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Jamie Rhome 2013 “Forecasting and Modelling Storm Surge” was used SLOSH model and computerized numerical model developed by the National Weather Service NWSto estimate storm surge height

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Declaration

I hereby certify the work which is being presented in this thesis entitled “Modeling storm surge for the South Central Coast of Vietnam” is an authentic record of my own work carried out under supervision of Dr Vu Thi Thu Thuy and Co-supervisor Ass Prof PhD Nghiem Tien Lam The master embodied in this thesis has not been submitted by me for the award of any other degree or diploma

Date: Aug 15, 2016

Author

Ninh Duy Quỳnh

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Acknowledgements

I would like to express my sincere gratitude to my advisor Dr Vu Thi Thu Thuy and Co-supervisor A/Prof PhD Nghiem Tien Lam for their guidance, suggestion and inspiration

I would like to express my sincere thanks to Thuy Loi University, professors and lectures at Department of Marine and Coastal Engineering of Thuy Loi University and professors and lecturers of the Niche programmer for supporting me throughout my study progress

Finally, I would like to express my special appreciation to my friends and colleagues for their support, encourage and advices Thank you so much!

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CONTENTS

LIST OF FIGUES iv

LIST OF TABLES ix

INTRODUCTION 1

1 Problem identification and the necessity of the study 1

2 Literature review 2

2.1 International researches on storm surge 3

2.2 Past studies on storm surges in Vietnam 6

3 Research objectives 7

3 The scope of research 7

4 Approach and methodology 8

5 Thesis structure 8

CHAPTER 1: PHYSICAL SETTINGS 9

1.1 Geographic conditions 9

1.2 Topographic conditions 9

1.3 Climatic conditions 11

1.4 Observation stations and hydro-logic conditions 11

1.4.1 Observation stations 11

1.4.2 Hydrologic conditions 13

1.5 Oceanographic conditions 14

1.6 Historical disasters of typhoons and storm surges 15

1.7 Conclusions 18

CHAPTER 2: MODELLING OF NON-TYPHOON CONDITION 20

2.1 Introduction 20

2.1.1 Introduction model MIKE 21 20

2.1.2 Module MIKE 21 Flow Model (MIKE 21 FM) 21

2.2 Model setup and boundary conditions 25

2.2.1 Analysis data and choose scope of model 25

2.2.2 Building mesh model two-way 26

2.2 Model calibration 32

2.2.1 Analysis and choice of time and calibration data model 32

2.2.2 The parameters and model calibration process 34

2.2.3 Results of model calibration 34

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2.3 Model verification 36

2.3.1 The parameter for verification 36

2.4.2 The result of verification model 37

2.4 Conclusions 38

CHAPTER 3: MODELING OF STORM SURGE 39

3.1 Introduction 39

3.2 Modeling of typhoon 40

3.2.1 Theoretical basis of establishing patterns of wind and barometric pressure in the storm 40

3.2.2 Wind field model in the storm 40

3.2.3 Modelling of pressure in storm 45

3.3 Model setup and boundary conditions 46

3.3.1 Analysing data 46

3.3.2 Set of hydraulic parameters 52

3.4 Model calibration 53

3.4.1 Analyze and choose the time and calibration data model 53

3.4.2 Parameters and model calibration process 53

3.4.3 Conclusion 54

3.5 Model verification 54

3.5.1 Set up model verification 54

3.5.2 The result of verification 56

3.6 Conclusions 56

CHAPTER 4: SENSITIVITY ANALYSIS MODEL 57

4.1 Role of pressure center in the storm 57

4.1.1 Set of hydraulic parameters 57

4.1.2 Results model 59

4.1.3 Results analysis 62

4.2 Role of parameters model (B) 62

4.2.1 Set of hydraulic parameters 62

4.2.2 Results model 63

4.2.3 Results analysis 64

4.3 Role of maximum wind speed in the storm 64

4.3.1 Set of hydraulic parameters 64

4.3.2 Results analysis 66

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4.4 Role of radius maximum in the storm 66

4.4.1 Set of hydraulic parameters 66

4.4.2 Results model: 67

4.4.3 Results analysis 68

4.5 Role of wind friction (Cd) 68

4.6 Role of trajectory of storm 71

4.6.1 Set of hydraulic parameters 71

4.6.2 Results model: 73

4.6.3 Results analysis 75

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS 76

5.1 Conclusions 76

5.2 Recommendations 78

REFERENCES 79 APPENDIXES

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LIST OF FIGUES

Figure 1: Administrative Map of South Central Coast 7

Figure 1 2 Observation stations in south central coast 12

Figure 1 3: Cau Da station – Khanh Hoa province 12

Figure 1 4: The monitoring sites of Vung Tau station 13

Figure 1 5: The significant wave height patterns in the East Sea 14

Figure 2 1: Introduction MIKE 21 20

Figure 2 2: Scope of model 26

Figure 2 3: Topography of study area 27

Figure 2 4 Simulated area 28

Figure 2 5 Building topography data 29

Figure 2 6 Model boundary conditions 31

Figure 2 7: Diagram of calibration process 32

Figure 2 8 Calibration station 33

Figure 2 9 Comparison of water level at Cau Da observation station 35

Figure 2 10 Comparison of water level at Vung Tau observation station 35

Figure 2 11 Comparison diagram in Cau Da station 37

Figure 2 12 Comparison diagram in Vung Tau station 37

Figure 3 1 Storm surge 41

Figure 3 2: Typhoon #21 in 2007 47

Figure 3 3: Typhoon #23 in 2009 47

Figure 3 4: Wind field model 48

Figure 3 5: Data provided for the wind field model 49

Figure 3 6: Wind speed in the typhoon in 2007 51

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Figure 3 7: Wind pressure in the typhoon in 2007 51

Figure 3 8: Comparison diagram in Cau Da station 11/2007 53

Figure 3 10: The parameter of storm #23 in 2009 54

Figure 3 11: Wind speed in the typhoon in 2009 55

Figure 3 12: Wind pressure in the typhoon in 2009 55

Figure 3 13: Comparison diagram in Cau Da station in 2009 56

Figure 4 1 The relationship between Vmax and ΔP 58

Figure 4 2 The positions extract 60

Figure 4 3 Storm surge in Quy Nhon – Binh Dinh 61

Figure 4 4 Storm surge in Nha Trang – Khanh Hoa 61

Figure 4 5 Storm surge in Vung Ro – Phu Yen 62

Figure 4 6 Storm surge in Quy Nhon – Binh Dinh 63

Figure 4 7 Storm surge in Nha Trang – Khanh Hoa 63

Figure 4 8 Storm surge in Vung Ro – Phu Yen 64

Figure 4 9 Storm surge in Quy Nhơn – Binh Dinh 65

Figure 4 10 Storm surge in Nha Trang – Khanh Hoa 65

Figure 4 11 Storm surge in Vung Ro – Phu Yen 65

Figure 4 12 Storm surge in Quy Nhon – Binh Dinh 67

Figure 4 13 Storm surge in Nha Trang – Khanh Hoa 67

Figure 4 14 Storm surge in Vung Ro – Phu Yen 67

Figure 4 15 Storm surge in Quy Nhon – Binh Dinh 69

Figure 4 16 Storm surge in Nha Trang – Khanh Hoa 70

Figure 4 17 Storm surge in Vung Ro – Phu Yen 70

Figure 4 18 Typhoon #23 in 2009 71

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Figure 4 20 The storm hits Nha Trang province 72

Figure 4 21 The storm hits Ninh Thuan province 72

Figure 4 22 Storm surge in Quy Nhon – Binh Dinh 73

Figure 4 23 Storm surge in Vinh Xuan Dai – Binh Dinh 73

Figure 4 24 Storm surge in Vung Ro – Phu Yen 73

Figure 4 25 Storm surge in Nha Trang – Khanh Hoa 74

Figure 4 26 Storm surge in Cam Ranh – Khanh Hoa 74

Figure 4 27 Storm surge in Mui Padaran – Ninh Thuan: 74

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LIST OF TABLES

Table 1 1 Statistics storm in Vietnam 15

Table 1 2 Statistics storm in South Central Coast province from 1951 to 2010 17

Table 2 1 Model boundary conditions 30

Table 2 2 the parameters effect to Nam Trung Bo model 31

Table 2 3 Relevance of NASH coefficient 34

Table 2 4 Results of model calibration 35

Table 2 5 Results parameter of model after calibration 36

Table 3 1 Wind speed according to the Beaufort wind scale 44

Table 3 2 Parameters of wind field 48

Table 3 3: The data of Typhoon #21 in 2007 (grade 11) 49

Table 3 4: Set of hydraulic parameters 52

Table 3 5: The result of model calibration 53

Table 3 7: The result in observation station in Storm 56

Table 4 1 The input parameters of the models 60

Table 4 2 The coordinate of positions extract 62

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1 Problem identification and the necessity of the study

The South Central Coast of Viet Nam is characterized by a long coastline with many rivers, estuaries , which is good condition for farming, fishing Its geography, terrain and natural conditions have strong influence on its geology, climate, hydrology, other natural resources This area often suffers a lot of natural disasters such as storms, floods and drought

The South Central Coast is an important region in defense and economic strategy Many seaports, transportation systems and railways and roads have been built in the coastal zone to facilitate economic and cultural exchanges between South – North; and international exchange However, this region is one of the most vulnerable places to natural disasters, especially floods (e.g Large floods occurred in Central and South Central in: 1952, 1964, 1980, 1990, 1996, 1998, 2003, 2008) In fact, there are at least

8 types of natural disasters and hazards which occur in this region such as: storms, floods (including flash floods), droughts, landslides, cyclones, salinity intrusion and erosion of the riverbanks, while there are five phenomena related to typhoons and storm surges

According to Hang et al (2010), on average, Vietnam suffers from 5 to 7 typhoons per year along its coastal zone From 1951 to 2006, the activities of typhoons in South East of Pacific Ocean tend to reduce in the number of weak and average typhoons, while the number of strong typhoons tends to increase In West Sea, the typhoons, which only act in sea, tend to increase, but typhoon’s intensity tends to reduce In recent years, the number of typhoons directly impacting on Northern reduces and the Southern in Vietnam increases The number of typhoons reduces, but more super typhoons appear, which causes great damage to people and property, such as Hurricane Katrina hitting the United States in 2005, Cyclone Nargis hit Myanmar in 2008, Typhoon Bopha in 2012

Almost population living in coastal area are often attached by typhoon When

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nearby coastal zone When typhoon combines with high tide, water level increase more and more, and consequently even more serious Hundreds of people dead or missing and thousands of people affected by the storm and flood each year Damage to property such as lost homes, crops, damaged the social-economic works of up to tens

of billions The South Central Coast is often threatened by coastal erosion, broken dike, flooding or salinization caused by storms, especially in the coastal area which is densely populated and developed economic Tourism is very vulnerable and at very high risk

Therefore, the study of storm surges for South Central Coast is essential We can forecast flood for vulnerable areas and the impact during storm landfall Beside, we proposed mitigation measures natural disasters, risk of environment in the context of climate change increasingly unpredictable and the effect of climate change will make typhoons increased more in the future

2 Literature review

Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide This rise in water level can cause extreme flooding in coastal areas particularly when storm surge coincides with normal high tide, resulting in storm tides reaching up to 6m or more in some cases

Storm surge is produced by water being pushed toward the shore by the force of the winds moving cyclonically around the storm The impact on surge of the low pressure associated with intense storms is minimal in comparison to the water being forced toward the shore by the wind

The maximum potential storm surge for a particular location depends on a number of different factors Storm surge is a very complex phenomenon because it is sensitive to the slightest changes in storm intensity, forward speed, size (radius of maximum winds-RMW), angle of approach to the coast, central pressure (minimal contribution

in comparison to the wind), and the shape and characteristics of coastal features such

as bays and estuaries The effects of storm surge very serious For example, when

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than 8 meters in some areas This led to widespread flooding, including almost all of the city of New Orleans where the sea defenses couldn't cope with the water level More than 1800 people were killed across the US by Hurricane Katrina, many of them

by the storm surge flooding

In Vietnam, the term "storm surge" as well as studies on the effects of it is new and very limited The statistics only indicate the impact of the storm, the damage and the consequences of them leaving and the reports of the coastal provinces every years don't analysis the main effects of the damage, therefore very limited in prevention

2.1 International researches on storm surge

In the world, the calculation of surges and flooding due to storm surges have been made through the mathematical model or software such as MIKE 21 Flood (Denmark), Sobek 2D (Netherlands), Delft3D, etc… there have been many waring systems sugers that developed in many countries in recent times as JMA Storm Surge system (Japan), KMA Storm Surge (Korea), SLOSH (USA), STORMY (Singapore)

Pamela Probst, Giovanni Franchello (2012) “Global storm surge forecast and inundation modeling” specified that storm surge is an abnormal rise of water above the normal astronomical tides, generated by strong winds and by a drop in the atmospheric pressure These atmospheric forcing generates long waves that can be simulated by the shallow water equations They used HyFlux2 model to simulate storm surge for 3 storms, iclude:

- Katrina (23-30 August 2005): This is one of the most damaging tropical cyclone

disasters in the history of the United States, Katrina formed over the Bahamas on August 23 and and crossed southern Florida (first landfall) as amoderate Category 1 hurricane on Saffir-Simpson Scale (Appendix A), causing deaths and flooding After Katrina moved westward, entering in the Gulf of Mexico, and began strengthening rapidly, reaching Category 5 on Saffir-Simpson Scale, with a maximum wind of 150 kts and a minimum of pressure of 902 mbar After the hurricane weakened to Category

3 and on August 29 it made the second (near Buras, Louisiana) and third landfall (near Louisiana/Mississipi border) on the northern Gulf coast Strong winds and an elevated

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level of Lake Pontchartrain, straining the levee system protecting New Orleans, and on August 30 significant failures in this system occurred, pouring water into the city which sits mostly below sea level After creating death and destruction in Louisiana, Mississippi, and Alabama, Katrina moved northward into Tennessee and Kentucky and headed northeast from there, dissipating on August 30 At least 1836 people died, the most significant amount of deaths occurred in New Orleans, Louisiana

The results indicate the rainfall amounts from Katrina, though rather high in some places, were not the main impact of this storm, the main reason is due to storm surge The atmospheric forcing obtained is then used in HyFlux2 to simulate the inundation area and the results show the most inundated area was Gulf of Mexico Also the maximum heights simulated by HyFlux2 are consistent with the observations A maximum height of 7.22 m is simulated in the region of Pass Christian and a value of 8.4 m has been observed in this area (Graumann et al., 2006) A complete storm surge analysis is presented in NOAA storm surge report The observed data shown in this article are compared with the HyFlux2 simulations The results of this comparison, for the area most inundated, are presented in report

- Nargis (27 April – 3 May 2008)

This is a strong typhoon occurred in 2008 that caused the worst natural disaster in the recorded history of Myanmar, killing in this region more than 22’000 people according

to Tyagi et al (2008), while 84’000 people died according to RSMC (2009)

The rainfall effect can influence also the value of maximum water height The maximum heights simulated by HyFlux2 are consistent with the values for the Irrawaddy delta region, with a value of about 3.6 m for this area

In all comparisons, the maximum heights about water level, wind,… simulated by HyFlux2 are lower than the observed data This could be due to the rainfall effect not included in the hydrodynamic model For Thetkethaung and Apoung the difference is more than 4 m, but the value of Apount disagrees with the value provided in Lin et al (2010) and comparing the HyFlux2 simulation with this data, the difference is 1.34 m and not 5.05 m The last comparison, with the data of Mulein Station (GLOSS Tide Gauge), shows a close agreement with the HyFlux2 simulation: a difference of only

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0.29 m is found Actually no more data have been found for a complete validation, because in Myanmar few observed data are available Nevertheless these comparisons have shown that an additional effort must be done in order to include the rainfall effect

in HyFlux2 code

- Yasi: Cyclone Yasi is massive tropical cyclones that caused damage to Queensland,

Australia, in 2011 It began developing as a tropical cyclone low northwest of Fiji on January 29 and started tracking on a westward direction The low pressure quickly intensified to a cyclone category and was called Yasi by Fiji Meteorological Service Then increase its intensity and began moving west-southwestward, accelerating

towards the tropical

Queensland coast The landfall happened on February 2 along the northeast coast of Queensland as a Category 4 on the U.S Saffir-Simpson scale (Appendix B) midway between Cairns and Townsville After landfall, it maintained a strong core with damaging winds and heavy rain, tracking westwards across northern Queensland Finally it weakened to a tropical low near Mount Isa At the time of writing there are

no verified observations of the maximum wind near the TC centre for a complete evaluation of the wind field, only some observation of mean sea level pressure are available, therefore actually no enough observational data are available to a complete assessment of the results of this TC and the reports was presented a preliminary analysis

Jamie Rhome (2013) “Forecasting and Modelling Storm Surge” was used SLOSH model and computerized numerical model developed by the National Weather Service (NWS)to estimate storm surge heights(and winds) resulting from historical, hypothetical, or predicted hurricanes to evaluation storm surges and impact for coastal area The author indicates the total water rise is included: surge storm, tides, waves and freshwater flow

Tao Shen (2009) “Development of a Storm Surge Model Using a High-Resolution Unstructured Grid over a Large Domain” showed the storm surge and inundation simulation results for two scenarios, Hurricane Isabel and Tropical Storm Ernesto used Description of ELCIRC model In this study, two separate grids have been generated

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Atlantic Ocean from Nova Scotia to Florida; the other is the small, limited domain grid covering the land parts in the Hampton Roads and Virginia Beach areas for the inundation prediction purpose and the results showed the storm surge model with a large domain grid was able to generate reasonable water elevation results during Hurricane Isabel using only a tidal boundary condition at the open boundary and the high-resolution inundation model using the water elevations output from the large domain model as the open boundary condition could generate a reasonable inundation map

2.2 Past studies on storm surges in Vietnam

Currently in Vietnam, there are have many research for storm surge, such as:

- Chiến Đ.Đ (2006) “Nghiên cứu tương tác sóng và nước dâng do bão bằng mô hình số trị” The report analyzed the interaction between the waves and storm surges based on results calculated waves and storm surges of Xangsane storm came to on Da Nang beach in 9/2006 by Suwat model The report have looked at the same time interaction between the tides, waves and storm surges, and pointed out that interaction of tides and storm surges will be increase wave height in center of the storm

- Chuẩn H.X et al (2008) “ Đánh giá một số phương pháp tính toán nước dâng do bão

ở Việt Nam” compared the advantages and disadvantages indicate the method of calculation of storm surges such as: surveying the statistical method, empirical formula method , theoretical method with emphasis on methods using modern models can calculate and forecast storms in wide range and ensure accuracy if have calibration and verification model

- Huy L.Q (2010) “Ứng dụng mô hình Delft 3D tính toán nước dâng do bão vùng biển ven bờ Việt Nam ” use Delf3D model calculate storm surge for all of provinces, the coastal cities in the Việt Nam, then, assessing the impact to each region

- Hiển N.X et al (2012) “Nghiên cứu, tính toán nước dâng tổng cộng trong bão cho khu vực ven biển Thành phố Hải Phòng” has analyzed storm surge for 64 typhoon in the past In the shoreline, storm surges in the total contribution of many factors, including tide: surges and atmospheric pressure, wind and wave surges

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These results are shown to be the effective, however, the analysis was old and new research for South Centre coastal is necessary

3 Research objectives

The main objective of this research is to use sensitivity analysis method to assess the parameters of storm surge modelling and simulation by MIKE model describe the water level under no storm and storm condition, thereby making the prediction, warning of flooding to the coastal region, preventing and mitigating natural disasters caused by hurricanes, especially for relocation, evacuation of communities coastal areas in case of danger

3 The scope of research

The study area includes the coastal provinces from Phu Yen province to Binh Thuan province, which is located in economic zones: South Central Coastal, Southeast and Southwest with an area of approximately 35.837 km2, population of about 12.655 million people

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4 Approach and methodology

The objectives of this study can be achieved by using the numerical modelling approach with following steps:

a Collecting related data:

+ Natural conditions, socio-economic

c Setting up a 2D hydrodynamic model to simulate storm surge The model will be calibrated and validated under typhoon conditions using observed water level

d Comparing the results from the model under storms and no storm condition

e Sensitivity analysis model

5 Thesis structure

The study has 5 main chapters as following:

Chapter 1: Physical settings

Chapter 2: Modelling of non-typhoon condition

Chapter 3: Modelling of storm surge

Chapter 4: Sensitivity analysis model

Chapter 5: Conclusions and recommendations

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CHAPTER 1: PHYSICAL SETTINGS

1.1 Geographic conditions

The study area is located in favourable geographical location It’s near Ho Chi Minh City and South East key economic triangle and also the gateway to the Central Highlands All provinces in the region back on Truong Son range and face East Sea The region from Binh Dinh province to Binh Thuan province is in the South Central Coast is adjacent North Central economic zone to the north, Central Highlands and Cambodia to the west and northwest, South East economic zone to the south, and South China Sea to the east In term of South Central Coast geography, the region has

a complex topography of hill, mountain, forest and sea which creates majestic landscapes and beautiful beaches This is favourable condition to develop tourism, especially sea – island tourism, the South Central Coast owning Hai Van Pass, the end

of the North Truong Son mountain range along with South China Sea, Paracel and Spratly Islands facilitates to develop international ports

On the other hand, provinces in the South have a part of Mekong delta In addition, located at the end of Indochina peninsula, adjacent the southern key economic zone, Mekong Delta owns the close and important two-way relationship Situated adjacent Cambodia and common Mekong River, the region offers favourable conditions to exchange and cooperate with other countries on the peninsula Besides, located in the end of the country’s southwest with 73.2 km long coastline and islands, such as Tho Chu Island, Phu Quoc Island - exclusive economic zones bordering South China Sea and Gulf of Thailand, Mekong Delta owns tourism potentials need explored Furthermore, the region belongs to the region of maritime transportation, international air transport between South Asia and Southeast Asia as well as Australia and other islands in Pacific This position plays an extremely important role in international exchanges

1.2 Topographic conditions

In contrast to most other coastal regions in Vietnam, the South Central Coast's terrain

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extending not only along the entire border with the Central Highlands but also to the coast, forming several passes, bays, peninsulas, and beautiful sceneries with beaches and mountain backdrops Many of the highest mountains are at or near the border with the Central Highlands, the highest of which is Ngọc Linh Mountain at 2598 meters There are several high peaks near the coast of Da Nang (696m on Son Tra Peninsula), Binh Đinh Province (up to 874m), Phu Yen Province (up to 814m), Khanh Hoa Province (up to 978m), and Ninh Thuan Province (up to 1040m) Several mountain passes function as geographic borders between the provinces of the region, with one or two provinces between two major passes Major passes include the Hai Van Pass on the northern border of the region (Da Nang), Binh De pass between Quang Ngai Province and Binh Đinh Province, Cu Mong pass between Binh Dinh Province and Phu Yen Province and Ca pass between Phu Yen Province and Khanh Hoa Province The region includes several islands Some of the larger ones are the Ly Son Islands, the Cham Islands, and Phu Quy island The Paracel Islands and the Spratly Islands are officially administered by Da Nang and Khanh Hoa Province However, sovereignty over them is disputed and Vietnam actually controls only some of the Spratly Islands The southern provinces of the Mekong Delta displays a variety of physical landscapes, but is dominated by flat flood plains in the south, with a few hills in the north and west This diversity of terrain was largely the product of tectonic uplift and folding brought about by the collision of the Indian and Eurasian tectonic plates about 50 million years ago The soil of the lower Delta consists mainly of sediment from the Mekong and its tributaries, deposited over thousands of years as the river changed its course due to the flatness of the low-lying terrain

The present Mekong Delta system has two major distributary channels, both discharging directly into the South China Sea The Holocene history of the Mekong Delta shows delta procreation of about 200 km during the last 6 kyr During the Middle Holocene the Mekong River was discharging waters into both the South China Sea and the Gulf of Thailand The water entering the Gulf of Thailand was flowing via

a paleo channel located within the western part of the delta; north of the Ca Mau Peninsula Upper Pleistocene prodeltaic and delta front sediments interpreted as the

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deposits of the paleo-Mekong River where reported from central basin of the Gulf of Thailand

The Mekong Delta is the region with the smallest forest area in Vietnam 300,000 hectares (740,000 acres) or 7.7% of the total area are forested as of 2011 The only provinces with large forests are Ca Mau Province and Kien Giang Province, together accounting for two thirds of the region's forest area, while forests cover less than 5%

of the area of all of the other eight provinces and cities

1.3 Climatic conditions

Summer temperatures average above 28°C along most of the coast with slightly lower temperatures further inland Winters are significantly cooler with average temperatures ranging from around 20 to 25°C Interestingly, the region includes some of the most arid (Ninh Thuan Province and Binh Thuan Province) as well as some of wettest climates in Vietnam (Da Nang, parts of Quang Nam Province, Quang Ngai Province), with the rest being somewhere in between While average precipitation per year exceeds 2800 mm in many parts of the three provinces in the north of the region, it is less than 800 mm in much of Ninh Thuan Province

Being a low-lying coastal region, the southern provinces are particularly susceptible to floods resulting from rises in sea level due to climate change The Climate Change Research Institute at Can Tho University, in studying the possible consequences of climate change, has predicted that, besides suffering from drought brought on by seasonal decrease in rainfall; many provinces in the southern provinces of study area will be flooded by the year 2030 The most serious cases are predicted to be the provinces of Ben Tre and Long An, of which 51% and 49%, respectively, are expected

to be flooded if sea levels rise by one meter Another problem caused by climate change is the increasing soil salinity near the coasts Ben Tre Province is planning to reforest coastal regions to counter this trend

1.4 Observation stations and hydro-logic conditions

1.4.1 Observation stations

The water level stations in the region is not much, some stations in the river, a number of

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Figure 1 2 Observation stations in south central coast

Within the scope of the study using measure data at 02 stations is:

* Observation stations and marine environmental analysis at Cau Da – Nha Trang City – Khanh Hoa province

Observation station at Cau Da - Nha Trang city was built in 1968, with volume 2x1.5x2.5m The water level in here is measured by water-poles, rods and tide gauges

It is daily observed monitoring water levels and weekly charted to replace the paper once Quarterly organization once dredging station aims tide water wells are connected

to the sea

Figure 1 3: Cau Da station – Khanh Hoa province

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* Observation stations and marine environmental analysis at Bà Rịa Vũng Tàu

Carry out the monitoring, collecting, updating, synthesizing and analysing of environmental data in the province in order to detect and announce to the authorities incidents of environmental pollution on land, coast and sea

Figure 1 4: The monitoring sites of Vung Tau station

1.4.2 Hydrologic conditions

The northern part (Da Nang – Ninh Thuan) where the coastline is located in N-S directions and can be divided into different section by headlands which are forming bays, lagoons with the mouth directions of E and SE The shelf is relatively narrow with depth contour of 200 m lying at distance of ≈ 30 km from the coast Most rivers are short with steep slope and low concentrations of suspended matter

The central part (Binh Thuan - Vung Tau) is where the coastline is oriented in NE-SW directions; it means the coastline direction is parallel with two main monsoon wind directions (NE and SW monsoons) The coast can again be divided into several sections by headlands which form bay with the mouth direction of SE However, the coast is relatively less separated in comparison with the northern part The shelf has a relative smaller slope compared to the northern part, with the depth contour of 200 m

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located at distance of ≈ 100 km offshore Almost all rivers are short, suspended matter concentrations are again relatively low

Figure 1 5: The significant wave height patterns in the East Sea

The coast from Ninh Thuan to Tra Vinh was affected during both monsoon phases The tidal regime along the study coast is from irregular diurnal tide in the northern part

to an irregular semi-diurnal tide regime in the southern part Mean high tide amplitude

is approximately 1 ÷ 2 m along Da Nang to Phan Thiet, and about 3 m along Vung Tau

to Ca Mau

Besides, the main hydro-dynamical processes in South Vietnam waters were driven by monsoonal wind regime Remarkable features are the region of strongest upwelling occurred in Ninh Thuan – Binh Thuan waters during SW monsoon period, and a strong jet current with low temperature during NE monsoon period which flows from north to south along Central Vietnam coast The mechanism inducing water upwelling is complicated, and not only depends on surface wind stress, but also depends on other factors like morphology, characteristics of circulation, etc Intensity of South Vietnam upwelling is highly related to ENSO phenomena In case of strong El Nino the upwelling intensity is weak, whereas, in case of weak El Nino or ENSO Neutral the upwelling intensity is stronger

1.5 Oceanographic conditions

In the South Central Coastal, there exist wind currents, steady current and tidal currents The tidal currents are of the weak speed and mixed type The depth homogeneity of the tidal currents does not express clearly and this shows the tide is a

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result of tidal waves coming from different directions and they have a complex interaction as known for the case of the tidal oscillation of water level Since this region is under the influence of the cold current system in the west of the East Sea the steady current has dominance among all other components

1.6 Historical disasters of typhoons and storm surges

Natural hazards include rare earthquakes and occasional typhoons (May to January) with extensive flooding, especially in the Mekong River delta Almost every year Vietnam is devastated by storms, floods and typhoons that kill hundreds people and cause millions of dollars of damage The problem created by disasters has been exacerbated by logging, erosion and over development An average of 430 people was killed each year by natural disasters between 2007-2011, with property losses estimated at 1 percent of gross domestic product

Vietnam's long 3,200-kilometers coastline is battered every year by up to 10 storms, killing hundreds, even thousands of people Approximately 71 percent of the population and 59 percent of the land area are vulnerable to disasters, with floods and storms as the most destructive occurrences with the highest number of fatalities and economic damage

Table 1 1 Statistics storm in Vietnam

Some meteorologist predict that global warming will bring more rain to the region more rain, stronger typhoons and higher sea levels and make the flooding problem worse, example:

- Between 1954 and 1999, there have been 212 typhoons landing in or directly

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Western Pacific Ocean each year of which about 10 are generated in the South China Sea Of these, an average of 4 to 6 hit of affect Viet Nam There are many years where

at least 10 typhoons arrive in Viet Nam: recent occasions are 1964 (18 typhoons), 1973 (12), 1978 (12), and 1989 (10), 1996 (10) The areas most affected by typhoons are the coastal Provinces of the North and Central Regions However, typhoons in the South, though less frequent, can still be extremely damaging About 62 percent of the population and 44 percent of the whole are frequently affected by typhoons which, on average, kill some 250 people every year The worst in this century were the 1904 typhoon in the South which caused death and injury to 5000 people, and the 1985 typhoon in Binh Tri Thien Province which killed 900 people

- In November 1997 Typhoon Linda swept across Vietnam's southern tip, killing 587 people and destroying crops It was the worst storm since 1904 Many of the dead were fisherman who we out at sea when the storm hit According to a report from the

UN Department of Humanitarian Affairs: During the night of 2 November 1997 Typhoon Linda hit South Vietnam affecting all the Southwestern provinces where, for two days, there were strong rains, in places as much as 100 -150 mm of rainfall The typhoon was the strongest recorded in the area for the last 100 years and caused unexpectedly huge losses The Government of Vietnam undertook every effort to warn populations in the areas at risk Thanks to these efforts, more than 3,500 fishermen were rescued The Government is also taking all measures to provide health and other services to the affected population As of 13 November 1997, information on damage caused by the typhoon was as follows:

+ 464 people killed, 857 people injured and 3,218 missing (or unaccounted for); + 3,122 boats sunk and 774 boats missing;

+ 76,609 houses destroyed and 139,445 houses damaged;

+ 2,254 school rooms destroyed and 4,022 school rooms damaged;

+ 349,232 rice paddies inundated

Depending on the table, from 1946 to 2012, there are 35 typhoon hit to South Central Coastal:

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Table 1 2 Statistics storm in South Central Coast province from 1951 to 2010

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1.7 Conclusions

- Research area of the master thesis is very large, so there are very few reports, research projects studied about the whole area Previous studies focused for a province (eg storm surge simulations for Phu Yen Province, Ba Ria Vung Tau Province ) or a specific region (South Central Coast and South East .) When storms go to the shoreline, storm surge not only affects one province but also affects several provinces, has the inter-regional nature, so need to have joint research, overall for the entire area from which propose solutions, general coordination mechanism between one or more

of the coastal provinces

- About geographic conditions, the region of the provinces from Quang Ngai to Binh Thuan have formed shoreline is rocky shoreline with innumerable coves interspersed, with this feature, will minimize the impact of surge storm to the mainland, due to the many bays shielding, facilitate the prevention and storm resident for fishermen boats However this area has many lagoons and coastal estuaries, so it will be hit hard from storms lead to changes coastal line and the shape of the lagoon, affecting aquaculture, seafood of the fishermen here, and significant impact to the tourism industry On the other hand, the South Central region have many beautiful beaches, luxury resorts such

as Nha Trang, Phan Thiet, Vung Tau so, typhoons and storm surge will affect very much to tourism activities

+ The southern provinces of Ben Tre from Vung Tau are the part of the Mekong Delta, the coastline is characterized by sand, mud so easily destroyed than the rocky coastline, the coast slope is small that make the storm surge higher so it will be severely affected when storms reach the shore

+ The area has a dense network of rivers and estuaries flowing into the sea, storm accompanied by heavy rainfall will cause flooding on the rivers up faster Reality has a lot of historical flood caused to the area causing severe consequences such as floods from (Eg have large floods in Central and South Central in the years: 1952, 1964,

1980, 1990, 1996 , 1998, 2003, 2008 )

- Climatic conditions

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+ The provinces from Binh Dinh to Binh Thuan have climate feature of climate eastern Truong Son regime with little rain, prolonged drought so reduce the impact of storm surges

+ The provinces from Vung Tau to Ben Tre is located in specific regions of tropical and equatorial monsoon For these provinces, there are two seasons in a years: rainy and dry seasons The annual monsoon season from August to November to coincide with the main time that effects of storm to area, thus increase the influence of flooding and saltwater intrusion Especially this area affected by tides, often flooding across the board In 2015, the highest of tide peak is 1.61m on 29/10, the highest level in 50 years

in the Ho Chi Minh City, if the storm combines high tide, the water level will increase, and the destruction will be even higher

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CHAPTER 2: MODELLING OF NON-TYPHOON CONDITION

2.1 Introduction

2.1.1 Introduction model MIKE 21

There are many hydrodynamics model in the world have been applied for many different purposes such as study, planning and construction system design, example: SORBEK, DELFT3D (Netherland), MIKE (Denmark) However, each model has own advantages and disadvantages and so far there has not been a comprehensive and detailed evaluation on their applicability of the models mentioned above After considering, comparing the mathematical models which are able to apply for suitable area with research target the author chose MIKE model

The modules of MIKE 21 allowed for simulating hydrodynamic conditions on the whole domain study instead of just at some points such as measured data In this study with simulating goal and calculating storm surge in the South Central Coast, the MIKE

21 model has been chosen to satisfied criteria:

(i) That is a software suite integrated multiple features (calculate water level, wave, currents…)

(ii) Have been use in read test cases worldwwide

(iii) friendly interface, easy to use and compatibility with many other GIS software

Figure 2 1: Introduction MIKE 21

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MIKE software is software package of DHI Water & Envinroment, sources for enviromental simulation, including river, river mouth, sea and coastal zone The software package has been utilized rather effectively in different countries

The MIKE 21 model suite contains modules, such as Hydrodynamic (HD); Transport (TR); ECO Lab (EL); Mud Transport (MT); Sand Transport (ST, and the master research mainly applies the module: Module Flow Model FM

Among the modules of MIKE 21, Hydrodynamic HD is basic module; it provides the hydrodynamic that is foundation for calculation process of other modules

2.1.2 Module MIKE 21 Flow Model (MIKE 21 FM)

MIKE 21 FM, which it a new model system in untilizing flexible girds node, is developed by DHI Water & Enviroment The model system is developed for studying about sea and envirironment of coastal zone The model consists of continunity equation, moment equation, concentration equation, salt equation

Hydrodynamic Module is the basic ingredient of MIKE 21FM system model, provide basic hydraulic mode for area calculation

General description

2D Shallow water equation of Basic hydrodynamic module is combined between the average of Navier- Stoke and Reynold coefficient It consists of continuity, temperature, satlt, concentration and momentum equations

Storm surge can be presented by the 2DH hydrodynamic equations for long waves in shallow water It includes the continuity equation presenting the mass conservation law and momentum equations for the x- and y-directions presenting the momentum conservation law

The continuity equation:

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x, y Cartesian co-ordinates in the horizontal directions (m)

Px,Py gradient of air pressure in x- and y-directions (kg/m²/s²)

Fx,Fy friction components in x- and y-directions (m/s²)

τwx,τwy wind shear stresses in x- and y-directions (kg/m/s²)

Swx,Swy radian stresses in x- and y-directions (m/s²)

τix,τiy internal stress components (m/s²)

The momentum equations include terms presenting the inertial term (1), convective terms (2,3), Coriolis term (4), gravity term (5), pressure term (6), friction term (7), free surface stress term (8), short wave influence (9), and internal stress term (10)

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The pressure term (6) accounts for the influence of atmospheric pressure

a x

a y

p

p P

The friction term accounts for the bottom friction (7)

x y

VVV (m/s)

Vx,Vy wind speed components in x- and y-directions (m/s)

The variation of wind field in a typhoon can be presented by the typhoon wind models such as the Modified Rankine vortex model (1947), Holland (1980), DeMaria (1992), Fujita (Tan, 1992), and SLOSH (Jelesnianski et al., 1992; Houston and Powell, 1994) The short wave influence (9)

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xy xx wx

S S

Where ε is the horizontal eddy diffusivity (m²/s)

The system of equations (1) to (3) can be solved numerically by a finite difference method (FDM), a finite element method (FEM) or a finite volume method (FVM) Boundary conditions are required for the model Model boundary locations should be selected far enough from the interested area at the places where there is almost no storm surge influence Therefore, only tidal levels can be used as model boundary conditions The tidal level can be computed based on tidal harmonic constants Together with parameters of the models presenting typhoon pressure and wind fields, the above coefficients of Chézy roughness coefficient (C), wind drag coefficient (Cd), eddy diffusion coefficient (ε) are model parameters and can be changed during model calibration process

There is many modeling software available that can be used to solve these above equations including sophisticated commercial models like Delft3D, MIKE 21, SMS,

…The advantages of these models are stable and reliable, easy to use because they are equipped with graphical user interface (GUI) and pre- and post-processing software The disadvantages of the models are not always available, expensive and are not allowed to change the computational code Beside of these, there are also many open source modeling codes such as POM, ECOMSED, HAMSOM These models are free and allowed to modify computational code if necessary

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In regard with rule of application, each model has to follow 3steps:

- Setup model: in this step, the model is set up; simulate real condition with boundary in a specific year to find out the parameters for the model

- Verification: assess the realization of the model

- Using the model to simulate different scenarios for the system

2.2 Model setup and boundary conditions

2.2.1 Analysis data and choose scope of model

2.2.1.2 The scope of model

Choose top and bottom boundary like the picture:

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Figure 2 2 : Scope of model

2.2.2 Building mesh model two-way

2.2.2.1 Domain and mesh count

a) Topography data

Domain model is based on terrain data area of South Central Ccoast, by the Ministry

of Natural Resources and Environment provided in 2010 By using MapInfo software, data is analysed and exported into a file with extension “xyz" The coordinate used is

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UTM-49 Topography obtained from measured data and the bottom topography data has been converted to the national height

b) Mesh count

Regional grid is set up to serve the regime calculations storm surge Domain and mesh count in the area is based on data from coastal by the Ministry of Natural Resources and Environment 2010 provides topographic data were edited and put on the national elevation system old The coordinate use is UTM-49

Figure 2 3: Topography of study area

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c) Create mesh calculator

The grid used in this model is the finite element mesh generated from MIKE zero models with 40467 elements and 23592 nodes The rate calculated net decreases from the ocean to the study area Step calculated for flood model is shown in detail and focus on the coastal area

Figure 2 4 Simulated area

Use triangular grid for offshore terrain with distance grid maximum is 17.475m and grid minimum is 64m The reason for using coarse mesh for the offshore deep water

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terrain because the sudden change of tide is so big, wave height doesn’t change much during the storm passed to the shore On the other hand, using coarse meshes helps to save computation time Meanwhile, the estuary area is divided into smooth meshing in order to calculate in detail, make the results more accurate terrain and these regions have many vary by region With the inside of the estuary and coastal zone, use detail mesh to ensure high accuracy when storms reach the shore

Figure 2 5 Building topography data

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d) Model boundary conditions

When setting up the model, determining boundaries is one of important factors, affecting the accuracy of the modeling results

Land boundary, the “boundary 1” is determined including the entire coastline of the South Central region

Water boundary includes:

+ Sea Border 2 (South)

+ Sea Border 3 (Southeast)

+ Sea Border 4 (East)

+ Sea Border 5 (North)

The north and south boundary perpendicular to the shoreline, shorelines connected with the sea boundary Sea boundary is parallel to the shoreline

Table 2 1 Model boundary conditions

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