Thesis of master degree: Study on flood risk assessment in downstream area in Ke Go reservoir, Ha Tinh province

MINISTRY OE EDUCATION AND MINISTRY OF AGRICULTURE AND

TRAINING RURAL DEVELOPMENT

THUYLOI UNIVERSITY

Reservoir.shp lood in October 2010

STUDY ON FLOOD RISK ASSESSMENT IN DOWNSTREAM

AREA OF KE GO RESERVOIR, HA TINH PROVINCE

Tran Ngoc Huan

Hanoi, 2015

MINISTRY OF EDUCATION AND MINISTRY OF AGRICULTURE AND

TRAINING RURAL DEVELOPMENT

Tran Ngoc Huan

STUDY ON FLOOD RISK ASSESSMENT IN DOWNSTREAM

AREA IN KE GO RESERVOIR, HA TINH PROVINCE

Major: Intergrated Water Resources Management

THESIS OF MASTER DEGREE

Supervisor: Asso Prof Dr Pham Thi Huong Lan

This research is done for a partial fulfilment of the requirement for Master of Science Degree at Thuyloi University

This Master Programme is supported by NICHE — VNM 106 Project

Hanoi, 2015

Flooding causes economic, social and environmental damages and life loss This fact increases the great attention on flooding by government, and science in many countries around the world As a country located in the tropical climate region, Vietnam has been facing various water related disasters since ancient time, particularly in central parts of Vietnam where featured by steep topography In recent years, Rao Cai river basin in Ha Tinh province is frequently flooded due to climate change impact, rapid infrastructure and urbanization growth This problem caused serious damages to human life, properties, and social — economic

development activities

Flood risk management is a new concept based on a proactive approach which

recently becomes a robust tool for reducing flood damage Main contents of flood risk management are flood risk assessment and flood preventive measures or flood

preventive planning Flood risk assessment is key part in flood risk management.

Flood risk assessment is a function of three main variables: flood hazards, vulnerability, and coping capacity Understanding of flood hazards, vulnerability, and coping capacity is the vital step for efficiency of flood risk assessment Flood risk management strategies have not been developed for Rao Cai river basin for

many years and there is no spatial planning approach for regional development.

This research aims at flood risk assessment for Rao Cai river basin based on the new concept of flood risk management mentioned above An incorporated

hydrological modeling approach for hazard assessment for Rao Cai river basin has

been adopted in this research The research objective divides into three parts: (1) Identification of flooding and potential reasons based on available natural, social and economic data; (2) The second part involved flood simulation and inundation mapping of events with chosen return periods using a MIKE package model (MIKE UHM, MIKE 11, and MIKE 11 GIS).The model was calibrated and verified based

on the data series in October, 2010 A flood from 24 to 6" October 2010 was usedto calibrate the model Another flood in October, 2010 (from 14” to 19", October)

was used to verify the model Results of calibration and verification were fit to measured data The flood simulations for selected return periods were generated for 200 and 1000 years corresponding to frequency of design and checking flood of Ke Go reservoir (3) Flood risk assessment is combined effect of flood depth (hazard factor) and population density (vulnerability factor) by weighing factors for both of them As for the results, the research revealed that flood risk assessment is helpful tool for flood risk management.

Flood risk maps were produced for the flood of 1000 year and 200 year return

period The level of hazard and risk were determined for each community in Cam

Xuyen, Thach Ha and Ha Tinh city These maps can be used for flood risk

management and mitigation planning for Ha Tinh province in general, Rao Cai riverbasin in particular.

Thereby certify that the work which is being presented in this thesis entitled, “Study

on flood risk assessment in downstream area in Ke Go reservoir, Ha Tinh

province” in partial fulfillment of the requirement for the award of the Master of Science in Integrated Water Resource Management, is an authentic record of my own work carried out under supervision of Asso Prof Dr Pham Thi Huong Lan The matter embodied in this thesis has not been submitted by me for the award of any other degree or diploma.

Date: February 15, 2015

Tran Ngoc Huan

I would like to express my sincere gratitude to my advisor Asso Prof Dr Pham Thi Huong Lan for her guidance, suggestion and inspiration.

I would also like to acknowledge Dr Vu Thanh Tu, Mr Duong Hai Thuan and Dr Bui Du Duong for their comments and suggestion.

I would like to thank the Hanoi University for Natural Resources and Environment, Ministry of Natural Resources and Environment, Vietnam and NICHE — VNM

106 Project for the award of a scholarship and also Hanoi Water Resources

University for giving me the opportunity for this special study.

I also wish to thank members of the master thesis committee consist of Prof.Dr Nguyen Quan Kim (chairman), Asso.Prof.Dr Mai Van Cong (examination), Asso.Prof.Dr Nguyen Mai Dang (examination), Dr Le Viet Son and Dr Dinh Thanh Mung for their comments, examination, and corrections.

Finally, I would like to express my special appreciation to my friends andcolleagues for their supports, encourages and advices The deepest thanks areexpressed to my family members for their unconditional loves.

2.1 Concepts of flood risk, hazard and vulnerabiÏIty «<< << £<ees+ 5

2.3 Previous Studies in Study AT€A - - 2c 111193119 1v vn HH kg rry 9

3.1 Physical Characteristics c1 3101113111891 1 911 11 11191 1H vn ng ng nếp 10

3.1.3 Hydro-meteorological characteristics cece eee eeeeeecesseeeeeeeeseeeseeeeees 12

E x00) 5 16 3.2.1 Rural area oo 17

3.3 Reservoir and current irrigation SS(€T ee 5 + + 1+ E*kEEserseeserrekre 18

3.3.1 Overview Of Ke Go T€S€TVOIT Ác vn HH ngư 18 3.3.2 Irrigation 0 ằ £Â£ẢA35 21

4.1.2 Method for estimating design hyetograph - - -«+s«ss++sessserssses 30

4.1.3 Method for developing design hydrograph on lateral flow in downstream

Ộaiiiiiiắảáấăắaẳ Ẽ 31

4.1.4 Method for simulation floods corresponding to various return period 31

4.2.1 Rainfall runoff model (MIKE - Unit hydrograph model) 32 4.2.2 Hydrodynamic model (MIKE 11 HD) eee eeeeeeeeeeeaee 33

4.2.3 Identification of inundation MAPS eeceeseeeteeesceeeteeeeeeeeeeeesneeeeeeees 34 4.3, Data USC mẽ - 35 4.3.1 Data COMeCtion ee eeseescssecerecssesseeseessecssesseessecsseseesseesseeaeseeeneesaes 35 4.3.2 Data anaÏS1S LH HH TH TH HH HH 36 CHAPTER 5: RESULTS AND DISSCUSIONS S11 40

5.1.2 Infrastructure impact nh ae 43 hy o0 43

5.2.1 Rainfall runoff mod€Ï1Tng - + s + 133119 E9 ESkkEeskesereserre 43 5.2.2 Flood Modeling ố ee 50

by i0 6n 58 5.3 Flood vulnerability ce eeecccsccessccesecsseeceseeeeeeeeaeceeeceseeeeaeeeeaeceseeeeseeeeeeesas 62 5.4 Flood risk in downstream area of the Ke Go T€S€TVOIT s52 65

CHAPTER 6: CONCLUSIONS AND RECOMMIENDATIONS 70

6.2 RecommenidafIOTNS - c1 93019111911 11910119 nh HH nh nh 71

REEERENCES co (G5 cọ HH 4 00 0000 08.060.060.0 000000 73

APPENDIYX Go 0 ee 76

Appendix 1: Frequency curve of maximum rainfall during | day of stations 77

LIST OF TABLES

‘Table 3- 1 Lists of meteorological stations 12 ‘Table 3- 2: The average of monthly rainfall at Ha Tinh station from 1975 - 2010 14 ‘Table 3- 3: Monthly discharge of Ke Go reservoir from 1957 - 2010, 1s ‘Table 3- 4: Population pattern 16 ‘Table 3- 5: Land use lụ ‘Table 3- 6: Technical parameters of reservoir 19 ‘Table 3- 7: Parameters of junction work items 19 ‘Table 3- 8: Technical parameters of Irrigation channels system 21 ‘Table 3- 9: Statistic of damages caused by rainfall and flood at Ha Tin city, Thách Ha and Cam Xuyen district occurred from 14 October to 19, October, 2010 24 Table 4- 1 Database used for research 36 ‘Table 5 - 1; Result of frequency analysis of maximum daily rainfall 44 ‘Table 5 - 2: Value of design rainfall distribution of Ha Tinh, Ky Anh and Huong Khe stations during 1 day corresponding to difference frequency (daily rainfall) 44

Table 5 - 3: Sub-catchment of Rao Cai river basin and weighting factors of meteorological station 46

‘Table 5 - 4: Parameters of UHM in MIKE RR model of Ke Go catchment AT ‘Table 5 - 5: Different in peaks of observed and simulated discharge for calibration mode at Ke Go reservoir 48 ‘Table 5 - 6: Different in peaks of observed and simulated discharge in verification at Ke Go reservoir 48 ‘Table 5 < 7: Parameters of UHM - SCS for Rao Cai's sub-catchments 50 ‘Table $ - 8 Runoff link of sub-catchments into river network in MIKE 11 model.S3 ‘Table 5 -9: Monitoring points for the calibrating and verifying hydraulic model

Table 5 - 10: Results of flood simulation form 2" Oct to 6" Oct, 2010 for

calibration of MIKE 11 HD model 35 ‘Table 5 - 11: Results of flood simulation from 12 Oct to 18 Oct- 2010 57 ‘Table 5 - 12: Maximum water level corresponding to design and checking flood of

Table 5 - 15 Flood hazard areas corresponding to design and checking flood 62 Table 5 - 16 Criteria of vulnerability map derived from population density for the downstream of the Ke GO reServOIr ccccccccsccseseceeesseceeesscecsseceeesseecesseeesessssesesseeess 63 Table 5 - 17 Criteria of vulnerability map derived from population density for the

Table 5 - 18 Flood risk map for the downstream area of Ke Go catchment in flood

LIST OF FIGURES

Figure 3- 1: Map of study aT€a - - c1 HH TH HH kg rh 10 Figure 3- 2: Topography of Rao Cai river basin in ASTER global DEM 11

Figure 3- 3: Hydro-meteorological station network of Rao Cai river basin 13 Figure 3- 4: The average of monthly rainfall at Ha Tinh station from 1975 - 2010.14 Figure 3- 5: Monthly discharge flow into Ke Go reservoir :ccessceeseeeteeeeeeeeeees 16 Figure 3- 6: The spillway of Ke Go Reservoir, there are two arc gates 19

Figure 3- 7: The Emergency spillway of Ke Go TeS€TVOIT - +55 << £++sc+sx2 19

Figure 3- 8: Flood at Ha Tinh city in October, 2010 0.0 cee eeeseesseeeteeeseeeseeeeeeeees 23 Figure 3- 9: Percentage of damages in terms of money for various categories

occurred from 14" to 19", October, 20 ÍŨ - - - Hs 25

Figure 3- 11: Inundation in the downstream of Ke Go reservoir in June 2TM 2013 27

Figure 4 - 1: Illustration of the research methodỌOgØ ««++<«£+se+ssee+s 29

Figure 4 - 2: Mass flow rate in and out of an elementary control volume 34

Figure 4 - 3: MIKE 11 GIS Input and Output eee - 5 5S 1+ sskersseeeseeres 35

Figure 4 - 5: Inflow of Ke Go reservoir in October, 2013 - eee eee eects 37

Figure 4 - 6: Water level at Phu and Hoi Bridge station in October, 2010 38 Figure 5 - 1: Annual rainfall change on the Rao Cai river basin from 1975 — 2005 41

Figure 5 - 2: Changing of maximum rainfall of Ha Tinh station 42

Figure 5 - 3: Inflow of Ke Go reservoir and actual rainfall 2013 - 43 Figure 5 - 4: Rao Cai watershed sub-basin schematizations and Thiessen polygon weighting computation of mean rainfall of sub-catchment in Rao Cai river basin 45

Figure 5 - 5: Parameters of UHM in MIKE RR model of Ke Go catchment 47

Figure 5 - 6: Observation and simulation of hourly discharge of Ke Go reservoir

Figure 5 - 7: Observed and simulated hourly discharge of Ke Go reservoir from 14Oct to 19 Oct — 2010 — Verification eee 20 G1 2311219 911911 TH ng 48Figure 5 - 8: Flood at Ke Go reservoir in 16 October 2013 -. -««++-<++ 49Figure 5 - 9: Hydraulic calculation network in downstream of Ke Go reservoir 51

Figure 5 - 10: Storage capacity of floodplain in downstream 52

Figure 5 - 11: Calculated and measured water level at Cau Phu (2" to 6" October, Figure 5 - 15 Some typical picture to determine flood hazard threshold 60 Figure 5 - 17 Flood hazard map of 0.5% design flood event 61 Figure 5 - 18 Flood hazard map of 0.1% design flood event 62

Figure 5 - 19: Frequency distribution of population of study area 63

Figure 5 - 20: Frequency distribution of population density of study area 63 Figure 5 - 21: Vulnerability map in Rao Cai river basin 6 Figure 5 - 22 Designed risk level for the downstream of the Ke Go roservoir 6Š Figure 5 - 23, Flood risk map for the downstream area of Ke Go river basin of flood in October, 2010 66 Figure 5 - 24 Flood risk map for 0.5% design flood 6 Figure 5 - 25 Flood risk map for 0.1% checking flood 68

LIST OF ARCONYM

Ha Tinh Committee for Flood and Strom prevention and Control and

HOPSCS and R

CCFSC | Central Committee for Flood and Storm Control UHM | Unit Hydrograph Model

RR Rainfall Runoft HD Hydrauie Dynamic

SCS Soil Conservation service

VHDIC | Vietnam Hydro-meteorological Data and Information Center DEM | Digital elevation model

CHAPTER 1 - INTRODUCTION

1.1 Problem statement

In recent years, the situation of flooding and tropical becomes more and more severe, especially in Vietnam's Central provinees With the rain increasing quickly both in quantity and intensity, many large floods as well as deforestation in the upstream appears Besides, there is also the impact of the socioeconomic development, such as the process of rapid urbanization, infrastructure construction (roads, channel systems), which are factors hindering the flow of water and increasing damage caused by floods Unsafe reservoirs contain a high risk According to the Steering Committee for Flood and Storm Control Central, in 2013, floods and typhoons have caused 264 deaths and 800 injured people, about 12,000 collapsed and damaged houses, and the loss of more than 300,000 ha of rice, 2 broken irrigation dams, etc, The estimated total material damage amounted to 000 billion dongs (2013), 16.000 billion dongs (2012) and 12.000 approximately

billion dongs (2011) (Hoai, 2013) It is undeniable that the effects of climate change have a significant impact on the weather in recent years and cause significant damage both to people and property,

‘The Ke Go reservoir, located on the Rao Cai river in Cam My commune, in the Cam Xuy n district of the Ha Tinh province, about 20 km from Ha Tinh city to the West, is selected as a case study The reservoir is located on one of the larger rivers of Ha Tinh province: the catchment area to the Ke Go hydrological station is

230 km? with the total length is 27 km The Rao Cai area to estuary is 892 km’,

including the whole Cam Xuyen distriet, Ha Tinh city and a part of Thách Ha province The Ke Go reservoir has the particularly important task to irrigate 20,896

ha of arable land of the two districts of Thách Ha and Cam Xuyen, to supply water

for Ha Tinh city and for industry, combining power generation, fish growth and flood control for the downstream This isthe largest irrigation headworks system of the central Vietnam and is constructed for a long time.

The flood risk research and assessment has particularly important implications for the prevention and mitigation of natural disaster Firstly, flood hazards as part of the management of flood risk can be understood as the probability that flood prone areas will be inundated for a given time period with a specific return period (Alkema, 2007), Flood modeling is a relatively new approach, which is used in many countries for flood hazard and risk assessment Flood hazard and risk based spatial planning must be applied to flood prone areas (Pender, 2007), Measures of flood control aimed at lowering the vulnerability of people and their property, also include a list of means, i river engineering works, such as dams, levees, embankments, and/or river training works, such as retention polders (Klijn, 3009) Traditionally, management on flood risk focuses on preventing floods by river training and dykes system There are several disadvantages to this approach, such as dyke break caused by erosion or overtopping of the embankment Nowadays alternative and more resilient management strategies are applied in many countries in the global (Bruija, 2005) The Decision Support Systems (DSS) are

supposed to be a robusttool for flood risk management; DSS is not only meant for

experts, as itis @ new trend to represent the final output of the experts’ research in er, for way to meet the decision makers’ skills and requests (Klin, 2009) Hows

many countries DSS is unfeasible, due to the lack of data and techniques as well as ‘experts, and the country of Vietnam is no exception.

Actually, there is Tittle research on flood risk assessment in Vietnam, for instance in the case of the Ke Go Catchment there has been only one study that has focused on the effects of flood scenarios to downstream areas without any detailed assessment information about the level of risk that can cause for people to have the

mitigation measures in place (Thai et al, 2011) The research of the topic “Study on

flood risk assessment in downstream area of Ke Go Reservoir ~ Ha Tinh province” will be a useful tool for decision-makers in view of spatial planning and future risk assessment for the region

1.2 Research objectives

General objective: Flood risk assessment in the downstream of the Ke Go reservoir, Ha Tinh province, to have measures in preventing and controlling damage due to floods for study area.

The specific objective of this research can be determined as:

~ Analyzing potential reasons cause flooding in the study area to have accurate estimation and suggestion for this research and local authority.

~ Understanding the flood apply for the study area.

isk assessment method to choose a suitable method

~ Generating flood risk maps of the downstream of the Ke Go reservoir based on hazard maps corresponding to flood scenarios and vulnerability maps to estimate risk level for each area, Based on local authority can determine where should emergency action being concentrated or having prepare plans and measures when flooding,

1.3 Scope of study

This study focuses on considering population density and flooding depth to assess flood risk in the downstream area of the Ke Go reservoir.

1.4, Structure of thesis

‘The thesis structure includes 6 chapters The brief explanation of those chapters is as followed:

Chapter 1 introduces problem statement of the research, the object of the research and scope of study

hazard and vulnerability, flood risk assessment methods and some previous researches relate to Chapter 2 reviews several studies about concept of flood ris

study area.

Chapter 3 reviews the physical characteristics as well as social and economic characteristics of the study area The chapter also indicates the Ke Go reservoir and current irrigation system and flooding situation in recent years.

Chapter 4, the general framework of this research will be mentioned including both methods and theory Besides, the data collected during the research was summarized and analyzed.

Chapter 5 shows results corresponds the research objective about potential reasons

caused flooding and flood risk assessment based flood hazard and vulnerability

factors on the maps MIKE package model setup, calibration and validation are described

Chapter 6 focuses on the main findings and recommendations for further studies and local authority

CHAPTER 2: LITERATURE REVIEW

2.1 Concepts of flood risk, hazard and vulnerability

Flood risk

In the series of document “Living with Risk”, the International Strategy for Disaster Reduction (ISDR) of United Nation describes risk is “the probability of harmful consequences, or expected losses, resulting from interactions between natural or human-induced hazards and vulnerable conditions” (UN, 2004) This definition emphasizes relevant vulnerabilities through that risk can be also defined as a function of hazard and vulnerability Risk is defined:

Risk = Hazard x Vulnerability

Emphasis to risk retention, Asian Disaster Reduction Center (ADRC, 2005) ‘mentioned flood risk as a function of probability of loss and loss:

Ris probability of loss x loss

Focus on the resilience capacity of society against to risk, ADRC in the report of “The role of local institutions in reducing vulnerability to recurrent natural disasters and in sustainable livelihoods development “developed a new term of risk generally,

particularly flood which is illustrated in the function below:

Hazard x vulnerability Risk =

Capacity of societal system

Generally, the term of flood risk is variable according to the purpose of particular research In this research, flood risk is understood as being a function of a probability of a specific flood event and vulnerability of societal systems.

© Flood hazard

According to Baas S, et al (2008) and United Nations (2004) hazard can be

srmined as “potentially damaging physical event, phenomenon or human activity

that may cause the loss of life or injury, property damage, social and economic disruption or environmental degradation” Hazards have different origins: natural

(geological, hydro-meteorological) or can be provoked by humane (environmental

degradation and technological hazards) Bach hazard is characterized by its location, frequency and probability of occurrence in a specific region within a specific time and magnitude The investigation of assessment of hazard is associated to study of physical aspects and phenomenon of the given hazard through collection and analysis of historical records, this process is defined as assessment of hazard (Geohazards, 2009) Aspects of exposure and vulnerability are not considered in the hazard term, since it focuses on the event or physical situation (Tamar, 2010),

Flood hazard is a function of: flood magnitude, depth of water and velocities, water rise rat duration, evacuation problems, and population size at risk, land use, flood awareness and warning time (CSIRO, 2000) Flood hazard

categories reflect the flood behavior across the floodplain and can be represented by

four degrees of hazard: low, medium, high and so high Above mentioned hazard

categories are subdivided as qualitative flood hazard categories and is very useful

for local communities and decision makers, Also quantitative manner of representation of flood hazard are very important for mitigation planning purpose as well as for risk assessment because they allow quantitative determination of the frequency and magnitude of flood (Tamar, 2010)

+ Flood vulnerability

Vulnerability is an essential part of risk study and it refers to the susceptibility of

2006) Vulnerability can be understood as the degree to which people are susceptible to los damage, suffering and death in the event of a dis ster

Vulnerability also encompasses the idea of response and coping, since it is

determined by the potential of a community to react and withstand a disaster (Trinh, 2009),

Vulnerability is also se as the extent to which a person, group or socioeconomic structure is likely to be affected by a hazard (Twigg, 2004) The author moreover

ts that the observable part of vulnerability is the emphasis on physical or ‘material aspects (Trinh, 2009),

Flood analysis mainly focused on physical characteristics of flood (such as flooding depth, flooding extent ) without socio-economic vulnerable assessment Tu and “Trình (2009) indicated a new approach in developing flood map is to assess the vulnerability to flood of community and economic sectors in flood-affected area

that isan effective tool for integrated flood management Economic flood damage

evaluation can estimate for tangible and intangible damages such as building, products, and health damage Damage level correspond to subjects is scientific basis to determine subject has high, medium or low vulnerability to have suitable ‘measure, In general, flooding depth is the most characteristic in damage estimation,

Damage magnitude strongly depends on the flooding depth, damage functions are developed as depth-damage curve relationship (Tu, 2009)

2.2 Flood risk assessment

Floodplain analysis and assessment of flood risk are important steps in management of flood risk to identify appropriate mitigation activities for reducing

flood damages to human health, economie activity

AS a result of hazard assessment any special aspect of given hazard can be ‘mapped, this provide information on hazard distribution in spatial dimension (Bell, 1999) The flood hazard maps provide users with information addressing to spatial and temporal probabilities of the floods (FEMA, 2010) Flood hazard mapping defined as one of the main steps in management of flood risk (Plate, 2002) and can be considered to be the important tool for different issues: local planning, risk assessment as they provide the information about past or possible hazards to local communities and decision makers Maps of flood hazard illustrate the intensity of flood situation and probability of occurrence The most important indicator for

assessment of flood hazard are flooding depth and flow velocity as they represent the most dangerous aspects for population and or property (Merz et al., 2007)

Nowadays, the using flood modeling is necessary in the water resources planning, ‘management in general, and flood risk assessment in particular,

Following the magnitude frequeney analyses the next step was the selection of an appropriate model for simulation of the flood process After the potential flood hazatd is identified for the given region, the most important is (o understand and identify the characteristics of hazard For thi ue the newly developed modeling approach can be used Output parameters from modeling should give users the correct characterizations of the flood processes and not only the flooding extend (like in traditional methodology for flood hazard mapping), but also for flooding depth, water flow velocity, warning time, duration (Alkema, 2007).

Flood modeling for flood hazard assessment and risk assessment became the

robust tool on different stages of flood management (Plate, 2002) It is necessary 10

choose the proper approach to simulate flood processes among available tools and software,

Now, one and two dimension modeling approaches are wide used for ‘modeling of rural flow and urban flow The equitation of Saint-Venant is widely used for ID flow modeling This (1D) approach was used to develop software like MIKE 11 (DHI, 2011), SOBEK and HEC-RAS (Hec-Ras, 2013) This approach is suitable to estimate possible flooding processes using river discharge within rural flow Specifically for modeling of river morphology MIKE 2IC, MIKE 21FM-Sediment transport (ST) modeling has been developed For flow modeling in complex terrain the best approach is 2D modeling and requires of representation of tenain topography in terms of DEM (Alkema, 2007) While the 2D flood modeling can be defined as best solution for simulation of inundation processes, combined 1D and 2D modeling is widely used in order to decrease the computation time and get realistic overflow water propagation parameters, Such approach is used by SOBEK,

ID2D SOBEK model has been developed by WL/Delit Hydraulics in The Netherlands (Deltares, 2014).

MIKE package is commonly used in the external world and Vietnam to solve water resources issues including flood risk management MIKE package not only solve well water -sources problem but also have a friendly user interface, So I will choose this model in my research,

2.3, Previous studies in study area

Ke Go reservoir is the largest reservoir in Ha Tỉnh province The reservoir

has a total capacity of 425 million mổ, active capacity of 345 million m’ and catchment area of 223 kmẺ, The reservoir has task to irigate for 20,897 ha of agricultural land, supply water for domestic consumption and industry 1.6m and

combine power generating in the irrigation period, Ke Go reservoir was built in during 1976-1988 Over the past 30 years working, the reservoir has well promoted their effects, turning arid areas of Cam Xuyen, Thach Ha districts to become the fertile plains, lush fields and gardens all year round In this area, there is litle research projects on dam safety and flood hazard, During the 2005-2006 a survey to evaluate the dam safety, found the expressions of degradation of main works as a n, 2010) In water repellent downstream of the main dam and auxiliary dam (Chỉ

2010, Thuy Loi University has done research on dam safety of Ke Go reservoir considering flooding depth in the downstream area of the Ke Go reservoir corresponding to flood scenarios to have scientific basis for damage prevention and mitigation of local authority (Thai et al, 2011) However research results only identify inundation area without any extended research on risk assessment including human health, economic act es, environment or cultural heritage

CHAPTER 3: DESCRIPTION OF STUDY AREA.

3.1 Physical characteristics 3.1.1 Location of this basin

“The Rao Cai river basin located in Ha Tinh province, center parts of Vietnam ‘The Rao Cai including to Thách Ha District, Ha Tinh City and Cam Xuyen District

with geographic coordinates as:

- Latitude 18° 19" + 18°37" - Longitude 185° 54° = 185° 99°

‘The Ke Go reservoir was built on the Rao Cai river in Cam My Commune, Cam Xuyen Distriet, and that is one of the main rivers of Ha Tinh province, This

far 20 km away from Ha Tinh City toward to the west

“The whole Rao Cai river basin is 892 Km, In the northern side is Can Lọc and

Loc Ha district, in the Southern side is Ky Anh district, in the Eastern side is South China Sea and the Western side is Huong Khe district

3.1.2 Topography conditions

3.1.2.1 In the upstream of Ke Go reservoir

‘The highest point of the catchment reaches to 1,222 m above sea level The average

slope of catchment to at Ke Go station is 0.23% In the left side of catchment is high

land and opposite side is middle land (VWRAP, 2003).

Source: USGS, 2011

Figure 3- 2: Topography of Rao Cai river basin in ASTER global DEM

4.1.2.2 In the downstream of Ke Go reservoir

In the downstream area is from Ke Go reservoir to a coastal sand bank, which runs from Cua Sot to Cua Nhuong The North near Tra Son Mountain and Cau Giang River, the East is near South of China and the South is near Rac River The profile gradually decreases from West to East, being quite flat with elevation reaching from 2.5 m to 10.0 m, the average altitude is 4.0 m (VWRAP, 2003) The average slope of downstream area is 0.22%

3.1.3, Hydro-meteorological characteristics

3.1.3.1 Hydro-meteorological station network

‘4 Meteorological station In the study area, the

factors, and Ke Go, Ho Do, Linh Cam, Trung Luong, Dai Loc, Song Rae and La

Khe measure rainfall (VWRAP, 2003) Besides, there are some meteorological is only HaTinh meteorological station measures whole

station as Huong Khe and Ky Anh, are near the study are, that is also considered for

better understanding of average rainfall in the study area

Table 3- I Lists of meteorological stations

No} Name Factor ÍNg | Name Factormeasuring measuring

1 [Reo x 6 [BaLae x 2 [HoDe x 7 [Rae River x 3 [inh Cam x 3 Jka Khe x 4 [Trang Lương x 9 [Hong Khe XTUV š [Ha Tinh XIUV [10 | Ry Anh XT Where: X: Rainfall V: Wind speed

T: Temperature U: Humidity

b, The hydrology

Rao Cai river system is one of the biggest ones in Ha Tinh province, which is

divided into Phu (Rao Cai) and Gia Hoi river in downstream area Besides, there are some stream flows into main rivers such as Rac river, Cau Nay river as shown in Figure 3.1

On the Rao Cai river basin, there are three hydrological stations including Ke Go, Thank Dong and Cua Nhuong The Ke Go station was built on the upstream of Ke Go reservoir, is unique station measure discharge from (1937 ~ 1942) and

(1957 ~ 1974) After the Ke Go reservoir constructed, the Ke Go station closed.

Period of activity of Ke Go is 27 year from (1973 ~ 1942 and 1957 ~ 1974) Thach Dong and Cua Nhuong stations located on Phu and Gia Hoi rivers respectively to measure water level in estuary area

In addition, in the downstream of Ke Go reservoir has two hydrological stations which measures water level, that to monitoring the release of Ke Go reservoir during flood season from 2006 to present Cau Phu station located on Phu river and Cau Ho located on Rao Cai river

Figure 3- 3: Hydro-meteorological station network of Rao Cai river basin

3.1.3.2 Climate characteristics

The Rao Cai river basin belong tropical monsoon climate area, The climate characteristics of basin have both characters of the North and East of Truong Son mountains due to location, physical features Therefore, climate regime is divided clearly to two seasons: rainy and dry season (Thong, 2014) The wet season is from August to November and the dry season is from December to July of next year

The annual average temperature is 23.7C and the monthly average temperature ranges from 17.7°C to 29.6°C according to statistics from 1960 ~ 2010

in Ha Tinh meteorological station (Ha Tinh, 2014)

‘The average annual rainfall of Rao Cai river basin is estimated 2657 mm, based on daily rainfall data of Ha Tinh station from 1975-2010 The rainfall in wet season is 1809 mm with total accounting for 70% of annual rainfall The biggest amount of monthly rainfall is October with 29% of annual rainfall, The rainfall in dry season is about 30% of annual rainfall

‘The average of monthly rainfall at Ha Tinh station

Figure 3- 4: The average of monthly rainfall at Ha Tinh station from 1975 - 2010

Table 3- 2: The average of monthly rainfall at Ha Tinh station from 1975 - 2010

Month | 1 | m | mm IV|V[VI VH VH ix | X | xt |xm

Average [100 | 61 61 77 |169|146 92 258 483 772 | 296 | 145

% đã [2% | 2% | 3% | 6% | 5% 3% 10% 18% 29% | 11% | 5M

Annually, in Rao Cai river basin, there are four to five rain event which has total rainfall from 100 to 150 mm per day, and one to to rains has total rainfall over 200 mm per day The period of heavy rainfall is normally from I to 3 days sometime up nh could be up 657 mm (1992) and to 5 days The maximum daily rainfall at Ha 1

reached to 888 mm (2010),

3.1.3.3 Hydrological characteristics

Hydrological regime have regulated rainfall pattern in a year Flow regime divides clearly 2 seasons in a year ~flood season and drought season

“The period of flood season from September and November, which often happens cold air activities, tropical low pressure and convergence with storms lead to heavy rain cause flooding Amount of flow in wet season occupies 60 65 % amount of flow in year October is the biggest monthly flow about 28 % amount of flow in year

Dry season extends 9 months from December to August of next year, but (otal of mount flow in this time only equal 39% of amount of flow in year

ebruary, March and April only 2 ~ 3 % of annual Minimum monthly flows include

In the carly summer months V and VI tropical depressions India -Cambodian development to the east to the territory of Laos and Thailand, the Southeast has the air inlet from the sea at the same time on both the inlet from the bay of Bengal to create equator along the meridian and rain chronic primary cause flood at the end of May in the basin (Thong, 2014)

According to Thong (2014) result of monthly discharge came to Ke Go reservoir are shown below:

Table 3- 3: Monthly discharge of Ke Go reservoir from 1957 - 2010

Month | IX | X XI xu] 1 [im | im) Ww) Vv VI|VH

Qim's) | 267 | 45.6 260 14.6) 8.17/ 5.06 401 336 6.18 6.21] 4.84

VIII Average

931 133

Monthly discharge flow into Ke Go reservoir from 1957-2010

Figure 3- 5: Monthly discharge flow into Ke Go reservoir

In the Figure 3- 5, discharge in wet season is round 25 ~ 45 mÌ/, which is higher

than 5 to 10 times than dry season,

3.2, Social and economic characteristies

[Irrigated area (ha) 438 +54 451 | Water shortage (ha) 38 38 8 € | Non-irigated area (ha) AI Bu 34

Ke Go reservoir on the Rao Cai River belongs to Cam My Commune, Cam Xuyen District, Ha Tinh Province, 20 km away from Ha Tỉnh City to the West ‘The project started to be constructed on 26/3/1976, stated to store water since February, 1978 The work was completed and formally put into operation and exploitation in 1983 The reservoir is responsible for confining water for 21,136 ha area of farmland of two districts of Cam Xuyen and Thách Ha, supplying water for the industry combined with generating power, fish-farming and preventing flood for the downstream It has no longer served for the power generation since 1988 (Thong, 2014).

The inrigation work of Ke Go reservoir includes major items such as the

main dam, three auxiliary dams, flood discharge spillway, intake culvert, hydropower plant and canal system, ete with basic structure, dimensions as

follows (Thong, 2014),

Figure 3- 6: The spillway of Ke Go

Reservoir, thete are two ate gates Go reservoir

Table 3- 6: Technical parameters of reservoir

No Parameters Unit value

1 Basin area Km? 223

2 Grade of headwork ụ 3 Irrigation water supply frequency % 15 4 Design flood frequency % 05 5 Checking flood frequency % 04 6 Emergency Flood frequency PME T7 Type of reservoir regulation Year 8 | Normal water level m 325 9 _ Design flood water level m

10 —_ Checking flood water level m 35.39

11 | Emergency Flood water level (PMF) m 3545 Source: VWRAP, 2003

‘Table 3-7: Parameters of junction work items

No Parameters Unit value

Main dam

‘Type of dam: soil dam

2 Length m 1,004

No Parameters Unit value

3 Elevation of soil dam crest m 35.60 Elevation of wave retaining wall crest 36601 Protected by grade M200 RC panels m 5x5x0.2 TM Auxiliary dam

1 Auxiliary dam 1

~ Type of dam: soil dam

~ Elevation of wave retaining wall crest m 36.10 2 Auxiliary dam 2

~ Type of dam: soil dam

~ Elevation of wave retaining wall crest m 36.10

3 | Auxiliary dam 3

‘Type of dam: soil dam

~ Elevation of wave retaining wall crest m 36.10 IIL Flood discharge spillway

1 Culvert two- side spillway

= Form: Deep discharge, regulated by valve gates

Dimensions m 2x3x4.5

= Elevation m +26.5

~ Design discharge mils 320

2 | Doc Mieu spillway

Form: surface discharge, regulated by valve

No Parameters value

~ Filled soil elevation m 35

‘The main channel system, channel grade 1, and channel grade 2 are mainly filled with soil

Afler finished, the work proved its responsibility for supplying water for the agriculture, industry, people's livelihood and mitigating flood for the lowland.

After 20 years of exploitation, the work is increasingly downgraded Now, the work is being repaired and upgraded at junction work items and channel system under the framework of Vietnam Water Resources Assistance Project (VWRAP, 2003),

‘Table 3- 8: Technical parameters of Irrigation channels system

No Parameters Unit value

1 Main channel

= Channel length Km 169 ~ Top channel discharge mils 298

~Botlom elevation m | TI3:A47 2 | Channel grade 1

= Quanity 12 channels

Total lenth Km 76 3 Chamnel grade 2 & 3: reinforcing some

necessary sections, dredging the section of

No Parameters Unit value

“Total lenath Km 776

- Discharge mis | 003+015

Source: VWRAP, 2003

3.4, Flooding situation in downstream area

One of the causes of flooding was widespread heavy rainfall associated with the

‘weather patterns such as hurricanes, tropical depression, the northeast monsoon In

flood plain area in which Cam Xuyen, Thach Ha district and Ha Tink city usually occur in July to October, lead to serious problem to environment, social-economy and resident

According to statistics data of flooding, in recent years the situation of flooding and inundation become more frequent and more serious, especially in 2010, 2012, 2013 3.4.1 The flooding events occurred in 2010

In the flood 2010, due to heavy rainfall in downstream combine with release flow of Ke Go reservoir cause inundation in downstream There are two flooded in October.

In the first event, total rainfall of Ha Tinh station form 29 September to 5 October is

603.5 mm and release from Ke Go reservoir is 490 m'/s caused flooded in all most area in downstream with flooding depth ranged from about 1.0 ~ 1.8 m, some place reached to 1.5 m In other event, this is historical flood in Rao Ca river basin in

during past 100 year happened form 14 October to 19" October Heavy rainfall

oecued not only in Rai Cai catchment, but also in whole province, with total rain fall was 1,126 mm, Ke Go 959 mm while annual rainfall of Ha Tinh is 2624 mm ‘This cause water level in reservoirs strongly inerease so they had to release into the

downstream, Ke Go released about 600m 4, This event caused flooded in large area,

flooding depth around 2.0 ~ 3.0 m

Source: Vy, 2013 Figure 3- 8: Flood at Ha Tình city in October, 2010

According to the report of Ha Tinh committee for Flood and storm prevention and

control and search and rescue, Ha Tinh City, Cam Xuyen and Thach Ha district:

Flood event from 29” September to 5" October: The water depth in the flooded area

varies from 0.5 (0 2 meter There were 4 communes of Thách Ha district and 5 communes of Cam Xuyen district The road in Cam Xuyen and the way to Ke Go reservoir were flooded deep about I to 1.8 meters, The number of dead is 3 persons “The total of tangible damages is estimated around 270 million VND (13000 USD),

In flood event from 14" October to 19" October, this was historical flood within

100 recent year The water depth is from I to 2.5 meters, somewhere flooded from 3

to 5 meters within 7 to 10 days The number of flooded commune was 58 which

15/27 communes in Cam Xuyen district, 27/37 communes in Thách Ha and 16/16 communes in Ha Tinh city and 23 communes were flooded deep There were 126 schools and about 600 ha of agriculture land under water According to report of

HCESCS, the total tangible damages is estimated around 1281.6 billion VND (60.3 Million USD) in 2011

Table 3- 9: Statistic of damages caused by rainfall and flood at Ha Tinh city, Thach Ha and Cam Xuyen district occurred from 14 October to 19, October, 2010

(Source: HCESCS, 2011)

m ‘Type of damages Unit Ha (Thách Cam | Total

Tinh Hạ Xuyencity

0) @ 8 8 184 |0 NG | Resident

NGO2 | - Dead Person | 2 ?

NGOS | - Hurt Person 7 4 11

NGÔ | - Flooded are Commine | 1ề 21 15 | 58

NGOS | - Deeply flooded area Commune 4 12 7 23

NGO | - Flooded household Household | 15700 | 25,180 18520 | 58570

> Damage to properties :

NGI ung Properties Per Household 59,370

NN Agriculture, foresry and fishery

NNOT | Flooded summer paddy ha 0 0 NN02 | - Flooded com ha o | s 116

NN03 | - Flood sweet potato ha 200 205 405

GD_| EdcaUon - Training

'6D0i | - Flooded xhools Building | 8 8Ð 40) 188

MT | Fresh water and rual sanitation

MTOT | -Poluted Nooded srea ha 3200 | 400 | 3000 | 11.600 MTO2 | -Number of household shortage | Household 25532 | 46,000 | 71.532

Figure 3- 9: Percentage of damages in terms of money for various categories

occurred from 1410 19°, October, 2010

From the Figure 3 ~9, the percentage of damages of each categories range from 2%

{© 60% In which, the percentage of resident damages is the biggest accounting for

60.0% including damages about death, flooded houschold and their properties Agriculture, forestry and aquaculture and Education and Training damage are

approximately to 10% The percentage of clinic, fresh water and rural sanitary and

irrigation system and embankment damage are about 2 to 6% The percentage of

damages of remain group include industry, construction are not much in the toal

damage In brief, the percentage of damages of resident, agriculture and school are

the biggest with its figure surpassing the rests, so thesis will focus on these sectors

{o assess in next part

3.4.2 The flooding events occurred in 2012

Due to impact of Northern-East monsoon, at downstream of Ke Go reservoir in general and HaTinh city in particular happened heavey rainfall from 7 PM of 23 November to 12 AM of 24 Septerber caused deep flooded to main roads Figure 3- 10: Flood at Ha Tinh city in October, 2012

3.4.3 The flooding events occurred in 2013.

In recently, due to tropical storm No.L1 - 2013, heave rainfall occurred only within 2 hours in Rao Cai river basin and but caused flooded city center area affected to

resident's activity, their property and agriculture production There are some

inundation images on the Rao Cai river basin in different period.