Determination of Depth of Closure Along Kelantan Coast

DETERMINATION OF DEPTHS OF CLOSURE ALONG THE KELANTAN COAST

NOR HISHAM BIN MOHD. GHAZALI

UNIVERSITI TEKNOLOGI MALAYSIA

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DETERMINATION OF DEPTHS OF CLOSURE

ALONG THE KELANTAN COAST

NOR HISHAM BIN MOHD. GHAZALI

A thesis submitted in fulfillment of the

requirements for the award of the degree of

Master of Engineering (Coastal and Maritime)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

FEBRUARY 2007

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In the name of Allah, the Compassionate, the Merciful

Dedicated to my loving wife Noriah Abu Bakar for sharing my life and

dreams, to my father and my mother for their relentless faith in me, and my sons

Hazim, Nadim and Aqil Zuhair for their unconditional love.

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ACKNOWLEDGEMENT

All praise be to Allah the Merciful, the Benevolent to Whom all will return

and Whose knowledge is infinite, eternal.

I would like to first thank my supervisor Associate Professor Dr. Ahmad

Khairi Bin Abd Wahab whose guidance, counsel and support were critical to the

direction, focus and completion of this thesis.

I am indebted to my employer the Department of Irrigation and Drainage

Malaysia and the Public Services Department Malaysia for providing me the

opportunity and the financial means to pursue this study, and especially to Ir. Tan

King Seng, Director of Coastal Engineering Division for his personal and professional

support.

My thanks extend to Khairol Azuan Bin Adam of the National Hydraulic

Institute of Malaysia for his assistance, comments and advice on numerical modelling

and the staff of the Coastal Engineering Division, Department of Irrigation and

Drainage Malaysia for their immense support.

And not in the least, my deepest and eternal gratitude to my wife Noriah

Binti Abu Bakar whose strength, love and encouragement were beacons in all my

pursuits.

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ABSTRACT

The design of beach-fill in beach nourishment works requires knowledge of the

cross-shore sediment transport process. By the theory of equilibrium profiles, beach-

fill material will be redistributed across the shore profile up to a seaward limit known

as the depth of closure or Dc. The determination of the depth of closure is a key

component of beach-fill design and is measured in the field from the study of

periodical surveys over the same beach profiles. The Hallermeier equation which

relies on the incident pre-breaking wave height is the only analytical means to predict

the depth of closure. This study has examined the applicability of the Hallermeier

equation in predicting depth of closure for the coastline of Pantai Sabak, Kelantan

using nearshore waves which were transformed from offshore waves through

numerical modelling. The predicted depth of closure was compared against measured

depth of closure at 13 profiles that were surveyed in 1998, 1999, 2000 and 2004. The

widely-accepted Standard Deviation of Depth Change (SDDC) and Fixed Depth

Change (FDC) methods to determine Dc were both explored and the Dc for monsoon,

annual and 5-year events were investigated. The research found that along the study

shoreline at Pantai Sabak, more than one closure point can occur across the same

profile over the seasonal and annual period. Hallermeier’s equation overpredicts

annual Dc by 43% and affirms previous findings that the predictive equation

determines an upper limit value of Dc. Within the limitations of the survey data

available, the annual depth of closure at Pantai Sabak can be equated to 1.5 times

H0.137.

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ABSTRAK

Pengetahuan mengenai proses pergerakan ampaian rentas pantai adalah

penting dalam kerja-kerja merekabentuk penambakan pasir pantai. Berpandukan teori

keseimbangan profil, pasir penambakan dijangka akan diangkut dan diendapkan ke

seluruh profil pantai sehingga satu lokasi kedalaman yang dinamakan kedalaman

tertutup atau Dc. Penentuan kedalaman tertutup merupakan salah satu komponen

penting dalam rekabentuk penambakan pasir dan ianya diperolehi melalui kajian ke

atas data ukur bersiri yang diperolehi daripada profil-profil pantai yang sama.

Persamaan Hallermeier yang bergantung kepada keadaan ombak sebelum pecah

merupakan satu-satunya kaedah analitikal yang ada untuk menentukan kedalaman

tertutup. Kajian ini telah menguji kesesuaian persamaan Hallermeier ini dalam

meramalkan kedalaman tertutup bagi Pantai Sabak, Kelantan dengan menggunakan

ketinggian ombak di kawasan dekat pantai yang diperolehi melalui permodelan

numerikal yang berasaskan ombak lepas pantai. Kedalaman tertutup yang dikira

dengan menggunakan persamaan Hallermeier telah dibandingkan dengan kedalaman

tertutup yang dianalisa di 13 profil pantai yang diukur dalam tahun 1998, 1999, 2000

and 2004. Kaedah Persisihan Piawai Perubahan Kedalaman dan Perubahan

Kedalaman Tetap telah digunakan untuk menentukan Dc bagi keadaan tengkujuh atau

monsun timur-laut, tempoh tahunan dan untuk tempoh 5 tahun. Penyiasatan ini telah

mendapati bahawa lebih daripada satu kedalaman tertutup boleh wujud dalam profil

yang sama. Ramalan Dc tahunan dengan menggunakan Persamaan Hallermeier

didapati tinggi dengan lebihan purata 43% dan ini mengesahkan hasil kajian-kajian

terdahulu yang menyatakan bahawa persamaan ini boleh menentukan nilai had teratas

untuk Dc. Tertakluk kepada data ukur yang terhad di Pantai Sabak, kedalaman tertutup

tahunan boleh disamakan dengan 1.5 kali ketinggian ombak H0.137.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xii

LIST OF FIGURES xiv

LIST OF ABBREVIATIONS xix

LIST OF SYMBOLS xx

LIST OF APPENDICES xxii

1 INTRODUCTION 1

1.1 Introduction 1

1.2 Background of the Problem 2

1.2.1 Erosion Control and Beach Nourishment in Malaysia 2

1.2.2 Study Shoreline 3

1.2.3 Beach Nourishment Design and Depths of Closure 5

1.3 Objectives of the Study 7

1.4 Benefits of the Study 7

2 LITERATURE REVIEW 8

2.1 Introduction 8

2.2 Cross-shore Sediment Transport and Equilibrium

Beach Profiles 8

2.3 Definition of Depth of Closure 9

2.4 Methods of Determination 12

2.4.1 Predictive Methods 12

2.4.2 Depth of Closure from Profile Surveys 15

2.4.3 Depth Change Criterion 16

2.5 Application of Depth of Closure 18

2.6 Depth of Closure – Malaysian Context 19

2.7 Summary 21

3 RESEARCH METHODOLOGY 23

3.1 Introduction 23

3.2 Scope of the Research 24

3.3 Research Methodology 27

3.3.1 Data Sets 27

3.3.2 Primary Data Collection 28

3.3.3 Numerical Modelling 29

3.3.4 Analysis 30

3.3.5 Depths of Closure from Beach Profile Data 30

3.3.6 Depth of Closure from Empirical Formulae 31

3.4 Summary 31

4 FIELD DATA ANALYSIS 33

4.1 Introduction 33

4.2 Study Area 34

4.3 Environmental and Climatic Conditions 35

4.4 Data Sets 36

4.5 Beach Profile Survey 36

4.5.1 Survey #1 - 1998 37

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4.5.2 Survey #2 - 1999 37

4.5.3 Survey #3 - 2000 38

4.5.4 Survey #4 - 2004 38

4.5.5 Survey Data Selection 38

4.5.6 Survey Data Filtering 42

4.6 Sediment Data 42

4.7 Wave 44

4.7.1 UKMO Design Wave Analysis 45

4.7.2 Measured Waves 50

4.8 Tidal Heights 52

4.9 Wind 54

4.10 Summary 55

5 NUMERICAL MODELLING 57

5.1 Introduction 57

5.2 Model Description 57

5.3 Numerical Modelling 59

5.3.1 Model Area and Orientation 59

5.3.2 Wave Breaking Conditions 59

5.3.3 Calibration 61

5.3.4 Prediction of Nearshore Waves from Wave Model 66

5.4 Summary 77

6 DETERMINATION OF DEPTHS OF CLOSURE 79

6.1 Introduction 79

6.2 Depth of Closure – Scope and Criteria 80

6.2.1 Definition 80

6.2.2 Algorithm for Determination of Dc from Profile Surveys 81

6.3 Predicted Depth of Closure, Dl,t 84

6.4 Monsoon Dc (1998-1999 surveys) 84

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6.4.1 Profile Descriptions and Application of Algorithm 84

6.4.2 Monsoon Dc at Ch.3100 and Ch.2700 84

6.4.3 Monsoon Dc at Ch.2300 and Ch.1900 87

6.4.4 Monsoon Dc at Ch.1500, Ch.1200 and Ch.800 88

6.4.5 Monsoon Dc at Ch.400, Ch.200 and Ch.00 91

6.4.6 Monsoon Dc at Ch.-400, Ch.-900 and Ch.-1400 95

6.4.7 Summary for Monsoon Dc 97

6.5 Annual Dc (1999-2000) 100

6.5.1 Profile Description and Application of Algorithm 100

6.5.2 Annual Dc at Ch.3100 101








6.5.10 Annual Dc at Ch-400, Ch.-900 and Ch.-1400 109

6.6 Summary for Annual Dc (1999-2000) 111

6.7 Time-interval Dc (1999-2004) 113

6.7.1 Profile Description and Application of Algorithm 113

6.7.2 Five-year Dc at Ch.3100 114








6.7.10 Five-year Dc at Ch.-400, Ch.-900 and Ch.-1400 122

6.8 Summary of 5-year Dc (1999, 2000 and 2004) 124

6.9 Comparison of Event and Time-Interval Dc 126

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6.10 Measured Dc vs. Hallermeier’s Equation 127

6.11 Simplified Dc Equations 129

6.12 Observation 131

7 CONCLUSIONS AND RECOMMENDATIONS 133

7.1 General Conclusions 133

7.2 Suggestions for Future Research 135

7.2.1 Dc Criteria and Survey Techniques 135

7.2.2 Wave Data 135

7.2.3 Profile Surveys and Bar Migration Phenomena 136

7.2.4 Determining a predictive formula for local Dc 136

REFERENCES 138

APPENDICES A - E 142-174

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LIST OF TABLES

TABLE NO. TITLE PAGE

4.1 Profile Survey Data Register 40 4.2 Starting And Ending Points Of Selected Survey Dataset (13 profile lines) off Pantai Sabak, Kelantan 41 4.3 Statistics of UKMO Wave Dataset 47 4.4 Tidal Levels Along Study Shoreline (meters, LSD) 53 4.6 Mean High Water (meters, LSD) 53 4.7 Difference between MSL and MLW at Study Coastline 54 4.8 Difference between MSL and MHW at Study Coastline 54 5.1 Results of Wave Model Calibration 63 5.2 Location of Offshore Points in Model Grid for Extraction of Wave Parameters 67 5.3 Predicted Wave Heights At 10 M Depth Based On Offshore wave of H0.137 = 2.9 m and Tm = 6.3 secs 74 5.4 Predicted Wave Heights at 10 m depth Based On Offshore Wave of H0.027 = 3.13 m and Tm = 6.54 secs 75 6.1 Depths of Closure (SDDC) for Monsoon Event 1998-1999 99 6.2 Depths of Closure (FDC) for Monsoon Event 1998-1999 99 6.3 Annual Dc (May 1999 – May 2000) 111 6.4 Five-year Dc (1999, 2000, 2004 surveys) for beach-fill design 125

6.5 Outer Closure Depths Dco (MLW) from Profile Plots 127 6.6 Effective Dc and Predicted depth of closure, Dl,t , MLW 128 6.7 Dc from simplified equations compared with effective Dc 130 6.8 Dc from simplified equation compared to Dco 130

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LIST OF FIGURES

NO. TITLE PAGE 1.1 Study Area - 4.5 km of Shoreline From Pantai Dasar Sabak to South of Kg. K.S.P. Besar (Sungai Pengkalan Datu) 4 1.2 Evolution of Beach-fill based on Theory of Equilibrium Profile 6 2.1 Zonation Of Seasonal Beach Profile (Hallermeier 1978,

1981); extracted from Rijkswaterstaat (1987) 10 3.1 Research Model 26 4.1 Location of Study Area 34 4.2 Close-up of Study Area from Kg. Pantai Dasar Sabak

to Kg. Senok 35 4.3 Profile Lines At The Study Area 39 4.4 Distribution of sediments along Pantai Sabak 1998, 1999

and 2004 (d50 averaged across all chainages) 43 4.5 Distribution of bed sediments along Pantai Sabak 1998-1999.

Negative chainages are south of the breakwater 43 4.6 Distribution of bed sediments along Pantai Sabak 2004 44 4.7 Location of Wavebuoy And UKMO Wavedata Source

Relative to Kelantan Coast. 45 4.8 Offshore Significant Wave Heights at 6.39N 102.92E; 28/05/1999 – 30/07/2004 46 4.9 Histogram of UKMO Waves 47 4.10 Wave Height vs. Wave Period for UKMO Offshore

Wave Records 1999 to 2004 48

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4.11 H0.137 Wave from 1999-2000 UKMO Wave Data 49 4.12 H0.027 Wave from 1999-2004 UKMO Wave Data 50 4.13 Wave Buoy Measurements at E19236.3 N33957

(Kelantan Cassini) off Pantai Sabak, Kelantan Coast; 30 June to 13 July 2004. 51

4.14 Comparison of Offshore (UKMO Data) and Nearshore Waves Measured at the -12 m LSD Contour 51 4.15 Location Of Water Level, Current and Wave Stations At Study Area. 52 4.16 Wind Rose for UKMO Offshore Wind Data (20 m Above MSL) 55 5.1 Orientation of rectangle model layout for the input

(offshore) wave approach conditions N330o, N0o, N30o, N60o, N90o and N120o 58

5.2 Sensitivity of kN parameter and location of breaking wave

based on waves in July 62 5.3 Water level measurements at Pantai Sabak during calibration

period 64 5.4 Wave Model Calibration – Wave Heights (for offshore waves

from 0 to 120 degrees) 64 5.5 Wave Model Calibration – Wave Directions (for offshore

waves from 0 to 120 degrees) 65 5.6 Location of extraction points in wave model 67 5.7 Wave Refraction Diagram; H0.137 = 2.9, Tm = 6.3 sec;

North approach. 68 5.8 Wave Refraction Diagram; H0.137 = 2.9, Tm = 6.3 secs;

N30o approach. 69 5.9 Wave Refraction Diagram; H0.137 = 2.9 m, Tm = 6.3 secs;


N90o approach. 70

5.11 Wave Refraction Diagram; H0.137 = 2.9 m, Tm = 6.3 secs; N120o approach. 70

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5.12 Wave Refraction Diagram; H0.027 = 3.13 m, Tm = 6.54 secs;

North approach. 71 5.13 Wave Refraction Diagram; H0.027 = 3.13 m, Tm = 6.54 secs;




N120o approach. 73 5.17 Predicted Maximum Wave Heights at 10-m depth ACD

contour along Pantai Sabak, Kelantan. 76 5.18 Predicted Wave Heights at 10-m depth (ACD) contour along

Pantai Sabak, Kelantan averaged over all directions 77 6.1 Monsoon Dc at Ch.3100 85 6.2 Monsoon Dc at Ch.2700 86 6.3 Monsoon Dc at Ch.2300 87 6.4 Monsoon Dc at Ch.1900 88 6.5 Monsoon Dc at Ch.1500 89 6.6 Monsoon Dc at Ch.1200 90 6.7 Monsoon Dc at Ch.800 91 6.8 Monsoon Dc at Ch.400 92 6.9 Monsoon Dc at Ch.200 93 6.10 Monsoon Dc at Ch.00 94 6.11 Monsoon Dc at Ch.-400 95 6.12 Monsoon Dc at Ch.-900 (slope 1:400) 96 6.13 Monsoon Dc at Ch.-1400; closure is not defined with

SDDC method at Ch.-1400 97

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6.14 Comparison of SDDC and FDC methods in determining

Monsoon Dc 100 6.15 Annual Dc at Ch.3100 101 6.16 Annual Dc at Ch.2700 102 6.17 Annual Dc at Ch.1500 103 6.18 Annual Dc at Ch.1200 104 6.19 Annual Dc at Ch.800 105 6.20 Annual Dc at Ch.400 106 6.21 Annual Dc at Ch.200 107 6.22 Annual Dc at Ch.00 108 6.23 Annual Dc at Ch.-400 109 6.24 Annual Dc at Ch. -900 110 6.25 Annual Dc at Ch.-1400 110 6.26 Radar Graph - Comparison between Dl,1-yr and

measured Annual Dc 112 6.27 Variation in Dl,1-yr and measured Annual Dc along

the study area 112 6.28 5-year Dc at Ch.3100 - Comparison of SDDC and mean

of FDC between consecutive surveys at Ch.3100 114 6.29 5-year Dc at Ch.2700 115 6.30 5-year Dc at Ch.1500 116 6.31 5-year Dc at Ch.1200 117 6.32 5-year Dc at Ch.800 118 6.33 5-year Dc at Ch.400; three closure points were detected 119 6.34 5-year Dc at Ch.200 120 6.35 5-year Dc at Ch.00 121 6.36 5-year Dc at Ch.-400 122

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6.37 5-year Dc at Ch.-900 123 6.38 5-year Dc at Ch.-1400 123 6.39 Comparison of 5-year Dc (effective Dc for beach-fill

design), Dco (outermost Dc) and Dl,5-yr 125 6.40 Variation in 5-year Dc (effective Dc for beach-fill design),

Dco (outermost Dc) and Dl,5-yr across the study area 126 6.41 Dc along Pantai Sabak, Kelantan 129 6.42 Dc based on different closure criteria 132

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LIST OF ABBREVIATIONS CED Coastal Engineering Division

CEM Coastal Engineering Manual

cm centimeter

DHI Danish Hydraulic Institute

DID Department of Irrigation and Drainage Malaysia

DSMM Department of Survey and Mapping Malaysia

HAT Highest Astronomical Tide

Kg. Kampung; village (malay)

LAT Lowest Astronomical Tide

LSD Land Survey Datum

m meter

mm millimeter

MSL Mean Sea Level

MHW Mean High Water

MHHW Mean Higher High Water

MLHW Mean Lower High Water

MLW Mean Low Water

MHLW Mean Higher Low Water

MLLW Mean Lower Low Water

Sg. Sungai; river (malay)

SSMO Synoptic Shipboard Meteorological Observation

UKMO United Kingdom Meteorological Office

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LIST OF SYMBOLS Dc depth of closure

Dc,1-yr depth of closure over 1 year

Dc,5-yr depth of closure over 5 years

Dci depth of closure, innershore; from profile survey

Dcm depth of closure, middleshore; from profile survey

Dco depth of closure, outershore; from profile survey

Dl predicted depth of closure; water depth at the seaward limit of

significant sediment transport

Dl,t predicted depth of closure over t years

Dl,1-yr predicted depth of closure over 1 year

Dl,5-yr predicted depth of closure over 5 years

d water depth

di lower limit of the shoal zone

dl lower limit of the littoral zone

d50 size of material of which 50% is finer

g acceleration due to gravity

H predicted depth of closure (Birkemeier's equation)

hc predicted depth of closure (Hallermeier's equation)

Hm0 energy-based wave height of the zeroth moment

Hs significant wave height

Hs50 median annual significant wave height

Hl,t significant wave height exceeded 12 hours over t years

H0.137 significant wave height exceeded 12 hours in a year

H0.027 significant wave height exceeded 12 hours in t = 5 years

He,t non-breaking significant wave height that is exceeded 12 hours per t

years or (100/730t) % of the time

kN Nikuradse's roughness parameter

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s standard deviation

t time

T wave period associated with a particular wave height

Te, t wave period corresponding to He,t

Tm mean wave period

Tp peak wave period

Ub maximum horizontal wave-induced near-bed velocity

xi measurement

xm mean of all measurements

n number of measurements

σH annual standard deviation of significant wave height

Φc sediment entrainment parameter

γ’ ratio of the difference in density between sediment and fluid density

γ1 wave breaking parameter which controls wave steepness condition

γ2 wave breaking parameter which controls limiting water depth

condition

α adjustable constant in energy dissipation equation

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A Profile Surveys from the coastline of Pantai Sabak, Kelantan

1998, 1999, 2001 and 2004 142

B Description of United Kingdom Meteorological Office

(UKMO) Dataset 159

C Summary of Grain Size Distribution from Pantai Sabak,

Kelantan Surveys 1998, 1999, 2004 165

D Tidal Data From Pantai Sabak, Kelantan;

2004 Survey 168

E Model Wave Bathymetry

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INTRODUCTION

1.1 Introduction

Beach nourishment is a preferred coastal protection measure for recreational

beaches. The provision of a wider dry beach, by placing sand on the eroding shore

that extends beyond the existing beach berm, is the main component of a beach

nourishment scheme. A re-nourished beach presents a wider surface area that both

dissipates wave energy impacting on the shoreline and creates more space for

recreational activities. Sand re-nourished beaches remain as a part of the nearshore

coastal system within which sediment can be moved freely by wave and tidal action.

Inherent in the engineering design of beach nourishment is an element of

prediction and projection based on the shoreline change trend of the concerned

beach. Typical beach nourishment schemes may require annual refill as the

nourished beach is exposed and continuously subjected to environmental forces. In

Malaysia, beach nourishment schemes are expected to last 5 years before re-

nourishment works are initiated again. In this approach, designs are based on a

general rate of erosion for the beach and a five-year re-nourishment interval. An

important aspect of beach nourishment design is the knowledge of the seaward limit

to which the beach-fill is expected to move. This point is called the depth of

closureand its determination involves the study of the nearshore profile over a period

of time.

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The beach nourishment projects conducted by the Department of Irrigation

and Drainage Malaysia (DID) in the past did not have the benefit of sufficient

periodical survey data needed to determine the depths of closure. Hence, the

predictive formula of depth of closure introduced by Hallermeier (Hallermeier,

1981) and its simplified forms (US Army Corps Of Engineers, 1984) have been

widely used. Since the completion of the beach nourishment projects, periodical

monitoring surveys have been conducted on selected re-nourished shorelines. The

situation now presents opportunities for further study and analysis of the depths of

closure with the view of improving the design of sand-fill in beach nourishment for

local conditions. This research determines and studies the depths of closure from

periodical surveys of a stretch of shoreline in Kelantan and examines the

applicability of existing predictive equations to the Kelantan shoreline.

1.2 Background of the Problem

1.2.1 Erosion Control and Beach Nourishment in Malaysia

The National Coastal Erosion Study (Unit Perancang Ekonomi, 1985)

determined that approximately 30% of Malaysia’s 4,809 km of coastline was

eroding. It proceeded to recommend immediate coastal erosion protection measures

on critical sites and led to the development of the Coastal Erosion Control Program

under the DID. Under this program, revetment-type protection and beach

nourishment schemes were constructed along Malaysia’s eroding coasts beginning in

the late eighties. Among the major beach nourishment projects implemented by the

Government of Malaysia under this program were:

(i) Kuala Terengganu to Kuala Ibai, Terengganu (1993);

(ii) Taman Robina, Seberang Perai Utara, Pulau Pinang (1994);

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(iii) Pantai Kundur, Melaka (1995)

(iv) Batu 4, Port Dickson, Negeri Sembilan (1996 and 2005) and;

(v) Kg. Teritam to Kuala Sungai Pengkalan Datu, Kelantan (1997)

Since the emergence of tourism as a dominant sector of the Malaysian

economy, the need to preserve the quality and aesthetics of public beaches have

become an important agenda under the Coastal Erosion Control Program. Therefore,

the understanding of the evolution of re-nourished beaches must be enhanced so as to

improve future planning and design works.

1.2.2 Study Shoreline

The northeast coastline of Kelantan has been selected for this study due to its

long-term erosion trend. This coastline is oriented along the northwest to southeast

direction. Wind fetch lengths spanning over 1500 km across the South China Sea

influence this stretch of coast. As a result, the long fetch and the predominant

northeasterly winds during the northeast monsoon combine to generate high waves in

the adjacent offshore area (Department of Irrigation and Drainage, 1993).

Furthermore, there are no large islands off the Kelantan coast to offer any cover from

the monsoonal waves.

The study is limited to the coastline from Kg. Pantai Dasar to Kg. S.P. Besar,

Kelantan which is shown in Figure 1.1. Locally known as Pantai Sabak, this

coastline has experienced erosion at an average rate of exceeding 5 meters per year

(Unit Perancang Ekonomi, 1985). The situation was later exacerbated by the

construction of a breakwater at Sungai Pengkalan Datu which was completed in 1986

as part of a flood mitigation and agricultural drainage project. The breakwaters

created a terminus to the littoral transport in the area and depleted the supply of

26

sediment to the adjacent shoreline of Pantai Sabak to the northwest. An erosion of

20 meters occurred within 7 months of the completion of the northern arm of the

breakwaters and the completion of the southern arm 10 months after brought about

an additional 60 meters of erosion in the following year (Lee, 1990). Studies by

Universiti Teknologi Malaysia indicated that minor sediment bypassing of the

Pengkalan Datu breakwaters in the northwest direction had begun within a few years

of its completion (Ahmad Khairi Bin Abdul Wahab, 1989). Nevertheless, this was

insufficient to reduce the erosion rate at Pantai Sabak.

In 1996, the DID implemented a beach nourishment project which laid 1.2

million m3 of sand along a 2.1 km stretch within the study area. The constructed

beach berms ranged from 70 m to 120 m. Whilst the study and design of the beach

nourishment scheme took into account the reduction in sediment budget due to the

breakwater, nearly 60% of the nourished volume was lost within a single monsoon

(Jabatan Pengairan dan Saliran Malaysia, 2002).

KELANTAN

Study area Kelantan, MALAYSIA

Study Area

Figure 1.1: Study area - 4.5 km of shoreline from Pantai Dasar Sabak to South of

Kg. K.S.P. Besar (Sungai Pengkalan Datu). (Source: Topo Maps #4068 [1985],

#3968 [1991], Jabatan Ukur dan Pemetaan Malaysia)

27

1.2.3 Beach Nourishment Design and Depths of Closure

The design of a beach nourishment scheme requires the same engineering

parameters as other coastal protection solutions. Apart from the established wave,

wind and tidal conditions, the design criteria for a typical DID beach nourishment

includes:

• a nourished beach slope as close as possible to the existing beach

slope;

• available funds to provide the widest beach berm possible based on a

pre-determined re-nourishment interval of 5 years;

• the availability of suitable sand-fill of grain size d50 greater than the

native beach.

From the Shore Protection Manual (US Army Corps Of Engineers, 1984), the

design approach can be summarised as follows: (i) determination of the beach berm

elevation and width (ii) determination of nourishment volume based on native and

borrow composite material characteristics (iii) determination of post-project beach

evolution.

In practice, a pre-erosion shoreline is determined and the berm width is

‘overbuilt’ beyond the pre-erosion shoreline position based on local erosion rates and

the expected interval of re-nourishment. Hence, if the local erosion rate is 5 meters

per year and a re-nourishment is planned after every five years, the berm width will

be built 25 meters beyond the desired shoreline. Artificial beach fills are created

based on a construction cross-section. Over time and due to the action of waves and

tides, the fill material forming the nourished profile of a constructed beach will be

shaped by natural processes into a profile of generally concave upward shape called

an equilibrium profile. This equilibrium profile concept was proposed by Bruun

(1954) with further elaboration by Dean (1977) and is illustrated in Figure 1.2. In

the application of this concept, it is assumed that there is a conservation of sediment

28

Dc = depth of closure

Evolved equilibrium profile

Original ground level

Original nourished profile

volume across the profile and that a loss of sand volume from the upper profile of the

beach is associated with a similar gain in volume in the lower profile. The seaward

limit for the volume exchange process is the depth of closure.

Figure 1.2: Evolution of beach-fill based on Theory of Equilibrium Profile

The depth of closure is effectively, the offshore limit of the active zone

within which a nourished beach adjusts to equilibrium under the prevailing coastal

conditions. Hence, a good estimate of the depth of closure is essential to a good

estimate of the beach fill volume required. With respect to post-nourishment beach

profiles, National Research Council (1995) refers to the depth of closure as a

reference typically used by designers to estimate the limit of profile widening.

These statements further confirm the importance of the depth of closure in beach

nourishment design.

Beach nourishment schemes have been built in Malaysia since 1992 but their

evolution has not been extensively studied. Due to the lack or absence of periodical

surveys then, the depth of closure has typically been predicted from empirical

equations. With regards to this, a comparative study of the predictive and measured

29

depths of closure, in the writer’s opinion, would contribute to the understanding of

the performance of beach nourishment schemes. In the Malaysian context, such

detailed comparisons have, to date, yet to be done and this dearth of knowledge is the

impetus to this research.

1.3 Objectives of the Study

The purpose of this research is to determine the depths of closure of a 4.5 km

stretch of sandy coast extending from north of Pantai Dasar Sabak to south of the

Sungai Pengkalan Datu in the state of Kelantan. The study will analyse beach profile

surveys, determine the depths of closure and to compare them against predicted

values calculated from the Hallermeier equation. The research will examine the

validity of this widely accepted equation for the Malaysian condition.

1.4 Benefits of the Study

In general, the study is expected to contribute towards an improved

understanding of cross-shore sediment transport and shore profile changes in the

Malaysian coastal environment. Knowledge of profile trends and depths of closure

will facilitate the design of coastal protection works primarily beach nourishment,

revetments, groynes and breakwaters. It is envisaged that from the results of this

research, engineers will be able to utilise a modified analytical method, specific to

the local conditions, to predict depths of closure with greater confidence for areas

where historical shore profile data is lacking.

Determination of Depth of Closure Along Kelantan Coast

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