10.7.1: Introduction

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Page ID: 16445

Judith Bosboom & Marcel J.F. Stive
Delft University of Technology via TU Delft Open

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In this section, we discuss how coastal erosion problems can be solved by nourishments with sand instead of by building structures of quarry stone or concrete. These types of solutions are called ‘soft’ solutions. The basic idea is to supplement sand by artificial means (dredge, truck) in places where the loss or lack of sand is causing problems. Sand nourishment leaves the coast in a more natural state than structures and preserves its recreational value. The method works if ample quantities of sand are available from a borrow area at a relatively short distance from the problem area.

Artificial nourishments can be applied for various reasons:

to compensate for losses as a result of structural erosion;
to enhance the safety of the hinterland against flooding and to protect the beach and dune area and properties built rather close to the edge of the dunes against storm erosion;
to broaden a beach, create new beaches (for recreation) or reclaim large areas of new land such as artificial islands.

The second and third applications refer to situations in which the nourishment is, in principle, a once-only measure. However, in the first situation of structural erosion, which is an ongoing process, the nourishment will have to be repeated from time to time. The interval between successive supply operations depends on the rate of erosion and on the cost of mobilising the dredging equipment. Generally an interval of 5 years between successive operations is considered acceptable.

With respect to structural erosion (application 1), a distinction between the ‘hard’ and the ‘soft’ methods is that the latter must be repeated from time to time, that it is flexible (in the sense that it is easy to modify the scheme if the results are not as expected) and that the cost of the operation is deferred in the sense that it is spread over a longer time. For conditions along the Dutch coast this makes the ‘soft’ solutions more economical than the ‘hard’ solutions. One could also argue that, since sediment is always added to the system, a nourishment can never go really wrong, although a badly designed nourishment may not be as effective as expected in counteracting the erosion problem under consideration, which may lead to damage to properties. Last, but not least, lee-side erosion does not occur with ‘soft’ solutions, as would be the case with structures, like a series of groynes.

In Sect. 10.7.2 some design considerations are given. Next, the three different applications as listed above are subsequently discussed in Sects. 10.7.3 to 10.7.5.

For further reference: many details related to the use of artificial nourishment are found in Coastal Engineering’s Special Issue on Artificial Beach Nourishment (1991) and in a report (see Van Rijn (2010)) prepared in the framework of the European Union funded project Conscience (Concepts and Science for Coastal Erosion Management). Both publications contain references to papers especially devoted to artificial nourishment.