A foreland with vegetation reduces the force of waves hitting the dike, and therefore the load on the dike. As a result, the dike itself does not need to be strengthened. That saves costs, because a sandy foreland or forebank is cheaper to build and maintain than the traditional approach to strengthening dikes with rock.
Furthermore, natural solutions are more sustainable and they enhance the natural values and recreational options in the area.
A trial section of 500 meters was built near the Houtrib Dike for the purposes of the pilot study. The trial section consists of approximately 85,000 m³ of sand and it varies in width and height. Different types of vegetation will be planted on one part of the section. That will make it possible to study different situations at the same time to assess the impact on flood protection.
The knowledge acquired during the course of the study can be used to apply the concept at different locations in the future. Ellis Penning, a project leader with Deltares: “Deltares will be evaluating the monitoring data. On that basis, a model will be developed for the broad application of the knowledge. From that point on, sandy forelands can be designed in safe, stable and cost-efficient ways for other locations. There is considerable interest in natural dike upgrades at the national and international levels. The need for flood protection is increasing, but people want natural and sustainable solutions.”
The trial section near the Houtrib Dike will be monitored for a period of four years. The provisional answer will be drafted in 2016 to the question of how to design a safe, stable and cost-efficient forebank of sand. The definitive and complete results of the pilot study will be published in 2018.
Rijkswaterstaat ordered this pilot study as part of the Second Flood Protection Programme (HWBP-2) and one of the innovative initiatives in that programme. The HWBP-2 is a collaborative programme bringing together the national government and the water management agencies with the aim of upgrading rejected dikes at 88 locations throughout the country.
The pilot study is being conducted by Ecoshape, a consortium of government authorities, hydraulic engineering companies and research institutions (including Deltares) with the aim of establishing new types of hydraulic engineering.
The dredging companies Boskalis and Van Oord are also involved in the Houtrib Dike pilot study alongside Deltares. They are responsible for building the trial section. The engineering firm Arcadis is the overall project leader. RoyalHaskoningDHV, HKV Line in Water and Alterra Wageningen University are also in the consortium.