Adaptive dyke reinforcement: Den Oever-Den Helder

Some sections of dyke between Den Oever and Den Helder do not meet current safety requirements. Witteveen+Bos and Hoogheemraadschap Hollands Noorderkwartier (HHNK), the water authority for the northern part of North Holland, are working on reinforcing these dykes with a solution that takes a unique approach. In total, around thirteen kilometres of dyke will be reinforced. An approved project decision is expected in 2023.

1.2 million North Holland residents

The dykes between Den Oever and Den Helder protect 1.2 million residents of North Holland against high water from the Wadden Sea. These dykes – the Wieringer Sea Wall, the Amsteldiep Dyke and the Balgzand Dyke – do not meet current safety requirements along their entire lengths. There is currently no danger, but the dykes need to be reinforced so that, in the future, residents in the area can continue to live, work and enjoy their free time safely. HHNK and Witteveen+Bos are carrying out the works as part of the national programme for protection against high water (HWBP).

Adaptive reinforcement

Not all sections of dyke are equally in need of reinforcement. This fact led to the choice for an adaptive approach, which means HHNK and Witteveen+Bos will determine the ideal moment for strengthening each section of dyke – without, of course, losing sight of water safety. In concrete terms, it means that the project will progress along two parallel tracks. The sections included in the first track – those requiring more urgent attention – will eventually form part of a project decision. Monitoring of the sections in the second (adaptive) track will help determine when and if reinforcement is needed. The composition of these tracks is not fixed: sections of dyke can change tracks during the process.

This staggered, adaptive approach is unique in dyke reinforcement and offers a flexible alternative to what is normally a linear process. This has several advantages, such as making use of the remaining lifespan of parts of the dyke. Also, by reinforcing the dyke in sections rather than all at once, the environmental effects are fewer; and, all the while, important information can be gathered about the natural build-up of sand and how this could play a role as an organic breakwater. An adaptive approach also offers the opportunity to take advantage of initiatives in the surrounding area or of similar projects that at the same time – or in the near future – will be carried out in the region. This is in line with the ideology behind the new Environment and Planning Act.

In a project like this one, with two parallel tracks, it is crucial that a structured design and selection process exists which ensures optimal exchange of information, adaptivity, and a clear notion of when and how to switch between tracks without compromising quality and, as a result, water safety. For HHNK, Witteveen+Bos is supplying the adaptive reinforcement process approach, including a reusable assessment framework to help navigate within the two-track approach. A smart monitoring tool is also part of the package. This tool provides insights into the current safety situation for each section of dyke.

Environment and Planning Act

The adaptive approach is not the only unique aspect of this project. Because the (design) plan products will be carried out after the Environment and Planning Act has come into effect on (according to expectations) 1 June 2022, HHNK has chosen to carry out preparations for the project in accordance with the Act.

The Environment and Planning Act brings together legislation and regulations on space, housing, infrastructure, environment, nature and water. In doing so, the Act forms the basis for a coherent approach to the physical living environment, while offering room for local, tailored approaches and enabling better and faster decision-making. The Environment and Planning Act puts the users first and promotes participation – for example, by involving residents and entrepreneurs as much as possible in the development of their living environment.