ASSESSMENT VAM CONG BRIDE’S IMPACT ON BASSAC RIVER TOPOGRAPHY BY NUMERICAL MODELING

The Government VN had planned to build Vam Cong Bridge (VCB) across Bassac (Hau) River at location of 7.5km downstream Long Xuyen Town and of 35.0 km upstream Can Tho City (see Fig. 1.3). It is one is largest objects of national project “Ho Chi Minh Road” lengthened along west side of Viet Nam land. There are two important facts: (i) The water discharge (including sediment and other mass...) through Hau River at this cross-section controls about 48-49% of total discharge of Mekong River entered to VN, so any it‟s change can induce large impacts on hydraulic and hydrological regime of Hau river (and Mekong river basin in general); (ii) The VCB is very big, so its concrete objects (including bridge piles, roads connected to bridge...) placed across Hau River and floodplain area of river‟s sides will generate large changes of hydraulic, flooded, erosion/deposition regimes of Hau River and closed to it areas. Among many problems induced by building VCB and related with him other infrastructures (This combined system will be note as “VCB”), most important is problem of river topographical changes. The assessments on these processes are needed to find optimal option for designing and constructing VCB. Adding to this, the predictions on impact of building VCB on river flow and flood inundation have big practical means for Vietnamese Mekong River Delta (Cuu Long river delta). 2. THE PURPOSE OF RESEARCH Assessing VCB‟s impact on Bassac river topography by numerical modeling. 3. OBJECTIVE, SCOPE AND CONTENTS OF STUDY River hydro dynamical and topographical processes in Hau River before and after building VCB for finding optimal option with minimal negative impact are main study objectives of present thesis. Hau River has pressured by heavy impacted by VCB is very small piece of very large river system in Cuu Long River Delta. So, the impact on VCB will spread for closed large area, particular in flooded season. Flow of this part of Hau River is very different for wet and dry seasons, particular for some months dry season, direction of water flow here has been changed and controlled by tidal fluctuation entered from East Sea. In general, for this part river, flow induced by upstream discharge will be 4- 5 times larger flow generated by tidal fluctuation.

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NGUYEN CANH THAN MASTER OF SCIENCE THESIS

HOCHIMINH CITY, JUNE 2012

University of Liège – Belgium

Water Resources University – Vietnam

Sustainable Hydraulic Structures

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UNIVERSITY OF LIÈGE – BELGIUM WATER RESOURCES UNIVERSITY – VIETNAM

ON

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CHAPTER 1: OVERVIEW 1

1.1 THE PROBLEM STATEMENT 1

1.1.1 NEEDS AND URGENCY OF THE PROBLEM 1

1.1.2 THE PURPOSE OF RESEARCH 1

1.1.3 OBJECTIVE, SCOPE AND CONTENTS OF STUDY 1

1.2 THE METHODOLOGY 4

1.2.1 OVERVIEW ON STUDIED OBJECTIVES 4

a NATURAL CONDITIONS RELATED WITH HAU RIVER TOPOGRAPHY 4

Tidal characteristics of main river system 13

b THE FACTORS IMPACTED ON STUDY RIVER 13

c GEOLOGICAL AND MORPHOLOGICAL PROPERTIES 15

d MASTER PLAN OF HO CHI MINH ROAD AND VCB PROJECT 17

1.2.2 THE SCIENTIFIC ACHIEVEMENTS ON RESEARCH PROBLEM 18

1.2.3 SUMMARY ON USED MODEL 21

CHAPTER 2: METHOD AND INPUT DATABASE 25

2.1 THE SCIENTIFIC BASES OF USED MODEL 25

a The curved- orthogonal coordinate and curved computed grids 25

b The hydro dynamical module 26

a Model for sediment transport 31

2.2 THE GENERAL PROCEDURE FOR USING MIKE21C 34

2.3 CONFIGURING WORKING MODEL 35

2.3.1 THE COMMON PHYSICAL PICTURE 35

2.3.2 DEFINITING COMPUTED DOMAIN 38

2.3.3 GENERATING COMPUTED MESH 41

2.4 GENERATING INPUT DATABASES 42

2.4.1 TOPOGRAPHICAL INPUT DATABASES 43

2.4.2 THE MANNING COEFFICIENT AND EDDY VISCOSITY 49

2.5 DATABASE CONFIGURED MORPHOLOGICAL PROPRETIES 51

2.6 OTHER MODEL’S PARAMETERS 54

2.7 THE HYDROLOGIAL DATABASES FOR OPEN BOUNDARIES 55

2.8 SUMMARY OF CHAPTER 2 64

CHAPER 3 STUDIED REULTS ON PRESESENT STATUS 65

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3.3.1 INTRODUCTION 65

3.3.2 RESULTS AND DISCUSSION 66

3.2 THE HYDODYNAMICAL PROPERTIES OF STUDIED RIVER DOMAIN 70 3.3 THE MORPHOLOGICAL FEATURES IN STUDIED AREA 77

3.4 SUMMARY 78

CHAPTER 4 ASSESSING VCB’S IMPACTS 84

4.1 IMPACT ON HYDRODYNAMICAL REGIME 84

4.2 IMPACT ON MORPHOLOGICAL REGIME 92

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS 97

5.1 CONCLUTIONS 97

5.2 RECOMMENDATIONS 98

5.3 OUTSTANDINGS IN THE IMPLEMENTATION PROCESS OF THE THESIS 98 5.4 PROPOSAL FOR FURTHER RESEARCH 99

REFERENCES 100

APPENDIX 102

A.1 THE INTEGRATED MODEL HYDROGIS 102

Testing and Verifying hydrodynamic engine of HydroGis 108

Practical applications 108

A.2 THE APPLICATION HYDROGIS IN THIS THESIS 109

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Through the training process under the affiliate program of the University of Water Resources and the University of Liège - Belgium, with the enthusiastic

guidance of the Teachers and encouragement, help of family, colleagues, friends

Master thesis topic "Assessment Vam Cong Bridge‟s Impact on Bassac River

Topography bu Numerical Modelling" has been completed.

Author thanks the Teachers of the Water Resources University as well as the University of Liège - Belgium, who imparted their valuable knowledge to the author

to obtain a knowledge of irrigation technology science firmly on the path to career of author

The author sincerely thanks the wholehearted instruction of Nguyen Huu Nhan, PhD, who mentor, told the author to complete this thesis

Author thanks the friends, colleagues for supporting the author to complete this thesis well

And in particular, the author thanks the families and loved ones always

encourage and create conditions for the author to complete the thesis

TP.Ho Chi Minh City

Author

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Master leaner : Nguyen Canh Than Page 1

1.1 THE PROBLEM STATEMENT

1.1.1 NEEDS AND URGENCY OF THE PROBLEM

The Government VN had planned to build Vam Cong Bridge (VCB) across Bassac (Hau) River at location of 7.5km downstream Long Xuyen Town and of 35.0

km upstream Can Tho City (see Fig 1.3) It is one is largest objects of national project

“Ho Chi Minh Road” lengthened along west side of Viet Nam land

There are two important facts: (i) The water discharge (including sediment and other mass ) through Hau River at this cross-section controls about 48-49% of total discharge of Mekong River entered to VN, so any it‟s change can induce large

impacts on hydraulic and hydrological regime of Hau river (and Mekong river basin in general); (ii) The VCB is very big, so its concrete objects (including bridge piles, roads connected to bridge ) placed across Hau River and floodplain area of river‟s sides will generate large changes of hydraulic, flooded, erosion/deposition regimes of Hau River and closed to it areas

Among many problems induced by building VCB and related with him other infrastructures (This combined system will be note as “VCB”), most important is problem of river topographical changes The assessments on these processes are

needed to find optimal option for designing and constructing VCB Adding to this, the predictions on impact of building VCB on river flow and flood inundation have big practical means for Vietnamese Mekong River Delta (Cuu Long river delta)

1.1.2 THE PURPOSE OF RESEARCH

Assessing VCB‟s impact on Bassac river topography by numerical modeling

1.1.3 OBJECTIVE, SCOPE AND CONTENTS OF STUDY

River hydro dynamical and topographical processes in Hau River before and after building VCB for finding optimal option with minimal negative impact are main study objectives of present thesis

Hau River has pressured by heavy impacted by VCB is very small piece of very large river system in Cuu Long River Delta So, the impact on VCB will spread for closed large area, particular in flooded season Flow of this part of Hau River is very different for wet and dry seasons, particular for some months dry season, direction of water flow here has been changed and controlled by tidal fluctuation entered from East Sea In general, for this part river, flow induced by upstream discharge will be 4-

5 times larger flow generated by tidal fluctuation

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In this case, one of most important steps in numerical modeling river

topographical and hydro dynamical processes is correct and optimal definition of geographical scope and representational open boundary locations for configuring a working model

Criteria for these are including:

- The location of open boundaries have to be enough far from VCB that its impact is zero or minimal on these places

- The upstream open boundary and open boundary downstream have to been located

at places enough far from each to other that they are have maximal Independent

- Resolution of computed mesh for numerical modelling has to be enough fine for maximal simulated accuracy

With mentioned facts and criteria above, we had defined the geographical scope for numerical modeling river topographical and hydro dynamical processes in Hau river before and after building VCB as shown fig 1.1 Also, we noted names of main roads, main rivers, hydrological stations, local administrations and river mouths that will used in this thesis on this Figure

The details of this geographical scope will be describing in chapter 4

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Fig 1.1: Studied domain and geographical notes used in thesis

In short word, present thesis configurates following contensts of study:

1 Over viewing on problem, objectives, scope, and methodology of research

2 Configuring working model for simulating river topographical and hydro

dynamical processes in Hau river included: Generating computed meshes (with and without VCB) and modifying them; Digitizing initial topographical database

on computed meshes; Generating hydrological databases at open boundaries

(water level, discharge…) by modeling hydro dynamical processes on whole low Mekong river basin with HydroGis Model; calibrating and validating working model

3 Simulating river topographical and hydro dynamical processes in Hau River before building VCB (Present situation) by MIKE 21C Model

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4 Simulating river topographical and hydro dynamical processes in Hau river after building VCB (proposal situation) by MIKE 21C Model

5 Analyzing model outputs, discussing results and making needed comments

1.2 THE METHODOLOGY

1.2.1 OVERVIEW ON STUDIED OBJECTIVES

TOPOGRAPHY

Mekong river and Hau River

The Mekong is Southeast Asia's largest rivers originate from the Tibet

mountains, runs through many climate regions, through six countries: China, Burma, Thailand, Laos, Cambodia and Vietnam, pouring into South China Sea (East Sea) by Cuu Long river network and (smaller part) the Gulf of Thailand The catchment area

of about 795000 km2, and near 4800 km of length The upstream of Mekong River in China is called Lancang with the total length about 2100km, and the downstream of Mekong River is about 2700km It flows across Phnom Penh and divided into two big branches are called Bassac River on the left and Mekong River on the right before pours into East Sea Mekong River is the world‟s 9th largest river The total average discharge is 475 billion cubic meters each year The Mekong river basin can be

divided into three parts, including upstream, middle and downstream

The upstream area of Mekong River rises from Tibetan Plateau which is located

at 5000 meters altitude and covered by snow year round in Yunnan, China This is a narrow land, about 19% in comparison with total basin area; the terrain consists of rugged mountains and many temporary torrents

The middle area of Mekong River includes China, Myanmar and Laos down to Kratie It has an area 453.150 km2, about 57% basin area In this basin, Mekong river get more flow from many sub-basin consists of Nam Tha river, Nam U, Nam Sung, Nam Khan, Nam Ngua, Nam Thon, Xe Bang Phac, Xe Bang Rieng, Xe Don, Xe

Cong, Xrepoc and Nam Mun river

The downstream area of Mekong River includes delta area from Kratie to East Sea that has an area about 190.800 km2, about 24% basin area When the river flows

to Phnom Penh, it links with Ton Le Sap River and acts as inlet and outlet of Great Lake At the time of lowest water level in years, the water surface area of Great Lake

is about 3000km2 and the highest water level is about 15.000km2 The lower river is located on the territory of Vietnam with catchment area of about 36,200 km2 and

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length of main flow 230 km The density of rivers and canals average here is about 4 km/km2

Table 1.1: Areas and discharge from countries basin

No Countries name Basin

area (Km2)

Portion (%) of total basin area

Portion (%)

of total country area

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Fig 1 2: Mekong river basin and main its characteristics

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The hydrological regime in the Mekong river delta has two distinct seasons: dry season and flood season Flood season in the Mekong river delta is coming later than

in the middle and upper river areas by regulation of Great Lake, and usually happens for May or June Main flood season is during from July to December with peak at period of September or October The flow of the flood season accounts for 80-83% of annual flow Dry season is during for 4 months from February to May The April has the smallest flow Great Lake water level changes between months of the year from 2m to 12m and the capacity of Great Lake is nearly 90 billion m3

Mekong River divided into two branches called the eastern Tien River and in the western branch called Hau River

Tien River flows across Tan Chau, SA Dec, My Thuan and then pours into East Sea with six estuaries are Cua Tieu, Cua Dai, Ba Lai, Ham Luong, Co Chien and Cung Hau Hau river flows across Chau Doc, Long Xuyen and Can Tho province and then pours into East Sea with two estuaries are Dinh An and Tran De

Tien river flows northwest to southeast, it crosses An Giang approximately 80

km The above of Vam Nao River has width lager than 1000m, particularly where extended to 2000m and the downstream has width from 800m to 1100m with average depth of about 20m, special place as 45m depth in the town of Tan Chau area Tien River is the most winding and branching river with many islets: Chinh Sach, Con Co, Cai Vung, Long Khanh, Tay islet and Gieng islet

Hau river flows parallel Tien river, it crosses An Giang approximately 100km, width above Vam Nao river is about 500m to 900m, width bottom Vam Nao is about 800m to 1.200m, particularly more than 2000m large in some places The average depth is about 13m, especially 34m in confluence of Chau Doc town Like Tien River, Hau River also have a large meandering river and branching in many stages by the islet Vinh Trương, Khanh Hoa, Binh Thuy, Ba Hoa, My Hoa Hung, Pho Ba and Con Tien islet

Vam Nao River is one of three major rivers; it‟s only less than the Tien and Hau River The river flows through An Giang province in the northeast-southwest along the town Phu My, Phu Tan district and Cho Moi district, 6.7 km long, 700m width and average depth of 17m In addition, Vam Nao River connects Tien and Hau rivers, and

it has a major role to regulate the flows between Tien and Hau River

Main river flows

Mekong river basin is affected of Asian monsoon that are South-west monsoon and North-east monsoon The South-west has too much humidity and bring more rain

to the basin, while the North-east monsoon bring more to head to create the dry season

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Every year, when the South-west monsoon starts on May, first rain is beginning

in the basin The flow of cross section at Kratie increased and become maximum

value on September or November and then slowly weakened and was replacing by the northeast monsoon Also, the flow through at Kratie cross section decreased and has

reached minimum value on April or May of last year

The flows of Me Kong river through cross section Kratie (Refer table 1.2) has

poured down to downstream about 500 billion m3 every year, flood water is from 85%

to 90% on June to November with the highest flow discharge was observed to 66700

m3/s However, dry season has just only 10% to 15% on January to May with

minimum discharge was observed about 1250 m3/s and the average discharge was

When the river flows through Phnom Penh, a part of flow discharge on Mekong

River, about 90 billion m3, flows to Ton Le Sap River which pours into Great Lake

(Refer table 1.3) on June to November Otherwise, this discharge comeback to

Mekong river on November to Jun last year

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Table 1 3: The average discharge from Great Lake was comeback downstream of

Mekong river from 1976 – 2006 (Observation station PrekKdam)

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

-2

488

-3

365

-8

153

Notes: Sign (-) was the discharge comeback to Mekong river; Sign (+) was

discharge from Mekong River to Great Lake

As described above, when Mekong River flows to Phnom Penh, it‟s divided into

two parts, which called Cuu Long River Delta The flows are going Tien River at Tan

Chau station and Hau River at Chau Doc station of An Giang province Also, it‟s only

10% to 15% discharge on dry season (Refer table 1.4) and 85% to 90% on flood

water Besides, the river discharge distributed at Vam Nao River; Tien River was

wider and deeper than Hau River, so Tien river discharge is larger than Hau river

discharge That‟s the reason why the flow of Tien River at Tan Chau station larger 4

to 5 times than Hau River

Maximum flow observed in the major flood season in 2000 at Tan Chau station

was 25.600 m3/s and Chau Doc station was 6.840 m3/s Otherwise, the discharge of

dry season observed at Tan Chau station was 882m3/s and Chau Doc station was

145m3/s

Table 1.4: The average discharge of Tien river and Hau river from 1976-2006

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With the value of monthly average flow, maximum flow, minimum flow of

stations has been presentation, we can see the flow of downstream of Mekong river

basin has clear contrast between rainy and dry season, the differences are 55 times,

which means fierce flooding and the heavy dry season

Beside, Vam Nao river is connected with Tien river and Hau river, deliver an

average discharge flow nearly 40% from Tien river and pours into Hau river (Refer

table 1.5) This means that, below Vam Nao, Percentage of discharge through Hau

River is about 4% and Percentage of discharge through Tien River is 51% o Vam Nao River was 9,670 m3/s in 2000 and the minimum discharge was 332 m3/s in 1998

Table 1 5: The average discharge of Vam Nao river from 1976-2006

Months Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

On the other hand, the downstream Mekong basin is not large enough to convey

a huge amount of water from upstream in flood season So, in the both sides of

Mekong is usually bank full flood from Kong Pong Cham to East Sea same as

low-lying areas between the Mekong and Ton Le Sap river

Likewise, flooded area are left bank of Mekong River (including Dong Thap

Muoi province), between Hau and Tien River, right bank of Hau River (including

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Long Xuyen Quadrangle) with 1-4 m depth and happen from 3 to 5 months So, the flood flows on Main River has been loss of water on the way out to Sea According to statistics for many years, the flooding in studied area is small (when maximal flood level at Tan Chau station below 400cm) accounting 14%, big floods (when maximal flood level at Tan Chau above 450cm) accounting 40%, the rest is average flood When the water level at Tan Chau is lower than 180cm, the water is flowing two-way phase of tidal oscillations On this level (>180cm), there is one-direction water flow When the water level at Tan Chau exceeds 300cm, flooding low-lying areas (valley fill process) and when water levels exceed 350cm, river runoff, causing flooding and began to overflow the current flow Overflow intensity increases with the depth of flooding At the height of the floods, the flow rate can be up to 30-35% of the total flow across the Mekong Delta floods

In general, according to observational data in many years, the maximal discharge

at Kratie was 53000 m3/s, but it‟s just only 44000m3/s when the river flows through 9 estuaries to the East Sea Furthermore, the flood flows is combined with tidal stream from East Sea, gulf of Thailand and rainfall So, the flood peak water level is higher and it‟s highest in late September and early October Otherwise, analysis of sequence data of flood peak water level (Hmax) from 1926 to 2006 (Refer table 1.6) shows that

three years have particularly large flood in 1961, 1966 and 2000 with flood peak water level measured at Tan Chau station was over 5.0m In contrast, the flood was also extremely low in 1998 at Tan Chau station with 2.81m

Table 1 6: The peak flood water level on Tien and Hau river from 1926-2005 (cm)

Station River Hmax

(average)

Hmax(1961)

Hmax(1966)

Hmax(1998)

Hmax(2000)

However, the discharge from headwater was small in the dry season So, water level on Tien and Hau River decreased and reached lowest level on April and May

Moreover, analysis of sequence data in lowest water level from 1977-2006 (Refer

table 1.7) show those three years 1978, 1986 and 2006 had lowest water level

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Table 1 7: The lowest water level on Tien and Hau river from 1977-2006 (cm)

(Average) Hmin (1978) Hmin (1986) Hmin (2006)

Sediment characteristics of main river system

Sediment transport was one of significant characteristics of flow They are main mechanism of sedimentation of river, canal and river delta There are bed load and

suspended transport Beside, suspended transport can be measured by machine and

bed load has no observation equipment So, at the present time, the empirical formulas

or experience are calculated

In general, suspended concentration of Cuu Long River was less high than Hong River and change greater with seasonal fluctuations Tien River was 1kg /m3 and

500g /m3 on Hau River In contrast, suspended concentration on dry season was not significant

Table 1 8: The average suspended concentration at Tan Chau and Chau Doc stations

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Tidal characteristics of main river system

In particular, tidal regime on main river system in the Mekong River is the result

of the propagation of tide from the East Sea and Gulf of Thailand

Irregular semi-diurnal tidal fluctuation from the East Sea is entering to study area through Tien River and Hau rivers The tidal range in the river mouths is average, from 3.0 ÷ 3, 5m in the period of spring period The tidal range in study area is near two times less than ½ (1.01.7m) of tidal range in Hau river mouth In flooded

season, tidal range in study is small (0.40.7m) The irregular diurnal tidal

fluctuation from the Gulf of Thailand almost is not impact on study area

According to tidal range, the Mekong Delta can be divided into three zones: (i) Zone with strong tidal impact within 50km from the sea; (ii) Zone with average tidal influence around 100km from the sea; and (iii) Zone with lightly tidal impact within 200km from the sea The upstream boundary of study area locates in zone with lightly tidal impact, but downstream boundary locates in zone with average tidal influence

In main rivers, the average tidal phase speed is about 22km/h in dry season and approximately 19km/h in flood season The distance from the sea of tidal impact along the main river can reaches 200÷250 km in dry season and 80 ÷100 km in flood season

Land topography and river network

The study area is belong Hau River which flows through the Long Xuyen city,

An Giang province, from Chau Thanh district boundary swept downstream to the boundary of Can Tho city (at the mouth of Cai San canal) has a length of about 30km Left bank of the studied river is Cho Moi district and its right bank is Long Xuyen city Its topographical structure is typical for Mekong Delta: low terrain with very fine sand, silt and clay Along the left side of Cho Moi, the average elevation is about 1m Along the right side of Long Xuyen city from the national highway 91 to Hau River mainly residential landowners, crowd residential areas, the average elevation is 2.5m

÷ 3.0 m The area from the national highway 91 back into the internal Long Xuyen quadrangle is the lowlands, the average elevation is from 1.0m ÷ 2.5 m Overall, and the study area along both river side areas is relatively low

The studied river part is located at the downstream of the gate poured out of Vam Nao River The main flow enters to it is combined flow through Chan Doc and Vam Nao cross-sections Here there is some very big river island as My Hoa Hung (Ong Ho island) and Cu Lao Cac that located direct on main river axis, so hydro

dynamical regime of this part Hau River is very complicated Along the left bank, there is some canals transferred water from Tien River to study part by canal Ong

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Chuong, canal Cai Tau Thuong Along right bank, there are canal Long Xuyen, Canal Cai San, which transport water from the Hau River to Long Xuyen quadrangle

Climate regime

The studied river domains as well as the Mekong Delta in general are influenced

by two seasonal winds are the northeast monsoon and southwest monsoon To serve hydrological research of Hau River flows through Long Xuyen city of An Giang

province, here we present some factors related to meteorological and hydrological regimes, such as temperature, Evaporation and rainfall of the Chau Doc

meteorological station which are typical representatives for the studied river domain

Temperature: average monthly temperature of the studied river domain is high

and very stable Temperature difference between the months of the dry season does not exceed 3oC, only less than 1.5oC ÷ 3oC (see Table 1.10) and this is worth the

difference in maximum temperature In the rainy months, this difference is quite

small, less than 1oC The highest temperature usually occurs in April, ranging from

36oC ÷ 38oC In contrast, the lowest temperature of the year usually occurs in

December, in the observed data series from1976 ÷ 2006, there is no year with lowest temperature below 18oC Air temperature amplitude between day and night in the rainy season is about 8oC and the lowest is 6oC (occurring in the most sultry days), while the dry season corresponding values of the temperature is 10oC and 12oC

(occurring on most hot and dry days)

Table 1 9: Mean monthly temperature of Chau Docstationfrom1976 to 2006

Temperature

(0C) 27,7 28,1 29,9 30,4 29,5 29,2 28,9 28,4 28,6 28,7 28,3 27,0

Rainfall: The total average rainfall in the studied river domain basin is about

1400 mm, divided into two distinct seasons that are rainy and dry seasons that

correspond to the southwest monsoon and northeast as described above Rainfall

characteristics are in Table 1.11 and 1.12

Table 1 10: Average monthly rainfall during the dry seasonfrom1976 to 2006inChau Doc

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Table 1 11: Average rainfall in Chau Doc of rainy monthsfrom1976 to 2006

Month May Jun Jul Aug Sep Oct Nov Total

Rainfall (mm) 185 105 175 210 260 228 143 1306

Evaporation: In the dry season, due to sunlight, low humidity, so evaporation

from rivers, streams, large, medium 110mm/month (see Table 1.13) In the rainy

season, water evaporation is lower than the dry season, an average about

85mm/month The total average annual evaporation of the studied river domain is around 1.238 mm

Table 1 12: Average monthly evaporation in Chau Doc from 1976 to 2006

Evaporation

(mm) 112 110 130 132 108 96 99 102 93 93 102 115

According to many researches [Ref 1, 3, 10, 22], the geological conditions of the studied river domains composed of three layers: the top is brown clay powder soft elastic state to plastic flow, the second layer is sand granules are less tightly to close state and the bottom layer has a gray-brown clay mud flowing state Density is 1.50 g/cm3 with small natural soil and dry density is 1g/cm3, with the small bond does not exceed 0.1 kg/cm2

Hydrogeological conditions with the water table is about 1.5m underground, the water is usually located on stable ground water level in the borehole with the

difference is not large, only about 20cm to 30cm This shows that the top layer of clay from the ground has a small hydraulic conductivity, water-containing materials due mainly clay particles Next is the layer of fine sand containing water that contact

directly with Hau river flow, water pressure is sand pore water pressure, it works to reduce stress acting on soil particles This shows that shear strength decreased less, giving the smooth sandy soil easily converted into flow state contributed to riverbank erosion

Riverbed soil structure is not significantly different from the riverbank land; the critical rolling speed of the particles sediment only about 0.7m/s, only the flow rate reaches 1-1.5m/s is likely to cause riverbank erosion, as well as river bed

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professional river trade, services, tourism, industry, handicrafts and aquaculture In fact, economical activity on the rivers of the studied river domain is mainly river sand mining, aquaculture and river transportation This is one of the activities likely to affect the hydrological regime of river domains

Sand mining activities along the river course mainly focuses on three fields of sand dunes is the Pho Que, Left branch is My Hoa Hung around hill Tien and Noi These three areas are serious sediment cause transportation congestion The total volume of sand is capable of exploiting these three areas can reach 6,000,000m3, can

be exploited every year around 1,500,000m3 River bed sand resources are renewable,

so exploitation the river sand for construction of economic development is essential, but also need the technical survey, organized exploitation of reason, avoid

indiscriminate exploitation focus, beyond recovery by mobilizing the natural laws of river sediment, otherwise will cause local changes in the riverbed and riverbank

develop fish farming along the Hau River flows through the Long Xuyen city was great In particular, where conditions are breeding better is around the hill of My Hoa Hung (excluding the tail) and the coast from the ferry Cho Moi from An Hoa swept downstream to the Cai San has about 100 fish villages The Hau River flows through the Long Xuyen city located below the gate down the Vam Nao river, which flows across the Tien River, the average width of the river near the 1000m, 8 ÷ 9 meters deep on average very suitable for career development fish village, but need a survey

of villages of fish and friends appropriately, avoiding a massive development would otherwise cause the phenomenon of compensation, river erosion and water pollution The Hau River, below the Vam Nao river, has quite large width and depth for using it in waterway activities Near the studied river domain there are two major ferries with names of Vam Cong ferry and An Hoa ferry passed about 60 million passengers and over 4,000,000 vehicles of all kinds each year In addition, there is military port My Binh and national port My Thoi with capable of receiving ships of

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20,000 tons with cargo volume of up to 2,000,000 tons / year The large waterway activities are inducing large waves caused landslide and topographical changes of Hau River

The Mekong river Delta is an area of poorly developed infrastructural systems Interlaced river network is main reason for difficult travel between the local places In present time, the ferries are main ways for passing across big rivers Now day, the growth rate and population growth in Mekong River delta had requested to replace the ferry by bridge suitable for this delta In last time, there are some big bridges had built

in Mekong River delta as Can Tho and My Thuan bridges Vietnamese government planned to urgently construct VCB for replacing Vam Cong ferry The location of VCB had shown in fig 1.1 In addition, the Vam Cong project is a one part of total national master plan for Ho Chi Minh road as had shown in fig 1.3

The VCB is very big bridge placed across Hau River and floodplain area of Mekong River Delta It will induce changes of hydraulic, flooded, erosion/deposition regimes of Hau River and closed to it area So, studying its impact on Hau river and Mekong river delta is very important work needed to find optimal option for designing and constructing VCB These problems are main objects of presented thesis and more detail descriptions about Vam Cong project will been give in next chapter

Among many methods to study above mentioned problem, method of

mathematical modeling is more suitable The method of physical modeling needs to very high price The method of measurement in situ is not suitable because bridge now had not built and needs high price too

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Fig 1.3: VCB and master plan of Ho Chi Minh road

1.2.2 THE SCIENTIFIC ACHIEVEMENTS ON RESEARCH PROBLEM

Erosion/deposition/slide of river has induced by interaction between the water flow and the river-bed, by sediment transport and by sediment balance These

processes always changing over time and space They are study objectives of many scientist and organizations The scientific achievements are very large

In developed countries such as USA, UK, France, Germany, Holland, Japan,

Canada, India, Russia, China, this science has high level of development and gets

excellent results in terms of theory and experimental application [Ref 2, 17, 22, and 24] Between 30 and 60 decades of the twentieth century, the study of the river

dynamics and river Erosion, deposition and landslide has grown strongly Since then,

as results of development of digital computers, many hard problems related with them had been resolved, greatly contributed to clarifying their bases [Ref 2, 17, and 24]

At present, method of mathematical modeling has been taking steps leap in

development With combined helping of professional hydraulic software as MIKE21, MIKE3, Delt3D, TeleMac, SMS, HydroGis worked in power computers…and using modern equipments such as ADCP, ADP… to measure real processes for calibrating and verifying the computing results, now we can study these processes with enough accuracy for practical applications [Ref 2, 12, and 22] Thereby, from day to day, the

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distance between the mathematical modeling and physical modeling (which is very expensive for application) becomes shorter

The crux of the problem for fully completing of coupled hydrodynamics- sediment logy mathematical model is including in fact that, unlike the equations of hydro dynamical and spectral models with strong theoretical bases, the almost

wave-equations of sediment transport are semi-empirical formulas with many experiential

coefficients [Ref 2, 17, 19, 22,24-26] which had been defined in simple case (steady flow, sediment and load sand evenly balanced…) The problem of sediment transport

is not simply like that usually happens in case of unstable water flow The sediment transport is irregular and unbalanced So the establishment of mathematical model for this is not consistent with reality For improving precision calculations, ensuring that the problem is stability and convergence, it is very important in combination of

theoretical and practical knowledge on studied objects with careful verifications of computed data through comparison with actual measured data in-situ [Ref 2, 22, and 24]

Despite technical advances in computing, such as improving the modeling of hydraulic phenomena, sediment transport still is too complex, and especially the

river/marine erosion, deposition and landslide forecast is still a "problem" of the

world

In regional scale there are some international organizations as Mekong River Commission (WRC) is working from 1966 to day Each country in Mekong River Basin has many national organizations So, there are many completed researches on the Mekong River Delta and knowledge databases about is very big Vietnam has big interests on protect and exploitation Mekong River Delta, so there are many scientific institutions had organized for studying it Just only area of water resources, the a lot of organizations as: Viet Nam Academy for water resources (VAWR); Water Resources University(WRU), Southern institute of water resource Research (SIWRR); Sothern Institute for water resources Planning (SIWRP); Institute of coastal and offshore

engineering (ICOE); Transport engineering Design Institute (TEDI) The some

important works had related to thesis topics for last years as following:

1 National project (2010-2013): “The sediment logical changes by sand mining in Mekong River delta” is carrying out by VAWR with heading by Ass Prof Le Manh Hung

2 National project (2011-2014): “Studying coastal alluvial sedimentation around Ca Mau Cape for generating scientific bases and technological measures for stable development of Ca Mau peninsula” is carrying out by ICOE with heading by Dr Nguyen Huu Nhan

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3 National project (2007-2009): “The landside in Mekong River delta and measures for mitigating” had completed by SIWRR with main products of database of

landslide and measures for mitigation The project had headed by Associate

Professor, Dr Le Manh Hung

4 National project (2009-2011): “Studying the changes of water resources Mekong River delta induced by Climate change and development in basin and measures for mitigating and responding” completed WRU with main products of databases and optima measures for using The project had headed by Prof Nguyen Quang Kim

5 National project (2007-2009): “The evaluation on the current and prediction on changes of environmental and water resources in Dong Thap Muoi (Mekong river Delta” had completed by WRU with main product of scientific bases for master plan The project had headed by Prof Dao Xuan Hoc

6 MODRE project (2000-2003): “The development of software and database for modeling flooding and salinity intrusion in Mekong River Delta” had realized by Hydro meteorological Center with main product is integrated HydroGiS Model had realizes by WRU Project header is Dr Nguyen Huu Nhan

7 MARD project (2009-2011): “The scientific bases for water resource planning in Mekong river Delta with adaption to Climate change and sea level rising” had completed by WRU with main product of scientific bases for master plan of water resource in Mekong river Delta Project had headed by Prof Nguyen Xuan Huy

8 MARD project (2009-2012): “The master water resource plan in Mekong river Delta with adaption to Climate change and sea level rising” had completed by SIWRP with main product of master water resource plan in Mekong river Delta Project had headed by Msc Nguyen Ngoc Anh

9 MODRE project (2000-2003): “The development of software and database for modeling flooding and salinity intrusion in Mekong River Delta” had realized by Hydro meteorological Center with main product is integrated HydroGiS Model had realized by ICOE Project‟s header is Dr Nguyen Huu Nhan

10 National Project (2005-2008): “Master Ho Chi Minh road” had completed by TEDI

The above mentioned works (and many another researches) had produced

massive scientific and methodological bases, databases and knowledgeable They are important bases for realizing this thesis study But river sedimentation in large and complex river delta as Mekong River delta is always very complex problem with wide range of variability in time and space, so this is still a problem of the world needed to continue the research for long time in future

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The main lesson from our literature reviewing had gone to concussing that, the application of mathematical modeling is one of more efficient method for study river sedimentation with and without man-made hydro technical engineering constructions, specially for forecasting impact of proposal constructions will been built in future only (non- existed in present time)

Next text of thesis will give short description about one model from many

models related to state above problem

1.2.3 SUMMARY ON USED MODEL

River-bed and related to him processes (as current, water depth, erosion,

deposition, interaction of river-bed, river-bed properties, mass and end energy

balances ), in common depends on many mechanisms are changing in time and space continuously For studied river, there are 5 types of processes/activities as following:

1 The processes active inside the water body as:

- Flow dynamics, sediment transport ;

- The density structure of water (heat, mud, sand ) ;

- Decay/sink of material/sediment inside water body

2 The processes active at the river bottom and shoreline (river-bed) as results of Interaction between river-bed and water flow (that transports sediment and other substances…) expressed by mechanisms: (1) Changing of depth of the water columns; (2) friction between water flow and river-bed; (3) water

infiltrating through the bottom and banks, (4) dissipating mechanical energy; (5) Decay/sinking of material/sediment on river-bed; (6) Depositing and re-suspending of sediment to/from river bed; (7) Changing of river-bed

topography; (8) changing of water flow induced by topographical change of river-bed

3 The processes active at the liquid (open) boundaries of studied river domain expressed by hydro dynamical parameters (discharge, water level…) of water flow and parameters of mass flows of mud, sand and other substances that are coming in or coming out through the open upstream boundaries and open

downstream boundaries of studied river domain In this thesis, these parameters had called hydrological boundary conditions

4 The processes active on the water surface due to interaction with the

atmosphere as: rainfall, wind, evaporation They had called the meteorological conditions

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5 The activities of human included any man-made constructions for training river flows, for building waterways, ports, sewers, dykes, bridge, sluice, dams,

culverts, dams, reservoirs … can induce to changes in river flow and flow other substances included sediment

The studied river domain is a very complex system It is high branched river system in delta with: (1) Very large variance of depth, width and geometrical

configuration along river; (2) asymmetrical river axis; (3) some very big river islands; (4) many beaches and islets; (5) VCB now just has place in proposal project, not has place in-situ So, it is not easy to configure a representative method for study it

In principle, there are three basic methods:

a Method of measurement in-situ This is basic method However, this method is very expensive if have to realize it for long time with enough fine measured grid in large studied area, and it is not feasible, especially to predict when the items they build and no adjustment in-situ

b Method of physical model based on the similar theory This is basic and very

expensive method too This method only used for special big projects or simply great The biggest weakness of this method is very difficult to establish the

physical model on the same relief is synchronized to all the parameters and

components: geometry, chemical-physical of water, the buffer, opened boundary conditions, especially for the tide and wave impact

c Method of mathematical modeling This is basic method It is inexpensive and very feasible for wide applications The hard requirements for applying this

method included: (1) Strong reliability of the mathematical models; (2)

Trustfulness and totality of input database and verification of output data The fundamental strengths of this approach is the ability of mathematical models in predicting, especially in the testing stage ideas, planning and design The

weakness of this method is that mathematical model just is approximated reality, because mathematical model approximated the actual processes, and computed model is just some software approximated it on digital computers

In some very important cases, people use a combination of all three methods to complement each other and overcome the weaknesses of each method It is reliable research methods, but very expensive

In practice, the more inexpensive and reliable method is combined method from basic method 1 and method 3, in which their role is allocated as follows:

- The field measured data had used for calibrating model, building the input database and verifying the quality of model output data;

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- The outputs of mathematical model (which had been carefully tested by

comparisons with real measured data) are used to specify the laws of river hydro-morphological processes without and with VCB project by the series of numerical experiments

The last combined method is simply called mathematical modeling (although it

is the trust combination of method of mathematical model and method of

measurement in-situ) This method has been applied widely in Vietnam and on the world In particular, due to its distinctive advantage, scientists and consultants around the world have created many tools for increasing its efficient Typically, there are many modern instruments such as ACDP, ADP GIS tools, remote sensing

technology, and especially there is a lot of professional software such as the Danish Hydraulic Institute's (DHI) MIKE, Hydraulic Institute Netherland‟s DELT-3D,

SBEACH of America, and TeleMac of France Almost of them had built for this purpose

So, there are many mathematical models with strong features and individual reliability acceptable to resolve the problems stated above Among these models, thesis orientates on those models that had recognized worldwide and had effective application in Vietnam as MIKE 21, MIKE 21 FM, MIKE21C, and MIK21/3 coupled Model FM, Delt-3D, and TeleMac Also, in practice each section of the river has its own characteristics and just only some factors will play a major role and some other factors are not important and may be ignored For example, for studied river branch,

we can ignore impact of waves and salinity In addition to this, VCB project may impact on limit area of Mekong River Delta, so computed area needed for modeling will be very small by comparison with whole Mekong River Delta Above facts give bases for simplifying our problem

After critical analyses of needs in outputs of stated problem and other real

situations related to them, we can make following conclusions:

- The studied river domain is quite good researched with last updated by

topographical, geological, hydrological and meteorological measured data It is very important fact for successful application of all above mentioned mathematical models

- Two dimension structural Model MIK21 with standard computed meshes of

rectangle is not suitable for this river domain, because its river beach and shoreline here are too complex for fitting by rectangle mesh This is trust 2-D model

- Two dimension unstructured Model MIK21 FM (Flexible Mesh) is good choice for fitting complex configuration of beaches and shoreline of studied river domain,

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but its numerical algorithm had is explicit and not suitable for long time for

morphological modeling with enough fine mesh This is trust 2-D model too

- Two/tree dimension models of MIK21/3 coupled Model FM, TeleMac and 3D is too expensive of application for our study In addition to this, the numerical algorithm of MIK21/3 coupled Model FM is explicit too

Delt-Among all of mentioned model, model MIK21C in curved- orthogonal

coordinate of DHI is best choose for modeling studied river domain by following advantages:

1 Its numerical algorithm is implicit It is very important for modeling processes needed in computing for long time with fine mesh in problem of river sediment logy with high accuracy of outputs and minimal price

2 It is coupled hydrodynamics and sediment logical model

3 Computed mesh in curved- orthogonal coordinate is quite good for fitting complex configuration of beaches and shoreline of studied river domain

4 Model MIK21C is 2-D model, but it allows including effects of the helical flow (secondary flow) for modeling river hydrodynamics and river-bed morphology

So, in other word, it is simplified version of full 3-D model

5 Model MIK21C allows including landslide of river bank, embankments…

6 The organization, where thesis had completed, has license for using this model With above shown points, thesis had chosen MIKE21C as main computed tool

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2.1 THE SCIENTIFIC BASES OF USED MODEL

The used model for modeling river hydrodynamics and morphology is MIKE 21C of DHI The Model MIKE 21C had developed specially for coupled hydro

dynamical and morphological modeling in curved and complex river system (without saline and wave effects) Here is short description on its scientific basses

a The curved- orthogonal coordinate and curved computed grids

In practice, most river bends any form, so to accurately simulate shoreline

requires using curved grids or unstructured grids Grid in MIKE 21C is curved by ordinate transformation by the system of equations

Where:

- x, y are the axes of the rectangular coordinate system,

- s, n are the axes of curved orthogonal coordinate,

- g is a density function defined as following:

All equations in model MIKE21C had been projected on space curvilinear grid

(j, k) with displacements of ∆s and ∆n along coordinates (s,n) as shown on Fig 2.1,

and all of them had approximated by method of finite difference for numerical

simulating coupled hydro dynamical and morphological processes of river domain

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Fig 2.1: The curvilinear computed grid in MIKE 21C and Finite Difference in (s, n) space Grid; p and q are water fluxes in two horizontal directions h is water

depth

b The hydro dynamical module

The hydrodynamic model (HD) is basic module in MIKE21C The curvature of the co-ordinate lines generates additional terms in the partial differential equation for flow The equations are solved by an implicit finite difference technique with

variables (water flux density P and Q in two horizontal directions and water depth H)

defined on a space staggered computational grid, as shown in Fig 2.1

In common case, the hydrodynamics of meanders and branched river system are characterized by a complex three-dimensional flow pattern This has to be taken into account when studying river morphology However, to apply a fully three-dimensional model for long-term simulating (for several months or some years) river morphology,

it requires unfeasible computational efforts In model MIKE21C, the governing

hydrodynamic equations had reduced to two-dimensional equations of conservation of momentum and mass in the two horizontal directions, then three-dimensional

(secondary flow) effects are maintained in the depth-averaged model by introducing a separated model of the helical flow and by assuming similarity of the vertical

distribution of the flow velocities for restoring 3-D flow structure

Model of the depth-averaged flow (main flow)

The hydrodynamic model solves the vertically integrated equations of continuity and conservation of momentum (the Saint-Venant equations) in two directions,

included water level h and discharge (p,q) of curvilinear co-ordinates (s,n)

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(2.3)

(2.4) (2.5) Where:

- s, n: Co-ordinates in the curvilinear co-ordinate system,

- p, q: Mass fluxes in the s- and n-direction, respectively,

- H: Water level,

- h: Water depth,

- g: Acceleration of gravity,

- C: Chezy roughness coefficient,

- R s , R n Radius of curvature of s- and n-line, respectively,

- RHS: The right hand side in the force balance, which contains (among others) Reynolds stresses , Coriolis force and atmospheric pressure

Model of the Helical flow (secondary flow)

When water flows into a river bend, an imbalance of centripetal force starts to generate an outward motion near the free surface and an inward motion near the bed The reason is that the main stream velocities in the upper part of the flow are greater than velocities in the lower part of the flow Therefore, water particles in the upper part of the water column must follow a path with a larger radius of curvature than water particles in the lower part to maintain nearly constant centripetal force over the

depth With velocity v and radius of curvature R, centripetal acceleration is v2/R

Simultaneously with generation of helical motion, a lateral free surface slope is created to maintain equilibrium between lateral pressure force, centripetal force and lateral shear force generated from friction along the bed The classical analytical

solution to this flow problem predicts a single helical vortex, which transports fluid downstream in spiral trajectories This spiral (or helical) flow pattern can be

considered as the sum of a longitudinal flow component (main flow) and a circulation

in a plane perpendicular to the main flow direction (secondary flow)

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The secondary flow is directed towards the centre of curvature near the bottom and outwards in the upper part of the cross-section as illustrated by Fig 2.2

Fig 2.2 The Helical flow in river bends

The intensity of the helical flow is the magnitude of the transverse velocity

component It is defined by de Vriend (1981a) as:

R

h u

= i

s

Where:

- u is main flow velocity,

- R s is radius of curvature of streamlines ,

- i s is Helical flow intensity

The secondary flow due to curving streamlines causes a small deviation s in flow direction near the bed, away from the main stream direction This also causes deviation in the bed shear stress direction

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Fig 2.3 The deviation of bed shear stress due to helical flow

The direction of bed shear stress in a curved flow field plays an important role in

a bed topography model for river bends The logarithmic model obtained by

Rozovskii (1957) and others yields a bed shear stress direction given by:

R

h -

=

s s

tan

Where:

- h is Water depth

- R s Radius of curvature of flow stream lines

- δ s Angle between bed shear stress and depth averaged shear stress (or flow)

The parameter β is defined as:

) C

g - (1

B

n

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Modeling the adaptation of secondary flow is complicated by the fact that

(according to numerical experiments) adaptation of the secondary flow profile is

considerably faster near the bed (where bed shear stresses act) than compared to

higher up in the water column Strictly speaking, the process of adaptation cannot be characterized by one length scale only Adaptation length is a function of water depth and friction number In the present morphological model, the following differential length scale is applied:

g

C h 1.2

Model for restoring the vertical velocity profiles

The hydrodynamic model is based on depth-averaged flow equations However, information about the vertical velocity profiles is required for determining the bed shear stress and for the suspended sediment transport calculations in the

morphological model To restoring vertical profiles, model MIKE 21C had made following procedures Introducing the Reynolds stress concept and the Brandt mixing length hypothesis, and assuming that viscous (laminar) friction is much smaller than turbulent friction, the shear stresses in the fluid can be expressed by formula:

z

u E

- E: Turbulent (eddy) viscosity coefficient;

- s : Shear stress in main flow direction

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A similar relation for n applies for the transverse direction

Introducing this into the Navier-Stokes equations (see Olesen, 1987) and

assuming steady conditions, then the equations for flow in the longitudinal, s, and the transverse direction, n, is emerging as following:

) z

u (E z

= s

P 1 + R

uv + z

u w + n

u v + s

u u

) z

v (E z

= n

P 1 + R

u - z

v w + n

v v + s

v u

2

(2.12)

On the other hand, assumed that v, w, u/ s =0 for calculating u, and u, w, v/ n

=0 for calculating v SO, In general, the vertical distribution of velocity has been

calculated by equation as:

(2.13) (2.14) (2.15)

a Model for sediment transport

The total sediment transport included suspended transport S sl and bed load

transport S bl that total sediment transport will be S=S sl + S bl

Model of suspended load transport

Fist, the vertical-averaged concentration of suspended sediment by water depth was calculated by solving equation:

(2.16) Where:

- R : Radius of curvature of stream line,

- s,n : Stream –wise co-ordinate and transverse co-ordinate,

- is Average concentration of suspended sediment,

- is Average concentration of saturated suspended sediment (calculated from empiric formula),

g kC

kC

g p H z p

u z

u

1 0

0 1

1

0

,ln,

/),()

(

] 1

ln 1

ln ln

2 2 ( ln

ln 2 2 [

; ln ),

( )

(

0 0

0

2 0

0 2 0 3

21

0 21

2 2

d d

d C

k

g p

A P p p R

H u z

v

c

e

C

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- ws : Fall velocity of sediment particles in suspension,

- i: Function change by time delay and advection-dispersion

After that, the concentration of suspended sediment at position ζ= z/H was

calculated by equation:

(2.18)

(2.19) (2.20) (2.21)

(2.22) (2.23)

(2.24)

Where: Z : Number Rouse and βz =(zebu/H)/(1-zb/H)

Using calculated u(z) ,v(z), c(z), now we calculate the suspended load transport

as integrals of function c(z).u(z ) and c(z).v(z )by water depth In general, beside

dynamic factor (main flow and helical flow), the main parameters of the model of

suspended sediment transport include some parameters as: fall velocity of sediment w s

, bottom roughness Zb and concentration of saturated sediment C e They are important

inputs of suspended sediment model The C e determine by equation below:

(2.25)

Where: ς=η, D are: operator of spatial derivative ς and :

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The Model for bed load transport

The interaction between the bed load and the alluvial bed is one of the most fundamental aspects of the morphological behavior of a river bend In contrast to the suspended load, it is assumed that the bed load responds immediately to changes in local hydraulic conditions Thus, there is no need for advection-dispersion modeling

in connection with bed load However, two important effects must be taken into

account:

1 The deviation of the direction of the bed shear stress from the mean flow

direction due to helical flow; and

2 The effect of a sloping river bed

The models of bed load transport almost are empirical formulas as following: The Shields parameter and critical shear stress calculated by equation show as below

(2.26) The model MIKE 21C supports tool for select needed model for bed load

transport from some its options as:

1 Meyer-Peter Muller (1947) model for bed load transport is simply formula as:

Instead of using a constant critical Shields parameter c (approximately equal to

0.06), Van Rijn assumes the following variation as a function of D * in Table 2.1:

2 3

3 2

s

3 50 2

5 2

)1(05

)1()7.0'(

3 50 3

0

*

1 2

) 1 ( 053

*

50

) 1 ( / ) /

d g 1) - (s g

C 0.05

=

5 2 tl

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2.2 THE GENERAL PROCEDURE FOR USING MIKE21C

The general procedure for applying MIKE21C to modeling coupled hydro

dynamical and morphological processes of studied river domain included following steps:

1 Analyzing of study objects for representative configuring working model with MIKE21C;

2 Defining computed area with representative locations of open boundaries and designing optimal computed grid for chosen area

3 Generating all needed input databases and digitizing all of them on computed grid;

4 Calibrating and validating model by comparisons of measured data and computed data to get the working model for coupled hydro dynamical and morphological processes of studied river domain

5 Using working model to simulate hydro dynamical and morphological processes in studied river domain without VCB ,

6 Analyzing model outputs for making conclusions on present hydro dynamical and morphological laws in studied river domain

7 Using working model to simulate hydro dynamical and morphological processes in studied river domain with VCB

8 Analyzing model outputs for making conclusions on hydro dynamical and

morphological laws after building VCB

9 Making needed conclusions and recommendations

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Studied steps and proposed their main productions era presented in Fig 2.4

Next is documentation of thesis‟s results for realizing of those jobs

2.3 CONFIGURING WORKING MODEL

2.3.1 THE COMMON PHYSICAL PICTURE

It is very clear that careful analysis of studied object based on real physical

properties studied river domain and neighbored other water bodies has prime

importance to configuring working model for assessing impact of VCB Some more important facts with closed relation for configuring working model are following

Fig 2.4 The working procedure and proposai relate results

Production

Defining computed area and

designing computed grid for chosen area

Generating and digitizing input

databases on computed grid

Calibrating and validating model

and input databases

Simulating coupled hydro

dynamical and morphological properties

in studied river domain without VCB

Predicting coupled hydro

dynamical and morphological properties

in studied river domain with VCB

All needed databases for modeling coupled hydro dynamical and morphological processes of studied river

domain Model parameters and input databases are trust for using; Model outputs are correcting and having needed accuracy

Output data on the GIS map, chart and table expressed laws of hydro dynamical and morphological processes at studied river domain in the present condition

Output data on the GIS map, chart and table expressed laws of hydro dynamical and morphological processes after building VCB

Recommendation, conclusion and comment

Analyzing all studied results

Analyzing objects, data for

configuring working model

The optimal domain and computed grid with the representative locations of

the open boundaries

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