the influence of river discharges, tides, and winds...

THE INFLUENCE OF RIVER DISCHARGES, TIDES, AND WINDS ON ESTUARINE PLUME IN NORTHWEST

PENINSULAR MALAYSIA

by

MUHAMMAD SYUKRI

Thesis submitted in fulfillment of the requirements for the degree

of Doctor of Philosophy

December 2006

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11

ACKNOWLEDGEMENTS

As a long journey and endeavour, this thesis was not a solo effort. I owe a

tremendous of gratitude to the many people that assist and support me, that it is

difficult to know where to begin and end this list. Even after one of the longest

acknowledgments list ever written in this thesis is done, I am sure I will have forgotten

some important people. To you I offer my apologies and implicit thanks. I would like to

thank the University of Syiah Kuala (USK), Darussalam, Banda Aceh, Indonesia for

providing the scholarship to support my study. I also wish to thank University Science

Malaysia (USM), for serving and the use of all facility, where I learnt so much from

being part of a graduate student here.

The very first, I want to pay special tribute to my advisor and friend Dr. Md. Noordin

Abu Bakar has served as a source of inspiration since the conception of this thesis,

helped me with advice, comments and suggestions. He was always available when I

needed his advice or wisdom, but gav~ me the freedom to work independently. He

has demonstrated impeccable leadership and has given me a strong foundation on

which to build my own independent research program. lnsya Allah, my career as an

oceanographer in the future will always reflect what I have learned as a student from

him. Further more, I also would like to thank to Ass. Prof. Dr. Khiruddin Abdullah as a

co-supervisor for reviewing some of the results. Then I would like to extent my thanks

to Dr. Zuhar Zahir Tuan Harith for guiding, suggestions and useful discussion during

my study.

lll

I would like to thanks the Malaysia Meteorological Service (MMS) for kindly providing

the meteorology and hydrographic data, the Hydrology and Water Resources

Division, Department of Irrigation and Drainage (DID) Malaysia for graciously .

providing the suspended sediment concentration, river discharge, and river stage

data, the Malaysian Mapping and Survey Department (MMSD) for pleasantly

providing the tide observation data, Centre for Marine and Coastal Studies (CEMAC)

USM for their friendship and all those who helped me with laboratory work for the

TSS analysis, Kedah Flying Club (KFC) for supplied aerial images from aerial surveys

with their small aircraft. These datasets contributed significantly to the quality of the

work and study presented in these pages.

I want to "thank the Dean School of Physics USM, all staff of Geophysics Laboratory,

School of Physics, for providing an atmosphere teeming with a collaborative spirit and

enthusiasm for the researGh. Special thanks also to my wonderful friends and team

works En. Yaakub Othman, En. Jamalludin, Uncle Abu Bakar, for their technical

advice, who helped me with field surveys of the days and nights and in all weathers.

They were also enthusiastic about my project and made the days I spent field

surveying enjoyable. En. Zainul Abidin, Shahil Ahmad, Shaiful Mahathir, and Faisal, a

very special thank you for all your help, cooperation, assistance and encouragement.

Further, I would like to express my special thanks to my parents, Usman Ismail and

(late) Djuairiah Sabi, and my parents-in-law, Soewardi Soekirman and Nur Aini Umar,

my sisters and brothers, k'lna and b'Samsoel, k' Nyanyak and b'Poel, k'lda and b'ljal,

and Ismail for their supporting and do'a during this very challenging period in my life.

Finally, especially and most importantly, to my wife and best friend Rini Safitri, and

my son and sources of inspiration Raushan al Kasyfie Muhammad, for their wonderful

IV

support, love, patience, distraction, and comfort during this trying odyssey know as

graduate school, and particularly during that rather surreal period know as "writing

up". I could not have done this without them, and dedicate my thesis to them.

v

Acknowledgements

Contents

List of Tables

List of Figures

List of Abbreviations

List of Symbols

List of Appendices

Abstrak

Abstract

Chapter One : Introduction

1.0 Introduction

1.1 Motivation

1.2 Hypothesis

1.3 Objectives and scope

1.4 Thesis Outline

Chapter Two : Literature Review

2.0 Estuary plume structures

2.1 Sediment transport

Contents

2.2 Factors affecting estuary plumes

2.2.1 River discharges

2.2.2 Tides

2.2.3 Winds and waves

2.3 Currents in coastal waters and estuaries

2.4 Remote sensing technology in detecting estuary plume

2.4.1 Innovative mapping and modeling

vi

Page

iii

vi

xiii

xiv

xxvi

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XXX

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xxxiii

1

1

2

4

6

7

9

9

14

19

19

20

22

25

27

27

2.4.2 Other remote sensing applications 32

Chapter Three : Methodology 34

3.0 Definition of the study areas 34

3.1 Site description and catchment area 36

3.2 Geological setting 39

3.3 Meteorological and hydrographic data 43

3.3.1 Climate data 45

a. Temperature 46

b. Relative humidity 48

c. Rainfall 48

3.3.2 Wind data 49

3.3.3 Tidal data 52

3.4 Field surveys 53

3.4.1 Muda surveys 54

3.4.2 Merbok surveys 68

3.4.3 Prai surveys 74

3.5 Laboratory work 81

3.6 Data processing and analysis 81

3.6.1 Mapping and contouring data 81

3.6.2 Density 82

3.6.3 Water masses 87

3.6.4 Water mixing 88

3.6.5 Validation of total suspended solids 89

Chapter Four : Muda Surveys 90

4.0 Introduction 90

4.1 River discharge influence 91

4.1.1 Salinity 91

a. Horizontal distribution 91

b. Vertical distribution 95

vii

4.1.2 Temperature 100



4.1.3 Density 110



4.1.4 Total suspended solids 118

4.1.5 Suspended sediment load in the river 121

4.2 Tidal influence 128

4.2.1 Salinity 129






4.2.3 Density 145




4.3 , Wind influence 156

4.3.1 Salinity 156


4.3.3 Density 160


4.4 Current characteristics 163

4.4.1 In the estuary 163

4.4.2 At the coastal zone 168

4.5 Discussion 176

4.5.1 River discharge influence 176

a. Salinity pattern 176

b. Temperature pattern 181

c. Density pattern 183

d. Total suspended solids pattern 186

viii

4.5.2 Tidal influence 191





4.5.3 Wind influence 205





4.5.4 Monsoon variability and atmospheric temperature 210

4.5.5 Water masses 215

4.5.6 Aerial surveys 217

4.6 Summary of field surveys 226

Chapter Five : Merbok Surveys 234

5.0 Introduction 234

5.1 River discharge influence 235

5.1.1 Salinity 235






5.1.3 Density 245




5.1.5 Secchi depth 251

5.2 Tidal influence 253

5.2.1 Salinity 253


ix


5:2.2 Temperature 257



5.2.3 Density 261





5.3 Wind influence 268

5.3.1 Salinity 268


5.3.3 Density 271



5.4 Current characteristics 274

5.5 Discussion 283

5.5.1 River discharge influence 283





e. Secchi depth pattern 292

5.5.2 Tidal influence 294





e. Secchi depth pattern 305

5.5.3 Wind influence 307




X

d. Total suspended solid pattern

e. Secchi depth pattern

5.5.4 Monsoon variability and atmospheric temperature

5.5.5 Water masses

5.5.6 Mixing Processes

5.5. 7 Aerial surveys

5.6 Summary of field surveys

Chapter Six : Prai Surveys

6.0 Introduction

6.1 River discharge influence

6.1.1 Salinity

6.1.2 Temperature

6.1.3 Density

6.1.4 Total suspended solids

6.2 Tidal influence

6.2.1 Salinity

6.2.2 Temperature

6.2.3 Density


6.3 Wind influence

6.3.1 Salinity

6.3.2 Temperature

6.3.3 Density


6.4 Discussion

6.4.1 River discharge influence

a. Salinity pattern

b. Temperature pattern

c. Density pattern

d. Total suspended solids pattern

6.4.2 Tidal influence

XI

310

311

312

317

319

324

332

335

335

336

336

338

339

340

. 341

341

342

343

345

346

346

347

348

349

351

351

351

353

354

355

357

a. Salinity pattern

b. Tempe!ature pattern

c. Density pattern


6.4.3 Wind influence

a. Salinity pattern

b. Temperature pattern

c. Density pattern


6.4.4 Aerial surveys

6.5 Summary of field surveys

Chapter Seven : Conclusions and Future Works

7.0 Conclusions

7.1 Recommendations and future work requirements

References

List of Publications

Appendices

Appendix A : All results of Muda surveys

Appendix B : All results of Merbok surveys

Appendix C : All results of Prai surveys

xii

357

358

359

360

362

362

363

363

364

365

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385.

398

CD

CD

CD

CD

List of Tables

Page

2.1 Discharge data for the world's largest rivers. 15

3.1 Field surveys (date ordered) on the Muda coastal area. 55

3.2 Summary of cumulative 5 days rainfall and river discharge. Tabulated 59 are the river discharge conditions under high and low discharge observed during study period.

3.3 Daily mean and maximum wind speed and direction data along the 67 survey days.

3.4 Field surveys (date ordered) on the lower Merbok Estuary. 69

3.5 River discharge condition, divide based on S values during study 73 period.

3.6 Field surveys (date ordered) on the Prai coastal area. 78

4.1 TSS concentrations during various field surveys. 154

4.2 Details of surveys to the Muda coastal region and around estuary 227 mouth during study period.

4.3 Data measured (date ordered) on the Muda coastal region and 229 around estuary mouth during study period ..

4.4 Summary of characteristics of estuary plume during field surveys on 232 the Muda coastal region.

5.1 River discharge: condition, density and TSS values during study 291 period.

5.2 The RL values for survey on 23 March 2003. 320

5.3 The RL values for survey on 19 May 2003. 320

5.4 The RL values for survey on 20 May 2003. 321

5.5 The RL values for survey on 7 June 2003. 321

5.6 Details of meteorological data to lower Merbok Estuary during study 333 period.

5.7 Data measured (date ordered) on the lower Merbok Estuary during 334 study period.

6.1 Details of surveys to Prai coastal area (Penang Channel) during 377 study. period.

6.2 Data measured (date ordered) on the Prai coastal area (Penang 378 Channel) during study period.

xiii

List of Figures

Page

1.1 (a) A schematic plan view of an estuary plume in the coastal water, 4 and (b). A vertical section of an estuary plume as the fresher water discharge from the estuary to coastal water.

2.1 Sketch of buoyant layer scales. (a) x and y are alongshore and 10 across-shore coordinate13. Dashed line denotes a bounding isopicnal contour for the buoyant layer. U is typical alongshore buoyant water velocity. L and yL are the alongshore and the across-shore length scale, respectively. (b) A typical across-shore vertical section with vertical coordinate z. Dashed line shows typical bounding isopicnal for the buoyant of typical depth h. (from Garvine, 1995).

2.2 Salinity distributions during the January 1997 flood. Upper panels: 12 near-surface (1.5m) salinity distributions; lower panel: cross-sections at estuary mouth. (from Geyer eta/., 2000).

2.3 Total suspended sediment distributions during the 1997 flood. Upper 13 panels: near-surface (1.5 m) suspended solids, based on water samples; lower panel: cross-sections at river mouth, based on water samples and optical backscatterance sensor (OBS) profiles (from Geyer eta/., 2000).

2.4 Schematic diagram illustrating estuary plume push by gravity driven 16 flow (from Wright eta/., 2001).

2.5 Conceptual diagram of river flow, according to the strength of outflow, 21 the plume may turn to left or right (from James, 1997).

:

2.6 A schematic diagram of the structure of surface density in the Gulf of 23 Mexico at the mouth of the Mississippi River during (a) the flood tide and (b) ebb tide (from Dagg eta/., 2001).

2.7 Structure of vertical salinity between 10 and 1m from surface in the 25 Rhine River. (a) Vertical salinity differences at location T = Ter Heijde (between Rotterdam Waterway and Scheveningen), N = Noorwijk, and Y = IJmuiden. and (b) Vertical salinity with predominantly winds from the east (± 7 m s"1

) (from De Ruijter eta/., 1997).

2.8 Sea surface salinity SLFMR maps from flights at 3 day intervals (a) -: 30 (d). Strong surface salinity gradients are prominent in all the maps with freshwater (<16 psu) in the channel and along the coasts. A transition zone of intermediate salinity (30-34 psu) marks the plume boundary (from Burrage eta/., 2003).

3.1 Map of the study areas, the square (a). Muda, (b). Merbok and (c). 35 Prai estuaries and coastal zones.

3.2 Satellite SPOT image of the study areas. (derived from CRISP- 36 IKONOS on 31 January 2005 at 03:41:18 Local Time)

3.3 Map of the catchments area in Kedah and Penang. 37

xiv

3.4 Geological map of the study area in Penang region (Source: Courtier, 41 1974).

3.5 Geological map of the study area in Kedah region (Source: Bean, 43 1969).

3.6 Southwest and Northeast monsoon patterns and wind directions. 47

3.7 Monthly rainfalls for the Penang region. 49

3.8 Monthly rainfalls for the Kedah region. 50

3.9 Wind Roses Summary (1985-2002) at station Butterworth for the 51 period a. April, b. May-September, c. October, d. November-March.

3.10 Annual Wind Roses Summary for cyclone studied from 1985-2002 at 52 station Butterworth. The concentric circles in the dashes represent the various percentage frequencies of time as labeled. The innermost full circle represents the percentage occurrence of calm (wind speed s 0.2 m/s), the value of which is inscribe within the circle. Various arms radiate from the innermost circle. The total length of each arm represents the total percentage frequency of time the wind blows from the direction concerned. Each arm is subdivided into a line and rectangles of different shades and sizes. These represent the various classes of speed as given in the key scale (Source: MMS).

3.11 Location of the coastal area under investigation. The number and 56 circle sign shows the location of stations of field survey on 7 April 2002. Bathymetry of the coastal region is also shown in meters.

3.12 Monthly mean and maximum river discharge (m3/s) hydrographs for 57 the Mud a River between 197 4 and 2002 at station Jambatan Syed Omar.

3.13 Monthly mean river discharge (m3/s) hydrographs for the Muda River 58 between 2001 and 2002 at Jambatan Syed Omar meteorological station.

3.14 The total monthly rainfall (mm) diagrams for the Muda River between 58 2001 and 2002 at Bumbung Lima and Pinang Tunggal meteorological stations.

3.15 Diagram of daily river discharge (m3/s) and river stage (m) at station 61 Jambatan Syed Omar during the months of survey.

3.16 Aerial digital image of plume boundary intersecting with oceanic 64 water, Muda River mouth area, captured on 20 January 2002.

3.17 Observation maximum tidal heights (m) at Swettenham Pier for the 65 year 2001-2002.

3.18 (a) Map of study area with details of the boundaries of the lower 70 Merbok Estuary and (b) location of the lower estuary area under investigation. The number and circle sign shows the location of stations of field survey on 10 April 2003, and the arrows indicates the transects direction.

3.19 Distribution of monthly mean rainfall at Sungai Petani meteorological 71 station for 20 years (1975-1995).

XV

3.20 Monthly rainfall histograms during the study surveys (2002-2003) at 72 Sungai Petani meteorological station.

3.21 The maximum tidal heights observation (m) at Station Swettenham 73 Pier for the year 2002-2003: -

3.22 (a) Map of study area with details of the boundaries of the Prai River 75 mouth and Penang Channel and (b) bathymetry (m) of the coastal region as the interest area of surveys study.

3.23 Aerial image of river plume boundary intersecting with oceanic water, 76 Penang Strait area, captured on 28 October 2001.

3.24 The total monthly rainfall (mm) diagrams for the Prai River between 79 2001 and 2003 at Butterworth meteorological stations.

3.25 The total monthly rainfall (mm) diagrams for the Prai River between 79 2001 and 2003 at Prai meteorological stations.

4.1 Horizontal distribution of surface salinity (%o) during high river 92 discharge surveys on (a) 8 November and (b) 17 October 2001.

4.2 Horizontal distributions of salinity (%o) during high river discharge 93 survey on 17 October at (a) 1.5 m and (b) 2.5 m depth.

4.3 Horizontal distributions of salinity (%o) during high river discharge 93 survey on 8 November at (a) 1 m and (b) 2m depth.

4.4 Horizontal distributions of salinity (%o) during low river discharge 94 surveys on (a) 9 March 2002 and (b) 4 July 2002.

4.5 Horizontal distributions of salinity (%o) during low river discharge 95 survey on 17 January 2002 at (a) 1 m and (b) 2m depth.

4.6 Horizontal distributions of salinity (%o) during low river discharge 96 survey on 11 June 2002 at (a) 1m and (b) 2 m depth.

4. 7 Vertical distributions of salinity (%o) during high river discharge at (a) 97 transect 1 (along shore) and .(b) transect 2 (across shore) survey on 8 November 2001.

4.8 Vertical distributions of salinity (%o) during high river discharge at 98 transect 1 (along shore) and (b) transect 2 (across shore) survey on 17 October 2001.

4.9 Vertical distributlons of salinity (%o) during low river discharge at 99 transect 1 (along shore) and (b) transect 2 (across shore) survey on 17 January 2002.

4.10 Horizontal distribution of tempera,ture (DC) during high river discharge 101 surveys on (a) 25 September 2001 and (b) 7 May 2002.

4.1·1 Horizontal distributions of temperature (DC) during high river 102 dischargesurvey on 25 October 2002 at (a) 1m and (b) 2m depth.

4.12 Horizontal distributions of temperature (DC) during high river 102 discharge survey on 7 May 2002 at (a) 1m and (b) 2 m depth.

4.13 Horizontal distribution of temperature (DC) during low river discharge 104 surveys on (a) 20 January and (b) 11 June 2002.

xvi

4.14 Horizontal distributions of temperature (°C) during low river discharge 105 survey on 20 January 2002 in (a) 1.5m and (b) 3m depth.

4.15 Horizontal distributions of temperature {°C) during low river discharge 105 survey on 1; June 2002 in (a) 1m and (b) 2m depth.

4.16 Vertical distributions of temperature {0C) during high river discharge 106 at (a) transect 1 (along shore) and (b) transeot 2 (across shore) survey on 25 September 2001.

4.17 Vertical distributions of temperature (0C) during high river discharge 107 at (a) transect 1 (along shore) and (b) transect 2 (across shore) survey on 8 November 2001.

4.18 Vertical distributions of temperature (°C) during low river discharge at 108 (a) transect 1 (along shore) and (b) transect 2 (across shore) survey on 20 January 2002.

4.19 Vertical distributions of temperature {0C) during low river discharge at 109 (a) transect 1 (along shore) and (b) transect 2 (across shore) survey on 11 June 2002.

4.20 Horizontal distribution of density (kgm3) during high river discharge 111

surveys on (a) 28 July 2001 and (b) 8 November 2001.

4.21 Horizontal distributions of density (kgm-3) during high river discharge 112

survey on 28 July 2001 at (a) 1.5 m and (b) 2.5 m depth.

4.22 Horizontal distributions of density (kgm-3) during high river discharge 112

survey on 8 November 2001 at (a) 1m and (b) 2 m depth.

4.23 Horizontal distribution of density (kgm-3) during low river discharge 113

surveys on (a) 6 February and (b) 6 June 2002.

4.24 Horizontal distributions of density (kgm-3) during low river discharge 114

survey on 6 February 2002 in (a) 1 m and (b) 2m depth.

4.25 Horizontal distributions of density (kgm-3) during low river discharge 115

survey on 6 June 2002 in (a) 2 m and (b) 3 m dept.h.

4.26 Vertical distributions of density (kgm-3) during high river discharge at 116

(a) transect 1 (along shore) and (b) transect 2 (cross shore) survey on 28 July 2001.

4.27 Vertical distributions of density (kgm-3) during low river discharge at 118

(a) transect 1 (along shore) and (b) transect 2 (cross shore) survey on 6 June 2002.

4.28 Horizontal distribution of TSS (mgl"1) during high river discharge 119

surveys on (a) 8 November 2001 and (b) 28 April 2002.

4.29 Horizontal distribution of TSS (mgl"1) during low river discharge 120

surveys on (a) 12 January and (~) 11 June 2002.

4.30 Monthly mean suspended sediment (tones/month) hydrographs for 121 the Muda River between 1976 and 2002 (26 years) at Jambatan Syed Omar station (Source: DID).

4.31 Muda River discharge (m3s-1) versus suspended sediment loads 122

(ton·es per day) between 1976 and 2002 (Source: DID).

xvii

4.32 Monthly mean suspended sediment (tones/month) hydrographs for 123 the Muda River during the month of surveys between 2001 and 2002 at Jambatan Syed Omar station.

4.33 Diagram of daily river discharge (m3/s) and- suspended sediment 124 (tones/day) at station Jambatan Syed Omar during the months of survey.

4.34 Muda River discharge (m3s-1) versus suspended sediment load (ton 128

per day) for the year of 2001.

4.35 Muda River discharge (m3s-1) versus suspended sediment load (ton 128

per day) for the year of 2002.

4.36 Horizontal distribution of salinity (%o) in spring tide condition for flood 130 tide, survey on 17 October 2001. and (b) ebb to flood tide survey on 12 August 2002.

4.37 Horizo11tal distribution of salinity (%o) in spring tide condition survey 132 on 17 October 2001 at (a) 1.5 and (b) 2.5 m depth.

4.38 Horizontal distribution of salinity (%o) in spring tide condition survey 132 on 12 August 2001 at (a) 1 and (b) 2m depth.

4.39 Horizontal distribution of salinity (o/oo) in neap tide condition for ebb 133 tide, surveyed on 25 October 2001 and (b) flood tide survey on 7 April2002.

4.40 Horizontal distribution of salinity (o/oo) in neap tide condition survey on 134 25 October 2001 at (a) 1 and (b) 2 m depth.

4.41 Horizontal distribution of salinity (%o) in neap tide condition survey on 135 7 April 2002 at (a) 1.5 and (b) 2.5 m depth.

4.42 Vertical distributions of salinity (%o) during spring tide at transect 1 136 (along shore) and (b) transect 2 (across shore) survey on 17 October 2001.

4.43 Vertical distributions of salinity (%o) during neap tide at transect 1 137 (along shore) and (b) transect 2 (across shore) survey on 25 October 2001.

4.44 Horizontal distribution of temperature (0C) in spring tide condition for 138 (a) flood tide, survey on 13 February 2002 and (b) ebb to flood tide survey on 12 August 2002.

4.45 Horizontal distribution of temperature (0C) in spring tide condition 139 survey on 13 February 2002 at (a) 1 and (b) 1.5 m depth.

4.46 Horizontal distribution of temperature (0C) in spring tide condition 140 survey on 12 August 2001 at (a) 1 and (b) 2m depth.

4.47 Horizontal distribution of temperature (0C) in neap tide condition for 141 (a) ebb tide, surveyed on 25 September 2001 and (b) flood tide surveyed on 7 April 2002.

4.48 Horizontal distribution of tempt;!rature (0C) in neap tide condition 142 survey on 25 September 2001 at (a) 1 and (b) 2 m depth.

xviii

4.49 Horizontal distribution of temperature (0C) in neap tide condition 143 survey on 7 April 2002 at (a) 1.5 and (b) 2.5 m depth.

4.50 Vertical distributions of temperature (0C) during spring tide at transect 144 1 (along shore) and (b) transect 2 (across shore) survey oif 13 February 2002.

4.51 Vertical distributions of temperature (0C) during neap tide at transect 145 1 (along shore) and (b) transect 2 (across shore) survey on 25 September 2001.

4.52 Horizontal distribution of density (kgm-3) in spring tide condition for 146

survey on (a) 17 October 2001 and (b) 11 June 2002.

4.53 Horizontal distribution of density (kgm-3) in spring tide condition 147

survey on 17 October 2001 at (a) 1.5 and (b) 2.5 m depth.

4.54 Horizontal distribution of density (kgm-3) in spring tide condition 147

survey on 11 June 2002 at (a) 1 and (b) 2 m depth.

4.55 Horizontal distribution of density' (kgm-3) in neap tide condition for (a) 148

flood tide, survey on 6 June 2002 and (b) ebb tide survey on 28 July 2001.

4.56 Horizontal distribution of density (kgm-3) in neap tide condition survey 150

on 6 February 2002 at (a) 1 and (b) 2m depth.

4.57 Horizontal distribution of density (kgm-3) in neap tide condition survey 150

on 28 July 2001 at (a) 1.5 and (b) 2.5 m depth

4.58 Vertical distributions of density (kgm-3) during spring tide at transect 1 151

(along shore) and (b) transect 2 (across shore) survey on 17 October 2001.

4.59 Vertical distributions of density (kgm-3) during neap tide at transect 1 153

(along shore) and (b) transect 2 (across shore) survey on 7 April 2002.

4.60 Horizontal distribution of rss· (mgl"1) during spring tide at flood tide, 155

surveyed on 12 January 2002 and (b) ebb to flood tide survey on 28 April2002.

4.61 Horizontal distribution of TSS (mgl"1) during neap tide at (a) ebb to 156

flood tide, surveyed on 17 January 2002 and (b) flood to ebb tide survey on 4 July 2002.

4.62 Horizontal distribution of (a) salinity (o/oo) during strong wind surveys 157

on (a) 28 July 2001 and (b) 12 January 2002.

4.63 Horizontal distribution of (a) salinity (o/oo) during weak wind surveys on 158 (a) 17 October 2001 and (b) 12 August 2002.

4.64 Horizontal distribution of temperature (0C) during strong wind surveys 159 on (a) 25 October 2001 and (b) 28 March 2002.

4.65 Horizontal distribution of temperature (0C) during weak wind surveys 159 on (a) 17 January 2002 and (b) 4 July 2002.

xix

4.66 Horizontal distribution of density (kgm-3) during strong wind surveys 160

on (a) 13 February 2002 and (b) 7 April 2002.

4.67 Horizontal distribution of density (kgm-3) during weak wind surveys on 161

(a) 8 November 2001 and (b) 12 August 2002.

4.68 Horizontal distribution of TSS (mgr1) during strong wind surveys on 162

(a) 25 September 2001 and (b) 28 March 2002.

4.69 Horizontal distribution of TSS (mgr1) during weak wind surveys on (a) 163

17 October 2001 and (b) 6 June 2002.

4.70 Tide prediction (m) data during the day of survey on 11 September 164 2004

4.71 Water level observations (m) on 11 September 2004 (spring tide). 164

4.72 Tide prediction (m) data during the day of survey on 25 September 165 2004.

4.73 Water level observations (m) on 25 September 2004 (neap tide). 165

4.74 Measured current magnitude (m/s) on 11 September 2004. 166

4.75 Measured current direction (deg) on 11 September 2004. 166

4.76 Measured current magnitude (m/s) on 25 September 2004. 167

4.77 Measured current direction (deg) on 25 September 2004. 167

4.78 Distribution of (a) the survey stations and (b) current magnitude 170 (cm/s) and direction (deg) at 0.5 m depth, survey on 12 August 2005.

4.79 Distribution of the current magnitude (cm/s) and direction (deg), 170 survey on 12 August 2005 at (a) 1 m and (b) 2m depth.

4.80 Distribution of current magnitude (cm/s) and direction (deg) at 3m 171 depth, survey on 12 August 2005.

4.81 Distributions of temperature at (a) 1 m and (b) 2 m depth survey on 172 12 August 2005.

4.82 Distributions of salinity at (a) 1 m and (b) 2 m depth survey on 12 173 August 2005.

4.83 Distributions of density at (a) 1 m and (b) 2 m depth survey on 12 173 August 2005.

4.84 Vertical distribution of temperature (0C) at along shore transect 174 survey on 12 August 2005.

4.85 Vertical distribution of salinity (%o) at along shore transect survey on 175 12 August 2005.

4.86 Vertical distribution of density (kgm-3) at along shore transect survey 175

on 12 August 2005.

4.87 Salinity-density diagrams along the date of surveys. 187

XX

4.88 Schematic diagrams in 3D model of the salinity distribution in the 195 Muda coastal water for (a) spring tide is characterized by stronger energy (bigger arrow), isohaline is closer to the coastline and the homogenous pattern and (b) neap tide is characterized by weaker energy (smaller arrow), isohaline is further to coastline and stratified pattern.

4.89 Horizontal distribution of (a) sa.linity (o/oo) and (b). temperature (DC) 211 survey on 8 November 2001.

4.90 Horizontal distribution of (a) salinity (o/oo) and (b) temperature (DC) 211 survey on 7 May 2002.

4.91 Horizontal distribution of (a) salinity (o/oo) and (b) temperature (DC) 212 survey on 12 January 2002.

4.92 Horizontal distribution of (a) salinity (o/oo) and (b) temperature (DC) 213 survey on 6 June 2002.

4.93 Horizontal distribution of temperature (DC) survey on (a). 17 October 215 2001 and (b). 28 March 2002.

4.94 An aerial digital image over the Muda coastal water, showing the 218 distinct edge of estuary plume, captured on 28 July 2001. The plume pattern was identified by field observation (TSS) during similar date (insert Figure).

4.95 Sequence of aerial digital images over the Muda coastal water, 220 showing the distinct edge of estuary plume, captured on 20 January 2002. The plume pattern was identified by field observation (TSS) during similar date (insert Figure).

4.96 Sequence of aerial digital images over the Muda coastal water, 223 showing the distinct edge of estuary plume, captured on 9 March 2002. The plume pattern was identified by field observation (TSS) during similar date (insert Figure).

4.97 Sequence of aerial digital im·ages over the Muda coastal water, 225 showing the distinct edge of estuary plume, captured on 1 September 2003.

5.1 Surface horizontal distributions of salinity (o/oo) during (a) high river 236 discharge, on 26 October 2002, and (b) low river discharge, on 23 March 2003.

5.2 Vertical distributions of salinity (%o) during high river discharge, on 20 . 238 May 2003 at (a) transect 1, along estuary and (b) transect 2, across estuary.

5.3 Vertical distributions of salinity (%o) during low river discharge on 17 239 June 2003 at (a) transect 1, along estuary and (b) transect 2, across estuary.

5.4 Surface horizontal distributions of temperature (DC) during (a) high 241 river discharge, on 26 October 2002 and (b) low river discharge, on 23 March 2003.

xxi

5.5 Vertical distributions of temperature (°C) during high river discharge 242 on 19 May 2003 at (a) transect 1, along estuary and (b) transect 2, across estuary.

5.6 Vertical distributions of temperatwe (0C) during low river discharge 243 on 7 June 2003 at (a) transect 1, along estuary and (b) transect 2, across estuary.

5.7 Diagram of maximum temperature (0C) at station Penang Airport 244 during the months of survey in (a) May and (b) June 2003.

5.8 Surface horizontal distributions of density (kgm-3) during (a) high river 246

discharge, survey on 26 October 2002 and (b) low river discharge, survey on 22 March 2003.

5.9 Vertical distributions of density (kgm-3) during high river discharge at 247

(a) transect 1, along estuary and (b) transect 2, across estuary, survey on 20 May 2003.

5.10 Vertical distributions of density (kgm-3) during low river discharge at 248

(a) transect 1, along estuary and (b) transect 2, across estuary, survey on 7 June 2003.

5.11 Surface horizontal distribution of TSS (mgl"1) during (a) high river 250

discharge, survey on 26 October 2002 and (b) low river discharge, survey on 07 June 2003.

5.12 Surface horizontal distributions of Secchi depth (em) during (a) high 252 river discharge, survey on 26 October 2002 and (b) low river discharge, survey on 22 March 2003.

5.13 Surface horizontal distributions· of salinity (%o) during spring tide, 253 survey on 17 June 2003 and (b) neap tide, survey on 7 June 2003.

5.14 Vertical distributions. of salinity (%o) during spring tide at (a) transect 255 1, along estuary and (b) transect 2, across estuary, survey on 23 March 2003.

5.15 Vertical distributions of salinity {%o) during neap tide at (a) transect 1, 256 along estuary and (b) transect 2, across estuary, survey on 7 June 2003.

5.16 Surface horizontal distribution of temperature {0C) during spring tide, 258 survey on 17 June 2003 and (b) neap tide, survey on 7 June 2003.

5.17 Vertical distributions of temperature (°C) during spring tide at (a) 259 transect 1, along estuary and (b) transect 2, across estuary, survey on 17 June 2003.

5.18 Vertical distributions of temperature (0C) during neap tide at (a) 260 transect 1, along estuary and (~) transect 2, across estuary, survey on 7 June 2003.

5.19 Surface horizontal distributions of density (kgm-3) during spring tide, 262

survey on 17 June 2003 and (b) neap tide, survey on 7 June 2003.

5.20 Vertical distributions of density (kgm-3) during spring tide at (a) 263

transect 1, along estuary and (b) transect 2, across estuary, survey on 17 June 2003.

xxii

5.21 Vertical distributions of density (kgm-3) during neap tide at (a) transect 265

1, along estuary and (b) transect 2, across estuary, survey on 7 June 2003

5.22 Surface horizontal distributions of TSS (mgr1) during spring tide, · 266

survey on 22 March 2003 and (b) neap tide, survey on 7 June 2003.

5.23 Surface horizontal distributions of Secchi depth (-em) during spring 268 tide, survey on 22 March 2003 and (b) neap tide, survey on 7 June 2003.

5.24 Surface horizontal distribution of salinity (%o} during strong wind, 269 survey on 17 June 2003 and (b) weak wind, survey on 23 March 2003.

5.25 Surface horizontal distributions· of temperature (0C) during strong 270 wind, survey on 22 March 2003 and (b) weak wind, survey on 26 October 2002.

5.26 Surface horizontal distributions of density (kgm-3) during strong wind, 271

survey on 22 March 2003 and (b) weak wind, survey on 23 March 2003.

5.27 Surface horizontal distributions of TSS (mgl"1) during strong wind, 272

survey on 7 June 2003 and (b) weak wind, survey on 26 October 2002.

5.28 Surface horizontal distributions of Secchi depth (em) during strong 273 wind, survey on 22 March 2003 and (b) weak wind, survey on 23 March 2003.

5.29 Distribution of (a) the survey stations and (b) current magnitude 275 (cm/s) and direction (deg) at 0.5 m depth, survey on 12 August 2005.

5.30 Distribution of the current magnitude (cm/s) and 9irection (deg), 276 survey on 12 August 2005 at (a) 1 m and (b) 2 m depth.

5.31 Distributions of temperature at (a) 1 m and (b) 2 m depth survey on 277 12 August 2005.

5.32 Distributions of salinity at (a) 1 m and (b) 2 m depth survey on 12 278 August 2005.

5.33 Distributions of density at (a) 1 m and (b) 2 m depth survey on 12 278 August 2005.

5.34 Vertical distribution of current magnitude (cm/s) at (a) transect 1, . 279 along estuary and (b) transect 2, across estuarysurvey on 12 August 2005.

5.35 Vertical distribution of temperature (0C) at (a) transect 1, along 280 estuary and (b) transect 2, across estuary survey on 12 August 2005.

5.36 Vertical distribution of salinity (%o) at (a) transect 1, along estuary and 281 (b) transect 2, across estuary survey on 12 August 2005.

5.37 Vertical distribution of density (kgm-3) at (a) transect 1, along estuary 282

and (b) transect 2, across estuary survey on 12 August 2005.

xxiii

5.38 The model structures of the isopycnals patterns in the lower Merbok 289 Estuary that influenced by (a) low river discharge and. (b) high river discharge.

5.39 Diagram of isopycnals that showing the movement and gradual 290 mixing that occurs as the salt water moves up the river.

5.40 Sa!inity-density diagrams for various surveys. 292

5.41 TSS-Secchi depth diagrams for various surveys. 295

5.42 Schematic diagram of the salinity distribution in the lower Merbok 298 River Estuary and the circulation pattern for (a) spring and (b) neap tide.

5.43 Horizontal distribution of (a) salinity (o/oo) and (b) temperature (0C) of 313 survey on 20 May 2003.

5.44 Horizontal distribution of (a) salinity (o/oo) and (b) temperature (0C) of 313 survey on 26 October 2002.

5.45 Horizontal distribution of temperature (0C) of survey on (a) 26 316 October 2002 and (b) 10 April 2003.

5.46 Location map (.) showing the current speed measurement in the 320 lo.wer Merbok Estuary (from Uncles eta/., 1990).

5.47 Variation of the layer Richardson number, RL, in 23 March 2003 322 (spring tide).

5.48 Variation of the layer Richardson number, RL, in 19 May 2003 (spring 322 tide).

5.49 Variation of the layer Richardson number, RL, in 20 May 2003 (spring 322 tide).

5.50 Variation of the layer Richardson number, RL. in 7 June 2003 (neap 323 tide).

5.51 Tide condition in both flight surveys on 9 March 2002 (neap tide) and 324 23 March 2003 (spring tide).

5.52 Approximate coverage area of segmentations captured on 23 March 326 2003 (spring tide).

5.53 Sequence of digital images over the lower Merbok Estuary captured 327 on 23 March 2003.

5.54 Approximate coverage area of segmentations captured on 09 March 330 2002 (neap tide).

5.55 Sequence of digital images over the lower Merbok Estuary captured 330 on 09 March 2002.

6.1 Horizontal distributions of surface salinity (o/oo) during (a) high river 337 discharge survey on 9 April 2003 and (b) low river discharge survey on 14 March 2002.

6.2 Horizontal distributions of surface temperature (0C) during (a) high 338 river discharge survey on 9 April 2003 and (b) low river discharge survey on 14 March 2002.

XXIV

6.3 Horizontal distribution of surface density (kgm3) during (a) high river 339

discharge survey on 9 April 2003 and (b) low river discharge survey on 14 March 2002.

6.4 Horizontal distribution of surface TSS (mgl"1) during (a) high river 341

discharge survey on 9 April 2003 and (b) low river discharge survey on 14 March 2002.

6.5 Horizontal distribution of surface salinity (%o) during (a) spring tide 342 survey on 14 March 2002 and (b) neap tide survey on 3 September 2003.

6.6 Horizontal distribution of surface temperature {0C) during (a) spring 343 tide survey on 14 March 2002 and (b) neap tide survey on 3 September 2003.

6.7 Horizontal distribution of surface density (kgm-3) during (a) spring tide 344

survey on 14 March 2002 and (b) neap tide survey on 3 September 2003.

6.8 Horizontal distribution of surface TSS (mgr1) during (a) spring tide 345

survey on 14 March 2002 and (b) neap tide survey on 3 September 2003.

6.9 Horizontal distribution of surface salinity (%o) during (a) strong wind 346 survey ori 9 April 2003 and (b) weak wind survey on 2 September 2003.

6.10 Horizontal distribution of surface temperature (0C) during (a) strong 348 wind survey on 9 April 2003 and (b) weak wind survey on 2 September 2003. -

6.11 Horizontal distribution of surface density (kgm-3) during (a) strong 349

wind survey on 9 April 2003 and (b) weak wind survey on 2 September 2003.

6.12 Horizontal distribution of surface TSS (mgl"1) during (a) strong wind 350

survey on 9 April 2003 and (b) weak wind survey on 2 September 2003.

6.13 TSS-Secchi depth diagrams along the date of surveys. 356

6.14 Sequence of aerial digital images over the Prai coastal water, 367 showing the distinct edge of estuary plume, captured on 28 July 2001.

6.15 Sequence of aerial digital images over the Prai coastal water,· 370 showing the distinct edge of estuary plume, captured on 28 October 2001. The plume pattern was identified by field observation (TSS) during similar date (insert Figure).

6.16 Sequence .of aerial digital images over the Prai coastal water, 372 captured on 9 March 2002.

6.17 Sequence of aerial digital images over the Prai coastal water, 37 4 showing the distinct edge of estuary plume, captured on 1 September 2003. The plume pattern was identified by field observation (TSS) during similar date (insert Figure).

XXV

List of Abbreviations

Name Definition Page

ADCP Acoustic Doppler current profiler 29

APHA American Public Health Association 98

AVHRR Advanced very high resolution radiometer 34

CDOM Coloured dissolved organic matter 38

DID Department of Irrigation and Drainage, Malaysia 54

DNPS Daya Bay nuclear power station 34

DOC dissolved organic carbon 18

E East 41

ENE East Northeast 82

ESE East Southeast 82

GF Glasfaser Rundfilter 98

GIS Geographic Information System 34

GPS Global Positioning System 66

I CAM Integrating cavity absorption meter 39

IPTS-68 The International Practical Temperature Scale of 101 1968

IUPAC International U~ion of Pure and Applied Chemistry 103

Landsat TM Landsat Thematic Mapper 38

LiDAR Light Detection and Ranging 38

MMS Malaysian Meteorological Services 58

MMSD Malaysian Mapping and Survey Department 54

mg Milligram 99

mg/1 Milligram per liter 99

MSL Mean Sea Level 53

MST 1 Malaysia Standard Time 53

N North 41

NE Northeast 79

NASA National Aeronautics and Space Administration 39

OBS Optical backscatterance sensor 15

xxvi

p Pressure 100

POC Particulate organic matter 18

ppt Parts per thousand 101

PSS-78 The Practical Salinity Scale 1978 36

psu Practical salinity units 29

ROFI Region of Freshwater Influence 65

s Salinity 79

s South 28

SBS Southern Brazilian Shelf 65

SCT Salinity, conductivity and temperature 65

SLFMR Scanning low frequency microwave radiometer 35

SPOT Satellite Pour !'Observation de Ia Terre, is a 28 commercial earth observation satellite

sw Southwest 79

SPM Suspended particulate matter 365

ssw South Southwest 82

T Ter.1 perature 65

TSS Total suspended solids 34

w West 79

WNW West Northwest 82

YSI Yellow Spring Instrument' 65

xxvii

List of Symbols

Name Definition Page A. Absorption coefficient for sediment 38

Bx Absorption coefficient for nonsediment constituents 38 a· Specific backscatter coefficient 38

A Weigh of filter + residue 99

B Weigh of filter 99

8 Buoyancy anomaly 20

c Volume of water sample filtered 99

C' Sediment volume concentration 19

Co Non-dimensional bottom drag coefficient 19

D Depth of typical plume 11

f Coriolis parameter 11

G Acceleration of gravity 11

H Depth 12

K Kelvin number 24

K Secant bulk modulus 100

L Along shore length 12'

yl Across shore length 12

Ri Richardson number 19

Rg Richardson gradient number 106

RL Layer Richardson Number 107

R'd Reflectance 37

Rbias Residual reflectance 37

ri Baroclinic Rossby radius 11

p Average density of plume water 11

Pa Density of ambient coastal water 11

Ps Density of siliceous sediment 20

u Current velocity 12

Umax Total current velocity 19

xxviii

Uw RMS wave orbital_velocity 20

Ug Average current velocity in x direction 20

v Specific volume 100

Vc Magnitude of along shelf current 20

%o Part per thousand (unit of salinity) 111

ct> Diameter 98

Ot Density 105

to(A.) Ozone and water vapor absorption optical depth for 37 channel A,

tr(A) Rayleigh optical depth for channel A 37

xxix

List of Appendices

Appendix A All results and data of Muda surveys

Appendix B All results and data of Merbok surveys

Appendix C All results and data of Prai surveys

XXX

Page

Appendix A-1 to Appendix A-17 5 Appendix 8-176 to Appendix 8-216

Appendix C-217 to Appendix C-234

PENGARUH LUAHAN SUNGAI, PASANG SURUT DAN ANGIN TERHADAP PLUM ESTUARI Dl BARATLAUT

SEMENANJUNG MALAYSIA

ABSTRAK

Tujuan thesis ini adalah untuk mengkaji struktur daripada plum estuari dan perairan

pantai secara spasial dan temporal di baratlaut Semenanjung Malaysia. Pengukuran

saliniti, suhu dan sedimen terampai (TSS) dijalankan bagi kawasan plum Muda, plum

Prai dan dibahagian bawah Estuari Merbok. Di samping itu imej digital (imej udara)

dan pengukuran arus juga diperolehi di beberapa tempat kajian yang terpilih. Luahan

daripada sungai Muda adalah satu orde kali ganda lebih tinggi daripada Sungai Prai

dan Sungai Merbok.

Keputusan yang diperolehi menunjukkan ciri-ciri permukaan plum bagi estu~ri dan

perairan laut yang dipengaruhi oleh luahan air sungai, tenaga pasang surut dan juga

oleh kekuatan angin. Semasa luahan tinggi, pergerakan bagi plum estuari Muda dan

plum Prai ke perairan laut adalah masing-masingnya sekitar 4 km dan 2 km dari garis

pantai. Keluasan permukaan yang dilitupi oleh estuari plum tersebut adalah bagi

masing-masingnya sekitar 30 km2 dan 13.5 km2• Semasa luahan rendah, jarak plum

akan berkurangan makin berdekatan sekitar 1-2 km dari garis pantai.

Pasang surut adalah penyebab kepada campuran dan penstrataan daripada plum.

Plum Muda dan bahagian bawah Estuari Merbok, semasa perubahan daripada

pasang surut perbani (spring tides) kepada pasang surut anak (neap tides}, struktur

plum bertukar daripada penstrataan separa atau homogen (pasang surut perbani)

kepada penstrataan tinggi (pasang surut anak). Kepekatan TSS yang tinggi adalah

konsisten bagi plum Muda dan plum Prai dan bahagian bawah Estuari Merbok

semasa pasang surut perbani dibandingkan dengan semasa pasang surut anak

disebabkan oleh tenaga pasang surut perbani yang lebih tinggi. Sebaliknya semasa

pasang surut anak perlakuan yang sama bagi kepekatan TSS tidak diperolehi. Tiada

korelasi yang jelas diperolehi diantara ciri-ciri plum dan kekuatan angin, kecuali

xxxi

semasa kekuatan angin yang kencang yang menunjukkan terdapat bukti bahawa

pergerakan plum adalah mengikuti arah angin.

Penderiaan jauh memberikan maklumat secara dua dimensi bagi struktur permukaan

plum estuari. lmej digital jelas menunjukkan bahawa plum Prai akan terherot ke arah

selatan/utara semasa luahan air sungai yang rendah/tinggi. Perlakuan ini dipengaruhi

oleh pasang surut.

XXXll

PENGARUH LUAHAN SUNGAI, PASANG SURUT DAN ANGIN TERHADAP PLUM ESTUARI Dl BARATLAUT

SEMENANJUNG MALAYSIA

ABSTRAK

Tujuan thesis ini adalah untuk mengkaji struktur daripada plum estuari dan perairan

pantai secara spasial dan temporal di baratlaut Semenanjung Malaysia. Pehgukuran

saliniti, suhu dan sedimen terampai (TSS) dijalankan bagi kawasan plum Muda, plum

Prai dan dibahagian bawah Estuari Merbok. Di samping itu imej digital (imej udara)

dan pengukuran arus juga diperolehi di beberapa tempat kajian yang terpilih. Luahan

daripada sungai Muda adalah satu orde kali ganda lebih tinggi daripada Sungai Prai

dan Sungai Merbok. Keputusan yang diperolehi menunjukkan ciri-ciri permukaan

plum bagi estuari dan perairan !aut yang dipengaruhi oleh luahan air sungai, tenaga

pasang surut dan juga oleh kekuatan angin. Semasa luahan tinggi, pergerakan bagi

plum estuari Muda dan plum Prai ke perairan !aut adalah masing-masingnya sekitar 4

km dan 2 km dari garis pantai. Keluasan permukaan yang dilitupi oleh estuari plum

tersebut adalah bagi masing-masingnya sekitar 30 km2 dan 13.5 km 2. Semasa luahan

rendah, jarak plum akan berkurang~m makin berdekatan sekitar 1-2 km dari garis

pantai. Pasang surut adalah penyebab kepada campuran dan penstrataan daripada

plum. Plum Muda dan bahagian bawah Estuari Merbok, semasa perubahan daripada

pasang surut perbani (spring tides) kepada pasang surut anak (neap tides), struktur

plum bertukar daripada penstrataan separa atau homogen (pasang surut perbani)

kepada penstrataan tinggi (pasang surut anak). Kepekatan TSS yang tinggi adalah

konsisten bagi plum Muda dan plum Prai dan bahagian bawah Estuari Merbok

semasa pasang surut perbani dibandingkan dengan semasa pasang surut anak

disebabkan oleh tenaga pasang surut perbani yang lebih tinggi. Sebaliknya semasa

pasang surut anak perlakuan yang sama bagi kepekatan TSS tidak diperolehi. Tiada

korelasi yang jelas diperolehi diantara ciri-ciri plum dan kekuatan angin, kecuali

semasa kekuatan angin yang kencang yang menunjukkan terdapat bukti bahawa

pergerakan plum adalah mengikuti arah angin. Penderiaan jauh memberikan

XXXI

maklumat secara dua dimensi bagi struktur permukaan plum estuari. lmej digital jelas

menunjukkan bahawa plum Prai akan terherot ke arah selatan/utara semasa luahan

air sungai yang rendah/tinggi. Perlakuan ini dipengaruhi oleh pasang surut.

XXXll

THE INFLUENCE OF RIVER DISCHARGES, TIDES, AND WINDS ON ESTUARINE PLUME IN NORTHWEST

PENINSULAR MALAYSIA

ABSTRACT

The aim of the thesis was to investigate the spatial and temporal structure of

estuarine plume and coastal waters in northwest Peninsular Malaysia. Measurements

of salinity, temperature, and TSS were carried out at the Muda plume, Prai plume and

the lower Merbok estuary. In addition, aerial images and current measurements were

also obtained through several selected field surveys. The discharge of the Muda

River was an order of magnitude more than Prai and Merbok Rivers. The results

suggest that the surface plume characteristics of the estuaries and coastal waters are

influenced by freshwater discharge, spring-neap tidal energy, and to some extent by

wind forcing. During high discharge, the offshore extent of the Muda and Prai estuary

plumes were approximately 4 km and 2 km respectively. The surface horizontal areas

covered by these plumes were 30.0 km2 and 13.5 km2, respectively. During low

discharge, the extent of plumes were closer to the coastline at about 1-2 km offshore.

Tides were responsible for the mixing and the stratification of the plumes. The Muda

plume and the lower Merbok Estuary, during the transition of spring-to-neap periods

that change the plume structure from partially-mixed or homogeneous (spring tide) to

highly stratified (neap tide). There were consistently higher TSS concentrations of

Muda and Prai plume waters and Merbok Estuary during spring tides than at neap

tides due to stronger spring tide energy. On the contrary, during neap tide a similar

behavior of TSS concentration was not found. No obvious correlation was found

between the plume characteristics and wind forcing, except during strong winds when

there were some evidence of plume movement according to wind direction. Remote

sensing provided information on the two-dimensional surface structures of the estuary

plumes. For example, the aerial images clearly showed snapshots of the Prai plume

being deflected to the south/north during low/high discharge. These behaviors were

influenced by tides.

XXXlll

1.0 Introduction

Chapter One

Introduction

In studying and observing the coastal and estuary, the very first it is important to

understand the basic concepts and their characteristics. The coastal area is

significantly affected by various forcing mechanisms occurring over a broad range of

spatial and temporal scales. The coastal ocean response to these various forcing

mechanisms depends critically on the geometry and topography of the region, as well

as the scale of the forcing. These relevant forcing mechanisms influencing the coastal

characteristics are: river discharge, tidal range, atmospheric events (wind, waves,

atmospheric temperature, rainfall, and density gradients (buoyant plumes)).

The estuary is a dynamic mixing areas for fresh and salt water, is particularly important

because their high productivity. The term estuary means the lower tidal reaches of a

river. Elliott and Mclusky (2002) concluded that as existing definitions would never be

suitable for all needs, a different approach is required. According to a contemporary

definition and most scientist accept the definition of Pritchard (1967), based on

physical characteristics: "an estuary is a semi-enclosed body of water having. a free

connection with the open sea and within which the seawater is measurably diluted with

freshwater draining from the land". The estuary functions as a buffer between the

ocean and the land. It can filter sediment and pollutants from the water before it flows

into the oceans. Basically, all estuaries will interact physically with the open coast. This

interaction is expressed in terms of both the influence of the estuary on the coast, and

the influence of the coast on the estuary. It is important to understand the dynamics of

estuarine systems, especially their water and sediment movement.

The movement of river waters into estuary and coastal region is part of an

interconnected environmental system. Freshwater discharge is one of the most

influential landscape processes affecting physical structure and function in estuaries,

deltas and coastal. As a natural process, rivers drain freshwater discharge from rainfall

events over land. The runoff and the downstream movement of materials is one of the

primary controls over the productivity of estuarine systems and coastal waters. The

river discharge collects a variety of materials as it moves through the river's

catchment, lands and waterways including nutrients, sediments and contaminants

depending on the catchment characteristics. Upon reaching the sea at the estuary

mouth, the discharge drives a buoyant plume into coastal and shelf waters. It is an

interesting phenomena that can be observed, a distinct color difference between the

river and seawater. The area that appears to be extension of more brown color river

water than seawater into the coastal zone is called a plume.

1.1 Motivation

The study areas are the estuaries and coastal waters of the Northwest of Peninsular

Malaysia, are well known for their !')roductive and diverse marine ecosystem, but little

is known about the physical oceanography of the region. The Muda, Merbok c;~nd Prai

Rivers, as a representative of tropical estuaries and coastal waters, drain into the

Malacca Straits. There are some other factors deciding upon the complexity of the

hydrodynamic phenomena such as: river discharges, tides, winds, atmospheric

temperatures changes and sediment transport that appears in the estuaries and

coastal waters.

2

Understanding the interactions between estuaries or coastal waters and global

changes cannot be achieved through estimation or laboratory studies alone.

Observational studies of key environmental processes is a significant and vital method

that must be used to achieve its overall objectives, particularly in view of the fact that

many of the uncertainties and real natural problems and processes occurring within

the estuaries and coastal waters. This thesis is intended as a guide for those wishing

to contribute to the objective of elucidating plume dynamics, suspended sediment

concentration, turbidity (Secchi depth), density, salinity and temperature distribution in

estuaries and coastal waters. Characteristics behavior of all these parameters directly

correlated with the plume, that also as a representative of tropical plume. Figure 1.1 a

shows a schematics plan view of an estuary plume while Figure 1.1 b illustrates a cross

shore section of the plume, with the less dense river water overlying the more dense

seawater. The vertical section shows how the plume floats out into the seawater,

creating strong turbulence along its boundary as the fresh river water is absorbed into

the seawater surroundings. The plume eventually spreads and mixes with ambient

coastal waters.

This study has historically been motivated by the desire to both exploit and preserve

resources in estuaries and coastal waters. It was done by the need to understand the

distribution and fate of these estuarine waters, after their release into the coastal zone.

The study will focus on the characteristics of the estuary plume in the study areas. The

study is designed as a 1-year research for Muda coastal zone, starting in July 2001

and ending in August 2002, 6-months in Merbok River estuary, and 4-months in Prai

coastal zone.

3

Estuary Mouth

Figure 1.1 (a) A schematic plan view of an estuary plume in the coastal water, and (b). A vertical section of an estuary plume as the fresher water

discharge from the estuary to coastal water.

1.2 Hypothesis

Studies on the temporal and spatial structures of the estuary plume are of

considerable interest not only because of its influence on the physical processes of the

shelf circulation but also because of its close relationship to environmental problems.

In particular, the vast amount of land-drained materials, suspended materials, and

sewage brought onto the continental shelf through the river discharge may significantly

4

affect the formation of the estuary plume in the coastal zone. It is, therefore, important

to have a general understanding of the coastal circulation as well as trace and predict

the pathways and distributions of estuary plume in coastal waters.

This study demonstrates the movement of estuary plumes from the estuary mouth to

inshore systems. Measurements taken near the mouth of the estuary systems are

more representative of the processes that are occur in rivers that are dependent on the

characteristics of that river system. Samples taken at close proximity to the mouth may

generally be high in suspended matter that are related to the river source and also

bottom sediment of coastal water.

The hypotheses or assumption made in this study are:

0 High/low river discharge that related to the wet/dry season is one of the most

influential factors affecting the physical structure of the estuary plume. As a

natural process, freshwater discharge forcing and the downstream movement

of sediments is one of the primary control of the characteristic of coastal sea.

During high discharges (wet season) are expected well develop of estuary

plume. On the other hand, ~rom low discharges (dry season) are expected

would result less or no plume.

0 Tidal forces would produces cross shelf plume water movements. A mixing of

sea and river water by tidal energy would determine the movement of plume

water from the coastal water. During neap tides, it is expected that the plume ,,

waters would pushed landward on flood phase. While, during spring tides it is

expected that the plume water would push further seaward on ebb phase. The

magnitude of plume movement in spring tides would be higher than in neap

tides.

0 Wind force will induce a shear stress on the surface water causing the plume

water to move in the general direction of the wind, and transfer energy to the

5

water column. During periods of strong winds, it is expected that the movement

of plume water would follow the direction of the wind. In periods of weak wind,

there is no significant influence on plume water movement.

1.3 Objectives and scope

The general objective of this study is to elucidate the basic physical processes

associated with the characteristics of estuary plume. In particular, the study will focus

on understanding river discharge, tidal, and wind forcing in determining the structure,

patterns and fate of the plume. One of the key contributions of this work is

quantification of both the along and cross shore motions of plume waters, and their

distribution around the lower estuary.

The study have .the following major objectives:

0 To investigation the spatial and temporal structure of the Muda, Merbok and

Prai Rivers estuary plume under a range of river discharge, tide and wind

regimes.

0 To carry out aerial surveys and observe their significant relationships with field

measurements.

0 To determine the physical mechanisms governing plume near the estuary

mouth and coastal zone.

To carry out the objectives of the study, the area of observation will be established and

will include: (1) the observations of salinity, temperature, density, total suspended

solids (TSS), and Secchi depths near the mouths of three rivers of many tributaries

flowing into coastal of Northwest Peninsular Malaysia, (2) the collection and

measurement of tidal phase, rainfall, river discharge, water level, atmospheric

6

temperature, current velocity, and wind speed and direction at specific locations inside

the coast, estuary and in land.

In order to achieve the above objectives, it is need to limit the scope of study and

provide some coherence. This study will focus on the theme of coastal and lower

estuary processes and exchange i.e., identifying and understanding processes that are

important in flowing plume water and associated seasonal, dynamical and physical

oceanography across and along the shore and lower estuary. Even this is not a new

problems in physical oceanography, however the objective of this study emphasis on

this problem in motivated by several factors:

0 To obtain a more thorough understanding of the hydrographic characteristics

and dynamics of the Muda and Prai coastal waters, lower Merbok Estuary and

the adjacent estuary mouth region.

0 To delineate the extent and distribution (spatial and temporal distribution) of the

Muda, Merbok and Prai Estuary plume in relation to the local hydrology

characteristics and assesses the potential processes that might control (or

have affected) the distribution of plume water in the coastal area and lower

estuary.

0 To use recent developments of instrumentation and techniques to gain new

insights into estuary and coastal processes, wind driven over coastal and

buoyant plumes associated with river discharge onto coastal waters.

1.4 Thesis outline

The study is done base on the need to understand processes occurring in estuary and

coastal region arises from a variety of historic and contemporary topics in physical

oceanography. It includes observation of the estuary and coastal dynamics in the

Northwest Coastal of Peninsular Malaysia. In particular, the study focuses on the

7

interactions of estuary (brackish estuarine) discharge in coastal after it leaves the

estuary mouth, and also in lower estuary. It is very interesting and importan~role in

coastal ocean and estuary dynamics because of it acts as a repository of organic

matter in marine sediments, and source of nutrients .and contaminants. This

phenomenon is one of the interesting features to understand from this study.

The thesis is organized as follows. In Chapter 2, a brief review of the relevant

theoretical and experimental investigations are presented in order to place the present

work its appropriate context. In chapter 3, study sites characteristic, meteorological

and hydrography data, field and laboratory works, and the methods are explained

briefly. In Chapters 4, 5 and 6 present results and analysis from all observation

conducted in the Muda, Merbok and Prai Rivers. Finally, Chapter 7 provides

conclusions and significant findings of the results and suggests directions for future

research.

8

Chapter Two

Literature Review

Studies of the characteristics and structures of estuary plume are very interesting not

only because of its influence on the physical processes of the coastal circulation but

also because of its close relationship to environmental and ecosystem problems. In

particular, it is important to have a general understanding of the coastal circulation as

well as to trace and to predict the trajectories and distributions of estuary plume in the

coastal ocean.

2.0 Estuary plume structures

Several research and observations show that estuary plumes have different structures

in different regions. In general, the plume structure is principally determined by the

local conditions like the total volume of freshwater outflow, winds, tides, coastal

currents and bathymetry. A review is given by Wiseman and Garvine (1995). Estuary

plumes can be characterized by a Kelvin number, the ratio of the width of the river

mouth to the baroclinic Rossby radius (Garvine, 1987):

and

K=w/r. l

9

2.1

2.2

where p is the average density of plume water, Pa is the density of ambient coastal

water, g is the acceleration of gravity, d is the typical plume depth, and f is the Coriolis

parameter. Physically for a plume with small K, the deflection of the plume alongshore

tends to be dominated by motion of ambient coastal water, not by the anticyclonic

turning action of Coriolis force, while for of order unity or larger effects of the earth

rotation or the Coriolis force becomes important. Garvine (1995) offered a method to

classify buoyancy flows in coastal waters. He considered the balance of the following

forces: horizontal advection, Coriolis, pressure gradient, wind stress and bottom

stress. Figure 2.1 shows an idealized buoyant plume.

y 1 ~~

\ /----~---,~-----------~ ·/\u- '' .... '''.~4:· ! dlscharge

source

z

J'tJ- ..lp

"

I .!' ..

)'L

I I

I .!'

I

h

Po

'f

.....

'·

(a)

(b)

Figure 2.1 Sketch of buoyant layer scales. (a) x and y are alongshore and acrossshore coordinates. Dashed line denotes a bounding isopycnal contour for the buoyant layer. U is typical alongshore buoyant water velocity. L and yL are the alongshore and the across-shore length scale, respectively. (b) A typical across-shore vertical section with vertical coordinate z. Dashed line shows typical bounding isopycnal for the buoyant of typical depth h. (from Garvine, 1995).

10

This kind of estuary pllJ.me is described by theoretical model to obtain approximate

solutions to several problems which are interpreted to yield new insights of these

phenomena (O'Donnell, 1990). However, James (1997) dealing with regions of the sea

where the dynamical effect of the coastal discharge .of relatively freshwater is

significant by developed the anticyclonic circulation model that can change the

expected direction of the discharge plume. For the mathematical description of plume

structure, Poulos and Collins (1994) predicted the spread of freshwater outflow for a

small river based upon a combination . of frictionally-controlled and buoyant plume

dispersal models. Here, the estuary plume decelerates rapidly for the first 400 m to

seaward of the estuary mouth, and at the transitional zone, the plume has lost then its

initial momentum and it is controlled now by buoyant forces and entrainment

processes.

Fennel and Mutzke (1997) studied the initial evolution of a buoyant plume. They stated

that estuary plumes are forced by two mechanisms: (i) momentum added to the ocean

at the estuary mouth and (ii) intrusion of buoyancy at the estuary mouth. Several

researchers such as, Ingram (1981), O'Donnell (1990), RU;ddick eta/. (1995), James

( 1997) and Broche et a/. ( 1998) implied that the study of estuary plume is a subject

related to river discharge. Since the river discharge is fairly small, mixing between river

water and seawater to be extremely small, thus the estuary plume might be disturbed

by turbulence advected from beyond the location. When the amount of river discharge

becomes much larger, the salt water is pushed out from the estuary mouth so that the

estuary plume becomes supercritical (Murata and Nakatsuji, 1988; Chao, 1998).

The freshwater inflow provides a direct input of momentum as well as a large

buoyancy source, both of which contribute to the motion over the shelf. The surface

salinity distribution and the suspended sediment distribution from the Eel River plume

exiting the mouth of the Bay are shown in Figure 2.2 and Figure 2.3. These

observations indicate that the suspended sediment was behaving nearly

11

conservatively within the plume during the high-flow, down welling conditions, and that

sediment was being lost to settling during the falling-flow, upwelling conditions. Beside

that, because of high rates of particulate and river discharge, the estuarine processes

usually take place on the adjacent continental shelf instead of in a physically confined

estuary (Dagg et at., 2004). The other results suggest that Fouha Bay (at southwest

coast of Guam) is flushed annually by waves generated from typhoons passing to the

• 40450'

40"40'

15

iO 5 {I 10

km From Go!lsl

Figure 2.2 Salinity distributions during the January 1997 flood. Upper panels: near-surface (1.5m) salinity distributions; lower panel: cross-sections at river mouth (from Geyer eta/., 2000).

12

0 ' ' y • .~' ~,. l~ e \~

5 \ ' . l I ,, .g ~o.,._._ ~ ....

·~. I ~tO !

15 I

• I 10 5 0 10 5 0 10 5 (l

km From 0Qa$t

Figure 2.3 Total suspended sediment distributions during the 1997 flood. Upper panels: nearsurface (1.5 m) suspended solids, based on water samples; lower panel: crosssections at river mouth, based on water samples and optical backscatterance sensor (OBS) profiles (from Geyer et at., 2000).

south of Guam. If sediment input can be substantially reduced through improved land-

use practices, water and substratum quality should improve and provide the conditions

for reef regeneration to occur (Wolanski eta/., 2005).

13

2.1 Sediment transport

Coastal areas and estuaries are an important element in cycle processes, because

much of the sediment found on the ocean floor is derived from land and reaches the

ocean through rivers and their estuaries. There are a variety of interesting and

important dynamical processes that occur within the coastal regions after the modified

river water leaves the estuary. A plume typically forms as the buoyant water spreads

away from the mouth of the estuary.

In coastal area, sediment transport in estuary plumes is controlled not only by the

trajectory of the freshwater plume, but also by rate of settling, the plume thickness and

plume velocity (Geyer et at., 2000). The dynamics and structure of plumes of small

rivers differ considerably from those of large rivers, due to differences in the physical

scales of the processes near the estuary mouth (Garvine, 1995) and relatively short

duration from small (e.g., Eel and Waipaoa River), and large sedim~nt input compared

to large river (e.g., Columbia, Mississippi, and Amazon River) (Wheatcroft, 2000). The

transport processes of sediment from the small river to the coastal ocean occurs in

freshwater plume, whose trajectories may strongly depend on discharge magnitude

and sediment load, the rate of flocculation of particles within the plume, and the

ambient oceanic conditions (currents and density structure) (Morehead and Syvitsky,

1999) and a region's climate and local drainage-basin characteristics (e.g., headwater

elevation) (Syvitsky and Morehead, 1999).

On the contrary, transport processes of estuary plume for large rivers cannot be

understood by simply scaling up the mag·nitudes and impacts of dominant processes in

smaller rivers. Time and space scales over which these transport and transformation

processes occur vary greatly, depending on factors such as scales of discharge,

suspended sediment loads, latitude of discharge, and winds and tides, which affect

plume behavior, and also affected by meteorology and climatology, bottom topography

14

of the receiving site and orientation of plume (Dagg eta/., 2001) and planetary rotation

(Simpson and Sharples, 1994; O'Donnell, 1990). For examples, these effects (river

discharge and the amount of sediment loads) for the world's largest river are

summarized in Table 2.1.

Buoyancy is a key mediating factor in the transports and transformations of estuary

plume in the coastal margin. The expansion, contraction, and alongshore orientation of

surface plumes are often influenced by tide and wind conditions (Davies and Xing,

2001; Schallenberg and Krebsbach, 2001; Joordens et a/., 2001 ), besides river

discharge and wave conditions (Scully eta/., 2004; Wright eta/., 2002; Aubertot and

Echevin, 2002; Durand et at., 2002; Wheatcroft, 2000; Mullenbach and Nittrouer,

2000).

Table 2.1 Discharge data for the world's largest rivers (from Dagg et al., 2001).

Water Sediment Drainage POC DOC River (Country) discharge discharge basin 1 06 ty"1 106 ty-1

109m3 -1 109m3 -1 106 km2

Amazon (Brazil) 6300 1150 6.15 13.0 19.1 Zaire (Zaire) 1250 43 3.82 2.8 10.15 Orinoco (Venezuela) 1200 150 0.99 2.0 4.5 Ganges-Brahmapura 970 10SO 1.48 nd nd (Bangladesh) Yangtze (China) 900 480 1.94 4.4 11.8 Yenisey (Russia) 630 5 2.58 0.17 4.86 Mississippi (USA) 530 210 3.27 0.8 3.5 Lena (Russia) 510 11 2.49 0.46 3.38 Mekong (Vietnam) 470 160 0.79 nd nd Parana/Uruguay (Brazil) 470 100 2.83 1.3 5.9 st.·Lawrence (Canada) 450 3 1.03 0.31 1.55 Irrawaddy (Burma) 430 260 0.43 nd nd Ob (Russia) 400 16 2.99 nd 3.69 Amur (Russia) 325 52 1.86 nd nd Mackenzie (Canada) 310 100 1.81 1.8 1.3 Xi Jiang (China) 300 80 0.44 nd nd Salween ( Burma) 300 100 0.28 nd nd Columbia (USA) 250 8 0.67 nd 0.5 Indus (Pakistan) 240 50 0.97 nd 0.75 Magdalena (Columbia) 240 220 0.24 nd nd Zambezi (Mozambique) 220 20 1.2 nd nd Danube (Romania) 210 40 0.81 nd nd Yukon (USA) 195 60 0.84 nd nd Niger (Africa) 190 40 1.21 0.66 0.53 Purani/FI New Guinea 150 110 0.09 nd nd

Notes: POC: particulate organic matter; DOC: dissolved organic carbon, nd: no data.

15

In addition to the surface plume, in some instances the freshwater also produces

coastal current locally and the fate of these coastal currents far downstream and over

long time scales as they move downstream due to the effects of turbulent mixing,

friction and other processes. The offshore penetration of buoyant water depends on

three dimensionless parameters: scaled inlet volume transport, scaled breadth and

scaled "diffusivity" (Narayanan and Garvine, 2002; James, 2002). A model of radial,

time dependent spreading of shallow buoyant layer over a motionless, deep ambient

layer is developed by Garvine (1984). Wright eta/. (2001) develop a simple model that

incorporates the influence of ambient shelf current on gravity-driven transport of

suspended sediment, shows in Figure 2.4 and Scully eta/. (2002) applied this model in

the Eel River, to examine the formation of the mid shelf flood deposit on the

continental margin. The governing equation for total current velocity Umax is (Wright et

a/., 2001 ):

{ 2 2 2 ) 112 umax = \uw +ug +vc 2.3

where Uw is rms wave orbital velocity, Ug is average velocity in x direction, and Vc, is the

magnitude of along shelf current. Richardson number is given:

Umax "'(U~2 + uri + Vc2) 112

Figure 2.4 Schematic diagram illustrating estuary plume push by gravity driven flow (from Wright eta/., 2001).

16

2.4

where g is acceleration of gravity, sis the submerged weight of siliceous sediment

relative to sea water, c' is sediment volume concentration, and 8 is buoyancy anomaly

integrated over the thickness of turbid layer.

For case of stratified gravity flows in which Umax=Ug, and combined with the classical

Chezy equation BsinB = C0 u; to yield:

R. = CD ' sinO

2.5

Co is a non-dimensional bottom drag coefficient, and the maximum sustainable flux

associated with the gravity driven flow is:

Qcr = UcrPsBcr = Ps(sinB)Ri2rU~ax gs gsCD

2.6

where Ps';:(, 2.65 is the density of siliceous sediment.

Many investigators have described the importance of physical characteristics of

estuary plumes and sediment transport phenomena from different perspectives, ~n the

basis of mathematical models (Poulos and Collins, 1994; Khondaker, 2000), numerical

model (Syvitski and Bahr, 2001; Wu and Falconer, 2000; Scully et a/., 2002; Davies

and Xing, 2001 ), remote sensing (Bowers et a/., 1998), laboratory experiments

(Gustafsson eta!., 2000; Savory and Toy, 2000; Thill eta!., 2001; Davies and Ahmed,

1996), field observations (Hill eta/., 2000; Liu eta/., 2000; Wright eta/., 2001; Emeis et

a/., 2002; Christiansen eta/., 2002).

17

Besides that, the settling behavior of sediment transport of a river flow, has been

studied elsewhere, for examples in the southern Brazilian shelf (Soares and Meller Jr,

2001), the Kara S-ea Rivers in Arctic Ocean (Harms eta/., 2000), the Tseng-wen River

in southern Taiwan (Liu et a/., 2002; Liu et a/., 2002a), the Eel River in northern

California continental shelf (Ogston et a/., 2000; Wright et a/., 2002; Geyer et a!.,

2000; Syvitski and Morehead, 1999), and the Satilla River Estuary, Georgia (Zheng et

a/., 2003).

In estuaries, the movement of a salt wedge into the estuary not only retards the

movements of bed load, it also has an effect on the suspended sediment transport.

Beside, freshwater runoff from river into the estuary is an important element of the

dynamics over many estuaries. There are a variety of interesting and important . .

dynamical processes that occur within the estuary. Since estuary outflows tend to be

less saline and hence lighter that the ambient shelf water, a plume typically forms as

the buoyant water spreads away from the mouth of the estuary.

The vertical and horizontal structure of buoyant plumes also varies. Most previous

studies have focused on the plumes distribution that influence by the direction and

strength of wind and discharge volume of the river. Some plumes, such as the

Pomeranian Bight River plume (Mohrholz eta/., 1999) was mainly control by the local

wind forcing as well as the baroclinic pressure gradients. This condition is contrast with

the situation in the ocean water estuary plumes that are mainly controlled by tidal

currents and the Coriolis force. However, under relatively different condition,· in dry

seasons during the winter, Wong et a/. (2004) modeled the small scale circulation

associated with the plume front in the Pearl River Estuary. Generally, the plume front

is formed by salinity gradient between the estuarine water and the higher salinity shelf

waters.

18

The relative importance of stratification-destratification processes in the Mobile Bay is

described by Schroeder eta/. (1990) and in the Merbok Estuary is described by Uncles

et a/. (1990). However, Garvine (1995) has provide a simple classification system for

buoyant discharge based on the Kelvin number (K), the ratio of the buoyant plume

width to the baroclinic Rossby radius. Then, Wiseman and Garvine (1995) stressed the

importance of the Kelvin number in characterizing anticipated plume behavior. They

showed that without strong external forcing, a northern hemisphere plume will turn

anticyclonically and attach to the coast, where it then merges into a coastal current.

2.2 Factors affecting estuary plume

A variety of different factors can influence estuary plume in the coastal, including tides,

winds, variations in the river discharge, and ambient shelf circulation (Hill eta/., 2000;

Geyer eta/., 2000; Tillis, 2000; Gelfenbaum and Stumpf, 1993)~

2.2.1 River discharges

The discharge of freshwater from river onto coastal region typically results in the

formation of a buoyant plume. Fennel and Mutzke (1997) stated that estuary plumes

forced by two mechanisms: (i) momentum added to ocean at the estuary mouth and

(ii) intrusion of buoyancy at the estuary mouth. It is occurs in river or estuary or out on

the continental shelf depends to a large part on the strength of the river discharge

(Gelfenbaum and Stumpf, 1993; Bowden and ElDin, 1966). Table 2.1 shows several

the word's largest river that have large enough discharge to produce a buoyant plume

each year. While small scale estuary plume such as the Koombana Bay plume,

Western Australia (Luketina and lmberger, 1987) the plume in the Tees River,

northeast coast of England (Lewis, 1984), the Eel River plume, northern California

19

(Mullenbach and Nittrouer, 2000; Wheatcroft, 2000; Curran eta/., 2002; Ogston and

Sternberg, 1999), the Satilla River plume, Georgia (Blanton et at., 2001), the Ebro . - . -

River plume, Spain (Durand eta/., 2002), and the plume some rivers along the Greek

shoreline (Poulos and Collins, 1994) had lengths of a few t~ a few tens of kilometers

and remained well defined for short time periods (several hours).

At large scales, the estuary plume show a common feature regardless of the size of

the plume or the amount of the freshwater introduced on the shelf (Gelfenbaum and

Stumpf, 1993). Estuary plume regions, the area in which influenced of freshwater and

the dynamical effect of coastal discharge occur. Garvine (1999) and then Narayan and

Garvine (2002) developed a three dimensional nonlinear model to define the fate of

plumes that produced by freshwater discharge from rivers and estuaries. Beside, Ye

and Garvine (1998) developed. for barotropic tidal flows, then the anticyclonic

circulation can deflected the estuary plume from its expected turning direction as it

leaves the estuary mouth (James, 1997). This is shown in Figure 2.5, which is a

coastal current flowing out of the river and a front cross the river between the stratified

zone and offshore water.

2.2.2 Tides

It is significant that the tides affected by bathymetry of the oceans, seas, bays, and

river estuaries as the tidal forces are transmitted and modified by fluid dynamic forces.

Several field studies were conducted to examine the spreading of surface plume

formed by buoyant water flowing from river into ocean. Marmorino et a/. (2000)

reported strong pulses of estuary plume from large estuaries, such as Chesapeake

Bay, and tends to bulge outward over the continental shelf. The tidal modulation near

the estuary mouth typically produces along the seaward edge of the discharge a

strong salinity front, which delineates the buoyant outflow from well-mixed, denser

20

t

' / Front

t Coa:>tal current

Figure 2.5 Conceptual diagram of river flow, according to the strength of outflow, the plume may turn to left or right (from James, 1997).

shelf water and which moves outward with the ebbing tidal current. Another example,

the largest delta environment on the Pacific coast of South America, the San Juan

River delta is dominated by tide. The interacting processes that influence the

hydrodynamics of the distributary channels in the delta are either fluvial and tidal

processes (Restrepo and Kjefve, 2002; Blanton eta/., 2002; Zheng eta/., 2004).

In addition, Liu eta/. (2002) stated that the basic influence of plume behavior is c'oastal

tide. Since the river runoff and sediment discharges are constant, the basic plume

dispersal pattern is determined by the interaction of the sediment-laden buoyant

effluent and the flow field (tidal currents). In the Chesapeake Bay estuary, the tidal

variability of the flows was dominated by semidiurnal constituents that displayed

greatest amplitudes and phase lags near surface and in the channel (Levinson et a/.,

1998). Schallenberg and Krebsbach (2001) describe the horizontal tidal movements

21

and salinity gradients in the Taieri Estuary during a flood tide period. They shown the

tidal movement covered 8.3 km downstream, which corresponded to a mean tidal

velocity of 1.18 kmh-1• De Ruijter et a/. (1997)- investigated- and illustrated the

phenomena of a pulsed estuary plume within the Rhine discharge along the

Netherlands coast effect as the tide advects river water along the coast, and the

spreading of the plume approximately 5 km offshore.

A much larger scale plume is found in the Gulf of Mexico at the mouth of the

Mississippi River (Dagg et a/., 2001) and at the Connecticut River (Garvine, 1986),

which is deflect the plume eastward with the ebbing tidal currents and westward with

the flood tidal current. Figure 2.6 show contrast structure of surface density a long

centerline of plume during flood and ebb phase in the Mississippi River, in which the

reduction of on plume density results from the reduced salinity of discharge.

2.2.3 Winds and waves

The ocean surface usually is a complex of many different kinds of waves, that

generated by wind. The faster the wind, the longer the wave blows, and the bigger the

area over which the wind blows, the bigger the waves. The association of hydrographic

structure of the outflow plumes at the estuary mouth has been studied in several

studies. Geyer et a/. (2000) have shown that a significant Eel Estuary plume forms

during early stages of floods, and generally moves northward along the coast under

influence of strong southerly winds that commonly occur at the leading edge of storm

systems. At the same sites, Hill et a/. (2000) described the effective settling velocities

as important mechanism for speeding the removal of sediment from the estuary

mouth. Ogston eta/. (2000) proposed an additional transport mechanism of estuary

plume seaward, that observed at wind and wave condition over the winter flood period,

with maximum wind speeds and wave heights were approximately 23m/sand 11.5 m.

22

flOODING TIDE

~ ,._.,..._~•.w \•M•~ i•N•"'• --- •'*''t!•*':•"i• _, ...... ~ .... ,. ... ..; •• t... '"""1- .filoM~wt .... ~

Figure 2.6 A schematic diagram of the structure of surface density in the Gulf of Mexico at the mouth of the Mississippi River during {a} the flood tide and {b) ebb tide (from Dagg eta/., 2001).

Beside, Kourafalou (2001) addressed circulation due to buoyancy and wind stress in

development and evolution of estuary plumes. Again, Soares and Moller Jr. (2001)

described the structure of the La Plata River plume, although located many kilometers

south of the Southern Brazilian Shelf (SBS), has its plume advected toward the SBS

by coastal currents where it interacts with Patos Lagoon runoff.

The importance of wind and wave to affecting the estuary plume were studied

theoretically by Thain et a/. (2001) using a numerical model to solve the free surface

flow induced by linear water waves propagating with collinear vertically sheared

turbulent current, to estimate the wave amplitude decay rate in combined wave current

23

flows. The other model described by Savory and Toy (2000) for determination of

variation of total circulation within plume with distance from the source that influenced

by a crosswind. Ruddick et at. (1995) found in their simulations the stratification and

alongshore salinity structure in Rhine-Meuse plume, with wind speed of 8.5 m/s the

stratification is reduced by wind-mixing and the plume is confined to coastal band 1 0

km wide. Then, Chiavassa eta/. (1995) used the same method in the same region and

compared with SPOT data, and found the accurate and same results.

Furthermore, Haren (2001) estimated the wave height and wind stress magnitude and

direction in central North Sea, using acoustic Doppler current profiler (ADCP). Liu eta/.

(2002) recently addressed a study of biogeochemical response to climate change in

the South China Sea and the western Philippines, where the surface circulation

changes drastically with season in response to the alternating monsoons. They found

a sharp contrast between both regions, and show strong seasonal changes of

phytoplankton distribution in this region. At the other site, the Tseng-wen River,

southern Taiwan, Liu et a/. (1999) examined the three mechanisms that control nears

bed suspended sediment concentration near the estuary mouth, those are: horizontal

advection, downward settling, and the _resuspension, and stated the important factors

of tidal phase and wind field in controlling the expansion and contraction of the estuary

plume.

De Ruijter et a/. (1997) stated that low frequency variations of stratification and

circulation in Rhine ROFI (Region of Freshwater Influence) are driven primarily by the

buoyant river input and varying wind stress at the surface, and Estournel et at., (2001)

determined the sensitivity for turbulence kinetic energy. They illustrated the spreading

of the plume as it turns towards the north with highest stratification condition lying 3 to

5 km offshore and lower stratification conditions shoreward are due to tidal, wind and

waves mixing show in Figure 2.7.

24

the influence of river discharges, tides, and winds...

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