Major Intergrated water resources Management: Impact assessment of regulation works in the Thai Binh river downstream

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURALDEVELOPMENT

IMPACT ASSESSMENT OF REGULATION WORKS IN THE THAI BINH RIVER DOWNSTREAM

Nguyen Vinh Nguyen

MSc Thesis on Integrated Water Resources Management

November, 2017

XMINSTRYOEEDLCXHONANDTRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT

‘THU ITY

Nguyen Vinh Nguyen

‘THESIS OF MASTER DEGREE

1 Assoc Prof Dr Nguyen Mai Dang 2 Assoc Prof Dr Ngo Van Quan

‘This research is done for the partial fulfilment of requirement for Master of Science Degree at Thuyloi University

(This Master Programme is supported by NICHE ~ VNM 106 Project)

‘November, 2017

Thereby certify that the work which is being presented in this thesis entitled, “Impact assessment of Regulation works in the Thai Bình river downstream” in partial fulfillment of the requirement for the award of the Master of Science in Integrated ‘Water Resources Management, is an authentic record of my own work carried out

under super

Van Quan.

ision(s) of Assoc Prof Dr Nguyen Mai Dang and Assoc Prof Dr Ngo

‘The matter embodied in this thesis has not been submitted by me for the award of any other degree or diploma

Date: 19/11/2017 Signature

Nguyen Vinh Nguyen

‘The Thai Binh River System's downstream is a major economic region whieh is located in the Red River Delta including Hai Phong city and Thai Binh province Currently, water distribution here is significantly unreasonable for the downstream water stakeholders,

‘Therefore, a research regarding current water allocation assessment need and hhas (© be conducted in order to find out appropriate solutions for solving and surmounting the issues In this study, the MIKE 11 model was used to simulate the recent status of the system and prediet the water distribution according to some proposed scenarios based on the system operation in the future

‘The study determined the existing problems and troubles in water distribution and water use in the Thai Binh River downstream, Accordingly the impact of structural measures proposed in this study on flow changing also was analyzed in details, In addition, the study ilustrated thatthe flow discharge of rivers in the system will be changed significantly after building the regulated structure works In addition,

the study proposed some alternatives aiming to strengthen the management of sy

operation as well as water use in the downstream of Thai Binh River.

Key words: Red River Basin, Thai Binh River, MIKE 11 model, flow regime

I would like to give a big thank to all people who have supported and assisted me during my master th research Thanks for their support, encouragement and

‘guidance that allowed me to complete this tudy in time.

Especially, I would like to express my appreciation to Assoc Dr Nguyen Mai Dang and Assoc Dr Ngo Van Quan for their unlimited encouragement, guidance, comments and technical supports as well as the thesis writing process from the beginning of this thesis research,

1 wish to thank Dr, Ilyas Masih, Assoc Dr, Nguyen Thu Hien and Assoe Dr [Ngo Le An for their feedbacks, references and support on the proposal process.

also want to thank to all instructors and staff of Thuy Loi University who have helped me a lot during the master course.

1 would like to give my appreciation to Dr Ho Viet Cuong, Mse Nguyen Thi Ngoc Nhan, Msc, Nguyen Van Bach and Mr Phan Van Thanh who was willing to help me with modelling application in the thesis.

1 also would like to thank the National Key Laboratory of River and Coastal Engineering and Institute of Vietnam Academy for Water Resources for their information and useful data input.

Last but not Lwant to take this opportunity to show my appreciation to my family, friends for their inspiration and support throughout my life; this research is simply impossible without you,

3.1 Description of the study area.

3.1.1 Geography and River Network 18 3.1.2 Climatic characteristics 20 3.1.3 Hydrological characteristics 23 3.1.4 Tide and tidal effects in the river mouth 26 3.2 Water deman

3.2.1 Water demand for agriculture 2 3.2.2 Water demand for aquaculture 28 3.2.3 Water demand for industry 29 3.2.4 Water demand for domestic 29 3.3 Water exploitation and utilization issues.

4 METHODOLOGY, 41 The MIKE 11 Model

4.1.1 Governing Equations 33 4.1.2 Methods used in the performance evaluation 34 4.2 Mike 11 Model Set-up.

4.2.1, Input data 35 4.2.1.2 Boundary conditions 37 4.2.1.3 Cross-sections 38

4.2.1.4 Meteorological and hydrological data 39 4.3, Modeling calibration

43.1, Step by step.

4.3.2 Initial conditions setup 40 4.3.3 Calibrating the hydraulic parameters 40 4.3.4, Modeling calibration in flood season ái

4.4.1 Modeling validation in flood season 48 4.4.2 Modeling validation in dry season

4.5 Proposed regulation works and scenarios 4.5.1, Proposed regulation works

4.5.2, Simulated Scenarios 5ã 5 RESULTS AND DISCUSSIONS.

$1 Scenario results simulated in August 1996 5.2 Scenario results simulated in January 200%

6 CONCLUSIONS AND RECOMMENDATIONS ss 72 6.1 Conelusions

6.2 Recommendations for further researches APPENDIX

List of figure

Figure 1.1 Thai Binh River downstream area 8 Figure 2.1 Simulation interface file of Mike 11 (HD Module) 15 Figure 3.1: Map of the study area focus on two districts: Vinh Bao and Tien Lang 18 Figure 4.1: The research flowchart 32 Figure 4.2: Schematic of network and reservoirs considered in the Red River basin 36 Figure 4.3: River network for simulation by Mike 11 model 37 Figure 4.4 Model calibration process 39 Figure 4.5: Hydraulic parameters interface 4 Figure 4.6: The observed and simulated water levels for the 1996 flood event at Ha Noi station in the case of calibration 4 igure 47: The observed and simulated water level in Van Uc River in 1/2006 — ‘Trung Trang Station 45 igure 4.8: The observed and simulated water level in Duong River in January 2006 — Thuong Cat Station 45Figure 4.9: The observed and simulated hydrographs at Son Tay Station 48 Figure 4.10: The observed and simulated hydrographs at Ha Noi Station in January 2007 49 Figure 4.11: The observed and simulated hydrographs at Tra Ly Station 50 in January 2007 50 Figure 4.12: Structure of the regulated dam in Moi River 52 igure 5.1 The locations of selected cross-sections 4 igure 5.2 Actual water level atthe selected points 55 Figure 5.3 Actual discharge at the selected points 55 Figure 5.4 Simulated water level of PAL 56 Figure 5 5: Simulated discharge of PAL 56 Figure 5.6: Simulated water level of PA2 5 Figure 57 Simulated discharge of PA2 5 Figure 5.8: Simulated water level of PAS 58 Figure 5.9: Simulated discharge of PA, 58 Figure 5.10: Simulated water level of PAL+2 59 Figure 5.11: Simulated discharge of PA 142 59 Figure 5.12: Simulated water level of PA1+3 60 Figure 5.13: Simulated discharge of PA +3 60

Figure 5.14: Simulated water level of PA 1+2+3 Figure 5.15: Simulated discharge of PA 1+2+3 Figure 5.16: Actual water level at the selected points Figure 5.17: Actual discharge at the selected points Figure 5.18: Simulated water level of PAL

Figure 5.19: Simulated discharge of PAL Figure 5.20: Simulated water level of PA2 Figure 5.21 Simulated discharge of PA2 Figure 5.22: Simulated water level of PA3 Figure 5.23: Simulated discharge of PAS Figure 5.24: Simulated water level of PA1#2.

Figure 5.25: Simulated discharge of PAL+2 Figure 5.26: Simulated water level of PA 1+3 Figure 5.27: Simulated discharge of PA1+3 Figure 5.28: Simulated water level of PA1+2+3 Figure 5.29: Simulated discharge of PAL+2+3.

List of table

Table 2.1 Comparison of different One-Dimensional (1D) models 12 Table 3.1, Monthly average temperature of the year at stations 21 Table 3.2 Typical average monthly rainfall at stations 2 ‘Table 3.3 Typical monthly average wind speed at three stations 23 ‘Table 3.4: Total water used for cultivation and livestock in year 2012 28 ‘Table 3.5: Water demand of cultivation in period of 2020 and 2030 28 ‘Table 3.6 Water demand of livestock in the period of 2020 and 2030 28 ‘Table 3.7 Water demand of aquaculture in 2012 29 ‘Table 3.8 Water demand of aquaculture in the period of 2020 và 2030 29 Table 3.9 Current status of water use of industrial zones 29 ‘Table 3.10 Water supply for domestic in Tien Lang and Vinh bao districts 30 ‘Table 3.11 Water demand of domestic in the period of 2020 and 2030 30 ‘Table 4.1: The upstream and downstream boundary of the model setup 39 Table 4.2: Calibrated Manning values of the river system 4đ Table 4.3: Model performance of the MIKE 11 for the calibration at some siations 44 ‘Table 4.4: Calibrated! Manning values of the Red and Thai Binh Rivers 46 ‘Table 4.5: Model performance of the MIKE 11 for the calibration in the dry season 47 Table 4.6; Error criteria of the model calibration in the 2002 flood event at some stations 49 Table 4.7; Model performance of the MIKE 11 for the model validation in the dry

season, 50

Table 5.1 Comparison between actual and simulated flows of PAI 56 Table 5.2 Comparison between actual and simulated flows of PA2, 5Table 5.3: Comparison of actual and simulated flows of PA3 58 ‘Table 5.4 Comparison of actual and simulated flows of PA1+2 59 ‘Table 5.5 Comparison of actual and simulated flows of PAI+3 60 ‘Table 5.6: Comparison of actual and simulated flows of PAL+2+3 6 ‘Table 5.7 Comparison of actual and simulated flows of PAL 68 Table 5.8 Comparison of actual and simulated flows of PA2 64 ‘Table 5.9: Comparison of actual and simulated flows of PA3 65 ‘Table 5.10: Comparison of actual and simulated flows of PAL+2 66 ‘Table 5.11 Comparison of actual and simulated flows of PA 1+3 6 ‘Table 5.12 Comparison of actual and simulated flows PA1+243 68

1.INTRODUCTION 1.1 Overview

Water is a useful natural resource and plays an important role in human being ‘The water users in a river basing include some stakeholders such as agriculture, industry, households, recreation and environment Obviously all human activities demand and need fresh water Fresh water is extremely essential for lives; no other natural resources can replace it This meant that water has a high potential use for human (Zaag & Savenije, 2013),

Nowadays, people have been using water resources in negative way.

Accordingly, water quality and quantity are both declining significantly There are some reasons for this statement including the effects of natural conditions, climate change, economic and social development, over exploitation of natural resources as ‘well as the poor management oflocal authorities,

Water crisis has been increasing and affecting widely all over the world It is about L2 billion people; similar to 1/5 global population, living in water shortage ‘areas and other 500 million people are being exposed by this trouble Water shortage is caused by natural phenomena and human activities Fresh water is available everywhere in our planet and much enough for human However, fresh water is distributed unevenly and overused tremendously on the world, In addition, fresh water has been polluted for decades by many polluted sources duc to economic development Unsustainable development also is one of the reasons for water crisis (FAO, 2007) According (0 plenty of water institutes, 1/3 countries in the world are facing with water shortage In year 2025, it will be predicted that approximately 35% of global

population will be able to face with tremendous water shortage problems

Based on the report of Ministry of Natural Resources and Environment (2009) Vietnam has about 3450 rivers with above 10 kilometers length There are 206 water sources which are considered as external water resources, Accordingly, total annual

‘water volume is about 830 bil m the biggest fet systems Total potential

‘groundwater amount is about 63 billion m’ per year and distributed mainly in the hilly

and mountainous regions (Le Mai, 2013) It can be seen that Vietnam has a lot of,

water due to the heavy rainy season and dense river intensity However, droughts and large scale water shortage occurred regularly in many provinces Vietnam currently has many challenges regarding water resources management, In addition, Vietnam is ranked as one of the most affected countries by climate change and sea level rise.

In recent years, the demand for water is rising day by day under the pressure of population and development - social growth Moreover, the uneven distribution of ‘water resources in time and space with the requirements of environmental flows, leading to water shortages appear Besides, the competing interest of different stakeholders even exaggerates the issue Besides, erosion and sediment deposition are happened more frequently on many river systems, These phenomena influences directly on lives, economics and lives surrounding affected areas as well as the safety of hydraulic works in the system One of the natural disasters that needed to be considered is sediment deposition at downstream areas of river system In the northern part of Vietnam, which includes Red and Thai Binh rivers, sediment deposition happening regularly Particularly, in Thai Binh river basin, at the downstream area, Hai Phong city is the most affected area by erosion, deposition as well as salinity

Hydrological models have been used frequently in water resources planning and management such as hydrological forecasting, reservoir operation, water qualit research on flood, inundation and drought, designing irrigation system and supporting for the integrated water resources management An appropriate model selection is ntial for each research project These selections thereby have to be based on study objectives, considering input data and output data, expected results and solutions.

There are many studies on the water field that use models as effective tools to solve problems The MIKE 11 model has been developed by DHI Water and Environment (Danish hydraulic institute) and is used popularly in Vietnam, This model is a

professional engineering software package for simulation of flow, water quality and

sediment transport in estuaries, rivers, irigation system, channels and others bodies “enarios and alternatives of (DHI 2011) This model will be used for simulation of

proposed management

1.2 Problem statement

“THAI mint

Figure 1.1 Thai Binh River downstream area,

‘According to the report of Hai Phong Department of Agriculture and Rural Development, In the Thai Binh River's downstream, salt intrusion at river mouths is increasingly happening because of the natural water distribution and sediment (Luoe river moving and developing on the left side of Van Ue River - Figure 1.1), Thai Binh River's downstream has been deposited by sediment since 1960 The average depth of river bed is fluctuating from I to 2 meters.

Besides, the water resources management here is causing a lot of negative impact on water use, Water quality and quantity are predicted that they are not good enough for ‘water supply in the area in the future Those problems mentioned above did, do and

will influence strongly on the socio-economic development of Tien Lang and Vinh Bao districts Because, these two areas play a role as key development of agricultural areas as well as water demand would be increased significantly,

at Do Son Beach due to the In addition, sediment transport is currently increasi

water diversion to Van Uc River leading to amount of sediment flowing to the sea This will affect tourism and economic development of Hai Phong City.

1.2.1 Objectives of the study

Overall objective is to assess the impact of water regulation works in the downstream of Thai Binh River by using hydrodynamic model To achieve the main objectives, the thesis consists of some detailed goals as follows:

+ Analyzing and assessing the current status of the study area in accordance with problems and troubles,

+ Using the MIKE 11 to simulate the flow regimes according t0 proposed solutions and scenarios in order to suggest the water allocation

+ Determining the water diversion between Red River and Thai Binh River in

‘general, particularly determining the impact of regulation works to flow regime in Thai

Bình river's downstream located in Hai Phong province Main purpose of the Constructions is to increase the flow in Thai Binh river and to decrease the flow in Van Uc river, Also, other purpose is to prevent saltwater intrusion in Thai Bình river as well

+ Proposing solutions for water allocation, water usagee, water management in

‘order o enhance the quality of water use in the study area,

1.2.2, Research questions

‘What is the current status of water use in the Thai Binh River passing Hai Phong city?

How does the flow regime in Thai Binh river's downstream area change if regulation works added?

‘What is the effective solution of water management?

1.2.8 Thesis overview

‘Structure of the thesis includes those parts:

Chapter 1: Introduction, presents problem statement, needs of study, research objectives, and overview of the study area

Chapter 2: Literature review, reviews the previous studies related to the content and cope of this research An overview of hydrodynamic models also analyzed here MIKE 11 model will be presented in this chapter as well,

Chapter 3: Study area and data collection, presents the natural conditions, climatic characteristies of the study area as well as the population character economics and society The water demand and management are also discussed in this study.

Chapter 4: Metholodology, shows the methodology and steps to achieve the ‘objectives of the thesis The chapter discusses the data input as well Modeling calibration and validation are also presented here.

Chapter 5: Results and discussions, analyses the model performances (MIKE 11) in order to obtain the research objectives.

Chapter 6: Cconclussions and recommendations, focuses on findings and recommendations, and future research.

In this chapter, existed issues, needs of study, research objectives were be showed, Because of the uneven river flow distribution between the Van Uc river and ‘Thai Binh river in the study area, Thai Binh river has high sedimentvolume and salt intrusion and Van Uc river has the erosion.

2, LITERATURE REVIEW

2.1 Over -w of Hydrodynamic Model

Any scientific field always needs to develop some processes such as monitoring data, recording and measuring data, simulation and explanation of natural phenomena, To have a better understanding of the processes of hydrology, they can be deseribed in laboratories by physical models Besides that numerical models have been developed increasingly due to their advantages such as costs flexibility and applied technology. Accordingly, hydraulic and hydrological models are tools to address the real hydrological cycle in a simplified way Such models are used for understanding the hydrological processes as well as making hydrological predictions in cases where ‘water resources management and utilization activities are implemented The models apply several algorithms to provide a quantitative relation between the input data (e.g rainfall, meteorological data) and output (e.g runoff) The hydrodynamic models have been used for energy production, sediment transportation, water quality and cavironment, Scientists have developed many ID, 2D and 3D dynamic models Those models are used for sustainable water resources management.

Estuaries can be seen as potential and valuable natural resources of environment, society and economics (Nordstrom, 1992), The research on sediment transportation in estuaries is normally difficult due to the fluctuation of sediment and impacts of other natural factors The s sdiment transportation process on rivers is relatively complicated including erosion process, sediment transport and deposition Those processes relate t0 flow regimes, particles characte ies, size and shape, and intensity and elements of the particles The morphological changes are the results of the nonlinear interaction between water and sediment and river bed (Hibma et al, 2004), However, numerical models are used as valuable tools for simulation of natural phenomena due to the development of technology in the past decades in order to get a better understanding of

013) physical processes and numerical technique (Jiang, Ranasinghe & Cowell

in

There are many numerical models from open sources, for example Delft3D developed by Deltares to commercial models MIKE models developed by DHI A lot Of hydraulic models that simulate the hydrologic regimes and sediment transport have been considered aiming to obtain an appropriate model The selected model need to be considered with many factors such as management, variables and main process, data available, and input and proposed solutions (Boorman et al., 2007) Hence, the input data of various models have to be collected aiming to get best understanding of advantages and disadvantages of them before the model application, Table 2,1 shows the comparison of different hydrodynamic models,

Eventually, according to the author's knowledge, natural conditions of the study area and available input, MIKE I1 model was selected as an effective tool for achieving the research study

Table 2.1 Comparison of different One-Dimensional (1D) models

Model [SWAT (Amoldet | MIKE TL HEC-RAS TRE

al,, 1995; Ndomba | (Doulgeris et al, | (Pappenberger et | (Vanet al.,

&Gri 2012) al 2008) 2012)

Manag |SWAT model was | The Mike 11 model | HEC-RAS model is | ISIS is a full cement | developed predict | isa software used forvariety | hydrodynamic issue | the impact of land | package for the | types of projects | simulator for

‘management simulation of flow, | suchas steady, | modeling

practices on water, | water quality, ‘unsteady and mixed | flows, water

sediment, and | sediment transport in | flow regimes The | levels in open

agricultural estuaries, rivers, | model is wed for | channels and

chemical yields in | channels and other | multiple purposes | estuaries large and complex | water bodies,

Taput | -DEM “Hydrological “Reach neiwork | “Hydrological

Data | -Soil and land use | -Topographie Cross section “Cross required | map “Cross section “Steady flow data _| Section’s

“Climate data “Meteorological | -Unsteady low | Geometry“Hydrological data | Sediment “Sediment Sediment

sdiment load concentration Key | The model is based | The model based | HEC-RAS modslis | The model is Variable | on the water fon Saint Venant’s | based onthe | based on one

And | balance equation | equation for continuity equation | dimensional process | for the soil water | continuity and and momentum | Saint Venant’s

content ‘momentum equation | equation equations.

Model [SWAT (Amold et | — MIKEI HEC-RAS ISIS

al., 1995; Ndomba | (Doulgeris et al, | (Pappenberger et | (Van et al.,

‘&Griensven, 2012) „ 2005) 2012)

Key |= Waierquality | Discharge -Sưeam Flow “Runoif

output | -Stream flow Water level Water level Water quality Surface runoff | -Water quality Sediment scour | -Sediment Sediment yield | -Sediment transport_| and deposition

Time | Dailytime step | Sec, Minute, Hourly | Minute, Hourly, | Minute Step and daily time step | Dail Hourly: Daily

‘Access [The user can | The user has lo pay | The user can access | The users can

bility to | access to modify | to use the model and | to modify the code | access freely

the the code of the | accesso the code, | of the model to the software

coding | model

Software |The SWAT model | This isnot open [IL is a_ public | ID component

cost | is free and a public | source software | domain and free of | as well asthe domain software, | The model is very | charge from HEC’s | whole ISIS

bút ArcGIS expensive website component is

Free for users,

(Source: Tania Hassan, 2016)

2.2, Briefs of Mike 11 Model

Modelling of rivers and channels, MIKE 11 is a versatile ID modelling package covering more application areas than any other river modelling package available MIKE 11 is a fully dynamic, one-dimensional modelling package It includes comprehensive facilites for modelling complex river channel networks, lakes and reservoirs, With the hydrodynamic engine as a core module, MIKE 11 offers a variety of add-on modules and large selection of hydraulic structures, including operational

structures lowing users to define complex control strategies as well as dam break structures Additional application areas include, rainfall-runoff, flood modelling, ecology and water quality, real time forecasting and sediment transport and river morphology assessments (DHI, 2007), MIKE 11 has been used widely all over the ‘world The model includes some modules as follows:

© HD Hydrodynamic.

‘© AD Advection-Dispersion,

B

‘This study estimates the proportion of sediment transportation before and after building reservoir systems on the Red River Un-coherence sediment transportation (ST) module is applied in this study The ST module requires the output from Hydrodynamic module (HD) including income and outcome water from each cross-section HD module can describe the critical discharge and super critical discharge throughout a flowchart Hydraulic structure is necessary in any model applications and MIKE 11 supplies all various standard structures There are some typical applications related to HD module including as below:

+ Flood analysis and flood alleviation design studies

+ Realtime flood or drought forecasting

+ Dam break analysis

+ Optimization of reservoir and canal gate and structure operations

+ Ecological and water quality assessments in rivers and wetlands

© Water quality forecasting

+ Sediment transport and long ferm asse fer morphology changes

Salinity intrusion in rivers and estuaries

+ Wetland restoration studies

«Integrated modelling of river and groundwater interaction

HD module requires the following input files: + Network editor *NWKIL

* Cross-section editor *XNSI + Boundary editor *.BNDIL

+ Time series files * DESO

+ HD parameter file HDI

+ Simulation editor *.SIML1

Figure 2.1 Simulation interface file of Mike II (HD Module) 2.3, Applications of Hydro-dynamic Model

All over the world, many researchers have experimented in order to estimate the flow changing (Yan et al, 2010, Lajoie et al, 2007, Matteau et al, 2009; Magilligan

15

and Nislow, 2005) Using the MIKE 11 model has become popular nowadays because of the effective simulation of model

‘Many kinds of hydraulic models have been applied widely in solving water resources issues such as ID models (MIKE 11, HEC- RAS, etc ) and 2D models

(MIKE 21, TUFLOW, F 3D ) In Vietnam, especially the MIKE models have ‘gained popularity lately These packages have been developed by the DHI water and environment (Danish Hydraulic Institute), which is a global organization dedicated to solving challenges in water environments worldwide There is the question is how much is modelling needed? Robyn Johnston and Vladimir Smakhtin illustrated that modelling needs to concentrate on uncertainties reports to assess the application of model in reali for policy and management processes New inventions are needed for improving quahiy and quantity of modelling (Johnston & Smakbtin, 2014) MIKE 11 model is used to Tink the hydrodynamic progress and morphological changes (Wang, 2014) This is a useful method for this study Numerical models are implemented by the combination of hydrodynamic proc

update Jiang etal, 2013),

s, wave, sediment transportation and depth,

In Vietnam, scientists assessed changes of the flow and sediment regime due to the effect of hydropower plants, hydraulic works, regulation works For example in the Red River Delta, there are some researches follows: environment flows (Nguyen Van Hanh and et al., 2010), sediment transportation (Do Minh Due, 2004), assessment of salinity intrusion (Do Thi Bich, 2000); the effects of river bed change, water intake capacity of hydraulic works (Le Van Hung and Pham Tat Thang, 2015): flow changes in dry and wet seasons to water distribution (Nguyen Thi Thu Nga and Ha Van Khoi, 2016): water diversion proportion and its effects to erosion and deposition (Nguyen Huu Hue et al, 2016).

‘To simulate the flows, except MIKE 11, number of models have been considered such as Q_SDM_BASIN_2014 (Dao Tan Quy, 2013), using 1-2D model to assess the effects of constructions on rivers on flow regime and salinity intrusion at estuaries (Luong Quang Xo, 2014) However, the model performances only showed the Nash Coefficient from 0.70 to 0.82 MIKE 11 model for flow modelling is still

applied in many projects (Nguyen Thanh Hung et al, 2015, Nguyen Van Tuan et al, 2014) However, the studies concentrated on surrounding areas and large scale as well as lack of information from the study area, Studying on the downstream area of Thai Binh river need to have available data and detailed conditions of study area In year 2016,1 tia Hasan and others studied for Hai Phong area However, this study was: only concentrated on sediment transportation due to the interaction of upstream

reservoir systems.

In order to solve completely the existing issues on the study area, this study will focus on gathering input data including natural conditions, society, water demands,

water management in Thai Binh River, Hai Phong city Besides, to strengthen the

effectiveness and accuracy of MIKE 11, this study will simulate the flood flow and dry flow by implementing the model calibration and validation processes.

‘The chapter presented overview of hydrodynamic model and focus on the MIKE 11 model Some reviews the previous studies related to the content and cope of this research were be presented as well Unlike previous studies, the study used two sets of parameters for the Mike model in the dry season and flood season The specificconditions of study area were be showed

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3 STUDY AREA

3.1, Description of Study Area

4.1.1 Geographic Characteristics and River Network

Figure 3.1: Map ofthe study aca focus on two distrits: Vinh Bao and Tien Lang

‘The Thai Binh River is included over 275 km length and 11 branches and estuaries in downstream These branches transfer the entire flows from Thai Binh River to four river mouths including Thai Binh, Van Uc, Lach Tray and Cam estuaries.

‘The geographic location of the study area shown as follows:

+ Bordered with Thai Thuy district, Thai Binh province in the South-East direction, close to the borders of Quynh Phu District, Thai Binh Province in the West direction, Hoa river is a natural border defined from the conjunction of Luoe and Thai Binh Rivers.

+ Bound by the East sea in the East direction, bordered with Van Uc river in the North-East direction defined from the upstream of Moi ~ Van Uc river's conjunction to the Sea.

+ Bordered with Hai Duong province in the North-West direction, bound by ‘Moi and Luoe rivers defined from the conjunction of Hoa and Luoe rivers to the conjunction of Moi and Van Ue Rivers,

‘Topography and geomorphology of Thai Binh River downstream are the results of geologic movement in million years in relation with sediment deposition of the Red and ‘Thai Binh River basins It can divide the geography into two main regions: the northern partis lowland terrace with hilly regions, the southem part is remained delta area,

The delta area has elevation fluctuating from 2.50 m up to 3.50 m and the clevation declining from the West to the East directions The surface mainly covered by mixed clay, sandy clay and sediment, In this area, there are many ponds, lakes and ‘wetlands affected by tidal fluctuation, These water bodies are laid along the large rivers such as Van Uc, Lach Tray, Thai Binh and Hoa rivers Particularly, the study ‘area has a long shoreline with many estuaries (Thai Binh and Van Uc estuaries) leading to transfer amount of sediment to the Sea significantly This helps forming the huge polders, mangrove forests or new economic areas such as Tran Duong, Vinh Quang, Tien Hung, Dong Hung, Tay Hung,

‘The geographic characteristics of Thai Binh River downstream influence the flow regime of the local rivers The incline of topography towards Northwest — Southeast directions leads to flow downwards once tidal happening.

“The study area’s river network consists of large main rivers which belong to Red ~ Thai Binh river system such as Luoe, Moi, Hoa, Thai Binh and Van Uc Rivers ‘The location of those rivers described as below:

‘Thai Binh River is flowing through Cat Khe and Phu Luong hydrological stations The river is then divided into wo tributaries including Thai Binh and Rang — Gua Rivers, A segment of Thai Bình tributary flows to Mia River, then merges with Van Uc Another segment of Thai Binh river right after Mia River is deposited strongly Dai Thang weir was built on this river to get water for irrigation purpose ‘Another segment of Thai Binh River identified from Quy Cao to the sea becomes a tributary of Luoc River However, the river bed of this segment has been deposited

19

tremendously and flood controlling capacity of this river is mostly zero Thai Bình River, a segment from the conjunction of Moi River to the sea, has low velocity and has been deposited by sediment, Currently, the river bed of this river is quite large but the river depth is relatively shallow The river bed elevation changes from -1.00 m down to -2.50 m, Due to the degradation of the river, the discharge of Luoe River flowing into this river is qui small, This will definitely lead to extreme salt intrusion, ‘Thai Binh River, from the conjunction of Moi River to the sea, plays an essential role in supplying water for Tien Lang district.

Van Ue River has several tributaries such as Mia, Moi, Gua and Lai Vu Rivers ‘This river divers a small amount of water to Lach Tray River Van Uc River's length is about 43.5 km, average width of the river is approximately 500-800 m, and river bed elevation changing from -10.00 m down to -16.00 m The lowest point reaches -47.00 m where located nearby Moi River.

Luoe River is a tributary of the Red River Luoc River transfers a small amount ‘of water to Hoa and Thai Binh Rivers, meanwhile, the entire water from thị river is transferred to Moi and Van Uc rivers A segment of Luoc River passing Hai Phong has length of 14 km, the average width of cross-sections here is 300 meters, bed elevation fuctuating frim -8.00 m down to -12.00 m, Luoe river plays a role as a natural border ‘of Vinh Bao (Hai Phong province) and Hai Duong as well as a main source of water supply for Vinh Bao and Tien Lanh districts,

Hoa River is another tributary of Luoc, which defined from Chanh Chu conjunction The river reaches to the ea throughout Thai Binh estuary The length of the river is about 37 km, and wide of river bed from 150 - 250 meters, elevation of river bed from -5.00 m down to -7.00 m, Hoa River is a natural border between Vinh Bao district and Thai Binh Province and is a water supply source for Vinh Bao district,

3.1.2 Climatic characteristies

“The study area is located in the southern part of Hai Phong city The topography of the area is mainly delta, Therefore, climatic and hydrologic conditions here have the characteristics of typical red river delta in general and Hai Phong city in particular.

‘The study area has the tropical monsoon climate of coastal zone There are two ‘opposite seasons here Summer season (South-West monsoon) is from May to October

with high humidity and a ot of rain, Winter season (North-east monsoon) is from

November to March of following year with cold temperature and less rain Main characteristics of climate of Hai Phong province described below:

« Temperature

‘The temperature in Hai Phong is normally high and suitable with development of annual agriculture, Due to the controlling of pole cieuladon, annually the temperature in Hai Phong is split into different seasons: hot summer has high

‘temperature of over 25°C, cold winter has lowest temperature of below 20°C Annual average temperature reaches 23°C, highest monthly average temperature reaches 29°C

in July at Hon Dau, Lowest monthly average temperature reaches 16.3 in January at Phu Lien, Maximum temperature, which was observed in Phu Lien and Hon Dau

respectively, was 41.5% in May ~ 1914 and 38.6°C in Jly-1985

Table 3.1 Monthly average temperature (°C) of the year at stations

Stations [1 jM [mm [iV [V [vt |VH[VHjIX X [XI |XH | Tot! PhuLien |I63 169] 194) 23) 265) 281 |284| 27.7 | 269 247|2L3|I79| 331 HonDan [168] 168|192|228) 27/285] 29| 284|a76 253|223| 19| 236 Bạch Long Vi | 168 | 166) 187/223 | 262| 28|287| 283/273 253|224|189| 233 © Rainfall

‘The rainy season starts usually from May and ends in October, The total rainfall, in this season obtains 85% of the total rainfall in year Accordingly, 15% of total rainfall happens in the dry season,

‘Annual average rainfall is approximately 1520 mm, The spatial distribution of annual rainfall is not too different, Annual yearly total rainfall reaches 1677 mm at Phu Lien, and 1534 mm at Thuy Nguyen, 1544 at Tien Lang and 1514 mm at Vinh Bao, Yearly rainfall at the northern parts is normally higher than the southern parts caused by the directions and effects of typhoons and tropical low pressure once they land deeply Hence, the maximum yearly infall is usually occurring in the years

Which affected by typhoons or tropical low pressure Typically, the maximum rainfall reached 2653 mm in 1973 at Tien Lang, and 2577 mm at Thuy Nguyen in 1973, 2271 mm in 1965 at Vinh Bao and 2298 mm at tien Lang in 1960 By contrast, the year 1991 obtained 826 mm at Phu Lien, and 493 mm was obtained in 1968 at Thuy Nguyen, 686 mm in 2007 at Vinh Bao and 637 in 1991 at Tien Lang.

In the rainy season, the rainfall of August reaches highest proportion of 20.9 % at Phu Lien in comparison with annual rainfall, and similarly 18.6% at Vinh Bao, 196% at Tien Lang and 20.7% at Thuy Nguyen The maximum rainfall of three ‘months (from July to October) accounts for 50.3 to 53.9 % of yearly rainfall.

In the dry season, the lowest rainfall in July only reaches 0.8 to 1% of yearly rainfall, minimum rainfall of three months (from December to February) accounts for 4.4% of yearly rainfall at Phu Lien, 4.7% at Vinh Bao, 3.9% at Tien Lang, 3.4% at “Thuy Nguyen

‘Table 3.2 Typical average monthly rainfallat stations

Phu Lien station | Vink Baostation | Tien Lang station | Thuy Nguyen station Month | AY€"@e | Proportion | Average | Proportion | Average | Proportion | Average | Proportion Toul | lố7 | 100 | ISHM | 100 | ISM | 100 | l5 | 180

Serainy season | — 8S sư 48 sĩ'5 dry season 15 16 15 B

Annually there are about 100 ~ 150 rainy days recorded in Hai Phong In the winter, there are about 8 to 10 rainy days in a month In the summer, there are normally 13 to 15 rainy days in a month, Particularly, August has many rainy days and highest rainfall rather than others.

© Wind and storm

~ Wind: The average wind speed was obtained relatively 3.0 mis at stations located in main land and reached 5 to 7 m/s at station located in Islands The wind direction in

year changes and fluctuates toward the circulations, Wind speed fluctuation depends

con high and distance from the sea level Annual wind speed reaches from 33 to 35 mis appearing mainly in typhoon season (July, August and September) The maximum

‘wind speed, which recorded on September 9" 1968, was 50 m/s.

‘Table 3.3 Typical monthly average wind speed (m/s) at three stations

Stations [1 |H [m [wv [v jvi [vn[vmjix [x [xi [xm [Nam Phutien | 34| 27) 27| 31| 33) a1| 32| 27| 28] 30| s0| 28) 30 HonDaun | 4§| 46) 4a] 47| se] s7| 6| 47| 46} s[a9[ a7) 5 BạchLongVi| S 77| 65] S9| 65] 68| 77] 59| 66| 77] §2| 78] 71

‘Typhoons and tropical low pressures: annually there are about 3 - $ typhoons or tropical low pressures landing into Hai Phong province (about 6 ~ 7 typhoons and tropical low pressures coming to Vietnam), Particularly, 1 or 2 typhoons or tropical low pressures land directly and damage the infrastructures such as dikes, dam as well as liv hoods Rainfall caused by storms accounts for high rates of total yearly rainfall (about 20 ~ 30%), especially storm rainfall accounts for 50 ~ 60% of total rainfall in August Once typhoons come to the land, wind speed would be very strong and high Average wind speed during typhoons normally is 30 ~ 40 mís, maximum value could bbe reached 50 ms

3.1.3 Hydrological characteristics

‘There are 9 hydrological stations located in Hai Phong City Trung Trang and Cua Cam are classified as level 1” stations However, total flows on Hai Phong's river systems are originated from Red, Thuong, Luc Nam and Cau Rivers, which are tributaries of the Hong ~ Thai Binh river system These flows are transferred through

2B

Duong and Luoe river to Kinh Thay and Thai Binh Rivers So the flow regime of rivers in Hai Phong is pretty similar to the upstream rivers.

Annual flow distribution:

Flows are distributed unequally in a year The flows in the study prolong from Jun to October, and account for 80% of total flows The flows in August are maximum, accounts for 24% of total flows Minimum flow usually appears in March accounting for | — 2,3% of total flows The flood season spreads in five months However, the amount of water in this season accounts for 80% of total flows The dry season spreads in seven months accounting for 20% of tata flows.

Flood flows:

‘The downstream area of Thai Binh river has been affected by flooding from the Duong and Luce rivers originated from the Red river, Cau, Thuong, Lục Nam rivers and depended on the tidal regime of the East sea as well as the topographic conditions of downstream rivers.

~ Duong River is one of the tributaries of Red River Duong River transfers ‘water from the Red River to downstream rivers surrounding Thai Binh River System ‘Therefore, the characteristics of Duong River are similar to the Red river Flood patlern of Duong River and Luoc River is the same hydrograph of Red River with smaller flood amplitude,

~ Luoe River: amount of water from the Red River is transferred to Luoe River accounting for 1/5 to 1/3 of water of the Red River, which is diverted to Duong River ‘Maximum annual average discharge of Luoe River measured at Trieu Duong station is

approximately 1,650 ms, equals 83% of Red river's discharge measured at Son Tay

Station, Luoe River has small slop The river bed of this river is shallower and narrower than Duong River, so that water from the Red river is diverted slightly A segment of Thai Binh river system from Ro sluice to the sea has been deposited progressively That leads to flood water from Luoc and Thai Binh mostly flowing to Van Uc River.

~ Cau, Thuong and Lue Nam Rivers are upstream rivers So they have various characteristics of flooding compering with the Luoc and Duong Rivers The flood season normally prolongs from the beginning of Jun to the end of September, 1 month earlier in comparison with the Red river Due to the small river basins, a short heavy rain event can even cause a large flooding.

In the Red river basin, there are some highest rainfall places surrounding Phai Lai (300 to 500 km), In the Thai Binh river system, the highest rainfall places are quite close to Phái Lai (50 to 150 km) So that, flooding from Cau, Thuong and Lue Nam rivers usually reaches Pha Lai earlier than the Red River The years that extreme flooding happened also coincided with the years of extreme flooding happening in three tributaries of Thai Binh river (1968, 1971 and 1996) This proved that the Red river and Thai Binh River have the same climatic pattern causing rain events,

‘The dry flow:

The flow in the dry season is only supplied by groundwater and surface water as well as retention water, which are stored in the end of wet season, On the other hhand, most rivers here are nearby the sea, so the dry flow is depended on the tidal regime mostly In the recent years, due to the operation of Thạc Ba Reservoir (Chay river), Tuyen Quang Reservoir (Lo River), Son La and Hoa Binh Reservoirs in Da River, the dry season flow in the Red River is increasing significantly This is helpful and necessary for agricultural development.

‘The flows in Cau and Thuong Rivers in the dry season are mostly stored by “Thác Huong and Cau Dom weirs So that, the flow from Thai Binh to Pha Lai is relatively small, Behind Pha Lai, due to the water diversion from the Red River, Thai Binh River gets more water discharge

‘The discharge of Duong and Thai Binh has been increasingly developing due to the water diversion from upstream reservoirs in Da River as well as river bed change ‘Therefore, water supply and salt intrusion prevention at the downstream of Thai Binh River have been improved also,

Water from Duong River is (he main source supplying for the downstream rivers of Thai Binh River system Amount of water measured at Thuong Cat in the dey season accounts for 66% - 80% of total water in dry season of Thai Binhìs downstream rivers Similar to the Red river, the dry season normally prolongs 7 months, from November to April of the following year

Water resources of Luoe River: the Red River's water, which is transferred to the downstream rivers through Luoe River, is relatively not much, only accounting for 30% of Duong at Thuong Cat In the dry season, severe tidal fluctuation from Ba Lat moves back to the upstream that keeps fresh water in river bed longer So, that is the reason why water diverted from the Red to Luoe Rivers is always available,

Cau, Thuong and Luc Nam Rivers supply small amount of water for the downstream area of Thai Bình The dry season in those rivers spreads normally longer than the Red river within 8 months, from October to May of following year Total "water of three rivers is only 1/3 of Duong River The seasonal distribution of flow of these rivers is unequally and dry flow is mainly supplied by ground water due to

severe evaporation,

Average water level above sea level of rivers pa ng Hai Phong City slightly

fMuctuating The highest average water level was measured in Van Uc River at Trung ‘Trang (0.58 m), the lowest average water level was measured in Lach Tray River at Kien An (0.01), Therefore, the lowest water level causes troubles for water intake of

nigation system

3.14 Tide and tidal effects in the river mouth

‘The influences of tidal regime play a important role in studying the coastal areas According to the tidal classification, tidal regime in the Northern part of Vietnam is mainly 24 hours changing from 1.9 to 2.6 meters From 1972 to 1990, the tidal amplitude is 1.92 meters The shape of river mouths depended on tidal regime and waves of rivers, The estuaries in the northern part of rivers have triangle shapes đúc to tidal force In the northern part, river mouths have U shape, Both tide and ‘waves impact on formation of river mouths (Pruszak et al., 2005) Tidal regime plays

‘an important role in water exchange and sediment transport at estuaries (Allen et all, 1080; Dyer 1986 and Sassi et al, 2011).

Due to the estuaries reaching the Gulf of Tonkin, water level fluctuation at the estuaries is usually similar to tidal fluctuation of the Gulf The tidal regime here is daily tide, and huge amplitude, which is one of the large amplitudes in Vietnam In one day, a tidal peak and tidal foot appear with the amplitude of 3.5 to 4.0 meters The strong tidal period is 11 hours and weak tidal period is 13 hours The strongest tide and standing tide normally appear in 15 days Inthe strong period of tide, flows on the Red and Thai Bình River are affected by the Gulf of Tonkin’s tide Particularly, the dry season is affected mostly rather than the wet season Tidal peaks in the dry season usually penetrate deeply inside rivers, about 150 km long and 50 to 100 km in the wet

‘The average tial water level is normally highest in the beginning of dry season from November to December, maximum value in October and minimum value at the end of January to April, particularly in March The magnitude of declined tidal regime reaches highest value in December and lowest value in March and April The ‘maximum amplitude was 3.94 m occurring in 23 Dec 1968,

3.2, Water Demand

‘The study area includes Tien Lang and Vinh Bao districts The fresh water is supplied for many purposes such as agriculture, aquaculture, industrial zones and domestics.

3.2.1, Water Demand for Agriculture

Water demand for agriculture is mainly supplied for cultivation, and a small amount of water is for livestock demand, Water supply for agriculture consists of two types of systems such as water storage and gravity Water demand for agriculture is extracted from surface water of upstream rivers transferring through irrigation system Based on the investigation of division of Agriculture and Rural development, water for cultivation and livestock is determined as the following table:

Table 3.4: Total water used for cultivation and livestock in year 2012

Na Areas Water supply (10° mỉ)

Tien Lang system 124,995

Source: Hai Phong PCC, 2015

‘The period of 2020 and 2030:

‘Table 3.5: Water demand of cultivation in period of 2020 and 2030

Vink Bao | 1% [a] ow [wm] we [nn] a] om | om] | om] wo] Am

Tien Lang | MỊ | n@ | s@ | om | 3M | | em | | os [os | ow) ae) 83

Source: Hai Phong PCC, 2015

‘Table 3.6, Water demand of livestock in the period of 2020 and 2030

Unit: Lm”

‘Areas | 1 |Th2jTh3|Th4|Th5 Th6|Th7|ThS|Th9jThI0|ThI|ThI2] Tông 2020

Vinh Bao [9BI]0IS|0BI|OiS]0, otis [ost [aust [ans] tốt | ane | 0BỊ | 178 Tien Lang [arss) aro) ors [orm [orss) w1a9]orss [ors] wiay) 133 | 01 | o1ss | 150

Vinh Bao [ois [aie] on [ons [arm] ars] ors [ai] ans] on [ons | one [ 2p ‘Tien Lang [019] 0H, 018 [oist | ois), ist] o1s9 jars] wisi) 069 | 05 | 01s» | 1x72

Source: Hai Phong PCC 2015

3.2.2 Water Demand for Aquaculture

Surface water from irrigation system is only used for aquaculture Water supply from Tien Lang accounts for large proportion with nearly 66 million cubie meters (37.6%).

Total water supply for aquaculture is over 1753 million mẺ Water supply for aquaculture is only 27.1% in comparison with cultivation and livestock.

‘Table 3.7 Water demand of aquaculture in 2012.

Unit: 10% mề

No Areas Water supply

1 Vinh Bao | 65,929

2 Tien Lang 22,631

Source: Hai Phong PCC, 2015

In the period of 2020 and 2030

‘Table 3.8 Water demand of aquaculture in the period of 2020 và 2030

Tien Lang |014| 666 | 838 [833 | $25 | 891 [0.51 [0.22 0.15] 706 | TÔI | 701 | 62.82

Source: Hai Phong PCC, 2015 3.2.3, Water demand for industry

In the Tien Lang and Vinh Bao areas, there are to industrial zone including Vinh Niem (14,5 ha) and Tien Lang (139,39 ha) Water supply for industrial zones in Hai Phong city was planned in details.

‘Table 3.9 Current status of water use of industrial zones

No | Industrialzones Area (ha) Volume (m*/day)

1 Vinh Niem 14 485 2 Tien Lang 13938 4181

Source: Hai Phong PCC, 2015 3.2.4 Water Demand for Domestic

‘Water supply for domestic is currently from intake sources of irrigation systems and groundwater constructions Surface water is the main source of water supply in

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these areas, Ground water for domex is taking a small amount and inclining extremely due to the water table subsidence and salt intrusion,

‘Table 3.10 Water supply for domestic in Tien Lang and Vinh bao districts

Dig well | Bored wells Tanks NM

SN | SL | §N | SL | SN_| (people)

No | Distriet | Total

156482 | 1934 | 2.100 32782 109715 3428 | 9335 | l6183

130466 | 1289 | 1.703 | 27.653) 92.904 | 3.173 (10133) T396,

Source: Hai Phong PCC, 2015 In the period of 2020 and 2030:

‘Table 3.11 Water demand of domestic in the period of 2020 and 2030

Source: Hai Phong PCC, 2015 3.3 Water Exploitation and Utilization Issues

‘Management and operation of the system:

‘The hydraulic works of the irrigation system was built since 1970s, 1990s and 2000s, The human resources for system operation is too large and unproductive The staffs for management and operation are 100 up to 200 people for each system The equipment of systems is too old and backward as well as is not suitable for ‘management requires Lack of information of water level and salinity, etc in order to serve the operation and management of the systems.

‘The hydraulic works have not been maintained, and repaired regularly, so that water intake is not productive and effective, In addition, due (o the urdimentary ‘method of operation processes, so the systems are not running 100 percent B

the canals, chanels and streams in these areas have been deposited and penetrated progressively causing unproductive water transfer,

Water storage:

Although, the income water in the study area is very huge, but most rivers have high sediment volume, or salt intrusion problems Therefore, water here cannot supply for socie-economic demands It is only used for other purposes such as navigation, transportation and tourism Water supply for socio-economic development is mainly extracted throughout 5 irrigation systems At some points in months and days, the ‘water level is very low causing the gravity system is not working So that, the pumping stations are used for water intake On the other hand, the river bed is occupied by loca people leading to decreasing water storage of rivers.

Water quality

Due to the location of rivers in th study area, most river here are progr sively affected by salinity intrusion 1% of salinity appears mostly on the hydraulic works within 10 hours/day and 10 days/month Alternatively, the turbidness of rivers is very high Average turbidness is approximately 15 NTU This will probably reduce the capacity of water supply f the systems

“The chapter presents the natural conditions, climatic characteristics of the study ‘area as well as the population characteristics, economics and society The water demand and management are also discussed in this study Although, the income water in the study area is very huge, but Thai Bình river has high sediment volume, or salt intrusion problems, So, water here cannot supply enough [or socie-economic demands,

31

In this study, according to the research objectives, the methodology consists of data collection survey, filed work and modelling The method of data collection survey and method of field work will conduct the objective 1 Meanwhile, Objective 2 and 3 will be obtained by the method of modelling.

‘The methodology used in this study will be expressed in detail as the below flowchart

To collect and process the — “4 Method of data available documents collection survey

Objective 1

lo implement Field surveying Method of from detailed plan fieldwork

To analyze and process

Objseive2 «——|

vet database

Method of

J Modelling

Objective 3 «—| Building information systems

‘Writing the report

Figure 4.1: The research flowchart

4.1 The MIKE 11 Model

The MIKE 11 model uses an implicit and finite differential mathematical scheme to compute unsteady flow in rivers and floodplains “In the model, a river network imulated like a system of storage tanks that are connected by channel sections, Such a simulated storage tank is called a node and a channel section joining ‘wo nodes is called segment.” (Dang, 2010, p.106).

Following assumptions were considered for the modeling (DHI, 2007a).

The water is incompressible and homogeneous (i-., negligible variation in density).

“The bottom slope is small, thus the cosine of the angle it makes with the horizontal may be taken as 1 The wave lengths are large compared to the water depth, assuming that the flow everywhere can be assumed to flow parallel to the bottom (.e., vertical accelerations can be ignored, and a hydrostatic pressure variation in the vertical direction can be assumed).

‘The flow is sub-critical (a super-critical flow is modeled in MIKE 11; however, more restrictive conditions are applied).

4.1.1 Governing Equations

Mass and momentum conservation equations are used for the mathematical expression of gradually varied, unsteady flow in open channels Two governing ‘equations for unsteady open channel flow are well known as Saint Venant’s equation system, The model was developed based on these principles It uses the unsteady free surface flow equations of continuity and momentum to find the discharge and water level in each cross-section,

‘The continuity equation or mass conservation equation is:

Equation 4.1

Equation 4.2

3

Where Q = discharge in m/s; A = cross sectional area in m?; ¢ = time in seconds; x = dis ance along the longitudinal axis of water course; q = lateral inflow in

(m'/s/m); h = water level above datum in m; C = Chezy roughness coefficient in

‘Vim /s; R= hydraulic radius in m; a= momentum distribution coefficient in sỀ/mÌ; ý = ‘gravitational acceleration in m”s

Mike 11 model solves Saint Venant’s equation for each channel segment, which is considered as basic finite difference elements For this study, continuity and momentum equations were solved numerically using an implicit finite difference Known as the si

point Abbott scheme, These equations are simultaneous, quasi-linear,

order, partial differential equations of the hyperbolic type The transformation of these equations into a set of finite difference equation is performed in a computational grid involving altering Q and H points Q point are always placed midway between ‘wo adjacent H points, while the distances between the H points may vary.

“A simulated segment linking two nodes possesses average geometric and hydraulic characteristics of the actual channel section A frictional co-efficient and inertial force exists between to nodes of a river segment Inflow and outflow of the node control the storage in a node A positive (+) sign and a negative sign are implied for inflow and outflow respectively Nodes are coded by positive integers from 1 to NN which is total number of nodes in the river network The constraint equations at the confluence of river tributaries are defined as follows:” (Dang , 2010, p 107)

Equation 4.3

sr Equation 4.4

4.1.2 Methods used in the performance evaluation

‘The level of accuracy and reliability of the model depend on the assessment of the model performance, Both graphical and statistical comparison between simulated and measured hydrographs are recommended by American Society of Civil Engin (ASCI

performance evaluation Firstly, in order to assess the model performance evaluation, 1993) The MIKE 11 model provides both graphical and numerical

‘graphical comparisons between modeled and measured hydrographs were done, For Sutcliffe the statistical assessment, this study followed on evaluation of Nas

efficiency (Nash & Sutcliffe, 1970) The equation of Nash-Sutcliffe efficieney is

NSE Equation 4.5

ge the observed data

Ông: the average observed data

nthe simulated data

a sample size.

“The Value of NSE lies between -2 to +1, The value I indicates a perfect match between measured and simulated data Model performance is perfect, if values of Nash-Suteiffe efficiency range from 09 to 1 Model performance is good and acceptable, ifthe values range from 0.8 to 0.9 and 06 to 0.8

4.2 Mike 11 Model Set-up

Within the scope of the thesis study, the author has inherited the input data from the National Key Laboratory of River and Coastal Engineering and Institute of Vietnam Academy for Water Resources Through Modeling calibration Modeling validation, the author will define a complete model parameters to simulate the flow regime of the study area

4.2.1 Input data

4.2.1.1 River network and model schematization

‘The Red and Thai Binh river system is a very complicated network with many large basins such as Da, Thao, Lo rivers in the upstream; and huge river delta in the downstream as well as dense river intensity The Red River is connected with Thai Binh river system by Duong and Luoc rivers The Red River's flow reaches to the

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