Master Thesis

Reassurances
Name: Pham Viet Dinh
Major: Sustainable Hydraulic Structures
Student ID # 148ULG010

This is my thesis with the topic "Probabilistic reliability analysis of Red river
dike system protecting Giao Thuy - Nam Dinh" under the guidance of Assoc. Prof. Mai
Van Cong - Thuyloi University and Prof. Radu Sarghiuta - University of Liege.
I hereby declare that this thesis is the scientific study of my own. The results and
data in the thesis are honest and no one published it in any other research.

Ha Noi,

October 2016

Pham Viet Dinh

Dinh Pham Viet – 148ULG010


Master Thesis

Acknowledgments
After a period of research, my master thesis with the topic "Probabilistic reliability
analysis of Red river dike system protecting Giao Thuy - Nam Dinh" has been
completed with the enthusiastic help of lecturers, friends, colleagues and my family.
To obtain results as today, I would like to express deep gratitude to the Assoc.
Prof. Mai Van Cong from Thuyloi University and Prof. Radu Sarghiuta from University
of Liege those who were enthusiastic to guide and provide knowledge, documentation,

scientific information as well as contribute valuable comments during the implementation
of this thesis.
I also sincerely thank the help, the assistance in terms of expertise and experience
of the teachers teaching in class, undergraduate and postgraduate training office;
classmate in Thuyloi University and all my family, friends have motivated, inspired,
create favorable conditions in all aspects to completing this thesis.
In the process of implementation of the thesis, due to the time and limited
knowledge, there are surely unavoidable mistakes, so I wish to receive the comments of
teachers, colleagues to help me improve knowledge in terms of learning and researching.

Sincere thanks!

Ha Noi,

October 2016

Pham Viet Dinh

Dinh Pham Viet – 148ULG010


Master Thesis

Table of contents
Chapter 1: General introduction ...................................................................................................... 1
1.1. Reasonable of this study ....................................................................................................... 1
1.2. General information .............................................................................................................. 2
1.3. International related research applications............................................................................ 3
1.4. Present situation of flood risks in Vietnam ........................................................................... 4
1.5. Study objectives .................................................................................................................... 5

1.6. Study approach ..................................................................................................................... 6
Chapter 2: Boundary conditions & description of study area ......................................................... 7
2.1. Description of dike systems in Vietnam ............................................................................... 7
2.2. Influence factors ................................................................................................................... 8
2.2.1. The influence of hydrology ............................................................................................ 8
2.2.2. The influence of the tide................................................................................................. 9
2.2.3. The influence of irrigation planning, traffic and construction ....................................... 9
2.2.4. The influence of the protected area .............................................................................. 10
2.2.5. The influence of other factors ...................................................................................... 10
2.3. Natural conditions ............................................................................................................... 11
2.3.1. Location........................................................................................................................ 11
2.3.2. Topographical characteristics ....................................................................................... 11
2.3.3. Hydrology..................................................................................................................... 12
2.3.4. Climatic condition ........................................................................................................ 12
2.4. Present situations of Huu Hong river dikes ........................................................................ 13
2.5. Practical issues in application of the standard criteria and norms: ..................................... 17
2.6. Overview of traditional design methods: ............................................................................ 17
2.6.1. Background information .............................................................................................. 17
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Master Thesis
2.6.2. Shortcoming in traditional design methods .................................................................. 19
2.7. Overview of probabilistic design method ........................................................................... 19
2.7.1. General background ..................................................................................................... 19
2.7.2. Historical development of probabilistic design method in the world .......................... 20
2.7.3. The approach of the method of probabilistic design .................................................... 21
2.8. Conclusion chapter 2 .......................................................................................................... 21
Chapter 3: Safety assessment & reliability analysis of Huu Hong river dike ............................... 23
3.1. Background theory .............................................................................................................. 23

3.2. Theoretical basis ................................................................................................................. 24
3.2.1. Risk analysis ................................................................................................................. 24
3.2.2. Reliability analysis of components in system .............................................................. 27
3.2.3. Mathematical basis of probabilistic design .................................................................. 28
3.2.4. Reliability analysis of system ....................................................................................... 36
3.3. Application of the probabilistic design in reliability of river dike system of the Huu Hong
river dike .................................................................................................................................... 37
3.3.1. Case study: Safety assessment of existing river dike system in Giao Thuy district .... 38
3.3.2. Possible failure mechanisms of the river dike.............................................................. 39
3.3.3. Fault Tree Analysis ...................................................................................................... 46
3.4. Conclusion chapter 3 .......................................................................................................... 46
Chapter 4: Application of probabilistic reliability analysis to assess safety of Huu Hong river dike
system ............................................................................................................................................ 48
4.1. Failure mechanisms to consider .......................................................................................... 48
4.1.1. Overflowing mechanism .............................................................................................. 48
4.1.2. Instability revetment mechanism ................................................................................. 51
4.1.3. Scouring mechanism at dike toe................................................................................... 54
4.1.4. Piping mechanism ........................................................................................................ 59
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Master Thesis
4.1.5. Inner slope instability mechanism ................................................................................ 63
4.1.6. Fault Tree Analysis ...................................................................................................... 65
4.2. Establishing fragility curve ................................................................................................. 68
4.3. Conclusion chapter 4 .......................................................................................................... 72
Chapter 5: Conclusions and recommendations ............................................................................. 73
5.1. Achieved results .................................................................................................................. 73
5.2. Existing problems ............................................................................................................... 74
5.3. Recommendations ............................................................................................................... 74

5.4. Further research directions.................................................................................................. 74
References ..................................................................................................................................... 76
Appendix 1 .................................................................................................................................... 77
Parameters and documentation used to calculate for the Huu Hong river dike ............................ 77
Appendix 2 .................................................................................................................................... 86
Result of probabilistic reliability analysis ..................................................................................... 86

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List of figures
Figure 2-1: Storms, natural disasters affect the coastal areas in Vietnam ....................................... 8
Figure 2-2: Administrative maps of Nam Dinh province .............................................................. 11
Figure 2-3: Location of Nam Dinh province on the map (from google map) ............................... 13
Figure 2-4: Overall system map dikes in Giao Thuy district - Nam Dinh province. .................... 14
Figure 2-5: Representative cross-section of Huu Hong river dike. ............................................... 15
Figure 2-6: Several photos of current situation of Huu Hong dike ............................................... 16

Figure 3-1: Framework of risk analysis (CUR 141 – 1990) .......................................................... 26
Figure 3-2: Reliability function is shown in the plane RS ............................................................ 28
Figure 3-3: Definition of the probability of failure and the reliability index ................................ 28
Figure 3-4: Diagram of failure analysis of serial system and parallel system .............................. 37
Figure 3-5: Diagram of flood defense system of Huu Hong river dike – Giao Thuy district – Nam
Dinh province ................................................................................................................................ 39
Figure 3-6: The failure mechanisms can occur in river dikes (CUR/TAW 1995) ........................ 40
Figure 3-7: Overflowing scheme ................................................................................................... 41
Figure 3-8: Instability revetment scheme ...................................................................................... 42
Figure 3-9: Scouring mechanism at dike toe scheme ..................................................................... 43

Figure 3-10: Rupturing scheme

Figure 3-11: Sand flowing scheme ....................................... 44

Figure 3-12: Slope sliding scheme ................................................................................................ 45
Figure 3-13: Fault Tree diagram of flood defenses system – Huu Hong dikes ............................. 46

Figure 4-1: Real measured data of dike crest level ........................................................................ 49
Figure 4-2: Distribution of dike crest level based on real measured data by using BESTFIT
software. ........................................................................................................................................ 49
Figure 4-3: Real measured data of flood water level ..................................................................... 50

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Figure 4-4: Distribution of flood water level based on real measured data by using BESTFIT
software. ......................................................................................................................................... 50
Figure 4-5: Influence of random variables to the overflowing mechanism. ................................. 51
Figure 4-6: Influence of random variables to instability revetment mechanism. .......................... 54
Figure 4-7: Real measured data of flood flow................................................................................ 56
Figure 4-8: Distribution of flood flow by using BESTFIT software............................................. 57
Figure 4-9: Influence of random variables to scouring mechanism at dike toe. ........................... 58
Figure 4-10: Real measured data of upstream water level ............................................................. 60
Figure 4-11: Distribution of upstream water level based on real measured data by using BESTFIT
software. ......................................................................................................................................... 60
Figure 4-12: Influence of random variables to the rupturing mechanism. .................................... 62
Figure 4-13: Influence of random variables to sand flowing mechanism ..................................... 63
Figure 4-14: Results of inner sliding stability by using Geostudio 2007 software ....................... 64
Figure 4-15: Diagram of Fault Tree Analysis for Huu Hong river dike system ........................... 66

Figure 4-16: Result of failure probability after using OpenFTA software .................................... 67
Figure 4-17: Graph of the iterative period with the highest water level at Ba Lat hydrology
station. ........................................................................................................................................... 69
Figure 4-18: Fragility curve of correlation between Pf system and FWL ......................................... 71

Figure 6-1: Iterative period according to highest water level at Hon Dau, Ba Lat hydrology
station ............................................................................................................................................ 78
Figure 6-2: Diagram of height of wave ......................................................................................... 81
Figure 6-3: Figure A1- Appendix A1 - TCVN 8421-2010 – Graph of determining wave factors
causing by the wind in deep water and shallow water .................................................................. 82
Figure 6-4: Figure A2- Appendix A1 - TCVN 8421-2010 – Graph of determining coefficient k i 83
Figure 6-5: Result of inner sliding stability by using Geostudio 2007 software ........................... 85
Figure 6-6: Result of overflowing mechanism in case FWL = 3.62m .......................................... 86

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Figure 6-7: Result of instability revetment mechanism in case FWL = 3.62m ............................. 86
Figure 6-8: Result of scouring mechanism at dike toe in case FWL = 3.62m .............................. 87
Figure 6-9: Result of rupturing mechanism in case FWL = 3.62m ............................................... 87
Figure 6-10: Result of sand flowing mechanism in case FWL = 3.62m ....................................... 88
Figure 6-11: Result of inner slope instability mechanism in case FWL = 3.62m ......................... 88
Figure 6 12: Diagram of Fault Tree Analysis in case FWL = 3.62m ............................................ 89
Figure 6-13: Result of overflowing mechanism in case FWL = 2.0m .......................................... 91
Figure 6-14: Diagram of Fault Tree Analysis in case FWL = 2.0m .............................................. 91

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List of tables
Table 4-1: List of random variables according to the overflowing mechanism. ........................... 50
Table 4-2: The probability of the failure and the influence coefficient of the random variables to
the overflowing mechanism. ......................................................................................................... 51
Table 4-3: List of random variables according to the instability revetment mechanism. ............. 53
Table 4-4: The probability of the failure and the influence coefficient of the random variables to
the instability revetment mechanism. ............................................................................................ 53
Table 4-5: List of random variables according to the scouring mechanism at dike toe. ................ 57
Table 4-6: The probability of the failure and the influence coefficient of the random variables to
the scouring mechanism at dike toe. ............................................................................................... 58
Table 4-7: List of random variables according to the piping mechanism. ..................................... 61
Table 4-8: The probability of the failure and the influence coefficient of the random variables to
the rupturing mechanism. .............................................................................................................. 61
Table 4-9: The probability of the failure and the influence coefficient of the random variables to
the sand flowing mechanism. ......................................................................................................... 62
Table 4-10: The probability of the failure of the inner slope instability mechanism. ................... 64
Table 4-11: Results of failure probability of Huu Hong river dike ............................................... 65
Table 4-12: Table of the iterative period with the highest water level at Ba Lat hydrology station.
....................................................................................................................................................... 69
Table 4-13: Probabilistic calculation with difference value of FWL ............................................ 70

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Chapter 1: General introduction
1.1. Reasonable of this study
Vietnam has about 3260 km of coastline, mainly consists of coastal lowland is protected
by a sea dike system, natural dunes, and mountains. More than 165 km of coastline in the Red
River delta, populated areas where there are significant changes and dynamic impact destroyed
with intense frequently from the sea (storms, changes in sea level, flow, etc.). Therefore, dikes
are important structures which are built, maintained and protected through generations to prevent
flood water, sea water and to protect the lives and property of the government and people, to
promote social and economic Social development, linked to national defense, security,
sovereignty, and national benefits. The process of formation and development of the dike system
always linked to the life and productive activities of the people from generation to generation.
Most dikes are now combined as roads in which many dikes pass through tourist areas, urban
areas and residential areas. During the development processes, requirements for dike system as
well as the direct impacts of human on the dike are growing and increasing in complex evolution.
In recent years, natural disasters and climate changes in Vietnam have had more abnormal
and complex. In particular, storms and floods are two types of natural disasters which frequently
occur and cause the most severe consequences, especially in the area of coastal estuaries.
However, most of the system of dikes and storm prevention, flood prevention existing today in
Vietnam is designed and constructed based on the experience accumulated from many
generations and applied safety standards which only suit economic situation - engineering
conditions of the country in some decades ago. Before the adverse effects of weather variations
and changes in an abnormal phenomenon of natural disasters due to climate change, coupled with
the requirement to ensure a higher level of safety of the protected areas to serve the sustainable
development of economic - society, the research and development applications in reliability
theory of optimal design system against storms, floods and on this basis build up the safety
assessment criteria according to reliability theory and construction process safety assessment
system of dikes in estuaries and coastal areas... according to theory of reliability in Vietnam
condition at the present time and the future is necessary.

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1.2. General information
Vietnam has a dense network of rivers and the coast stretching from North to South, so
the system of dikes and bank protection structures play an extremely important role in the
prevention, disaster mitigation and protecting the safety of the cultural center, the political,
economic and residential areas stretching along the vast river basin, the coastal regions of the
country.
According to the general trend of development, nowadays coastal areas are a key
economic zone dynamic contribution and increasingly more important role in the national
economy and national security. Therefore, the requirements for the protection of the population
and economy against the destruction of hurricanes, floods, surges are becoming ever more
urgent. Besides the consolidation and upgrade the dike system has had, the planning for river
bank protection, coastline and building the new dike system is in place in all three regions of the
country.
In the current issue of global climate change, Vietnam is one of the countries which is
most severely affected. In addition, the trend of development in Vietnam as well as the countries
close to the sea in the world is seaward development, big cities concentrate on coastal. So
development of marine resources, tourism, and waterway transport are very important. Therefore
the system of dikes and bank protection structure have a very important role. It not only is the
task of protecting people and infrastructure, but also has the task of creating the resort location,
beautiful natural landscape, creating refuge areas for ships, port protection when storm coming.
In recent years, in the world, the risk of disaster in general and flood, in particular, has
significantly increased trend of frequent occurrence and level of influence. The events of the
recent flooding disaster with considerable history as New Orleans, USA 2005; The UK and
Eastern Europe (2007), Bangladesh and South Asia (2007), Pakistan (2008), and most recently

the flooding disaster in the history of the capital Bangkok of Thailand (2011). The floods caused
heavy damage to people and property. So minimizing the risk of floods are now particularly
interested in many countries around the world.

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1.3. International related research applications
Many hallmarks of scientific & the research program around the world related to flood
prevention, dikes safety, application development of reliability theory in system and structure
safety can be listed as follows:
Netherlands: Netherlands was known as a leading country in flood prevention since they
continually invested in research and technology related to this field. One of their achievements
was a reliability theory. It has been put into the application to design the crucial components of
Deltaplan program in the 70s. Reliability theory continued to develop and extend its application
and became a compulsory subject in civil engineering major in the 1985s. After that, design
standards following reliability theory were updated in 1990, 1995 and 2000. Then, with the
purpose to update calculation technologies and safety simulation methods in a dike system of
reliability theory to be high reliability and minimum margin of error, VNK project was
implemented from 2001 to 2003 by Strategic Research Institute PNO, Deft Hydraulics and Deft
University of Technology. This project provides reliability criteria updated in design standards.
Next, VNK2 project (2007-2010) and SBW (2008-2011) were implemented by the same research
group in VNK Project. These projects focused on improving the accuracy of the models
simulating with random loads and the durability of the flood prevention structure. These are
critical inputs of structure’s reliability analysis. Besides, the effect of the dikes system length in
safety assessment also investigated profoundly. 3D model design following reliability theory also

appeared. In addition, flood risk standards were checked and updated according to not the only
person, community and economy view, but also the culture, history, and the environment, etc.
Britain and Europe: Britain and Europe inherited and developed the study of the
Netherlands to apply to their own country’s characteristics. “Reliability of Flood Defenses and
Integrated Flood Risk Management” project (FLOODSite) was implemented from 2005-2009 by
38 institutes & major universities from 20 countries in the region. The project gave out the
synthetic approach in the safety assessment of flood prevention, flood management, and flood
mitigation systems. Reliability theory was confirmed and developed as a core model for the
safety assessment of the system and risk analysis of the flood prevention system. Safety
assessment models, optimal design systems and simulated models of loss due to flood were

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developed and examined by the experimental application in the countries. Integrated models,
Solution 1& 2, were developed to apply in EU member countries. Member countries came to an
agreement to develop and use the same standard safety assessments in dike systems and flood
prevention.
U.S. and Canada: These two countries developed the application of the reliability theory
in dam’s safety, especially high dams in the 90s. Standard system was converted completely from
traditional safety standard (safety factor) to safety methods following allowable reliability [β].
Recently, a typical application in design standards according to reliability in U.S. was a design
project, planning in flood prevention system of New Orleans with system allowable reliability of
[β] =4.2.
Russia and China: Russia and China applied the reliability theory in quantitative
structure safety following the technical standards using allowable reliability [β]. The application

was mainly applied in dam design. China limited the reliability of several specific structures by
fixed reliability value. For example, the reliability value of reinforced concrete was 3.6 ≤ β ≤ 4.2.
Russia used reliability β to adjust several coefficients in design such as overloading factor, etc.
The standards of risk management and flood prevention structure safety assessment are
constructed and applied in 5 recent years.
1.4. Present situation of flood risks in Vietnam
To evaluate an overview of the work of dikes and issues of safety of flood prevention in
Vietnam, we can cite several points stated in the "National Strategy for Prevention and Disaster
Reduction 2020" as follows:
Vietnam is located in the tropical monsoon, one of five storms of the Asia - Pacific
region, often faced with this kind of natural disaster, floods and storms at most.
In recent years, natural disasters occurring in all areas of the country have caused loss of
life, property, infrastructure, economic, cultural, social and environmental adverse impacts. In the
recent 10 years (1997-2006) the disaster killed, missed nearly 7500 people and the damage is
estimated at 1.5% of GDP. Due to the impact of global climate change, Vietnam is among

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countries most affected by sea level rise and other impacts of natural disasters increase in size as
well as iterative period and unpredictable.
For decades, the investment of government and the effort of people have created the
infrastructure system of prevention and mitigation of natural disasters and relatively uniform
across regions. The system of river and sea dikes on the 4500 km, large reservoirs serving the
flood reduction, water regulation, electricity generation was based on the fixation of large river
basins. The irrigation-transportation structures, construction of residential flood prevention,

prevent floods and erosion control projects, boats mooring zones to avoid the storm, forecasting
warning system, communications, rescue aid victims... have progressed, increasingly improving
disaster prevention before coming. Red river delta has been coping with flood frequency of 500
years, which is the level of regional guarantee. Mekong Delta lives with floods increasingly
proactive, continuous agricultural production and harvest stability during the past decade, ...
International cooperation development is of importance of prevention and mitigation of
disasters. Vietnam has actively participated in and contributed to the forums and international and
regional commitments to the prevention and mitigation of disaster risk and climate change
framework action Hyogo, Kyoto Protocol, Asian general agreement about the cooperation deal
before the disaster. The international community has helped Vietnam to train human resources,
transfer of technology, experience, raise awareness, build models. Especially ODA projects
intended for flood prevention structure and mitigation of natural disasters; the non-refundable
ODA projects for the local industry have brought very practical effect.
1.5. Study objectives
- The purpose of this study can be presented as follows:
+ Safety assessment of existing river flood defenses of Giao Thuy.
+ Determination of the reliability of Huu Hong Dike section for present condition.
+ Establishment of the statistical probability distribution of loads (water level, discharge)
and strength (soil properties) of the dike section.
+ Quantifying the risk due to flooding in the protected area.

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- Expected outcomes:
+ Using analysis methodology and the scientific basis of risk analysis and reliability

theory to perform a safety assessment of the river dike system.
+ Safety of Huu Hong river dike sections protecting the Giao Thuy district and
recommendation of how to improve the safety of the system
1.6. Study approach
In this research, the following approach will be used in the study:
- Collect the necessary data from all possible sources, including the subject.
- Point out the future predictions of the probability of failure mechanisms for Giao Thuy dike.
- Review of previous related studies that deal with Huu Hong river dike.
- Review the existing dike design in Vietnam.
- Evaluate and determine the safety of the river dike in Giao Thuy by applying reliability
analysis.


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Chapter 2: Boundary conditions & description of study area
2.1. Description of dike systems in Vietnam
Vietnam is a country located in the tropical monsoon climate with abundant and diverse
geomorphic, topography; West mountain, Northern-West mountain, and East mountain are
surrounded by the sea and dense river systems. Residential areas, cities, and agricultural areas
often develop along the riverside areas and often are influenced by factors and risk of flood. Dike
system along the river branches is a solution of flood prevention which was used for a long time
ago to protect residential area along riverside and entire delta region from the risk of flooding.
For a long time of development, the current dike system in the country is a large-scale structured
system with about 13,200km of dike, of which about 10,600 km river dike and nearly 2,600km

sea dike. The main river dike system with over 2,500 km of the dike from grade III to special
grade; remaining dike is under grade III and has not been yet decentralized. In which:
- Dike systems of North and North Central: 5,620km of length, with flood protection is
responsible for flood protection, ensuring safety for the Northern Plains and North Central.
- River dike system, estuarine areas of Central and South Central: a total length of 904km.
- The system of river dikes, embankments in Mekong Delta area: 4,075km of length.
In terms of the socio-economic development of the country at present, the requirements
for the protection of the population and economy against the destructive of hurricanes, floods,
surges are becoming ever more urgent. Besides the consolidation and upgrade the dike system
has had, the planning for river bank protection, coastline and building the new dike system are set
out in all three regions of the country.
In the current issue of global climate change, Vietnam is one of the countries which is
most severely affected. In addition, the trend of development in Vietnam as well as the countries
close to the sea in the world is seaward development, big cities concentrate on coastal. So
development of marine resources, tourism, and waterway transport are very important. Therefore
the system of dikes and bank protection structure have a very important role. Besides the task of

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protecting people and infrastructure, it also has the task of creating the resort location, beautiful
natural landscape, creating refuge areas for ships, port protection when having a storm.

Figure 2-1: Storms, natural disasters affect the coastal areas in Vietnam
2.2. Influence factors
2.2.1. The influence of hydrology

Hydrologic factor influences markedly on the dike crest level for river dike and estuary
dike. Component affects to the calculation formula of the dike crest level consist of design flood
water level; rising water level due to wind and wave.
The design flood water level of the dike is determined to correspond to the guaranteed
frequency of flood prevention design of the dike (to be taken according to the level of the dike by
norm). Flood frequency curve is built from a series of annual measured flood data.
Water rising due to the wind causes the influence of hydrology by these factors: wind
direction; wind velocity; wind momentum; the depth of the water level in front of the dike.
The height of wave run-up depends on many factors such as the parameters of the wave in
front of the dike, dike slope coefficient, guaranteed wave run up levels, roughness and
permeability of slope, wind velocity, depth of the water level in front of the dike, the direction of
wave propagation… etc. In which, the influence of the hydrologic factors including: wind

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direction, wind velocity, the time the wind blows continuously, wind momentum, the parameters
of the waves in front the dike, the depth of the water level in front of the dike.
2.2.2. The influence of the tide
The tide affects considerably to the crest level of the dike and estuary dikes. Composition
affects to the calculation formula dike crest level, including calculation sea level, height storm
surge, and height of wave run-up.
Sea water level is calculated from a guarantee frequency in the work place, including the
astronomical tide and variable values due wave, flood, earthquake, fake tidal, water changing
level, long-period variable, etc.... without regard to the storm surge.
The height of the rising water level is determined by the frequency and latitude. In this

case, real measured data of tide is used to analyze the frequency. If the tide has components
including surges, no need to calculate this quantity anymore.
2.2.3. The influence of irrigation planning, traffic and construction
Irrigation planning, traffic planning and building planning transform boundary conditions
of the dike crest level computing, such as conditions of topography, hydrology, hydraulic... In
particular:
- The construction of the system of reservoir in upstream of the river basin will change the
flow of water in the river to downstream;
- The construction of hydraulic structures, traffic on the river as the dam, bridge across the
river... changes the hydraulic regime of rivers;
- The planning of construction of transport routes at downstream will change the direction
of flood drainage, and it also affects the capability of flood drainage to the sea;
- The construction of urban planning, infrastructure of presidential area would reduce the
flooding storage zone and narrow the section of flood drain...

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2.2.4. The influence of the protected area
In the approach of the traditional method, the scale of protected area affects directly to the
level of the dike design. Then it affects the guaranteed frequency and allowable safety for the
dike.
In the approach of the probabilistic method, the scale of protected area affects the level of
damage when the failure occurs. The level of damage of the failure affects the risk because the
risk is a function of the failure probability and the consequences. The dike crest level is defined
as the optimal balance plan between risk level and investment costs of constructing the system, or

in other words, the dike crest level is determined based on the probability or frequency of
acceptable damage of protected areas. Therefore, the scale of protected areas directly impacts the
dike crest level.
2.2.5. The influence of other factors
In addition to the above factors and other factors also affect the dike crest level, such as
topography, geology, the cross-section shape of the dike, functions and tasks of the dike, etc.:
- Topography affects the wind factor, wave in front of the dike;
- Geology can affect the shape of cross-sectional structure, from that it affects to the wave
factor of the dike. In addition, the foundation of dike also affects to the settlement of the dike;
- Topography and geology also affect the changing of the river bed, river bank, coast,
sediment and main flow;
- Shape cross-section of dike affects the wave factor in front the dike as the wave run-up;
- Functions of the dike also affect the dike crest level as wave-breaking, dike allows water
to spill over or does not allow water to spill over, the position and functions of dike protection
system consisting of two or more dike axis (main dike; coffer dike…)

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2.3. Natural conditions
2.3.1. Location
Giao Thuy district is located in the South East of Nam Dinh province, which is in the
Northern Delta of Vietnam. Its coordination is 20°21’N 106°21’-106°35E.
- Giao Thuy district is bordered by Thai Binh province to the North East, Xuan Truong
district to the North West, Hai Hau district to the West and East Sea to the South.
- Giao Thuy district has good conditions for both waterway and roadway, which makes a

good connection to other districts of the province or other provinces. The total area of the district
is 238.24 km2.

Figure 2-2: Administrative maps of Nam Dinh province
2.3.2. Topographical characteristics
The topography of the study area is quite flat and lower from North to South; it can be
divided into two parts: inside ground and alluvial ground along the seaside. Soil condition of the
district facilitates the agricultural development, especially for cultivating. With 32km seaside,
wide fishing ground, a variety of sea creatures and beautiful beaches, the district also has a good
condition for fisheries and tourism.

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2.3.3. Hydrology
River system: Giao Thuy district has a complex river system. Depend on the
topographical characteristics, rivers flow from the North to the South. Downstream of some big
rivers such as Red river flow through the area so they have a wide river bed, not so deep and the
flow speed is slower than the upstream. The water level of rivers can be divided into 2 seasons:
flood season and dry season.
2.3.4. Climatic condition
Giao Thuy has an almost climatic condition of the Red River Delta area that is affected by
a tropical monsoon climate with four distinct seasons: Spring, Summer, Autumn and Winter.
Temperature: the annual average temperature is 20°C, the highest is 39°C in June and the
lowest is 5°C in December and January.
Sunshine: Annually, there are about 250 sunny days, total sunshine hours are about 16501700 hours. 3 months of the summer (May, June, July) have the most sunshine hours with the

average of 170 – 200 hours per month. November has the least sunshine hours with about 40-45
hours per month.
Humidity: the humidity of the atmosphere is pretty high with an average of 75-80% and a
large amplitude. Sometimes the humidity is up to 90%, but sometimes it is lower than 30%.
Rainfall: the average rainfall is 1400-1600mm. The rainfall distributes irregular, rainy
season from May to October make about 75% of the total rainfall in a year, especially in July,
August, and September. Because of that distribution, it usually has flood in the rainy season. The
flood has a bad effect on agriculture and the environment.
Wind: the most common wind direction is Southeast but it changes due to the season. The
common wind direction in winter is North-East then changing into East direction, and the most
common wind direction in summer is a West wind (the wind from Laos). Moreover, this area
usually has a tropical storm with high-speed wind and heavy rain, which makes flood and
devastates sea dikes and the Red river dike system.

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Master Thesis

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2.4. Present situations of Huu Hong river dikes
Nam Dinh province is a part of the coast of Vietnam with a total length of about 70 km,
which is protected by a system of river dikes and sea dike. The dike system has been severely
eroded and severely damaged to the flood defense system. There were many times of dike break
which caused serious flooding and losses. The present situation of Nam Dinh dikes can be
considered a typical coastal area in Northern part of Vietnam. In general, the erosion and
damages of coastal defenses occur frequently, so it results in serious economic consequences as
well as the social consequences of the relevant locations.


Figure 2-3: Location of Nam Dinh province on the map (from google map)
Giao Thuy, a coastal district belong to the Nam Dinh province, locates at the edge of the
Red River delta, and far 45 km from Nam Dinh City to the south. Flood defense system of Giao
Thuy district, including 31.161 km of sea dike from K0+000 to K31+161 and nearly 30km river
dike in which 11.702 km length of

Huu Hong dike segment locates from K208+000 to

K219+702 (see figure 2-4). Dike crest level from +4.5m to +5.0m; width of crest surface from

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Master Thesis

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4.5m to 5m which has been renovated and reinforced for many years. This dike also is public
roads for 6 communes and Ngo Dong town along the dike.
- For the dike from K208 + 153 to K208 + 735: The current dike crest surface is a
concrete road that is still relatively good.
- For the dike from K208 + 735 to K210 + 670: The current dike crest surface is concrete
roads which were heavily damaged, does not guarantee the load conditions and necessary to
remove and reinforcement.

Figure 2-4: Overall system map dikes in Giao Thuy district - Nam Dinh province.
Dikes of Giao Thuy district were built a long time ago (about 250 years) on a weak
foundation (sediment accretion of the Red River system). Dikes stretch from the estuary of Red
River in the North (beginning of the line) to So River (Ha Lan estuary) in the South (end of the
line) that has a complex terrain with terrain conditions and geological conditions change

frequently. Not only being directly influenced by tides and winds of the storm from the South
China Sea but also being affected by flood flows into the South China Sea from inland
waterways. So the coastline in Giao Thuy became complicated for some years ago. Middle of
coastline which is faced to the sea was occurred seriously erosion.

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6.0
4.0
2.0
0.0
−2.0

Figure 2-5: Representative cross-section of Huu Hong river dike.

Filled soil in dike body and the foundation is low quality in many dike segments, which
almost is sand and sandy soil, so it is easy to be slided by rain and wave. The important location
was protected by dike revetment but often being ruined because revetment structure and the toe
of revetment were not suitable (revetment was constructed of dry masonry). Some sluice was
built about 40 years ago, and some of the sluices were shorter than dike body, so the form and
structure were outdated or even has been damaged and degraded. Therefore, it does not meet the
requirements of present flood defense.
Although existing dikes were built and upgraded through periods in order to meet the
requirement of flood prevention safety standards at 1/100 years for river dike. The fact is that the
failure still frequently occurs at critical locations along the river dikes.

In recent times, along with the global climate change, the damage caused by natural
disasters tends to increase around the world. Those storms have a strong upward trend, and they
can become the destructive heavy typhoon. The phenomenon of heavy rain, gust, tornadoes also
occurs more frequently. In many parts of the world, the phenomenon of earthquakes and tsunamis
also occur frequently and cause more serious consequences immensely.
The socio-economic activities in coastal and seaside cause changing in the natural
environment in the direction of disadvantage and increase the damage of natural disasters. In
many areas, mangroves and coastal forests have been lost that lead to not only cause changing in
the ecological environment in ways that are harmful, but also make billow hit straight into the sea
dike, causing sea dike breaking and flooding.
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Master Thesis

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Figure 2-6: Several photos of current situation of Huu Hong dike

Pham Viet Dinh – 148ULG010