THÔNG TIN TÀI LIỆU
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 : Kiennm4125@wru.vn Mobile Phone Number : +84979209988 Supervisor Email : Assoc Prof Dr NghiemTien Lam : lamnt@wru.vn Co-supervisor Email : Prof ir HIVER Jean-Michel :Jean-Michel.Hiver@ulb.ac.be 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 Problem statement 1.2 The meaning of flood map .2 1.3 Literature review .3 1.4 Objectives and methods: 1.5 Structure of thesis CHAPTER 2: SOCIAL AND NATURAL CONDITIONS OF THE STUDY AREA 2.1 Natural condition of study area 2.1.1 Geographical location of study area .6 2.1.2 Topographical conditions .6 2.1.3 Climatic and hydrographical conditions 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) 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 in Sensitivity test cases of n values 76 Figure 69: The velocity at point in Sensitivity test cases 77 Figure 70: The water depth at point in Sensitivity test cases of mesh size 78 Figure 71: The velocity at point in Sensitivity test cases of mesh size 78 Figure 72: Computed time step is seconds and minutes at point 79 Figure 73: Breach bottom elevation is 56m and 46m (Sensitivity testing) at point 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 Table 2: Climate factors of the irrigated area Table 3: Maximum wind speed Table 4: Evaporation Table 5: Evaporation loss Table 6: Rainfall Table 7: Network and available surveyed factors Table 8: Flow statistics at Da Ban Table 9: Flow distribution at Da Ban 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 priority subprojects as part of the mentioned loan, as follows: - Dau Tieng water resources subproject Niche-CEM&TLU-ULG master program Master thesis Figure 70: The water depth at point in Sensitivity test cases of mesh size Figure 71: The velocity at point in Sensitivity test cases of mesh size 78 Niche-CEM&TLU-ULG master program Master thesis 4.6.4.3 Sensitivity testing of computed time step This test includes changing the computed time step, but make sure the stability of the model Adjusting computed time step from seconds to minutes.(Figure 72) Figure 72: Computed time step is seconds and minutes at point 4.6.4.4 Sensitivity testing of estimating dam break parameters In this test, two values of bottom elevation of breaching gap at 56 m and 46 m, respectively, is simulated The comparison of water depth at Point is shown in Figure 73 79 Niche-CEM&TLU-ULG master program Master thesis Figure 73: Breach bottom elevation is 56m and 46m (Sensitivity testing) at point 4.6.5 Conclusion From the calculation results we can see that when changing the input parameters, we get the different results With the normal scenario (without dam break) Manning's n values affected the most to results of the model In the dam break case, breach characteristics are the most effect factors - Manning's n values affected considerably to output results So if there is not enough observed data for calibrating the model, we need to define precisely the specific area where have different roughness as well as the value of each region follow the results of real experiments - Computational mesh size also impacts to results However, if we divide the mesh size small enough for the essential and sensitive areas, the difference is acceptable - Regarding computed time step, if the computed time step is suitable, a small change will not impact to results considerably - Breach characteristics: this is a very sensitive factor When performing a dam breach analysis, one must first estimate the characteristics of the breach One 80 Niche-CEM&TLU-ULG master program Master thesis breaching characteristic is estimated, then HEC-RAS can be used to compute outflow hydrograph from the breach and perform the downstream routing A dam’s potential breach characteristics can be estimated in several ways, including comparative analysis (comparing our dam to historical failures of the dam of similar size, materials, and water volume), regression equations, and physically based computer models All these methods are viable techniques for estimating breach characteristics However, each method has strengths and weaknesses and not utilize as absolute values The Simplified Physical breaching method allows the user to enter velocity versus breach down-cutting and breaches widening relationships, which are then used dynamically to figure out the breach progression versus the actual velocity being computed through the breach, on a time step by time step basis This data is often very difficult for coming by and requiring the modelers have to have many experiences 4.7 Constructing flood hazard map by ArcGIS RAS Mapper creates files in the GeoTIFF file format (Geospatial Tiff with tif file extension) The GeoTIFF is a file standard and can be used directly in ArcGIS 10 and higher and other software packages The user can simply drag and drop the GeoTIFF files into an ArcGIS project Then with ArcGIS, we can construct flood hazard map easily on many difference maps Products of flood hazard mapping: A flood hazard map graphically provides information on flood inundation (inundation depths, extent, flow velocity etc.) expected for an event of given probability or several probabilities The key items are incorporated in a flood hazard map for a given probability of occurrence are: - Flood extent (areas covered by water) - Water depth (m) The hazard maps superimposed on the available topographic map with ground elevations and physical features The general scale of hazard maps is 1:25,000, in 81 Niche-CEM&TLU-ULG master program Master thesis necessary cases we can set up maps with smaller scale for each certain area Maps mainly cover populated, developed or developing areas as well as traffic routes The final hazard maps are presented in Figure 74 to Figure 76 82 Niche-CEM&TLU-ULG master program Master thesis Figure 74: Flood hazard map in case of flood frequency 0.5% 83 Niche-CEM&TLU-ULG master program Master thesis Figure 75: Flood hazard map in case of flood frequency 0.1% 84 Niche-CEM&TLU-ULG master program Master thesis Figure 76: Flood hazard map in dam break case with flood frequency 0.1% 85 Niche-CEM&TLU-ULG master program Master thesis CONCLUSIONS AND RECOMMENDATIONS Conclusions In this study of applying the HEC-RAS model to develop the flood hazard map for downstream of Da Ban reservoir, the major contents of work have been completed as follows: - An overview on the general mapping methods and GIS method to develop flood maps in particular The process of inundation mapping implemented in this study are combined of GIS and HEC-RAS modelling - The thesis has successfully applied the model HEC-RAS with support from ArcGIS tool to simulate and to calculate flood area downstream of Da Ban reservoir for different scenarios: + Two scenarios of the upstream flood of frequencies 0.5% and 0.1% + One scenario corresponding to dam break when discharging flow with the flood frequency 0.1% The combination of GIS and HEC-RAS hydraulic model in simulating inundation is an accurate and real method, demonstrating the strength of GIS and hydraulic model application in researching inundation, as the scientific basis for flood protection planning, selection of measures, the design of flood control projects From calculation results with different scenarios we have inundated area, water depth map, velocity map, water surface elevation map and other parameters The results indicate that inundated area is very large with the calculation cases see Figure 77 and Figure 78 The hazard maps are also shown many resident areas, industry area, roads and other was covered by flood water The affected area is almost the whole downstream of Da Ban River The peak discharge at downstream are 1218,28m3/s, 1497,80 m3/s and 3307,60 m3/s, respectively with calculation scenarios 86 Niche-CEM&TLU-ULG master program a, Master thesis b, Figure 77: A resident area before and after covered by flood water a, b, Figure 78: Velocity changes from river to floodplain With the flood discharge of frequency 0.5%, the inundation area is 21.89 km2 With the flood discharge of frequency 0.1%, the inundation area is 25.95 km2 With the flood discharge of frequency 0.1% and a dam breaking, the inundation area is 36.91 km2 With the current capacity of the river when the design or checking flood discharge appears, many regions in downstream of Da Ban reservoir will be inundated Therefore, it is necessary to have evacuation plans for people and properties or to have a solution for operating reservoir to reduce the flood discharge to downstream In this research, the author also calculated with many difference discharge to find out the capacity of the 87 Niche-CEM&TLU-ULG master program Master thesis downstream river The results indicated that the inundated area is not significant with the flow is smaller than 500 m3/s as Figure 79 Figure 79: The flow through a resident area with the discharge of 500 (m3/s) The scenario of dam-break is the most dangerous case, so mitigating the disaster from dam-break is very important There are some ways to mitigate it by: - Specify measures to minimize dam failure risks such as maintenance and upgrading of the dam and headworks; - The reservoir needs regulating with a certain water level to discharge flow to downstream which is smaller than an allowable discharge - Operational flood mitigation: To extent the time of flooding to reduce the flooding level as a longer flood is still not worse than a higher flood - Based on the flood hazard maps to support for land use management of the floodplain; - Provide detailed downstream flooding information to develop resident relocation plans and specific response; - Specify measures to alert and assist the local and state emergency service; 88 Niche-CEM&TLU-ULG master program Master thesis Recommendations Due to limitations of time, data and knowledge, besides the results achieved, the thesis are still the following restrictions: - Obtained terrain data is limited A better terrain model is recommended to get a better flood maps - There are not observed data about historic flood to calibrate or validate the model Therefore, hydrologic measurements for model calibration and validation are suggested Collecting the specific topography in downstream of Da Ban reservoir, especially the data related to cross sections of river and other works such as roads, channel network, pools, etc, to increase the accuracy of the terrain model Conduct more research on floods in different years, creating a scientific basis for the managers can plan preventive measures, reducing damage caused by floods Calculating different dam break scenarios to see the effects of disaster levels It can be applied in combination of GIS and an hydraulic model with the hydrologic model as SWAT for flow prediction Besides of modeling results such as inundation, flooding depth, flow rate, other influences of natural and human factors to the flow such as the amount of sediment and chemicals generated from agricultural activities may be considered in the hazard maps 89 Niche-CEM&TLU-ULG master program Master thesis References Anderson, J R., Hardy, E E., Roach, J T., & Witmer, R E (1976) A Land Use and Land Cover Classification System for Use with Remote Sensor Data USGS Professional Paper 964, 28 Approved, F., No, O M B., & Brunner, G (2014) Using HEC-RAS for Dam Break Studies, (August) Brunner, G W (2000) Problems When Performing an Unsteady Flow Analysis Problems When Performing an Unsteady Flow Analysis, 1–48 Brunner, G W (2016) HEC-RAS River Analysis System : User’s Manual, (February) Brunner, G W., Warner, J C., Wolfe, B C., Piper, S S., & Marston, L (2016) HEC-RAS, River Analysis System Applications Guide US Army Corps of Engineers Hydrologic Engineering Center, (February), 150 Cameron, T A., & Gary, W B (2008) Dam Failure Analysis Using HEC-RAS and HECGeoRAS World Environmental and Water Resources Congress 2008: Ahupua’A, Colorado, S of (2010) Guidelines for Dam Breach Analysis, (303), 68 Edom, E (2008) Numerical Calculation of the Dam-Break Riemann Problem with a Detailed Method and Comparison with a Simplified Method Gilles, D., & Moore, M (2010) Review of Hydraulic Flood Modeling Software used in Belgium , The Netherlands , and The United Kingdom Europe Kalyanapu, A J., Burian, S J., & McPherson, T N (2009) Effect of land use-based surface roughness on hydrologic model output Journal of Spatial Hydrology, 9(2), 51–71 Retrieved from http://spatialhydrology.net/index.php/JOSH/article/view/84 Luu Duy Vu & Nguyen Phuoc Sinh (2012), 1–6 Moody, V (2015) Dam Break Modeling With Building Strong ® Phillips, B J V, & Tadayon, S (2006) Selection of Manning ’ s Roughness Coefficient for Natural and Constructed Vegetated and Non- Vegetated Channels , and Vegetation Maintenance Plan Guidelines for Vegetated Channels in Central Arizona Geological Survey Scientific Investigations Report 2006-5108, 41 Seattle, C O F., & Manual, S (2015) Appendix F Hydrologic Analysis and Design, (September) Tobergte, D R., & Curtis, S (2013) No Title No Title Journal of Chemical Information and Modeling, 53(9), 1689–1699 http://doi.org/10.1017/CBO9781107415324.004 Udupa, A (2015) Thesis presentation http://doi.org/10.1017/CBO9781107415324.004 90 Niche-CEM&TLU-ULG master program Master thesis USACE (2016) HEC-RAS Hydraulic Reference Manual US Army Corps of Engineers Hydrologic Engineering Center, (February), 547 Valc, Q I (2007) Comparison Between 1D and 2D Models To Analyze the Dam Break Wave Using the Fem Method and the Shallow Water Equations Thesis, (May), 1–36 Vanderkimpen, P., & Peeters, P (2008) Flood modeling for risk evaluation: a MIKE FLOOD sensitivity analysis Proceedings of the International Conference on Fluvial Hydraulics, Cesme, Izmir, Turkey, September 3-5, 2008: River Flow 2008, 2335–2344 Version, M (1989) Guide for Selecting Manning ’ s Roughness Coefficients for Natural Channels and Flood Plains United States Geological Survey Water-supply Paper 2339 Area, 2339(2339), 39 http://doi.org/Report No FHWA-TS-84-204 WMO (2013) Flood Mapping Integrated Flood Management Tools Series, (20), 88 Retrieved from www.apfm.info Xiong, Y (2011) A Dam Break Analysis Using HEC-RAS Journal of Water Resource and Protection, 03(06), 370–379 http://doi.org/10.4236/jwarp.2011.36047 Song Da consulting joint stock company, 2009, Technique design Profile of Da Ban spillway N02, Khanh Hoa province 91 Niche-CEM&TLU-ULG master program Master thesis (Valc, 2007) (Edom, 2008) (Anderson, Hardy, Roach, & Witmer, 1976) (Approved, No, & Brunner, 2014) (Brunner, 2000) (Brunner, 2016) (Brunner et al., 2016) (Cameron & Gary, 2008) (Colorado, 2010) (Edom, 2008) (Gilles & Moore, 2010) (Kalyanapu, Burian, & McPherson, 2009) (Kalyanapu et al., 2009) (Moody, 2015) (Phillips & Tadayon, 2006) (Seattle & Manual, 2015) (Tobergte & Curtis, 2013) (Udupa, 2015) (Vanderkimpen & Peeters, 2008) (Version, 1989) {Formatting Citation} 92 ... 0, 50 0, 10 0 ,01 m3/s 16 50 2 200 27 90 106 m3 54,44 67 ,58 84,79 P0,5% 200 0 .00 Q(m3/s) 1 500 .00 100 0 .00 500 .00 0. 00 0 .00 10. 00 20. 00 30. 00 40. 00 50. 00 60. 00 70. 00 Times (hour) Figure 15: Chart of hydrograph... with frequency 0, 5% P 0, 1% 2 500 .00 Q(m3/s) 200 0 .00 1 500 .00 100 0 .00 500 .00 0. 00 0 .00 10. 00 20. 00 30. 00 40. 00 50. 00 60. 00 70. 00 Times(hour) Figure 16: Chart of hydrograph with frequency 0, 1% 29 Niche-CEM&TLU-ULG... ( 201 3), the standard scale of hazard maps is varying from 1:5 ,00 0 to 1:25 ,00 0 A scale of 1: 10, 000 is a good scale to identify the features which inundated The hazard map should superpose on the
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