IJsselmeerdijk opts for robust and sustainable foreshore

The challenge: strong winds, high waves and extreme water levels

The IJsselmeerdijk, with a length of almost 18 kilometres, it is the most challenging dike in the Flevopolder. This dike is exposed to severe conditions, such as strong winds, high waves and extreme water levels, which results in a considerable design challenge. The design loads are exceptionally high, with design waves reaching heights of over 3 metres and the design water level almost 2.5 metres above the average level. The water board also has ambitious goals, such as increasing biodiversity and integrating innovation and sustainability into the reinforcement project. The integration of the dike reinforcement is complex due to the immediate vicinity of three marinas, a transhipment terminal and an important power station. In addition, the IJsselmeer is a protected Natura 2000 area, the A6 motorway borders the dike and a new wind farm has been constructed 500 metres from the dike. These factors make the integration of the dike reinforcement a challenging task. 

The solution: a sustainable foreshore

In an extensive plan study, various solutions were investigated and developed, with local stakeholders closely involved from the outset. Both the water board and the stakeholders emphasised the desire for sustainable, biodiverse and future-proof dike reinforcement. 

Using a parametric 3D model, various alternatives were developed to obtain a clear picture of the integration, quantities and costs. An innovative sustainability dashboard was developed to weigh up these alternatives, allowing aspects such as CO2 emissions, biodiversity, reuse and emissions to be properly considered. This dashboard formed the basis for a broad assessment framework that was completed and elaborated in collaboration with stakeholders.

Despite the relatively deep location of the IJsselmeer, reducing wave energy proved to be a highly effective measure. The preferred option for a large part of the dike section is therefore a sandy adaptive foreshore instead of a traditional 2-metre dike elevation. The foreshore has been designed in such a way that the current dike revetment and dike height remain adequate, while enormous gains in biodiversity are achieved. The functioning of the foreshore has been extensively tested with both model studies and physical wave flume tests. This has led to major optimisations in the design, including a reduction in environmental impact and significant cost reductions.

The result: a boost for nature development 

A widely supported preferred option has been embraced by both the authorities and the wider community. An adaptive foreshore will be constructed over a large area, an innovative solution that was not initially obvious in this area. However, this approach proved to be no more expensive than traditional dike reinforcement, while offering enormous added value for the ecology and being much more adaptable for the future. Here, nature development and dike reinforcement go hand in hand.  

The project was completed to the great satisfaction of the water authority Zuiderzeeland, with specific appreciation for the targeted sustainability approach. We will now work with the water authority and the contractor to realise this innovative project.