meters of water. There'll be extra space for another 5.2 million cubic meters. This means we can temporarily hold more water during extreme weather before it goes to the sea.

Dry Feet 2050

The northern provinces and water boards are collaborating on the 'Dry Feet 2050' project. They are investigating how we can prevent flooding until the year 2050. Additional water storage in De Onlanden is one of the measures. In this way, we ensure that people in Drenthe and Groningen keep their feet dry, even in extreme weather conditions.

De Onlanden can currently hold 7.5 million cubic meters of water. This will be expanded to 12.7 million cubic meters. This will be done within the existing quays. The water level will be temporarily raised during periods of heavy rainfall. This will allow more water to be collected in De Onlanden.

To make this possible:

• Are we raising the quays?
• Are we building two new weirs?
• Are we modifying an existing dam?
• Are we taking nature-based measures?
• Are we taking additional measures such as modifying pumping stations and protecting homes in the area?

During extreme rainfall, we store the water in the water storage facility for a few days. It is then released into the sea in a controlled manner. This prevents flooding in Groningen and the surrounding area.

In May 2025, the General Board of the Noorderzijlvest Water Authority decided to make an additional €15 million available for the implementation of works in De Onlanden. This amount is in addition to the €7 million previously allocated for exploration and plan preparation. We can now start work on improving De Onlanden's capacity to collect rainwater. The water board can also use this money to implement mitigating measures (to prevent negative effects of the additional water storage). Water storage De Onlanden is part of the Dry Feet 2050 project, which aims to prevent flooding in Groningen and Drenthe. 

The money will be used, among other things, to: 

• Weirs installed to better regulate the water 
• Pumps from pumping stations improved 
• Buildings protected 
• Roads, quays, and dikes raised 
• Nature measures implemented as marshland and refuge mounds for animals 

The water storage facility is used flexibly and is intended for extreme rainfall. Approximately once every 25 years, the additional water storage facility will need to be used to its full capacity. Partial use of the additional water storage facility may occur more frequently, approximately once every 10 years. An EU subsidy of more than €1.5 million has also been requested. Because the area is not only a water storage facility but also an important nature reserve, money is also being invested in nature. 

De Onlanden already collects water during heavy rainfall. The water now flows in automatically. For example, in February 2022, a lot of water was collected in the water storage facility after heavy rainfall.
Climate change is causing this to happen more often. That is why extra space is needed. We are now creating this space within the existing quays of the current water storage facility. We are building two new weirs, modifying an existing weir, adjusting the capacity of pumping stations, and raising the quays. This will allow the water storage facility to hold an additional 5.2 cubic meters of water. The extra water storage will not be used automatically but will be controlled. With the help of the weirs, we can determine how much extra water we can temporarily store there.

The extra water storage is only used in extreme weather conditions, such as heavy rainfall in a short period of time. The water then remains in the area for a few days before flowing into the sea.

We expect that it will be necessary to use the maximum capacity of the water storage facility once every 25 years on average. Once every 10 years, a portion will suffice. We will then temporarily store the water in the water storage facility, after which it will slowly be discharged into the sea.

Without this measure, the water level would rise too quickly and flooding could occur.
 

Without additional water storage, flooding may occur, especially in the Zuidelijk Westerkwartier. This is a low-lying area where water cannot easily drain away.

De Onlanden will gain 5.2 million cubic meters of extra space for water. If we cannot accommodate that there, it will have to go somewhere else. In extreme weather conditions, this accommodation is desperately needed to prevent flooding.

Water storage areas have also been created in the Southern Westerkwartier, such as De Drie Polders and the Lettelberter Boezem.