UNIVERSITI PUTRA MALAYSIA

EHSAN GOODARZI

FK 2010 65

OVERTOPPING RISK AND UNCERTAINTY ANALYSIS OF EMBANKMENT DAMS

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OVERTOPPING RISK AND UNCERTAINTY ANALYSIS OF

EMBANKMENT DAMS

EHSAN GOODARZI

DOCTOR OF PHILOSIPHY

UNIVERSITY PUTRA MALAYSIA

2010

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OVERTOPPING RISK AND UNCERTAINTY ANALYSIS

OF EMBANKMENT DAMS

By

EHSAN GOODARZI

Thesis submitted to the school of graduate study, Universiti Putra Malaysia, in

Fulfillment of the Requirements for the Degree of Doctor of Philosophy.

October 2010

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DEDICATION

I dedicated this thesis to my parents. I hope that this achievement will complete the

dream that they had for me all those many years ago when they choose to give me the

best education that I could.

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Abstract of thesis presented to the Senate of University Putra Malaysia in fulfilment of

the requirement for the Degree of Doctor of Philosophy

OVERTOPPING RISK AND UNCERTAINTY ANALYSIS

OF EMBANKMENT DAMS

By

EHSAN GOODARZI

October 2010

Chairman: Professor Lee Teang Shui, PhD

Faculty: Engineering

Abstract

The main objectives of this study are the evaluation of overtopping risk in conjunction

with uncertainty for two embankment dams in the south of Iran (Fars province) and north

of Iran (Mazandaran province). Dams are one of the most significant structures that

contribute to the survival of the human race. The main benefits of this structure for

human society are; flood controlling, generation of hydro-electric power, and supply

water for different purpose such as agriculture, irrigation, recreation, and tourism

attraction. Annually, natural disasters like earthquake, flood, drought, and thunders

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happen in different parts of the world. Malfunctioning of a dam can result in serious

economic damage to the owners, and environmental problems such as pollution,

sedimentation in the downstream areas and can also result in the loss of human lives. Iran

is one of the ten foremost countries sensitive to the unexpected phenomena and natural

disasters. Flooding is one of the most important disasters in Iran and losses during 1951-

2000 exceeded more than 11,500 people. So, constructing new flood control structures

and assessment safety of existing dams are essential.

There is main gap with regards to apply new statistical tools and techniques for

overtopping risk analysis and assessment the safety of dams. Furthermore, considering

various events such as wind in conjunction with flood which increase the probability of

failure is a crucial task of hydrosystem engineers. Hence, this research presents the

application of risk and uncertainty analysis to dam overtopping. A flood frequency

analysis of annual maximum discharge was done for the Doroudzan and Meijaran dams

applying the General Extreme Value (GEV) probability distribution. Risk of overtopping

were calculated for six extreme floods taking into consideration inflow hydrograph,

initial water level, discharge coefficient of spillway, and the reservoir geometry as

uncertain variables. The reservoir routing technique was used to compute the highest

water levels and the Monte Carlo simulation (MCS) and Latin hypercube sampling (LHS)

were applied for uncertainty analysis. To consider the effect of wind speed on the

overtopping risk, frequency analyses were performed on the wind data and consequently

extreme wind speeds, highest wind set-up and wave run-up were calculated. The

maximum risk considering the effects of wind speeds in the study was 1.5 to 3.5 times

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larger than the risk of overflowing due to only floods using Latin hypercube sampling

(LHS) and Monte Carlo simulation (MCS) approaches, respectively. The results of this

study show that, initial water level, and inflows to reservoir have significant effects on

the overtopping probability of the Doroudzan and Meijaran dams. Overtopping risk

increases with increase in magnitude of stated parameters. Trends of computed risks for

the Doroudzan dam indicate that calculated probabilities with Latin hypercube sampling

were slightly higher than the Monte Carlo simulation, while in the Meijaran dam, there

was no any specific trend between the MCS and LHS results.

The major findings and main contributions of this study are; solving the flood model

(reservoir routing) in uncertain conditions, estimating wind set-up and wave run up to

solve the wind model with considering uncertainties, estimating the probability of failure

due to overtopping under different hydrologic conditions, and compare the results based

on two applied uncertainty models (MCS and LHS) for two mentioned dams.

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Abstrak Tesis Yang Dikemukakan Kepada Senat Universiti Putra Malaysia Sebagai

Memenuhi Keperluan Untuk ijazah Doktor Falsafah

ANALISIS RISIKO DAN KETIDAKPASTIAN PARAS TERLAMPAU TINGGI

EMPANGAN BENTENG

Oleh

EHSAN GOODARZI

October 2010

Pengerusi: Prof Lee Teang Shui, PhD

Fakulti: Kejuruteraan

Tujuan utama kajian ini ialah penilaian risiko paras terlampau tinggi berkaitan dengan

ketakpastian untuk dua empangan tanah terletak di Iran Selatan (daerah Fars) dan di Iran

Utara (daerah Mazandaran). Empangan adalah diantara struktur bererti yang

menyumbang kepada keadaan terus-hidup manusia. Keuntungan utama struktur ini bagi

masyarakat adalah: kawalan banjir, penjanaan kuasa elektrik dan bekalan air untuk tujuan

berbeza saperti pertanian, pengairan, rekreasi dan penarikan pelancongan. Setiap tahun,

bencana alam seperti gempabumi, banjir, kemarau dan petir berlaku di merata rata

tempat di dunia. Empangan pincang tugas boleh menyebabkan kerosakan ekonomi serius

kepada pemilik dan masalah alam sekitar saperti pencemaran, pengendapan di kawasan

hilir dan juga boleh menyebabkan kehilangan nyawa. Iran adalah diantara sepuluh negara

yang peka kepada bencana alam dan fenomenon luar dugaan begitu. Banjir adalah satu

malapetaka yang penting di Iran dan pada 1951 – 2000, melebihi 11,500 nyawa

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terkorban. Jadi, pembinaan struktur baru untuk mengawal banjir dan penialaian

keselamatan empangan yang sedia ujud adalah diperlui.

Terdapat kekurangan dari segi mengaplikasi alat statistic dan teknik analisis risiko

terlampau tinggi dan penilaian keselamatan empangan. Tambahan pula, penilaian

mengambilkira beberapa peristiwa seperti angin bersama sama banjir akan meningkatkan

kebarangkalian kegagalan merupa tugas kritikal jurutera hidrosistem. Jadi, kajian ini

mempersembahkan aplikasi risiko dan analisis ketakpastian kepada empangan yang

menghadapi paras terlampau tinggi. Satu analisis kekerapan banjir aliran maksimum

tahunan telah dibuat untuk empangan Doroudzan dan empangan Meijaran dengan

menggunakan taburan kebarangkalian Nilai Ekstrim Umum. Risiko (GEV). Risiko paras

terlampau tinggi dikira untuk enam banjir ekstrim dengan mengambilkira hidrograf aliran

masuk, paras air awal, angkali aliran alur limpah dan geometri takungan sebagai

perubahan takpasti. Teknik penghalaan takungan diguna untuk mengira paras air tertinggi

dan simulasi Monte Carlo (MCS) dan pensampelan Latin Hypercube (LHS) diguna untuk

analisis ketakpastian. Demi untuk mengambilkira kesan halaju angin terhadap risiko

paras terlampau tinggi, analisis kekerapkalian dibuat untuk data angin dan akibatnya,

halaju ekstrim angin, kenaikan paras air tertinggi dan panjang gelombang kerana angin

dikirakan. Dengan menggunakan pendekatan LHS dan pendekatan MCS, terdapat risiko

maksimum dengan ambilkira kesan halaju angin adalah 1.5 ke 3.5 kali lebih besar

daripada risiko paras terlampau tinggi sahaja masing masing. Keputusan kajian ini

menujukkan bahawa paras air awal serta aliran masuk ke takungan ada kesan bererti

terhadap kebarangkalian paras terlampau tinggi bagi empangan empangan Doroudzan

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dan Meijaran. Risiko paras terlampau tinggi kian tambah selaras dengan tambahan

magnitud parameter tersebut. Risiko dikira untuk empangan Doroudzan menunjukkan

kebangkalian dikira dengan LHS lebih tinggi dibandingkan dengan MCS, akan tetapi

untuk empangan Meijaran, tidakpastinya bandingan keputusan MCS dan LHS.

Penemuan utama dan sumbangan terpenting kajian ini adalah; menyelesaikan model

banjir (penghalaan takungan) didalam keadaan taktentu, penaksiran kenaikan paras air

tertinggi dan panjang gelombang kerana angin dengan mengambilkira ketidakpastian,

penaksiran kebarangkalian kegagalan disebabkan paras terlampau tinggi dalam keadaan

hidrologi berbeza, dan membandingkan keputusan berdasarkan dua model ketidakpastian

(MCS dan LHS) bagi dua empangan tersebut.

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ACKNOWLEDGEMENTS

Praise belongs to God who has been the source of inspiration, strength and confidence

throughout my life and especially during the postgraduate program.

My most earnest acknowledgment must go to my supervisor, Professor Ir. Dr. Lee Teang

Shui, who continually and convincingly conveyed a spirit of adventure in regard to

research and scholarship, and an excitement in regard to teaching. Without his guidance

and persistent help this dissertation would not have been possible.

Thanks are also due to my committee members, Prof. Ir. Dr. Desa Bin Ahmad, and Prof.

Dr. Assoc. Prof. Dr. Abdul Halim Ghazali, for their time and constructive criticisms.

My deepest appreciation belongs to my parents for their personal support, patience and

tolerance during many years of my academic endeavour.

Lastly, there are a number of people in my everyday circle of colleagues who have helped

me in various stages of this research. I would especially like to thank Mina, Majid, and

Raeis for their support and help.

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I certify that an Examination Committee has met on date of viva voce to conduct the final

examination of Ehsan Goodarzi on his Doctor of Philosophy entitled

“OVERTOPPING RISK AND UNCERTAINTY ANALYSIS OF EMBANKMENT

DAMS” in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980 and

Universiti Pertanian Malaysia (Higher Degree) Regulations 1981. The Committee

recommends that the student be awarded the (PhD degree).

Members of the Examination Committee were as follows:

Mohd Amin Mohd Soom

Professor

Engineering

Universiti Putra Malaysia

(Chairman)

Thamer Ahmed Mohamed, PhD

Associate Professor

Engineering

Universiti Putra Malaysia

(Internal Examiner)

Badronnisa Yusuf, PhD

Doctor

Engineering

Universiti Putra Malaysia

(Internal Examiner)

Kwok-wing Chau, PhD

Associate Professor

Engineering

Hong Kong Polytechnic University

(External Examiner)

BUJANG BIN KIM HUAT, 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 university 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:

Lee Teang Shui, PhD

Professor

Faculty of Engineering

Universiti Putra Malaysia

(Chairman)

Desa bin Ahmad, PhD

Professor

Faculty Engineering

Universiti Putra Malaysia

(Member)

Name of member 2, PhD

Title: Assoc. Prof. Dr. Abdul Halim Ghazali

Faculty of Engineering

Universiti Putra Malaysia

(Member)

HASANAH MOHD GHAZALI, PhD

Professor

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 other

institutions.

Ehsan Goodarzi

Date: 19/10/2010

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TABLE OF CONTENTS

Page

DEDICATION ii

ABSTRACT iii

ABSTRAK vi

ACKNOWLEDGEMENT ix

APPROVAL xi

DECLARATION xii

LIST OF TABLE xvi

LIST OF FIGURE xix

LIST OF ABBREVIATIONS xxiii

CHAPTER

1 INTRODUCTION

1.1 Hydrosystem 1

1.1.1 Risk-based hydrosystems engineering 2

1.2 Explanation of uncertainty 3

1.2.1 Types and sources of uncertainty 3

1.2.2 Measurement of uncertainty 4

1.3 Engineering Reliability and Risk Assessment 5

1.4 Statement of the problem 7

1.5 Objectives 8

1.6 Scope of work and limitations of the study 9

1.7 Significance of the study 10

2 LITERATURE REVIEW

2.1 Introduction 12

2.2 An overview of Probable Maximum Flood (PMF) 14

2.3 An Overview of Risk and Uncertainty 15

2.4 Analysis of Empirical Studies for Risk and Uncertainty 20

2.4.1 Empirical studies of risk 20

2.4.2 Empirical studies of uncertainty 27

2.5 Measuring Risk and Uncertainty 28

2.5.1 An overview of uncertainty analysis techniques 29

2.5.1.1 Analytical techniques 29

2.5.1.2 Approximation techniques 32

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2.6 An Overview of Reliability (Risk) Analysis Techniques 39

2.6.1 Event Tree 40

2.6.2 Fault tree 41

2.6.3 Direct integration method 43

2.6.4 First-order second-moment (FOSM) method 43

2.6.5 Empirical studies of risk and uncertainty in

hydrosystem

46

2.7 An overview of overtopping problem and spillway design 52

2.8 Empirical studies of overtopping failure 53

2.9 Data requirements in risk-based approach 59

2.10 Summary 60

3 METHODOLOGY

3.1 Introduction 62

3.2 Doroudzan Dam Description 63

3.3 Meijaran Dam 69

3.4 Overtopping Model in the Risk Analysis 74

3.4.1 Solve routing equation 75

3.4.2 Effect of uncertainty in the reservoir routing

equation

76

3.5 Risk Model 79

3.6 Wind Model 82

3.6.1 Importance of wind speed calculation 82

3.6.2 Wind set-up and wave run-up calculation 84

3.6.3 Wind set-up 84

3.6.4.Wave run-up 87

3.7 Computer Program (@Risk Microsoft Excel) 89

3.8 Assessing Risk 90

3.9 Approaches to Quantifying Risk 92

3.10 Simulation 92

3.11 @RISK Simulation Analysis 93

3.12 Generation of Random Numbers (Sampling) 95

3.13 Sampling in @RISK 96

4 RESULTS AND DISCUSSIONS

4.1 Introduction 98

4.2 Data Analysis of Doroudzan Dam 99

4.3 Selection Annual Maximum Discharge 100

4.4 Univariate Flood Frequency of Doroudzan Data 101

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4.5 Uncertainty Analysis of Overtopping of the Doroudzan Dam 104

4.6 Uncertainty Analysis of Overtopping of the Meijaran Dam 106

4.7 Solving routing equation regarding uncertain parameters 108

4.8 Results of Overtopping Risk of Flood of the Doroudzan Dam 111

4.9 Overtopping Risk of Flood of the Meijaran Dam 121

4.10 Overtopping risk of flood and wind 126

4.10.1 Risk of overtopping for combined flood and wind

for Doroudzan Dam

126

4.10.2 Risk of overtopping for combined flood and wind

for Doroudzan Dam

140

4.11 Summary of Results 143

4.11.1 Comparison overtopping risk in Doroudzan and

Meijaran dams

145

5 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

5.1 Introduction 149

5.2 Summary of Results 150

5.2.1 Comparison overtopping risk in Doroudzan

and Meijaran Dams

152

5.3 Conclusions of the Study 154

5.4 Recommendations for Doroudzan and Meijaran

Dams

155

REFERENCES 157

APPENDICES 166

BIODATA OF THE AUTHOR 260