MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT 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 Luan van MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT 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 Hanoi, 2015 Luan van 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) Luan van 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 Luan van 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 Luan van Acknowledgements 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 and colleagues for their supports, encourages and advices The deepest thanks are expressed to my family members for their unconditional loves Luan van i TABLE OF CONTENTS CHAPTER - INTRODUCTION 1.1 Problem statement 1.2 Research objectives 1.3 Scope of study 1.4 Structure of thesis CHAPTER 2: LITERATURE REVIEW 2.1 Concepts of flood risk, hazard and vulnerability 2.2 Flood risk assessment 2.3 Previous studies in study area 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 Luan van ii 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 day of stations 77 Appendix 2: Roughness coefficient 81 Luan van iii LIST OF TABLES Table 3- 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- Database used for research 36 Table - 1: Result of frequency analysis of maximum daily rainfall 44 Table - 2: Value of design rainfall distribution of Ha Tinh, Ky Anh and Huong Khe stations during day corresponding to difference frequency (daily rainfall) 44 Table - 3: Sub-catchment of Rao Cai river basin and weighting factors of meteorological station 46 Table - 4: Parameters of UHM in MIKE RR model of Ke Go catchment 47 Table - 5: Different in peaks of observed and simulated discharge for calibration mode at Ke Go reservoir 48 Table - 6: Different in peaks of observed and simulated discharge in verification at Ke Go reservoir 48 Table - 7: Parameters of UHM - SCS for Rao Cai’s sub-catchments 50 Table - Runoff link of sub-catchments into river network in MIKE 11 model 53 Table - 9: Monitoring points for the calibrating and verifying hydraulic model 53 Table - 10: Results of flood simulation form 2nd Oct to 6th Oct, 2010 for calibration of MIKE 11 HD model 55 Table - 11: Results of flood simulation from 12 Oct to 18 Oct- 2010 57 Table - 12: Maximum water level corresponding to design and checking flood of Ke Go reservoir 57 Table - 13 Designed flooding hazard level scale for the downstream of the Ke Go reservoir 58 Table - 14 Flood hazard areas for flood event in 2010 60 Luan van iv Table - 15 Flood hazard areas corresponding to design and checking flood 62 Table - 16 Criteria of vulnerability map derived from population density for the downstream of the Ke Go reservoir 63 Table - 17 Criteria of vulnerability map derived from population density for the downstream of the Ke Go reservoir 65 Table - 18 Flood risk map for the downstream area of Ke Go catchment in flood in October, 2010 65 Table - 19 Statistic table of flood risk of different floods 68 Luan van 67 Flood risk map for design flood and checking flood with 200 year and 1000 year return period was built by intersecting hazard map and population density map to give an assumption how is risky if 0.1% and 0.5% flood occurs at the moment It does not mean that this map will depict exactly risk situation in future due to changing of population distribute land use, demographic density and other aspects as well Figure - 24 Flood risk map for 0.5% design flood Luan van 68 Figure - 25 Flood risk map for 0.1% checking flood Table - 19 Statistic table of flood risk of different floods Hazard zone Low Medium High Very high Total Design flood Area (km2) Percentage (%) 70.0 16.9% 164.4 39.6% 112.3 27.0% 68.5 16.5% 415.1 Checking flood Area (km2) Percentage (%) 64.4 14.1% 178.9 39.3% 123.5 27.1% 88.9 19.5% 455.7 Following Table - 19 shows risk areas, at four different levels correspond to design and checking flood of Ke Go reservoir Overall, the total risk area of checking flood case is higher than design flood case because flow of the former is higher than last one Medium and high risk areas are nearly total affected area with above 70% In both case, percentage of affected medium and high area were equal with 39 % and 27% respectively Only having change in low area and very high area Luan van 69 The statistical results of table 5-15, figure 5-17 and figure 5-18 show that the flooding depth in downstream area of Ke Go reservoir is quite severe Because this is an important area, there is a need to prepare some effective measures to minimize damages to the Ha Tinh city and surrounding area To flood risk management, we can use structural and non-structural measures The structural measures can design dykes or build levees along Rao Cai and Gia Hoi rivers At the present, a number of measures are applied all over the world to ensure safety for particularly important areas The nonstructural measures are structure elevation or structure relocation by moving structure in low land to high land Beside, awareness increase of resident about flood control and mitigation solution is very important in flood risk management Luan van 70 CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS 6.1 Conclusions The Rao Cai is one of the largest rivers in Ha Tinh province In recent years, floods have been increasing not only frequency but also intensity and affect to all aspects of lives Climate change, improper management of natural resources, inadequate awareness on flood risk, etc., response for the question ―Why flood become increasingly serious?‖ To minimize negative impacts of flood on local people, it is necessary to make an efficient flood risk management Flood risk assessment based on flood modeling has an important contribution to this progress To assess flood risk, in this study, the MIKE package including MIKE UHM, MIKE 11 HD and MIKE 11 GIS, was used to simulate the previous flood events in 2010 and other floods as 0.5% and 0.1% The main objective of this study is to develop inundation maps corresponding to the floods as mention above That is the foundation to assess the flood risk by overlapping vulnerability and hazard layer To assess risk of the flood events, the following conclusions could be depicted as elements of research procedure: + Main reasons and causes of flood in study area are affected by heavy rainfall with high intensity and more frequency Those are impact of climate change + Digital Elevation Model (DEM), which represents the floodplain’s surface, is the input information for simulating and estimating the flooding extend and depth The DEM in the research was derived from interpolation of elevation spots and contour lines of different spatial data such as, contour maps with variable scales, transportation system maps, dyke system maps, and hydrological maps The DEM was built from topography with scale of 1:10,000 + For the, in order to simulate the lateral inflow of sub-catchments in downstream of Ke Go reservoir, the regionalization method was applied by using the model parameters of Ke Go catchment; Luan van 71 + The combination of flooding depth (hazard factor) and population density (vulnerability factor) with the weighing factors for both of them, flood risk assessment was done and mapped 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 management 6.2 Recommendations Due to limited time and knowledge, this thesis have focused on simple hazard and vulnerability such as flooding depth and population density, to have valuable result we have to considering to other aspect such as: velocity, during flooded (hazard factor) and vulnerability about agriculture, infrastructure (road, railway…) Besides to improve result flood simulation, inundation map need good data, in study area are almost data from local supply (water level at upstream, downstream, release flow of Ke Go reservoir, which can be reedited for an another reason (political, …) From this study, the following issues are strongly recommended: - Technical issues: Before using the recorded data of a station, it is necessary to firstly check the data for continuity and consistency - Research issues: flood risk assessment is difficult but necessary for flood risk management and the results of hazard and risk assessment should be represented to the local and regional decision makers Recommendations for future research: The results of flood modeling and flood characteristics can be improved if better resolution and quality DEM is used for flood simulation Research was based on the topography in 10,000 scales The usage of better resolution and quality DEM and considering infrastructure such as road, railway, and building or … using satellite image and classify image of past flood to improve quality of hydrodynamic model are topic for future research Besides, it is undeniable that awareness of resident about flood it is very important in flood control and mitigation and it is effect to result flood risk Luan van 72 The study of flood hazard should be more considering with others scenarios to obtain the higher results of risk assessment for the region in order to quantify the expected damage for different return periods Recommendations for the Local Administrative Authorities and local communities: It should be improved the risk perception of local community regarding to flood process and its hazardous effect on population and their property New hazard maps should be represented to the population and they should be informed about probable results According to of European Union, the risk maps should be rebuilt after years It should be prohibited to use dikes for cattle pasture Dikes should be built up to protect population along rivers Construction of small channels and rising vines with ground will decrease the water level on cultivated land and protect it from inundation Raising the awareness of people about flood, hazard and mitigation ways Luan van 73 REFERENCES Alkema, D (2007) Simulating floods: on the 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Environmental Hazards 7(2): 106-114 Thai, N C., Lan, P T H., Huan T N (2011) Study effects of dam breaking at Ke Go reservoir – Ha Tinh in downstream area Water Resources and Environment Journal, Thuy loi University, Vol 11, pp 18 - 25 Thong, L Q., (2014) Study on effect of wave to Ke Go emergency dam Master thesis of Thuyloi university, Vietnam Twigg, J (2004), Disaster risk reduction: Mitigation and Preparedness in development and emergency programming Humanitarian Practice Network London Kingdom Luan van 76 Tamar Tsamalashvili (2010) Flood risk assessment and mitigation measure for Rioni River, University of Twente; Tu, V T (2009) Flood inundation, damage and risk assessment in Hoang Long basin, Vietnam, AIT Dissertation, Asian Institute of Technology United States Department of Agriculture (USDA) (1986) Urban hydrology for small watersheds Technical Release 55 (TR-55) (Second Edition ed.) Natural Resources Conservation Service, Conservation Engineering Division USGS (2013) Satellite image of Ha Tinh area http://www.usgs.gov/pubprod/ USGS (2011) DEM of Ha Tinh area, http://www.usgs.gov/pubprod/http://gdex.cr.usgs.gov/gdex/ Vi, D N (2013) Nhìn lại trận lụt kinh hồng Việt Nam Retrieved January 2014 from http://vtc.vn/nhin-lai-8-tran-lut-kinh-hoang-tai-viet- nam.2.456814.htm Viet, T Q (2009) Flood risk assessment for the Thach Han river basin, Quang Tri province, Vietnam Cologne University of applied science Vietnam Water Resources Assistance Project (VWRAP) (2003) Feasibility study for modernization of Ke Go project, Ha Noi, Haskoning Vnexpress (2010) Miền Trung vật lộn với lũ 10 năm Retrieved January 2014 from http://vnexpress.net/tin-tuc/thoi-su/mien-trung-vat-lon-voi-lu-dunhat-10-nam-2896392.html Vnexpress (2013) The flooding in Oct, 2013 in central Vietnam Retrieved January 2014 from https://www.google.com/maps/d/u/0/viewer?mid=zGR_qj798D2c.kLUgSscZ XoJk&msa=0&iwloc=0004e8ea5f790918f950c Luan van 77 APPENDIX Appendix 1: Frequency curve of maximum rainfall during day of stations 1000 900 800 Rainfall (mm) 700 600 500 Actual 400 Design 300 200 100 1st 2nd 3th Time (day) Hyetograph of design rainfall of Ha Tinh stations corresponding to 1000 years return period 800 700 Rainfall (mm) 600 500 400 Actual 300 Design 200 100 1st 2nd 3th Time (day) Hyetograph of design rainfall of Ha Tinh stations corresponding to 200 years return period Luan van 78 800 700 Rainfall (mm) 600 500 400 Actual 300 Design 200 100 1st 2nd 3th Time (day) Hyetograph of design rainfall of Ky Anh stations corresponding to 1000 years return period 700 600 Rainfall (mm) 500 400 Actual 300 Design 200 100 1st 2nd 3th Time (day) Hyetograph of design rainfall of Ky Anh stations corresponding to 200 years return period Luan van 79 700 600 Rainfall (mm) 500 400 Actual 300 Design 200 100 1st 2nd 3th Time (day) Hyetograph of design rainfall of Huong Khe stations corresponding to 1000 years return period 600 Rainfall (mm) 500 400 300 Actual 200 Design 100 1st 2nd 3th Time (day) Hyetograph of design rainfall of Huong Khe stations corresponding to 200 years return period Luan van 80 FFC 2008 © Nghiem Tien Lam FREQUENCY CURVE OF MAXIMUM RAINFALL DURING DAY - HA TINH STATION 1130 Maximum rainfall during day TB=304.81, Cv=0.41, Cs=0.86 1030 Pearson Type III Distribution TB=304.81, Cv=0.43, Cs=0.89 930 830 Rainfall, X(mm) 730 630 530 430 330 230 130 30 0.01 0.1 10 20 30 40 50 60 70 80 90 99 99.9 Frequency, P(%) FFC 2008 © Nghiem Tien Lam 99.99 © FFC 2008 FREQUENCY CURVE OF MAXIMUM RAINFALL DURING DAY OF KY ANH 920 Ky Anh_Maximum rainfall during day TB=292.62, Cv=0.36, Cs=0.60 820 Frequency curve of maximum rainfall during day of Ky Anh TB=292.62, Cv=0.36, Cs=0.60 720 Rainfall (mm) 620 520 420 320 220 120 20 0.01 0.1 10 20 30 40 50 60 70 80 90 99 99.9 Frequency, P(%) FFC 2008 © Nghiem Tien Lam 99.99 © FFC 2008 FREQUENCY CURVE OF MAXIMUM RAINFALL DURING DAY OF HUONG KHE 790 740 maximum rainfall during day of Huong Khe TB=246.72, Cv=0.37, Cs=0.62 690 frequency curve TB=246.72, Cv=0.37, Cs=0.82 640 590 540 Rainfall (mm) 490 440 390 340 290 240 190 140 90 40 0.01 0.1 10 20 30 40 50 60 Frequency, P(%) Luan van 70 80 90 99 99.9 99.99 © FFC 2008 81 Appendix 2: Roughness coefficient River Chainage (m) Raocai Raocai 1382 Raocai 2676 Raocai 3593 Raocai 4558 Raocai 4638 Raocai 5588 Raocai 6576 Raocai 7951 Raocai 9651 Raocai 11438 Raocai 15969 Raocai 26702 Raocai 36140 Raocai 41238 Raocai 43098 Raocai 43210 GiaHoi GiaHoi 1010 GiaHoi 3006 GiaHoi 3061 GiaHoi 5429 GiaHoi 7888 GiaHoi 17624 GiaHoi 20869 GiaHoi 23294 GiaHoi 27864 GiaHoi 32229 GiaHoi 33131 GiaHoi 33210 Luan van Manning (n) 0.03 0.031 0.031 0.029 0.029 0.029 0.029 0.029 0.029 0.024 0.024 0.024 0.024 0.024 0.024 0.024 0.024 0.028 0.028 0.028 0.028 0.028 0.024 0.024 0.024 0.024 0.022 0.022 0.022 0.022 ...MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT THUY LOI UNIVERSITY Tran Ngoc Huan STUDY ON FLOOD RISK ASSESSMENT IN DOWNSTREAM AREA IN KE GO RESERVOIR, HA TINH. .. 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. .. of flooding in a specific area, flood hazard assessment should be done Flood hazard assessment depends on many parameters such as flooding depth, flooding duration, flood velocity, timing and