Introduction

Regular assessments of the safety of a dike are undertaken in the Netherlands. During a recent long term assessment, the anticipated performance of the sea dikes and dunes subjected to a storm surge with an incidence of occurrence of 1 in 10 000 years (the Dutch flood protection standard) was tested.

The sea defence dike along the North Holland coast near Petten was deemed not to be able to satisfy the safety requirements over the next 50 years. Accordingly, the coastal defences have to be upgraded. Several parties are concerned about this issue, including the water board Hollands Noorderkwartier, the Dutch Ministry of Infrastructure and Environment, the Province of North-Holland, local municipalities and some nature organisations.

The dike along this stretch of coast is a hard, stone and concrete defence structure. With the new insights on combating the erosion of the Dutch coast by sand nourishment and the experience of the Sand Engine in mind, we are required to design a nature friendly solution to this problem.

Where is the Hondsbossche and Pettemer Sea Defence located?

The Hondsbossche and Pettemer Sea Defence is located in the province of North-Holland, as depicted in the map. The coastal defence used to be 2 separate dikes, but over time they have been upgraded to one contiguous sea defence structure.

Some hints

• The North Holland coast has many naturally occurring dunes and is strongly influenced by the wind and waves.
• This sea defence has an extended history of multiple dike upgrades, and further dike heightening is not desirable.
• A safe design for the next 50 years (without dike heightening) is a challenging task that requires knowledge on how nature will affect your design.
• The effects of some natural processes are easier to predict than others, but many are still uncertain or even unknown. Experience from the Sand Engine and other interventions along the coast is adding to the knowledge of ecosystem responses to mega nourishments.

Additional knowledge clips on coastal systems and coastal interventions

Have a look at the videos below. These videos are part of the MOOC Water and Climate, also from Delft University of Technology. They will provide you with additional knowledge on coastal systems and coastal engineering.