Tài liệu Constructing the flood hazard map for downstream of da ban reservoir, khanh hoa province, vietnam

THUY LOI UNIVERSITY & UNIVERSITY OF LIEGE ---------- NICHE-CEM &TLU-ULG MASTER PROGRAM MASTER THESIS CONSTRUCTING THE FLOOD HAZARD MAP FOR DOWNSTREAM OF DA BAN RESERVOIR, KHANH HOA PROVINCE, VIET NAM Submitted by NGUYEN MANH KIEN Ha Noi, August 2016 THUY LOI UNIVERSITY & UNIVERSITY OF LIEGE ---------- NICHE-CEM &TLU-ULG MASTER PROGRAM MASTER THESIS CONSTRUCTING THE FLOOD HAZARD MAP FOR DOWNSTREAM OF DA BAN RESERVOIR, KHANH HOA PROVINCE, VIET NAM Student’s Name Birthday : Nguyen Manh Kien : January 05, 1980 Student Code Email address : 1481580203008 : [email protected] Mobile Phone Number : +84979209988 Supervisor Email : Assoc. Prof. Dr. NghiemTien Lam : [email protected] Co-supervisor Email : Prof. ir. HIVER Jean-Michel :[email protected] Ha Noi, August 2016 Niche-CEM&TLU-ULG master program Master thesis DECLARATION I declare that this submission is my own original work, and I have not used any source or mean without proper citation in the text. Any idea from others is clearly marked. This thesis contains no material published elsewhere or extracted in whole or in part from a thesis or any other degree or diploma. Ha Noi, August 2016 Nguyen Manh Kien i Niche-CEM&TLU-ULG master program Master thesis ACKNOWLEDGEMENT During last six months of research and prepare of this master thesis, I have been accompanied and supported by many people. I would like to thank them all for their support, guidance and encouragement throughout this work. Firstly, I would like to express my sincere gratitude to my supervisor, Assoc. Prof. Dr. NghiemTien Lam, for his guidance, support, and provision of critical information sources for me to complete my research. I also really appreciate all the support that I have received from my co-supervisor, Prof. ir. HIVER Jean-Michel, who provided great recommendations and lots of references for my thesis writing. Secondly, I would like to warmly thank all the lecturers in NICHE-CEM & TLU-ULG Masters’ program for providing me so much knowledge during this course. Thirdly, I would like to thank Song Da Joint Stock Company for giving me access to a lot of important data and information on my selected area for this thesis. And last but not least, I would like to thank my family and friends, who always stay by my side and have helped me a lot to finish this program. Ha Noi, August 2016 Nguyen Manh Kien ii Niche-CEM&TLU-ULG master program Master thesis CONTENTS CHAPTER 1: INTRODUCTION ..........................................................................1 1.1 Problem statement ...........................................................................................1 1.2 The meaning of flood map...............................................................................2 1.3 Literature review .............................................................................................3 1.4 Objectives and methods: .................................................................................4 1.5 Structure of thesis............................................................................................5 CHAPTER 2: SOCIAL AND NATURAL CONDITIONS OF THE STUDY AREA 6 2.1 Natural condition of study area ......................................................................6 2.1.1 Geographical location of study area ...............................................................6 2.1.2 Topographical conditions ...............................................................................6 2.1.3 Climatic and hydrographical conditions. ........................................................7 2.2 Socio-economic conditions ............................................................................10 2.3 Flood risk in downstream of Da Ban reservoir ............................................11 CHAPTER 3: THEORETICAL BASIC FOR FLOOD MAPPING...................12 3.1 General overview ...........................................................................................12 3.1.1 Background of flood mapping ......................................................................12 3.1.2 Objectives of this tool ..................................................................................12 3.1.3 Flood mapping process .................................................................................12 3.1.4 Products of flood hazard map .......................................................................14 3.2 General about the hydraulic problems in river network .............................15 3.2.1 1D steady Flow ............................................................................................15 3.2.2 1D unsteady Flow ........................................................................................16 3.2.3 2D unsteady flow hydrodynamics ................................................................17 3.3 General about the hydraulic modeling .........................................................18 3.4 HEC-RAS model ...........................................................................................18 3.4.1 Introduction..................................................................................................18 3.4.2 HEC-RAS two-dimensional flow modeling capabilities for calculation case of this study ...................................................................................................................20 3.4.3 Basic steps to modeling ................................................................................21 CHAPTER 4: CONSTRUCTING THE FLOOD MAP OF STUDY AREA ......23 iii Niche-CEM&TLU-ULG master program Master thesis 4.1 Implementation diagram...............................................................................23 4.2 Constructing database ...................................................................................24 4.2.1 Project data ..................................................................................................24 4.2.2 Topography data ..........................................................................................27 4.2.3 Landuse data ................................................................................................28 4.2.4 Hydrologic data............................................................................................29 4.3 ARC-GIS software application to construct DEM data, cross-section data, and landcover ..........................................................................................................30 4.3.1 DEM data .....................................................................................................30 4.3.2 Cross-sectional data of Da Ban river ............................................................30 4.3.3 Land cover data ............................................................................................31 4.4 HEC-RAS modeling application for flood simulation and calculation .......32 4.4.1 Selection and construction of model domain ................................................32 4.4.2 Developing a terrain model for use in 2D modeling and results in mapping .32 4.4.3 Development of a 2D model .........................................................................36 4.4.4 Creating a spatially varied Manning’s roughness layer .................................39 4.4.5 Boundary conditions ....................................................................................43 4.4.6 Initial conditions ..........................................................................................45 4.4.7 Dambreak analysis .......................................................................................47 4.4.8 Running the unsteady flow model ................................................................51 4.4.9 Viewing 2D output using RAS Mapper ........................................................56 4.5 Validation numerical model with analytical solution ..................................65 4.5.1 Analytical Solution by Ritter ........................................................................65 4.5.2 Modeling the 2D Dam-Break wave ..............................................................67 4.5.3 Comparing the model results and the analytical solution by Ritter (1892) ....71 4.6 Sensitivity testing ...........................................................................................72 4.6.1 Introduction..................................................................................................72 4.6.2 Considering the factors affect the model results ...........................................73 4.6.3 Choosing position on model for analyzing results ........................................74 4.6.4 Sensitivity testing results ..............................................................................75 4.6.5 Conclusion ...................................................................................................80 4.7 Constructing flood hazard map by ArcGIS .................................................81 iv Niche-CEM&TLU-ULG master program Master thesis CONCLUSIONS AND RECOMMENDATIONS..................................................86 Conclusions ..............................................................................................................86 Recommendations ...................................................................................................89 LIST OF FIGURES Figure 1: Geographical location of study area (source: Google Map) ....................................... 6 Figure 2: Representation of terms in the energy equation ....................................................... 16 Figure 3: Implementation diagram ........................................................................................... 23 Figure 4: Da Ban reservoir ....................................................................................................... 24 Figure 5: Headworks before upgrading.................................................................................... 25 Figure 6: Headworks after upgrading ...................................................................................... 25 Figure 7: Inner slope of earth dam ........................................................................................... 25 Figure 8: Outer slope of dam ................................................................................................... 25 Figure 9: Existing spillway ...................................................................................................... 26 Figure 10: Intake ...................................................................................................................... 26 Figure 11: New spillway .......................................................................................................... 27 Figure 12: Da Ban river............................................................................................................ 27 Figure 13: (DEM) 30mx30m of study area .............................................................................. 28 Figure 14: LandsatGLS\ TM_Multispectral_2000................................................................... 28 Figure 15: Chart of hydrograph with frequency 0,5% ............................................................. 29 Figure 16: Chart of hydrograph with frequency 0,1% ............................................................. 29 Figure 17: DEM study area ...................................................................................................... 30 Figure 18: Create cross sectional data for Da Ban river .......................................................... 31 Figure 19: Land cover of study area from Landsat sources ..................................................... 31 Figure 20: Downstream of Da Ban reservoir ........................................................................... 32 Figure 21: RAS Mapper with a Terrain Data Layer added. ..................................................... 33 Figure 22: RAS mapper with a channel (river) terrain data layer created. .............................. 34 Figure 23: Original terrain model (top) and new terrain model with channel data (bottom). . 35 Figure 24: HEC-RAS 2D modeling computational mesh terminology ................................... 36 Figure 25: 2D computational mesh .......................................................................................... 37 Figure 26: 2D flow area mesh generation editor...................................................................... 37 Figure 27: The storage area connected to the 2D flow area.................................................... 38 Figure 28: Adding the parameter of the reservoir .................................................................... 38 Figure 29: SA/2D Area Hydraulic Connection editor.............................................................. 39 Figure 30:Parameters of a,new spillway and b, gates .............................................................. 39 Figure 31: RAS Mapper’s new land classification .................................................................. 41 Figure 32: Set Manning’s n override land cover values at some regions ................................ 42 Figure 33: Spatially varied Manning’s roughness layer .......................................................... 43 Figure 34: Boundary condition ................................................................................................ 44 Figure 35: Hydrograph with frequency 0,5% .......................................................................... 44 Figure 36: Hydrograph with frequency 0,1% .......................................................................... 45 Figure 37: Normal depth in downstream ................................................................................. 45 Figure 38: Initial condition of Reservoir.................................................................................. 46 Figure 39: 2D flow area computational options....................................................................... 47 v Niche-CEM&TLU-ULG master program Master thesis Figure 40: Breach parameter calculator from regression equations......................................... 49 Figure 41: Shape and dimensions of calculated breach ........................................................... 49 Figure 42: Flow hydrographs from dam to downstream without dam break (flood frequency 0.1%) ........................................................................................................................................ 50 Figure 43: Flow hydrographs from dam to downstream effect by dam break (flood frequency 0.1%) ........................................................................................................................................ 51 Figure 44: Unsteady flow analysis window for a plan (plan 3). .............................................. 56 Figure 45: Display results map parameters .............................................................................. 57 Figure 46: RAS Mapper with depth results layers. .................................................................. 57 Figure 47: RAS Mapper with velocity results layers. .............................................................. 58 Figure 48: RAS Mapper with WSE Results Layers. ................................................................ 59 Figure 49: Example Time Series Plot of Depth from three different Plans. ............................ 60 Figure 50: Example Time Series Plot of Velocity from three different Plans. ........................ 61 Figure 51: Example Time Series Plot of WSE from three different Plans. ............................. 62 Figure 52: Example velocity plot with color and direction/magnitude arrows........................ 63 Figure 53: Example of the particle tracing visualization option on top of a depth layer. ........ 63 Figure 54: Profile Line turned on and selected for plotting options. ....................................... 64 Figure 55: Example profile line plot of Water Surface Elevation (WSE) ............................... 64 Figure 56: Results Mapping Window. ..................................................................................... 65 Figure 57: Analytical solution by Ritter (water height) ........................................................... 67 Figure 58: Geometry model ..................................................................................................... 67 Figure 59: Hydraulic structure with a dam break..................................................................... 68 Figure 60: Water hight follow model at t=0s ........................................................................... 69 Figure 61: Water depth profile along the river at t=20s ........................................................... 69 Figure 62: Water depth profile along the river at t=40s ........................................................... 70 Figure 63: Water depth profile along the river at t=60s ........................................................... 70 Figure 64: Analytical solution by Ritter (blue) and simulated results (orange): water depth at t=20s ......................................................................................................................................... 71 Figure 65: Analytical solution by Ritter (blue) and simulated results (orange): water depth at t=40s ......................................................................................................................................... 71 Figure 66: Analytical solution by Ritter (blue) and simulated results (orange): water depth at t=60s ......................................................................................................................................... 72 Figure 67: The position on model for analyzing results .......................................................... 75 Figure 68: The water depth at point 3 in Sensitivity test cases of n values ............................. 76 Figure 69: The velocity at point 3 in Sensitivity test cases ...................................................... 77 Figure 70: The water depth at point 3 in Sensitivity test cases of mesh size .......................... 78 Figure 71: The velocity at point 3 in Sensitivity test cases of mesh size ................................ 78 Figure 72: Computed time step is 5 seconds and 2 minutes at point 3 .................................... 79 Figure 73: Breach bottom elevation is 56m and 46m (Sensitivity testing) at point 1.............. 80 Figure 74: Flood hazard map in case of flood frequency 0.5% ............................................... 83 Figure 75: Flood hazard map in case of flood frequency 0.1% ............................................... 84 Figure 76: Flood hazard map in dam break case with flood frequency 0.1%.......................... 85 Figure 77: A resident area before and after covered by flood water........................................ 87 Figure 78: Velocity changes from river to floodplain.............................................................. 87 Figure 79: The flow through a resident area with the discharge of 500 (m3/s). ...................... 88 vi Niche-CEM&TLU-ULG master program Master thesis LIST OF TABLES Table 1: Climate specification ................................................................................................... 8 Table 2: Climate factors of the irrigated area............................................................................. 8 Table 3: Maximum wind speed .................................................................................................. 8 Table 4: Evaporation .................................................................................................................. 9 Table 5: Evaporation loss ........................................................................................................... 9 Table 6: Rainfall......................................................................................................................... 9 Table 7: Network and available surveyed factors ...................................................................... 9 Table 8: Flow statistics at Da Ban.............................................................................................. 9 Table 9: Flow distribution at Da Ban ......................................................................................... 9 Table 10: Flow and total flood ................................................................................................. 10 Table 11: Situation of soil and forest sources .......................................................................... 10 Table 12: Elevation volume curve ........................................................................................... 24 Table 13: Max flow and total flow in Da Ban in accordance with frequencies ....................... 29 Table 14: Manning’s n values are used for the model ............................................................. 40 Table 15: Eddie viscosity transverse mixing coefficients ........................................................ 53 Table 16: Calculation cases...................................................................................................... 55 Table 17: Calculation cases of Sensitivity test......................................................................... 73 vii Niche-CEM&TLU-ULG master program CHAPTER 1: 1.1 Master thesis INTRODUCTION Problem statement Viet Nam has abundant and diverse water resources with dense river network. However, water discharge is not distributed evenly over different seasons in a year. Discharge in the rainy season is much greater than that in the dry season. As an agricultural country in its process of industrialization, Vietnam has built thousands of big and small reservoirs on river basins in order to regulate water flow and reduce flood's impact, to supply water for irrigation in agriculture and aquaculture, and to generate hydropower, etc. Construction of reservoirs offered tremendous efficiency to economic sectors. Construction of reservoirs raised a major concern for safety due to potential risks to downstream areas, for example whenever a major flood appears. A large flood flow or break of dam flow leads to a sudden rise of water level, and higher velocity in downstream. This situation represents a serious threat to the lives and properties of people living at the project’s downstream areas. Most of the reservoirs were designed following outdated standards and are not matching for current national and international standards. Additionally, nowadays serious degradation of upstream forest areas leads to more unpredictable and complicated flood patterns. Being aware of the situation, the project VWRAP has provided Vietnam Government financial assistance in strategic change with the capital loan. This loan was to upgrade and modernize the irrigation system, improving irrigation services through management improvement, operation, maintenance, and financial management. Notably, the effort also encouraged active participation of water users, especially farmers. In 2000, Ministry of Agriculture and Rural Development, together with World Bank’s consultants, investigated and determined 6 priority subprojects as part of the mentioned loan, as follows: - Dau Tieng water resources subproject. 1 Niche-CEM&TLU-ULG master program - Yen Lap water resources subproject. - Ke Go water resources subproject. - Cam Son - Cau Son water resources subproject. - Da Ban water resources subproject. - Phu Ninh water resources subproject Master thesis Along with upgrade and modernization of these six dam areas, safe operation and management were also considered in VWRAP study. With the aim to reduce damages caused by flood, to propose the solution of flood prevention through predicting probable inundation area with different flood scenarios (upstream floods and dam breaking), this thesis focuses on “Constructing the flood hazard map for downstream of Da Ban reservoir, Khanh Hoa province". The results will provide inputs to manage reservoir, develop resident relocation plans and specific responses. 1.2 The meaning of flood map A flood map is a visual tool that allows its users to know about inundation level corresponding to the forecasted water surface elevation at a certain position of the study area. This is very important for decision makers in the cases of emergency. The aims of flood mapping is: 1. To show the inundation area, water depth, flow velocity and other parameters at any position in flood region when input data is known; 2. To provide a foundation for selecting or associating flood prevention methods; 3. To support for performing land management of floodplains; 4. To serve as a basis for studying flood prevention methods in basic construction; 5. To provide information for designing and operating flood prevention works in the future. 2 Niche-CEM&TLU-ULG master program 1.3 Master thesis Literature review Flood is one of the natural disaster types which caused serious damages to people. Management and assessment of floods’ impacts on people's lives through simulation, development of flood map have now become more and more familiar with a research topic. Recently, one of the most common methods is by applying a hydraulic model to develop flood map causing rainfall and dam breaking. Some typical studies in this field and approaches will be mentioned briefly in the following section. Gilles and Moore (2010) used the hydraulic models MIKE 11 and USACE Hydrologic Engineering Center’s River Analysis System (HEC-RAS) to simulate floods in Netherlands, Belgium and the United Kingdom. Their study used model aiming at flow management, forecast, and construction of national flood forecasting system. Vanderkimpen and Peeters (2008) simulated flood by MIKE FLOOD model application to setup an evacuation plan in a timely manner for a coastal delta region of Belgium. By using MIKE FLOOD model, several effects of floods to the inundation area and to evaluate damages were able to indentify. Xiong (2011) analyzed dam break using HEC-RAS. This study described the dam break from both theoretical and modeling application aspects. Breach parameters prediction, understanding of dam break mechanics, and peak outflow prediction were all shown to be essential for the analysis of dam break, and eventually helped to determine the loss or damages. He also used an application example of Foster Joseph Sayers Dam break, further modeled and analyzed using HEC-RAS model based on available geometry data. Ackerman and Brunner (2011) did a research on the flood that causes dam break by using HEC-RAS model and HEC-GeoRAS. They have shown practical combination between HEC-RAS model and HEC-GeoRAS tool to develop a dam breaking model and understand effects of a flood caused by the event. HEC-GeoRAS will export the geometry data from topography map system and transfer that data into HEC-RAS model. HEC-RAS will simulate unsteady flow from the dam break process. This result associates with GIS technology to establish the flood mapping for flood preparedness and prevention. 3 Niche-CEM&TLU-ULG master program Master thesis Currently, in Vietnam, there are many hydraulic models that have been applied in studying floods by of government agencies and research institutes, such as MIKE FLOOD, HEC-RAS, WMS, etc. Each model has its own advantages and the features can be used separately to complete, depending on the subject that the researchers chose. Some study cases can be listed as follows: Luu Duy Vu and Nguyen Phuoc Sinh (2012) applied WMS model to forecast flood for downstream of Da Nang city. In this study, the authors used WMS to simulate the exceptionally large floods in 2007 and 2009 to find out the model parameters and validation, thereby creating flood scenarios for Da Nang city. The WMS was chosen because it can simulate flood well. Especially, this model can be combined with another free model such as HEC-RAS, HEC-HMS, TR-20, etc. In developing flood maps for downstream of the Vu Gia-Thu Bon river, Tran Van Tinh (2013) applied HEC models including HEC-HMS, HEC-RAS, and HEC-GeoRAS in combination with GIS data to simulate inundation area and depth at lower Vu Gia-Thu Bon river basin with floods in 2009 and another flood of design frequencies of 1%, 2%, 5%. It can be clearly seen that using the hydraulic model to simulate flow and flood mapping is very common nowaday. The combination of HEC-RAS model and GIS is a suitable approach for this problem. Especially in the recent time, HEC-RAS model has developed a two-dimensional hydraulic model. This development will bring a lot of advantages in flooding simulations. With this model, we can simulate well the flow in the river as well as on the flood plain. It is necessary for the study area downstream of Da Ban Reservoir. 1.4 Objectives and methods: The objective of this study is to apply the hydraulic modeling to develop a flood hazard map for downstream area of Da Ban reservoir, Ninh Hoa district, Khanh Hoa province, Viet Nam with different scenarios of upstream floods and dam breaking. The results will provide inputs for decision making processes in reservoir management and the development of resident relocation plans and specific responses. 4 Niche-CEM&TLU-ULG master program Master thesis In present, there are two major methods which are used worldwide for flood mapping including: a. Flood mapping based on the investigation of the high flood in history. b. Flood mapping by mean of numerical simulation using hydraulic models. This study the second method will be used, focusing on the application the hydraulic modeling and GIS software and data for the flood mapping. 1.5 Structure of thesis The thesis is organized with the following parts: Chapter 1: Introduction Chapter 2: Social and natural condition of the study area Chapter 3: Theoretical basis for flood mapping construction Chapter 4: Development of the flood map of study area Conclusions and recommendations. 5 Niche-CEM&TLU-ULG master program CHAPTER 2: Master thesis SOCIAL AND NATURAL CONDITIONS OF THE STUDY AREA 2.1 Natural condition of study area 2.1.1 Geographical location of study area Figure 1: Geographical location of study area (source: Google Map) 2.1.2 Topographical conditions The Da Ban river basin situated in Ninh Hoa district, Khanh Hoa province. The coordinates are 109003’ east longitude, 12034’ north latitude. It is 50 km north of Nha Trang city, and 10 km west of 1A National Highway. The main flow direction of the Da Ban river is Northern-Southern. The river is originated from the Da Den mountain, Truong Son mountain range, from an elevation of 1150 m. The river has 37 km length and a basin area of 358 km2 with high riverbed 6 Niche-CEM&TLU-ULG master program Master thesis slope. The Da Ban river is one of the main distributaries of the Ninh Hoa river with the conjunction near Lac Hoa. The river basion has low vegetation cover with the forest area holds between 28% and 35%. The forests are one of the monsoons tropical forests with large leaves and are prevailed at elevation +100 m. In the dry season, there are many falling leaves (the land degraded after the forest was destroyed to make milpa in a long time), so the water – retaining capacity is low. Major penology is yellow, red laterite soil, eroded easily, especially in the forest destroyed to make milpa. Since the construction of the Da Ban Reservoir, downstream area has been changed significantly due to sedimentation. 2.1.3 Climatic and hydrographical conditions. The climatic and hydrographical conditions of the river basin have been studies and reviewed by the consultant of the Join Adventure between Nippon Koei (Japan) and Royal Haskoning (Holland) in a feasibility study. Based on this study, we sum up the main characteristics of the climatic and hydrographical conditions. 2.1.3.1 Climatic condition The climatic characteristics of the Ba Ban river basin in particular and another area in Vietnam, in general, have a dry season with rainfall lower than evaporation and a water excess in the rainy season. The most notable characteristic of the basin is the ocean curing intersection so temperature and moisture lower than same latitude area but a deep seat in the mainland. On the contrary, this area is under flood effect with average wind speed, maximum wind speed, annual rainfall, maximum rainfall rather high. Near Da Ban reservoir, there are meteorological stations of Ninh Hoa, Da Ban, Dong Trang, Nha Trang, Ea Krong Hin which are recording data of all meterological parameters over a long period. - Measurement network and factors of climate in the basin 7 Niche-CEM&TLU-ULG master program Master thesis Surveyed stations: Da Ban station, Dong Trang station, Ninh Hoa station, Nha Trang station and Ea Krong Hin station. Surveyed factors: Air temperature, moisture, evaporation, rainfall. - The climate specifications are shown in Table 1: Table 1: Climate specification Month 1 2 3 4 5 6 7 8 9 10 11 12 Year - Air temperature (0C) 23.9 24.4 25.7 27.4 28.4 28.4 28.4 28.4 27.6 26.5 25.5 24.3 26.6 Relative humidity (%) 79 81 81 81 79 78 77 77 81 83 82 81 80 Wind speed (m/s) 3.5 3.4 3 2.6 2.3 1.8 2 1.9 2 2.7 3.8 4.1 2.8 Evaporation (mm) 133 117 119 114 124 120 126 125 106 88.5 112 135 1418 Climatic conditions of the irrigated area are shown in Table 2 Table 2: Climate factors of the irrigated area Month 1 2 3 4 5 6 7 8 9 10 11 12 Average Temperature (0C) 23.90 24.40 25.70 27.40 28.40 28.40 28.40 28.40 27.60 26.50 25.50 24.30 26.60 Relative humidity (%) 79 81 81 81 79 78 77 77 81 83 82 81 80 Wind speed (m/s) 3.5 3.4 3.0 2.6 2.3 1.8 2.0 1.9 2.0 2.7 3.8 4.1 2.8 - Annual rainfall at Da Ban: X0lv= 1950 mm - Maximum wind speed shown in Table 3 Evaporation (mm) 133 117 119 114 124 120 12 125 106 88.5 112 135 1418 Sunshine hours (h) 190 215 266 258 262 225 248 226 198 168 141 138 2536 Table 3: Maximum wind speed Direction North Northeast East Southeast South Southwest West Northwest V4% (m/s) 26.97 25.54 22.61 14.77 17.42 22.80 16.28 18.98 8 Niche-CEM&TLU-ULG master program V50% (m/s) - 13.53 13.20 Master thesis 10.36 10.76 9.32 7.29 10.75 10.40 Evaporation conditions in Table 4 Table 4: Evaporation No. 1 2 3 - Factor Surface evaporation: Z0 Basin evaporation: Z0 Increment of evaporation due to reservoir : Z Unit mm mm mm Value 1480 876 604 Loss of raised evaporation Z in Table 5 Table 5: Evaporation loss Month 1 2 3 4 5 6 7 8 9 10 11 12 Year Z 71.5 79.6 93.9 79.5 52.1 29.8 27.6 25.9 20.4 30.2 39 54.5 604 (mm) - Rainfall are shown inTable 6 Table 6: Rainfall No. 1 2 3 Factors Annual rainfall, X0 Unit mm Value 1950 Max. rainfall in one day, X1, P0,5% Max. rainfall in 3 days, X3, P0,5% mm 688 mm 952 Remarks Thiessen method for 2 stations: Ea Krong Hin and Da Ban Arithmetic average, 2 stations: Ea Krong Hin and Da Ban Same as above 2.1.3.2 Hydrological condition of the basin - Hydrological network and available measurement factors see in Table 7 Table 7: Network and available surveyed factors No. Station name River name Basin Recording Years of area, period record km2 - 1 Dong Trang Cai river in Nha Trang 1445 18832001 19 2 Da Ban Da Ban river 126 19761983 8 Hydrological specifications are shown in Table 8 Table 8: Flow statistics at Da Ban Specification Annual flow Q0 (m3/s) 4.29 Value - Coefficient of variation, Cv 0.43 Coefficient of skewness, Cs 1.22 Q75% (m3/s) 2.94 Flow distribution at Da Ban see Table 9 Table 9: Flow distribution at Da Ban Month 6 7 8 9 10 11 12 1 2 3 4 5 Year 9 Niche-CEM&TLU-ULG master program Master thesis Q75%(m3/s) 1.48 1.40 0.85 2.58 7.71 12.20 8.62 0.63 0.10 0.84 0.72 1.15 2.94 Q50%(m3/s) 1.89 1.42 1.11 0.99 1.75 2.12 2.58 1.42 5.43 8.49 16.87 3.20 3.94 - Flow and total flood see in Table 10 Table 10: Flow and total flood No. Specifications Unit 1 2 Design flow, Qp Design flood volume, Wp m3/s 106 m3 Design frequency, P % 0,50 0,10 0,01 1650 2200 2790 54.44 67.58 84.79 2.1.3. Ecological specification of animal, vegetation The basin surface mostly has weathered soil with acrisols, ferralsols, and histosols. Along the stream banks, there is alluvium fluvisol with the firm mechanical part, high fertility, suitable for rice and farm production in a small area. The arid soil has a large area with the heavy mechanical part which is impoverished and the ferals type with firm components, suitable with fruits, industrial trees, and medical plants. Leptosol is popular on slope soil and high mountain with low richness, suitable with secondary forest. The Table 11 indicates situation of soil and forest sources Table 11: Situation of soil and forest sources No. 1 2 3 4 a b c 2.2 Soil type General area Agricultural soil Forest Other Specific soil Housing area Unused soil Area (ha) Ninh Hoa Van Ninh 119555 55000 27915 8333 42491 16781 9849 1458 37842 1587 497 27812 Total (ha) 174565 36248 59272 11436 1955 65654 Socio-economic conditions Followings are the figures from the technical design profile of Da Ban spillway N02, Khanh Hoa province which was implemented by Song Da Consulting Joint Stock Company in 2010. The area belongs to Ninh Son commune, Ninh Hoa District, Khanh Hoa Province includes the ethnic groups of Kinh, Dao, Tay, and Day Thai with the population of 40,000 people in 2006. However, the Kinh ethnic group holds 90%, almost of them are immigrants from other areas, in about 1980s. The major economy is agriculture, main products are maize, tapioca, and rice. In the area around Da Ban Reservoir, people also plant flowers and transports it to the North or South provinces. Beside this, there are some people breeding fish in Da Ban Resevoir. 10 Niche-CEM&TLU-ULG master program Master thesis Presently, average food income per capita is low (200 kg/capita/year). They are dreeding cattle and poultry for their own usage. Other sectors such as handicraft and tourism service are undeveloped. The total average income is about 0.9×106 VND/capita/year. The poor and hungry rate is over 36% (in which more than 10% households are ever-hungry). In the areas downstream of the dam (Village 5, Ninh Son commune) the economy is mainly agricultural production with simple tools, and low productivity, poor material facilities. Crop plants are based on rainfall or water source from irrigation canal systems. Culture and society: The rate of households with electricity power supply is 85% (almost households in the village have a television). Other services such as telephone, computer and other culture-spirit living in the area nearly not developed yet. Healthcare service lacks equipment with only two physicians and three nurses. In the commune, there is an elementary school and high school with poor equipment. Nowadays, Da Ban Water Resource System is one of tourist attractive place but it has not received tourists frequently yet. At the weekend, some tourists go fishing here, however, the service is poor. 2.3 Flood risk in downstream of Da Ban reservoir Since the Da Ban Reservoir was built, inundation issues were reduced with the regulation ability of reservoir. However, the flood risk in downstream can occur in cases of the reservoir discharge flow with design flood or rare-frequency flood. The restricted river channel and high-density resident along the river banks will affect the inundation situation in case of severe floods. 11