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Houtrib Dike Pilot Project
The dike between the cities of Lelystad and Enkhuizen, the Netherlands
The Houtribdijk is a dike in a lake environment. When a dike becomes inadequate for its intended purpose, the traditional approach to dike reinforcement—building a bigger dike—is usually the first option that comes to mind. In this case, however, creating a sandy foreshore was an alternative solution that was more attractive for several reasons: it was cheaper to install and maintain than a traditional dike upgrade and it is more sustainable and improves nature and leisure facilities in the area. The sandy foreshore was constructed in 2014; in 2015, a section was partially planted with a variety of vegetation. The different conditions will be monitored and evaluated for their effectiveness. This pilot project was implemented as part of EcoShape’s Building with Nature innovation program. The Rijkswaterstaat’s Dutch Flood Protection Program was the project’s client.
Producing Efficiencies
A sandy foreshore to strengthen a dike is already a proven solution on seashores. For lake environments, however, more evidence is needed about the foreshore’s effectiveness and usefulness under specific circumstances. This pilot project was designed to provide answers to questions about the impact of waves on the foreshore and the effect of vegetation growth on the stability of the foreshore. This knowledge can be used to shape future location criteria for this solution. The foreshore test section was monitored for four years, from 2014-2018; monitoring includes water level and wave strength measurements. Two cameras were installed to photograph the site every hour and a topographic survey was conducted several times per year. All the data collected will be analyzed to answer the research questions. This pilot program has already provided important information and insights since its construction, and this knowledge has already been applied to other reinforcement projects.
Using Natural Processes
A sandy foreshore is created by depositing a large quantity of sand in front of a dike and is constructed with a shallow, vegetated slope. This body of sand attenuates the waves and consequently eliminates or reduces the impact of the waves on the dike, thereby eliminating the need to strengthen the dike.
Broadening Benefits
The goal of this pilot project—which was part of the Dutch Flood Protection Program—was to test a sandy foreshore that protected the dike by reducing wave action against the dike. In this location, a sandy foreshore is cheaper to install and maintain than a traditional dike upgrade. This approach is also more sustainable and provides opportunities for enhancing natural habitat and creating new recreational possibilities in the area.
Promoting Collaboration
EcoShape collaborated with several administrative bodies and stakeholders in the area, including the initiator of the project, Rijkswaterstaat. The following organizations also contributed to the success of the project: research institutions, Deltares and Alterra Research Institute at Wageningen University & Research; contractors, Boskalis and Van Oord; and engineering companies, Arcadis, Royal HaskoningDHV, and HKV – Lijn in Water. Deltares and Alterra were in charge of the monitoring program; Arcadis was responsible for the overall program management.
