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

NGUYEN CANH THAN
MASTER OF SCIENCE THESIS

HOCHIMINH CITY, JUNE 2012

ASSESSMENT VAM CONG BRIDGE’S IMPACT ON BASSAC
RIVER TOPOGRAPHY BY NUMERICAL MODELING
The Joint Education Master Program
University of Liège – Belgium
Water Resources University – Vietnam
Sustainable Hydraulic Structures
THE JOINT EDUCATION MASTER PROGRAM
UNIVERSITY OF LIÈGE – BELGIUM
WATER RESOURCES UNIVERSITY – VIETNAM
ON
SUSTAINABLE HYDRAULIC STRUCTURES


MASTER OF SCIENCE THESIS


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


by
Nguyen Canh Than

Supervisor
Nguyen Huu Nhan (ICOE), PhD

Date of Submission
30.06.2012

TABLE OF CONTENTS
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
3.1. CALIBRATING AND VALIDATING MODEL 65
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

ACKNOWLEDGEMENTS

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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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
a. NATURAL CONDITIONS RELATED WITH HAU RIVER
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 km
2
, 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 km
2
, 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 km
2
, 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 3000km
2
and the highest water level is about 15.000km
2
. The lower river is
located on the territory of Vietnam with catchment area of about 36,200 km
2
and

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length of main flow 230 km. The density of rivers and canals average here is
about 4 km/km
2
.
Table 1.1: Areas and discharge from countries basin
No
Countries name
Basin
area (Km
2
)
Portion
(%) of total
basin area
Portion (%)
of total country
area
Portion %
of flow
1
2
3
4
5
6
CHINA

MYANMAR
LAOS
THAILAND
CAMBODIA
VIET NAM
165.000
24.000
202.000
184.000
155.000
65.000
21
3
25
22
20
9


97
36
86
20
16
2
35
18
18
11

Total area:
795.000
100
Total flow:
475 km
3

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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 m
3
.
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 m
3
every year, flood water is from 85%
to 90% on June to November with the highest flow discharge was observed to 66700
m
3
/s. However, dry season has just only 10% to 15% on January to May with
minimum discharge was observed about 1250 m
3
/s and the average discharge was
13970m
3
/s
Table 1. 2: The average discharge of Mekong river cross section Kratie from
1976 to 2006
Months
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug

Sep
Oct
Nov
Dec
Monthly
average
Discharge
Q (m
3
/s)
3643
2694
2196
1700
3605
13690
31662
41517
50905
38060
20081
7953
Percentage
to yearly
average
Discharge
(%)
1,67
1,24
1,01

0,78
1,66
6,29
14,54
19,07
23,38
17,48
9,22
3,65
When the river flows through Phnom Penh, a part of flow discharge on Mekong
River, about 90 billion m
3,
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
Q (m
3
/s)
476
346
5
600
6
957
4
7232
-
687
2
-
488
3
-
365
8
-

153
4
-
661
-371
-
102
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 m
3
/s and Chau Doc station was 6.840 m
3
/s. Otherwise, the discharge of
dry season observed at Tan Chau station was 882m
3
/s and Chau Doc station was
145m
3
/s.
Table 1.4: The average discharge of Tien river and Hau river from 1976-2006.

Station
Months
Jan.
Feb.
Mar.
Apr
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Chau
Doc
on
Hau
river
Q (m
3
/s)
1368
787
483
419
661
1454
2834
4904

5925
5758
4052
2486
Percentage
to average
flows (%)
4,39
2,53
1,55
1,35
2,12
4,67
9,10
15,8
19,0
18,5
13,0
7,99
Percentage
to
Q
TC
+Q
CĐ

(%)
18,1
16,5
16,4

16,4
16,9
22,3
25,7
22,4
23,6
21,6
18,5
16,2

Q (m
3
/s)
6171
3990
2464
2134
3261
5059
8181
16997
19153
20916
17803
12865
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Tan
Chau
on
Tien
river
Percentage
to average
flows (%)
5,19
3,35
2,07
1,79
2,74
4,25
6,88
14,3
16,1
17,6
15,0
10,8
Percentage
to
Q
TC
+Q
CĐ

(%)
81,9
83,5

83,6
83,6
83,1
77,7
74,3
77,6
76,4
78,4
81,5
83,8
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 m
3
/s in 2000 and the minimum discharge was 332 m
3
/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.
Q (m
3
/s)
2424
1561
1022
858
1279
2630
4721
7184
8116
7650
5602
3521
Percentage
to average
discharge
(%)
5,2
3,35
2,19
1,84

2,75
5,65
10,14
15,43
17,43
16,43
12,03
7,56
Percentage
to Tan
Chau
station
(%)
39,3
39,1
40,5
40,2
39,2
52
57,7
42,2
42,4
36,6
31,5
27,4
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 m
3
/s, but it‟s just only 44000m
3
/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 (H
max
) 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
H
max

(average)
H
max

(1961)
H
max

(1966)
H
max

(1998)
H
max

(2000)
Tan Chau
Tien
438
511
503

281
506
Chau Doc
Hau
385
490
476
255
490
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).
Station
River
H
min

(Average)
H
min
(1978)

H
min
(1986)
H
min
(2006)
Tan Chau
Tien
-36
-52
-48
-56
Chau Doc
Hau
-50
-58
-68
-68
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
Years

1980
1981
1982
1996
2001
2002
2003
2004
2005
Tan
Chau
station
August
413
1333
982
734
349
561
334
428
191
October
413
1080
864
708
291
407
368

383
139
September
441
732
502
470
214
281
278
350
216
Chau
Doc
station
August
314
495
407
300
140
364
314
282
178
October
326
244
242
200

73,3
147
244
166
123
September
86,0
88,0
107
120
89,4
58,1
120
87,2
87,7

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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.
b. THE FACTORS IMPACTED ON STUDY RIVER
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 3
o
C, only less than 1.5
o
C ÷ 3
o
C (see Table 1.10) and this is worth the
difference in maximum temperature. In the rainy months, this difference is quite
small, less than 1
o
C. The highest temperature usually occurs in April, ranging from
36
o
C ÷ 38
o
C. 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 18
o

C. Air temperature amplitude between day and night in the
rainy season is about 8
o
C and the lowest is 6
o
C (occurring in the most sultry days),
while the dry season corresponding values of the temperature is 10
o
C and 12
o
C
(occurring on most hot and dry days).
Table 1. 9: Mean monthly temperature of Chau Docstationfrom1976 to 2006.
Month
Jan.
Feb.
Mar.
Apr
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Temperature
(
0
C)

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.
Month
Dec.
Jan.
Feb.
Mar.
Apr
Total
Rainfall (mm)
29,5
5,6
0,7
19,4
75,2

130,4


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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
Month
Jan.
Feb.
Mar.
Apr
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Evaporation
(mm)
112
110
130
132
108
96
99
102
93
93
102
115
c. GEOLOGICAL AND MORPHOLOGICAL PROPERTIES

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/cm
3
with small natural soil and dry density is 1g/cm
3
, with the small bond does not
exceed 0.1 kg/cm
2

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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Socio-Economical activities

The left bank of the studied river domain is an agricultural district of Cho Moi,
the population is nearly 40,000 people, and population density is 1,000 people per
km
2
. The inhabitants are mainly in riparian farming and fishing. Right bank of the
studied river domain is Long Xuyen city, the population is nearly 23,000 people, and
population density is 2300 people per km
2
. The inhabitants are mainly made by
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 6,000,000m
3
, can
be exploited every year around 1,500,000m
3
. 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
erosion.
Fisheries fishing, aquaculture of wetland inhabitants in general, residents of An
Giang in particular exist for so long. However, fish farming along the river with
friends large and thriving today are formed in recent years. Fishing village along the

river are relatively stable river or riverbank erosion slightly, was not riverbed erosion
and accretion. Adapted to the requirements of the fishing villages, the ability to
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.
d. MASTER PLAN OF HO CHI MINH ROAD AND VCB PROJECT
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- wave-
sediment logy mathematical model is including in fact that, unlike the equations of
hydro dynamical and spectral models with strong theoretical bases, the almost
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.