Initation
On the basis of an interim safety test in 2003 it appeared that the safety against flooding could not be guaranteed between Petten and Camperduin.
Both the Hondsbossche and Pettemer sea dike and parts of the sandy dunes failed the test. The wave overtopping criteria were not met and also the stability of the rear slope grass layer was questionable.In 2004, the coast was designated by Rijkswaterstaat (Directorate-General of Public Works and Water Management in the Netherlands) as one of the Weak Links along the coastline. Which is a qualification to tackle the problem with priority. However, it still took until 2011 before the upgrading of the dike was addressed as an integral project within the framework of the HWBP (the High Water Protection Program). In the meantime, a number of temporary measures were taken because the coastal defense of the area was even weaker than expected in 2003. These temporary measures included a sheet wall and increased slope roughness.
Selecting alternatives
There were several alternatives (see sketches below) to improve the dyke safety in this area: crest raising, foreshore nourishment, making the dyke overtopping-resistant and constructing dunes with a foreshore. The decision to construct dunes with a foreshore prevailed (option 4 in below image). Choosing a sandy solution is in line with the national coastal policy to apply a soft sea defence made of sand where possible. Furthermore, fighting structural erosion by replenishment of sand is also a proven method.
The other three design alternatives have some negative points which include the following:
- Crest raising would cause too much impact on inside of dike (option 1)
- Only foreshore nourishment would not provide adequate safety (option 2)
- Upgrading of hard protection on seaside and land side of dike would not be sustainable and intensify erosion of foreshore (option 3)
A sandy defense structure such as the Hondsbossche dunes (option 4) has multiple benefits (random order):
- Creates opportunities for nature, recreation and tourism
- Has minor impact on the environment
- Small risk of project delay
- Broad support from stakeholders
- Ready before the end of 2015
- Easy to adapt (future climate changes)
- Verification: straight forward
- In line with our governmental policy
- Proven method