Luận văn thạc sĩ Xây dựng công trình thủy: Modeling storm surge for the south central coast of Vietnam

4: The monitoring sites of Vung Tau station Figure 1, 5: The significant wave height patterns in the East Sea Figure 2 1: Introduction MIKE 21 Figure 2 2: Scope of model Figure 23: Topog

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 Quynh

‘nally, 1 would like to express my special appreciation to my friends and colleagues

for their support, encourage and advices Thank you so much!

2.1 International researches on storm surge

2.2 Past studies on storm surges in Vietnam

3 Research objectives

3 The scope ofresearch

4, Approach and methodology

5 Thesis structure

CHAPTER 1: PHYSICAL SETTINGS

1.1 Geographic conditions 91.2 Topographic conditions, 91.3 Climatic conditions u1.4 Observation stations and hydro-logie conditions "1.4.1 Observation stations "1.4.2 Hydrologic conditions B

1.5 Oceanographic conditions 14

1,6 Historical disasters of typhoons and storm surges 181.7 Conclusions 18CHAPTER 2: MODELLING OF NON-TYPHOON CONDITION 20'2.1 Introduction, 202.1.1 Introduction model MIKE 21 202.1.2 Module MIKE 21 Flow Model (MIKE 21 FM) 212.2, Model setup and boundary conditions 252.2.1 Analysis data and choose scope of model, 25

2.2.2 Building mesh model two-way 26 2.2, Model calibration,

2.2.1 Analysis and choice of time and calibration data model.

2.2.2 The parameters and model calibration process 342.2.3 Results of model calibration 342.2.4 Conclusion: 36

2.3 Model verification

2.3.1 The parameter for verification

2.4.2 The result of verification model.

3.2.2 Wind field model in the storm

3.2.3, Modelling of pressure in storm

3.3 Model setup and boundary conditions

3.3.1 Analysing data

3.3.2 Set of hydraulic parameters

3.4, Model calibration

3.4.1 Analyze and choose the time and calibration data model

3.4.2 Parameters and model calibration process

3.4.3 Conclusion

3.5 Model verification

3.5.1 Set up model verification

3.5.2 The result of verification

3.6 Conclusions

(CHAPTER 4: SENSITIVITY ANALYSIS MODI

4.1, Role of pressure center in the storm

4.1.1 Set of hydraulic parameters,

4.1.2 Results model

4.1.3 Results analysis:

4.2 Role of parameters model (B)

42.1 Set of hydraulic parameters

4.22 Results model

423, Results analysis

4.3 Role of maximum wind speed in the storm.

43.1 Set of hydraulic parameters

43.2, Results analysis

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4.4 Role of radius maximum in the storm

4.4.1 Set of hydraulic parameters

4.4.2 Results model:

4.4.3 Results analysis:

4.5 Role of wind friction (Ca)

4.6 Role of trajectory of storm,

4.6.1 Set of hydraulic parameters

4.6.2 Results model:

4.6.3 Results analysis

66666T686877Tà75CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS 65.1 Conclusions

5.2 Recommendations,

REFERENCES

APPENDIX!

167879

LIST OF FIGUES

Figure I: Administrative Map of South Central Coast

Figure 1 2 Observation stations in south central coast

Figure 1 3: Cau Da station ~ Khanh Hoa province

Figure 1 4: The monitoring sites of Vung Tau station

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

Figure 2 1: Introduction MIKE 21

Figure 2 2: Scope of model

Figure 23: Topography of study area

Figure 24 Simulated area

Figure 25 Building topography data,

Figure 26 Model boundary conditions

Figure 27 Diagram of calibration process

Figure 2 8 Calibration station

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

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

Figure 2 11 Comparison diagram in Cau Da station

Figure 2 12 Comparison diagram in Vung Tau station

Figure 31 Storm surge

Figure 32: Typhoon #21 in 2007

Figure 3 3: Typhoon #23 in 2009

Figure 34: Wind field model

Figure 3 5: Data provided for the wine field model

Figure 3 6: Wind speed in the typhoon in 2007

41

4747

48

49

sl

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

Figure 3 8: Comparison diagram in Cau Da station 11/2007 =Figure 3 10: The parameter of storm #23 in 2008 sFigure 311: Wind speed inthe typhoon in 2009 sFigure 3 12: Wind pressure in the typhoon in 2009 sFigure 3 13: Comparison diagram in Cau Da station in 2009 56

Figure 41 The relationship between Vinax and AP sFigure 4 2 The positions extract 60Figure 4 3 Storm surge in Quy Nhon ~ Bình Dinh otFigure 4 4 Storm surge in Nha Trang ~ Khanh Hoa otFigure 4 5 Storm surge in Vung Ro~ Phu Yen “Figure 46 Storm surge in Quy Nhon ~ Bình Dinh 6Figure 4 7 Storm surge in Nha Trang — Khanh Hoa 63Figure 4 8 Storm surge in Vung Ro ~ Phu Yen, 6Figure 4 9 Storm surge in Quy Nhơn ~ Bình Dinh 65Figure 4 10 Storm surge in Nha Trang ~ Khanh Hoa 6Figure 411 Storm surg in Vung Ro~ Phu Yen 6Figure 4 12 Storm surge in Quy Nhon ~ Bình Dinh oFigure 4 13 Storm surge in Nha Trang ~ Khanh Hoa oFigure 4 14 Storm surge in Vung Ro~ Phu Yen 6

Figure 4 15 Storm surge in Quy Nhon ~ Binh Dinh ©Figure 4 16 Storm surge in Nha Trang ~ Khanh Hoa 70Figure 4 17 Storm surge in Vung Ro~ Phu Yen 20Figure 4 18 Typhoon #23 in 2009 mFigure 4 19 The storm hits Binh Dinh province 2

Figure 4 20 The storm hits Nha Trang province

Figure 421 The storm hits Ninh Thuan province

Figure 4 22 Storm surge in Quy Nhon ~ Binh Din

Figure 423 Storm surge in Vinh Xuan Dai ~ Binh Dia

Figure 424 Storm surge in Vung Ro~ Phu Yen

Figure 425 Storm surge in Nha Trang ~ Khanh Hoa

Figure 4 26 Storm surge in Cam Ranh ~ Khanh Hoa

Figure 4 27 Storm surge in Mui Padaran ~ Ninh Thuan,

72

73

737747474

LIST OF TABLES

‘Table 1 1 Statistics storm in Vietnam

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

Table 2 1 Model boundary conditions

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

Table 2 3 Relevance of NASH coefficient

‘Table 2 4 Results of model calibration

Table 2 5 Results parameter of model after calibration

‘able 3 1 Wind speed according tothe Beaufort wind sele

Table 3 2 Parameters of wind fied

‘able 3 3: The data of Typhoon #21 in 2007 (grade 11)

‘Table 3 4: Set of hydraulic parameters

‘Table 3 5: The result of model calibr ion

Table 3 7: The result in observation station in Storm

‘Table 4 1 The input parameters of the models

Table 4 2 The coordinate of positions extract

3031343536

4448

49325356

60

1 Problem identification and the necessit 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 anderosion of the riverbanks, while there are five phenomena related to typhoons andstorm surges,

According to Hang et al (2010), on average, Vietnam suffers from 5 to 7 typhoons peryear along its coastal zone From 1951 to 2006, the activities of typhoons in SouthEast 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 inereases The number of typhoons reduces, but more super

typhoons appear, which causes great damage to people and property, such as HurricaneKatrina 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

typhoons hit coastal area, water level increases, and destroying structures and houses

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 toproperty such as lost homes, erops, damaged the social-economic works of up to tens

of billions, The South Central Coast is often threatened by coastal erosion, broken

di 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 ofclimate change increasingly unpredictable and the effect of climate change will maketyphoons 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,

‘hich is defined as the water level rise due to the combination of storm surge and theastronomical tide, This rise in water level can cause extreme flooding in coastal areasparticularly when storm surge coincides with normal high tide, esulting in storm tidesreaching 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 eyelonically 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 ofdifferent factors Storm surge is a very complex phenomenon because it is sensitive tothe 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

Hurricane Katrina approached the US coast in 2005, it generated a storm surge of more

than 8 meters 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 levelMore 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 statisties 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 effe s ofthe 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 beenmade through the mathematical model or software such as MIKE 21 Flood (Denmark),Sobck 2D (Netherlands), Delf3D, etc there have been many waring systems sugersthat 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 atmosphericpressure 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 cyelonedisasters in the history of the United States, Katrina formed over the Bahamas onAugust 23 and and crossed southern Florida (first landfall) as amoderate Category Ihurricane on Saffir-Simpson Scale (Appendix A), causing deaths and flooding AfterKatrina moved westward, entering in the Gulf of Mexico, and began strengtheningrapidly, reaching Category 5 on Sallir-Simpson Seale, with a maximum wind of 150kts 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

pressure drop created an extreme storm surge, causing fatalities and damage Most of

the damage had due to a secondary effect of this surge: the surge caused a rise of the

3

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 citywhich sits mostly below sea level, After creating death and destruction in Louisiana,Mississippi, and Alabama, Katrina moved northward into Tennessee and Kentucky andheaded 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 lan and a value ofmulated in the region of Pass Chri

8.4 m has been observed in this area (Graumann et al., 2006) A complete storm surge

analysis 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 therecorded 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 notincluded 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 mand not 5.05 m The last comparison, with the data of Mulein Station (GLOSS TideGauge), shows a close agreement with the HyFlux2 simulation: a difference of only

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 comparisonshave 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 is intensity and began moving west-southwestward, accelerating

towards the tropical

Queensland coast The landfall happened on February 2 along the northeast coast ofQueensland as a Category 4 on the U.S, Saffir-Simpson seale (Appendix B) midway

between Caims and Townsville, After landfall, it maintained a sương core with

damaging winds and heavy rain, tracking westwards across northem 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 completeevaluation of the wind field, only some observation of mean sea level pressure areavailable, therefore actually no enough observational data are available to a completeassessment of the results of this TC and the reports was presented a preliminaryanalysis,

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 coastalarea, The author indicates the total water rise is included: surge storm, tides, waves andfreshwater flow

Tao Shen (2009) “Development of a Storm Surge Model Using a High-ResolutionUnstructured 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,One is the large domain grid for the storm surge prediction purpose covering the

Atlantic Ocean from Nova Scotia to Florida; the other is the small, imited domain gridcovering the land parts in the Hampton Roads and Virginia Beach areas for theinundation prediction purpose and the results showed the storm surge model with alarge domain grid was able to generate reasonable water elevation results duringHurricane 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 B.D (2006) *Nghiên cứu tương tác sóng và nước ding do bão bằng mô hình sí

trị” The report analyzed the interaction between the waves and storm surges based onresults 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 HLX etal, (2008) * Banh giá một số phương pháp tính toán nước ding do bao

ở Việt Nam" compared the advantages and disadvantages indicate the method ofcalculation of storm surges such as: surveying the statistical method, empirical formulamethod , 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 tinh toán nước ding do bao ving biển

ven bở Việt Nam ” use Delf3D model calculate storm surge for all of provinces, thecoastal cities in the Vigt Nam, then, assessing the impact to each region

- Hign N.X et al (2012) *Nghiên cứu, tinh toán nước dâng tổng cộng trong bão chokhu vực ven biển Thành phố Hải Phong” 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

‘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 ease 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 km*, population of about 12.655

milion people.

7

4 Approach and methodology

The objectives of this study can be achieved by using the numerical modelling

approach with following steps:

Collecting related data:

+ Bathymetric data

+ Water level

+ Storm parameter: wind speed, wind direction, atmospheric pressure andtyphoon tracks

b, Setting up a 2D hydrodynamic model to simulate water level under normal

condition The model will be calibrated and validated under non-typhoon conditionsusing observed water level

e Setting up a 2D hydrodynamic model to simulate storm surge, The model will becalibrated and validated under typhoon conditions using observed water level

«4, Comparing the results from the model under storms and no storm condition

e Sensitivity analysis model

5 Thesis structure

The study has Š main chapters as following:

Chapter I: 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.

CHAPTER 1: PHYSICAL SETTINGS,

1.1 Geographic conditions

The study area is located in favourable geographical location It’s near Ho Chỉ MinhCity and South East key economic triangle and also the gateway to the CentralHighlands 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 CentralCoast 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 majesticlandscapes 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 zoneMekong Delta owns the close and important two-way relationship Situated adjacent

‘Cambodia and common Mekong River, the region offers favourable conditions toexchange 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 Seaand Gulf of Thailand, Mekong Delta owns tourism potentials need explored.Furthermore, the region belongs to the region of maritime transportation, internationalair transport between South Asia and Southeast Asia as well as Australia and otherislands in Pacific This position plays an extremely important role in internationalexchanges

1.2 Topographic conditions

In contrast 1o most other coastal regions in Vietnam, the South Central Coast's terrain

is not mainly flat It has a diverse topography with mountain ranges and hills

extending not only along the entire border with the Central Highlands but also to thecoast, forming several passes, bays, peninsulas, and beautiful sceneries with beachesand mountain backdrops Many of the highest mountains are at or near the border withthe 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 Dinh Province (up to 874m), Phu Yen Province (up to 814m), Khanh HoaProvince (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 onthe northern border of the region (Da Nang), Binh De pass between Quang NgaiProvince and Binh Dinh Province, Cu Mong pass between Binh Dinh Province andPhu 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 andwest 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 theMekong and its tributaries, deposited over thousands of years as the river changed itscourse due to the flatness of the low-lying terrain,

The present Mekong Delta system has two major distributary channels, bothdischarging directly into the South China Sea, The Holocene history of the MekongDelta 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 westem part of the delta; north of the Ca Mau

Peninsula, Upper Pleistocene prodeltaic and delta front sediments interpreted as the

10

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 300,000hectares (740,000 acres) or 7.7% of the (otal area are forested as of 2011 The onlyprovinces 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 lowertemperatures further inland, Winters are significantly cooler with average temperaturesranging from around 20 to 25°C Interestingly, the region includes some of the mostarid (Ninh Thuan Province and Binh Thuan Province) as well as some of wettestclimates 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 ofthe region, it isless than 800 mm in much ofNinh Thuan Provinee

Being a low-lying coastal region, the southern provinces are particularly susceptible tofloods resulting from rises in sea level due to climate change The Climate ChangeResearch Institute at Can Tho University, in studying the possible consequences ofclimate 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 theprovinces ofBen Tre and Long An, of which $1% and 49%, respectively, are expected

to be flooded if sea levels rise by one meter Another problem caused by climatechange is the increasing soil salinity near the coasts Ben Tre Province is planning toreforest 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

stations in the sea, the facilities are not sufficient which leads to lack of monitoring data

Figure I 3 Observation stations in south central coastWithin 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

2

* Observation stations and marine environmental analysis at Ba Ria Vang Tau

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

Figure 1 4: The monitoring sites of Vung Tau station1.4.2 Hydrologic conditions

‘The northern part (Da Nang - Ninh Thuan) where the coastline is located in N-§

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 NI

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 arelative smaller slope compared to the northern part, with the depth contour of 200 m

located at distance of ~ 100 km offshore, Almost all rivers are short, suspended matter

concentrations are again relatively low

‘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 otherfactors like morphology, characteristics of circulation, ete 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 tidalcurrents The tidal currents are of the weak speed and mixed type The depthhomogeneity of the tidal currents does not express clearly and this shows the tide is a

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

16 Historical disasters of typhoons and storm surges

‘Natural hazards include rate 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

ss has beencause millions of dollars of damage The problem created by diss

‘exacerbated by logging, erosion and over development An average of 430 people waskilled each year by natural disasters between 2007-2011, with property lossesestimated at I 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 andstorms as the most destructive occurrences with the highest number of fatalities and

‘economic damage

Table 1 1 Stasisties storm in Vietnam

Tone TS] Wea TET—T a] TT

- Between 1954 and 1999, there have been 212 typhoons landing in or directlyinfluencing Viet Nam On average, there are about 30 typhoons originating in the

1s

Westem 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 leas 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 thecoastal Provinces of the North and Central Regions However, typhoons in the South,though ess frequent, can still be extremely damaging About 62 percent of thepopulation and 44 percent of the whole are frequently affected by typhoons which, onaverage, kill some 250 people every year, The worst in this century were the 1904typhoon in the South which caused death and injury to 5000 people, and the 1985typhoon in Binh Tri Thien Province which killed 900 people

= In November 1997 Typhoon Linda swept across Vietnam’s southern tip, killing 587people 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, Thetyphoon was the strongest recorded in the area for the last 100 years and causedunexpectedly huge losses The Government of Vietnam undertook every effort to warnpopulations in the areas at risk ‘Thanks to these efforts, more than 3,500 fishermenwere rescued, The Government is also taking all measures to provide health and otherservices 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 CentralCoastal:

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

No | Name of storm ‘Type Date

1 as ‘Typhoon 18-26 NOV 1951

2 #1 Super Typhoon —_ | 16-25 DEC 1952

3 m9 Super Typhoon —_ | 17-20 OCT 1952

4 #18 Typhoon 15-26 OCT 1952

3 #26 ‘Typhoon (09-13 OCT 1957

6 2 Super Typhoon — [13-22 DEC 1959

7 29 ‘Typhoon 25 NOV-01 DEC 1962

17 128 Super Typhoon — |1522OCT1978

18 #2 ‘Typhoon 30 SEP-15 OCT 1979

19 #21 Typhoon 30 OCT-08 NOV 1984

32 196 Super Typhoon —_ |25OCT-07NOV2006

33 m8 ‘Typhoon 25 SEP-02 OCT 2006

3 13 Typhoon 25 OCT-02 NOV 2009

35 #1 ‘Typhoon 25-29 SEP 2009

1.7 Conelusions

= 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 aspecific region (South Central Coast and South East ) When storms go to theshoreline, storm surge not only affects one province but also affects several provinces,

hhas 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 BinhThuan 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 theother 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 veryuich (o 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, stormaccompanied by heavy rainfall will cause flooding on the rivers up faster Reality has alot of historical flood caused to the area causing seve

from (Eg have large floods in Central and South Central in the years: 1952, 1964,

1980, 1990, 1996 , 1998, 2003, 2008

'onsequences such as floods

= Climatic conditions

+ The provinces from Binh Dinh to Binh Thuan have climate feature of climatecastern 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 tropicaland 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 destruetion will be even higher

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 manydifferent purposes such as study, planning and construction system design, example:SORBEK, DELFT3D (Netherland), MIKE (Denmark) However, each model has ownadvantages and disadvantages and so far there has not been a comprehensive anddetailed 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 thewhole domain study instead of just at some points such as measured data In this studywith simulating goal and calculating storm surge in the South Central Coast, the MIKE

21 model has been chosen to satisfied crileria

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

(Gi) Have been use in read test cases worldwwide

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

Figure 21: Introduction MIKE 21

20

MIKE software is softwate package of DHT Water & Envinroment, sources for

enviromental simulation, including river, river mouth, sea and coastal zone Thesoftware 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 EM, which it a new model system in untilizing flexible girds node, isdeveloped by DHI Water & Enviroment The model system is developed for studyingabout sca and envirironment of coastal zone The model consists of continunityequation, moment equation, concentration equation, salt equation

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

General description

2D Shallow water equation of Basic hydrodynamic module is combined between theaverage 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

XY Cartesian co-ordinates in the horizontal directions (mn)

" ‘water surface elevation above the reference level (datum) (m)

h total water depth, h = d + n (m)

4 ‘water depth below the reference level (datum) (m)

v depth-averaged flow velocity in x direction (m/s)

v depth-averaged flow velocity in y direction (m/s)

4 Rate of inflow (sim?)

t Coriolis parameter (inertial frequency) (1/9)

# acceleration due to gravity (m/s?)

" air density (kg/m?)

p water density kg/m’)

PAP, gradient of air pressure in x- and y-directions (kg/m/s?)

FF, friction components in x- and y-directions (m/s°)

TeoTey Wind shear stresses in x- and y-directions (kg/m/s*)

SwoSwy _Fadian stresses in x- and y-directions (mv/s*)

Tasty {internal stress components (m/s)

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

2

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

(1921), Takahashi (1939), Fujita (1952), Mayers (1954) and Jelesnianski (1965),

‘The friction term accounts for the bottom friction (7)

& \wind drag coefficient (dimensionless)

v the wind speeds at 10 m above the surface, v= 2 +V2 (amis)

VaVy wind speed components in x- and y-directions (mis)

The variation of wind field in a typhoon can be presented by the typhoon wind modelssuch 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)

Where Sy, Sqy,Sy are radiantion stresses in x- and y-directions (kg/s) ‘These

quantities can be computed by a wave model likes SWAN,

‘The internal stress term (10)

0)

Where «is the horizontal eddy diffusivity (m/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 (C,),

eddy diffusion coefficient (e) 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 areequipped 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 freeand allowed to modify computational code if necessary

”

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 spectie yea o find out the parameters forthe model

= Verification: assess the realization of the model

~ Using the model to simulate diferent scenarios forthe system

2.2, Model setup and boundary conditions

2.2.1 Analysis data and choose scope of model

2.2.1.1, Analysing data

~ Topography.

‘Topography data is obtained from the project”Xdy dựng bản đồ ngập lụt do nước bién

«dang trong tinh huồng bão mạnh, siêu bão ~ 2016",

- The oceanographic data,

+ Boundary condition

+ Observation station isthe stations are collected from the project "Xây dựng bản đổ

ngập lụt do nước biển dang trong tinh huống bão mạnh, siêu bão ~ 2016”

+ Analysing data

Hydrological data consist of water level; they are observed in stations that have tofollow the national elevation The study is based on using the numerical model (MIKE21) to simulate surge of typhoons, so calibration and verification have to define theaccurate parameters to apply for real problem

2.2.1.2 The scope of model

Choose top and bottom boundary like the picture:

Domain model is based on terrain data area of South Central Ceoast, 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

26

UTM-49 Topography obtained from measured data and the bottom topography data

thas been converted to the national height

+b) Mesh count

Regional grid is set up to serve the regime calculations storm surge Domain and meshcount in the area is based on data fom coastal by the Ministry of Natural Resources

and Environment 2010 provides topographic data were edited and put on the national

clevation system old, The coordinate use is UTM-49

©) Create mesh calculator

The grid used in this model is the finite clement mesh generated from MIKE zero

‘models with 40467 elements and 23592 nodes The rate calculated net decreases fromthe ocean to the study area, Step calculated for flood model is shown in detail andfocus on the coastal area,

28

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 regionshave many vary by region With the inside of the estuary and coastal zone, use detail

‘mesh (0 ensure high accuracy when storms reach the shore

4d) 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 theSouth Cental region

Water boundary includes:

+ Sea Border 2 (South,

+ Sea Border 3 (Southeast)

+ Sea Border 4 (Eas

+ Sea Border 5 (Nosh

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

TT Border ‘Type Data

1 Border 2 (South) ‘Water boundary Tidal

2 Border 3 (Southeast) ‘Water boundary Tidal

3 Border 4 (East) ‘Water boundary Tidal

4 Border 5 (North Water boundary Tidal

§ Land boundary Land boundary Tidal

30

wes

MB SE MTB cod Land bunsary

Figure 2 6 Model boundary conditions 2.2.2.2 Set up basin hydrodynamic parameters

Table 2 2 the parameters effect to Nam Trung Bo model

Parameters Volume Domain: NTB_O2.mesh

No, of time steps: 22464Time step interval: 60

‘Simulation start date

Time 10/01/2007 (12:00:00 AM)

‘Simulation end date:

10/16/2007 (2:24:00 PM)

“Module Selection: HD, SW

Minimum time step = 0.018

Solution Technique: Minimum time = 60s