Master thesis Major Sustainble Hydraulic Structures Coastal Engineering and Management: Constructing the flood hazard map for downstream of Da Ban reservoir, Khanh Hoa province, Vietnam

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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

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THUY LOI UNIVERSITY & UNIVERSITY OF LIEGE

CONSTRUCTING THE FLOOD HAZARD MAP FOR DOWNSTREAM OF DA BAN RESERVOIR, KHANH HOA.

PROVINCE, VIET NAM

‘Student's Name + Nguyen Manh Kien

Birthday January 05, 1980. Student Code 1481580203008

Email address Kiennm4125/2wruvn

Mobile Phone Number 384919209088.

Supervisor + Assoc, Prof Dr NghiemTien Lam,

Email lam wruxn

Co-supervisor : Prof ir HIVER Jean-Michel Email 2Jean-MiehelHiver/2ulbaae.be

Ha Noi, August 2016

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Niche- EMS&-TLU-ULG master program Master thesis

declare that this submission is my own original work, and I have not used any source ‘or mean without proper citation inthe text Any idea from others is clearly marked This thesis contains no material published elsewhere or extracted in whole or in pat from a thesis or any other degree or diploma.

Ha Noi, August 2016

‘Nguyen Manh Kien

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Niche-CEM&TLU-ULG master program Master thesis

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, [also really appreciate all the support that I have received from my co-supervisor, Profit 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 Jot of important data and information on my selected atea 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,

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2.1 Natural condition of study area 241.1 Geographical location of study area

Flood risk in downstream of Da Ban reserVoif - sec.

CHAPTER 3: THEORETICAL BASIC FOR FLOOD MAPPING 2 4⁄1 General overview 2 3.1.1 Background of flood mapping, 2

3.13 Flood mapping process 12 3.14 Products of flood hazard map “

3.2 General about the hydraulie problems in river network IŠ 3.2.1 ID steady Flow Is 3.22 ID unsteady Flow 16

3.2.3 2D unsteady flow hydrodynamics " 3.3 General about the hydraulic model 18

34 18

3.4.1 Introduction, 18 3.4.2 HEC-RAS two-dimensional flow modeling capabilities for calculation case of

this study 20 3.43 Basic steps to modeling 21

CHAPTER 4: CONSTRUCTING THE FLOOD MAP OF STUDY AREA 23

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432 Cross-seetional data of Da Ban river 30 433° Land cover data 31

44 HEC-RAS modeling application for flood simulation and caleuladion 2

44.1 Selection and construction of model domain 32 44.2 Developing a terrain model for use in 2D modeling and results in mapping 32 44⁄8 Running the unsteady flow model sĩ 449° Viewing2D output using RAS Mapper 56

4.5 Validation numerical model with analytical solution.

45.1 Analytical Solution by Ritter 6s

452 Modeling the 2D Dam-Break wave ø

4.53 Comparing the model results and the analytical solution by Ritter (1892) 7! 4.6 Sensitivity testing,

4.6.1 Introduction n 4.62 Considering the factors affect the model results B 4.63 Choosing position on model for analyzing results 4 464 Sensitivity testing results 75 465 Conclusion 80 47 Constructing flood hazard map by ArcGIS

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Niehe-CEM&TLU-ULG master program Master thesis

CONCLUSIONS AND RECOMMENDATIONS -5-<86 Conclusions.

LIST OF FIGURES

Figure 1: Geographical location of study area (souree: Google Map), 6 Figure 2: Representation of terms inthe energy equation 16 Figure 3: Implementation diagram, 23 Figure 4: Da Ban reservoir, 24 Figure 5: Headworks before upgrading 2 Figure 6: Headworks attr upgrading 25

Figure 7: Inner stope of earth dam, 25

Figure 8: Outer slope of dam, 25 Figure 9: Existing spillway 26 Figure 15: Chart of hydrograph with iequcney 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 (iver) terrain daa 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 Tlow are, 38 Figure 28: Adding the parameter ofthe reservoir 38 Figure 29: SA/2D Area Hydraulic Connection editor 39 Figure 30:Parameters ofa,new spillway and b, gates 39 Figure 31: RAS Mapper’s new land classification ái Figure 32: Set Manning’sn override land cover values at some regions 2 Figure 35: Spatially varied Manning's roughness layer dã

Figure 34: Boundary condition 44

Figure 35: Hydrograph with frequeney 0.5% 44 ydrograph with frequency 0 45 Figure 37: Normal depth in downstream 45

Figure 38: Initial condition of Reservoir 46

Figure 39: 2D flow area computational options 4

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Breach parameter caleulatr from regression equations 49

Shape and dimensions of calculated breach 40

Flow hydrographs ffom dam to downstream without dam break (Mood frequency 50 Flow hydrographs from dam to downstream effect by dam break (lood frequeney SI ‘Unsteady flow analysis window for a plan (plan 3) 56 Display results map parameters 37 RAS Mapper with depth results layers, 37 RAS Mapper with velocity results layers ` RAS Mapper with WSE Results Layers 59 Example Time Series Plot of Depth from three different Plan, 0 [Example Time Series Pot of Velocity from thee different Plan 61 ‘Example Time Series Pot of WSE from three different Plans 62 Example velocity plot with color and diection/magnitude arrows 6 Example ofthe particle tracing visualization option on top oF a depth layer 63 Profile Line tumed on and selected for plotting options 4 Example profile line plot of Water Surface Elevation (WSE) 64 Results Mapping Window: 65 Analytical solution by Ritter (water height) 6 Geometry model 61 Hydraulic structure with a dam break, 6 ‘Water hight follow model a 0s 6 ‘Water depth profile along the river at 20s 6 Water depth profile along the river at 40s 0 ‘Water depth profile along the river at 608 0 Analytical solution by Ritter (blue) and simulated results (orange): water depth at

‘The position on model for analyzing results T5 “The water depth at point 3 in Sensitivity test cases of values T6 The velocity at point 3 n Sensitivity test cases n

‘The water dept at point 3 in Sensitivity test eases of mesh size T8

‘The velocity at point 3 in Sensitivity test cases of mesh size 78 ‘Computed tim step ìsŠ seconds and 2 minutes at point 3 19 Breach bottom elevation is S6m and 46m (Sensitivity testing) at point 1 80 Flood hazard map in case of flood frequency 0.5% 83 Flood hazard map in ease of flood frequency 0.1% ¬ Flood hazard map in dam break case with flood frequency 0.1% 85 A resident area before and after covered by flood water, 87 Velocity changes from river to floodplain, 87 The flow through a resident are with the discharge of S00 (mis) `

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LIST OF TABLES

“Table I: Climate specification 8 ‘Table 2: Climate factors ofthe itrigated area, 1 Table 3: Meximum wind speed # Table 4: Evaporation 9 Table 5: Evaporation loss °

Table 7: Network and available surveyed factors, 9 ‘Table &: Flow statistics at Da Bạn, ° ‘Table 9: Flow distribution at Da Bạn, °

‘Table 11: Situation of sol and forest sources 10 ‘Table 12; Elevation volume eure 24 Table 13: Max flow and total flow in Da Ban in accordance with frequencies, »

Table 14; Manning's n values are used for the model 40

‘Table 15: Eddie viscosity transverse mixing coefficients 33 Table 16; Calculation cases 5s Table 17; Caleulation eases of Sensitivity test T3

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CHAPTER 1: INTRODUCTION LA 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 indus alization, Vietnam has built thousands of big and small reservoits 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, ete Construction of reservoirs offered tremendous efficieney to economic sectors

Construction of reservoirs raised a major concern for safety due to potential risks lo ‘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 atthe project's downstream areas,

Most ofthe 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

Being aware of the situation, the project VWRAP has provided Vietnam Government financial ass tance in strategic change with the capital loan This loan was to upgrade

‘and modernize the irrigation system, improving irigation 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 ofthe mentioned

Toan, as follows:

~ Dau Tieng water resources subproject.

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= Yen Lap water resources subprojeet = Ke Go water resources subproject.

= Cam Son - Cau Son water resources subproject.

= Da Ban water resources subproject.

= Phu Ninh water resoures subprojeet

‘Along with upgrade and modemization 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

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 very important for decision makers in the eases of emergency The aims of

flood mapping is:

1 To show the inundation area, water depth, flow velocity and other parameters at any postion in flood region when input data is known;

2 To provide a foundation for seleting or associating flood prevention methods:

3 To suppor for performing land management of looplins;

4, To serve as a basis for studying flood prevention methods in basic constuction;

5 To provide information for designing and operating flood prevention works in the

future

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13 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 caus ng 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 River Analysis System (HEC-RAS) to simulate floods in Netherlands, Belgium and the United Kingdom Their study used model aiming at flow Engineering Center's

‘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 deseribed the dam break from both theoretical and modeling application aspeets Breach parameters prediction, understanding of dam break mechanics, and peak outflow prediction were all shown to be essential for the analysis ofdam break, and eventually helped to determine the loss ‘or damages He also used an application example ofFoster Joseph Sayers Dam break, further modeled and analyzed using HEC-RAS model based on available geometry

‘Ackerman and Brunner (201 1) địd 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, HE C-RAS will imulate unsteady flow from the dam break process This result associates with GIS technology to establish the flood mapping for flood preparedness and prevention

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‘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, ete, 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:

Lun Duy Vu and Nguyen Phuoe 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 ereating 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, ete

In developing flood maps for downstream of the Vu Git

(2013) applied HEC models including HEC-HMS, HEC-RAS, and HE(

“Thu Bon river, Tran Van Tinh

-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%,

Itean be elearly seen that using the hydraulie 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 forthe study area downstream of

Da Ban Reservoir

14 Objectives and methods:

‘The objective ofthis study is to apply the hydraulic modeling to develop a flood hazard

map for downstream area of Da Ban reservoir, Ninh Hoa disriet, Khanh Hoa provinee, 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.

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In present, there are two major methods which are used worldwide for flood mapping, including

4 Flood mapping based on the investigation ofthe 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,

Structure of thesis

“The thesis is organized withthe following pars

“Chapter: Introduetion

‘Chapter 2: Social and natural condition of the study area

‘Chapter 3: Theoretical bass for flood mapping construction

‘Chapter 4: Development ofthe flood map of study area

‘Conclusions and recommendations

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‘Niche-CEM&TLU-ULG master program Master thesis

CHAPTER 2: SOCIAL AND NATURAL

CONDITIONS OF THE STUDY AREA

21 Natural condition of study area 211 Geographical location of study area

‘The Da Ban river basin situated in Ninh Hoa district, Khanh Hoa province The

‘coordinates are 109°03" east longitude, 1234" 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 Nonhem-Southem 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 kn with high riverbed

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slope The Da Ban river is one of the main distributaries of the Ninh Hoa river with the ‘conjunction near Lae 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,

213 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 climatie 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 inthe mainland.

‘On the contrary, this area is under flood effect with average wind speed, maximum wind speed, annual rainfall, maximum rainfall rather high,

inh Hoa, Da Ban, Dong Trang, Nha Trang, Ea Krong Hin which are recording data of all meterological ‘Near Da Ban reservoir, there are meteorological stations of N

parameters over a long period,

= Measurement network and factors of elimate in the basin

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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

Manh | AiFtemperature | Relative ‘Wind speed | Evaporation

= Climatic conditions of the irrigated area are shown in Table 2

Table 2: Climate factors ofthe irrigated area

Month | Temperature | Relative ‘Wind speed | Evaporation | Sunshine

= Annual rainfall at Da Ban: XOlv= 1950 mm = Maximum wind speed shown in Table 3

‘Table 3: Maximum wind speed

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3 [ Increment of evaporation due to reservoir: AZ| mm “04

= Loss of raised evaporation AZ in Table 5

Table 5: Buapraton oss

Noam eT vee

a2 [115/16] 09| m3] 01 290 216 as9|204, 202 |29/ 45 [oe = Rainfall are shown inTable 6

Table 6: Rainfall

No, | Factors Unit_| Value_| Remarks

1) Annual rainfall, Xo mm | 1950 | Thiessen method Tor 2 Salons: Ea Krong llin and Da Bạn

2 | Max rainfall in one day, | man [688 | Arithmetic average, 2 stations: Fa

Xu Pas% ‘Krong Hin and Da Ban

3 | Max rainfal n3 days, | mm |95Z | Same as above Xa, Past

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 Bị Recording | Yearsof

area, | period | record

T | Dong Trang | Cairiveria Nha Trang [TS | 18832001 | 19 2 | DaBan Da Ban river 126 197621983 | &

= Hydrological specifications are shown in Table 8

‘Table 8: Flow statistics at Da Ban

‘Specification ‘Annual flow [Coefficient ot | Coefficient of | Que (as) Qwim's) variation, Cv | skewness Cs

Value 429 0.43 12 251

= Flow distribution at Da Ban see Table 9

Table 9: Flow distribution at Da Ban

[Mon Te TT Í§ [9 [to jH l2 j1 [2 11.11 |]š [Ww

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b2gm 3) 14Š 140055 255 TTTT 1230 8621063 10100841072 Lis QuPs(mis) 189 [142/111 [0997 1.75

= Flow and total flood see in Table 10

2I2 258

‘Table 10: Flow and total ood

No Specifications Unit

142 5431 K49,

Design frequency, P %

050 oor 1 Design flow Qp mis | 1650 [2700

2 | Design flood volume, Wp [10m T544 [6758 | 84.79

16.87 32013

2.1.3, Ecological specification of animal, vegetation

“The basin surface mostly has weathered soil with acrisols, feralsols, 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 frm ‘components, suitable with fiuits, 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

a_— [Specific sil 3Ø TS Tre

1b Housing area 1488 497 1985,| Unused soit 3784 Z2 58651

3⁄2 Socio-economic conditions

Followings are the figures from the technical design profile of Da Ban spillway N°2,

Khanh Hoa province which was implemented by Song Da Consulting Joint Stock

Company in 2010 The area belongs to Ninh Son commune, Ninh Hoa Disti L Khanh

Hoa Province includes the ethnie 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 produets 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, here are some people breeding fish in Da Ban Resevoir.

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Presently, average food income per capita is low (200 kg/capila/year) They are cdreeding cattle and poultry for their own usage, Other sectors sueh as handicraft and tourism service are undeveloped, The total average income is about 0.9*10*

NDicapita/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 8

(almost households in the village have a television), Other services such as telephone,

‘computer and other culture-spiri living in the area nearly not developed yet Healtheare 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 bu, inundation issues were redueed with the regulation ability of eservoi, However, the flood risk in downstream can oecur in eases

ofthe reservoir discharge low 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 ease of severe floods.

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CHAPTER 3: THEORETICAL BASIC FOR FLOOD MAPPING

BL General overview

3.11 Background of flood mapping

According to WMO ( 2013), map shows flood hazards, flood-prone areas, and related spatial information are necessary parts for an effective approach to integrated flood ‘management This is especially important when discussing the problems ofspace, such as land use planning in flood management framework Flood maps can help people to gine from flood assessments The flood assessments and flood mapping have a close

relationship, Thete are a lot of difference formats of flood mapping and flood

assessment such as risk map, hazard map, ete Flood maps are preliminary and detailed

which depend on technical expertise as well as human and financial resources.

3.12 Objectives of this toot

WMO (2013) also indicates that flood maps play an important role in flood management The basic aims of flood maps are to provide information about shape, size, speed of flood in the past as well as their impacts, which help in decision-making ‘on various aspects of integrated management of floods Objectives of flood maps include changing land uses and climate change; land use regulations and building codes;

impacts of urbanization; emergency response; asset management; or overall public

3.1.3 Flood mapping process

“The flood mapping is a process which depends on local conditions The process and

production often implement following steps:

= Selection of object and purpose of map;

= Selection of map type:

= Selection of approach;

= Collection of available data;= Implementation and updating

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Implementation of flood assessments and development of flood maps which requires some relevant considerations before the programme launch,

3.1.3.1 Objectives ofa flood mapping programme

WMO (2013) suppose that objective of flood mapping programme includes purpose, target audience, and target area, so it has to answer the following questions:

= What are these maps produced for?

= Who is using the maps?

- Which areas are covered? (river basin, particular flood plain, river reach, particular settlement, a whole province, ete.)

3.13.2 Type of maps

‘There are different types of maps such as event map, hazard map, vulnerability map and

risk map It depends on the objectives of the project, the resources available and the

potential benefit achievable,

For example, inthis study, a hazard map is considered,

41.3.3 Mapping approach and methodology

In this part, I only present for flood hazard map Three different approaches for developing flood hazard maps:

le historic approach is based on past flood events: To develop flood zones, the documents can be used including written reports, old maps or photographs ‘or any other documents, These documents may provide relevant information,

“The historie approach is often used for the calibration of the detailed mapping stage or preliminary and ger ral purpose flood assessments

= Geomorphologic approach: This approach uses the distinet marks that flood leaves in the landscape to develop flood maps As a historic approach, the

geomorphologic approach also serves the preliminary and general purpose flood

assessment and their respective maps It is often used for the calibration of the detailed mapping stage.

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= Modeling approach: In this approach, hydraulic models are applied to simulate floods of a particular magnitude occurring in area study, The modeling approach ‘often serves the detailed flood assessment.

“The choice of approach depends on the stage of mapping, purpose, and available data In this thesis, the hydraulic modeling approach is applied for the area study.

3.1.34 Data needs and availability

‘A good flood hazard mapping involves various data sets

= Topographic data: Topographic maps with contours, digital elevations models, river cross-sections and similar data

= The magnitude of hazard: this data includes rainfall, steam gauge, and ydraulie data such as channel geometry, bed roughness, et

= Exposure: this is the data of socio-cconomie activities such as works,

population, residents, industries, and the economie value of exposed assets, Such

data may be not always readily available

~ Vulnerability: Often such data are not available Vulnerability classes have to be attributed to land-use classes, such as housing estate, industrial complex, transport infrastructure, ete

3.1.3.5 Implementation and update process

According to WMO (2013), the updating process has to be defined before the mapping

starts, Updating should occur regularly every 10 to 15 years or after we get new information

314 Products of flood hazard map

3.1.4.1 Content of maps

AA flood hazard map gives information on flood inundation such as inundation depths, ‘extent, flow velocity ete The basie information includes:

= Flood extent (areas covered by water),

= Flow velocity (ru),

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According to WMO (2013), the standard scale ofhazard maps is varying from 1:5,000 1o 1:25,000 A scale of 110,000 is a good seal to identify the features which inundated ‘The hazard map should superpose on the available topographic map with ground

‘elevations and physical Features

3.143 Purpose and use

[As mentioned previously, the flood hazard maps provide basic information for various Aoodplain management issues and help different stakeholders including local

governments make decisions in flood management, Flood hazard maps play an essential

role in assessing of flood risk, development of flood mitigation plans, preparing flood risk management schemes, and in particular for local urban planning Flood hazard maps form the basis for the flood risk maps, flood emergency maps, and other related

3.2 General about the hydraulic problems in river network.

In fact, the flow in the river system or another area is the complex spatial flow.

"Nowadays to resolve the hydraulic problems in the channel, river network, one often calculates using equations of one-dimensional (1D) steady flow, or one-dimensional

unsteady flow, or two-dimensional (2D) unsteady flow, or event three-dimensional (3D) unsteady flow.

3.2.1 1D steady Flow

3.2.1.1 Equations for basic profile calculations

Water surface profile is computed from one cross section to next by resolving the energy ‘equation which is written as follow:

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“ sư

BE ey tbh Got“ưng 20%

Where Z,,Z,: elevation of main channel inverts;

16,1: depth of water a eross section;

2,0; velocity weighting coefficients; a: gravitational acceleration,

1, energy head loss.

Figure 2: Representation of terms in the energy equation 321.2 Limitations of 1D steady flow

‘Thote ae limitations ofthe ID steady flow suchas: = Flows steady.

+ low is gradually varied

= Flow is one dimensional

= Rivers have small slopes 3.2.2 1D unsteady Flow

“The basic system of equations used for unsteady flow are (2-2) and (2-3) which include the continuity equation and the momentum equation.

‘The continuity equation:

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Niehe-CEM&TLU-ULG master program Master thesis Acarea of river eros section (mỆ);

S: er0ss section area of storage (m);

4; extra flow on the river per length unit (ms);

VI: average velocity of section (ms):

gravitational acceleration (nM+);

2: water level at caleulation section (m);

Sự hydraulic slope

3.23 2D unsteady flow hydrodynamics

Similar to 1D unsteady flow problem, the basic system of equations for 2D unsteady flow has one continuity equation and two motion equations.

“The mas (continuity) conservation ï

Where L is time, u and v are the velocity components in the x- andy- direction respectively , and q is @ source/sink flux term.

7

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“The momentum conservation

When the horizontal length scales are much larger than the vertical length scale, volume ‘conservation implies that the vertical velocity is small The Navier-Stokes vertical ‘momentum equation can be used to justify that pressure is nearly hydrostatic In the absence of baroclinic pressure gradients, strong wind forcing, and non-hydrostatie

‘pressure a vertically-averaged version of the momentum equation is adequate Vertical velocity and vertical derivative terms can be safely negleeted The shallow water

‘equations are obtained.

2 Hyd gD (220) ery,aa ay ex

6-6)

Where w and v are the velocities in the Cartesian directions, g is the gravitational acceleration, sis the horizontal eddy viscosity, is the bottom friction coefficient, and

is the Coriolis parameter

33° General about the hydraulic modeling

With the development of science, especially computer science, there are many

numerical models have been developed to solve the above hydraulic problems

Thete are alot of numerical models which can solve ID steady flow and 1D unsteady flow such as MIKE 11, VRSAP, HEC-RAS.

The numerical models which can solve 2D unsteady flow problems are very common including MIKE 21, MIKE 21 HD, MIKE FLOOD, HEC-RAS, ete

In this study, HEC-RAS has been selected to solve the ID and 2D flooding problems.

34 HEC-RAS model

341 Introduetion

The U.S, ArmyCorps of Engineers’ River Analysis System(HEC-RAS) is software that allows user to perform one-dimensional steady flow hydraulies: one and

two-1g

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‘dimensional unsteady low river hydraulics calculations; quasi-unsteady and full unsteady flow, sediment transport ~ mobile bed modeling; water temperature analysis; and generalized water quality modeling (nutrient fate and transport)

“The HEC-RAS software was developed at the Hydrologic Engineering Center (HEC), Which isa division of the Institute for Water Resources (IWR), U.S Army Corps of Engineers The software was designed by Mr Gary W Brunner, leader of the

HEC-RAS development team The two-dimensional unsteady flow modeling capabilities were developed by GaryW Brunner, Mark R, Jensen, Steve S Piper, Ben Chacon

(Resource Management Consultants, RMA), and Alex J Kennedy.

According to USACE (2016) beside the one-dimensional (1D) version, nowadays HEC has had two-dimensional (2D) hydrodynamic routing within the unsteady flow analysis

portion of HEC-RAS, Users can now perform one- dimensional (1D) unsteady flow modeling, two-dimensional (2D) unsteady flow modeling (Saint Venant equations or Diffusion Wave equations), as well as combined 1D and 2D unsteady flow routing The

2D flow areas in HEC-RAS can be used in a numier of ways.

“The follow this guideline book, HEC-RAS can perform:

= Detailed 2D channel modeling

~ Detailed 2D channel and floodplain modeling = Combined 1D channels with 2D floodplain areas.

= Combined 1D channels/loodplains with 2D flow areas behind levees.

~ Directly connect 1D reaches into and out of 2D flow areas

~_ Direetly connect a 2D flow area to ID Storage Area witha hydraulic structure ~ Multiple 2D flow areas inthe same geometry.

= Directly connect multiple 2D flow areas with hydrauli structures

Simplified to very detailed Dam Breach analyses

= Simplified vo very detailed Levee Breach analyses

= Mixed flow regime, The 2D capability (as well as the ID) can handle the supercritical and subcritical flow, as well as the flow transitions from suberitical 1o supercritical and supercritical to subcritical (hydraulic jumps).

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3.4.2 HEC-RAS two-dimensional flow modeling capabilities for calculation case of this study

‘The 2D flow routing capabilities in HEC-RAS have been developed to allow the user to perform 2D or combined ID/2D modeling The 2D flow modeling algorithm in HEC-RAS has the following capabilities:

1, Can perform 1D, 2D, and combined 1D and 2D modeling, HEC-RAS can perform 1D modeling, 2D modeling, and combined 1D and 2D modeling,

3 Saint-Venant or Diffusion Wave Equations in 2D The program solves either the 2D Saint Venant equations (with optional momentum additions for turbulence and

Coriolis effects) or the 2D Diffusion Wave equations In general, the 2D Diffusion

Wave equations allow the software to run faster and have greater stability properties 43 Implicit Finite Volume Solution Algorithm The 2D unsteady flow equations solver uses an Implicit Finite Volume algorithm The implicit solution algorithm allows for

larger computational time steps than explicit methods, This method improves this stability and robustness 2D flow areas can start completely dry, and handle a sudden rush of water into the area Additionally, the algorithm can handle subcritical, supercritical, and mixed flow regimes (Nlow passing through critical depth, such as a

hydraulic jump).

4 Connecting between lateral structure, storages area and 2D flow area

Algorithms of software allow user can connect easily to many components such as storage area, structures, and 2D flow area Besides, the soliware has a tool which allows ‘and support in dam break calculation, so itis very suitable fora case study of the thesis 5 Unstructured or Structured Computational Meshes The software was designed to use unstructured computational meshes, but can also handle structured meshes, The ‘computational cells can be triangles, squares, rectangles, or even five and six-sided ‘elements (the model is limited to elements with up to eight sides) The mesh can be @ mixture of cell shapes and sizes.

6, Detailed Flood Mapping and Flood Animations Mapping of the inundated area, as well as animations of the flooding can be done inside of HEC-RAS using the RAS 20

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Mapper features, The mapping of the 2D flow areas is based on the detailed underlying terrain and not the computational mesh cell si

7 Tightly combine with other software, HEC-RAS can combine with many software to use input data or analysis results ARC-GIS is a good combination and was used in

this study.

34.3 Basie steps to modeling

‘The following are the basic steps for performing 2D modeling within HEC-RAS

(Brunner, Warner, Wolfe, Piper, & Marston, 2016):

1 Establish a horizontal eoordinate projection to use for the model, from within HEC:

RAS Mapper.

2, Develop a terrain model in HEC-RAS Mapper The terrain model is used to establish, the geometric and hydraulic properties of the 2D cells and cell faces iis also needed in

EC-RAS Mapper ‘order to perform any inundation mapping in

3 Develop a land classification data set within HEC-RAS Mapper in order to establish Manning’s n values within the 2D Flow Areas, Additionally, HEC-RAS has an option

for user defined polygons that can be used to override the land classification data or as calibration zones,

4, Add any additional mapping layers that may be needed for visualization, such as acrial photography, levee locations, road networks, ete

5 From within the Geometry Editor, draw a boundary polygon for each ofthe 2D Flow Areas to be modeled Or we can import the X, Y boundary coordinates from another

6 Layout any break lines within the 2D flow area to represent significant barriers to flow, such as levees, roads, natural embankments, high ground between the main ‘channel and overbank areas, hydraulic structures, ete.

the 2D Flow Area editor, create the 2D computational mesh for each 2D Flow

2

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8 Edit the 2D Flow Area mesh in order to improve it, such as: add additional break Fin increase or decrease cell density as needed.

9 Run the 2D geometric pre-processor from RAS Mapper in order to create the cell and face hydraulic property tables.

10 Connect the 2D Flow Areas to ID Hydraulic elements (river reaches, lateral structures, storage area/2D flow area hydraulic connections) as needed,

11 Add any necessary hydraulic structures inside of a 2D Flow Area.

12 From the Geometric Data editor, draw any external boundary condition lines along the perimeter of the 2D flow areas.

13 Enter all of the necessary boundary and initial condition data for the 2D flow areas

in the Unsteady Flow data editor.

14 From the Unsteady Flow Simulation window, set any necessary computational ‘options and settings needed for the 2D flow areas,

15 Run the Unsteady flow simulation.

16 Review the combined 1D/2D output in RAS Mapper, as well as using the existing

‘output capabilities for the ID portions of the model

By

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CHAPTER 4: CONSTRUCTING THE FLOOD MAP OF STUDY AREA

4.1 Implementation diagram

‘The development of the flood map for the study area is presented in this chapter following the diagram in Figure 3.

Terainmodel ] [Genet | [Unset fow

Figure 3: Implementation diagram

3

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4.2 Constructing database

4.2.1 Project data

a) Reservoir

‘The Figure 4 shown image of Da Ban Reservoir The main characteristics of the reservoir is the stage — volume relationship This curve for the Da Ban Reservoir is

presented in Table 12.

Figure 4: Da Ban reservoir

Table 12: Elevation volume curve

Zim) | VAG Gm) | Zim) | V.10%m')

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“The main partis an earth dam with the length of 347,50 m, the height of 42,50 m, the crest width of 12 ind the outerthe erest elevation of 67 m, the outer slope of 3:1,

slope of 2,5:1 (Figure 5 to Figure 8).

Figure 5: Headworks before upgrading Figure 6: Headworks after upgrading

(Source: Google Map) (Source: Google Map)

+ The spillway (Figure 9) is made by reinforced concrete, 3 radial gates operated ‘manually using a capstan The dimension of the radial gate is BxH = 3⁄6 m,

3B

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Figure 9: Existing spillway

~The intake is made of reinforced conerete (see Figure 10), located direetly under the spillway, The service gate isa vertical rising one, located at upstream The ‘operating gate is radial gate located at downstream, operated using a screw

~The new free spillway (Figure 11) was built to the right of the earth dam with

total width of 100 m and the sill elevation is 63 m,

26

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Figure 11: New spillway

(Source: Google Map)

422 Topography data

~ Topographic data of the river downstream of Da Ban with the scale 1:10,000 are ‘ross-sectional data surveyed by NIPPONKOIER and OSAKA in May 2006

(Figure 12)

A cross-section of river

?

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Figure 13: (DEM) 30mx30m of s dy area

4.2.3 Landuse data

“The land use data is based on the Landsat GLS'TM_Multispectral_ 2000 imagery

(Figure 14)

2

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424 Hydrologic data

‘The inflows to the reservoir have been calculated by NIPPONKOIER and OSAKA

(2006), The results are presented in Table 13 and ( Figure 15 and Figure 16), Table 13: Max flow and total flow in Da Ban in accordance with frequencies

Frequency P%

No Spevifications Unit

050 [0A0 [oor

1 | Design peak flow, Qp mis | 1650 |2300 | 2790 2 | Design flood volume, Wp | 10m’ 4444 [67,38 | 84.79

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4.3 ARC-GIS software application to construct DEM data, cross-section data, and landcover

43.1 DEM data

Based on the DEM developed for Khanh Hoa province, the boundary of the study area,

‘we can ereate DEM data for the study area as in Figure 17.

43.2 Cross-sectional data of Da Ban river

“The cross sectional data was created from the topographic data of the area by HEC-GeoRAS tool in AreGIS software (Figure 18).

‘The topographic data is used to create triangulated inegular network (TIN) before making the cross-section data

0

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Master thesis

Figure 18: Create cross sectional data for Da Ban river

4.3.3 Land cover data

Land cover data is created from Landsat data sources in order to estimate the Manning's 1 values into to 2D flow area properties tables.

In this part, the classification tool in ArcGIS is used to analysis data from Landsat data

(Figure 19)

3

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