Research, identification scientific arguments and proposal of phu quoc – con dao marine spatial planning for sustainable development

3: Diagram of water level without Durian storm at around Con Dao islands according to scenario 0 .... 25: Diagram of water level difference when Durian typhoon occurred at point 4 accord

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DECLARATION

I hereby declare that is the research work by myself under the supervision of Assoc Prof PhD Vu Minh Cat The results and conclusions of the thesis are fidelity, which are not copied from any sources and any forms The reference documents relevant sources, the thesis has cited and recorded as prescribed The results of my thesis have not been published by me to any courses or any awards

Ha Noi, date 12 July 2016

Author of the thesis

Nguyen Thi Lan

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ACKNOWLEDGEMENTS

First and foremost I would like to thank the supervisor Ass Prof PhD Vu Minh Cat for his great contribution in this thesis, for supporting me and guiding me stay on the right trend I also want to show deep thanks to Ass Prof PhD Tran Thanh Tung who is main co-ordinator, making value contributions to success in Master course In addition, please allow me to send my best gratitude to the “Research, identification scientific arguments and proposal of Phu Quoc – Con Dao marine spatial planning for sustainable development” subject, Code: KC.09.16 /11-15, which support a lot of valuable data for

my thesis

Ha Noi, date 12 July 2016

Author of the thesis

Nguyen Thi Lan

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TABLE OF CONTENT

LIST OF FIGURES vi

LIST OF TABLES vii

INTRODUCTION 1

1 The necessity of the study 1

2 Study objectives 1

3 Objects and scope of the study 2

4 Study approaches and methodology 2

5 Structure of the thesis 3

CHAPTER 1: OVERVIEW ON STORM SURGE STUDY AND GENERAL DISCRIPTION ON CON DAO ISLANDS 4

1.1 LITERATURE REVIEWS 4

1.1.1 Introduction about storm in Con Dao islands 4

1.1.2 International researches on storm surge 6

1.2.3 Storm surge researches in Viet Nam 12

1.2 GENERAL DISCRIPTION ON STUDY AREA 14

1.2.1 Natural conditions 14

1.2.2 Climate 16

1.2.3 Oceanographic regime 18

1.2.4 Socio-economic activities 19

CHAPTER 2: APPLICATION OF DELFT3D TO STUDY STORM SURGE 22

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2.1 Description of model 22

2.1.1 Delft 3D model 22

2.1.2 Typhoon model 25

2.2 Data used for the simulation 31

2.2.1 Topographical data 31

2.2.2 Hydrodynamic data 31

2.3 Model set up 32

2.3.1 Simulated domain and computed mesh 32

2.3.2 Model calibration 35

2.3.3 Model verification 39

CHAPTER 3: SIMULATION OF STORM SURGE IN CON DAO ISLANDS 42

3.1 Typhoon scenarios in the areas announced by Vietnam government 42

3.2 Extraction of water level around study islands 45

3.3 Simulation of storm surge based on suggested scenarios 47

3.3.1 Scenario 0: Simulation of water level in Con Dao without Durian typhoon47 3.3.2 Scenario 1: Simulation of Durian typhoon 48

3.3.3 Scenario 2: Simulation of Durian storm with changing wind speed 55

3.3.4 Scenario 3: Simulation of Durian typhoon with changing only its trajectory60 3.3.5 Comparison of scenarios 66

3.4 Chapter’s conclusion 69

CHAPTER 4: INUNDATED MAPPING DUE TO STORM SURGE 70

4.1 Introduction ArcGIS 70

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4.2 Building inundated maps and inundated calculation for research area 71

4.3 Build up inundation maps due to storm surge in Con Dao islands with scenarios accordingly 73

4.3.1 Building inundated mapping and calculation of inundated area for 1st scenario 76

4.3.2 Building inundated mapping and calculation of inundated area for 2nd scenario 77

4.3.3 Building inundated mapping and calculation of inundated area for 3rd scenario 79

4.4 Chapter’s conclusion 80

CONCLUSIONS AND RECOMMENDATION 81

CONCLUSIONS 81

1 Major results 81

2 Drawback 81

RECOMMENDATION 82

REFERENCES 83

APPENDIX 1: RESULTS OF MODEL CALIBRATION 86

APPENDIX 2: RESULTS OF MODEL VALIDATION 95

APPENDIX 3: WATER LEVEL IN CON DAO ISLANDS ACCORDING TO 4 SCENARIO 99

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LIST OF FIGURES

Figure 1 1: Storm Surge vs Storm Tide 6

Figure 1 2: Map of Con Dao Island 14

Figure 2 1: System architecture of Delft3D 23

Figure 2 2: Sketch of wind velocity field for a moving cyclone 28

Figure 2 3: Computed Mesh created for Con Dao area 34

Figure 2 4: Topography of Con Dao islands 34

Figure 2 5: The water level line between observed water level and computed water level with C= 55 m0.5/s 37

Figure 2 6: The water level line between observed water level and computed water level with C= 75 m0.5/s 38

Figure 2 7: The water level line between observed water level and computed water level with C= 68 m0.5/s in hydraulic model verification 40

Figure 2 8: The water level line between observed water level and computed water level with C= 68 m0.5/s in Storm model verification 41

Figure 3 1: Partition of the storm risk of Vietnam coastal area 43

Figure 3 2: Extracted water level points in Con Dao 46

Figure 3 3: Diagram of water level without Durian storm at around Con Dao islands according to scenario 0 47

Figure 3 5: Trajectory of Durian typhoon 49

Figure 3 6: Diagram of water level at point 1 according to 1st scenario 51

Figure 3 7: Diagram of water level at point 2 according to 1st scenario 52

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Figure 3 8: Diagram of water level at point 3 according to 1st scenario 52

Figure 3 9: Diagram of water level at point 4 according to 1st scenario 52

Figure 3 10: Diagram of water level at point 5 according to 1st scenario 53

Figure 3 11: Diagram of water level at point 6 according to the1st scenario 53

Figure 3 12: Diagram of water level at point 7 according to the 1st scenario 53

Figure 3 13: Diagram of water level at point 1 according to 2nd scenario 57

Figure 3 14: Diagram of water level at point 2 according to 2nd scenario 57

Figure 3 15: Diagram of water level at point 3 according to 2nd scenario 57

Figure 3 16: Diagram of water level at point 4 according to 2nd scenario 58

Figure 3 17: Diagram of water level at point 5 according to scenario 2 58

Figure 3 18: Diagram of water level at point 6 according to 2nd scenario 58

Figure 3 19: Diagram of water level at point 7 according to 2nd scenario 59

Figure 3 20: Diagram of water level at point 8 according to 2nd scenario 59

Figure 3 21: Tracks of Durian typhoon according to the 3rd scenario 62

Figure 3 22: Diagram of water level difference when Durian typhoon occurred 62

Figure 3 23: Diagram of water level difference when Durian typhoon occurred 63

Figure 3 24: Diagram of water level difference when Durian typhoon occurred 63

Figure 3 25: Diagram of water level difference when Durian typhoon occurred at point 4 according to 3rd scenario 63

Figure 3 26: Diagram of water level difference when Durian typhoon occurred 64

Figure 3.27: Diagram of water level difference when Durian typhoon occurred at point 6 according to 3rd scenario 64

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Figure 3 28: Diagram of water level difference when Durian typhoon occurred at point 7

according to scenario 3 64

Figure 3 29: Diagram of water level difference when Durian typhoon occurred at point 8 according to scenario 3 65

Figure 3 30: Diagram of water level difference at point 1 66

Figure 3 31: Diagram of water level difference at point 2 66

Figure 3.32: Diagram of water level difference at point 3 67

Figure 3 33: Diagram of water level difference at point 4 67

Figure 3 34: Diagram of water level difference at point 5 67

Figure 3 35: Diagram of water level difference at point 6 68

Figure 3 36: Diagram of water level difference at point 7 68

Figure 3 37: Diagram of water level difference at point 8 68

Figure 4 1: DEM map in Con Dao islands 74

Figure 4 2: Contour line in Con Dao islands 74

Figure 4 3: Inundated mapping in Con Dao islands due to storm surge in Durian typhoon according to 1st scenario 76

Figure 4 4 Inundated mapping in Con Dao island due to storm surge in Durian typhoon according to 2nd scenario 77

Figure 4 5: Inundated mapping in Con Dao island due to storm surge in Durian storm according to 3rd scenario 79

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LIST OF TABLES

Table 1 1: Statistic of storm in Con Dao in the last 50 years 4

Table 1 2: The average temperature of air in the Con Dao Island 16

Table 2 1: Data of model 32

Table 2 2 Parameters of Con Dao grid 33

Table 2.3: Tidal harmonic constants at borders 35

Table 2 4: Parameters of model 36

Table 2 5 Table synthesis error values when calibration models 38

Table 3 1 Basic characteristics and the potential affected by storm to coastal areas in Vietnam 43

Table 3 2 Potential of storm surge and total water level for Vietnam coastal areas 44

Table 3 3 Co-ordination and depth of extracted water lever points in Con Dao 46

Table 3 4: General information of the Durian typhoon 48

Table 3 5 Parameters of Durian typhoon 50

Table 3 6 The highest WL difference and appeared time at 8 points 54

Table 3 7 Parameters of Durian typhoon according to the 2nd scenario 55

Table 3 8 The highest water level difference and appeared time at 8 extracted points according to 2nd scenario 59

Table 3 9: Parameters of Durian typhoon according to 3rd scenario 61

Table 3 10 The highest water level difference and appeared time 65

Table 4 1 Parameters of DEM map in Con Dao 73

Table 4 2 Inundated area in Con Dao islands according to 1st scenario 76

Table 4 3 Inundated area in Con Dao islands according to 2nd scenario 78

Table 4 4 Inundated area in Con Dao islands according to 3rd scenario 79

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INTRODUCTION

1 The necessity of the study

In recent years, the impact of global climate change, natural disasters has become more complex, especially storms, accompanied by sea level rise, which caused inundation in coastal area Storm surges can cause inundation to coastal areas and can cause dike break, especially if storms occur during high tides Therefore, studying, calculation and forecasting on the extreme water level during storm at coastal locations and assessment of inundated risk by storm is very important for finding the solutions and positive measures to prevent and mitigate damages

Storm surge is a dangerous natural phenomenon, which caused a lot of damage

to people and property In Vietnam, the highest water level has recorded as 3.6 m in

1989 by Dan storm Storm surge is particularly dangerous when the storm occurs at the same time with spring tides and in this situation, total water level rising combined with strong wave can cause dike breaks and wave overtopping and also cause heavy damages to people and property

In Vietnam in general and Con Dao islands in particular, although there are a lot of studies of sea level fluctuations in storm, but most of which focus on water level fluctuations on a large scale The fluctuations of water level in coastal locations and inundated risk have not been interested adequately yet, especially when assessing the inundated risk of coastal area Therefore, studying of extreme water levels in storm, in consideration of tides, storm surges, waves and inundated risk to coastal area takes a great scientific meaning The result of study will contribute to mitigate the unfavourable impact of storm surges, serve for protection and maintenance, upgrading

of coastal structures, shoreline protection, requirement for socio-economic development, environmental protection and sustainable development

2 Study objectives

To assess situation of inundation due to storm surge for Con Dao islands

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3 Objects and scope of the study

- Objects of the study: The extreme water level during storm at the shoreline, including tides, storm surges and inundated risk from the sea

- Scope of the study: The area around Con Dao archipelago

4 Study approaches and methodology

To achieve the above mention objectives, the methodology of this thesis has been developed base on the characteristics of Con Dao islands The thesis has been performed in sequence the following steps:

Set up Model (Delft 3D, GIS…)

Analysis and Discussion

Collect data (Winds, waves, tide, water depth, Storm…)

Simulated Results of Storm

Conclusions and Recommendations

Simulation storm surges

Inundated mapping

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5 Structure of the thesis

Besides the introduction, conclusion, recommendation and annexes, the study is consisted 4 chapters as following:

Chapter 1: Overview on storm surge study and general description on Con Dao

Chapter 2: Application of DELFT3D to study storm surge

Chapter 3: Simulation of storm surge for Con Dao islands

Chapter 4: Inundated mapping due to storm surge for Con Dao islands

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CHAPTER 1: OVERVIEW ON STORM SURGE STUDY AND GENERAL DISCRIPTION ON CON DAO ISLANDS

1.1 LITERATURE REVIEWS

1.1.1 Introduction about storm in Con Dao islands

Southern Vietnam is the region where has rare storm, but if the storm occurs then the damage is very serious because people have not experience in storm prevention as in Central and Northern coastal provinces For over 50 years, several storms have occurred, of which 3 hurricanes caused severe damage, such as Thin typhoon in 1904, Linda typhoon in 1997 and Durian typhoon in 2006 Below is a statistical table of typhoon occurs in Con Dao in the last 50 years (from 1962 to 2012)

Table 1 1: Statistic of storm in Con Dao in the last 50 years

Source: http://weather.unisys.com

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18 TWENTYFIVE Tropical Depression 14-14 NOV, 2012

- In principle, typhoons attacked Viet Nam Coasts are originated from west pacific ocean and entering to East sea and typhoon track is seasonally changed The first half of the storm season, typhoons approach mostly to northern and central coasts

of Viet Nam, but the latter half of the season, storms move gradually to the south and affected to south-central and southern coasts of Viet Nam On average, typhoons are less likely to affect Vietnam from January to May From June to August, they are most likely to affect the Northern regions and moving to central and southern regions from September to December annually

- In the latter half of the year, typhoon’s trajectories often more complicated than first half of typhoon season The trajectory of the storm in the East Sea can be divided into five main types: stable, complex, parabolic, weaken at sea and becomes stronger as be near the shore Among them, the complex form and the form of becomes stronger as be near shore are the most unpredictable

Table 1.1 shows the storm landed in Con Dao from October to December each year belonging latter half of the storm season At this time, trajectory of typhoon becomes more complex and less predictable

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1.1.2 International researches on storm surge

Along the coast, storm surge is often the greatest threat to life and property from a typhoon In the past, large death tolls have resulted from the rise of the ocean associated with many of the major typhoons that have made landfall Typhoon Katrina (2005) is a prime example of the damage and devastation that can be caused by surge

At least 1500 persons lost their lives during Katrina and many of those deaths occurred directly, or indirectly, as a result of storm surge

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 20 feet or more in some cases

Figure 1 1: Storm Surge vs Storm Tide

Currently research of storm surge (and monsoon) has achieved a lot results The country suffered damage by storm surges as US, Japan, Russia, China has self-construction and development of appropriate software and also provided other

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countries use as India, Bangladesh There are several methods of calculation and forecast storm surge such as method uses semi-empirical formula, diagram method, artificial neural network method and numerical model methods

In the method using semi-empirical formula (Ippen and Hallerman, 1966), surge magnitude is calculated based on ground level according to wind speed, wind fetch length, the angle between the wind direction and the axis perpendicular to the shoreline and the water depth This method is very simple, but precision is not high because which did not describe all the factors impact on storm surges

Diagram method (Yang et al, 1970, Horikawa, 1985) is often used to forecast storm surges for some ports, where have many monitoring data on typhoons and storm surges The content of the method is to construct the monogram based on the relationship between monitoring data of water level with parameters of typhoon storm (the largest wind speed, wind direction, reduce of pressure in the centre) Therefore, there is very limited when there is insufficient data or data series is not long enough (usually around 100 years if requirement of high precision result) and often only true for the nearest observation station

Numerical models method was created to overcome the deficiencies of empirical measurement data The advantage of this method is reduction of cost compared with experimental measurement methods In addition, this method also allows calculation, forecast the evolution of the phenomenon based on a lot of proposed scenarios, which is not yet existed in reality, but likely to happen in the future

In “Damage Assessment from Storm Surge to Coastal Cities: Lessons from the Miami Area” Genovese, Hallegatte and Dumas focused on the two contiguous counties of Miami, Dade and Broward In this research, authors considered the impact

of different storm surges predicted by the computerized model SLOSH1 and investigate flood risks with current sea level, considering different typhoon parameters (storm category, track, wind speed, and tide level) For each impact, authors apply a

In the “Developments in storm and in combination with tide modeling and risk assessment in the Australian region” Bruce Harper, Thomas Hardy, Lucian Masonand Ross Fryar emphasized the need for integrated planning and forecasting approaches for storm tide risk assessment The importance of the meteorological forcing and the appropriate modeling of each of the storm tide components, namely astronomical tide, storm surge, breaking wave setup and coastal inundation is discussed The critical role

of tropical cyclone “best track” datasets for risk assessment studies and the potential impacts on design criteria and risk assessment studies is highlighted, together with the challenge of developing credible enhanced-greenhouse climate change scenarios It is concluded that storm tide modeling needs to be undertaken in a holistic framework that considers the relative uncertainties in each of the various elements - atmospheric, hydrodynamic and data, as well as addressing operational forecasting, design and

planning needs

Methods used to simulate and assess storm surge

(1) Analytical methods to determine storm surge: The linear relationship between storm and storm surges can not cover the storm surge phenomenon fully Previously when computer technology and methodology has not developed the analytical methods have been mentioned This method can be found in the documents of Russia, Spain and Japan Currently, this method is almost undeveloped, except for some establishments want to have very fast approximate forecast results

of storm surge can be determined in coastal areas

(3) Statistical and regression methods: This is one of the methods to be applied widely

in the world, where measured data is available or the monitoring of storm surges simultaneously with other environmental factors Statistical methods are used in combination with probability theory and extreme method Murty (1978), Harris (1962) was the first authors to propose statistical methods to apply in forecast, calculation of storm surge Firstly Harris created datasets of storm surges including monitoring data, data of interpolation, extrapolation and additional data from the source of results from numerical model, which is got by the linear model From these data sets, the author had built equations of linear regression to predict surges

Although there are many advantages to forecast storm surges, however statistical methods only offer best results once applied on defined area To build a regression equation to forecast of storm surges, we need to consider the impact relations follow the impact function

The form of equation of general linear regression could be written as follows (Murty 1978)

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- i, j: Indexes corresponding to monitoring stations

- k: indexes of monitoring stations

- Fi,k(t – i t ): Quantities characterize for meteorological parameters, which has k form from j monitoring stations at time (t – i t)

- ai,j,k ( x0, y0): Coefficients corresponding to dependent parameters This coefficients can be determined by theory or empirical datas

To determine the height of water rise, people often use empirical formulas, which is summarized from the actually observed documents for each area In Vietnam, Bui Xuan Thong and Nguyen Tuong have based on survey of relationship between heigh

of storm surges with wind speeds from 1959 to 1970 in Northern coastal area, they have given the calculated expression as follows:

h = 0.175  W2

max (1-2)

In which:

Wmax - The average wind speed of storms (m/s)

h – the height of storm surge (cm)

In the past time, in order to calculate the height of storm surge when design the warehouse, Soviet Union has often applied the formula of Karausev A.V, Labzovski N.A, especially norms like:

+ According to the 06.04.82 normative of Soviet Union

h = kw (W2.X/gH).cos  (1-3)

+ According to the 22 TCN 222-95 branch standard of Ministry of Transport

h =kw(W2.X/g(H+0.5 h) cos  (1-4)

Representing the group of analog electrochemical methods is the Russian authors as Macarov and Menzin (1970), Ishiguro (1972) In principle, the electric network is designed as real hydraulic network and electric parameters is replaced as hydraulic system such as water level, discharge etc Since dynamic processes are simulated on the analog network, Ishigura was suggested as follows (1) The external forces make

up water flow in the hydrodynamic system has similar nature like current electric in electric network, (2) current electric flow through the absorption of electrical power generated voltage, likewise due the dynamic nature of currents will create different water levels, (3) the law of energy conservation through the continuity of line appear

in both real and same network and (4) Timing is the same in both network systems (5) Hybrid method: Holz (1977), Funke and Crookshank (1979) tested hybrid model in the tidal estuary The mathematical and physical meaning of Hybrid model show in the combination of propagation of long wave through coastal area by 2 models, which simulate at the same time in deep water and shallow water and through dynamic model and hydraulic model Two models simulate at the same time, water level at the

(6) Methods of numerical simulation: This is the main content of the mathematical modeling techniques to simulate storm surge This technique includes the following steps

- The first step is to build an understanding about the nature of the physical phenomena of storm surge and processes expressed in real terms This step, the researcher completely can do and must do it

- The second step is to find out the formation process of mathematical equation to describe storm surge

- The third step is the techniques to identify forming forces of storm surge, the closed system of equations Determine the type of boundary conditions including hard boundary, liquid boundary and side boundary

- The fourth step is the technique to solve a system of equations, which have been set

up This is the digital part, which relating to calculated grids, difference method, select the programming language

- The fifth step is the techniques to calibrate model, the stability of the model

1.2.3 Storm surge researches in Viet Nam

Vietnam is a coastal country, where have high storm surges risk so researches

of storm surges have been done for a long time and many models and technology of storm surge forecast were built Besides the development of numerical models to simulate the storm surge, some studies tend to use commercial models or open source model to calculate storm surges to coastal areas of Vietnam The business model may

In the project namely “σghiên c u đ c p nh t, chi ti t hóa b s li u c b n v tri u, n c dâng d c b bi n t Qu ng σinh đ n Qu ng Nam ph c v tính toán thi t

kê, nâng c p tuy n đê bi n” conducted by Dinh Van Manh and partners, based on data base of tides, storm surges and total levels of tide and storm surges along the coasts from Quang Ninh to Quang Nam were established, in which, data of statistical arising storm was built by Monte Carlo method based on probability distribution of the parameters storms occurred in the past

Following this direction, in “σghiên c u xây d ng h th ng d báo tác nghi p khí t ng th y v n bi n (g m dòng ch y, sóng và n c dâng do bão) vùng bi n ông

và ven bi n Vi t σam” project, Le Trong Dao and partners have used Delft 3D model

to set up and simulation, forecasting storm surges to coastal areas in Vietnam

In addition, Nguyen The Tuong, Tran Hong Lam et al (2007) in the framework

of cooperation between Vietnam - China research project used a package of models such as 3D Delft of the Netherlands, JMA (Japan Meteorological Agency storm surge model) of Japan and CTS (China typhoon Surge) of China to calculate and provide forecasting water surges fo the coasts of Viet Nam

Source: KC.09.16 Subject

Figure 1.2: Map of Con Dao Island

Con Dao district has great potentials for development of tourism, exploitation and processing of seafood, port development, petroleum and gas complex services and shipping Coast with a 200 km of length, with many beautiful beaches like Dat Doc,

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Bai Canh, Dam Trau, Hon Cau, Hon Tre In addition, the Con Dao National Park is

an area of nearly 6.000 ha on mainland and 14.000 ha on sea with a variety of trees and rare animals

1.2.1.2 Characteristics of topography and geomorphology

Con Dao archipelago was formed in stage of volcanic activity in the late Jurassic

and lasted until late Paleogenic era Because tectonic activity of volcano in the period mentioned above, the archipelago was formed and exists to the present day Con Dao has soil texture and terrain more complex than other islands

Floating Island Region: Con Dao Islands consists of 14 floating islands, including Con Son Island, which is the largest island with area of approximately 58km2, three other islands with area of over 5 km2 as Hon Ba, Hon Bay Canh and Hon Cau and ten remaining islands has an area of less than 1km2 Con Dao has low mountainous terrain (Thanh Gia mountain with the highest peak of 577 m), mountains was formed by magma eruption

Coastal zone: The shoreline of Con Dao Island has complex structure, texture

of rock mailly formatted by magma eruption and intrusion The distribution and positions of shoreline are not fixed, depending on tide, sedimentation and erosion Coast are composed of erupted magma distributed in the northeast of Con Dao and Hon Tai, Bay Canh, Hon Cau and some other small islands in the northwest Features

of eruptive rocks are highly alkaline Coast are composed by shallow intrusion magma

is the stretch of shore in Ben Dam, Thanh Gia mountain, Ta Be mount, Chim cape and northwest shore of Bay Canh island Coast is composed of discrete Quaternary rocks distributed in central areas of Con Dao - the first coast of Co Ong airport valley The sediment here mostly is fine sand originated by sea

The seabed: The seabed have abrasives and accumulate surface in depths from 3-10m: It is not great area, mainly distributes in the northeast coast, central and south western of Con Dao islands This is the underground shelf of Northeast gulf, Con Son bay, Ben Dam bay Largely of surface is sand, fine-grained sand mixed with organism

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debris Some surface areas have coral reefs developing rapidly such as Con Son Gulf, Ben Dam Bay Particularly in Con Son Gulf, which near the pier exists negligible accumulation, is mud

The bottom area has abrasion accumulates surface at depths from 10 to 20 m: Focusing mainly in Northeast bay and Con Son Gulf Bay which in southwest Con Dao island Bottom topography in the north-eastern and central regions is relatively flat; bottom sediments are mostly fine sand and sand-sea creatures The bottom topography

of southwest of Con Dao has more complex surface roughness Bottom sediments are mainly sand, gravel and mixed into sea creatures, coarser composition of grain

1.2.2 Climate

1.2.2.1 Temperature

Con Dao locates in the area of tropical monsoon climate and has two distinct seasons: rainy seasons and dry seasons, surrounded by sea, so climate of Con Dao is influenced by ocean climate regime therefore Con Dao climate regime is more moderate than the mainland Air temperature in Con Dao doesn’t not oscillates largely, the average temperature of months in year ranges between 26-290C, full-year average temperature is 27,80C (high absolute temperatures is 360C and low absolute temperatures 180C) (Dang Ngoc Thanh, 2003) This is the most moderated areas of coastal zone in Vietnam with the oscillation amplitude of temperature annually is low, not over 3,10C - 40C Monthly average temperature is highest in May with 28,30C and lowest in January with 25,20C (table 1.2)

Table 1 2 : The average temperature of air in the Con Dao Island

Source: Nguyen Van Au, 2002

T (0C) 25,2 25,7 26,9 28,2 28,3 27,8 27,5 27,5 27,2 26,9 26,7 25,7

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1.2.2.2 Rainfall regime

Rainfall regime of Con Dao region depends heavily on air masses, especially humid equatorial air masses Moreover, the impact of storm and the role of topography also contribute significantly decide to the rainfall of Con Dao Island According to statistics document show that the average rainfall for many years in Con Dao Island is quite large, about 2055 mm/year The rainy season lasts from May to October with average rainfall reached 200-250 mm/month, accounting about 70% of annual rainfall The dry season lasts from November last year to April next year, an average of 6-7 days of rain/month, average rainfall for month is about 40-66mm/month

1.2.2.3 Wind regime

Con Dao archipelago locates in the South East Sea climate area, the climate is tropical oceanic equatorial monsoon Every year, climate and weather here are affected alternately by two monsoon types, they are northeast monsoon and the southwest monsoon:

+ The northeasterly wind is usually northeast and east (to the prevailing direction is east), blows from late October to early April next year The average wind speed of 3.5-4.5 m/s, the strongest winds to 18-20 m/s, when a storm wind speeds can

be up to 30-35 m/s

+ The southwest monsoon is usually south west and south, blowing from late April to early October, the average wind speed reaches 2,5-3,5 m/s, the strongest winds reaches 20-25 m/s Typhoons usually appear in 10-12 months (low frequency), winds can reach 25-27 m/s

The transition period between the two seasons, the prevailing wind is east to southeast, with an average speed of approximately 4 m/s

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1.2.3 Oceanographic regime

1.2.3.1 Tide

Tidal regime at Con Dao Sea is of mixed type including some diurnal days, but prone

to irregular tide Tidal range in Con Dao in spring period is from 3,0 4,0 m and 1.5 2.0 m in ebb tide Fluctuation band of relatively large sea level (0,5 - 0,7 m), fluctuating around 0.45 in average The maximum water level was recorded at 4,1 m and minimum is 0,21m, 2,47m average, average tide recorded in Con Dao is 2,29m 1.2.3.2 Wave regimes

-Due to the impact of the monsoon circulation and influence of geographical conditions, the wave regime of Con Dao has relatively complex behavior and there have two large wave seasons annually Direction, wave height and wave length are related closely to the wind regime in the year In the northeast monsoon, the prevailing wave direction is northeast and northeast-east with wave frequency is 60% and the average wave height is of 0.5-1.8 m In the southwest monsoon, the prevailing wave direction is southwest and west-southwest with an average wave height of 0.3-1.5 m 1.2.3.3 Ocean circulation

Besides oscillations by wind, waves, Con Dao island has movement of sea currents Under the acting of flows, sea water in Con Dao islands is circulated and exchanged with surrounding sea areas, which have changed and regulated climate, formation of sand bars and contribute to increase the area of alluvial around island…

Flow around Con Dao Island is dominated mainly by tidal current and topography In winter, the direction of flow in Con Dao area is northeast - southwest with average velocity of 0.8 to 1.5 m/s and in summer flow has the opposite direction, with a medium flow rate approximately 0.7 to 1.5 m/s

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1.2.4 Socio-economic activities

In 2014, the socioeconomic situation in Con Dao district has many positive changes The economic structure of developed properly orientation: Service-tourism: 87.25%, industry-construction: 7.96%, agriculture- forestry - fisheries: 4.8% The industrial production value is estimated at 136 billion, up 9.64% compared to 2013; total service revenues is 1,079 billion, up 10.09%; fishery production value estimated at 35.63 billion, up 11,8% compared to last year Estimated total budget revenues reached 285.87 billion in 2014 At the same time, Con Dao district has also done good work of healthcare, education, culture, sports, public administration reform, and policies to ensure social security, environmental protection, national defense, security

1.2.4.1 Population and labour

According to the document of People's Committee of Con Dao district, the years from

1980 to 1990, population of Con Dao district ranged between 2000-3000 people, to the years 2000-2010, population of Con Dao district increased to 4000-6000 people and which reached 6600 people in 2012 They live in ten neighborhoods Con Dao town focus of residential, resort for tourists and administrative units of Con Dao district The proportion of male / female is 51% and 49% In addition to the mechanical population growth as above, the population in Con Dao has increased by natural way Because more than 70% of residents are officials and civil servants are seriously implementing the Policy on Population and Family Planning, so the rate of natural population growth in Con Dao is very low, only 1-3% a year

Report of Ministry of Home Affairs on situation of the first six months in 2012: In Con Dao, the number of people in working age is 3,780 people, of which more than 2900 people have stable jobs Occupational structure includes: Officers - Service: 1970 people; Industry - construction: 583; Agriculture: 370 people; Homemaker: 384 people Moreover there are 29 old men have age over 80 year old, and more than 1,500 students from preschool to high school The total number of households is 1577

* Commerce and Services

Domestic and foreign tourists come to Con Dao islands more and more Currently, in addition to two flights from Tan Son Nhat (Ho Chi Minh) and Vung Tau, Con Dao has five large ships, which have 100 beds and three cargo ships from 50 to 250 tons There are also Phi Yen hotel, Saigon Tourist hotel and guest houses of Con Dao National Park

As planned, Ben Dam bay will build four ports: seafood port, petroleum technical services port, maritime services port and military port Con Dao will prioritize investment:

- Development of telecommunications infrastructure to ensure smooth communication

at high speed between the island with nation and oversea countries

- Development of vehicles to transport passengers and cargo on the quality and quantity between the Con Dao and inland

- Development of financial services and banking

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- Encourage the development of services of training for human resources and wellness Currently, Con Dao is transferred gradually toward focus develop service, tourism to promote potentials and advantages of the district

to regulators and government officials, all of whom are active in one or more of the stages of the design, implementation and management cycle

Delft3D-FLOW is a multi-dimensional (2D or 3D) hydrodynamic (and transport) simulation program which calculates non-steady flow and transport phenomena that result from tidal and meteorological forcing on a rectilinear or a curvilinear, boundary fitted grid In 3D simulations, the vertical grid is defined following the sigma co-ordinate approach

The Delft3D program suite is composed of a set of modules (components) each of which covers a certain range of aspects of a research or engineering problem Each module executes independently or in combination with one or more other modules The information exchange between modules provides automatically by means of a so-called communication file; each module writes results required by another module to this communication file and reads from the file the information required from other modules Other, module-specific, files contain results of a computation and used for visualisation and animation of results

The hydrodynamic conditions (velocities, water elevations, density, salinity, vertical eddy viscosity and vertical eddy diffusivity) calculated in the Delft3D-FLOW module are used as input to the other modules of Delft3D, which are (see Figure 2-1):

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• Delft3D-WAVE short wave propagation

• Delft3D-WAQ far-field water quality

• Delft3D-PART mid-field water quality and particle tracking

• Delft3D-ECO ecological modelling

• Delft3D-SED cohesive and non-cohesive sediment transport

• Delft3D-CHEM chemical components and interactions

• Delft3D-MOR morphodynamic simulations

Figure 2 1: System architecture of Delft3D

In the thesis, Delft 3D-Flow module is used to simulation storm scenarios in Con Dao region

Basic equations

The hydrodynamics of continent shelf in the storm conditions is simulated by solving the system of two-dimensional of shallow water equations that consists two of horizontal momentum equations and one continuity equation:

Conservation of momentum in x-direction (depth and density averaged)

g U v P

(8): External force by wind

(9): Depth averaged turbulent stress

In which:

C: Chezy coefficient

d: Bottom depth

f: Coriolis parameter

: Diffusion coefficient (eddy viscosity)

: Water level above a reference level

u,v: Depth averaged velocity

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w: Mass density of water

U: Absolute magnitude of total velocity, U=(u2+v2)1/2

wx wy: x, y: components of wind shear stress Wind shea stress is determined by the widely used quadratic expression, w= aCdW2 , where a : air density, Cd: wind drag coefficient, W: wind speed at 10m above the free surface

Assumptions:

The vertical momentum equation is reduced to the hydrostatic pressure relation Vertical accelerations are small compared to the gravitational acceleration (g), so it is negligible The fluid is incompressible and using Boussinesq approximation No dynamic coupling between changes in topography and flow In small-scale flow, complete Reynolds stress tensor is used In vertical direction, the so-called - coordinate is used that means the number of layer is constant over horizontal computational area In this study, only depth- averaged model is used corresponding to one layer in vertical

Storm surge in shallow water influence of water depth and coastal shape:

In order to simulate flows under typhoon condition, it is necessary to set up a typhoon

model to simulate storms including two separately parts: pressure field and wind field

The results of the model are pressure field and wind field on the sea surface under

storm condition that will be the data set required putting into hydrodynamic model

+ Typhoon pressure computation

The decrease of pressure causes a rise of water level In the equilibrium state, a water

level has one centimetre increase for every millibar decline of atmospheric pressure

The larger the water depth the stronger the influence of atmospheric pressure field In

shallow water although the effect of atmospheric pressure itself exerts the water

surface is small compared to wind stress, it plays an important role in driving wind

pn [mb]: is the environmental atmospheric pressure not affected by typhoon;

p0 [mb]: is the atmospheric pressure at the centre of the typhoon;

R [km]: is the radius associated with maximum wind speed

1

;4

n a

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For all of the above models, pn has a value of pn = 1 atm = 1013 mb The value of p0 is obtained from Best Track The magnitude of R varies in time during the development

of a typhoon It can be taken directly from observed data of atmospheric pressure field

or estimated by minimising the error between observation and computed values

 Wind field

Surface wind stress terms represent the drag force produced by wind over the water surface This is important for shallow water areas in storm conditions where very strong winds occur It is even much more important than the role of pressure in driving storm surge Actually, typhoon wind fields are usually intensive, spatially inhomogeneous and directionally varying The large gradients in wind speed and rapidly varying wind direction of typhoon vortex can generate very complicated flow However, for practical application, the wind field data may be taken from observation

or forecasts using several simple parametric wind models as an ideal typhoon model

Figure 2 2: Sketch of wind velocity field for a moving cyclone

Actually the wind speed (W) has two components: one is related to the typhoon centre movement and the other is the gradient wind speed component and present in Cartesian co-ordination Fully wind speed model is described

0 2

0 2

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F: wind speed component related to moving centre of typhoon at a distance r from the center of the typhoon

Fx, Fy: x- , y – components of velocity related to moving centre of typhoon

Wr: typhoon gradient wind speed at a distance r from the centre of the typhoon

 : Angle between x –axis and the line connecting calculation point and typhoon center

 : Angle made by the gradient wind speed with isopiestic line

C2: empirical coefficient in the range of 0.6 to 0.8

Wind speed components of the typhoon:

+ The first component of wind speed related to moving centre can be calculated by following formula (Masami, 1962)

500 1 r f

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f: Coriolis coefficient; f= 2 sin = 0.525sin in which is the angular speed of Earth;

is the latitude

There are some well-known parametric wind models presented as follow:

-The modified Rankine vortex model (1947):

In which Wmax: the maximum wind speed X is shape parameter ranging 0.3 < X< 0.8

to adjiust the wind speed distribution in radial direction can be determined empirically from observed data

- SLOSH model (1992)

max 2 2

2r

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To estimate the wind direction, it is necessary to take into consideration a bias angle

 between geostrophic wind and real wind, as regards typhoons, in the literature it is sometimes assumed that the wind velocity is directed toward its center and makes an northern hemisphere For s stationery tropical cyclone, the inflow angle at the surface

is approximated as Bretschneider in (Phadke at al , 2002)

2.2.2 Hydrodynamic data

Tidal boundary: The tidal harmonic constants (M2, S2, N2, K2, O1, K1, P1, Q1) are

used to calculate the predicted tide at the open boundaries as input data for hydrodynamic model Data from the harmonic constants were taken from Delft Dashboard model

The information of storm: The information of Durian typhoon such as the storm’s trajectory (typhoon position, movement speed, measure of reduced pressure at the centre, the largest wind speed) is taken from collection of data BEST TRACK of the

US National Oceanic and Atmospheric Administration (NOAA) (http://weather.unisys.com/hurricane/)