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Overview of Theme 8

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Versie door Tasomerville (Overleg | bijdragen) op 17 sep 2008 om 01:22

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Overview of Theme 8

This article is under construction. The overview article will be adapted when new relevant articles for Theme 8 appear in the Coastal Wiki.

subject

The subject of Theme 8 is: 'New sustainable coastal engineering techniques', or more general: ‘Coastal engineering techniques’.

Coastal engineering techniques are applied (must be applied) in practice when serious ‘coast related problems’ have to be resolved.

With the help of adequate Coastal Zone Management plans (partly based on fair insights in, and thorough knowledge of, occurring natural coastal processes) many real life problems might be avoided. [Cf. Theme 3, Theme 5 and Theme 10 (for getting ‘new’ generations of skillful people).]

However, many (felt) problems remain; with the help of well-selected, and well-applied Coastal engineering techniques one might resolve a problem.

The notion ‘techniques’ in Coastal engineering techniques is in Theme 8 mainly used as a technique to resolve real life problems. To develop and to run for instance a complicated morphological computer model, and to judge the outcomes of such a model, might also be considered as a ‘technique’; however that is not meant in Theme 8. In Theme 8 ‘techniques’ are mainly meant as skillful and proper applications of (existing and new) methods in coastal engineering to resolve e.g. erosion problems or methods to properly protect a coast.

main emphasis and limits

Within the basic framework of ENCORA the main emphasis of Theme 8 is on Coastal Engineering (techniques) related to morphological developments of coasts (e.g. erosion, accretion) and to shore protection (e.g. approach, methods, tools). That means that many quite interesting parts of Coastal Engineering (e.g. breakwater design, offshore platforms, offshore windmills, wave energy conversion devices, port planning and port layout) are not dealt with.

A well-developed system of Integrated Coastal Zone Management (ICZM) is especially important if many different (often: conflicting) interests play a role in the coastal zone. It is felt that along a sandy coast in general more interests must be taken into account than along e.g. a muddy coast (compare for instance recreation and housing topics). This means that in Theme 8 hardly any attention will be paid to muddy coasts.

The functional design aspects of e.g. a proper coastal protection scheme are the main items in Theme 8. (E.g. position and crest height of a detached submerged breakwater). Although very important in practice, structural design aspects (e.g. how to determine the mass of an armour layer of a submerged breakwater?) are not dealt with.

In preparing this overview article for Theme 8 the restrictions as have been pointed out up here, are taken into account.

Furthermore it is assumed that the reader is somewhat familiar with general notions related to Coastal Engineering like tides, tidal currents, wave characteristics (e.g. wave height H and wave period T), orbital motion, wave driven currents and e.g. sediment properties.

Theme 8 Rationale

effective management to avoid problems in future

Effective management of coastal zones is crucial. With a proper (also legally supported) coastal zone management policy, many problems in future are to be avoided. However, more or less 'autonomous', 'free' and (in retrospect) ‘unwanted’ project developments in the coastal zone in the past, might have led to a less desirable situation.

The (not optimal) present situation often calls for protection and preservation of for instance coastal communities. The present situation in e.g. a coastal community is important, but also the expected situation over a timescale of the order of 50 till 100 years. The present autonomous morphological developments of the stretch of coast, but also possible changing developments due to global sea level and climate changes, must be taken into account.

Long-term geo-morphological change of coastal and estuarial systems is a main topic of Theme 5. That includes promotion of the development and demonstration of emerging and new methods for the prediction of the behaviour of coasts, and dissemination of this new knowledge across Europe.

human involvement

Human involvement with the present situation in a coastal zone and the occurring morphological developments in that zone, leads to notions like 'good' and 'bad' situations and/or developments. [See also Par. 'Time-perspective' in protection against coastal erosion.]

Often felt 'bad' situations and/or developments must be redressed in better ones. Theme 8 deals with methods and tools to redress undesirable situations and developments of coastal zones.

It is stressed that the notion 'undesirable' is meant from the points of view of people living, working and using the coastal zone. These points of view might be quite different if ‘nature’ or ‘environment’ would be a starting point.

A proper application of e.g. a tool to protect a stretch of coast, calls for a proper insight in the occurring coastal processes, but also for a fair knowledge of the impact on the morphological processes of the tool as is applied.

Insufficient knowledge of the under-lying processes might easily result in the selection of an inadequate protection tool.

Although morphological developments are a main issue, of course various other aspects (e.g. ecological aspects) must also be taken into account.

rationale

The rationale of Theme 8 is to clarify the dilemma’s a practitioner or a responsible Authority encounters in selecting, designing and applying Coastal engineering techniques in resolving coastal engineering problems.

The topic is relevant for almost every member state of the European Union. Quite obviously for member states bordering open seas, but the topic might be also relevant for the ‘coasts’ of large inland lakes.

The aim of this overview article is two-fold:

  1. Guide through various articles.
  2. Supported by a fair reasoning, to arrive at some important ‘lacking items’ which, when they would be available, might result in even better applications of Coastal engineering techniques.

Insight in those lacking items might be helpful to overview our limitations in dealing with vulnerable coastal systems.

Identification of lacking items might be also helpful when a reserarch agenda has to be defined. (E.g. at European level.) In the article laking items Theme 8 a brief summary of various topics is given.

Within the ENCORA project it was decided to develop the Coastal Wiki as an effective tool for networking and dissemination of state of the art knowledge and experiences.

Relevant topics for Theme 8

List of topics

In this overview of Theme 8 the following topics are identified as helpful to get a clear picture of the content of Theme 8, or being of particular relevance:

  1. Overview of coastal engineering problems to be addressed
  2. Various types of erosion
  3. Under-lying causes of problems; morphological developments; quantification of problem
  4. Design requirements
  5. Selection of methods and tools (‘hard’ / ‘soft’)
  6. Ultimate morphological effects (near field / far field)
  7. Guidelines for policy makers and practitioners of sustainable approaches

The rest of this article provides an overview of, and introduction to, these topics.

Topics 1, 2, 4 serve as some kind of background information; they provide the context of the Theme 8 field of interest. Serious numbers of lacking items are not foreseen with respect to these topics. At most they could be extended and better clarified.

With respect to Topics 3, 5 and 6 much is known, and belongs to the skills of a Coastal Engineering expert. However, besides that various lacking items can be identified. [See lacking items Theme 8.]

Based at the present state of the art of the field of interest of Theme 8, the content of Topic 7 can be summarized. Because of the ever developing knowledge and experience, the content of Topic 7 is a permanently changing content. The improving and extending content of the Coastal Wiki is a good tool to serve that goal.

Overview of coastal engineering problems to be addressed

A series of real life examples of coastal engineering problems is listed. The list does not cover the entire field of interest, but is intended to give a fair first impression of the type of problems one might encounter in coastal engineering and calls for a proper solution.


Creating a fixed transition between mainland and sea

A fixed transition between mainland and sea is often wanted in a coastal community. For a proper recreational development for instance is such a clear transition wanted. A seawall / boulevard combination might serve that goal.

See: seawalls and revetments.

Protecting infrastructure built rather close to the edge of the mainland

Protecting infrastructure built rather close to the edge of the mainland from attacks by storm (surges) is often wanted / necessary in a coastal community. Various methods are available to achieve that aim.

See: dune erosion; seawalls and revetments; beach nourishments; light revetments built-in into artificial dunes.

Protecting the (low-lying) hinterland by flooding

In some cases a (low-lying) hinterland is protected from attacks by the sea by a (slender) row of dunes. Flooding due to a breakthrough of the dunes during a severe storm surge should be avoided. In such a case the dunes act, just like a seadike, as a sea defence. If the existing row of dunes does not fulfil the requirements, reinforcements are required. Various methods might be applied to reach that aim.

See: dune erosion; seawalls and revetments; beach nourishments; light revetments built-in into artificial dunes.

Protecting a piece of coast prone to structural erosion

Protecting a piece of coast, prone to structural erosion, from further erosion is a large problem in Coastal engineering. Sooner or later properties built at, and infrastucture present on the mainland become at stake and might be destroyed. Various methods might be applied.

See: protection against coastal erosion; detached shore parallel breakwaters; groynes; shore nourishment; beach nourishments.


Stabilizing the position of a river mouth or a tidal inlet

The position of a river mouth or the position of a tidal inlet while crossing the coastline, is often changing all the time because of natural 'autonomous' morphological developments. This might cause serious problems to people using the coastal area. Sometimes this a reason that one likes to stabilize the position of the river mouth or tidal inlet.

See: typical examples of structural erosion.

Application of a sand by-pass system

In order to artificially restore the occurring sediment transports because of the construction of a set of breakwaters of a port, or of a set of jetties to stabilize the position of a river mouth or a tidal inlet, sometimes a sand by-pass system is applied. With the help of such a system the typical erosion and accreting problems in the vicinity of the structures can be avoided.

See:

The wish to improve the width of beaches for recreation purposes

When it is felt that the width of beaches is too small for e.g. recreation purposes, the beaches should widened.

See: beach nourishments.

The wish to create sandy beaches in a situation where natural beaches do not exist

See:

The wish to create land reclamation

In some cases an large extension of the mainland in seaward direction is required. The 'new' created land might be used for several useful purposes.

See:

The wish to build a port along a sandy coast

See: port breakwaters and coastal erosion; typical examples of structural erosion.

The wish to get a proper insight in the effects of global sea level rise and / or climate changes on the stability of an existing coast

See:

..........

Various types of erosion

Erosion of the dunes or mainland occurs because of various mechanisms and processes. For the owner of a building e.g. built close to the sea it is less important to know by which process his or her building was ultimately destroyed. For a Coastal Zone Manager who has the task to prevent erosion, a fair insight in the real reason of erosion is required in order to develop a proper protection plan. Two types of erosion are relevant.

  • Structural erosion (continuously; year after year).

See: structural erosion; typical examples of structural erosion; types and background of coastal erosion.

  • Episodic erosion of the mainland because of a severe storm surge.

See: types and background of coastal erosion; dune erosion.

Underlying causes of problems; morphological developments; quantification of problem

In the following for each type of erosion a few relevant aspects are mentioned. During the further development of the Coastal Wiki the various aspects will be addressed. When available links are given.

  • mainly due to waves
  • mainly due to tidal currents
  • combination of waves and currents
  • quantification of structural erosion problem:
  • from field observations; aerial photographs; satellite observations
  • from calculations with the help of morphological computation models
  • effects of global sea level rise and / or climate changes on the rate of structural erosion
  • achieving a proper set of (existing) boundary conditions
  • quantification of episodic erosion:
  • computation models to calculate rate of erosion of unprotected dunes / mainland under design conditions (design conditions: often far beyond known experience from real occurrences from the past)
  • computation models to calculate rate of erosion of protected dunes / mainland under design conditions (calculation of scour holes in front of a seawall or revetment)
  • computation models to calculate rate of erosion of unprotected dunes / mainland under design conditions near the transition of a protected and an unprotected part of a coast

Design requirements

For coastal engineering works it is of utmost importance to formulate a clear set of requirements an intended work has to meet. Next an alternative has to be chosen which satisfies the requirements.

A few different examples are given from which it becomes clear how important it is to be quite specific in formulating the requirements. With a, at a first glance small, difference in requirements, some alternatives might become not possible anymore. Links to relevant articles which address the various options are given.

  • Protection (e.g. no further structural erosion) of a given stretch of coast; lee side erosion allowed.
  • Protection (e.g. no further structural erosion) of a given stretch of coast; lee side erosion not allowed.
  • Protection and gain (e.g. no further erosion, but also some widening of the beaches / coast; e.g. to return to the situation of a couple of years ago) of a stretch of coast.
  • Protection of properties built rather close to the edge of the dunes against episodic storm (surge) events.
  • Improving safety level of low-lying hinterland.
  • Port project. Sand by-pass system is considered not necessary.
  • Port project. Sand by-pass system is one of the requirements.
  • ........

Selection of methods and tools (‘hard’ / ‘soft’)

Given a clear set of requirements a solution of a well-defined problem has to meet, various alternatives, applying various tools, can be developed. A list of tools with links to relevant articles:

  • Artificial beach nourishments.

See: Artificial nourishments; shore nourishment.

  • Artificial shoreface (under water) nourishments.

See: Artificial nourishments.

  • Seawalls / revetments.

See: seawalls and revetments.

  • Shore parallel detached breakwaters.

See: detached shore parallel breakwaters.

  • Series of groynes / row of piles.

See: groynes.

  • Floating breakwaters

See: floating breakwaters.

  • Beach dewatering systems.

See: beach drainage.

  • Sand by-pass system.

See:

  • Widening of dunes.

See:

  • ......

Ultimate morphological effects (near field / far field)

During the design phase of a project proper estimates must be made of the near field and far field morphological effects of various possible alternatives. Insight in these effects is indispensable for a proper judgment and selection process of the various alternatives. Our possibilities to make proper estimates of near field and far field morphological effects are still rather poor. (Near field effects are considered even more difficult to estimate than far field effects.) With a proper monitoring program (covering a fair prior to the work period and a fair post work period) a lot of data is gathered which might be helpful to improve estimation tools. (Cf. Theme 9 - Assessment of field observation techniques.)

Various results of research studies and case studies are mentioned; links are provided.

Guidelines for policy makers and practitioners of sustainable approaches

Guidelines should contain clear statements and approaches, based on state of the art knowledge and insights. Because of ever growing knowledge, insights and experiences, Guidelines must be adapted continuously. A Wiki format for developing Guidelines (with quality checks), might serve that aim.

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


See also

Alphabetic overview of articles in theme 8