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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


3.7 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


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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