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UNIVERSITI PUTRA MALAYSIA
AMIR MONTAKHAB
FK 2012 59
FLOW CHARACTERISTICS AND SEDIMENT TRANSPORT IN A CHANNEL WITH EMERGENT FLEXIBLE VEGETATION
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FLOW CHARACTERISTICS AND SEDIMENT TRANSPORT IN A
CHANNEL WITH EMERGENT FLEXIBLE VEGETATION
By
AMIR MONTAKHAB
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfillment of the Requirements for the Degree
of Doctor of Philosophy
May 2012
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DEDICATION
To
My Father and Mother…
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Abstract of the thesis presented to the senate of Universiti Putra Malaysia in fulfillment of the requirements for the Degree of Doctor of Philosophy
FLOW CHARACTERISTICS AND SEDIMENT TRANSPORT IN A CHANNEL WITH EMERGENT FLEXIBLE VEGETATION
By
AMIR MONTAKHAB
May 2012
Chairman : Badronnisa bt. Yusuf, PhD
Faculty : Engineering
The effect of vegetation on open channel hydraulics is evident through the
magnitudes, the profiles of the flow depth and the velocity, which relate to
the plant characteristics. A number of vegetation characteristics affect the
flow. Among these parameters, vegetation density is the key factor that
contributes to the flow behavior and resistance in the vegetated channel.
However, in current research practices, vegetation density only covers the
number of vegetation and not the other physical characteristics. In reality,
natural aquatic vegetation is herbaceous in nature and diverse in
characteristics, so the determination of vegetation density in terms of
number may be very difficult. For a solution, vegetation porosity which is
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based on the vegetation volume is suggested. Thus, this study aims at
acquiring a practical method for porosity measurement, and applying it to
the study of the effect of emergent flexible vegetation to velocity
distribution, turbulence characteristics and sediment transport in
continuous and discontinuous distributions of vegetation in a channel.
This study consists of three main parts. In the first part of the study,
several porosity measurement methods based on vegetation frontal area
(two-dimensional) and vegetation volume (three-dimensional) were applied
to estimate the porosity of vegetation (Lepironia articulata) in a laboratory
flume for various flows and vegetation characteristics. The aim is to
explore several methods, and hence, to suggest a method that is practical
and accurate for vegetation porosity estimation, as well as to derive the
relationships between porosity, velocity and flow depth. Velocity
measurements using Acoustic Doppler Velocimeter (ADV) were made at
different spatial locations along the flume, and the effects of varying
incident flow rates (0.16–0.32ms-1) and vegetation porosity (88-96%) were
investigated. The volumetric method for porosity measurement, which
considers the fraction of the actual volume of the vegetation to the volume
of water, is considered as more practical and accurate than the other
methods. It was found that by assuming the vegetation as cylindrical in
shape and considering only the frontal area of the most upstream
vegetation, the porosity could be underestimated in average by 14%.
However, the digital image analysis gave porosity difference of only 5%.
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From the laboratory data, correlations between the mean velocity, water
depth and vegetation porosity were established. It was observed that by
reducing the vegetation porosity by 8% would results in the velocity being
reduced between 35% and 60% depending on the flow rate.
The second part of the study explores the effect of porosity of vegetation
patches on the velocity distribution and turbulent characteristics of flows
that encounter them. It was observed that the flow encountering a single
patch formed a turbulent wake at the downstream of vegetation, which
then intensified the Reynolds stress and increased turbulence and sediment
transport rate. Within this wake, the Reynolds stress increased
downstream initially, reached the maximum and then decayed. The
location of the maximum point of Reynolds stress was observed to be
dependent on the vegetation porosity and flow rates. When the second
patch was positioned within the region where the Reynolds stress was
maximum, the Reynolds stress was decreased between 50% and 25%
depending on vegetation porosity and flow rate. The patches revealed
great performance in reducing the Reynolds stress at lower velocity and
lower porosity. To sum up this part, flow and turbulence characteristics
depend on the vegetation porosity and the distance between patches.
In the final part of the study, sediment transport through continuous and
patch vegetations was studied at different porosities and flow conditions.
Water samples were collected from several locations along the channel,
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and the total suspended solid (TSS) test was applied for sediment trapping
measurement. The results showed that porosity, location of patches and
flow rate had a significant effect on the sediment transport. In addition, it
was observed that the sediment transport in the vegetation channel was
reduced up to 70% depending on the porosity value. The vegetation in
patches could increase trapping sediment up to 90%. The results suggest
that the patchy vegetation system is more efficient in reducing the
Reynolds stress as well as sediment transport compared to continuous
distribution. Finally, it can be concluded that porosity is an important
component and it significantly affects velocity, turbulence and sediment
transport in a vegetated channel.
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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Doktor Falsafah
CIRI ALIRAN DAN PENGANGKUTAN ENAPAN DI DALAM SALURAN DENGAN TUMBUHAN MUNCUL BOLEH LENTUR
Oleh
AMIR MONTAKHAB
Mai 2012
Pengerusi : Badronnisa bt. Yusuf, PhD
Fakulti : Kejuruteraan
Kesan tumbuhan ke atas hidraulik saluran terbuka dapat dibuktikan melalui
magnitud, profil kedalaman saliran dan halaju, yang berkait dengan ciri-ciri
tumbuhan. Beberapa ciri tumbuhan yang mempengaruhi aliran adalah
seperti; bentuk dan struktur stem dan daun, kelenturan stem, ketumpatan
(atau keliangan) dan agihan tumbuhan. Daripada kesemua parameter
tersebut, ketumpatan tumbuhan merupakan faktor utama yang
mempengaruhi kelakuan dan rintangan aliran di dalam saluran
bertumbuhan. Walau bagaimanapun, dalam praktis kajian semasa,
ketumpatan tumbuhan hanya mengambil kira bilangan tumbuhan dan
bukannya ciri fizikal yang lain.. Secara realiti, tumbuhan semulajadi aquatik
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adalah jenis herbaceous dan terdapat dalam pelbagai ciri, maka penentuan
ketumpatan tumbuhan dalam terma bilangan adalah tidak mudah. Sebagai
penyelesaian, keliangan tumbuhan berdasarkan isipadu tumbuhan
dicadangkan. Oleh itu, tujuan kajian ini adalah untuk memperoleh kaedah
yang praktikal untuk menentukan keliangan, dan mengaplikasikannya
dalam kajian kesan tumbuhan muncul dan boleh lentur kepada halaju, ciri
turbulen dan pengangkutan sedimen agihan di dalam saluran dengan
agihan tumbuhan berterusan dan tak berterusan (tompok).
Kajian ini merangkumi tiga bahagian utama. Bahagian pertama, beberapa
kaedah penentuan keliangan yang bergantung pada luas hadapan (dua-
dimensi) tumbuhan dan isipadu (tiga-dimensi) tumbuhan digunakan untuk
mengira keliangan tumbuhan (Lepironia articulata) di dalam saluran di
makmal dengan aliran dan ciri tumbuhan yang berbeza. Analisis imej digital
adalah antara kaedah yang digunakan untuk mengira keliangan. Tujuannya
adalah untuk mengkaji beberapa kaedah, dan untuk mencadangkan satu
kaedah yang praktikal dan tepat untuk mengukur keliangan tumbuhan dan
juga untuk menerbitkan hubung kait antara keliangan, halaju dan
kedalaman aliran. Pengukuran halaju menggunakan Acoustic Doppler
Velocimeter (ADV) dilakukan pada lokasi spatial di sepanjang saluran, dan
kesan kadar aliran (0.16–0.32ms-1) dan keliangan tumbuhan (88-96%)
yang berbeza dikaji. Kaedah isipadu untuk menyukat keliangan yang
mengambil kira pecahan isipadu sebenar tumbuhan kepada isipadu air,
didapati lebih praktikal dan tepat berbanding kaedah lain. Dengan
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mengandaikan tumbuhan dalam bentuk silinder dan hanya mengambil kira
luas hadapan tumbuhan di paling hulu, keliangan boleh terkurang
anggaran secara purata sebanyak 14%. Walau bagaimanapun, dengan
kaedah imej digital perbezaan keliangan hanya 5%. Daripada data
makmal, korelasi antara halaju purata, ketinggian air dan keliangan
tumbuhan dihasilkan. Pengurangan liang tumbuhan sebanyak 8% boleh
mengurangkan halaju diantara 35% dan60%, bergantung pada kadar
aliran.
Bahagian kedua kajian ini mengkaji kesan keliangan pada tompok
tumbuhan terhadap agihan halaju dan ciri-ciri turbulen. Dari permerhatian
didapati, aliran yang mengaliri satu tompok tumbuhan membentuk keracak
turbulen di hilir tumbuhan, yang kemudiannya meningkatkan tekanan
Reynolds dan turbulen dan kadar pemindahan sedimen. Dalam keracak ini,
pada permulaan, tekanan Reynolds meningkat di hilir mencapai tahap
maksimum dan kemudian berkurangan. Didapati lokasi tekanan Reynolds
maksimum bergantung pada keliangan tumbuhan dan kadar alir. Apabila
tompok kedua ditempatkan di lokasi berlakunya tekanan Reynolds
maksimum, tegangan Reynolds tersebut menurun dalam julat di antara
50% dan 25% bergantung kepada keliangan tumbuhan dan kadar alir.
Tompok tumbuhan didapati lebih efektif dalam mengurangkan tekanan
Reynolds pada halaju dan keliangan yang lebih rendah. Sebagai
kesimpulan untuk kajian kedua ini, ciri aliran dan turbulen bergantung
pada keliangan tumbuhan dan jarak antara tompok tumbuhan..
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Pada bahagian terakhir kajian ini, pengangkutan sedimen melalui
tumbuhan dengan agihan berterusan dan tompok dikaji pada keliangan
dan aliran yang berbeza. Sampel air diambil dari beberapa bahagian di
dalam saluran dan ujian jumlah pepejal terampai (TSS) dilakukan bagi
menentukan kepekatan sedimen terampai. Hasil kajian menunjukkan
keliangan, lokasi tompok dan kadar alir memberi impak yang penting
terhadap pemindahan sedimen. Selain itu, didapati bahawa pengangkutan
sedimen berkurangan sehingga 70% bergantung kepada nilai keliangan.
Tompok tumbuhan boleh meningkatkan jumlah sedimen yang
terperangkap sebanyak 90%. Hasil ini menunjukkan agihan tumbuhan
bertompok adalah lebih berkesan bagi mengurangkan tekanan Reynolds
dan juga pengangkutan sedimen berbanding dengan agihan tumbuhan
berterusan. Secara kesuluruhan, adalah dirumuskan bahawa keliangan
adalah komponen penting dan ia sangat mempengaruhi halaju, turbulen
dan pengangkutan sedimen dalam saluran tumbuhan.
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ACKNOWLEDGEMENTS
I would like to express my gratitude and sincere appreciations to my
supervisor Dr. Badronnisa Yusuf for giving me the chance to work on this
interesting project and complete the study under her great tutelage and
guidance. During this study, she showed a great deal of encouragement,
support, and friendship.
I wish to express my sincere appreciation to my supervisory committee
members, Associate Professor Dr. Abdul Halim Ghazali, and Professor Dr.
Thamer Ahmed Mohamed for their invaluable advice and guidance
throughout this study, and their priceless comment in reviewing my papers
and thesis.
My gratitude also goes to Dr Andrew M. Folkard from Lancaster University
for the critical insight, invaluable guidance and comments on the second
part of the study. His input in the process of writing-up papers is much
appreciated.
This work was partly supported by the research grant from Fundamental
Research Grants Scheme (FRGS) giving by Universiti Putra Malaysia. All
experiments were conducted in the Irrigations and Drainages laboratory at
Universiti Putra Malaysia. The support given by the technicians and staff
especially Professor Dr. Lee Teang Shui (Head of Irrigations and Drainages
Laboratory) is appreciated.
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The author is grateful to Putrajaya Wetland for their cooperation in
supplying vegetation for this research.
It is also my great pleasure to give a due recognition to my parents and
brothers for their all time love, understanding and support in the course of
this program and also for their words of encouragement whenever my
enthusiasm waned.
This study would not have been possible without the encouragement,
patience and overwhelming support of my lovely wife Farnaz during the
period of this research. Her continuous support is specially acknowledged.
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I certify that a Thesis Examination Committee has met on
……………………… to conduct the final examination of Amir Montakhab on
his thesis entitled “FLOW CHARACTERISTICS AND SEDIMENT TRANSPORT
IN A DRAINAGE WITH EMERGENT FLEXIBLE VEGETATION” in accordance
with Universities and University Colleges Acts 1971 and the Constitution of
the Universiti Putra Malaysia [P.U. (A) 106] 15 March 1998. The Committee
recommends that the student be awarded the Doctor of Philosophy.
Members of the Thesis Examination Committee were as follows:
Mohd Amin Bin Mohd Soom, PhD Professor Faculty of Engineering Universiti Putra Malaysia (Chairman) Lee Teang Shui, PhD Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Amimul Ahsan, PhD Senior Lecturer Faculty of Engineering Universiti Putra Malaysia (Internal Examiner) Bruce Melville, PhD Professor Department of Civil and Environmental Engineering University of Auckland New Zealand (External Examiner) ________________________ SEOW HENG FONG, PhD Professor and Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date:
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This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfillment of the requirement for the degree of Doctor of Philosophy. The members of the Supervisory Committee were as follows:
Badronnisa bt. Yusuf, PhD Senior Lecturer Faculty of Engineering Universiti Putra Malaysia (Chairman) Abdul Halim Ghazali, PhD Associated Professor Faculty of Engineering Universiti Putra Malaysia (Member) Thamer Ahmad Mohammad, PhD Professor Faculty of Engineering Universiti Putra Malaysia (Member)
_______________________
BUJANG BIN KIM HUAT, PhD Professor and Dean School of Graduate Studies Universiti Putra Malaysia
Date:
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DECLARATION
I declare that the thesis is my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously, and is not concurrently, submitted for any other degree at Universiti Putra Malaysia or at any other institutions.
AMIR MONTAKHAB
Date: 22 may 2012
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TABLE OF CONTENTS
Page
ABSTRACT iii
ABSTRAK vii
ACKNOWLEDGEMENTS xi
APPROVAL xiii
DECLARATION xv
LIST OF TABLES xix
LIST OF FIGURES xx
LIST OF ABBREVIATIONS xxv
CHAPTER
1 INTRODUCTION 1
1.1 Background 1
1.2 Vegetation in an Open Channel 3
1.3 Problem Statement 5
1.4 Objectives 6
1.5 Thesis Organization 7
2 LITREATURE REVIEW 9
2.1 General 9
2.2 Introduction 10
2.3 Effect of Vegetation on Flow Characteristics 16
2.3.1 Vegetation Porosity Estimation in a Vegetated Channel 21
2.3.2 Effect of Vegetation Porosity on Flow Resistance 26
2.4 Effect of Vegetation Distribution on Flow 31
2.4.1 Flow and Turbulence in Patchy Distribution Vegetation in a Channel 36
2.5 Sediment Transport through Vegetation 39
3 MATERIALS AND METHODS 44
3.1 Introduction 44
3.2 Field Study 47
3.2.1 Velocity measurements 47
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3.2.2 Field Study Locations 51
3.3 Experimental Facilities 54
3.3.1 Open Channel Flume 54
3.3.3 Vegetation 59
3.4 Vegetation Distribution 60
3.5 Vegetation Porosity Estimation (Study 1) 61
3.5.1 Vegetation Porosity Estimation Methods 62
3.5.2 Experimental Design 64
3.6 Experimental Set-up for Flow and Reynolds Stress in Discontinuous Distributions in a Channel (Study 2) 66
3.6.1 Experimental Design 67
3.7 Sediment Transport in Continuous and Discontinuous Distributions of Vegetation (Study 3) 71
3.7.1 Sediment Preparation 71
3.7.2 Open Channel Set-up 73
3.7.3 Water Sampling 76
3.7.4 Total Suspended Solid (TSS) 76
3.7.5 Turbidity 77
3.7.6 Experimental Design 78
4 RESULTS AND DISCUSSION 81
4.1 Effect of Vegetation Porosity on Flow (Study 1) 81
4.1.1 Vegetation Porosity Estimation 82
4.1.2 Relationship between Porosity, Velocity and Water Depth 85
4.1.3 Effect of Porosity and Flow Rate on Flow Resistance 89
4.2 Flow and Reynolds Stress in Discontinuous Distributions of Emergent Vegetation in a Channel (Study 2) 98
4.2.1 Relationship between , Velocity and Vegetation Porosity 107
4.3 Sediment Transport in Emergent Vegetation Channel (Study 3) 110
4.3.1 Sediment Transport in the Channel without Vegetation 110
4.3.2 Effect of Porosities on Sediment Transport 111
4.3.3 Effect of Flow Rate on Sediment Transport 115
4.3.4. The Relationship between TSS and Turbidity 119
4.3.5 Effect of Vegetation Patches on Sediment Transport 120
4.3.4 Effect of Patches on Sediment Transport with Different Velocities 124
5 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 129
5.1 Summary 129
5.2 Conclusions 130
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5.3 Recommendations 133
REFERENCES 135
APPENDICES 146
BIODATA OF STUDENT 164