Dunes: the Netherlands Soft But Secure Sea Defences
Type:
Presented during:
WODCON XVIII - 2007 Orlando, Florida, USA
Authors:
Van-Koningsveld, et al
Abstract: A major part of the Netherlands lies below or around sea level and has to be protected from flooding by the sea. Along the coast natural dunes are the first line of defence. Research in the 70’s and 80’s of the 20th century yielded methods to quantify dune strength for coastal safety assessments. This enabled coastal managers to engineer the soft and dynamic dune area to be a robust coastal defence of a predetermined strength. Further, research in the 80's yielded quantitative approaches to prevent structural coastal erosion. This enabled coastal managers to implement a national policy to counter structural coastal erosion by sand nourishment. The main objective of this paper is to explain the Netherlands’ sandy coastal policies in order to convey the importance of sand nourishment as a coastal engineering measure in the Netherlands and its potential for other coastal areas. To illustrate how these policies are implemented in practice two case examples (both for the Delfland coast) are discussed.
The Dynamic Preservation case, dealing with coastline management, shows that annual coastline checks result in substantial nourishment efforts (1 Mm3 with a 2-3 year return period). Nourishments of this order of magnitude are well capable to maintain the coastline position not landward of its established 1990 reference. The paper discusses the procedure that provided the trigger for intervention and outlines the order of magnitude of the intervention.
The Coastal Safety case, dealing with dune strength, illustrates how the five yearly review of criteria led in 2001 to the identification of a number of weak links along the North Sea coast. To meet the prescribed safety standards, strengthening measures have been designed and discussed publicly. The plans not only focus on safety from flooding but also account for aspects like natural values and spatial quality. The currently preferred alternative for the weak link of Delfland is a sandy intervention involving approximately 20 Mm3 of sand, to be dredged in the North Sea. Execution is scheduled to start in 2008.
Based on experiences in the Netherlands we can see that working with sand works. Sand based coastal management strategies are clearly effective, sustainable and flexible. Years of research and experience have shown that sandy coasts, although soft and dynamic, can in fact be engineered to provide predefined safety levels while supporting other functions as well.
Keywords: coastal policy, safety, coastline preservation, coastal defences, sand nourishment 1