02 coastal stabilization and alternative solutions

1

COASTAL STABILIZATION AND ALTERNATIVE SOLUTIONS

including Geosystems IN INTERNATIONAL PERSPECTIVE

• Krystian Pilarczyk, The Netherlands; k.pilarczyk@planet.nl

2

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; k.pilarczyk@planet.nl(see also CEM 2002)

3

Example of coastal erosion:Typhoon Damrey 27Sept’05 Vietnam

4

(Alternative) systems and materials

in

5

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

6

• 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.

7

Systems & Materials

Headlands

examples

8

Direct & In-direct protection

Reduction hydraulic loading

9

Granular materials:

from sand to rock

Systems & materials:examples

Prefabricated systems

10

Identification of coastal problem

and

Functional Design

Starting point

Selection technology

See also:http://www.unesco.org/csi/pub/source/ero18.htm

11

Coastal basics/principles

• Sediment transport capability

• Episodic (Storm) erosion vs. structural erosion

• Coastal control measures

• Efficiency

• Alternatives

12

Problem definition

Jan van de Graaff, TUDelft

13

14

15

Problem analysis

Restored cross section: sand nourishment

Cross section after coastal recession

Cross section eroded:

sand nourishment on dune and/or beach

17

‘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

18

19

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

20

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

21

Headlands, groynes and offshore breakwaters

22

23

24

• 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)

25

Headlands and groynes

26

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

27

Groynes (see CEM 2002)

28

29

Sedimentation polders

Netherlands

Thailand

30

(CEM 2002)

31

32

Some remarks on Low-crested Structures (LCS)

See also: www.delos.unibo.itSee also: www.delos.unibo.italberto.lamberti@mail.ing.unibo.italberto.lamberti@mail.ing.unibo.it

DELOS

33

Distribution of waves along the center of reef (Ohnaka&Yoshizwa, 1994)

Functions and definitions

or beach

34

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

35

Functionality of offshore breakwaters in relation with sediment transport

J. Van der Graaff, TUDelft

36

DK

Close to the coastline

UK

Holly Beach US

Far from the coastline;

37

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

38

(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

39

Distribution of H1/3 along the center of reef

Reduction of wave height

Reduction of wave period

Prototype measurements for Yugawara reef, Japan

40

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

41

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):

42

Comment on functional design

Use 2- or 3D numerical models for functional design

43

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

44

Artificial reefs Reef Balls

http://www.artificialreefs.org/

Aquareef Japan

rubble stone Aquareef

cage of reinforcing bars

(onshore)

foot protection block

(5t)

(offshore)

45

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

46

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

47

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

48

http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=ARTICLES;349

Cape May Point, New Jersey Section 227 Demonstration Site

49

Some other systems

• DRIM distorted ripple mat

• Beach drainage

• Gravel beaches

• Geosystems

• Etc.

51

DISTORTED RIPPLE MAT (Japan)

Concept of DRIM mat

52

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

53

Gravity drainageJapan

http://www.pari.go.jp/bsh/ky-skb/hyosa/hpj/english/02menb/yana/yana.htm

54

Gravel beaches

Granular materials are still the most popular materials / systems

55

Geosystems

Geomattresses

Geobags

Geotubes

Geocontainers

Geocurtains

Artificial seaweed

Etc.

56

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.

57

before and after the storm

Geomattresses

58

Sandbags Suriname

Coronie

after first storm

Sandbags

59

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

60

Applications Geobags

Hannover tests

61

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

62

Geotubes

New developments

63

Geotubes and design aspects

64

Failure modes: design aspects & execution

65

Design Geotubes:Shape & strength

PalmertonPalmerton

66

Geotubes

Pocked beach

67

Failures (US examples)

Hole in geotube

68

AmWaj Island, Bahrein

at low water

Example of project:

69

Transmission characteristics of reefs for AmWaj Island, Bahrein; Delft Hydraulics, 2002

For preliminary design

70

Execution

AmWaj Island, Bahrein

Offshore breakwater at design water level CD+3.5 m

50 m

71

Leshchinsky’s programmaDesign and execution

with geotubes

73

Non-woven

WovenGeocontainers

74

Geocontainers

75

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

76

Other geosystems

Artificial seaweed

anchorhttp://www.scourcontrol.co.uk/academic.html ; http://www.scourcontrol.co.uk/index.html

77

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.

79

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.

81

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.

82

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.

83

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

84

Thank you

engineered solutions for an innovative world

85

(never) good enough !!???

The knowledge is in continue development/transition;

we have to follow these developments

86

Thank you

The End

88

90