Study on flood risk assessment in downstream area in ke go reservoir, ha tinh province

THUYLOI UNIVERSITY STUDY ON FLOOD RISK ASSESSMENT IN DOWNSTREAM AREA OF KE GO RESERVOIR, HA TINH PROVINCE Tran Ngoc Huan MSc Thesis on Intergrated Water Resources Management Hanoi, 20

THUYLOI UNIVERSITY

STUDY ON FLOOD RISK ASSESSMENT IN DOWNSTREAM AREA OF KE GO RESERVOIR, HA TINH PROVINCE

Tran Ngoc Huan

MSc Thesis on Intergrated Water Resources Management

Hanoi, 2015

THUY LOI UNIVERSITY

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

Abstract

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 2nd to 6th, October 2010 was used

to calibrate the model Another flood in October, 2010 (from 14th to 19th, 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 river basin in particular

Declaration

I hereby 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

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

TABLE OF CONTENTS

CHAPTER 1 - INTRODUCTION 1

1.1 Problem statement 1

1.2 Research objectives 3

1.3 Scope of study 3

1.4 Structure of thesis 3

CHAPTER 2: LITERATURE REVIEW 5

2.1 Concepts of flood risk, hazard and vulnerability 5

2.2 Flood risk assessment 7

2.3 Previous studies in study area 9

CHAPTER 3: DESCRIPTION OF STUDY AREA 10

3.1 Physical characteristics 10

3.1.1 Location of this basin 10

3.1.2 Topography conditions 11

3.1.3 Hydro-meteorological characteristics 12

3.2 Social and economic characteristics 16

3.2.1 Population 16

3.2.1 Rural area 17

3.3 Reservoir and current irrigation system 18

3.3.1 Overview of Ke Go reservoir 18

3.3.2 Irrigation system 21

3.4 Flooding situation in downstream area 22

3.4.1 The flooding events occurred in 2010 22

3.4.2 The flooding events occurred in 2012 25

3.4.3 The flooding events occurred in 2013 26

CHAPTER 4: METHODOLOGY AND DATA USED 28

4.1 General framework 28

4.1.1 Methods to flood risk assessment 29

4.1.2 Method for estimating design hyetograph 30

4.1.3 Method for developing design hydrograph on lateral flow in downstream

31

4.1.4 Method for simulation floods corresponding to various return period 31

4.1.5 Method for inundation mapping 31

4.2 Governing equation in MIKE package 31

4.2.1 Rainfall runoff model (MIKE - Unit hydrograph model) 32

4.2.2 Hydrodynamic model (MIKE 11 HD) 33

4.2.3 Identification of inundation maps 34

4.3 Data used 35

4.3.1 Data collection 35

4.3.2 Data analysis 36

CHAPTER 5: RESULTS AND DISSCUSIONS 40

5.1 The reasons cause the flooding in downstream area 40

5.1.1 Climate change impacts 40

5.1.2 Infrastructure impacts 43

5.2 Flood hazard 43

5.2.1 Rainfall runoff modeling 43

5.2.2 Flood modeling 50

5.2.3 Flood hazard maps 58

5.3 Flood vulnerability 62

5.4 Flood risk in downstream area of the Ke Go reservoir 65

CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS 70

6.1 Conclusions 70

6.2 Recommendations 71

REFERENCES 73

APPENDIX 76

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

Appendix 2: Roughness coefficient 81

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 15

Table 3- 4: Population pattern 16

Table 3- 5: Land use 17

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 Tinh city, Thach 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 47

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 5 - 8 Runoff link of sub-catchments into river network in MIKE 11 model 53 Table 5 - 9: Monitoring points for the calibrating and verifying hydraulic model 53

Table 5 - 10: Results of flood simulation form 2nd Oct to 6th Oct, 2010 for calibration of MIKE 11 HD model 55

Table 5 - 11: Results of flood simulation from 12Oct to 18 Oct- 2010 57

Table 5 - 12: Maximum water level corresponding to design and checking flood of Ke Go reservoir 57

Table 5 - 13 Designed flooding hazard level scale for the downstream of the Ke Go reservoir 58

Table 5 - 14 Flood hazard areas for flood event in 2010 60

Table 5 - 15 Flood hazard areas corresponding to design and checking flood 62Table 5 - 16 Criteria of vulnerability map derived from population density for the downstream of the Ke Go reservoir 63Table 5 - 17 Criteria of vulnerability map derived from population density for the downstream of the Ke Go reservoir 65Table 5 - 18 Flood risk map for the downstream area of Ke Go catchment in flood

in October, 2010 65Table 5 - 19 Statistic table of flood risk of different floods 68

LIST OF FIGURES

Figure 3- 1: Map of study area 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 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 reservoir 19

Figure 3- 8: Flood at Ha Tinh city in October, 2010 23

Figure 3- 9: Percentage of damages in terms of money for various categories occurred from 14th to 19th, October, 2010 25

Figure 3- 10: Flood at Ha Tinh city in October, 2012 26

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

Figure 3- 12: Flood in Ha Tinh city in October, 2013 27

Figure 4 - 1: Illustration of the research methodology 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 35

Figure 4 - 4: Inflow of Ke Go reservoir in October, 2010 37

Figure 4 - 5: Inflow of Ke Go reservoir in October, 2013 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 from 2 Oct to 6 Oct – 2010 for calibration model 47

Figure 5 - 7: Observed and simulated hourly discharge of Ke Go reservoir from 14 Oct to 19 Oct – 2010 – Verification 48

Figure 5 - 8: Flood at Ke Go reservoir in 16 October 2013 49

Figure 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 (2nd to 6th October, 2010) 54

Figure 5 - 12: Calculated and measured water level at Cau Ho (2nd to 6th October, 2010) 55

Figure 5 - 13: Calculated water level and measured water level at Cau Phu(12 Oct to 18 Oct- 2010) 56

Figure 5 - 14: Calculated water level and measured water level at Hoi Bridge (12 Oct to 18 Oct- 2010) 56

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 64

Figure 5 - 22 Designed risk level for the downstream of the Ke Go reservoir 65

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 67

Figure 5 - 25 Flood risk map for 0.1% checking flood 68

LIST OF ARCONYM

HCFSCS Ha Tinh Committee for Flood and Strom prevention and Control and

Search and Rescue

CCFSC Central Committee for Flood and Storm Control

UHM Unit Hydrograph Model

RR Rainfall Runoff

HD Hydraulic 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 provinces 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 approximately 25,000 billion dongs (2013), 16.000 billion dongs (2012) and 12.000 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 Xuyen 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 km2 with the total length is 27 km The Rao Cai area to estuary is 892 km2, including the whole Cam Xuyen district, Ha Tinh city and a part of Thach Ha province The Ke Go reservoir has the particularly important task to irrigate 20,896

ha of arable land of the two districts of Thach 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 is the 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.e river engineering works, such as dams, levees, embankments, and/or river training works, such as retention polders (Klijn, 2009) 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 (Bruijn, 2005) The Decision Support Systems (DSS) are supposed to be a robust tool for flood risk management; DSS is not only meant for experts, as it is a new trend to represent the final output of the experts’ research in way to meet the decision makers’ skills and requests (Klijn, 2009) However, for

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 little 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 risk assessment method to choose a suitable method apply for the study area

- 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

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

Risk = probability of loss × 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:

Risk =

Hazard x vulnerability

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 determined 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) Each 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 rate, 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 people, communities or regions to natural or technological hazards (Kumpulainen 2006) Vulnerability can be understood as the degree to which people are susceptible to loss, damage, suffering and death in the event of a disaster 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 seen as the extent to which a person, group or socioeconomic structure is likely to be affected by a hazard (Twigg, 2004) The author moreover insists 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

Trinh (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 is an 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, economic 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 is 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 frequency analyses the next step was the selection of an appropriate model for simulation of the flood process After the potential flood hazard is identified for the given region, the most important is to understand and identify the characteristics of hazard For this issue 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 to 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 1D 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 21C, 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 terrain 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

1D-2D SOBEK model has been developed by WL/Delft 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 resources 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 Tinh province The reservoir has a total capacity of 425 million m3, active capacity of 345 million m3 and catchment area of 223 km2 The reservoir has task to irrigate for 20,897 ha of agricultural land, supply water for domestic consumption and industry 1.6m3/s 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 little 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 water repellent downstream of the main dam and auxiliary dam (Chien, 2010) In

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 activities, 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 Thach Ha District, Ha Tinh City and Cam Xuyen District with geographic coordinates as:

- Latitude: 18o19’ ÷ 18o 37’

- Longitude: 185o54’ ÷ 185o99’

The Ke Go reservoir was built on the Rao Cai river in Cam My Commune, Cam Xuyen District, and that is one of the main rivers of Ha Tinh province This work is as far 20 km away from Ha Tinh City toward to the west

Figure 3- 1: Map of study area

CAN LOC DIS

LOC HA DIS

HUONG KHE DIS

BOC NGUYEN RESERVOIR

THUONG TUY RESERVOIR

KY ANH DIS

The whole Rao Cai river basin is 892 Km2 In the northern side is Can Loc 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

Sot river mouth

Boc Nguyen Reservoir

Ke Go Reservoir

3.1.2.2 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

Table 3- 1 Lists of meteorological stations

Factor measuring

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 a 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 23.70C and the monthly average temperature ranges from 17.70C to 29.60C 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

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

Rainfall (mm)

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 two rains has total rainfall over 200

mm per day The period of heavy rainfall is normally from 1 to 3 days sometime up

to 5 days The maximum daily rainfall at Ha Tinh could be up 657 mm (1992) and reached to 888 mm (2010)

– 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 total of mount flow in this time only equal 39% of amount of flow in year Minimum monthly flows include February, March and April only 2 – 3 % of annual

flow

In the early 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 XII I II III IV V VI VII VIII Average

Q (m3/s) 26.7 45.6 26.0 14.6 8.17 5.06 4.01 3.36 6.18 6.21 4.84 9.31 13.3

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

In the Figure 3- 5, discharge in wet season is round 25 – 45 m3/s, which is higher than 5 to 10 times than dry season

3.2 Social and economic characteristics

3.2.1 Population

Table 3- 4: Population pattern

No Item District Total

Sources: VWRAP, 2003

3.2.1 Rural area

Table 3- 5: Land use

No Item District/City Total

ha area of farmland of two districts of Cam Xuyen and Thach 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 irrigation 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, etc with basic structure, dimensions as follows (Thong, 2014)

Figure 3- 6: The spillway of Ke Go

Reservoir, there are two arc gates

Figure 3- 7: The Emergency spillway of Ke

Go reservoir Table 3- 6: Technical parameters of reservoir

Source: VWRAP, 2003 Table 3- 7: Parameters of junction work items

I Main dam

1 Type of dam: soil dam

No Parameters Unit value

II 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 III Flood discharge spillway

1 Culvert two- side spillway

- Form: Deep discharge, regulated by valve

gates

2 Doc Mieu spillway

- Form: surface discharge, regulated by valve

No Parameters Unit value

After 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

3 Channel grade 2 & 3: reinforcing some

necessary sections, dredging the section of

No Parameters Unit value

channel

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 Tinh 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 m3/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 Cai river basin in during past 100 year happened form 14 October to 19th October Heavy rainfall occurred 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 increase so they had to release into the downstream, Ke Go released about 600m3/s This event caused flooded in large area, flooding depth around 2.0 – 3.0 m

Source: Vy, 2013 Figure 3- 8: Flood at Ha Tinh 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 29th September to 5th October: The water depth in the flooded area varies from 0.5 to 2 meter There were 4 communes of Thach 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 1 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 14th October to 19th October, this was historical flood within

100 recent year The water depth is from 1 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 Thach 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

HCFSCS, 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

Thach

Ha

Cam Xuyen

NG04 - Flooded area Commune 16 27 15 58

NG05 - Deeply flooded area Commune 4 12 7 23

NG08 - Flooded household Household 15,700 25,150 18,520 59,370

NN01 - Flooded summer paddy ha 90 90

NN02 - Flooded corn ha 60 55 115

NN03 - Flood sweet potato ha 200 205 405

(Source: HCFSCS, 2011) Figure 3- 9: Percentage of damages in terms of money for various categories

occurred from 14th to 19th, October, 2010 From the Figure 3 - 9, the percentage of damages of each categories range from 2%

to 60% In which, the percentage of resident damages is the biggest accounting for 60.0% including damages about death, flooded household 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 total 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

to assess in next part

3.4.2 The flooding events occurred in 2012

Transportation, 5.2% Other, 0.7%

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

(a): Flooded on Nguyen Du street

(b): Flooded into resident house in

Ha Tinh City

Source: Hieu, 2012 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.11 - 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

Source: USGS, 2013

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

Source: Vnexpress, 2013 Figure 3- 12: Flood in Ha Tinh city in October, 2013