FLOOD VULNERABILITY ASSESSMENT OF DOWNSTREAM AREA IN THACH HAN RIVER BASIN, QUANG TRI PROVINCE. 1 Đang Đinh Kha, Tran Ngoc Anh and Nguyen Thanh Son

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1 FLOOD VULNERABILITY ASSESSMENT OF DOWNSTREAM AREA IN THACH HAN RIVER BASIN, QUANG TRI PROVINCE 1 Đang Đinh Kha, Tran Ngoc Anh and Nguyen Thanh Son Faculty of Hydro-Meteorology and Oceanography, Hanoi University of Science, Vietnam National University, Hanoi In the past few decades, flood analysis mainly focused on physical characteristics of flood (such as flood depth, flood extent ) without socio-economic vulnerable assessment. In recent years, 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. Base on flood hazard assessment (flood extent, peak velocity, flood duration) using hydrodynamic modelling - MIKE FLOOD, combining with landuse map and resistant capability of local communities, this study established the vulnerable flood map in downstream of Thach Han river basin, Quang Tri province. This result provides a scientific and practical basis, an useful tool for managers, policymakers in integrated flood management. Besides, local residents will also be able to perform damage-reducing measures in the study area. Keywords: Flood vulnerability, flood hazard, MIKE FLOOD, Quang Tri. 1 Correspondence author: dangkha.net@gmail.com 1. Introduction The natural disasters such as catastrophic flood, drought, earthquake, tsunami are happening more frequently over the world causing vast damage of the human society. Among them, flooding was responsible for two-thirds of these affected and caused over one-third of the total estimated economic damage (Pilon, 2003). The assessment of flood damage is not only based on the flood risk but also the interaction between flood hazards with other human activities. Any changes in contemporary society such as population increase, economic development, urbanization, deforestation, expansion of residential areas, increased labor mobility, population ageing make society more vulnerable to natural hazards (Takeuchi, 2006). Without effective flood risk management, the scale of the impacts of flood disasters on people, property, local industry and economics will increase (NFRAG, 2008). In the past few decades, flood analysis mostly focused on physical dimensions of flooding (water depth, flood extent, etc.) and on the direct damages of the event in economic terms. That was the natural nature of the flood in the context of topography, landuse, etc therefore the former approach has not yet integrated the socio-economic activities. Hence the next development of flood risk management should be to assess the vulnerability of community to flood disaster with the multi-disciplinary approach.

2 There are several concepts and definitions of vulnerability in literature. Overviews of them could be found in Leon (2006), Adger (2006), Fuchs (2009) or Samuels et al. (2009). Trinh et al (2010) study the flood risk as a summation of hazard and vulnerability of which, vulnerability was a function of landuse and population density. This approach bases only on the value density of each cell in study domain therefore implies that the vulnerability of communities with similar economic conditions are the same. Dang et al (2010) tried to include the factors for social issue such as risk perception, spiritual value, income of the community beside the other economic factors while Birkmann (2006) mentioned to institutional dimension. Lugeri et al (2010) defined vulnerability of the assets under flood threat as by mean of depth-damage function for each landuse class. The above approaches basically used the economic aspects to estimate the vulnerability and did not take into account the coping capacity of the community such as awareness and risk perception, preparedness, measures for flood protection etc which had very important impacts in total damage of given flood events. Conner (2007) did an effort to include the state of structural and non-structural countermeasure when estimating the flood vulnerability index that implying the coping capacity of the community. Sheuer et al (2010) put forward when determines flood vulnerability as an integration of probability, impact (damage) and coping capacity. These studies have some advances but mainly focus on the community itself while not have any reflection of the exposure of that community to flood therefore the vulnerability of riparian communities to flood might be equal to those of communities living in the highland regions. Since 2006, Villagran de Leon has proposed the relation between vulnerability, exposure, susceptibility and coping capacity as: while guideline of UNESCO-IHE Institute for Ware Education ( shows another type of relation: In practical situation, it rather difficult to assess the susceptibility, resilience and coping capacity separately for the low-income communities, therefore those aspects might be combined into coping capacity, then the vulnerability would be estimated as:

3 and can be defined by the characteristics of the system that describe its potential to be harmed (Messner and Meyer, 2006). And this approach was applied to investigate the vulnerability of downstream area in Thach Han river system, Vietnam. 2. Study area Thach Han river system is the largest river system in Quang Tri province with catchment area is 2.660km2 occupied 56% total provincial area. Thach Han river originates in mountainous area in Dakrong district, next to the border with Thua Thien Hue province flowing into the Eastern Sea (Fig. 1). Downstream region of Thach Han river basin is an active region with concentration of residents, towns, historic spots and other socio-economic activities but is also the region most prone to flood from Thach Han river causing a huge damage (Long et al, 2010) especially in 2010 flood event. Fig 1: Location of study area 3. Development of vulnerability map A vulnerability map gives the precise location of sites where people, the natural environment or property are at risk due to a potentially catastrophic event that could result in death, injury, pollution or other destruction (Edwards, 2007). As a result, vulnerability map represents the information about the impacts of flood risks on the exposed elements. These maps used to be created using GIS tools, landuse map and some mathematic models to predict the potential risk (hazard) for a certain region. There are several studies on the flood hazards in this study region, among that a comprehensive simulation and inundation maps were conducted by Anh (2011). These inundation maps were then put on top of landuse map provided by Department

4 of Natural Resource and Environment (DONRE), Quang Tri province to determine the exposure of cells together with field survey to estimate the coping capacity. The conceptual framework is summarized as in Fig 2. Fig 2: Conceptual framework for flood vulnerability assessment Table 1: Relative weights of flood hazard indicator Indicator Flood depth Flood duration Flood velocity Weight (m) Weight (days) Weight (m/s) Weight > > > In the study by Anh (2011), the Mike models (Mike NAM, Mike Flood) were applied with digital elevation model (DEM) to produce series of inundation maps correspondence to catastrophic floods and scenarios. The layers of flood depth, peak velocity and flooding duration of 1% event (Fig. 3a 3c) were selected to establish the flood danger map (Fig. 3d) using overlapping method with the indicators (Tab. 1) proposed by Dang et al (2010). Base on the landuse map collected from DONRE (Fig 4), the soil groups were assigned the increasing values from [0-1] as for fallow, forestry land, farmland, rural residential land, urban residential land and public land. This map was put over the

5 flood danger map to determine the flood exposure map. Exposure map here is interpreted as the values that are present at the location where floods can occur. The level of exposure again was ranked into 5 levels from very low to very high and depicted in Fig. 5. Fig 3a: Flood depth map Fig 3b: Flood duration map Fig 3c: Flood velocity map Fig 3d: Flood danger map Coping capacities refer to the means by which people use resources before, during or after the disaster to cope with its adverse consequences (Leon, 2006). In order to quantitatively estimate the coping capacity of the system and communities, several field surveys were carried out in study area in combination with socioeconomic statistical data analysis. The surveys conducted in beginning of 2011 June

6 in areas most prone to flood, focusing on: local people perception of flood risk, early flood warning system, measures of flood protection and mitigation, recover ability of communities after the flood, the support from local government and social organizations Those results from questionnaires were then classified and marked into level of coping from very low to very high, then assigned to communities as communes (Fig. 6). Fig 4: Landuse map Fig 5: Exposure map Fig 6: Coping capacity map Fig 7: Vulnerability map

7 Exposure Level A flood vulnerability matrix is developed from the exposure level and coping capacity level. Flood vulnerability scale is created by overlaying levels of exposure and coping capacity (very low, low, medium, high and very high) (Tab. 2) then showed in Fig. 7. Table 2: Designed vulnerability levels Very high (5) Very high High (4) High Medium (3) Medium Low (2) Low Very low (1) Very low Very low (1) Low (2) Medium (3) High (4) Very high (5) Result Mark Level Coping capacity Level Vulnerability 4. Conclusion In this study, the flood vulnerability of the local community in downstream of Thach Han river basin were investigated using anew approach relating the flood vulnerability with exposure and coping capacity. Although the vulnerability map is still in qualitative form but is an effective tool for local authorities and communities in proposing the measure to reduce flood vulnerability. It also shows that in some area with high level of flood danger but their vulnerability is in medium level since they have longtime experience in coping with such disaster. And it confirms that, the role of community perception, early warning system, preparedness plan are very important in flood damage mitigation. 5. Acknowledgement This study was partially financially supported by VNU research project code: QGTD We would like to thank DONRE of Quang Tri province and Quang Tri provincial committee of flood and storm control (PCFSC) for their great supports in data collection process. 6. Reference 1. W. Neil Adger (2006), Vulnerability, Global Environmental Change Vol.16 p Tran Ngoc Anh (2011). Flood inundation mapping for downstream region of Thach Han and Ben Hai river, Quang Tri province. Vietnam National

8 University Journal of Science, Natural Sciences and Technology, Vol. 27 (1S),p. 1-8 (In Vietnamese). 3. Jorn Birkmann (2006). Approaches to flood vulnerability assessment, first expert meeting. Guidelines on flood maping, United Nations University. 4. Richard F. Conner. Flood vulnerability index. WWF4_FVI.pdf 5. Nguyen Mai Dang, Mukand S. Babel, Huynh T. Luong (2010), Evaluation of food risk paramerter in the Day River flood Diversion Area, Red River Delta, Vietnam. Nartural Hazards and Earth System Sciences, Springer, Accepted: 13 May DOI /s x. 6. Janet Edwards (2007). Handbook for Vulnerability Mapping. EU Asia ProEco project. 7. Messner F, Meyer V (2006). Flood damage, vulnerability and risk perception of challenges for food damage research. In: Schanze J, Zeman E, Marsalek J (eds) Flood risk management of hazards, vulnerability and mitigation measures. Springer, p Fuchs S (2009) Susceptibility versus resilience to mountain hazards in Austria of paradigms of vulnerability revisited. Nartural Hazards and Earth System Sciences, Vol.9 p Villagran de Leon JC (2006). Vulnerability conceptual and methodological review. Studies of the university: research, counsel, education, publication series of UNU-EHS4/2006. Bonn. 10. Vu Duc Long, Tran Ngoc Anh, Hoang Thai Binh và Dang Dinh Kha (2010). An introduction to flood forecast technology in Ben Hai and Thach Han river systems using MIKE 11 model. Vietnam National University Journal of Science, Natural Sciences and Technology, Vol. 26 (3S), p (in Vietnamese). 11. Nicola Lugeri, Zbigniew W. Kundzewicz, Elisabetta Genovese, Stefan Hochrainer, Maciej Radziejewski (2010). River flood risk and adaptation in Europe assessment of the present status. Mitig Adapt Strateg Glob Change Vol. 15 p Pilon PJ (ed) (2003). Guidelines for reducing flood losses, report. UN Department of Economic and Social Affairs (DESA). Inter-Agency Secretariat of the International Strategy for Disaster Reduction (UN/ ISDR), UN Economic and Social Commission for Asia and the pacific (UNESCAP), United States of America, National Oceanic and Atmospheric Administration (USA NOAA), World Meteorological Organization (WMO). Available via DIALOG: guidelines.pdf. Accessed 13 July 2011.

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