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COASTAL STABILIZATION AND ALTERNATIVE SOLUTIONS
including Geosystems IN INTERNATIONAL PERSPECTIVE
• Krystian Pilarczyk, The Netherlands; [email protected]
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Getting olderI understand more and more
how little I know (how little my knowledge is)
ThereforeI have to disappoint you
I have more to say onWhat we do not know
thanWhat we do know
Why
What
How
COASTAL STABILIZATION AND ALTERNATIVE SOLUTIONS
What I do know
• Krystian Pilarczyk• (former) Rijkswaterstaat/Public Works Dpt., Delft, NL
• HYDROpil Consultancy; [email protected](see also CEM 2002)
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Example of coastal erosion:Typhoon Damrey 27Sept’05 Vietnam
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(Alternative) systems and materials
in
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Disappearing beaches: engineering solutions
• Humans are very clever at finding technical solutions to environmental problems but they seldom remove the causes of such problems. When trying to protect the land from the sea, they underestimate how powerful the sea can be, because large storms do not occur often enough.
Dr J Floor Anthoni (2000)
www.seafriends.org.nz/oceano/beacheng.htm
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• Line in the sand Beaches and dunes have natural periods of growth and erosion. Many people believe that we do not give our beaches enough space to wax and wane naturally. Once property is threatened, the beach is lost.
• Renourishment When the beach erodes and the sand disappears, people's first reaction is to bring new sand in from elsewhere. Little attention is paid to the reasons why the sand disappeared, and beach erosion continues.
• Beach drainage By draining the beach, the sand is able to dry and the sea wind is able to re-create a dry beach. It is a cheap and effective way for beaches whose sand cannot dry easily
• Sea walls Where beach erosion appears unstoppable, sea walls are built to protect property, business and life, but the natural beach disappears.
• Groynes Beaches strung between headlands are less prone to erosion from long-shore currents. Groynes (groins) are artificial headlands between which sand accumulates. But they cause problems too and look ugly.
• Jetties Jetties are long dams jutting out in the sea, designed to keep the entrances to harbours open and navigable. They also cause serious beach erosion
• Breakwaters Breakwaters are artificial barriers erected parallel to the shore. Sand gets trapped behind them. But extreme events destroy them. A new fad is the breakwater for surfing.
• Sand mining Sand is bountiful in the sea but mining it attracts opposition, but is it really damaging the beaches?. With our newly found insights, we can support mining in certain places and conditions.
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Systems & Materials
Headlands
examples
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Direct & In-direct protection
Reduction hydraulic loading
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Granular materials:
from sand to rock
Systems & materials:examples
Prefabricated systems
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Identification of coastal problem
and
Functional Design
Starting point
Selection technology
See also:http://www.unesco.org/csi/pub/source/ero18.htm
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Coastal basics/principles
• Sediment transport capability
• Episodic (Storm) erosion vs. structural erosion
• Coastal control measures
• Efficiency
• Alternatives
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Problem definition
Jan van de Graaff, TUDelft
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Problem analysis
Restored cross section: sand nourishment
Cross section after coastal recession
Cross section eroded:
sand nourishment on dune and/or beach
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‘Soft’ measures• artificial beach nourishments
• shoreface nourishments• Nourishments:
• have to be repeated• no lee-side effects• look so ‘soft’, but are a very good solution• at the end: rather cheap• argument: “we are a developing country, so we can’t afford
beach nourishments”, is not a strong argument
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Initial considerations
Environmental conditions
Functional pre-design alternative
Selection of preferred scheme
Detailed design
In the design process one has to distinguish between functional design and structural design.
Functional design concerns the impacts and performance of the coastal alternative with respect to coastal protection, improvement of recreational conditions and conservation of natural living resources.
Structural design concerns the resistance of the coastal structure to the actions of waves and currents
BASIS PRINCIPLES Design Starting Points
www.delos.unibo.itwww.delos.unibo.it
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Interference with sediment transport
To resolve a structural erosion problem (dSx/dx ≠ 0) with the help of structures (‘hard’ solution), the structures must interfere in the existing sediment transports.
If we apply beach nourishments: we must nourish the ‘Loss’
J. Van der Graaff, TUDelft
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Headlands, groynes and offshore breakwaters
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• Seawalls / revetments
• initial erosion occurs always in this case (under water)
• With revetment:
• loss from dunes is physically prevented; lowering of beaches in front of revetment; loss of beaches
• with time: heavier and more frequent attack to revetment; damage of revetment at the end of the day
• large problems; high costs; angry people
• (shame for our profession)
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Headlands and groynes
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GROINS. Background and definitions. Groins are the oldest and most common shore-connected, beach stabilization structure. They are probably the most misused and improperly designed of all coastal structures.They are usually perpendicular or nearly at right angles to the shoreline and relatively short when compared to navigation jetties at tidal inlets. As illustrated schematically in Figure , for single and multiple groins (groin field) the shoreline adjusts to the presence of the obstruction in longshore sediment transport.Over the course of some time interval, accretion causes a positive increase in beach width updrift of the groin. Conservation of sand mass therefore produces erosion and a decrease in beach width on the downdrift side of the groin. The planform pattern of shoreline adjustment over 1 year is a good indicator of the direction of the annual net longshore transport of sediment at that location.http://www.ce.ufl.edu/~mcdougal/CEM/Part_V_Coastal_Project_Planning_and_Design/V-3_Shore_Protection_Projects.pdf
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Groynes (see CEM 2002)
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Sedimentation polders
Netherlands
Thailand
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(CEM 2002)
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Some remarks on Low-crested Structures (LCS)
See also: www.delos.unibo.itSee also: www.delos.unibo.italberto.lamberti@[email protected]
DELOS
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Distribution of waves along the center of reef (Ohnaka&Yoshizwa, 1994)
Functions and definitions
or beach
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Ls
LCS LCS
G
X
Initial shoreline
CL
Ls
Effectiveness Low-crested structures
or beach
Wave transmissionGeometrical Lay-out; Ls/X
Flow pattern
But also Sediment transport
Waves
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Functionality of offshore breakwaters in relation with sediment transport
J. Van der Graaff, TUDelft
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DK
Close to the coastline
UK
Holly Beach US
Far from the coastline;
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0.0
0.2
0.4
0.6
0.8
1.0
-3 -2 -1 0 1 2 3 4
Relative Freeboard, R/H
Tra
nsm
issi
on C
oeff.
, Kt
transmission over crest
transmission by runup andovertopping
transmission throughrubblemound
SW
L
Ahrens (conceptual)
Japan
Van der Meer 1991
Narrow–crested breakwaters
General transmission characteristics (past)Sawaragi, 1995
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(offshore) (onshore)
foot protection block
rubble stone Aquareef
0.0 0.1 0.2 0.3 0.4 0.5 0.60.0
0.2
0.4
0.6
0.8
1.0
B/L1/3
Ht/H
1/3
R / H1/3 =
1.00.80.60.40.2
0.0
Example of Aquareef
transmission
0.0 0.1 0.2 0.3 0.4 0.50.0
0.2
0.4
0.6
0.8
1.0
1.2
B/L1/3
Ht/H
1/3
R / H1/3 0.0 ~ 0.2
0.00.10.2
Transmission results for water levels close to the crest
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Distribution of H1/3 along the center of reef
Reduction of wave height
Reduction of wave period
Prototype measurements for Yugawara reef, Japan
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opeH
B
H
RK
sisi
ct
5.0
31.0
164.04.0
d ’ A n g r e m o n d e t a l . , 1 9 9 6 , f o r B / H s < 8
F i n a l r e s u l t
N e w f o r m u l a f o r B / H s > 1 2
opeH
B
H
RK
sisi
ct
41.0
65.0
151.035.0
L o w e r b o u n d a r y : K t = 0 . 0 5 U p p e r b o u n d a r y : K t = 0 . 9 3 - 0 . 0 0 6 B / H s
L o w e r b o u n d a r y : K t = 0 . 0 7 5 U p p e r b o u n d a r y : K t = 0 . 8
I n t e r p o l a t i o n 8 < B / H s < 1 2
DELOS: transmission
www.delos.unibo.itwww.delos.unibo.it
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Tombolo: Ls/X > 1.0/(1-Kt) Andrew, 1997 (field data)
Ls/X >0.65 islands and reefs
or X/Ls< 1.0 (1-Kt),
Salient: Ls/X < 1/(1-Kt) Ls/X <1.0 - islands
(assume KT = 0 for islands and 0.5 for reefs) Ls/X <2.0 - reefs
or X/Ls> 1 (1-Kt),
For salients where there are multiple breakwaters: GX/Ls2> 0.5(1-Kt)
(G= gap width)
Where Ls is the length of a breakwater and X is the distance to the shore, G is the gap width,
and the transmission coefficient Kt is defined for annual wave conditions.
X
Ls
X off
D R D L
D tot
Y off
Offshore Obstacle
Salient Undisturbed Shoreline
B Transmission coef. in Tombolo-Salient relations
(proposed by Pilarczyk as an example)
Existing criteria (a choice from many):
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Comment on functional design
Use 2- or 3D numerical models for functional design
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Burger/Delft 1995
Structural designStructural design
Stability: Stability: Comparison (Delos/AalborgComparison (Delos/Aalborg * * is lower limit)is lower limit)
Design diagram for start of damage using rock
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Artificial reefs Reef Balls
http://www.artificialreefs.org/
Aquareef Japan
rubble stone Aquareef
cage of reinforcing bars
(onshore)
foot protection block
(5t)
(offshore)
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Prefabricated Erosion Prevention (P.E.P.) Reefs
http://chl.erdc.usace.army.mil/%5CMedia/3/5/2%5Ccoas_19_202_684_722.pdf
Prefabricated systems/elements
Beachsaver reef
Wave block
http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=ARTICLES;349
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http://chl.erdc.usace.army.mil/%5CMedia/3/5/2%5Ccoas_19_202_684_722.pdf
http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=ARTICLES;349
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USACE demonstration program
National Shoreline Erosion Control Development and Demonstration Program (Section 227)
http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=PROGRAMS;3its objectives are to provide state-of-the-art coastal shoreline protection
A variety of shore protection devices and methods are being constructed, administered, and evaluated at a number of sites throughout the United States with diverse shoreline morphologies. These shore protection structures must have scientific support for projected performance and must not affect the aesthetic appeal of the area. Both patented devices and nonproprietary methods are permissible.
Cape May Point, New Jersey Section 227 Demonstration Site
Example:
http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=PROJECTS;48
Cape May Point, NJ - Evaluating a prefabricated submerged breakwater and double-T sill for beach erosion prevention
http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=PUBLICATIONS;50
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http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=ARTICLES;349
Cape May Point, New Jersey Section 227 Demonstration Site
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Some other systems
• DRIM distorted ripple mat
• Beach drainage
• Gravel beaches
• Geosystems
• Etc.
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DISTORTED RIPPLE MAT (Japan)
Concept of DRIM mat
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http://www.beachdrainage.com/ http://www.shoregro.com/
http://www.unesco.org/csi/pub/source/ero11.htm
Beach drainage
Pressure Equalizerhttp://www.ecoshore.com/
Gravity drainage Japan
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Gravity drainageJapan
http://www.pari.go.jp/bsh/ky-skb/hyosa/hpj/english/02menb/yana/yana.htm
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Gravel beaches
Granular materials are still the most popular materials / systems
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Geosystems
Geomattresses
Geobags
Geotubes
Geocontainers
Geocurtains
Artificial seaweed
Etc.
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Geosystems have been devised as an alternative to traditional breakwater designs.
A high strength synthetic fabric is cast into bags, mattresses, tubes or containers which are then filled with sand or mortar. They are used in the following ways:
Mattresses applied as slope or bed protection;
Bags are suitable for slope protection, retaining walls, toe protection, and in the construction of groynes, perched beaches or offshore breakwaters;
Tubes and Containers are mainly used for the construction of groynes, perched beaches or offshore breakwaters, and bunds in reclamation projects.
Geosystems have to date been commonly used as temporary measures due to limitations, including low resistance to waves and currents and low durability to vandalism and UV. The sand-filled variety can now be used as permanent structures and offer a number of advantages over traditional breakwaters, mainly: reduction in cost, quick installation, minimal impact on the environment, low skilled labour, use of local materials and equipment. As with most options it has its advantages and disadvantages, but geosystems have greatly improved since their early beginning.
However, further work on improving designs and the need for testing under various conditions is still required.
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before and after the storm
Geomattresses
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Sandbags Suriname
Coronie
after first storm
Sandbags
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B-B
Description: Date: Feb 2003
Scale: n.t.s.
2.5m Soft Rock Dimensions
Full Container
Section A-A Section B-B
2.5m Soft Rock Sea Wall Proposal
This document is not to be considered a full design and is provided without obligation. Complete engineering design must be performed by a suitably qualified engineer
3
650
2 4001 800
650
2 400
1 800
A A
B
B
3
B-B
B-B
B-B
B-B
B-B
B-B
B-B
B-B
B-B
5223R (2.5m )Soft Rock Containers
terrafix 600R 0.0 AHD
-1.0 AHD
Toe Detail
terrafix 600R
5223R (2.5m )Soft Rock Containers
Encapsulated self healing toe
Wall X-Section
Toe Detail
2152R (0.75m )Soft Rock Containers
3
3
3
Geobags
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Applications Geobags
Hannover tests
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More recent, large scale tests in Hannover, with large geobags, can be found on the website:
http://sun1.rrzn.uni-hannover.de/fzk/e5/projects/dune_prot_0.html
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Geotubes
New developments
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Geotubes and design aspects
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Failure modes: design aspects & execution
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Design Geotubes:Shape & strength
PalmertonPalmerton
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Geotubes
Pocked beach
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Failures (US examples)
Hole in geotube
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AmWaj Island, Bahrein
at low water
Example of project:
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Transmission characteristics of reefs for AmWaj Island, Bahrein; Delft Hydraulics, 2002
For preliminary design
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Execution
AmWaj Island, Bahrein
Offshore breakwater at design water level CD+3.5 m
50 m
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Leshchinsky’s programmaDesign and execution
with geotubes
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Non-woven
WovenGeocontainers
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Geocontainers
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0.03
0.16
0.28
0.28
0.36
0.44
0.16
0.52
0.36
0.60
0.44
0.68
0.52
0.76
0.84
1.08
1.08
0.68 0.76
0.84
1.40
1.24 1.241.40
0.920.92
t = 2.12 s
0 10 20 30 40 50 x(cm)
splitbarge
leg ofsplitbarge
numbers = time(s)
Dumping trajectory of geocontainer
Accuracy of placement still a problem
Breakwater
Submerged reef, Gold Coast
a view
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Other geosystems
Artificial seaweed
anchorhttp://www.scourcontrol.co.uk/academic.html ; http://www.scourcontrol.co.uk/index.html
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Conclusions on Geosystems
Remaining questions:
- durability
- execution
- damage and repair
- quality control
In general it can be said that geosystems as well as all engineering systems and materials have (some) advantages and disadvantages which should be recognized before a choice is made. There is not one ideal system or material. Each material and system has a certain application at certain loading conditions and specific functional requirements for the specific problem and/or structural solution.
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ConclusionsThere is certainly a future for alternative structures
- erosion control
- reduction of wave loading
The author does not intend to provide the new design rules for alternative structures. However, it is hoped that this information will be of some aid to designers looking for new sources, who are considering these kinds of structure
and improving their designs.
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The more intensive monitoring of the existing structures will also help in the verification of new design rules.
International cooperation in this field should be further stimulated.
These new efforts will bring future designers closer to more efficient application and design of these promising coastal solutions.
Continued research, especially on submerged breakwaters and alternative systems, should further explore improved techniques to predict shore response and methods to optimise functional and structural design.
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Conclusions/end remarks• A number of concepts still need further
elaboration to achieve the level of design quality comparable with more conventional solutions and systems.
• A number of uncertainties can be solved in the scope of graduation works and doctoral dissertations. However, for a number of systems more practical experience is also still needed under various hydraulic conditions.
• The realization of this need is only possible if manufacturers, clients and researchers cooperate closely.
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Information sources (some websites)
http://chl.erdc.usace.army.mil/%5CMedia/3/5/2%5Ccoas_19_202_684_722.pdfhttp://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=ARTICLES;349
Prefabricated breakwaters
See also:Silvester, R. and Hsu, J.R., 1993, Coastal Stabilization, Prentice Hall Inc., Englewood Cliffs.
ALTERNATIVE SHORELINE STABILIZATION DEVICES
http://www.env.duke.edu/psds/docs.htm
http://www.coastal.crc.org.au/coast2coast2002/proceedings.htmlhttp://www.cne-siar.gov.uk/minch/coastal/coastal1-06.htm#P1407_126482
http://www.beachdrainage.com/
www.ieindia.org/publish/cv/1103/nov03cv3.pdf
http://coastal.tamug.edu/capturedwebsites/cepraconference/glo_coastal_presentations/samplejay/sld001.htm
http://www.scourcontrol.co.uk/academic.html ; http://www.scourcontrol.co.uk/index.html
http://www.artificialreefs.org/
www.delos.unibo.itwww.delos.unibo.it
See also References and Websites in the paper
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Thank you
engineered solutions for an innovative world
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(never) good enough !!???
The knowledge is in continue development/transition;
we have to follow these developments
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Thank you
The End
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