BONSAI and Oeverdijk Hoorn

What will happen?

Boosting FlOod ResilieNce in estuarine System Anticipating shifting clImate zones 

Bonsai comes from the group that worked together at the Hedwige and Prosperpolder. HHNK participates to optimize our monitoring for both water safety (i.e. sand and water) and biodiversity. Here again, other colleagues can follow along with our lessons learned.

We look and learn with like-minded people across national borders. Interesting and fun! We are happy to share the findings with interested colleagues during this project.

The levee is an innovative solution of a soft berm as a foreshore. This provides opportunities for nature and for easy climate-adaptive maintenance. 

The Oeverdijk

The Oeverdijk consists of a profile of sand constructed in front of the old dike. It completely takes over the water safety function. 

The required volume of sand of the safety profile should be present during the plan period (until 2071). 

The Alliance has been given the task of designing a safe dike for the next 50 years. Only regular maintenance is allowed from the administrator. 

For the Oeverdijk, this actually means the desire to achieve a design that is as low maintenance as possible, while minimizing the risk of additional sand replenishment. Therefore, the design includes a wearing course to enable the dynamic behavior of the embankment without directly affecting the total volume of sand in the safety profile. 

Reason for monitoring sand and water

At present, there is no unambiguous method to arrive at a realistic estimate for the volume of sand required in the wearing course. This is because not enough is yet known about the dynamic behavior of a sandy foreshore in a lake situation. In order to be able to make a sand volume estimate, the embankment dike has been model-based. 

For this it is important to monitor the behavior of the embankment within the project period of five years and, if necessary, to adjust the design. We are doing this monitoring within the European Interreg project BONSAI. This means the project has been granted a subsidy from Brussels and the Province of North Holland. Monitoring is crucial to understand the behavior of the dike and to ensure water safety.

Who do we work with?

Bonsai is pulled by Foundation for Applied Water Research (STOWA). We work together with 17 partners within the Netherlands and with partners from Belgium, France and Germany; both from practice and research.

Our practice partners in the field of flood risk management are:

  • Netherlands: Rijkswaterstaat, HZ University of Applied Sciences, Ministry of Defense, Noorderzijlvest Water Board, Radboud University;
  • Belgium: Katholieke Universiteit Leuven, Université Catholique de Louvain, Department of Mobility and Public Works, De Vlaamse Waterweg, Institute for Nature and Forest Research;
  • Germany: Universität Siegen;
  • France: Université de Lille, CEREMA, ISL Ingénierie, ESTP - Grande école d'ingénieurs de la Construction.

When will the project take place and how long will it take?

The project officially started on Jan. 1, 2025, and will last until June 30, 2029.

Results and goals

The main results are:

  1. a transnational strategy for national authorities and three action plans for regional and local authorities;
  2. five solutions for increasing robustness and resilience and improving disaster management;
  3. multiple training programs and courses on flood disaster management and resilience and one joint transnational flood academy.

Through a holistic approach, BONSAI strives for resilience of the flood defence system (short/long term) and improved disaster management. Different NWE countries address these challenges from their own perspectives. Because estuarine systems and climate change cross borders, transnational cooperation among NWE regions (and beyond) is essential. The BONSAI approach is unique:

  1. It bridges the three layers of multilayer water safety: prevention, disaster management and land use planning.
  2. It simulates shifting climate zones by applying insights from southern regions to northern regions.
  3. It strengthens cooperation between countries to learn from each other, with the North learning from the South and the South learning from the North.

Budget

The total budget of HHNK's project is approximately € 580,605.68, 60% of which co-financing comes from the European Interreg North West Europe Programme 2021-2027.

The total project budget is €10,699,561.10, of which €6,419,736.62 comes from the European Regional Development Fund (ERDF). https://bonsai.nweurope.eu/ 

The Province of North Holland is co-financing the project and has provided €87,091.