Dune erosion

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Revision as of 10:45, 7 May 2008 by Jan van de Graaff (talk | contribs) (See also)
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Definition of Dune erosion:
Dune erosion involves that, during a severe storm surge, sediments from the mainland and upper parts of the beach are eroded and settled at deeper water within a short time period; this is a typical cross-shore sediment transport process.
This is the common definition for Dune erosion, other definitions can be discussed in the article

The basis of this article is especially written for the Coastal Wiki by the main author referred to at the bottom of this page.


Dunes as sea defense

River and sea dikes are good examples of structures to protect low-lying areas from flooding. Also a dune area (dune row) serves that aim in some cases. E.g. the safety of large parts of The Netherlands, often with ground levels even below Mean Sea Level (MSL), relies on dikes, but also on dunes for their protection against flooding.

Visiting the beach and the coastal zone in e.g. The Netherlands under normal weather conditions would easily give the impression that the dunes are certainly strong enough to properly protect the hinterland. However, during a severe storm surge, with under design conditions water levels at sea which are approximately 5 - 6 m above MSL and together with the much more severe wave conditions than normal (cf. wave heights Hs ≈ 7 - 9 m and peak periods Tp ≈ 12 -18 s), the dunes will be eroded in a very short period of time.

Existing design rules in The Netherlands yield erosion rates of 80 - 100 m of the dunes during design storm conditions. (The rates of 80 - 100 m are given as an order of magnitude value only to facilitate the further discussion; the actual erosion rates under design conditions depend on the specific local conditions; e.g. shape of initial cross-shore profile and particle size of the dune material.) It must be realized that because of the specific Dutch conditions, the design conditions in The Netherlands are very strict.

Rather wide dune area is sea defense

Often the dune areas in The Netherlands are wide enough to accommodate 80 - 100 m of dune erosion during a single severe storm surge. In some cases, however, the row of dunes is rather slender; a careful judgement has to be passed whether the dunes provide the required rate of protection. Is a break-through expected under design conditions?, and if yes: what reinforcement is necessary to fulfil the requirements?

So far in the discussion the safety problem of people living behind the dunes was raised as the main issue. In the following Paragraph 'Large and small scale safety problems' of this article it will be shown that more issues related to dune erosion are relevant to a coastal zone manager. Aspects like the safety of single houses and hotels in the erosion zone are dealt with.

Also topics like how to deal with structural erosion and global sea level rise are relevant topics for a coastal zone manager. They are briefly discussed in this article with the present Dutch policy and insights as starting points.

From the discussions it will become clear that for many reasons a proper insight in the rates of dune erosion as a function of the boundary conditions is necessary. Paragraph 'Quantification of rate of dune erosion' will deal with the dune erosion process and the methods to quantify the rates of erosion during a severe storm surge.

See also

The main author of this article is Jan van de Graaff
Please note that others may also have edited the contents of this article.

Citation: Jan van de Graaff (2008): Dune erosion. Available from http://www.coastalwiki.org/wiki/Dune_erosion [accessed on 12-07-2020]