De Onlanden gets new weirs to prevent flooding

Len van Rosmalen, Director of Water Systems and Water Safety at the Noorderzijlvest Water Authority:
“We have gone through an intensive process together with our regional partners to reach this point. Thanks to the cooperation with other authorities, consultants, and nature organizations, we are now able to take this step. De Onlanden is a unique area where nature and water management go hand in hand. It is very important that both functions remain in balance. By balancing lake the capacity of the balancing lake from 7.5 to 12.7 million cubic meters of water, we are building a future in which we keep our feet dry and give nature space.”

Smart water management

Two new weirs will be built on Hooiweg/Matsloot: the Vischlust weir (north) and the Rowolder weir (south). Under normal circumstances, these weirs are weirs , allowing water to flow freely. During heavy rainfall, they are raised to temporarily retain water. The Doolhof weir will be fitted with a new valve and raised, along with the quays on either side. 

Adrie Masteling, operations manager at Oosterhuis: "We have started with the northern weir. We will then continue with the southern weir and the Doolhofstuw. The work on the weirs completed in the spring of 2026. We are delighted with this contract for Noorderzijlvest. We have also previously worked on De Onlanden. We feel a close connection, because in 2012, when the balancing lake was balancing lake ready, we had a lot of flooding here. We worked through the night to lower a quay so that the balancing lake could fill balancing lake . So we know why we are doing this."

 

Follow-up measures and attention to nature

At the beginning of 2026, the quays in the De Onlanden water storage area will be raised. At the same time, we will take additional measures such as protecting homes. Nature conservation measures will also be implemented. For example, refuge islands will be created for animals during high water levels and the area will be enriched with marshland, which will benefit species such as the bittern.

Martijn Bakker, team leader at Staatsbosbeheer, explains: “These interventions make nature more resilient and better able to withstand extreme weather conditions. The partners in the collaboration are now getting the most out of it for both water and nature. That is important, because we are working together on a larger, integrated task: water availability, water quality, and water safety. In De Onlanden, water and nature must form a single robust system."

The Noorderzijlvest Water Authority and nature organizations have agreed that nature will also be taken into account as much as possible during construction. Earthworks will take place outside the breeding season. In addition, fences will be installed to prevent otters and other animals from crossing the Hooiweg during the work.
 

Larger balancing lake climate change

Due to climate change, we are experiencing more extreme precipitation and need more space for balancing lake. That is why Noorderzijlvest is increasing the capacity of balancing lake Onlanden balancing lake from 7.5 to 12.7 million cubic meters. This will be done within the existing quays. Part of the expansion will be completed by early 2026. The entire project will be completed in 2027. The extra space is expected to be needed in full once every 25 years and in part once every 10 years. The collected water will then be discharged in a controlled manner via Lauwersmeer lake to the sea.

Part of Dry Feet 2050

The expansion of De Onlanden is part of the Dry Feet 2050 program, in which the northern provinces and water boards are working together on solutions for flooding. Within this program, pumping stations are being pumping stations , new water storage areas are being created, and quays and dykes and reinforced.
 

Staying informed about the work

During the project preparation phase, Noorderzijlvest held extensive discussions with residents of the area and with local partners. The environmental manager will also be available to answer questions during the construction phase. Anyone interested can stay up to date on the progress of the work via the website and newsletter Waterberging De Onlanden.

Activities | Noorderzijlvest Water Authority

Expansion of De Onlanden balancing lake | Noorderzijlvest Water Authority