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Effectiveness of low-crested (submerged) breakwater in wave attenuation

by

Mohd Ayub Mohd Yaakob

Dissertation submitted in partial fulfillment of the requirement for the

Bachelor of Engineering (Hons) (Civil Engineering)

JUNE 2010

Universiti Teknologi PETRONAS Bandar Seri Iskandar

31750 Tronoh

Perak Darul Ridzuan

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CERTIFICATION OF APPROVAL

EFFECTIVENESS OF LOW-CRESTED (SUBMERGED) BREAKWATER IN WAVE ATTENUATION

by

Mohd Ayub Mohd Yaakob

A project dissertation submitted to the Civil Engineering Programme Universiti Teknologi PETRONAS in partial fulfilment of the requirement for the

Bachelor of Engineering (Hons) (Civi Engineering)

Approved:

Assoc. Prof. Ahmad Mustafa Hashim

ýý

Project Supervisor

UNIVERSITI TEKNOLOGI PETRONAS TRONOH, PERAK

June 2010

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CERTIFICATION OF ORIGINALITY

This is to certify that I am responsible for the work submitted in this project, that the original work is my own except as specified in the references and acknowledgements, and that the original work contained herein have not been undertaken or done by unspecified sources or persons.

Mohd Ayub Mohd Yaakob

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ABSTRACT

Nowadays, submerged offshore breakwater has been constructed widely all over the world as one of the coastal protection scheme. The main purpose is to attenuate incoming wave and thus alter the wave condition on the lee side. This research deals with low crested (submerged) offshore breakwater. The objectives of this research are to find out the relationship between the variables of factors affecting wave attenuation and to produce a well research in producing an effective and optimum design of submerged offshore breakwaters. In this report, the author has outlined the methodology on how the research has been conducted in the laboratory followed by the analysis of the results and comparisons with the previous researchers. This research is focused mainly on two variables that affect the wave attenuation which are depth of submergence and crest width of the structure. The result shows that these two variables do have effect on the wave attenuation where their relationships are the wave attenuation is inversely proportional with the crest width while the wave attenuation is directly proportional with the relative crest elevation.

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ACKNOWLEDGEMENTS

First and foremost, I would like to show my highest gratitude towards Allah for giving me opportunity to work in my Final Year Project from the beginning until the end, InsyAllah. This opportunity is one of the greatest moments for me in learning so many things and His endless knowledge in this world. May Allah bless me for this project and my life ahead.

Secondly, I would like to thank my Final Year Project Supervisor Assoc. Prof.

Ahmad Mustafa bin Hashim for his guides and assistances throughout this project.

Even though there are some difficulties and obstacles, he would not give up on me from the very beginning towards the end. I believe there is not such a thing in this world that could repay his kindness and may Allah pay him with great rewards in this world and hereafter.

Not to forget special thanks to Mr Meor Asniwan and Mr Idris, the Ocean &

Offshore Laboratory technician for helping me during the laboratory testing. To build a breakwater in the laboratory really needs advices and their helps so that the progress will become smoother. I really appreciate your helps and advices throughout this Final Year Project. May Allah bless you all.

To my colleagues, Mr Muhammad Aminudd n bin Zulkefli, Mr Mohd Faiz Ikhwan bin Abdullah and Ms Azlina Aminulla, working under the same supervisor will be the nice moment when we are holding meeting together in a room. Your ideas, helps, advices and guidance throughout this Final Year Semester are really appreciated. Hope Allah will reward each of you with Jannah.

And last but not least, to all people surroundings that helping me directly and indirectly, I would say millions of thanks and may Allah bless on what you are doing in this world.

Thank You.

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TABLE OF CONTENTS

ABSTRACT

... i

ACKNOWLEDGEMENTS ... ii

LIST OF TABLES ... v

LIST OF FIGURES ... vi

LIST OF ABBREVIATIONS ... viii

CHAPTER 1 INTRODUCTION ... 1

1.1 Background of Study ... 1

1.2 Problem Statement ... 2

1.3 Objectives ... 2

1.4 Scope of Study ... 2

CHAPTER 2 LITERATURE REVIEW ... 4

2.1 Basic Characteristic of Submerged Breakwater ... 4

2.2 Advantages of Submerged Offshore Breakwater ... 6

2.3 A Monitoring Study on Offshore Submerged Breakwater ... 7

2.4 Factors of Consideration for Offshore Submerged Breakwater ... 8

2.5 Reef Breakwater ... 9

2.6 Breakwater Structure Design Guideline ... 9

2.7 Relationship between Factors Affecting Wave Attenuation ... 13

2.7.1 Research about Run-up Height Problem at Leeward Side... 14

2.7.2 Research about Prediction of Performance of Submerged Breakwater ... 15

2.7.3 Research about Porosity of Submerged Breakwater in Non- Breaking Wave Condition ... 16

CHAPTER 3 METHODOLOGY ... 19

3.1 Laboratory Testing ... 19

3.2 Data Analysis ... 23

CHAPTER 4 RESULT AND DISCUSSION ... 24

4.1 Literature Review (Past Research) ... 24

4.2 Laboratory Result & Discussion ... 25

4.3 Errors and Modification ... 29

CHAPTER 5 CONCLUSION AND RECOMMENDATION ... 31

5.1 Conclusion 31

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5.2 Recommendation

... 32 CHAPTER 6 ECONOMIC BENEFIT

... 33 6.1 Emerged and Submerged Breakwater ... 33 REFERENCES

... 35 APPENDICES

... 38 Appendix A pictures during lab testing ... 39 Appendix B

... 42 Appendix C

... 43 Appendix D

... 48

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LIST OF TABLES

Table I Design parameter tested in the research (Seung et. al 2007) ... 14 Table 2 Breakwater Configuration Model

... 19 Table 3 Wave Characteristics

... 20 Table 4 Breaking Wave Height

... 21 Table 5 Gantt Chart

... 48

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LIST OF FIGURES

Figure 1 Basic parameter of a submerged breakwater ... 5

Figure 2 Overview of submerged breakwater tested in a research (Rambabu and Mani 2005) ... 16

Figure 3 An experimental set up in a laboratory testing (Sidek, F. J., Abdul Wahab, M. A. J., 2007) ... 17

Figure 4A physical model to be tested in laboratory ... 18

Figure 5 Result on comparing porosity values from present and past study (Sidek, F. J., Abdul Wahab, M. A. J., 2007) ... 18

Figure 6 Plan view of Breakwater with core unit and armor unit ... 21

Figure 7 Back view of Complete Breakwater ... 22

Figure 8 Submerged Breakwater in The Wave Tank ... 22

Figure 9 From wave absorber side ... 22

Figure 10 Transmission coefficient over and through low-crested structures ... 24

Figure 11 Transmission coefficient for regular wave at rubble-mound breakwater (Tanaka, 1976) ... 25

Figure 12 Comparison graph between data tested and Tanaka's graph ... 26

Figure 13 Comparison of result of submerged and emerged breakwater with the Tanaka's graph ... 28

Figure 14 Difference of crest level of emerged and submerged breakwater (Francisco T. P and Ana Christina, 2004) ... 34

Figure 15 Core Unit of Breakwater ... 39

Figure 16 Difference in wave height with the existence of submerged breakwater ... 39

Figure 17 When the waves hit breakwater ... 40

Figure 18 The wave generator ... 40

Figure 19 The wave gauges and vectrinox ... 41

Figure 20 Function of Breaker Index and Graph of Breaker Index ... 42

Figure 21 Comparison between tested experimental data ranges with Tanaka's graph for submerged breakwater ... 43

Figure 22 Comparison between tested experimental data ranges with Tanaka's graph for submerged & emerged breakwater ... 44

Figure 23 Comparison between tested experimental data ranges for 0.1 wave height at submerged breakwater ... 45

Figure 24 Comparison between tested experimental data ranges for 0.15 wave height at submerged breakwater ... 46

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Figure 25 Comparison between tested experimental data ranges for 0.2 wave height at submerged breakwater ... 47

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LIST OF ABBREVIATIONS

F- freeboard

H- the height of the structure above the bottom

d- the water depth at the seaward toe of the structure Kr - is the wave transmission coefficient

Ht - the height of the transmitted wave on the landward side of the structure

H; - the height of the incident wave on the seaward side of the structure

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CHAPTER 1 INTRODUCTION

Offshore breakwaters are constructed to bring about wave attenuation, primarily through selective breaking of the highest waves and promoting sand accretion in the sheltered area. It is generally used to protect inlet, beaches and harbours from the wave action directly. There are various kinds of structures for offshore breakwater to be constructed depending on the suitability and conditions of the coastal areas such as emerged or submerged offshore breakwaters. However, in this research, the author is focusing mainly on the submerged offshore breakwaters specifically on the structure

itself.

1.1 Background of Study

In design criteria of an offshore breakwater, there are lots of aspects that have to be considered. Other than external aspects such as wind, wave heights and directions, the designer should know how to design an effective structure which is economical and fully functional. A well study on the structure of the breakwater is needed due to the higher popularity of this type of breakwater compared to emerged ones in engineering practices nowadays.

Some guidelines for the purpose of designing an offshore breakwater also discussed in the literature review to provide an overview related to varying variables in order to produce an optimum design. In this research, the author investigated the responses of various design aspects on the structure itself under different wave conditions. The important variables pertaining to the geometrical features if such breakwater include its height, width, side slopes of the structure and the crest freeboard.

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At the end of the study, the author has produced a relationship between the factors affecting the wave attenuation towards the effective design of a low crested offshore breakwater.

1.2 Problem Statement

A well designed low crested breakwater scheme will serve as another technical solution to coastal erosion while offering as attractive feature that can satisfy local aesthetic requirement. Several earlier studies have been carried out to develop understanding and to derive related general design criteria.

Current conditions are more challenging than before. More optimize and innovative design is required not only to obtain a more economical costal protection structure but also more effective and aesthetic. Further research is necessary to explore further understanding and derive more representative relationships. Thus, this research investigates the performance of various geometrical combinations under different testing wave conditions.

1.3 Objectives

The objectives of my project are:

i. To investigate the relationship between the variables of the factors affecting wave attenuation specifically on crest width and depth of submergence.

ii. To produce a well research in producing an effective and optimum design of submerged offshore breakwaters.

1.4 Scope of Study

There are several factors related to the structural geomtry that affecting the wave attenuation such as height of the breakwater, width of the structure, side slopes and etc. However, the only factors that will be varied are the crest width of the structure and the depth of submergence in order to produce optimum and effective design of submerged offshore breakwaters.

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Thus, the scope of study covered;

i. The relationship between the factors that influence the wave attenuation such as depth of submergence, widths and etc.

ii. The relationship between the shape of the structure with the varied waves characteristics such as wave height and velocity.

iii. A study on existing project of submerged offshore breakwater based on the external resources data given by consultants or Department of Irrigation and Drainage, Malaysia.

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CHAPTER 2 LITERATURE REVIEW

Offshore breakwater is one of the coastal protection schemes. The main purpose is to induce wave attenuation coming from the sea. The presence of the offshore breakwater itself will alter the wave condition on the lee side. This research deals

with low crested and submerged offshore breakwater. The author has reviewed various related journals and books where the findings are presented in this chapter.

The low crested and submerged offshore breakwater is becoming very popular in the engineering practices nowadays. In order to achieve the purpose of offshore breakwater which is reducing the hydraulic loading to the respective level, the breakwater structures are designed to allow limited transmission of the wave energy through over the structure by wave breaking and energy dissipation on shallow crest (Pilarczyk, 2003).

Many seawalls and vertical caisson breakwaters (CIRIA, 1986b; Oumeraci, 1994) around the world are being damaged due to some factors of failures. It may be due to extreme wave actions, through displacement of the entire structure, or a failure gradually starting from the weakest point, or from the failures of the base of structures, or due to overtopping and toe erosion (Muni Reddy, 2004). Thus, in some cases, offshore breakwaters are effective alternative in reducing impact of direct incoming waves.

2.1 Basic Characteristic of Submerged Breakwater

In order to examine the performance of a submerged breakwater, there are some characteristics where involved in wave attenuation that need to be considered. These characteristics are important and are further discussed in this chapter.

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Below is the overview of the submerged breakwater structure.

ý still watet 1e-, -e iSW ) fieeborud =F

=h -d watri drpth =d

submerged breakwater

structme CI? 5l

wlilth= B S11llcºllIe

hei`ýit = It

, r-bottom

structure base width

Figure 1 Basic parameter of a submerged breakwater

The freeboard is defined as the structure height minus the water depth, F=h-d

where F is the freeboard, h is the height of the structure above the bottom, and d is the water depth at the seaward toe of the structure.

The dimensionless parameter for the relative freeboard is the freeboard ratio, which is defined as the freeboard divided by the water depth,

F h-d hd HHHh

With this definition of the freeboard ratio, an emergent or sub aerial breakwater has a positive value for the freeboard ratio (F/d > 1.0), while a submerged breakwater has a negative value for the freeboard ratio (F/d < 1.0).

These three dimensionless quantities, d/h, h/d, and F/d, indicate the relative height of

the breakwater compared to the water depth, and are used to determine the magnitude

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of the wave and current forces on the breakwater, and the effectiveness of the structure in attenuating wave energy. Another important dimensionless parameter used for determining the interaction between the waves and a breakwater structure is the freeboard divided by the wave height, which can be expressed as:

F h-d hd HHHh

where H is the height of the wave, measured from the bottom of the trough to the top of the crest. The use of the wave height in this ratio provides a direct comparison between the height of the structure above or below the still water level, and the height of the waves impacting the structure.

The effectiveness of a breakwater in attenuating wave energy can be measured by the amount of wave energy that is transmitted past the structure. The greater the wave transmission coefficient, the less the wave attenuation. Wave transmission is quantified by the use of the wave transmission coefficient,

K` Ht Ht

where KK is the wave transmission coefficient, H, is the height of the transmitted wave on the landward side of the structure, and H; is the height of the incident wave on the seaward side of the structure (U. S. Army Corps of Engineers, 1984).

2.2 Advantages of Submerged Offshore Breakwater

According to Aminti et al. (1983), in some respects shared by an author, the submerged breakwater is better than emerging one which typically designed as long continuous structures thus avoiding gaps and drawbacks connected with them. The long shore transport is also partly intercepted by the growing cusp, sometimes arrested altogether if a tombolo arises. Thus, the submerged breakwater will dissipate

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wave energy, usually even more efficiently than the emerging breakwater counterparts does in the same situation (Pilarczyk, 1996).

On another aspect, the submerged offshore breakwater also more aesthetic in appearance as compared to unsightly emerged breakwater. Thus, many resorts prefer to build submerged offshore breakwater rather than emerging ones. The construction cost for the submerged offshore breakwater is also less expensive than the emerged breakwater as the structure is built not as high as the emerged breakwater. Thus, it is an economical construction.

The crest elevation of the offshore breakwater is an important design consideration as it affects the water level on the lee side of the structure. Longuet-Higgins (1967) had developed a theory for submerged breakwater based on momentum considerations and no wave energy dissipation that demonstrated the increase in water level. Another two dimensional models studies by Diskin et al. (1970) showed that when the water overtopping the breakwater, it will increase the water level at the side nearby the coastal area. It was found that the increasing water level at the lee side is inversely proportional with the decreasing still water submergence to a maximum water level where the structure crest elevation was approximately 0.7 times the incident wave height.

2.3 A Monitoring Study on Offshore Submerged Breakwater

Funakoshi et al. (1994) conducted a monitoring study about submerged breakwater at Nigita on the Western shore of Honshu Island in Japan where the breakwater is constructed in a water depth of 8.5 m, 540 m long, 400 m from the shore, with crest elevation of 1.5 m. Groins of 200 m long located near each end of the breakwater extend a substantial distance toward the breakwater, resulting in a partial compartmentation in the lee of the breakwater. After a period of 5 years, wave and current data were collected both landward and seaward of the breakwater. Based on his monitoring study during the storm events, there was a net horizontal current divergence from behind the breakwater consistent with the interpretation here of water overtopping and redirection of this water in the alongshore direction.

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Furthermore, scour of about 1m was observed immediately at the landward of the breakwater.

2.4 Factors of Consideration for Offshore Submerged Breakwater

As outlined by Hanson and Kraus (1989,1990,1991), shoreline response to the offshore breakwater is controlled by at least 14 variables where nine of the variables are considered primary which are;

1) Distance offshore

2) Length of the structure

3) Transmission characteristic of the structure

4) Beach slope and/or depth at the structure (controlled in part by the sand grain size)

5) Mean wave height 6) Mean wave period

7) Orientation angle of the structure 8) Predominant wave direction

9) Gap between segments (for segmented detached breakwater)

The efficiency of submerged breakwater (reefs) and the resulting shoreline response primarily depends on the layout of the structure and the transmission characteristics.

From the eight primary variables, four variables are related to the structure of the offshore breakwater which is distance offshore, length of structure, transmission characteristic of the structure and the orientation angle of the structure (Hanson and Kraus (1989,1990,1991).

The efficiency of the submerged breakwater depends on the crest free board, crest width and permeable material characteristics. Many researchers have studied on the wave transmission and reflection characteristics.

Based on the monitoring study on submerged breakwater and model studies by Dean

et a1. (1997), the results indicated that the detached breakwater modified both the

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wave and current fields which are depending substantially on the crest elevation relative to the still water level.

However, there are not many papers are concerning on the related topic such as reduction of forces to seawall by the breakwater. For partial barrier of any configuration, irrespective of the porosity and flexibility, full reflection always occurs when the distance between the end-wall and the barriers is an integer multiple of half- wave length hence overturning and moment will be vanished (Yip et al. 2002).

2.5 Reef Breakwater

One of the most popular types of submerged offshore breakwater is the reef breakwater. The advantages of the reef breakwater are it can be effective shoreline protection with low environmental impact only if it is implemented in conjunction with beach nourishment. Reef breakwaters is a structure where it is permanently submerged detached breakwaters and most often are constructed from rubble mound structures. Another alternative material used for the construction include special shaped concrete blocks, geotubes, reef "balls", and any suitable material in order to create an artificial reefs and submerged sills ( Valeri Penchev et al. 2005).

As described by Valeri Penchev et at. (2005), the reef breakwater provides some space at the top of the structure for the water flow circulation in order to avoid stagnant zones where the water cannot move freely and stuck at a place. By using the reef breakwater, the water will circulate over the structures without any obstructions between the reef and the shoreline;

2.6 Breakwater Structure Design Guideline

The material of armour type/weight used for the reef breakwater can be stone or concrete depending on the site condition suitability, cost, required lifetime of the structure and others.

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Generally, the selection of the armour type whether stone or concrete is depending on the height of the design wave and the availability of the materials. However, these are some guidelines in choosing the material (CIRIA, 1991);

i) Stones are used when:

1) Design wave conditions are relatively moderate, less than about 4.5m 2) Suitable rock is economically available to meet the required design

criteria.

ii) Concrete is used when:

1) Design wave is substantial requiring greater interlocking wave energy absorption.

2) Suitable quarried stone is not available for the rubble mound breakwater.

3) Controlling runup is a critical design criterion.

The crest height is determined based on the wave transmission, constructability, structural integrity, functional use and aesthetics all must be considered. A higher crest can provide a wider platform (for any given elevation) for shore side construction while the lower crest will provide an improved view but might expose any kind of structures at the shoreline to the problem of overtopping waves. Thus, factors to consider include:

1) Wave conditions such as height, period, depth of water 2) Acceptable level of overtopping and/or transmission

3) Constructability based on equipment working from crest during high tides

4) Armour stability and lifecycle cost

5) Functional use as road access to dock or other facility 6) Aesthetic for panoramic view of open water

7) Wind break

On permeable structures subjected to long wave period, low crested breakwater heights may allow unwanted wave action in harbour due to wave transmission. If the

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core is impermeable, the wave may be transmitting through the crest. Thus, increasing crest width may help (ACSE, 1982).

Usually the crest width is governed by the size of the primary armour and other considerations include the method used to place the armour units (barge/crane or access from shore), and the functional use of the breakwater (e. g. road). Among the factors considered in designing the crest width:

1) Wave conditions such as height, period, angle of obliqueness and local water depth

2) Functional use

3) Construction methods and/or availability of local equipment and material

When calculating the breakwater overtopping, the leeward side should be designed for breaking wave impact and generally the crest width dimension has a minimum of three armour stones wide (U. S Army Corps of Engineers Dept., 1984).

The side slopes are designed for stability based on the site-specification conditions.

Typically, the cost of producing quality armour rock will determine the slope angle.

A more gradual slope allows use of smaller armour units, which may reduce the costs and create a more stable structure. The slopes are normally not steeper than 1: 1.5 and not flatter than 1: 5 unless using a dynamically stable beach. The leeward slope is usually 1: 1.5. In order to design the side slopes, the following need to be factors that have to considered:

1. Wave conditions such as height, period, angle of obliqueness and water depth

2. Hydraulic boundaries : tides, currents, seismic activity, sediment processes, run-up, run-down, overtopping, transmission, reflection 3. Availability of suitable local quarried stone

4. Construction methods and capacity and reach of available equipments

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Based on ASCE (1982) guidelines, a soft foundation material may need a more gradual slope in order to distribute the load and if the local rock produced is of good quality but smaller sizes, consider flattening the breakwater slopes to optimize use of the quarry. The slopes of 3: 1 or flatter may begin causing refracting wave and this can be used to benefit for the wave attenuation.

Wave energy is absorbed by layering several sizes of rock. A three layer sections is commonly used, however the two layers system works well for wave heights of less than 1.5 m. The armour layer for rock is normally about twice the thickness of the underlying filter. The layer thickness is normally two stone diameters. The determination of layer thickness is based on:

1) Wave conditions such as height, period, angle of obliqueness and water depth

2) Wight and grading of armour (rocks) 3) Density of armour

4) Stone quality/shape 5) Breakwater slope

6) Allowable wave run-up

Clarification of profile survey methods and surface definition may be beneficial in determining the slope thickness during construction. If controlling run-up is critical to

design, an armour layer of 3 units thick would be beneficial. (CIRIA, 1991).

In shallow water where less than about 6 m, the design of the toe is subject to scour as waves break on the structure. If possible, the preferred method of design is to place a dredged trench at the toe thereby lowering the elevation at the toe. The three stone minimum widths are commonly used for the toe.

In determining the toe details, the designer should consider:

1) Wave conditions such as height, period, angle, water depth, breaking and non-breaking waves

2) Arrangement of toe geometry 3) Construction methods

4) Weight and density of armour

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5) Littoral processes and variability in thickness and composition of bed material

The toe may be eliminated if the bed material is comprised of nearly the same size cobble as the rubble mound structure. If the bed material varies in thickness seasonally or from storm events the toe must be designed for the lowest beach elevation during the life of the structure. The breakwater toe should not be placed on flat or down sloping bedrock. Placing a large breakwater toe on the inside of the basin may become a navigation hazard and should be avoided.

A study on the existing project such as the submerged offshore breakwater at Kerteh, Terengganu shows that it is a successful project for low crest (submerged) offshore breakwater system in front of Rantau Petronas Complex. The three breakwaters were built in an optimum way in relation to the boundary condition imposed by the down coast headland, while still stabilizing the entire coastal stretch in front of the complex.

An initial nourishment of 400,00 m3 would be required to reduce erosion problem of the actual shoreline during salient formation.

Hence, a system where 3 segmented submerged offshore breakwaters and well dimensioned placed alongshore, constitutes a defense scheme with the purpose to reduce erosion problems in front of and down coast of Rantau Petronas Complex.

The size of the breakwaters varies according to the requirements which included two 400 m long breakwaters some 600 m apart, followed by a 200 m breakwater some 400 m down coast, at a distance about 200 m offshore. This coastal protection is combined with nourishment of 10,000 m3 at the north side, 200,000 m3 at the south

side and a further 100,000 m3 spread along the coastline section.

2.7 Relationship between Factors Affecting Wave Attenuation

Many journals and articles related to the submerged breakwater have been referred.

This has help in providing reasonable understanding and thus determined the laboratory testing that have been carried out in this research.

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2.7.1 Research about Run-up Height Problem at Leeward Side

Seung et al. (2007) have addressed this problem where the mean sea level at the leeward of the rubble mound breakwater has been observed raised. As the result, the erosion problem has occurred and it makes the rate of erosion bigger. Thus, the researchers have made an investigation on how a submerged breakwater can be placed in front of the rubble mound breakwater and reduced the water level at the leeward of the rubble mound breakwater. In order to produce an effective submerged breakwater, the researchers have investigate several factors affecting the wave attenuation such as height of the structure, width and the distance between the submerged breakwater of the rubble mound breakwater.

For the laboratory testing purposes, the researchers also give different wave heights to the structure in order to observe the performance of the submerged breakwater.

However, this research has specifically investigated several factors only such as width, height of the structure while others are constant. The variables that have been tested in the experiment are listed in Table 1:

Table 1 Design parameter tested in the research (Seung et. al 2007)

Variable Range

Significant wave height 6,8,10,12,14 cm

Significant wave period 1.4,1.8,2.2,2.6,3.0 sec

Submerged structure width 25,50,75 cm

Submerged structure height 25,35 cm

Distance between structure 1.0,1.25,1.50 m

Water depth 50 cm

Breakwater height 90 cm

Tetrapod weight 640 g

Breakwater slope 1: 1.5

Permeability coefficient 0.5

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At the end of this experiment, the researcher found out that the run-up height is affected with the existence of the submerged breakwater. From the result, the water level at the leeward side can be reduced by 30% - 100% after the installation of the submerged structure and it is dependent on the relative height. The width of the submerged structure also affecting the run-up height where the wider the structure, the lower the run-up height.

Another observation on the wave steepness parameter have been made where in the relative height of 0.5, the run-up height increases while at relative height 0.7, the run- up height shows no certain pattern. It may be due to the decreasing in wave energy when the wave breaks at the crown of submerged structure and the reflection by the submerged structure. Furthermore, the relative distance does not play major role in affecting the run-up height at the leeward side of the breakwater. (Park et al. 2007).

2.7.2 Research about Prediction of Performance of Submerged Breakwater

Rambabu and Mani (2005) have done a research on numerical model on the prediction of the performance on the submerged breakwater based on numerical model. This study is made based on the past studies on solid and permeable type submerged breakwater determined that when the breakwater nears zero submergence, it can reduce the incident wave energy about 50% (Dick and Brebner, 1968).

Earlier study by Seelig (1980) discovered that the top width and depth of

submergence play major roles in evaluating the performance where the near zero

submergence structures will reduce the incident wave energy efficiently.

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Cc 7. iýT1IIl: Tr, ý. n>i..: ^: cl'ý: aý: _ 4

I1i, 132-. t v 9`: c

4 -

ý ý

Figure 2 Overview of submerged breakwater tested in a research (Rambabu and Mani 2005)

Based on Rojanakamthorn et al. (1989) works on the performance of submerged breakwater, Based on mild slope equation, if the height of the structure is half of the water depth, the transmission coefficient is varied between 0.4 to 0.7.

This research found that the relative depth does have effect on the transmission coefficient, KT. It was suggested that at dS/d<0.625 and H; /gT2>0.006, the breakwater will be able to reduce the incident wave about 60%. The reseacher also recommending the crest width of the breakwater affecting the KT where the optimum ratio of B/d is 0.75. At the end, the reseacher also did some test on series of breakwater and found that the clear spacing between the breakwaters are not much affecting the transmission coefficient, KT. (Rambabu and Mani, 2005).

2.7.3 Research about Porosity of Submerged Breakwater in Non-Breaking Wave Condition

Sidek and Abdul Wahab (2007) have done a research on effects of porosity of submerged breakwater on wave attenuation. The research is conducted by using several physical models and tested in laboratory.

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It has been done with respect to several coefficients such as;

i. Transmission coefficient, KT ii. Reflection coefficient, KR iii. Wave energy loss, KL

This research was made based on several references from past research such as Dattatri et at. (1978) where the experiment is about the effects of porosity on the wave transformation over the permeable submerged breakwater using a range of porosity which were 1 (a thin plate), 0.42,0.41 and 0 (impermeable). The researcher

concluded that these small values of porosity do not have significant effects on the transmission coefficient, KT. Other works by Gu and Wang (1991), Losada (1995 1996), Huang (2003) and Ting et at. (2004) covered similar experiment but with different range of porosities between 0.35 to 0.42.

Thus, Sidek and Abdul Wahab (2007) have come out with another set of range for the values of porosity in order to investigate the effectiveness of porous submerged breakwater in wave attenuation under varying the wave conditions. Sketch showing the experimental set-up and photos of the physical model of the porous breakwater are shown in Figure 3 and 4.

:; ; -h 1 D-1 ; 1cumz

Mýxie_ II

ý , '4 L:

Figure 3 An experimental set up in a laboratory testing (Sidek, F. J., Abdul Wahab, M. A. J., 2007)

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--: ý >'ýýL°Jlt .. ý. =ifR.

- -. --- _.. ____

. S LS . ý.

9: n

sttý. sat fraLxw'crc _ Sc:. Sm

a Sketched dmieusious oT the to t model rectaugtilar steel

Li The isbricated fr3Illewoik tL: ed

in The t2ýt series

Figure 4A physical model to be tested in laboratory (Sidek, F. J., Abdul Wahab, M. A. J., 2007)

R. S11lTS II0111 The })I: S: 11T llit-zST1Q:? ilOlli Results IIOn1 TmQ ei al ý=UO41 toiCl.

ii=U3 20I11_li=U. '_

Poro-.; in- n: 1» Ký Porosity

U. 40 0.; --U. ý" 0-11-0.351 0. -9-0.9: 0.421 O. 5U-0. -6 0.0ý-0? 0 U. 6? -0. S?

0. (%0 fý. 44-0 6) 0,06-0.27 U.. rSS 0 6-0

. SO 0.01-0.19

0.30 0.01-0.24 U. -1-U. S3- O. Sfý; 0-ý-0.51 0.02-0.10 0.53 -0.68 Figure 5 Result on comparing porosity values from present and past study (Sidek, F. J., Abdul Wahab, M. A. J., 2007)

Based on the table of result from the research and other past result of researchers, here are some conclusions that have been made with respect to the tested variables:

i. The porosity has slight effects on transmission coefficient, KT where the highest value of Kt is 0.7 for the porosity of 0.80.

ii. The reflection coefficient, KR is decreased with the increasing porosity where the highest value of KR 0.31 is at the lowest tested porosity.

iii. The wave energy loss, KL also decreased with the increasing porosity value where the lowest wave energy loss, KL 0.71 occurs at the highest porosity value.

L. .,.

- _ýý ýý'ýr°yn`.. C.. Y. _iý

ý-ýý ý--. ý: rr: sýý. °

. ?., u-

9a cm Tr-r., a% 04 it T

'" 149 a aM a o"

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CHAPTER 3 METHODOLOGY

This chapter presents the methodology adopted in this project. The main experiment involved physical model executed in the laboratory.

3.1 Laboratory Testing

The laboratory testing was conducted using several physical models of a submerged offshore breakwater in the Offshore and Ocean laboratory. The physical models were made with various dimensions in crest width and depth of submergence so that the result covers part of the gaps left by previous experimental testing.

In this test, several models were made by emulating typical arrangement of submerged breakwater at the site with various crest width and depth of submergence.

In order to determine the effect of these 2 parameters, the experiment maintained other factors constant such as height and slope of the structure. Below is the table that contains all variables involved in the testing.

Table 2 Breakwater Configuration Model

Series

Code

Submergence Depth, R,,, (m)

Crest Width, B (m) Front Slope, 0

Al 1.0 1: 1.5

A2 0.0 1.25 1: 1.5

A3 1.5 1: 1.5

B1 1.0 1: 1.5

B2 0.1 1.25 1: 1.5

B3 1.5 1: 1.5

CI 1.0 1: 1.5

C2 0.2 1.25 1: 1.5

C3 1.5 1: 1.5

DI 1.0 1: 1.5

D2 0.3 1.25 1: 1.5

D3 1.5 1: 1.5

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The test series were determined to investigate range of working conditions and covering various crest width and depth of submergence.

By having several models tested, the laboratory testing also varied the incoming period and height of the wave in order to produce range of results for different

conditions. Table 3 provides the range of wave conditions used in the investigation.

Table 3 Wave Characteristics

Wave Series Wave Height (m) Period (s)

wl 0.1 1.75

W2 0.1 2.5

W3 0.1 3.5

W4 0.15 1.75

W5 0.15 2.5

W6 0.15 3.5

W7 0.2 1.75

W8 0.2 2.5

W9 0.2 3.5

A simple calculation is made in order to ensure the wave is not breaking before hitting the front side of breakwater. It is important to the breakwater to receive the real wave condition in order to ensure the structure is not affected with the common wave conditions.

Checking the wave breaking condition, Hb

Where Hb / db = Breaking index (refer attachment for breaking index graph) Hb = breaking wave height

db =water depth

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Based in a "flat" nearshore slope (tan 0.00) used in the experiment, the breaker index was taken as approximately 0.78.

The breaking wave heights then were estimated using this formula where, Hb

Hb = 0.78 * db

Thus, the expected breaking wave height for different water depths used in the experiment can be tabulated as in Table 4.

Table 4 Breaking Wave Height

Water Depth (m) Breaking wave height, Hb (m)

0.4 0.312

0.5 0.390

0.6 0.468

0.7 0.546

From the table above, it shows that the lowest breaking wave height is 0.312 m which is above the highest produced wave height by the wave generator in the experiment.

Thus, the wave will not break before it hits the breakwater. Figure 6,7,8 and 9 will show the construction process of the breakwater in the wave tank.

Figure 6 Plan view of Breakwater with core unit and armor unit

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Figure 7 Back view of Complete Breakwater

-. ý-ft

Figure 8 Submerged Breakwater in The Wave Tank

Figure 9 From wave absorber side

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Before the experiment was executed, the wave gauges used in measuring the wave height were calibrated. The calibration was made for every change in water depth. It has to be done in order to ensure the wave height is measured correctly where the incoming and transmitted wave is accurate according to the determined values.

3.2 Data Analysis

After the laboratory testing were finished, the data was analyzed based on several criteria in order to relate with previous data from past researches. This is important to

give a better view on the result of the tested data.

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CHAPTER 4

RESULT AND DISCUSSION

After reading several journals and articles about the same test executed by previous researchers, the author found that there are some gaps that can be filled with some ranges in order to complement results from previous studies. It involved range of crest width and the depth of submergence.

4.1 Literature Review (Past Research)

Figure 10 Transmission coefficient over and through low-crested structures

The wave transmission is defined by the height of transmitted wave over the height of incident wave where the number will be bigger when the height of transmitted wave is higher. It means that the higher the wave transmission, KT the less effective the structure in attenuating the incoming waves.

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Based on the literature review from Chapter 2, it can be expected that the longer crest width will contribute to lower wave transmission, KT, while the narrower crest width will contribute to higher wave transmission, KT.

to 0.9 -1! 0.8 C 0.7

U a. a C ýe. 3 e 0-2 F- o

-2. S -2.0 -t. S -1.0 -0. S 0 0. S 1.0 1. S 2.0 2. S

Relative Crest Elevation , hJ}

Transmission coefficient for regular waves at rubble-wound breakwater (Tanaka 1976).

Figure 11 Transmission coefficient for regular wave at rubble-mound breakwater (Tanaka, 1976)

On the other hand, the depths of the submergence of the structure have also been tested against several dimensions. As we discussed in the Chapter 2, the higher the depth of submergence will contribute to higher wave transmission that means low effective compared to lower depth of submergence.

4.2 Laboratory Result & Discussion

After series of laboratory testing of the designated test ranges, the results were compared into graph made by earlier studies by Tanaka (1976).

ý ý

ý ý

ý " ýý

"

.... .ý

-B /L. =0. t0 B/[.

o=0.0? 5

B/La = 0.2 0 =, B4=00 W

-2. S -2.0 2. S

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Comparison between experimental test ranges and Tanaka's graph

_

\

_

i.

ý' - -` +-

1.2

1 -*- B/L=0.025 ý ýý

-ft. -M- B/L=0.050

0.8 B/L=0.10

V rz

av 0

V

C 6-

0

N

0- Vf

E

N C2.5

-2

Ö/\ \2ý

-ý- B/L=0.20 -ýr-ýB/L=0.314

B/L=0.15 B/L=0.26 B/L=0.13 B/L=o.

zi

0 B/L=0.1025

-1.5 -1 -0.5 0B/L=0.0523

m

Relative Crest Elevation, he / Ho

Figure 12 Comparison graph between data tested and Tanaka's graph

Earlier findings by Tanaka (1976) were represented by the dotted line in Figure 12 while results from the current research are incorporated in the same graph as the solid line. The slope of this submerged breakwater used on this investigation was maintained at 1: 1.5 m whereby Tanaka's submerged breakwater used in the earlier experiment tested by using 1: 2.0 m.

The trend of this graph for this research is a little bit different with the Tanaka's graph since the parameter might be different in terms of incoming wave, size of breakwater, rocks type and etc. However, the main trend of this graph is about the same with the Tanaka's graph since all graphs are decreasing. It is linear with theory where the wave transmission is directly proportional with the depth of submergence.

ý ý- -

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The idea on how the depth of submergence playing a role in wave attenuation is that when the depth of submergence is increasing, the wave height will not hitting the crest of the submerged breakwater. Thus, the wave will not break at the designated area. When it is happens, the wave will not be reduced at the shoreline and it would

make the submerged breakwater is having failure in performance.

In order the correct depth of submergence, the engineers need to consider several parameters so that the submerged breakwater will be operated at its optimum design.

The parameters involved are depth of water at the designated construction, wave heights, tidal season and others.

Another parameter that has been varied in this research is the crest width. From the graph, we can see that the crest width is also play a role in wave attenuation. It is shown that the wave transmission is inversely proportional with the crest width where the smaller crest width will allow more wave transmission over the submerged breakwater.

The transmission wave over the submerged breakwater is affected when the length of the crest width is changed. In better understanding, the crest width will make the submerged breakwater has more area in order to make the wave hitting the breakwater. Thus, increasing the crest width will help the breakwater in wave

attenuation and produce calmer wave at the lee side of the submerged breakwater.

Other than these two parameters, there are more aspects that can affect the wave attenuation of submerged breakwater. However, these two aspects which are crest width and depth of submergence are selected because at the end of this research, the author want to extend the research made by Tanaka during 1976 and make a clear comparison between results produced by this research with the Tanaka's graph.

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TANAKA 1976 - Transmission coefficient for regular waves at rubble mound breakwater

1 0.9

-1.5 -1

ý 0.8

ý

\ 0.7 O. S.

b. 5 f-- ýf

ý- - Q. 4 E'

-0.5 0.5

Relative Crest Elevation, he / Ho

1 1.5

-+- B/L=0.025 -W B/L=0.050 B/L=0.10 -X- B/L=0.20 -B/L=0.209

B/L=0.1025 B/L=0.0523

Figure 13 Comparison of result of submerged and emerged breakwater with the Tanaka's graph

Graph shown above was the last test made by the author in order to make full comparison with the reference graph made by Tanaka (1976). From the graph, the negative values for relative crest elevations are representing the submerged breakwater while the positive relative crest elevations are representing the emerged breakwater.

In wave attenuation, the emerged breakwater has advantage more than the submerged breakwater where the statement is supported by presented graph above. It shows that the transmission coefficient is lower at the right hand side (emerged breakwater) rather than at the left side (submerged breakwater). However, the submerged breakwater is the alternatives other than emerged breakwater where the function is still the same which is wave attenuation.

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The only matter in this issue is the required wave height at the lee side of breakwater where it depends on the situation of the area. In some cases, it is enough to reduce the wave at the required wave height so that the area will have less impact of wave. Thus, in these cases, if the submerged breakwater can perform and produce the designated wave height at the lee side, then it would be the best choice to solve the problem.

On the other hand, the submerged breakwater is suitable for the resorts and tourism attractive places since the view from the shoreline will not be obstructed by an emerged breakwater. In this aspect, the submerged breakwater has advantages which are performing to reduce the wave impact and have aesthetical values.

Other than that, the submerged breakwater will save the total cost of construction since it requires fewer amounts of rocks. Although it might not a big issue at certain areas that can spend so much amount of money on anything, it would be a big saving in building a breakwater that will perform to its optimum design if the design criteria is effective and fully functional.

4.3 Errors and Modification

In conducting the laboratory testing, there are several errors that have happened that can cause errors in the result produced. Before the testing is conducted, all wave gauges need to be calibrated with the control computer so that the graph produced will cover all parts of wave height.

Another problem during the laboratory testing is sometimes the computer is not recording the accurate wave height produced by the wave generator. When this happens, the wave height will be measured manually at the wave tank and a correction factor will be found out in order to add or reduce the produced wave heights from the computer. This problem is caused by the error in the wave gauges calibration before the testing stated. Thus, the calibration needs to be conducted again so that the computer will generate the right values of wave heights.

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After all, during the laboratory testing, the same errors are happened when the calibration is wrong at the first place. Thus, the problem can be solved if the calibrations of the wave gauges are correct and accurate before the testing is conducted.

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CHAPTER 5

CONCLUSION AND RECOMMENDATION

At the end of this research, the author found out the relationship between the factors affecting the wave attenuation for submerged breakwater. In this research, the author decided to select two factors which are crest width and depth of submergence. This research is the extended version of the Tanaka (1976) works where the data range tested in this research is based on his works.

5.1 Conclusion

Theoretically, the crest width and depth of submergence of a submerged breakwater does have impact on wave attenuation where it was clearly shown from the reference graph made by Tanaka. From the result and discussion in Chapter 4, the result of this research is clearly found that relationships between the factors tested against the wave attenuation.

The relationships between factors affecting the wave attenuation are:

1 The wave attenuation is inversely proportional with crest width

1 The wave attenuation is directly proportional with relative crest elevation

Referring to the methodology in Chapter 3, there are 2 methods of executing this research. The laboratory testing and data analysis are made in the same time where the result from the laboratory testing has been analyzed in order to figure out their relationship. However, in order to collect external data, a visit to Department of Irrigation & Drainage at Kuala Lumpur has been conducted in order to discuss and gather some information related to this research.

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5.2 Recommendation

In order to make complete study on submerged breakwater, there are lots of aspects that can be studied where in this research, the author only cover two aspects which are crest width and depth of submergence.

Other aspect that can be varied is the front slope of the submerged breakwater. In this research, the front slope is made constant as I: 1.5 m because the research is not focusing on the slope matter. The slope can be varied in the range of 1: 1.5 m to 1: 4 m. From the graph of this research, it seems that the slope have impact on the wave attenuation.

In this research, the submerged breakwater is constructed using granite rocks taken from the quarry. Further research using various available concrete interlocking units is also recommended for future investigation.

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CHAPTER 6 ECONOMIC BENEFIT

In this chapter, the author will make a comparison between emerged breakwater and submerged breakwater in terms of the cost, where it will give more exposures on the reader due to economical aspect. The cost discussed will be only the construction cost of the respective submerged breakwater.

6.1 Emerged and Submerged Breakwater

The main difference in these two breakwaters is on the volume needed to complete the construction. The submerged breakwater has the lower volume of rocks because the crest is below the water level while the emerged breakwater has crest level above the water level. Thus, the emerged breakwater requires more volume of rocks which will cost the contractor more cost on the volume of rocks needed compared to the submerged breakwater.

On the other hand, the rocks used in the construction of breakwater are not the typical rocks found on the road. It uses granite rocks so that the endurance will be longer and stiffer than the typical rocks. Thus, the resources of these rocks are not always available at all places where sometimes it needs to be transported far away. Thus, in this matter the volume on rocks needed is very important since it will reflect to the cost.

Other than that, all the materials or type of construction is same as the emerged breakwater since the only difference in the crest level. It depends on the situation where the major concern in choosing the best type of breakwater is the wave height at the lee side. It is known that the emerged breakwater has better wave height at the lee side.

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However, if the submerged breakwater has served its optimum function where it gave the required wave height at the lee side, then why need to spend more on the cost by selecting the expensive one?

The figure shown below is showing the crest height of the emerged breakwater and submerged breakwater on its usual condition built at the respective areas.

Figure 14 Difference of crest level of emerged and submerged breakwater (Francisco T. P and Ana Christina, 2004)

More or less, the submerged breakwater has advantages more on the emerged breakwater in terms of their cost since the volume needed is much lower than the emerged breakwater. Thus, this research has it means to bring out the effectiveness of the submerged breakwater so that it can be implemented throughout the country.

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REFERENCES

ASCE Manual No. 50. Task Committee on Marinas 2000.1982. Planning and Design Guidelines for Small Craft Harbors. New York. Pg. 136-138.

CIRIA Special Publication 83. CUR Report 154.1991. Manual on the Use of Rock in Coastal and Shoreline Engineering. Rotterdam/Brookfield: Balkema, A. A. Pg. 418- 420.

CIRIA, 1986b. Sea Walls: survey of performance and design practice. CIRIA (Construction Industry Research and Information Association), London, Technical Note 125.

Dattatri, J., Raman, H. and Shankar, IN, 1978. Performance characteristics of submerged breakwaters. Proceedings of the 16th International. Conference in Coastal Engineering, ASCE, Hamburg, Germany, pp. 2153-2171.

Dean, R. G., Renjie Chen, Browder, A. E., 1997. Full scale monitoring study of a submerged breakwater, Palm Beach, Florida, USA. Coastal Eng. 129,291-315.

Dick, T. M., Brebner, A., 1968. Solid and permeable submerged breakwaters.

Proceedings of the 111h International Conference on Coastal Engineering 1968;

1141-1158.

Diskin, M. H., Vajda, M. J. and Amir, I., 1970. Piling up behind low and submerged breakwaters. J. Walterw. Harbors Div. ASCE, 96(WW2): 359-372.

Funakoshi, H., Shiozawa, T., Tadokoro, T., and Tsuda, S., 1994. Drifting characteristics of littoral sand around submerged breakwater (field study on NiigataWest Coast). In: Proceedings, International Conference on Hydro Technical Engineering for Port and Harbor Construction, Yokosuka, pp. 1157-1178.

Gu, Z., Wang, H. 1991. Gravity waves over porous bottoms. Coastal Engineering, 15; 497- 524.

Hanson, H. And Kraus, N. C., 1989. GENESIS: generalized model for simulating shoreline change. Report 1: Technical Reference, Tech. Rep. CERC-89-19, US Anny Engr., Viksburg, MS.

Hanson, H. And Kraus, N. C., 1990, Shoreline response to a single transmissive detached breakwater, Proc. 22"d Coastal Engrg. Conf., ASCE, The Hague.

Hanson, H. And Kraus, N. C., 1991, Numerical Simulation of shoreline change at

Lorain, Ohio. J. Of Waterways, Port, Coastal Engrg. Vol. 117, No. 1,

January/February.

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Huang, C. J., Chang, H. H., Hwung, H. H. 2003. Structural permeability effects on the interaction of a solitary wave and a submerged breakwater. Coastal Engineering, 40: 1- 24.

Hu-Hsiao Hsu, Yung-Chao Wu, 1997. Scattering of water wave by a submerged horizontal plate and a submerged permeable breakwater. Pergamon, pp. 325-326.

J. William Kamphuis, 2000, Introduction To Coastal Engineering And Management, Singapore.

Krystian W. Pilarczyk, Ryszard B. Zeidler, 1996. Offshore Breakwaters And Shore Evolution Control. A. A Balkema, Rotterdam.

Krystian W. Pilarczyk, Rijkswaterstaat, 2003. Design of low-crested (submerged) structures, pp. 1-2.

Longuet-Higgins, M. S, 1967. ON the wave induced difference in mean sea level between the two sides of a submerged breakwater. J. Mar. Res., 25(2): 148-153.

Losada, I. J., Losada, M. A. and Martin, F. L. 1995. Experimental study of wave induced. flow in porous structure. Coastal Engineering, 26: 77-98.

M. G. Muni Reddy, S. Neelami, 2004. Hydrodynamic studies on vertical seawall defenced by low-crested breakwater. ScienceDirect, 747-749.

Omeraci, H., 1994. Review and analysis of vertical breakwater failures - lesson learned. Coastal Eng. 22,3-29.

Rambabu, A. C., Mani, J. S. 2005. Numerical prediction ofperformance

of submerged breakwater. Department of Ocean Engineering, Indian Institute of Technology, Madras.

Robert G. Dean, Renjie Chen, Albert E. Browder, Full scale of monitoring study of a submerged breakwater, Palm Beach, Florida, USA, ELSEVIER, pp. 291-293.

Rojanakamthorn, S., Isobe, M., Watanabe, A., 1989. Design equation for transmission at submerged rubble mound breakwaters. Coastal Engineering in Japan 32,209-234.

Seelig, W. N., 1980. Two-dimensional tests of wave transmission and reflection characteristics of laboratory breakwaters. Tech. Rept. No. 80-1, US Army Coast.

Engrg. Res. Ctr., Fort Belvoir, VA.

Seung Hyun Park, Seung Oh Lee, Tae-Hwa Jung, and Yong-Sik Cho. 2007.

Effects of Submerged Structure on Rubble-mound Breakwater: Experimental Study.

Sidek, F. J., Abdul Wahab, M. A. J., 2007. The effects of porosity of submerged breakwater Structures on Non-Breaking Wave Transformations, Universiti Teknologi Malaysia.

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Tanaka, N. 1976. Effect of Submerged Rubble-Mound Breakwater on Wave Attenuation and Shoreline Stabilization. Proceeding of Japanese Coastal Engineering

Conference.

Ting, C. L., Lin, M. C., Cheng, C. Y. 2004. Porosity effect on non-breaking surface waves over permeable submerged breakwaters. Coastal Engineering, 50: 213-224.

U. S. Army Corps. of Engineers, Dept. of the Army. 1984. Shore Protection Manual. CERC. Vicksburg, Mississippi. U. S. Government Printing Office. Vol. 1&2.

Valeri Penchev, Jens Scheffermann, Shirin Shukrieva, Claus Zimmermann, 2005. Evaluation of Reef Breakwater Efficiency from Physical and Numerical

Simulations, pp. 169.

Yip, T. L., Sahoo, T., Chwang, A. T., 2002. Trapping of surface waves by porous and flexible structures, J. Wave Motion 35,41-54.

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APPENDICES

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APPENDIX A

PICTURES DURING LAB TESTING

Figure 15 Core Unit of Breakwater

H

I

Figure 16 Difference in wave height with the existence of submerged breakwater

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Figure 17 When the waves hit breakwater

Figure 18 The wave generator

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Figure 19 The wave gauges and vectrinox

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APPENDIX B

Function of the breaker index (Hb

db

)

(McCowan, I894, Munk, 1949)

Yb=

Hb

db

-Weggel (1972), values for the breaker index:

ýddb

=(c1-Ci

Tbz ) S

c, = 43.75(1- e-'9')

1.56

CZ =

(1 + e-iv. sm )

1.6

TAMP - 0. 20

1.4- 1

TAH0- 0.10

1.2

'0 a

TMI/ - 0.05

1 .0 a 0.

0.01

TMI/ <DO

0.8

.6

0.000 0.004 0.008 0.012 0.016 0.020

Hb /9T 2

Figure 11-4"2. Breaker depth index as a function of N(gT=) (Weggel 1972)

Figure 20 Function of Breaker Index and Graph of Breaker Index

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APPENDIX C

Comparison between experimental test ranges and Tanaka's graph

1.2

B/L=0.025 --ý, B/L=0.050

->4-

B/L=0.10 B/L=0.20 B/L=0.314 B/L=0.15 B/L=0.26 B/L=0.13 B/L=0.21 B/L=0.1025 B/L=0.0523

-2.5

0

.2 -1.5

Relative Crest Elevation, he / Ho

-1 -0.5

0

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TANAKA 1976 - Transmission coefficient for regular waves at rubble mound breakwater

1

w

0.9

0.8

-ý- B/L=0.025 B/L=0.050 B/L=0.10 ->E- B/L=0.20 --ý °B/L=0.209

B/L=0.1025 B/L=0.0523

-1.5 -1

-ft.

ý

-0.5 0

o. s

1 1.5

Relative Crest Elevation, he / Ho

Figure 22 Comparison between tested experimental data ranges with Tanaka's graph for submerged & emerged breakwater

ý ý _-- --ý- -

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Transmission coefficient for regular wave at RMB

1.2

1

0.8

0.6

0.4

ý,. 0.2

3.5 3 2.5 2 1.5 1 0.5 0

Relative crest height, he / Hi

Figure 23 Comparison between tested experimental data ranges for 0.1 wave height at submerged breakwater

, 7, --B/L=0.15 B/L=0.078 --ý-B/L=0.31 -ýE--B/L=0.26

. B/L=0.13 B/L=0.065 B/L=0.209 B/L=0.1025 B/L=0.0522

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Transmission coefficient for regular wave at RMB

1.2

I

1

0.8

0.6

0.4

`y 0.2

0

2.5

2 0.5 0

Figure 24 Comparison between tested experimental data ranges for 0.15 wave height at submerged breakwater

1.5

Rujukan

DOKUMEN BERKAITAN

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