Integrated flood risk assessment for the day river flood diversion area in the Red River, Vietnam | |
| Author | Nguyen Mai Dang |
| Call Number | AIT Diss. no.WM-09-01 |
| Subject(s) | Floods--Risk assessment--Vietnam--Red River Flood control--Simulation methods--Vietnam--Red River |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Water Engineering and Management, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. WM-09-01 |
| Abstract | Flood disasters are increasing worldwide due to numerous reasons such as global changes (land use and climate), urbanization, industrialization, and socioeconomic development. The Red River Delta (RRD) in Vietnam is one of the most flood-prone areas in the world and also densely populated. The RRD suffers increased risk due to frequent floods and the rise in sea level, especially in the Day River Flood Diversion Area (DRFDA) and Hanoi city. Other factors causing increased flood vulnerability in the DRFDA include high population growth, increased infrastructure development, and social and environmental implications. An integrated approach to flood risk assessment is, therefore, essential for the DRFDA to improve flood management in the Red River. The study developed here provides a methodology to define the flood risk parameters and quantify weights to them. A review of the literature on this subject, in conjunction with expert analysis, has been employed in this dissertation to define and select flood risk parameters, while a household survey has investigated flood risk perception and flood preparedness and mitigation in the DRFDA. The Analytical Hierarchy Process (AHP) method has been applied to convert qualitative scores (which were rated by experts) to the quantitative value of weights to each parameter. The data processing has been done using the SPSS. The research recognizes that integrated flood risk is a product of both multi-indicator flood hazard and comprehensive flood vulnerability. Flood hazard is assessed using depth, duration, and velocity indicators. Flood vulnerability is analyzed from economic, social, and environmental points of view. Here, economic susceptibility is represented by parameters such as residential buildings, special public use buildings, public infrastructure, and agriculture; social susceptibility is contributed to by factors like population, flood risk perception, spiritual values, and income; environmental susceptibility is represented by such indicators as pollution, erosion, and open spaces. An assessment of potential flood in Hanoi and the DRFDA in the RRD has been carried out by analyzing flood trends, future flood frequencies, and the rise in sea level. The techniques of linear regression, exponential smoothing, Data-Fit functions, stochastic modeling, and artificial neural network (ANN) have been investigated. The modeling of flood propagation in the RRS -including the flood diversion zones as well as the operation of the flood control system -was carried out using the 1-D hydrodynamic model (MIKE 11) and the 2-D hydrodynamic model (MIKE 21). The Decision Tree Analysis (DTA) method, in conjunction with dummy simulation skills, was applied to describe the flood control system and its rules of operation. As will be seen, results of the trend analysis indicate an increase in flood peak discharge in the Red River by 4.4, 9.9, and 20.9% and the rise in sea level by 0.10, 0.22, and 0.46 m in 2025, 2050, and 2100 correspondingly (compared to 2005). The maximum water level in Hanoi is likely to increase by 0.95 m by the end of this century. Hanoi will, however, not be affected by the rise in sea level even in the worst case scenario of an increase by 1.0 m. In contrast, the DRFDA can be greatly influenced by both flood from the upstream catchment area and the rise in sea level because of topographical conditions. For example, as predicted for 2100, the flood volume diverted to the Day River will increase by 48.7% due to flood increase in the Red River, and the water level will rise by an average of 0.54 m due to a combination of flood waters from the upstream and the rise in sea level. Based on flood simulation for various scenarios in the RRS, the hydrographs of flood divergence to the DRFDA have been computed using the MIKE 11 model. Accordingly, flood risk in the flood diversion zones has been assessed for each flood-cell (90 by 90m) using the MIKE 21 model, GIS software, and statistical techniques. The digital maps of flood hazard, food vulnerability, and flood risk in the flood diversion zones have also been developed. In both flood diversion zones -the Head Zone and Middle Zone—the overall contribution to flood risk of the flood hazard component is 55%, and the flood vulnerability component is 45%, even though the weight given to hazard is only half of that given to vulnerability. Flood duration dominates other indicators (flood depth and flood velocity) due to high weight and long duration. The overall contribution to flood hazard by the depth indicator is higher than that by the velocity indicator, even though the weight to depth indicator is much lower than that to velocity. For flood vulnerability, the Head Zone faces maximum risk from environmental factors (65% contribution) such as erosion and social factors (25% contribution) such as dense inhabitation and low income. Inversely, the Middle Zone is most susceptible from the angle of social issues (48% of the overall contribution), especially since there is poor flood risk awareness and low income. Moreover, this zone is also susceptible to environmental factors by a considerable level (45%) under which erosion and pollution are primary. Noticeably, economic susceptibility has been weighted equal to environmental vulnerability and is the double of social vulnerability, but its overall contribution in both the Head and Middle Zones is less than 10%, much lower than the contribution of social and environmental implications. The sensitivity of flood hazard and vulnerability parameters of flood risk for future scenarios has been analyzed during the course of research and in conjunction with that, a questionnaire survey was also carried out to determine suitable measures to reduce flood risk in the DRFDA. It has been found that flood hazard in the flood diversion zones is likely to increase by 8% in the year 2100, and flood duration always dominates other indicators although acceleration of the relative increase of the depth indicator is most rapid. Two structural measures, namely improving the drainage capacity and strengthening the dyke system, have been suggested to mitigate flood hazard in the flood diversion zones. The development of residential buildings and agricultural activities in flood diversion zones increases economic vulnerability. Population growth and lessening/increasing spiritual values result in more social vulnerability, whereas an improving income helps lessen social susceptibility. Pollution due to industrialization also leads to more environmental susceptibility. In general, the increase of flood vulnerability will be higher than the increase of flood hazard in the future, though flood hazard is always greater than flood vulnerability. On the other hand, the weight to vulnerability is double that of the weight to hazard; thus, several nonstructural measures such as evacuation, public awareness about flood risk, land use management etc. are recommended to decrease flood vulnerability. The study has presented an integrated approach to flood risk assessment for the flood diversion area in the Red River. The AHP was appraised as quite satisfactory for quantifying the weights to parameters contributing to flood risk. The DTA, in conjunction with dummy simulation skills, was an effective tool in the operation of a complex flood control system created using the MIKE 11 model. The outputs of integrated flood risk assessment provide valuable information for policy-makers, responsible authorities, and local residents in planning for flood risk reduction in the study area. |
| Year | 2010 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. WM-09-01 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Engineering and Management (WM) |
| Chairperson(s) | Babel, Mukand S.; |
| Examination Committee(s) | Sutat Weesakul;Takara, Kaoru;Huynh Trung Luong;Gupta, Ashim Das; |
| Scholarship Donor(s) | WaterSPS;MARD-DANIDA;Vietnam; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2010 |