Dike reinforcement Den Oever-Den Helder
The dikes between Den Oever and Den Helder protect 1.2 million North Hollanders from high water from the Wadden Sea. It concerns the Wieringer Zeewering, the Amsteldiepdijk and the Balgzanddijk. These dikes must be reinforced because they do not meet the latest safety requirements in all places.
For now, it's not unsafe. But to ensure that everyone can continue to live, work and recreate safely here and in the hinterland in the future, we are looking at which solutions are best suited. We like to do this in consultation with the environment.
Would you like to know what is involved in a dyke reinforcement project? You can find out in the book 'DIJKEN voor beginners'.
Latest project status
The project is evolving rapidly. Since the summer of 2023, important steps have been taken, but also new insights have been gained that affect the design and planning. The goal remains unchanged: to ensure a safe and strong dike so that living, working and recreation in the hinterland remains possible in the future.
New insights, new approach
By June 2023, a complete draft was on the table, along with a draft version of the Water Act Project Plan and Environmental Impact Assessment (EIA). Shortly thereafter, however, new technical insights and developments came to light. These made it clear that some assumptions had to be adjusted.
To ensure the long-term safety of the dike, the water safety task was reassessed. This led to a revision of the design and, more importantly, to the conclusion that additional kilometers of dike must be reinforced.
Water safety tasks
| Failure mechanism | Description of failure mechanism | Balgzand dyke | Amsteldiepdijk | Wieringer Seawall |
|---|---|---|---|---|
| Inward stability (STBI). | The dike is not stable enough to resist high water. As a result, parts of the dike may shear on the land side, causing the dike to collapse. | 3.65 km | ||
| Asphalt lining water overprinting (ASP). | During high water, the water table inside the dike rises. When the water level outside the dike body drops rapidly, the water level inside the dike can cause a large pressure from the inside of the dike against the underside of the revetment. If the asphalt revetment cannot provide sufficient counter pressure, the dike collapses. | 1.60 km | 2.24 km | |
| Zetsteen lining (ZST). | Waves and currents can damage the different layers of bedrock. When the carpet pad erodes, the dike can collapse. | 3.25 km | ||
| Grass cladding (GEBU). | The grass revetment on the outer embankment may erode due to load from wave impacts or wave run-up. | 0.5 km | ||
| Asphalt cladding corrugations (AKG). | Repeated wave impacts on the asphalt revetment can cause cracks in the asphalt and cause the dike to fail. | 1.6 km |
Dike strengthening measures explained by dike
Balgzand dyke
Inside
To improve the stability of the dike, a longitudinal construction is being placed on the inner side (Balgzand Canal side) over a length of 3.65km. This wall goes 12 to 30 meters deep into the ground and contains regular openings to allow groundwater to flow properly.
Exterior
The lower edge of the existing asphalt overlay will be replaced with set stone. This new covering will be 1.5 to 2.5 meters higher. Under the settstone will be layers of crushed stone, geotextile and a thick clay layer, which together provide better protection against wave action and water pressure.
Amsteldiepdijk
On the Amsteldiepdijk and a section of the Balgzanddijk, the outer dike revetment will be reinforced over a length of 2.24 kilometers. As with the Balgzand dike, the lower edge of the asphalt will be removed and replaced with bedrock.
Wieringer Seawall
On the Wieringer Seawall, the dike reinforcement design consists of replacing the outer dike revetment in three forms: replacing zetestone revetment (section 3), applying open stone asphalt (section 4), replacing asphalt revetment (section 5).
Over a length of 3.25 km, the current bedrock will be replaced with new bedrock. The current settlement consists of basalton columns with a column height of 35 cm. The basalton pillars will be replaced by the same height (Basalton STS+). An ecotop layer of lava rock will be applied to the new headstone. This creates a rough surface that provides better adhesion opportunities for flora and fauna. The appearance of the dike will remain the same as it is today.
In four sections totaling about 500 meters, the current grass revetment will be replaced with open stone asphalt (OSA). This revetment will be laid concealed: the sod and upper soil layer will be removed. Below this will be a layer of geotextile containing the open stone asphalt (OSA), and on top of the OSA will be a living layer 30 cm thick, in which grass and herbs can grow.
The new grass layer will be sown with an herb-rich mixture appropriate to the management of dikes by HHNK. After the work, the dike will continue to look green and natural, similar to the current situation.
In two sections totaling 1.6 kilometers, the existing asphalt lining of the dike will be partially replaced. The top layer (wearing course) will be removed and replaced with a new layer of hydraulic asphalt concrete (WAB), which will be applied to the existing foundation. At the transitions from asphalt to grass on the crest of the dike, grass concrete tiles will be placed. These tiles have openings through which grass can grow. This provides extra strength and a natural transition to the grass revetment.
Where are we now?
The schedule for the coming period is as follows:
- Until the end of September: Finalize design, prepare draft Project Decision and permit applications
- Early October 2025: Publication of the draft Project Decision (including the EIA and nature tests) and permit applications
- Late October - early December 2025: Draft Project Decision (including the EIA and nature tests) and permits are available for inspection
- Summer 2026: Project decision and permits are final
During the inspection period, you can view the draft and respond to it. The submitted views will be carefully answered and where necessary processed in the final decision. After that there is still the possibility to appeal to the Council of State.
Outlook
After the public consultation period, we will continue preparing for implementation. We expect the realization phase to start in 2027. The actual implementation of the dike reinforcement will take about three years and is scheduled to start in 2028.
Notification participation
In this dike reinforcement project in the Noordkop, we are working according to the guidelines of the Omgevingswet. Therefore, at the start of the planning phase (early May 2021) we published the participation notification. In it we indicated how and when we would inform the surrounding area and ask them to participate, with the ultimate goal of arriving together at an established Project Decision.
Preferred Alternative
The Executive Board adopted the preferred alternative (VKA) for strengthening this dike section on June 23, 2020. The most suitable solution per dike section (Wieringer Zeewering, Balgzanddijk, Amsteldiepdijk) is now known and can now be worked out in more detail.
What's going on?
On the outer side of all three dike sections, the revetment, consisting of zetestone, asphalt and grass, does not comply in large parts. And along the Balgzand Canal, the dike is not stable enough on the inside in certain sections.
What does the VKA look like?
During the reconnaissance phase, we looked at a wide range of possible solutions for all three levees together with the environment. The VKA consists of:
- On different parts of the three dike sections we are reinforcing the revetment on the outside. It concerns asphalt, grass and stony revetment.
- Of the Balgzand dike, we are reinforcing the inner toe of the dike by a paving in certain sections.
Between 2017 and 2019, we organized several dike evenings (meetings) for stakeholders, local residents and other interested parties. During these meetings, among other things, we showed possible solutions for the dike reinforcement. We also provided feedback on questions and wishes we collected from the surrounding area. In the fall of 2019, we presented the preliminary choice for the preferred alternative. The Executive Board adopted the preferred alternative on June 23, 2020. The preferred alternative was designed together with the environment.
Working on a project decision
At the end of the plan development phase, the board lays down the design for the dike reinforcement in a project decision. This decision must be approved by the Provincial Executive of the province of North Holland.
Why a notification?
The next project phase, the plan execution phase, started in 2021 and ends with a project plan/project decision. This phase involves working with the surrounding area to develop and design the preferred alternative (VKA). This phase determines what the dike will look like after the reinforcement. This phase will also include determining which co-option opportunities can be implemented. The purpose of the announcement is to inform you about the participation during the planning phase. View the full announcement.
More information about the dyke sections
Wieringer Seawall
The Wieringer Zeewering is the section of dike that runs from Den Oever to the Amstelmeer and is over 10 kilometers long. The dike is loaded directly from the Wadden Sea. The hinterland is the former island of Wieringen and is mainly rural in nature. The foreland is the Wadden Sea, an area of high natural value. Along the dike are places like Den Oever and Hippolytushoef.
Amsteldiepdijk and Balgzanddijk
The Amsteldiepdijk connects to the Wieringer Zeewering and runs to the Van Ewijcksluis. The Balgzand dyke is an extension of this and continues up to the sluice at Oostoever.
The dikes are enclosed by water on both sides; on the outside is the Wadden Sea. The Amsteldiepdijk was constructed in 1924 as a pilot for the Afsluitdijk, creating the Amstelmeer on the inside. On the inside of the Balgzand dike is the Balgzand Canal, an important drainage canal for the Water Board. In some places there is a foreland barrier, a dike in front of the dike into the sea. Together, the Amsteldiepdijk and the Balgzanddijk are about 10 kilometers long.
Contact
Do you live near the Den Oever-Den Helder dike reinforcement project or are you otherwise involved in this area? This news page will keep you informed of current developments surrounding the dike reinforcement.
For more information about this project, contact environmental manager Britte Mussche at 072 - 582 8282, dijkversterkingdodh@hhnk.nl or through the contact form.
Opinions, reports and notes
- Read aloud HHNK A0-posters Visualization adjustments Den Oever-Den Helder with ReadSpeaker docReader
- Read aloud Participation plan 2021 with ReadSpeaker docReader
- Read aloud Notification further detailing participation 2021 with ReadSpeaker docReader
- Read aloud Infographic adaptive reinforcement with ReadSpeaker docReader
- Read aloud Notification of preferred alternative adopted with ReadSpeaker docReader
- Read aloud EIA committee opinion on scope and detail level 2018 with ReadSpeaker docReader
- Read aloud Press release committee on EIA interim test 2019 with ReadSpeaker docReader
- Read aloud Input note scope and detail level EIA 2018 with ReadSpeaker docReader
- Read aloud Notitie scope and detail level EIA 2018 with ReadSpeaker docReader