ThesisPDF Available

Improvement of flood risk assessment under climate change in Ho Chi Minh City with GIS applications

Authors:

Abstract and Figures

Ho Chi Minh City is the largest city in VN. The city is the most important center of economy, society and culture in the southern region of Vietnam. However, due to characteristics of natural conditions with low topography and borders touch the sea so that since the late 20th century with the rapid economic and urban development there are environmental problems have arisen. One of the problems is flooding issue caused by high tide. With these natural conditions and sea level rise of climate change in the future, Ho Chi Minh City is considered as one of the most affected and damaged cities in the world. Therefore, many policies have been set out from the national to local levels in Vietnam to prepare for adaptability of impacts and risks of the sea level rise and the climate change. And this has also been considered in Ho Chi Minh City as the development policies of the city authorities have to consider in the context of the sea level rise and the climate change. A number of researches have been conducted to assess the impact of climate change to Ho Chi Minh City in the future. However, these researches are still need to be enhanced further. The flooding problem is a major issue of the sea level rise in Ho Chi Minh City. And to make a good result, the flood model needs a lot of requirements that ensure fine quality of input data, suitable model and a relied procedure. In the available research, the input data is not really the highest quality in the available context in Ho Chi Minh City. As the flood model is implemented, one of the input data requirements of the model is information detail of elevation in the flooded area. And this is more necessary than in geophysical urban areas such as Ho Chi Minh City. And to assess fully flood risk issues for flooding caused by tidal phenomenon in Ho Chi Minh City, the determination of many characteristics of flood model is very useful for users who need to apply the results of the model for the planning development in Ho Chi Minh City in the future. Besides adopting a uniform environment as GIS for managing all the data of flooding problem and making conditions for the development of decision support systems is very necessary for flood management in the future. The research has been carried out and its results have been generated on the flood risk assessment associated context of the sea level rise due to climate change with high emissions scenario A1FI in 2030 for the current houses, the population and the land use types. The results have shown a lot of the areas where are inundated in the future with the increasing flooding duration, depth and frequency even though they are not flooded at the current because there are some protective structures. This will be helpful for suggesting a forecast of the development direction to decision makers in Ho Chi Minh City for next time period. And the last part is the proposal for decision and policy makers, authorities and planners as well. Moreover, the results of this research can be used as the references and the foundations for further researches and so that the problems that Ho Chi Minh City may be encountered due to flood risk caused by climate change to the economic and social aspects of the development in Ho Chi Minh City will encounter. And the problem of adaptation to climate change will be more completed and more thoroughly so that it is to minimize the damage of climate change for the city.
Content may be subject to copyright.
Improvement of Flood Risk Assessment under
Climate Change in Ho Chi Minh City with GIS
Applications
A thesis approved to the Faculty of Environmental Sciences
and Process Engineering at the Brandenburg University of
Technology in Cottbus - Senftenberg in partial fulfillment of the
requirement for the award of the academic degree of Doctor of
Philosophy (Ph.D.) in Environmental Sciences.
by
Master of Science
Tran Thong Nhat
Matriculation Number: 3000078
from Song Cau Town, Phu Yen Province, Viet Nam
Supervisor: Prof. Dr. Dr. h.c. Michael Schmidt
Supervisor: apl. Prof. Dr-Ing. habil. Frank Molkenthin
Day of the oral examination: July 9, 2014
„Gedruckt mit Unterstützung des Deutschen Akademischen Austauschdienstes“
Entwicklung des Hochwasserrisikos beeinflusst
durch den Klimawandel in Ho Chi Minh Stadt
mittels GIS
Von der Fakultät für Umweltwissenschaften und
Verfahrenstechnik der Brandenburgischen Technischen
Universität Cottbus zur Erlangung des Akademischen Grades
eines Doktors der Philosophie (Ph.D.) in
Umweltwissenschaften genehmigte Dissertation
vorgelegt von
Master of Science
Tran Thong Nhat
Matriculation Number: 3000078
aus Song Cau Town, Phu Yen Province, Viet Nam
Gutachter: Prof. Dr. Dr. h.c. Michael Schmidt
Gutachter: apl. Prof. Dr-Ing. habil. Frank Molkenthin
Tag der mündlichen Prüfung: July 9, 2014
Declaration/Affiant
Tran Thong Nhat i
Declaration/ Affiant
The following Philosophy of Doctor thesis was prepared in my own words without any
additional help. All used sources of literature are listed at the end of the thesis.
I hereby grant to Brandenburg University of Technology Cottbus – Senftenberg
permission to reproduce and to distribute publicly paper and electronic copies of this
document in whole and in part.
Cottbus, December 17 2013 Tran Thong Nhat
Dedication
Tran Thong Nhat ii
Dedication
The first dedication is given my parents who always wish their children attaining
further steps in the way of human knowledge. I also want to dedicate the thesis to my
son who usually play and make obstreperousness beside as I did the research. The final
I would like to dedicate to my wife who always suggests a lot of strange ideas and
sometimes cooks for a funny meal
Acknowledgement
Tran Thong Nhat iii
Acknowledgement
To make the research in Brandenburg University of Technology Cottbus – Senftenberg
I received many supports from persons and organizations. It is very difficult to give
list of thank that can express my gratitude satisfactorily.
The first thank I would like to give to Prof. Dr. Dr. h.c Michael Schmidt and Dr. Harry
Storch, who brought the chance for me participating to this research by enrollment and
supervision for whole time of the research with valuable comments and advices.
The second thank I would like to give to BMBF and DAAD which supported for fund
within time of the research.
I am also indebted to Mr. Ho Long Phi who consumed a lot of time to discuss and
address valuable ideas for the research. Moreover, he also supported and provided for
collecting data for my research that needs for a long time and is very close relationship
with the data management organizations in the Vietnam situation.
It is a pleasure to thank my friends in Vietnam, Mr. Phan Nguyen Viet and Mr.
Nguyen Hong Dung who helped in collecting data. Additionally, I also want to give
thank to Mr. Hoang Tung who is always willing to support for data that he is
managing. I would like to thank Assoc. Prof. Dr. Nguyen Kim Loi and Mr. Bao Van
Tuy who supported for me in the updating researches in Ho Chi Minh City relating to
climate change.
I am very grateful for the advices and consultant from apl. Prof. Dr. Manfred Wanner,
apl. Prof. Dr.-Ing. habil. Frank Molkenthin, Dr. Dmytro Palekhov, Mr. Nigel Keith
Downes, and Mr. Hendrik Rujner. Their supports are very useful for my presentation
in the defense. Additionally, I also want to give thank to Mr. Le Duc Tho and Ms.
Antje Katzschner who support for translation of the abstract.
Finally, I indeed thank to the staff in the project Megacity City Research Project. Ho
Chi Minh - Integrative Urban and Environmental Planning Adaptation to Climate
Change Framework and many other people whom I can not list all them here.
However they have had a lot of the supports in the live, study and administration
issues to authority in Cottbus and BTU.
List of Abbreviations
Tran Thong Nhat iv
List of Abbreviations
Abbreviation
Full Descriptions
2D Two Dimensions
3D Three Dimensions
ADB Asian Development Bank
AGC-DOST Applied GIS Center - Department of Science and Technology
BFCI-DARD
Bureau of Flood Control and Irrigation - Department of Agriculture
and Rural Development
BMBF German Ministry of Education and Research
DEM Digital Elevation Model
DHI Danish Hydraulic Institute
DTM Digital Terrain model
ESRI Environmental Systems Research Institute
FC FLOODsite Consortium
GDLA General Department of Land Administration
GPS Global Positioning System
HCMCPC Ho Chi Minh City's People Committee
HCMCSO Ho Chi Minh City Statistical Office
ICEM International Centre for Environmental Management
ICEM International Centre for Environmental Management
IND Industry
IPCC Intergovernmental Panel on Climate Change
JICA Japan International Cooperation Agency
LIDAR Light Detection And Ranging
MONRE Ministry of Natural Resources and Environment
NSWDOC-
MHL
New South Wales Department of Commerce - Manly Hydraulics
Laboratory
OGC Open GIS Consortium
OSP Open Space
PUB Public
RES Resident
List of Abbreviations
Tran Thong Nhat v
SCFC
Steering Center of the urban Flood Control program of Ho Chi Minh
city
SF Structure Forum
SIHYMETE
Sub Institute of Hydrometeology and Environment of South Viet
Nam
TIN Triangle Irregular Network
TL Tide level
UST Urban Structure Types
UTM Universal Transverse Mercator
VNGov. Vietnamese Government
VNUHCM Vietnam National University Ho Chi Minh City
WB World Bank
Table of Content
Tran Thong Nhat vi
Table of Content
Declaration/ Affiant.................................................................................. i
Dedication… ........................................................................................... ii
Acknowledgement................................................................................. iii
List of Abbreviations............................................................................. iv
Table of Content .................................................................................... vi
List of Figures......................................................................................... x
List of Tables ....................................................................................... xiii
Abstract……….. ................................................................................... xvi
Chapter 1. Introduction ....................................................................... 1
1. Statement of problem .................................................................................1
2. Aims and objectives ....................................................................................6
2.1. Aims ...................................................................................................................... 6
2.2. Objectives ............................................................................................................. 6
3. Significance of the study.............................................................................6
4. Methodology ................................................................................................8
5. Content summary......................................................................................11
Chapter 2. Literature Review ............................................................ 13
1. Study area ..................................................................................................13
2. Geographic information system (GIS)....................................................14
3. Flood models..............................................................................................16
4. Climate change..........................................................................................17
Table of Content
Tran Thong Nhat vii
5. Researches related to the thesis...............................................................19
Chapter 3. Data and database........................................................... 22
1. Collecting data...........................................................................................22
2. Editing and correcting data .....................................................................23
3. Population data .........................................................................................24
4. Analyzing and calculating climate data..................................................24
4.1. Identifying climate change trend and rules .................................................... 24
4.2. Identifying the future time point to assess flood risk..................................... 26
4.3. Identifying peaks and their appearance number of the tide level ................ 27
4.4. Calculating climate data at the future time point .......................................... 27
Chapter 4. Building Flood Model and Flooding Maps..................... 30
1. Selecting a suitable flood model for the research ..................................30
1.1. Build criteria of selection .................................................................................. 30
1.2. Analysis and selection the most suitable flood model .................................... 30
2. Interpolating roads elevations .................................................................31
3. Buildings height interpolation .................................................................34
4. Classifying the rivers causing flood.........................................................36
5. Building the flooding model.....................................................................36
6. Results of flood model and flooding maps..............................................40
6.1. Digital Terrain model and drainage system ................................................... 40
6.2. Flooded area maps............................................................................................. 42
6.3. Flooding depth modeling for the research ...................................................... 45
6.3.1 Method................................................................................................................. 45
6.3.2 Result and discussion .......................................................................................... 46
6.4. Flooding duration modeling for the research ................................................. 52
6.4.1 Method................................................................................................................. 53
6.4.2 Result and discussion .......................................................................................... 53
Table of Content
Tran Thong Nhat viii
6.5. Flooding frequency modeling for the research............................................... 60
6.5.1 Method................................................................................................................. 60
6.5.2 Result and discussion .......................................................................................... 61
Chapter 5. Flood Risks of Houses.................................................... 68
1. Introduction...............................................................................................68
2. Method .......................................................................................................69
3. Result and discussion................................................................................71
3.1. Affected areas..................................................................................................... 71
3.2. Depth grades ...................................................................................................... 73
3.3. Duration grades ................................................................................................. 77
3.4. Frequency grades............................................................................................... 80
Chapter 6. Flood Risk of Population ................................................ 85
1. Introduction...............................................................................................85
2. Method .......................................................................................................86
3. Results and discussion ..............................................................................87
3.1. Affected population ........................................................................................... 87
3.2. Depth grades ...................................................................................................... 89
3.3. Duration grades ................................................................................................. 92
3.4. Frequency grades............................................................................................... 97
Chapter 7. Flood Risk of Land Use................................................. 102
1. Introduction.............................................................................................102
2. Method .....................................................................................................103
3. Results and discussion ............................................................................105
3.1. Affected areas................................................................................................... 105
3.2. Depth grades .................................................................................................... 113
3.3. Duration grades ............................................................................................... 117
3.4. Frequency grades............................................................................................. 121
Table of Content
Tran Thong Nhat ix
Chapter 8. Conclusion and Recommendation............................... 127
1. Conclusions..............................................................................................127
1.1. Flood model and flooded areas in Ho Chi Minh City .................................. 127
1.2. Flood risk of houses ......................................................................................... 129
1.3. Flood risk of population.................................................................................. 130
1.4. Flood risk of land use ...................................................................................... 132
2. Recommendations ...................................................................................134
2.1. Authorities and decision makers.................................................................... 134
2.2. Planner.............................................................................................................. 135
2.3. Outlooks and further researches.................................................................... 136
Appendixes. ........................................................................................ 138
Appendix A.1: Tide peaks and their duration (hour) at levels 1.50m
and 1.85m…. ....................................................................................... 138
Appendix A.2: Tide peaks and their frequency (time/month) at levels
1.50m and 1.85m................................................................................. 139
Appendix B.1: Land use types at flooding depth grades in urban
zones of Ho Chi Minh City ................................................................. 140
Appendix B. 2: Land Use Types in Flooding Duration grades in
urban zones of Ho Chi Minh City....................................................... 142
Appendix B. 3: Land use types at flooding frequency grades in
urban zones of Ho Chi Minh City....................................................... 144
Appendix C: Land use classes transferred from UST ..................... 146
Literatures and References ............................................................... 150
List of Figures
Tran Thong Nhat x
List of Figures
Fig. 1. 1: Methodology flowchart .........................................................................10
Fig. 4. 1: Flow chart of the interpolation procedure.............................................32
Fig. 4. 2: Principle of flooded area model.............................................................38
Fig. 4. 3: Digital Terrain Model and drainage system in Ho Chi Minh City........41
Fig. 4. 4: Flooded area map at the tide levels in urban zones Ho Chi Minh City.42
Fig. 4. 5: Flooded areas at the tide levels in urban zones of Ho Chi Minh City...44
Fig. 4. 6: Flooded areas of flooding depth grades at the tide levels in Ho Chi
Minh City ..............................................................................................................48
Fig. 4. 7: Flooding depth maps at 1.50m tide level in urban zones Ho Chi Minh
City ........................................................................................................................49
Fig. 4. 8: Flooding depth maps at 1.85m tide level in urban zones Ho Chi Minh
City ........................................................................................................................50
Fig. 4. 9: Flooded areas of flooding depth grades at the tide levels in urban zones
of Ho Chi Minh City .............................................................................................52
Fig. 4. 10: Flooded areas of flooding duration grades at the tide levels in Ho Chi
Minh City ..............................................................................................................55
Fig. 4. 11: Flooded areas of flooding duration grades at the tide levels in urban
zones of Ho Chi Minh City...................................................................................57
Fig. 4. 12: Flooding duration maps at 1.50m tide level in urban zones of Ho Chi
Minh City ..............................................................................................................58
Fig. 4. 13: Flooding duration maps at 1.85m tide level in urban zones of Ho Chi
Minh City ..............................................................................................................59
Fig. 4. 14: Flooded areas of flooding frequency grades at the tide levels in Ho
Chi Minh City........................................................................................................63
Fig. 4. 15: Flooded areas of flooding frequency grades at the tide levels in urban
zones of Ho Chi Minh City...................................................................................65
List of Figures
Tran Thong Nhat xi
Fig. 4. 16: Flooding frequency maps at 1.50m tide level in urban zones of Ho Chi
Minh City ..............................................................................................................66
Fig. 4. 17: Flooding frequency maps at 1.85m tide level in urban zones of Ho Chi
Minh City ..............................................................................................................67
Fig. 5. 1: Affected houses map at the tide levels in Ho Chi Minh City................72
Fig. 5. 2: Affected house areas at the tide levels in urban zones of Ho Chi Minh
City ........................................................................................................................73
Fig. 5. 3: Affected house areas of flooding depth grades at the tide levels in Ho
Chi Minh City........................................................................................................74
Fig. 5. 4: Affected house areas of flooding depth grades at the tide levels in
urban zones of Ho Chi Minh City.........................................................................76
Fig. 5. 5: Affected house areas of flooding duration grades at the tide levels in
Ho Chi Minh City..................................................................................................78
Fig. 5. 6: Affected house areas of flooding duration grades at the tide levels in
urban zones of Ho Chi Minh City.........................................................................80
Fig. 5. 7: Affected house areas of flooding frequency grades at the tide levels in
Ho Chi Minh City..................................................................................................82
Fig. 5. 8: Affected house areas of flooding frequency grades at the tide levels in
urban zones of Ho Chi Minh City.........................................................................84
Fig. 6. 1: Affected inhabitant at the tide levels in urban zones of Ho Chi Minh
City ........................................................................................................................88
Fig. 6. 2: Affected inhabitants so flooding depth grades at the tide levels in Ho
Chi Minh City........................................................................................................90
Fig. 6. 3: Affected inhabitants of flooding depth grades at the tide levels in urban
zones of Ho Chi Minh City...................................................................................92
Fig. 6. 4: Affected inhabitants of flooding duration grades at the tide levels in Ho
Chi Minh City........................................................................................................94
List of Figures
Tran Thong Nhat xii
Fig. 6. 5: Affected inhabitants of flooding duration grades at the tide levels in
urban zones of Ho Chi Minh City.........................................................................96
Fig. 6. 6: Affected inhabitants of flooding frequency grades at the tide levels in
Ho Chi Minh City..................................................................................................98
Fig. 6. 7: Affected inhabitants of flooding frequency grades at the tide levels in
urban zones of Ho Chi Minh City.......................................................................100
Fig. 7. 1: Flooded land use maps at 1.50m tide levels in Ho Chi Minh City .....106
Fig. 7. 2: Flooded land use maps at 1.85m tide levels in Ho Chi Minh City .....107
Fig. 7. 3: Areas of affected land use types at the tide levels in Ho Chi Minh City
.............................................................................................................................109
Fig. 7. 4: Flooded areas of land use types at the tide levels in urban zones Ho Chi
Minh City ............................................................................................................111
Fig. 7. 5: Flooded areas of built up types at the tide levels in urban zones of Ho
Chi Minh City......................................................................................................113
Fig. 7. 6: Flooded areas of built up types at the tide levels in flooding depth
grades in Ho Chi Minh City................................................................................116
Fig. 7. 7: Flooded areas of built up types at tide levels in flooding duration
grades in Ho Chi Minh City................................................................................120
Fig. 7. 8: Flooded areas of built up types at tide levels in flooding frequency
grades in Ho Chi Minh City................................................................................125
List of Tables
Tran Thong Nhat xiii
List of Tables
Tab. 2. 1: Increasing the number of heavy rains over time serial.........................19
Tab. 2. 2: Sea level rises SLR (cm) compared with SL of period 1980 - 1999....20
Tab. 3. 1: The summary of data to use in the research .........................................25
Tab. 3. 2: Sea level rising SLR (cm) relate to SL of period 1980 - 1999 in Ho Chi
Minh City ..............................................................................................................26
Tab. 3. 3: Interval average tide level increment (cm) at the forecast times in Ho
Chi Minh City........................................................................................................26
Tab. 3. 4: Tide height and frequency in 2030 with daily tide level peaks............28
Tab. 3. 5: Frequencies of daily sea level peaks over 1.5m in three emission
scenarios and average times per month at year 2030............................................28
Tab. 4. 1: Flooded areas at the tide levels in urban zones of Ho Chi Minh City..43
Tab. 4. 2: Flooded areas of flooding depth grades at the tide levels in Ho Chi
Minh City ..............................................................................................................47
Tab. 4. 3: Flooded areas of flooding depth grades at the tide levels in urban zones
of Ho Chi Minh City .............................................................................................51
Tab. 4. 4: Flooded areas of flooding duration grades at the tide levels in Ho Chi
Minh City ..............................................................................................................54
Tab. 4. 5: Flooded areas of flooding duration grades at the tide levels in urban
zones of Ho Chi Minh City...................................................................................56
Tab. 4. 6: Flooded areas of flooding frequency grades at the tide levels in Ho Chi
Minh City ..............................................................................................................62
Tab. 4. 7: Flooded areas of flooding frequency grades at the tide levels in urban
zones of Ho Chi Minh City...................................................................................64
Tab. 5. 1: Affected house areas at the tide levels in urban zones of Ho Chi Minh
City ........................................................................................................................71
List of Tables
Tran Thong Nhat xiv
Tab. 5. 2: Affected house areas of flooding depth grades at the tide levels in Ho
Chi Minh City........................................................................................................74
Tab. 5. 3: Affected house areas of flooding depth grades at the tide levels in
urban zones of Ho Chi Minh City.........................................................................75
Tab. 5. 4: Affected house areas of flooding duration grades at the tide levels in
Ho Chi Minh City..................................................................................................77
Tab. 5. 5: Affected house areas of flooding duration grades at the tide levels in
urban zones of Ho Chi Minh City.........................................................................79
Tab. 5. 6: Affected house areas of flooding frequency grades at the tide levels in
Ho Chi Minh City..................................................................................................81
Tab. 5. 7: Affected house areas of flooding frequency grades at the tide levels in
urban zones of Ho Chi Minh City.........................................................................83
Tab. 6. 1: Affected inhabitant at the tide levels in urban zones of Ho Chi Minh
City ........................................................................................................................87
Tab. 6. 2: Affected inhabitants of flooding depth grades at the tide levels in Ho
Chi Minh City........................................................................................................89
Tab. 6. 3: Affected inhabitants of flooding depth grades at the tide levels in urban
zones of Ho Chi Minh City...................................................................................91
Tab. 6. 4: Affected inhabitants of flooding duration grades at tide levels in Ho
Chi Minh City........................................................................................................93
Tab. 6. 5: Affected inhabitants of flooding duration grades at the tide levels in
urban zones of Ho Chi Minh City.........................................................................95
Tab. 6. 6: Affected inhabitants of flooding frequency grades at tide levels in Ho
Chi Minh City........................................................................................................97
Tab. 6. 7: Affected inhabitants of flooding frequency grades at the tide levels in
urban zones of Ho Chi Minh City.........................................................................99
Tab. 7. 1: Land use types in the research............................................................105
Tab. 7. 2: Areas of affected land use types at the tide levels in Ho Chi Minh City .
List of Tables
Tran Thong Nhat xv
............................................................................................................................ 108
Tab. 7. 3: Flooded areas of land use types at the tide levels in urban zones of Ho
Chi Minh City......................................................................................................110
Tab. 7. 4: Flooded areas of built up types at the tide levels in flooding depth
grades in Ho Chi Minh City................................................................................115
Tab. 7. 5: Flooded areas of built up types at the tide levels in flooding duration
grades in Ho Chi Minh City................................................................................118
Tab. 7. 6: Flooded areas of built up types at the tide levels in flooding frequency
grades in Ho Chi Minh City................................................................................124
Abstract
Tran Thong Nhat xvi
Improvement of Flood Risk Assessment under Climate
Change in Ho Chi Minh City with GIS Applications
Abstract
Ho Chi Minh City is the largest city in VN. The city is the most important center of
economy, society and culture in the southern region of Vietnam. However, due to
characteristics of natural conditions with low topography and borders touch the sea so
that since the late 20th century with the rapid economic and urban development there
are environmental problems have arisen. One of the problems is flooding issue caused
by high tide. With these natural conditions and sea level rise of climate change in the
future, Ho Chi Minh City is considered as one of the most affected and damaged cities
in the world.
Therefore, many policies have been set out from the national to local levels in Vietnam
to prepare for adaptability of impacts and risks of the sea level rise and the climate
change. And this has also been considered in Ho Chi Minh City as the development
policies of the city authorities have to consider in the context of the sea level rise and
the climate change. A number of researches have been conducted to assess the impact
of climate change to Ho Chi Minh City in the future. However, these researches are
still need to be enhanced further.
The flooding problem is a major issue of the sea level rise in Ho Chi Minh City. And
to make a good result, the flood model needs a lot of requirements that ensure fine
quality of input data, suitable model and a relied procedure. In the available research,
the input data is not really the highest quality in the available context in Ho Chi Minh
City. As the flood model is implemented, one of the input data requirements of the
model is information detail of elevation in the flooded area. And this is more necessary
than in geophysical urban areas such as Ho Chi Minh City. And to assess fully flood
risk issues for flooding caused by tidal phenomenon in Ho Chi Minh City, the
determination of many characteristics of flood model is very useful for users who need
to apply the results of the model for the planning development in Ho Chi Minh City in
the future. Besides adopting a uniform environment as GIS for managing all the data
Abstract
Tran Thong Nhat xvii
of flooding problem and making conditions for the development of decision support
systems is very necessary for flood management in the future.
The research has been carried out and its results have been generated on the flood risk
assessment associated context of the sea level rise due to climate change with high
emissions scenario A1FI in 2030 for the current houses, the population and the land
use types. The results have shown a lot of the areas where are inundated in the future
with the increasing flooding duration, depth and frequency even though they are not
flooded at the current because there are some protective structures. This will be helpful
for suggesting a forecast of the development direction to decision makers in Ho Chi
Minh City for next time period.
And the last part is the proposal for decision and policy makers, authorities and
planners as well. Moreover, the results of this research can be used as the references
and the foundations for further researches and so that the problems that Ho Chi Minh
City may be encountered due to flood risk caused by climate change to the economic
and social aspects of the development in Ho Chi Minh City will encounter. And the
problem of adaptation to climate change will be more completed and more thoroughly
so that it is to minimize the damage of climate change for the city.
Keywords: GIS, Sea Level Rise, Flood Risk, Climate Change, Ho Chi Minh City.
Abstrakt
Tran Thong Nhat xviii
Entwicklung des Hochwasserrisikos beeinflusst durch den
Klimawandel in Ho Chi Minh Stadt mittels GIS
Abstrakt
Ho Chi Minh Stadt ist die größte Stadt in Vietnam. Sie ist das wichtigste Zentrum für
Wirtschaft, Gesellschaft und Kultur in der südlichen Region Vietnams. Durch den
rasanten wirtschaftlichen Aufschwung und die damit einhergehende Stadtentwicklung
gibt es seit dem Ende des 20. Jahrhunderts Umweltprobleme. Dies wird durch die
natürlichen Bedingungen, eine wenig ausgeprägte Topographie und die Nähe zum
Meer begünstigt. Überschwemmungen durch Hochwasser stellen ein großes Problem
dar. Mit diesen natürlichen Bedingungen und dem prognostizierten
Meeresspiegelanstieg durch den Klimawandel ist Ho Chi Minh Stadt zukünftig als
eine der am stärksten betroffenen und geschädigten Städte der Welt zu betrachten.
Daher sind viele Maßnahmen auf nationaler und lokaler Ebene in Vietnam entwickelt
worden, um sich den Auswirkungen anzupassen, und den Risiken des Anstieges des
Meeresspiegels und des Klimawandels zu begegnen. In Ho Chi Minh Stadt muss das
aufgrund der oben genannten Bedingungen besonders betrachtet werden. Eine Reihe
von Untersuchungen wurden durchgeführt, um die Auswirkungen des Klimawandels
in Ho Chi Minh Stadt in der Zukunft zu beurteilen. Allerdings müssen diese
Untersuchungen noch weiter entwickelt und verbessert werden.
Das Überschwemmungsproblem durch den Anstieg des Meeresspiegels, ist ein
wichtiges Thema in Ho Chi Minh Stadt. Um ein gutes Ergebnis zu bekommen, müssen
die Qualität der Eingangsdaten sowie das Modell gut sein. In der derzeitigen
Forschung, haben die Eingangsdaten nicht die höchste Qualität im Kontext von Ho
Chi Minh Stadt. Als das Hochwassermodel implementiert wurde, war eine der
Eingangsdatenanforderung des Modells, die Information der Höhe der
Überschwemmung. Dies wird in städtischen Gebieten noch wichtiger aufgrund der
geophysikalischen Gegebenheiten von Ho Chi Minh Stadt.
Für eine umfassende Beurteilung der Hochwasserrisikofragen von
Überschwemmungen beeinflusst zusätzlich durch die Gezeitenphänome in Ho Chi
Minh Stadt , ist die Bestimmung vieler Eigenschaften für die Ergebnisse des
Abstrakt
Tran Thong Nhat xix
Hochwassermodells sehr nützlich für Anwender, die die Ergebnisse des Modells für
die Planung der Entwicklung in Ho Chi Minh Stadt in der Zukunft anwenden werden.
Hierfür wäre die Einführung einer einheitlichen Umgebung im GIS zur Verwaltung
aller Daten von Überschwemmungsproblemen und Herstellungsbedingungen für die
Entwicklung von Entscheidungsunterstützungssystemen in der Zukunft für das
Hochwassermanagement sehr wichtig.
Vorliegende Arbeit hat Ergebnisse in Bezug auf Hochwasserrisiko basierend auf
dem Emissionsszenario A1FI im Jahr 2030 , verbunden mit dem darin prognostizierten
Anstieg des Meeresspiegels, für die aktuelln Bebauung, Bevölkerung und
Landnutzungstypen generiert. Die Ergebnisse zeigen eine Menge Bereiche, in denen in
Zukunft mit zunehmender Überschwemmungsdauer, -tiefe und -frequenz gerechnet
werden muss, auch wenn sie aktuell nicht überflutet werden, da sie einige noch
Schutzstrukturen besitzen. Dies wird hilfreich für Prognosen der weiteren Entwicklung
für Entscheidungsträger in Ho Chi Minh Stadt in der nächste Zeit sein.
Zusätzlich bietet der letzte Teil der Arbeit einen Vorschlag für die
Entscheidungsfindung der Entscheidungsträger, Behörden und Planer. Darüber hinaus
können Ergebnisse dieser Forschung, sowie Referenzen und Grundlagen, für weitere
Forschungen verwendet werden, so dass den Problemen in Ho-Chi-Minh-Stadt
aufgrund des Hochwasserrisikos, beeinflusst durch Klimawandel und die damit
verbundenen wirtschaftlichen und sozialen Aspekte, begegnet werden kann. Dadurch
kann das Problem der Anpassung an den Klimawandel angegangen weden, so dass der
Schaden des Klimawandels für die Stadt minimiert werden kann.
Stichwort: GIS, Anstieg des Meeresspiegels, Hochwasserrisiko, Klimawandel, Ho
Chi Minh Stadt, Vietnam
Chapter 1. Introduction
Tran Thong Nhat 1
Chapter 1. Introduction
Climate change is a global problem and human has to face. Climate change has also
been performing that its impacts are very serious to Viet Nam. All reports that have
researched on climate change list Viet Nam as a greatly affected countries of climate
change because of its topography and geography (WB, 2007). The most terrible issue
is rising of sea level.
The impacts of climate change affect the areas located along the coast stretching from
north to south of Vietnam. One of the most important city and it severely affected that
is Ho Chi Minh City (HCMC).
With the high concentration of population and demands for housing, many areas in Ho
Chi Minh City have been excessive urbanization and land use changes dramatically
not only in the central area but also in the surrounding rural areas. This has created
problems about environment. One problem is the phenomenon that occurs frequently
flooded over the city.
Research, Improvement of Flood Risk Assessment under Climate Change in Ho Chi
Minh City with GIS Applications, is seen as a part of a research project, Megacity City
Research Project. Ho Chi Minh - Integrative Urban and Environmental Planning
Adaptation to Climate Change Framework, conducted by the Brandenburg University
of Technology Cottbus - Senftenberg. The project is a part of the research program
"Sustainable Development of the Megacities of Tomorrow - Climate and Energy
Efficient Structures in Urban Growth Centres", has been sponsored by the German
government, Ministry of Education and Research (BMBF).
1. Statement of problem
According to official web site of Ho Chi Minh City People’s Committee (HCMCPC,
2010), Ho Chi Minh City is “located from 10°10’-10°38’ north and 106°2’-106°54’
east. The city center is 50km from the East Sea in a straight line. Ho Chi Minh City
belongs to a transitional region between the southeastern and Mekong Delta regions.
The general topography is that Ho Chi Minh City terrain gets lower from north to
Chapter 1. Introduction
Tran Thong Nhat 2
south and from east to west. There are three types of terrain. The high terrain lies in
the northern-northeastern area and part of the northwestern area encompassing
northern Cu Chi, northeastern Thu Duc and District 9. This is the bending terrain with
average height of 10-25 meters. Long Binh Hill in District 9 is the highest at 32
meters. The depression terrain lies in the southern-southwestern and southeastern part
encompassing district 9, district 8, district 7, Binh Chanh rural district, Nha Be rural
district and Can Gio rural district. The area’s height is in the range of 0.5 to 2 meters.
The medium-height terrain lies in the middle of the city, encompassing most old
residential areas, part of districts 2 and Thu Duc district, and the whole of district 12
and Hoc Mon rural district. The area’s height is 5-10 meters” and 72.3% of the whole
urban area of Ho Chi Minh City is below 2 m mean sea level (Storch, Downes, Thinh,
Thamm, Phi, Thuc, Thuan, Emberger, Goedecke, Welsch and Schmidt, 2009).
About hydrology, Ho Chi Minh City is located in the downstream of Dong Nai - Sai
Gon river system and there are two large water storage reservoirs including Dau Tieng
reservoir connected to the Saigon River and Tri An reservoir connected to the Dong
Nai river. Ho Chi Minh City has a network of rivers and canals are very diverse. In
addition to the main rivers, the city also has an intricate system of canals such as Lang
The, Bau Nong, Rach Tra, Ben Cat, An Ha, Tham Luong, Cau Bong, Nhieu Loc-Thi
Nghe, Ben Nghe, Lo Gom, Kenh Te, Tau Hu, Kenh Doi. Sometimes the rivers and the
canals serve in irrigation, but are influenced by the fluctuations of regime of semi-
diurnal tide from the South China Sea. Tidal penetration in land has caused adverse
impacts on agricultural productivity and limits the water drainage in urban areas.
Average rainfall in the city reached 1.949 mm/year. Each year, average number of rain
days in the city is 159. The rain days are most concentrated for the months from May
to November, accounting for about 90%, especially in the two months June and
September. On whole extent of the city, rainfall is unevenly distributed and tends to
increase southwest – northeast axis. The core districts and northern districts have a
higher precipitation that the other areas.
Since the elements of topography, hydrology and meteorology, it is to see that Ho Chi
Minh City from natural conditions is very sensitive to variability and change of
climate. Climate change, particularly changes in precipitation, storm intensity and sea
level rising will affect Ho Chi Minh City. They are causes of flooding and threaten not
only the low land areas, but also extend to other areas.
Chapter 1. Introduction
Tran Thong Nhat 3
Besides natural factors, human and social factors are also an issue to regard. The
causes of serious problem of urban flooding are the ongoing rapid urbanization
process, which has changed the land-use patterns. Ho Chi Minh City has the largest
population in Vietnam and its urbanization rate is very high. With the demands of
economic development and housing for residents in urbanization progress combining
with the weakness in construction control and management the city has loss the green
space areas, water bodies and agricultural land that are converted to impervious
surfaces rapidly (JICA, 2004; Van, 2008; Viet, 2008). Natural streams, channels,
lakes, wetlands and vegetation structures that can maintain the urban water balance
have been replaced by impermeable surfaces causing increased surface run-off
flow. With state of land use change inappropriately consequently, problems of urban
environment have appeared and one of which is a phenomenon of urban flooding.
According to experts, the phenomenon of flooding in Ho Chi Minh City began
appearing in the early the 90s of 20th century (Lai, 2005). At the early time, the
phenomenon appeared in low frequency and in small areas. However, day to day level
of flooding has increased rapidly along with the urban development in Ho Chi Minh
City (JICA, 2004; Lai, 2005; Viet, 2008). Even if at the current, the flooding is
appearing more and more serious as it is heavy rain and tide and flooding come every
month of year (Nhan, 2006; Phi, 2007). Under this situation, the city government has
tried to eliminate the flooded sites drastically but the situation has not improved since
the old flooded sites disappeared, the new ones come. Therefore, urban flooding in Ho
Chi Minh City is already doing a lot of suffering for regions when rain and high tide
appear. Urban flooding has made sustainable development plan of Ho Chi Minh City
that has been facing many challenges at the current and the future (SCFC, 2010; WB,
2007).
The urban flooding in Ho Chi Minh City can be divided into two groups based on
supplying water source to flooding phenomenon. The first is raining and the second is
due to difference between water levels of the system of canals and inland elevation in
Ho Chi Minh City. In the second group includes the phenomenon of tides, flooding
caused the flood discharge in the lakes on the Sai Gon and Dong Nai River upstream
making the water level rising in the rivers and canals. The flooding caused by rainfall
mainly concentrates for six-month of rainy season from May to November. The
flooding caused by the high tide is most serious because it occurs with high frequency
Chapter 1. Introduction
Tran Thong Nhat 4
in all months. Moreover, regime of semi-diurnal tide in Ho Chi Minh City has caused
flooding tide occurring two times per day. For the flooding caused the discharge from
the reservoirs, this is not often and it only occurs in heavy rains. But in the fact that the
discharge is often not the main cause of the flooding is an enhanced factor for the
severity of flooding. Due to the supplying of water resources as the above analysis, the
flooding of the first group is called rainfall flooding and the flooding of the second
group is called tidal flooding.
In addition to the natural factors cause Ho Chi Minh City became a flood-prone areas
due to low land, tide is located in the geography when there are often monsoon rains,
the flooding in Ho Chi Minh City is contributed by human activities. Because the
natural factors are fixed and existed for long time, but the phenomenon of flooding
occurs and becomes severe for around the last two decades. The human causes are
factors decide to the nature and extent of the current flooding. In the human factors,
the direct factor causing the flooding in Ho Chi Minh City is urbanization that has
changed the land-use patterns. Natural streams, channels, lakes, wetlands had been
occupied and fill up to be residential areas (Phi, 2009). Consequently, infiltration
ability has been reduced a lot and water when it is rain and discharge from reservoirs
in river upstream comes would not have places to store for balance of water. Besides,
vegetation structures that can maintain the urban water balance have been replaced by
impermeable surfaces so that land has been reduced infiltration ability and it causes
increasing surface run-off flow. Another factor is the drainage system of Ho Chi Minh
City has been very old, obsolete and damaged so that the drainage system has
overloaded when it is rain (Phi, 2007; Thang, 2010; Trung, 2009). As a result, when
rainfall comes surface flow will not be able to escape for short time and the flooding
appears. The extent of the flooding is more severe if the rain is heavy and continues
for long time.
Additionally, Ho Chi Minh City is located on a weak stratum and a low relief. That the
stratum under this city is very feeble and the rapid urban growth builds resident areas
where construct many high buildings and blocks. In the new residential areas, demands
of living water are inquired and increased day by day but infrastructure of living water
supply can not solve. As a result, the households in the areas have to conduct
extraction of groundwater for their needs uncontrollably (Nga, 2006). Combination
between the extraction of groundwater and the increasing of impermeable surface has
Chapter 1. Introduction
Tran Thong Nhat 5
made water table has reduced a much more so that land subsidence has appeared
(Dinh, Trung, Sarti, Dransfeld and Hanssen, 2008; Nga, 2006; Trung & Dinh, 2009).
After for a period of time, the areas is lower and lower and as a result flooding
happens obviously and frequently as flood tide.
Recent studies on the urban flooding problem in Ho Chi Minh City have proven that
local impacts of climate change and rising tide levels are coming to Ho Chi Minh City.
Especially sea level rising has affected seriously. According to Ho Long Phi (2007),
rainfall events which have high precipitation are increasing dramatically for some last
recent decades (Table 2.1). In addition a report delivered by Vietnamese Ministry of
Natural Resources and Environment (MONRE) in 2009 estimates that sea level rise in
the area of Ho Chi Minh City is in the situation of alarming. With average emission
scenario by 2050 sea level rising may be up to 33cm and be 75cm at the end of 21st
century (Table 2. 2).
Thus the problem of urban flooding in Ho Chi Minh City is related to two following
issues:
Land use change is not suitable having caused more and more serious
flooding in Ho Chi Minh City. This situation has affected the lives of
people and the urban development in Ho Chi Minh City.
Additionally, local climate change and sea level rising are coming and
happening more clearly so that the flooding situation will be worse in the
future.
With the urban development and infrastructure as stated above if Ho Chi Minh City
authorities do not have any improvement on management and planning, flooding areas
are more serious and deeper from consequences of climate change impacts. Moreover,
not only will many flooding areas appear and spread in the near future but also flood
risks about environment to habitant living in the areas will issue if authorities do not
have any strategies for adaptation and mitigation.
With the problem of urban flooding in Ho Chi Minh City, this research would like to
contribute on understanding and clarifying the risks and effects and damage of
flooding to current houses, people, and urban systems in the future with sea level rise.
Chapter 1. Introduction
Tran Thong Nhat 6
2. Aims and objectives
2.1. Aims
Aims are to show the general targets that researcher yearn toward after the research
completes the entire study. In this study there are two goals that are expected to
progress:
To improve the accuracy of results of flood model with optimizing the
digital terrain model and determining more flooding characteristics
To identify and expose the current and future risks of urban flooding to the
current houses, population and land use
2.2. Objectives
To achieve the aims, implementation procedure will need to achieve the specific
objectives of the various stages towards completion of the aims that had been set. In
that sense the objectives of the research will be:
To improve the digital terrain model for the flood model
To optimize the flooding characteristics for the flood model
To produce hazard maps of urban flooding to current houses, population
and land use
To exposure and evaluate future flood risks to current houses, population
land use
To announce and warn to decision makers, planners on a suitable land use
planning integrated climate change scenarios
To give helpful information to people where are safe areas for resettlement
under conditions of climate change in the future
3. Significance of the study
Ho Chi Minh City is one of the most major and important center of economic, cultural
and education of Vietnam. And the city has the largest population of Vietnam, more
Chapter 1. Introduction
Tran Thong Nhat 7
than 7 million of people in 2009 (HCMCPC, 2011; Wikipedia, 2013). Ho Chi Minh
City is one of the city has a great influence to the economic development for its
country. Ho Chi Minh City located in the North of Mekong Delta, and the down
stream of Dong Nai river system. This is also a transition area between the
southeastern and southwestern regions. This is a traffic hub linking the provinces in
the region and the international gateway. Based on that favorable strategic position, the
city has been developing rapidly; that can say Ho Chi Minh City is the fastest in
Vietnam of all aspects.
In the progress of development and international integration, Ho Chi Minh City has
always maintained a central role in economic, financial, trade and services of the
country and is the kernel of the southern key region on economy that is one of three
largest key economic regions. The city is also a driving force for the social economic
development in the southern areas and whole the country for the national strategy of
industrialization and modernization. Ho Chi Minh City is keeping the leading role of
the economy in Vietnam. The city accounts for 0.6% area and 8.34% populations in
Vietnam but accounts for 20.2% GDP in 2009 (HCMCSO, 2011; Wikipedia, 2013).
Because the city is one of the most important centers for the economic development in
the southern region and Vietnam, the facing and suffering with urban flooding that
occurs regularly and continuously severe have been enforced Ho Chi Minh City in a
very difficult situation to ensure the city being able to continue to maintain strong and
sustainable growth in the future. Therefore, researches solving environmental
problems in the city to make recommendations to decision makers and planners who
will deliver policies and spatial planning appropriately to help the city continue to
develop steadily will have very important meaning in the moment and the future.
This study is an applied research that applies a new method, geographic information
system (GIS), for studying and assessing under influences and impacts of urban
flooding in Ho Chi Minh City. It is important and the most significant of this research
is the its results will contribute a scientific basis for planning and policy making of the
managers who make policies that are appropriate for sustainable development in the
future under the impacts of climate change becoming more severe. Additionally, the
research will also contribute to flood risk management in the city with the GIS
technology.
Chapter 1. Introduction
Tran Thong Nhat 8
4. Methodology
In order to assess impact, risk and vulnerability of flooding to Ho Chi Minh
metropolitan areas needs digital flooding maps at the time points from the current to
future when climate and land use are changed. A flood model has to be evaluated and
selected and then it is used to produce digital flooding maps from input data such as
elevation, land use, soil, drainage, hydrology and climate data. After the chosen flood
model is completed it will be applied to two scenarios: situation of flooding for current
urban system and climate conditions, situation of flooding for current urban system
and future climate conditions that are impacted by climate change.
In order to choose a suitable flood model easily needs to assess existing situation of
flooding in the city of Ho Chi Minh City, the study's requirements and the
characteristics of existing flood models. Flooding phenomenon in Ho Chi Minh City
can be divided into two types based on water supplying sources caused flooding. They
include the first source provided by rainfall or precipitation and the other one provided
by the canals due to difference of water levels between water level in canals and
ground elevation, called the tide level.
With the first source, the flooding phenomenon is formed as following process. When
it is heavy rain, surface flow will occur if rainy water could not infiltrate into soil in
rained areas. The surface flow then reaches to drainage network system if it is
existential. If the drainage network system can not flow out rivers and canals in the
area the rained areas will be flooded locally. After that time the flooded areas will
spread into around places. The spreading speed and areas depend on precipitation,
rainfall intensity, areas elevation, the drainage network system, land use/ land cover
and soil types. The precipitation is an item of climate therefore climate change will
effect direct to potential flooded areas in the future.
Differently, the flooding in the situation of tide is different source to supply water and
drainage factor. In this case the catch basins and the manholes or the rivers and the
canals are the water providers. And then spreading procedures of the water extends
over ground surface to around areas. The drainage factor depends on hydrologic
system, absorption and infiltration of soil in the area. In reality, the probability of the
two reasons occur together is able and consequences of flooding is more serious.
Chapter 1. Introduction
Tran Thong Nhat 9
Understanding the causes of flooding in Ho Chi Minh City will help a lot for the
selection of flood model consistent with context of the Ho Chi Minh City. At the
current there are many flood models on over the world, in general they have been
integrated on GIS environment. Therefore, choosing the most appropriate flood model
with the flood situation in Ho Chi Minh City is an important step needing to
determine. In order to does this step, the first task has to classify the types of flood
model nowadays on over the world, then build a set of criteria to select a model that is
the most appropriate model with context of Ho Chi Minh City. After that determining
the most appropriate model for Ho Chi Minh City done, the model will be used to
identify flooded areas and flooding maps. The flooding maps combined with the
information of the urban system will expose risk degree at the flooding areas in Ho
Chi Minh City. Based on exposure of the degree, some predictions, warnings and
suggestions will be sent to policy, decision makers and planners. It is helpful and
useful to get up the awareness around policies of adaptation and reducing living costs
as the scenarios that are able to happen with the conditions of climate change.
From the analysis of the above factors, a process of the research is described in the
flowchart as figure 1. The research process will begin with a review and evaluation
indoor about current flood models on over the world. Then the second step will build a
set of evaluation criteria for choice the most appropriate flood model in context of Ho
Chi Minh City. The next step is to collect data for the research, including data for
implementing the model and data for assessing the damage, the impact of flooding.
Once data collection is done, analysis will be conducted that founds trends and rules of
climate change which will be able to calculate the values of weather in the future. The
construction of evaluation criteria for choice the model is based on three aspects:
theory to construct models, data input of models and requirements to satisfy the
research output.
After the evaluation criteria has completed, the choice of the most flood model will be
carried out. To get reliable results after implementation, the model need to conduct
calibration validation. The calibration process will be accepted after the validation
process gets a high satisfaction. With the calibrated parameters the chosen model will
be implemented to identify flooded areas and create flooding maps. The results,
flooding maps, will be used to analyze and evaluate the impact and risk to the urban
system. The evaluation is based on the spatial relationships. And last step that will be
Chapter 1. Introduction
Tran Thong Nhat 10
done basing on the assessment of flood impact, risk and vulnerability is predictions,
suggestion, recommendations to decision makers and planners. The flooding maps will
be produced with 2 scenarios: current climate data and future climate data. And based
on the flooding maps assessment of flood risks is carried out for the current houses,
population and land use.
Spatial data:
Elevation, Soil, Drainage,
Hydrologic Network...
Climate data:
Precipitation, Tide
level...
Land use
Current
Future
Climate change
trends and rules
FutureCurrent
The most
suitable flood
model
Flooding maps
Urban system Assessment of flood risk
Predictions, warnings,
suggestions to decision
makers and planners
Calibrations
Validation
Yes
No
Critiria of
model
evaluation
Identify
Review and
evaluate flood
models
Fig. 1.1: Methodology flowchart
Chapter 1. Introduction
Tran Thong Nhat 11
5. Content summary
The thesis is organized into seven chapters to describe whole the tasks carried out of
the research. The content of the thesis is performed ordinarily from introduction to the
conclusion. These chapters are summarized as the followings.
In the chapter, there is a general introduction about the thesis. The chapter draws a
main picture for the thesis. It includes a general review problem in Ho Chi Minh City
and then determining objectives of the thesis, methodology, and steps to implement for
the investigation and summary content of the chapters in the thesis that the thesis will
be conducted.
The chapter 2 shows literature review of the research. The chapter reviews researches
relating and applied to this study. It includes GIS and remote sensing, flood models,
emission scenarios and climate change and done researches on the flood and climate
change in Ho Chi Minh City. The target of the chapter is to evaluate facilities to help
the research can be completed and gaps of flood problem in Ho Chi Minh City with
climate change conditions.
The chapter 3 the first one describes the real tasks of the research. This chapter
presents all stages of the data and database process that includes collecting, editing and
errors processing. Besides calculated secondary data are to serve next steps.
The next chapter motivates steps by steps about flood model. It shows choosing the
most suitable approach to determine flood areas and its characteristics for the research.
And based on the approach, a flood model is built. Further, problems that help to
improve the accuracy of result from the model are also mentioned and detailed.
In the chapter 5, chapter 6 and chapter 7 the approaches on flood risk analysis and
assessment are described and presented in GIS environment. The steps and theories
that are applied of assessment and analysis are mentioned detailed for each of ground
objects matching to the research aims such as houses, population, and land use. And
results based on theories will be determined. The results are calculated and computed
to identify flood risk grades and impact to residents and their properties. Additionally,
the discussions of the results are mentioned and explained for the results.
The last chapter is conclusions and recommendations that are collected from chapter 5,
chapter 6 and chapter 7. This chapter also mentions suggestions to the stakeholder in
Chapter 1. Introduction
Tran Thong Nhat 12
the study area such as decision makers, planner and residents living in the flood risk
suitable warnings. Moreover, in the chapter, there are assessments that give what the
research archives and what the research should be conducted further in the future.
Chapter 2. Literature Review
Tran Thong Nhat 13
Chapter 2. Literature Review
1. Study area
Study area is located at Ho Chi Minh City center. In the area there are many typical
features for Ho Chi Minh City specially and that for urban areas in Viet Nam
generally. The characteristics of the study area are described in the next sections
(HCMCPC, 2010; HCMCPC, 2011).
Geography: Ho Chi Minh City is located from 10°10’-10°38’ north and 106°2’-
106°54’ east (HCMCPC, 2011). Moreover, Ho Chi Minh City touch with South China
Sea so that the city has conditions that are sensitive with the climate change especially
sea level rise in the future.
Topography: the study area is located in Ho Chi Minh City which belongs to a
transitional region between the southeastern and Mekong Delta regions. The general
topography is that Ho Chi Minh City terrain gets lower from north to south and from
east to west. So the study are has the medium-height terrain lies in the middle of the
city, encompassing most old residential areas.
The area’s height is 5-10 meters in Vietnamese vertical reference system that is chosen
mean sea level at Hon Dau, Hai Phong for the level zero. The height of the area does
not have suddenly change except the areas of a river and canals. The trend of height
increases slowly from east to west and from north to south. Moreover there are more
than 72.3% areas of the whole urban area of Ho Chi Minh City is below 2 m in
Vietnamese vertical reference system (Storch et al., 2009).
Ecology: The ecology of the study area is classified into basic types: the area of trees
with some parks, the area of river and canals with water surface, and the other one
with resident region with most small and low houses.
Climate: the study area is located in Ho Chi Minh City so it also has climate as Ho Chi
Minh City. The city lies in the tropical climate region near the equator. Like southern
provinces, it has a high temperature all the year and two distinct seasons, the dry and
the rainy. The rainy season lasts from May to November and the dry season from
Chapter 2. Literature Review
Tran Thong Nhat 14
December to April. According to records of the meteorological observatory at Tan Son
Nhat airport, the city’s climate has the following features: rich radiation, high rainfall,
humidity averages, around 79.5% per year (HCMCPC, 2010).
2. Geographic information system (GIS)
As the name of the GIS, geographic information system, the nature of GIS technology
is a combination of processing power to solve problems relating to spatial and non
spatial data processing. Therefore, GIS can solve almost applications and simulate
spatial phenomena. Consequently nowadays many applications of many other
disciplines and fields apply GIS as a environment to integrate and develop their tools
so that the applications will be managed, implemented, stored, computed and
displayed much better, more visual, easier analysis and more convenient delivering to
end users. Moreover GIS is also an environment to develop spatial decision support
systems that is helpful for managers and decision makers who make more precise and
effective resolutions.
With that tendency, flood management field also applies GIS to make a basic
environment for the development of the tools that serve for simulations, computations,
analysis and visual display to users. The tendency is promoted strongly nowadays
(Vieux, 2005). The process and generation of flooding in reality is very complex to
simulate similarly to the real process so that the establishment of the theory to model
this process is actually a simplification to simulate a relatively consistent for each
specific situation. It is also the answer why many flood models are built. With the
trend of development on an advanced nowadays, requirements about flood models
must be made the results more accurate and thus the technologies that are used to
support to processes of spatial simulation of flood model software are strong. As a
result, the requirements of spatial processing for flood models have been meeting the
spatial processing functions of GIS. Additionally, the results of GIS are also easily
visualized and interpreted to the end users. Moreover, to extract the reports with
formats such as maps and tables is also a strong feature of GIS. All these are reviewed
and expressed specifically in the book, The GIS Applications for Water, Wastewater,
and Storm water Systems, written by Uzair M. Shamsi in 2005 (Shamsi, 2005). The
authors focus on applications related to water in urban areas. The book brought to the
readers the specific case studies for characteristic applications on water that help the
Chapter 2. Literature Review
Tran Thong Nhat 15
readers being understood and would be able to apply for the same situation easily. Not
only GIS is mentioned but the book also showed the integration of remote sensing into
the GIS for applications on water. For an example, high resolution satellite images can
be used to update information about the changes large-scale land surface such as land
use, or environmental damages can be detected based on satellite imagery after
disasters such as floods, earthquakes or tsunamis.
Besides, GIS can be applied to the fields of water related to urban regions as Uzair M.
Shamsi written it can also apply to model for applications relating to water in the areas
where there are more extend such as basins, delta and catchments…. The applications
are considered in the document titled Geographic Information Systems in Water
Resources Engineering written by Johnson in 2009. The document has shown the
methods and provided GIS applications for most of the problems about water
resources at basin level as surface water hydrology, groundwater hydrology,
wastewater and storm water, and floodplains.
GIS can not only apply the problems of flooding, a lot of researches and
documentation have shown that GIS is also used as a powerful analytical tool in
analyzing the risks, damage assessments of natural disasters. These are expressed
through the cases of study in book Geospatial Techniques in Urban Disaster Hazard
Analysis edited by Showalter and Lu (2010). Documents gathered plenty of applied
researches which use geospatial techniques for analyzing, evaluating and managing
risk, damage caused by natural disasters. Especially in this document there is a
separated section for the representation of GIS applications for sea level rise and flood
analysis. This section includes 5 chapters containing chapter 3 and chapter 5 focusing
on vulnerability assessments (Maantay, Maroko and Culp, 2010; Pavri, 2010), chapter
4 and chapter 6 focusing on risk analysis and management (Bizimana & Schilling,
2010; Deckers, Kellens, Reyns, Vanneuville and Maeyer, 2010) related to flood
analysis and sea level rise. The other chapter, chapter 2, relates to apply GIS for
modeling of sea level rising on the world (Usery, Choi and Finn, 2010). As the editors
summarized in the text, in the chapter 2, Usery, Choi, and Finn’s use GIS to create
global animation of sea level rise. Their research is offered not as a predictive model
but to demonstrate a methodology for using GIS data layers to create models, animate
data, and provide the basis for more detailed modeling which can lead to improved
coastal policy-making.
Chapter 2. Literature Review
Tran Thong Nhat 16
3. Flood models
Flooding problem is a natural phenomenon occurring in the world for a long time.
Flood can be defined on FLOODsite (FC, 2009) as follows: "a temporary covering of
land by water outside its normal confines". Because of the severity of the flood
affected people's lives flood has been studied for a long time in the world (Aronica,
Hankin and Beven, 1998a; Bates & De Roo, 2000; Chow, 1973; Cunge, 1975; Cunge,
2003; Horritt, 2004).
Today, flood models and their theories as well are very popular over the world and
continuously upgrade day by day. Currently the world there are many models
simulating flooding in the reality. These flood models do not only compute but also
they can display the results of visualization on the GIS environment (DHI, 2004; DHI,
2007a).
There are many flood models to determine flood characteristics. Depending on goals,
accuracy and available data in the study area of each research, there are a lot of flood
models applied in the real (Apel, Aronica, Kreibich and Thieken, 2009; Bates & De
Roo, 2000; Sanders, 2007). If separation bases on using hydraulic model in the flood
models there are two groups. The first is non used hydraulic model and the second is
the used hydraulic model.
The flood models that are non used hydraulic model are not based on computation of
water wave motion. For this group, there are two types. The type 1 uses a comparison
method that considers differences between elevation of ground surface and water level
height. Therefore this method is called planar surface (Horritt & Bates, 2001; Nhat,
2011; Nhat & Loi, 2010; Priestnall, Jaafar and Duncan, 2000). The type 2 is based on a
statistical relation regression between flooded area and discharge of the sub
catchment and called statistical approach (Townsend & Foster, 2002). To apply the
second one in a new study area, there is an area where similar to the new study area
and has relationship between flooded area and discharge. Then in the new study area a
SAR image is captured and a combination between SAR and the relationship, the
characteristics of flood in the new study area are computed including flooded area,
depth and duration. The advantages of the group are simple and low computation cost
and not needed advance data. However, the results tend more exaggerated than reality
because they do not have lost of energy due to transmission (Dung, 2011).
Chapter 2. Literature Review
Tran Thong Nhat 17
The flood models used hydraulic models are complicated models to simulate all the
processes with water wave motion, conservation of energy and momentum of water.
To model the process of a flood, the researchers would analyze the flooding process
that consists of many smaller processes, but are merged into two major processes such
as hydrological and hydraulic processes. Two processes are built to models called
hydrological model and hydraulic model. In each process also includes many delicate
processes such as the infiltration, evaporation, transpiration, runoff generation process.
These processes are modeled by mathematical equations. The method chosen to solve
this equation also makes many differences for results of the flood model (NSWDOC-
MHL, 2006). To resolve a lot of the aspects, these processes are simulated by equation
system. The equation system contains plenty of unknowns related to position, energy
and momentum of the water. And depending on the number of spatial unknowns that
the model can solve the flood model is called story cell (Bates & De Roo, 2000;
Cunge, 1975; Hunter, 2005; Nien, 1996), one dimensional hydraulic (Chaudhry, 2008;
Dac, 2005; DHI, 2004; Hoa, Nhan, Wolanski, Tran and Haruyama, 2007; Horritt &
Bates, 2002; Pappenberger, Frodsham, Beven, Romanowicz and Matgen, 2007;
Werner, 2004), two dimensional hydraulic (Aronica, Tucciarelli and Nasello, 1998b;
Carrivick, 2006; DHI, 2007a; Hervouet, Hubert, Janin, Lepeintre and Peltier, 1994),
couple one –two dimensional hydraulic (DHI, 2007b; Dung, 2008; Frank, Ostan,
Coccato and Stelling, 2001; Hoa et al., 2007; Vorogushyn, Merz, Lindenschmidt and
Apel, 2010) and three dimensional hydraulic (Wilson, Yagci, Rauch and Olsen, 2006).
To implement of the flood models the input data is available with the elevation in the
river bed or at least cross sections of the rivers and canals. The advantages of the
models are really approximate simulations so that the results are computed have more
accuracy than the first group. However, the disadvantages are needs of detail input
data, resources and high computation cost.
4. Climate change
Climate change is one of hot problems in the world nowadays. This change of climate
is due to the behaviors of human into the environment so that global warming impacts
to the climate and weather of the earth. Depending on the geography and regional
natural conditions, different regions of the world are affected at different scales by the
climate change. The climate change impact assessments on over the world are
presented in the IPCC reports (IPCC, 2001; IPCC, 2007). In the reports IPCC has built
Chapter 2. Literature Review
Tran Thong Nhat 18
the impact on emissions scenarios of the world and based on frame data of IPCC the
countries would downscale and calculate the results of climate change at the national
level.
For Vietnam, the climate change is a significant and highlight problem because of
potential impacts of sea level rise. The reason of that is because Vietnam has a long
coastline that is along country from north to south through a lot of areas of the country.
According to the studies on the impacts of sea level rise, Vietnam is one of the
countries that are seriously affected but especially the low land of delta in southern and
northern regions. Realizably those issues Vietnamese state and government have built
and developed a national program to study this problem (VNGov., 2008). The national
program on climate change and sea level rise is one of important programs which set
out the objectives and stages of the preparation for facing impact, risks in Vietnam
caused by climate change in the medium and long term.
Based on objectives of the national program on climate change, a lot of researches on
climate change are deployed. In 2009, Ministry of Natural Resources and Environment
(MONRE) reported results on climate change and sea level rise on regions in Vietnam
with interval ten years in the 21st century (MONRE, 2009; Phung & Working Project
Team, 2011). And then with frame data of the report, the provincial governments
downscales and calculates more detail of result on climate change and sea level rise for
their province matching with the real local climate data.
With that direction of the development, Ho Chi Minh City government has been
improving the studies related to climate change and sea level rise to serve management
and planning. The first thing is to provide the results on climate change and sea level
rise in Ho Chi Minh City. The research “Study to build an evaluable model of climate
change impacts to natural, human and social economy in Ho Chi Minh City” of Sub
Institute of Hydrometeology and Environment of South Viet Nam (Phung & Working
Project Team, 2011) had released the results of climate change and sea level rise in Ho
Chi Minh City in 2011. That is one of the reference materials for the analysis and
calculation of the value weather and rising sea level in this study.
Chapter 2. Literature Review
Tran Thong Nhat 19
(Source: Phi, 2007)
5. Researches related to the thesis
In the recent decades, some researchers began to study the problems concerning to
urban flooding in Ho Chi Minh City and shown the causes but they were discrete (Phi,
2007; Phi, 2009; Thang, 2010) or a beginning combination makes sense of the causes
for phenomenon of urban flooding in Ho Chi Minh City (Trung, 2009). However, no
comprehensive and systematic study on the issue of flooding at the entire city level is
made to solve the urban flooding problem here. In the studying of flooding field in Ho
Chi Minh City, the researcher, Ho Long Phi has had the researches which are more
concentrated for urban flooding problems in Ho Chi Minh City. In climate change
research and urban flooding in Ho Chi Minh City (2007), Phi made conclusions about
climate change phenomenon is affecting urban flooding problem in Ho Chi Minh City
from hydrographic data as shown in table 2.1. From this study Phi showed a tendency
to increase the number of heavy rains over time serial. The tendency will make a
serious dimension to the problem of urban flooding in Ho Chi Minh in the future.
Tab. 2.1: Increasing the number of heavy rains with volume more than 100m
Period 1952-1961 1962-1971 1972-1981 1982-1991 1992-2002
Counts 0 1 2 2 4
Additionally, in the research Local Climate Change Research and Urban Flooding in
Ho Chi Minh City (2009), Phi pointed out that water level rising in Ho Chi Minh is not
only by global climate change but also by local factors as urbanization and land use
change which have caused increasing tidal level in the area. The increased rainfall has
also exposed a cause of the Ho Chi Minh urban flooding that is poor drainage system
in Ho Chi Minh. The status of the drainage system can not be improved from new
projects because by problems about setting construction standards for drainage system
in Vietnam that have not kept to update with changing climatic conditions in the
locality (Thang, 2010).
Besides the researches, a number of organizations have conducted studies to
implement urban upgrading projects to address environmental issues and especially,
urban flooding is one of them. Currently there are many projects large and small to
Chapter 2. Literature Review
Tran Thong Nhat 20
solve urban flooding problem, but the most important projects are the three followings:
Ho Chi Minh City Environmental Sanitation Project – Nhieu Loc Thi Nghe Basin, Tan
Hoa Lo Gom Canal Sanitation and Urban Upgrading Project, and Drainage and
Pollution Treatment in Tham Luong – Ben Cat – Nuoc Len Canal Project. These
projects focus on environmental improvement and urban upgrading in order to reduce
the urban flooding status in the three major basins of the Ho Chi Minh. To improve the
urban flooding status, the projects have studied to design large sewer systems to
enhance storm water drainage for the city. But according to experts evaluations, these
projects have not been put into operation, they were outdated because the hydrologic
data that had been used as requirements of construction standards for the design were
not consistent with and less than real values. Therefore, when these projects will be
completed, the problem of urban flooding is still continuing (Phi, 2009).
Tab. 2.2: Sea level rises SLR (cm) relate to SL of period 1980 – 1999
Years
Emission scenarios 2020 2030 2040 2050 2060 2070 2080 2090 2100
Low (B1) 11
17
23
28
35
42
50
57
65
Medium (B2) 12
17
23
30
37
46
54
64
75
High (A1FI) 12
17
24
33
44
57
71
86
100
A key document on climate change in Ho Chi Minh is a report that is released by the
Ministry of Natural Resources and Environment. This report is based on a research in
the Institute of Hydrometeorology and Environment to construct climate change
scenarios that used downscaling approach in the scenarios of global climate change
scenarios in the assessment report of the IPCC fourth time in 2007 (IPCC, 2007). In
this report, MONRE calculated and delivered values of sea level rising and trends of
rainfall variability under climate change scenarios in all regions of Vietnam.
Particularly, Ho Chi Minh City data on sea level rising are shown in table 2.2.
The latest the document on the impact of climate change to Ho Chi Minh City is a
synthesis study report of Asian Development Bank (ADB) in 2010 (ADB, 2010). This
is a study report of a project named Ho Chi Minh City Adaptation to Climate Change.
This project is to assess the impact, damage, risk and vulnerability at the large scale on
all aspects in Ho Chi Minh City as the economy, society, environment, transportation,
(Source: MONRE, 2009)
Chapter 2. Literature Review
Tran Thong Nhat 21
infrastructure, agriculture, industry in 2050 under climate change conditions to assist
the Ho Chi Minh City People's Committee and its results is to recommend the
adaptation policies to help cities sustainable development in the future. The project
had focused largely on vulnerability assessment, impact of climate change in 2050
based on scenarios that were integrated of sea level rising, precipitation increasing in
the status of typhoons. To build inundated areas, a hydraulic model HydroGIS (Hoanh,
Phong, Trung, Dung, Hien, Ngoc and Tuong, 2012; Nhan, Hoa, Cong and Diep, 2009;
Thai, 2011) had been used and then assessing impact, damage, risk and vulnerability to
the areas in Ho Chi Minh City is based on the results of the model. Generally this is a
comprehensive study project for the projected impacts of climate change to Ho Chi
Minh City in 2050. However, with using HydroGIS model to identify flooding areas
was not appropriate and accurate. That is because HydroGIS model built based on
river flooding. Moreover, HydroGIS model can not simulate the street elevation and
irrigation system for controlling flow water from rivers. Thus applying this model will
not correct for flooding phenomenon in urban areas such as Ho Chi Minh City. And a
gap of the study that is the results had not considered the impact of land subsidence
flooding in Ho Chi Minh City (ADB, 2009a; ADB, 2009b; WB, 2010). The next one is
procedure of the model implementation duration that there was not the calibration
process for parameters of the model before the model was applied to create scenarios
for future so that the results are not highly reliable.
To be able to say up to now, the studies related to urban flooding in Ho Chi Minh City
are also discrete. The studies to current urban flooding problem have not been
completed or perfect, the studies toward the future there is the ADB project that is
fairly complete however the project focuses only on analyzing the impact of climate
change scenarios to urban in Ho Chi Minh City. It has not been implemented
systematic study on the existing flooding situation. Additionally, the tool used for the
study has not been scientific because the study only tries to run the model to reap
outputs without regard to the appropriate context of performance of the model.
Chapter 3. Data and database
Tran Thong Nhat 22
Chapter 3. Data and database
1. Collecting data
This is big problem for any researches in Vietnam because the regulations of
publishing and updating data are very strict and not consistent. The data for the study
can be divided into the following groups: climate data, data for flood model and data
for assessments. The data groups are described in the following paragraphs with data
information and evaluation in the context of the research requirements.
Climate data include tide level, rainfall and temperature for a reference time period of
calculated climate change. The reference time period shown by the IPCC and Vietnam
is from 1980 to 1999 (IPCC, 2007; MONRE, 2009). The data for the reference time
period are collected and almost this serial data are not missed. Moreover to calculate
tide level, precipitation of rain and temperature in the future time, the scenarios of sea
level rise in Ho Chi Minh City, rainfall and temperature changes are collected.
Data for a flood model include data for implementation and data for calibration. Data
for implementation need a perfect terrain or river-canal network and their cross
sections, drainage system and land use in the study area. The research collected
terrestrial elevation points, drainage system, cross sections of Nhieu Loc-Thi Nghe
canal sub catchment and land use of whole the city. This data group is missed almost
the cross sections for river – canal network besides the observed data serves for
calibration and verification of flood model.
Data for assessments the research has collected data of urban system including: the
latest administration boundary at the community level, population data in 2009, traffic
system and build up footprint in 2006.
Results of data collection are shown in table 3.1. These data are available in many
formats, consequently editing task that change to a standard GIS data consumes many
time. Basically there are three types of collected main data: GIS data, tables and text.
GIS format includes the following data: elevation points excluding river and canal
network, river-canal network, the latest administration boundary at the community
Chapter 3. Data and database
Tran Thong Nhat 23
level, traffic system, buildup footprint and land use. Although these data in GIS
formats, but there is still a lot of errors of spatial relationship that needs to edit and
correct.
Tabular data includes: population, climate data, and climate change scenarios. All this
data should be transferred to GIS format or associated with spatial objects in GIS
respectively. Besides they need to be checked the accuracy before being used for
research.
Text data includes: drainage system and cross sections of Nhieu Loc Thi Nghe sub
catchment. The conversion and editing data in GIS format takes a lot of time.
Currently data is being prioritized for editing and progress. Together with the editing,
checking and correcting is carried out.
2. Editing and correcting data
In GIS, there are two types of information for each object. The first is the spatial
information related to the geometry and position of the object. The second is
information related to nonspatial or in the other word called object attributes. The
editing data is mostly issues concern in terms of the geometry and spatial problems of
the object that are emended and corrected exactly in geographical location. The object
attributes are almost unchanged because they have been determined by management
agencies in Vietnam.
The spatial data have many types of error that are based on the geometry features with
polygon, line or point. The errors occur in the polygon data are the overlays and the
gaps between objects in the same feature class due to defect in snapping between the
vertices of two adjacent objects. The errors appearing in the linear data are primarily
caused from missing of the digitization processing such as snapping of adjacent
features in the feature class. The errors include overlap and self overlap, pseudo nodes
and dangles. Additionally, the data also need to check the lines of the data must be
within Ho Chi Minh City. And the last geometry type of the data is point. With the
point in the research there are elevation data and out-inlet gates. In these data, the
elevation points need to check because there are some residual points between terrain
points and features points such as misunderstood points in roads, buildings, bench
mark.
Chapter 3. Data and database
Tran Thong Nhat 24
Method of identifying errors is to check problems about geometry, location and the
spatial relationships between objects in the same feature class or between data layers
with each other that are based on regulations called topology rules. After identifying
the errors, method for correcting errors depends on the types of errors. If the errors
show wrong locations, the features in the data will be corrected to right locations based
on the satellite image. With the features are misunderstood, they will be deleted.
3. Population data
Population data includes information at the time points that the research interests for
assessment at the current and future scenarios. For the current scenario, the population
data is collected at the commune level that is surveyed and inventory whole the
country on the first April 2009.
Data are collected and used in the research are shown in the table 3.1. In the table the
columns describe the information of the data including data name, published date and
data source. Published date is year when the data is official delivered popularly to third
parties which need to use the data. The data source is legal organizations which can
issue for the other organizations for using.
4. Analyzing and calculating climate data
4.1. Identifying climate change trend and rules
This task is being considered as the scenarios of climate change. Therefore, this action
is part of the collected data. The data on climate change trend and rules are presented
as table 3.2 and table 3.3. Table 3.2 shows sea level rising in Vietnam and Ho Chi
Minh City for 21st century with interval of 10 years (Phung & Working Project Team,
2011). The sea level rising is compared with sea level of referent time 1980-1999.
Additionally, to calculate the tide level in the future time when there is climate change
needs to identify value of interval average tide level increment. The values are shown
in the table 3.3 (Phung & Working Project Team, 2011).
Chapter 3. Data and database
Tran Thong Nhat 25
Tab. 3.1: The summary of data to use in the research
Data
Name Format Coordi-
nate
Object
Type
No. of
objects
Attribu
-tes Year Source
Elevation
Points
Geo-
database
HCMC
-VN2000
Point 529799 Eleva-
tion 2004
Rivers -
Canals
Geo-
database
HCMC
-VN2000
Poly-
gon 1761 Name,
Area 2006
Buildings Geo-
databse
HCMC
-VN2000
Poly-
gon 787860
Storey
number
,
Area,
2006
Line
Roads
Geo-
database
HCMC
-VN2000
Line 47721 Length 2006
Polygon
Roads
Geo-
database
HCMC
-VN2000
Poly-
gon 20473 Name,
Area 2006
Admini-
stration
Boundary
Geo-
database
HCMC
-VN2000
Poly-
gon 322
Name,
Area,
Populat
ion
2006
Mr. Phan
Nguyen Viet
Geomatic
Center -
VNUHCM
Dike
system Shapefile
HCMC
-VN2000
Line 569 Length,
Height 2012
Out-Inlets
gates Shapefile
HCMC
-VN2000
Point 521 2012
Mr. Nguyen
Hong Dung
- BFCI-DARD
Land Use Shapefile
UTM48
-WGS84
Poly-
gon 16319
UST
Code,
Area
2011
BMBF-
Megacity
Research
Project:
TP.Ho Chi
Minh, Vietnam
-
Adaptation To
Climate Change
Tide level
Text N/A N/A (*) N/A 1980-
1999
Mr. Ho Long
Phi - SCFC
Popula-
tion Text N/A N/A (**) N/A 2009 HCMCSO
(*) Tide levels was recorded at the Phu An Station in the Sai Gon River in hourly
(**) Population data is enclosed with each of the communes
Chapter 3. Data and database
Tran Thong Nhat 26
Tab. 3.2: Sea level rising SLR (cm) relate to SL of period 1980 - 1999 in Ho Chi Minh
City
Years Emission scenarios
2020 2030 2040 2050 2060 2070 2080 2090 2100
Low (B1) 13
18
23
28
34
39
44
49
54
Medium (B2) 15
21
27
31
41
48
56
64
72
High (A1FI) 15
22
30
38
47
57
68
80
93
(Source: Phung & Working Project Team, 2011)
Tab. 3.3: Interval average tide level increment (cm) at the forecast times in Ho Chi
Minh City
Interval (year) 10
20
50
100
dhi (cm) 14
19
25
30
(Source: Phung & Working Project Team, 2011)
4.2. Identifying the future time point to assess flood risk
The identifying the future time point to assess flood risk needs to be chosen to match
the planning data. At the time point the planning data can be evaluated flood risk to
types of land use when climate change. Additionally, the time point should be
predictable and suitable accuracy. Because if the time point is close from the present
time, purpose of forecast is not too high but if the time point is too far from the present
time, the accuracy is not high and the fact that the planning at that time has been
modified. Moreover, the forecast data of sea level rise scenarios are updated for each
tidal cycle of 20 years.
Differently to ADB research in 2009 (ADB, 2009a; ADB, 2009b) the future time point
to assess is based on the spatial planning map for Ho Chi Minh City by 2025 vision
2050 so that ADB decided to choose 2050 for assessment. However, as the above
considerations and analyses, this research selects year 2030 for the evaluation and
comparison flood risks.
Chapter 3. Data and database
Tran Thong Nhat 27
4.3. Identifying peaks and their appearance number of the tide
level
Identifying and calculating tide level peaks in the study area daily are important.
Additionally, the peaks are shown the tide heights that impact flooded areas it also
address the frequency of the flood can appear for the time. Based on those the flood
risk can be explored.
In Ho Chi Minh City, the tidal regime is of semi-diurnal tide so that tidal peak number
each day is usually two times. Therefore there are a difference amount of flood
between flooding by max level and peak of tide per day and calculating peak number
of tide per day is essential for flood risk assessment.
To identify and calculate the tidal daily peaks, the research carry out analyze chain
data of tide at the Phu An measurement station on Sai Gon River with time interval is
hourly. The method to define tidal peak is comparison value of tide level at a time
point with before and after adjacent values (Mudelsee, 2010). If the value of tide level
is more than before and after adjacent values, the value is peak and otherwise the value
is not. The chain data is analyzed continuously time by time for whole the period of
time (1980-1999).
The next step is computation of number of the tide peaks in the value chain. Method of
determining number of the appearance of the tide peaks is based on the set of the tide
peaks. Then a processing of count from the set of tide peaks will be done to determine
a number of appearances for each of tide peak value.
To process the tasks, the research develops a program in the Freemat programming
language (Sourceforge.net, 2012) to analyze and identify the tide peaks. The result of
the tide peak and frequency is shown the table 3.4.
4.4. Calculating climate data at the future time point
Calculating tide level at a station under climate change at the future time point is based
on three elements (as shown in equation 3.1): high tide at the reference time, rising sea
level at the time point and interval average tide level increment at that time point (dhi).
To determine the value of dhi is complicated because this task needs support of many
software and data to analyze the harmonic astronomical cycles. However, there is a
research with title “Study to build an evaluable model of climate change impacts to
Chapter 3. Data and database
Tran Thong Nhat 28
natural, human and social economy in Ho Chi Minh City” (Phung & Working Project
Team, 2011) that determined the experimental values of dhi in Ho Chi Minh City, as
shown in table 3.3.
Ht = Hc + dhct + dhi Equ. 3.1
Where:
Ht: tide level at the forecast time
Hc: tide level in the referenced time
dhct: sea level rising at the forecast time
dhi: interval average tide level increment at the forecast time
Tab. 3.4: Tide height and frequency in 2030 with daily tide level peaks
Scenarios
Scenarios
Scenarios
Value
B1
(cm)
B2
(cm)
A1FI
(cm)
Fre
Value
B1
(cm)
B2
(cm)
A1FI
(cm)
Fre
Value
B1
(cm)
B2
(cm)
A1FI
(cm)
Fre
101
140
143
144
190
114
153
156
157
84
127
166
169
170
19
102
141
144
145
154
115
154
157
158
87
128
167
170
171
17
103
142
145
146
185
116
155
158
159
78
129
168
171
172
10
104
143
146
147
178
117
156
159
160
72
130
169
172
173
13
105
144
147
148
205
118
157
160
161
52
131
170
173
174
10
106
145
148
149
180
119
158
161
162
53
132
171
174
175
7
107
146
149
150
187
120
159
162
163
44
133
172
175
176
6
108
147
150
151
151
121
160
163
164
45
134
173
176
177
4
109
148
151
152
153
122
161
164
165
45
135
174
177
178
5
110
149
152
153
125
123
162
165
166
36
136
175
178
179
1
111
150
153
154
125
124
163
166
167
38
137
176
179
180
1
112
151
154
155
109
125
164
167
168
28
139
178
181
182
1
113
152
155
156
106
126
165
168
169
23
142
181
184
185
1
The data in the table 3.4 shows that the peaks of tide level in 2030 on SLR of the
emission scenarios in Ho Chi Minh City are 181cm with B1, 184cm with B2 and
185cm with A1FI. They are not so much different. Table 3.4 is a calculation of tide
height and frequency in 2030 with daily tide level peaks.
Tab. 3.5: Frequencies of daily sea level peaks over 1.5m in three emission scenarios
and average times per month at year 2030
Scenarios AF/month
B1 5
B2 7
A1FI 8
Chapter 3. Data and database
Tran Thong Nhat 29
In the table 3.5 the frequency of tide peaks is more than current average tide level
1.5m on the scenarios is very much. The result of the frequency is shown in the table
3.5 This means with the current flooded areas at the tide level 1.5m will be inundated
more than from 5 to 8 times per month matching to the scenarios. This information is a
warning to the residents who are living there because of flood impact of their life
activities.
Chapter 4. Building Flood Model and Flooding Maps
Tran Thong Nhat 30
Chapter 4. Building Flood Model and Flooding
Maps
1. Selecting a suitable flood model for the research
1.1. Build criteria of selection
The construction of evaluation criteria is to be able to choose the most appropriate
model for flooding context and data in Ho Chi Minh City of this study. These criteria
are an attachment between goals of the study, the flooding context and the available
data in the Ho Chi Minh City. Therefore the criteria will be integrated and expressed
the following requirements:
Research outcomes: Outcomes of the model must be calculated for whole
of the city.
Available data on flooding study in Ho Chi Minh City: At least the flood
model determines the flooded areas with sea level rise.
Abilities of flood model software: to be able to determine the flooded area,
flooding depth, flooding duration, and flooding frequency.
Complexity of the model software on the operation and learning it: the
model software is the most simple as possible.
Cost of software: the least fee is priority.
1.2. Analysis and selection the most suitable flood model
As mentioned in the flood model review of chapter 2, the flood models are classified
two groups: non used hydraulic model (Horritt & Bates, 2001; Nhat, 2011; Nhat &
Loi, 2010; Priestnall et al., 2000; Townsend & Foster, 2002) and used hydraulic model
(Aronica et al., 1998b; Chaudhry, 2008; Cunge, 1975; Dac, 2005; DHI, 2007a; Dung,
2008; Nhan et al., 2009; Nien, 1996; NSWDOC-MHL, 2006; Vorogushyn et al., 2010;
Wilson et al., 2006). Base on the criteria of selection a suitable flood model, the
Chapter 4. Building Flood Model and Flooding Maps
Tran Thong Nhat 31
research outcome covers whole of the Ho Chi Minh City but availability of input data
for hydraulic model is not completed so that flood models of the second group is not
suitable.
In the first group, there are two approaches for build flood model that are the planar
surface and statistical. The second approach requires a similar study area to Ho Chi
Minh City with relationship between flooded area and discharge but in the reality there
is not any region on over the world be able to satisfy these conditions. Therefore the
first approach called planar surface is the most suitable flood model to implement for
the research.
The planar surface approach has many advantages when it is implemented GIS
environment. This reasons due to GIS functions:
Very fast and accurate for modeling terrain surface with digital terrain
model (DTM)
Interpolate values for the others values accurately and efficiently
Simulate ground features more detailed so that the terrain surface is the
most approximate with reality
Tide records, one of input data are integrated GIS easily
Computing the flood characteristics such as depth, duration and frequency
conveniently
Results from the approach are suitable for flood risk assessments of the
next tasks
And if this approach is selected, there is not more the cost for software
2. Interpolating roads elevations
Interpolating roads elevations is based on the discrete elevation points inside of the
roads (Nhat, 2012). That is to make the roads with continuous along road height so
that the roads can be barriers to protect low land preventing flooding. Basically the
process is carried out based on the elevation interpolation of along a road with known
height information of the start and end points of a line (ESRI, 2011). From that
Chapter 4. Building Flood Model and Flooding Maps
Tran Thong Nhat 32
principle, the road elevation interpolation of polygons will be converted to that of
interpolation of line and then use interpolated road line to build a terrain model in TIN
format (Abdul-Rahman & Pilouk, 2008; Gold, 2005; Wilson & Gallant, 2000; Zhou,
Lees and Tang, 2008) before all the points of each the road polygons are computed.
Steps of the procedure are as shown in figure 4.1.
The first step is selecting elevation of the points inside road polygons then converting
road polygons to road center polylines. It is accuracy to split lines, each point is used
only once for the nearest road with it. Consequently, the discrete elevation points must
be snapped to road center polylines before split is carried out. The distance for using in
the snap should be the maximum width of the roads. In the study case the maximum
width is 50m.
Fig. 4.1: Flow chart of the interpolation procedure
Chapter 4. Building Flood Model and Flooding Maps
Tran Thong Nhat 33
After split has done, start and end points of the road center polylines will be extracted
and then assigned height values to them. There are two types of the start and end
points of the road center polylines. The first type is the coincided points with discrete
elevation points at the split position. The second one is the start and end points that
existed before splitting. With the first case, their height values are same as the discrete
elevation points at the split positions.
n
ii
n
ii
i
k
l
l
z
z
1
1
1 Equ. 4. 1
Where:
n: number of the road lines connected to the end point k
zk: elevation of the end point k
zi: elevation of the road line i
li: the length of the road line i
With the second, one more step must be done that is elevation interpolation for them
from the lines assigned elevation and connected the start and end points that need
elevation information. The elevation interpolation of these points will be calculated
considerably with the inversion distance weight (Gold, 2005; Longley, Goodchild and
Maguire, 2005; Sheimy, Valeo and Habib, 2005) based on length of the road lines
connected with the points. If the end point called k is common of n road lines and each
of the road lines has length li (i = 1…n). The elevation of the end point zk is calculated
as shown in the equation 4.1.
The next step is attaching height values from the start and end points to attributes of
the each of road center polylines. And after the each of the road center polylines
contains height values, the height interpolation procedure for all vertices of the
polylines is conducted. The method to do this task is linear interpolation (Loi, Dinh
and Nhat, 2008; Longley et al., 2005) with distance weight to the start and end points
of the polylines. Result of the interpolation is road center polylines in three dimensions
(3D).
And then is using the road center polylines 3D combine with the discrete elevation
points to build a TIN (Abdul-Rahman & Pilouk, 2008; Zhou et al., 2008) for
Chapter 4. Building Flood Model and Flooding Maps
Tran Thong Nhat 34
interpolating the road polygons. In this step the interpolation method is the nearest
neighbor with sample distance 25m. That this will make the heterogeneity of the
vertexes of the road center polylines and road polygons will be reduced and increase
the high accuracy of the road polygons. Final step will get the road polygons in 3D.
3. Buildings height interpolation
Nowadays, to determine height of the ground objects there are approaches to conduct
this task. However, these approaches require a lot of resources of technology and cost.
With the latest technology the first one that should be mentioned for getting elevation
of ground objects with high accuracy need to be listed is LIDAR (Cobby, Mason and
Davenport, 2001; El-Omari & Moselhi, 2008; Madhavan, Wang, Tanahashi, Hirayu,
Niwa, Yamamoto, Tachibana and Sasagawa, 2006; Oude-Elberink & Vosselman,
2011; Pu, Rutzinger, Vosselman and S., 2011; Yang, Fang and Li, 2013; Yoon,
Sagong, Lee and Lee, 2009). And one more technology is applied common almost the
countries for producing cartography is stereo aerial photo (Ahmadabadian, Robson,
Boehm, Shortis, Wenzel and Fritsch, 2013; Altmaier & Kany, 2002; Baltsavias, 1999;
Barnea & Filin, 2013; Gabet, Giraudon and Renouard, 1997; Pollefeys, Koch,
Vergauwen and Van-Gool, 2000; Zebedin, Klaus, Gruber-Geymayer and Karner,
2006). The final, oldest and best accuracy is geodesy (Wahr, 1996). And some latest
decades, a new technology that complements for geodesy for surveying the ground
locations of the objects is GPS (El-Rabbany, 2002; Grewal, Weill and Andrews, 2007;
Samama, 2008). With the technologies the vertical information of the ground objects is
collected to the accuracy depended on application requirements. However because of
limitation of the resources, this research can not use these approaches to get the
vertical information of the ground objects. To apply only available resources, the
research develops and builds a new approach to derive the vertical information that is
based on spatial relationship of elevation between ground objects to each other.
To determine an interpolation method to derive base height of the buildings, the first
task should be highly considered that is the building objects relationship with other
ground objects that have already height information. To do the task, the analysis of
building characteristic of construction in the study area is applied. Here there are able
to divide two types of building. The first is built in clusters and the second is discrete.
Most of the cluster buildings are usually constructed in urban zone with roads in front
Chapter 4. Building Flood Model and Flooding Maps
Tran Thong Nhat 35
of them. About the discrete buildings are usually located in rural areas and constructed
on the productive land.
For cluster buildings, their characteristic of base elevation is related to base height of
roads in front of the buildings. In these buildings, there are two types of spatial
relationship with the roads. The first type touches to a road and the second does not.
With the first type, base elevation of the buildings is normally higher a difference than
the road surface height. The value of the difference does not equal to whole the
buildings but an average different value is chosen for this research based on the
construction forum in Ho Chi Minh City (SF, 2007). The average different value is 30
cm above road surface height. The second type is not touched with the roads but they
are touched with buildings of the first type. Therefore their base elevation will be
interpolated from buildings elevation of the first type. The process is propagated
gradually with increasing distant values from buildings that is the closest the roads to
further ones. The values of searching radius to define spatial relationship between
buildings had base elevation and buildings not had base elevation are also changed
gradually from low to high that appears because is not all buildings touched with
another. The process is loops to add the base elevation of buildings and the highest
searching radius threshold is 20m. The threshold is an average road width of the new
developing urban clusters but there have not been updated road data. The loops will be
implemented the first time with searching radius is 0m and then there is not any
building in the searching radius then radius distance will be increased to 1m. And the
process will be iterated similarly to searching radius reaches to 20m.
With the discrete buildings in the rural area, the building foundation height is
interpolated ground height and plus a difference between building ground floor and
land surface. In the Ho Chi Minh City, the buildings in the rural area are usually
constructed higher natural ground surface around 0.4m – 1m (SF, 2007).
In general, building foundation height formula is shown in the equation 4.2
Zh = Zref + dZ Equ. 4.2
In that Zref: the referent height. In the cluster buildings case, Zref is the height of the
closest street, and the discrete one Zref is ground elevation at the place where the
building is located.