Đặc điểm biến động địa hình các vùng cửa sông ven biển bắc trung bộ tt tiếng anh

MINISTRY OF EDUCATION

VIETNAM ACADEMY OF

AND TRAINING

SCIENCE AND
TECHNOLOGY

GRADUATE UNIVERSITY OF SCIENCE AND
TECHNOLOGY

-----------------------------

NGUYỄN CÔNG QUÂN

GEOMORPHOLOGY OF COASTAL ESTUARIES IN
NORTHERN CENTRAL VIETNAM

Major: Geomorphology and Paleogeomorphology
Codename: 09 44 02 18

DOCTORAL DISSERTATION SUMMARY

Hanoi 2019


The doctoral dissertation was accomplished at the Graduate
University of Science and Technology – Vietnam Academy of
Science and Technology.

Principal supervisor
Dr. PHẠM VĂN HÙNG – Institute of Geological Science, VAST

Secondary/Other supervisor
Dr. PHẠM QUANG SƠN – Institute of Geological Science, VAST

Reviewer 1:
Reviewer 2:
Reviewer 3:

The final doctoral dissertation defense will be defended in front of
University Dissertation Committee at… (hrs), … 2019 in the
Graduate University of Science and Technology, Vietnam Academy
of Science and Technology.

The dissertation can be accessed in
- Graduate University of Science and Technology, VAST library.
- National Library of Vietnam.


INTRODUCTION
1. Background
Coastal estuaries locate on where the rivers meet the sea, with
many favorable physical conditions for human to settle and develop.
Large urbans with concentrated residental areas, economic zones,
national defense and security regions are gradually expanded on
those areas to serve the people such as industrial sites, administrative
area, civil works, airports, harbors, services, trades, etc.
The topology of the coastal estuaries on Vietnam Northern
Central coast has formed and developed under the interplay of

numerous external, internal and artificial dynamical processes;
furthermore, these are also stage for complex river-ocean
interactions. The consequence of those processes has made coastal
estuaries prograde toward the sea since Pleistocene epoch to the
modern day, formed identical type of landform from shoals,
sandbars, sand barriers to deltas. Coastal estuaries are normally
favourable places for socio-economic developments, but they are
also intimidated as sea level risings which can cause coastal erosion,
flooding… and damage coastal construction and lives of local
residents.
In the context of global climate changes and sea level rise, and
under the pressure of the economy, growing socio-economic
development, the topology of coastal estuaries on the Northern
Central Vietnam has been drastically transformed at many time and
spatial scales. This dissertation titled “Geomorphology of coastal
estuaries in northern central Vietnam” is the final result of studies to
fulfill the necessarirarity of many urgent objectives toward
sustainable socio-economic development and environment
protection.
2. Objectives
- Interpret the geomorphological features of coastal estuaries in
1


northern central Vietnam.
- Estimate the course of morphological changes and
geomorphological dynamic processes in the study area.
3. Research subjects and Study
- Research subjects: Morphology and modern geomorphological
dynamic processes of coastal estuaries in northern central Vietnam.

- Study area: the main study areas are the coastal estuaries of Ma,
Thach Han and Huong rivers (from bifurcation channel to subtidal
flats). The interested morphological changes of the study areas are
focused during those following phases: late Upper Pleistocene –
middle Lower Holocene, middle Lower Holocene – Upper Holocene,
and Upper Holocene – present.

Figure 1: Map of study area

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4. Data and methodology
Data and methodology of the doctoral dissertation including
documents, database was collected and analysed by the author during
the course.
5. Research Objectives
Research objective 1: The morphology of coastal estuaries in
northern central Vietnam is heterogenous, complicated and spatially
diverged to latitudinal pattern. Landform of the interested coastal
estuaries were classified following morphodynamic genesis
approach: the Ma estuary is classified as “delta”, including the
alluvial, mixed and marine dynamical processes with the number of
morphological unit of 3, 7, and 3 accordingly. The two others are
classified as “Liman” type, with respective landform units of alluvial
– mixed – marine dynamical processes are 4, 7, 6 units for Thach
Han estuary, and 4, 9, 4 units for Huong estuary.
Research objective 2: During late Quaternary to present, the
morphology of interested coastal estuaries had undergone 3 phases:
late Upper Pleistocene – middle Lower Holocene, middle Lower

Holocene – Upper Holocene, and Upper Holocene – present, and
propagraded at different grades. The present development at each
estuary is ranging from progradation (Ma estuary) to severe coastal
erosion and retrogradation (Thach Han and Huong estuaries).
6. New findings in the dissertation
The detailed geomorphological maps of the three coastal estuaries
had been established using high resolution remote sensing images,
GIS technology and other traditional research methods, to classify
and interpret landforms into groups of similar morphogenesis and
age. The geomorphological maps were adapted to understand the
morphological changes in the studied areas from late Upper
Pleistocene to Holocene.
The late Upper Pleistocene shorelines of the Thanh Han and
3


Huong coastal estuaries, and the late Middle Holocene shoreline of
the Ma coastal estuary had been reconstructed using
geomorphological and geological evidences. Database compiled
from topological maps, remote sensing data and GIS was used for
reconstruction of temporal shorelines in Thach Han and Huong
estuaries for the period from 1952-2017, and shorelines in Ma
estuary from 1965-2017.
Modern morphology change patterns of the three estuaries had
been determined. Dominant process in Ma estuary is progradation to
form new seaward landform, meanwhile coastal erosion is dominant
in Thach Han and Huong estuaries and causes retrogradation.
7. Scientific and practical significances:
Scientific significance: Results of the dissertation provide sufficient
database on the morphological changes, estimate the orientation of

geomorphological evolution of coastal estuaries in northern central
Vietnam.
Practical significance: the scientific outcomes can be used to
improve the territorial management capacity of local authorization
offices on the rational use of territorial resources and environmental
protection of coastal estuaries in northern central Vietnam.
8. Dissertation layout
Chapter 1: Research methodology on morphological changes of
coastal estuaries;
Chapter 2: Estuary morphological change characteristics and
controlling factors in the northern central Vietnam;
Chapter 3: Geomorphology of coastal estuaries in northern central
Vietnam;
Chapter 4: Morphological changes and the rational use of territorial
resources of coastal estuaries in northern central Vietnam.

4


CHAPTER 1: RESEARCH METHODOLOGY ON
MORPHOLOGICAL CHANGES OF COASTAL ESTUARIES
1.1. Overview
1.1.1 Definition of estuary
River mouth or estuary is the area where the river meets the sea,
characterized by the gradually shifting from terrestrial alluvial to
marine regime, including massive transformation of physicochemical
nature of the water columna, biological properties, morphologic
formation and delta initation processes.
1.1.2. Estuary classification in the study area
The estuary classification using in the study was based on the

synthetic geology-geomorphology criteria:
- Convex type (delta) on Hoi river mouth where characterized by
front submerged bars.
- Straight type (liman) on Viet and Thuan An river mouths,
characterized by low sediment concentration and parallel sand
barriers and enclosed lagoons.
1.2. Literature review
1.2.1. Global research
Globally, the methodology for coastal estuary study becomes
more synthetic and completed with the adaption of modern
technologies toward quantification outcomes.
1.2.2. Vietnam
Most studies on this field in Vietnam implemented modern
morpho-dynamic processes evaluation and their correlation to typical
natural hazards of coastal estuaries in northern central Vietnam on
determine the cause, estimate potential risk and propose mitigation/
damage reduction measures.
1.2.3. Northern central Vietnam
Study on the morpho-dynamic issues of coastal estuaries for
planning and territorial organization for socio-economic
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development in the northern central Vietnam is scarce, thus it is
necessary to perform more concrete and detail research on each
estuary.
1.2 Methodology
1.3.1. Approach
1.3.2. Methodology
1.3.2.1. Field survey and measurement technique

1.3.2.2. Remote sensing method
1.3.2.3. Cartography and GIS
1.3.2.4. Geomorphological method
1.3.2.5. Geological method
1.3.2.6. Synthetic evaluation method
CHAPTER 2: ESTUARY MORPHOLOGICAL CHANGE
CHARACTERISTICS AND CONTROLLING FACTORS IN
THE NORTHERN CENTRAL VIETNAM
2.1 Study area overview
Coastal estuaries in the northern central Vietnam are located on
the coastal plains of from Thanh Hoa province to Thua Thien – Hue
province. Physical settings in the study areas are diverse and
favourable for socio-economic development in the northern central
Vietnam.
2.2 Geological system
2.2.1 Geological settings
The geological settings of the study areas consist of various
formations dated from Proterozoic to modern.
2.2.2 Neotectonic structures
Weak uplifting activities in the mainland, such as Thanh Hoa –
Tan Ky uprising, are favourable for denudation-erosion processes,
create abrasion terraces to the west and seaward accumulation of Ma
river estuary. Subduction structure develops northwest-southeast,
parallel to the modern coast in Quang Tri – Hue province, promotes
6


heterogenesis accumulation terrains in the estuaries of Thach Han
and Huong rivers.
2.2.3 Modern and neotectonic faults

Severe erosion has occurred on river banks and coastal sections
where are active faults intersections.
2.3 Morpho-dynamic systems
2.3.1 Holocene sea-level fluctuations
Sea-level fluctuations on the northern central Vietnam in
Holocene were similar to the general trend in Vietnam and adjacent
regions.
2.3.2 Climate regime
Study area lies in the monsoon tropical climate, with two
separated dry and rainy seasons, under significant influence of
marine atmosphere.
2.3.3 River flow and sediment patterns
Water and sediment discharge of Ma river are considerably
greater than those of Thach Han and Huong rivers, thus the role of
Ma river to the formations of its estuary on the initiation and modern
morphology changes is more dominant than the other two rivers.
2.3.4 Wave, tidal and nearshore current regimes
Wave influence to the coastal estuaries in the study area is
dominant in the winter, thus the coast is severe shaped and erosion.
Tidal regime in the estuary of Ma river is greater than the other
estuaries, thus increase its influence to the estuarine formations.
Smaller tidal amplitude in Thach Han and Huong estuaries play less
significant role in morphological changes of those areas.
2.3.5 Modern sea level rise and climate changes
Sea level rise is a significant factor that has direct influence to the
morphological change of coastal estuaries in northern central
Vietnam.
2.4 Anthropogenic elements
7

2.4.1 Hydro power plants and irrigation systems
The total number of reservoirs and dams in the northern central
Vietnam may reach to over a thousand and playing a crucial role as
they become sediment traps and reduce natural flow discharge, thus
emphasize the influence to the morphological change.
2.4.2 Aquaculture and land reclamation
Aquaculture contributes great benefit to the local economy, but
the rise of water bodies for aquaculture and practice transformation
from rice paddy to fish/shrimp farms on the coastal zone may not
only change natural morphology but also increase salt water
intrusion in the coastal estuaries.
2.4.3 Construction of residental settlements and industrial areas.
Original landforms were artificially modified under the pressure
of socio-economic development. New constructions had been built
including infrastructures and residental settlements.
CHAPTER 3: GEOMORPHOLOGY OF COASTAL
ESTUARIES IN NORTHERN CENTRAL VIETNAM
3.1 Overview
Major morphological structures of the study areas developed in
northwest-southeast and semi-latitudinal directions, including
mountainous, hilly, plain and beach landforms.
3.2 Geomorphology of coastal estuaries
3.2.1 Establishment of the geomorphological map of coastal
estuaries
Methodology: the synthetic geomorphological map was established
by using the homogenetic and age uniformity to classify similar
features into homogeneous groups for the coastal estuaries of Ma,
Thach Han and Huong rivers.
Content: morphologic features which have similar origin and age

were classified into group. Each morphological group was
established according to its age and morphology.
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3.2.2 Geomorphology of Ma estuary
- Karst formations: karst formations in the study area distribute as
isolated mounts with height over 30m, scattered to the north and
southwest of the Thanh Hoa city and northwest of Ham Rong
mountain.
- Abrasion formations: those formations distribute scattered in the
study area, as isolated mounts and hills over 20m on different kinds
of bed rock.
- Alluvial formations: deposition formations by alluvial processes
distribute along the main channel of Ma river. They are classified
into 3 units: Upper Holocene shoals (1-2m); Upper Holocene low
sandbars (1-2m); and Upper Holocene high sandbars (1-2m).

Figure 3.1. Geomorphological map of Ma estuary
- Marine formations: this group includes 3 morphological units:
Upper Holocene accumulation terraces widely distribute in Hoang
Hoa, Quang Xuong districts and Sam Son city, height of 2-3m;
Lower-Middle Holocene accumulation terraces distribute to the west
of Hoang Hoa, Dong Son, Thieu Hoa districts and Thanh Hoa city,
height of 3-4m; modern beaches lie along the coast of Hau Loc,
Hoang Hoa, Quang Xuong districts and Sam Son city.
9


- Heterogeneous formations: this group contains 7 formations of

various processes including alluvial, marine, bog and aeolian.
Scattered Upper Holocene alluvial-bog accumulation surfaces at the
height of 1-2m narrowly stretch across some communes of Quang
Xuong district and Thanh Hoa city (Ham Rong, Dong Son, Nam
Ngan… wards). Upper Holocene alluvial-marine-bog accumulation
surfaces at the height of 1-2m distribute as riparian shallow depresses
across Hoang Hoa, Quang Xuong, Hau Loc districts and Sam Son
city. Upper Holocene marine-bog accumulation surfaces at the height
of 1-2m distribute mainly in Quang Xuong district. Semilongitudinal Upper Holocene alluvial – marine accumulation
surfaces at the height of 2-5m distribute in Hoang Hoa district and
Sam Son city. Lower-Middle Holocene alluvial-marine accumulation
surfaces at the height of 2-5m widely distribute across Hoang Hoa,
Quang Xuong, Dong Son districts and Thanh Hoa city. Upper
Holocene reformed marine-aeolian sanddunes are small, elongated
stripe of sanddunes, distributed from the north of Lach Truong river
mouth to the south of Quang Xuong district.
3.2.3 Geomorphology of Thach Han estuary
- Volcanic formations: those are denudation-erosion landforms
developed on Quaternary basalt hilly surfaces to the north-northwest
of the study area on Gio Linh district, at the height of 10-30m.
- Abrasion formations: abrasion formations distribute to the southsouthwest of the study area, including 2 surfaces of Upper
Pleistocene and Lower-Middle Pleistocene at the height of over 20m
and 40-80m, respectively.
- Alluvial formations: alluvial formations contain 4
geomorphological units: Upper Holocene shoal, at 1-2m; MiddleUpper Holocene low sandbar, at 2-3m; Lower-Middle Holocene high
sandbar, at 3-5m; Upper Pleistocene class 1 accumulation terraces, at
10-15m; Middle-Upper Pleistocene class 2 accumulation terraces, at
10

over 20m; Upper Holocene abandoned river channels. Alluvial
formations concentrates mainly on the riparian of Cam Lo (Hieu) and
Thach Han rivers.

Figure 3.10: Geomorphological map of Thach Han estuary.
- Marine formations: this group includes modern beaches along the
coastline; Lower-Middle Holocene accumulation surfaces distribute
across Gio Quang, Gio Viet, Ha Tay and Ai Tu county; Upper
Pleistocene and Middle-Upper Pleistocene abrasion terraces, at the
height of 12-20m and 25-35m respectively, to the west of the study
area and on the margin of the deposition plain.
- Heterogeneous formations: this group contain formations which
developed by alluvial, marine, bog and aeolian processes. The most
widespread formation is Lower-Middle Holocene alluvial-marine
accumulation surfaces at the height of 2-6m which accounting major
area of Thach Han estuary. Middle-Upper Holocene and Upper
Holocene deposition plains narrowly elongate across Gio Mai,
Tuong Van, Cao Ly at the height of 2-4m and 1-2m, respectively.
Upper Pleistocene alluvial-marine accumulation surfaces spread as
small patches in western Gio Quang, Dai Ang at the height of 6-15m.
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Upper Holocene and Middle-Upper marine-bog accumulation
surfaces distribute at the height of 1-2m and 1-3m, respectively and
scattered as small patches, flooded year-round. Elongated marineaeolian coastal sand dunes spread along the modern coastline.
3.2.3 Geomorphology of Huong estuary
- Abrasion formations: compiled denudation formations distribute at
the height over 20m in Huong Ho, to the south of Kim Ngoc village,
Gia Kho, Nguyet Bieu, Duong Xu, An Ha.

- Alluvial formations: river channels widely developed in the study
area during late Holocene. Late Upper Holocene high sandbars
distribute at 3-5m along Huong river in Phu Xuan, beneath railway
brigde Trieu Son Dong. Middle-Upper Holocene class I river terraces
spread dispersedly along Huong river, Ngoc Ho, Tuan ferry, Nam
Hoa at the height of 3-6m. Lower-Middle Holocene class II river
terraces distribute as elongated stripes along Huong, Ta Trach, Huu
Trach rivers at the height of 10-25m.
- Marine formations: modern beaches are formed in Middle-Upper
Holocene, at the height of 3-5m, spreading from Thai Duong Thuong
to Ke Sung. Lower-Middle Holocene accumulation surfaces widely
distribute along the coastline at the height of 4-6m for approximately
15km length. Upper Pleistocene marine abrasion terraces are
relatively levered at the height of 15-30m.
- Heterogeneous formations: Middle-Upper Holocene alluvialmarine accumulation surfaces distribute along O Lau, Bo and Huong
rivers, stretching to the south of the coastal plain. Middle-Upper
Holocene alluvial-marine-bog accumulation surfaces distribute in
Quang Vinh, Phong Hien, Phu Da. Middle-Upper Holocene marinebog accumulation surfaces distribute along the shore of Tam Giang
lagoon and Ha, Thuy Tu marshes. Lower-Middle Holocene alluvialmarine surfaces distribute in Huong Thuy district. Lower-Middle
Holocene alluvial-marine-bog accumulation surfaces distribute as
12


narrow stripes in Phu Bai at the height of 10-15m, contain greyish
blue – bluish black clayey-silty sand. Upper Holocene sand dunes
distribute along the coastline as dunes, mounds and sand bars at the
height of 10-30m.

Figure 3.17. Geomorphological map of Huong estuary.
CHAPTER 4: MORPHOLOGICAL CHANGES AND THE

RATIONAL USE OF TERRITORIAL RESOURCES OF
COASTAL ESTUARIES IN NORTHERN CENTRAL
VIETNAM
4.1 Morphological evolution of coastal estuaries in northern
central Vietnam
4.1.1 Middle – Late Pleistocene era
In Middle-Late Pleistocene era, the tectonic activities became
diverged as subsidence to the east, uplifting to the west of coastal
estuaries in northern central Vietnam. Marine transgressive boundary
shifted inland which was favourable for sedimentation in the east,
while abrasion terraces initiated and developed to the west of study
13


area.
In the estuary of Ma river, the 15-35m abrasion terraces initiated
in Tho Xuan and Trieu Son districts (Thanh Hoa province).
Denudation and denudation-erosion on mounts and hills over 40m
height took place in Yen Dinh, Tho Xuan and Trieu Son districts.
Subsidence occurred beneath and to the east Ma estuary in coherence
with marine transgression were the dominant environment for the
formations of marine and alluvial-marine landforms.
On the coastal estuaries of Thach Han and Huong river, abrasion
terraces also distributed to the west of study area, at the height of 1535m. Prodominant morphodynamic processes including denudation,
denudation-erosion and abrasion occurred in the background of
uplifting to the west of study areas, and stepping subsidence and
deposition on the major of Thach han and Huong estuaries. Uplift
activities promoted surficial denudation, erosion and eluviation to
form slope denudation, denudation-eluviation, denudation-deposition
surfaces, abrasion marine terraces. Mountains developed on uplifting

blocks were the Hoang Gay range to the far southwest, Dong Hoang
and Kho Quan mounts to the south, Dong Kieu and Kim Phung
mounts to the west and the others such as Ngu Binh, Dong Mieu…
Weathering crusts and thin layers of eluvium, deluvium… appeared
on slope surfaces, sometimes bedrock outcrops. The low-lying and
levered hill series to the south of the 1A highway were classified as
abrasion marine terraces at the height of 20-30m. This level was the
highest ancient shoreline of the era marked on the topology of study
areas. The central bottom of coastal estuaries in the study area was
filled by thick layer of alluvium, alluvial-marine sediment dated
middle-late Pleistocene.
4.1.2 Early-Middle Holocene era
In the coastal estuary of Ma river, sedimentation in the earlymiddle Holocene had created the Thieu Hoa formation, including
alluvial, alluvial-marine and marine landforms widespread in Ma
14


estuary. Weak uplift to the west of the estuary and other
morphodynamic processes such as denudation, denudation-erosion
took place on former middle-late Pleistocene formations.
Marine transgression in Thach Han and Huong estuaries favored
alluvial-marine and marine sedimentation as predominat
morphodynamic processes. Basalt floods as result of active tectonics
covered some locations. In early Holocene, basalt lava occurred to
the north of study area in Gio Linh district and formed dome basalt
hills at the height of 20-40m. In Huong estuary, alluvial-marine and
marine floodplains distributed as northwest-southeast elongated
stripes from Huong Phong commune to Phu Luong – Phu Da
communes. These formations widely distributed to the south margin
of Huong estuary: along 1A Highway, Hue Imperial City, Huong Ho,

Huong Long, Huong An, Huong Thuy and northern area of Phu Bai
Airport. The surficial height was 5-10m in average, in some places it
could reach up to 20m such as Nam Giao Esplanade where was
relatively levered, composed from gravely sand mixed up with
yellowy red clayey silt, tampered, occasionally laterization. The
alluvial-marine-lagoonal deposition plains widespreaded and
accounted for the majority of Hue coastal plain in Phu Vang and
Huong Thuy districts.
4.1.3 Late Holocent to present
In Ma estuary, local subsidence in Ma rivermouth was filled by
thick layer of late Holocene sediment, which reached up to 30m as in
drillcore LK11.SS in Lach Trao river mouth. Other morphodynamic
processes were alluvial, alluvial-marine, marine-bog… Deposition
landforms distributed along the river channels, coastal zone and river
mouths. The sedimentation determined the modern formation of sand
bars, sand barriers, sand ridges and dune systems in Ma estuary. In
Len river mouth, tidal flats, sand bars and shoals enlarged
continuously and gradually due to abundant sediment supply.
Shoreline advance rate in this area reached up to 40-50m per year.
Sediment supply in Hoi river mouth was smaller, thus the
15


sedimentation was also weaker, accumulation occurred to both north
and south sides of the river mouth, shoreline advance rate was 5-10m
annually.
In Thach Han and Huong estuaries, tectonic activity was diverged
with prominently subsidence to form floodplains, marshes and
lagoons as narrow strips along the coastline from Duong Thuong to
Ke Sung. Beside, alluvial formations also emerged on the riparian of

Thach Han and Huong rivers as multiple level sand bars; alluvialmarine-lagoonal deposition formations had been dried out gradually
and distributed dispersedly in Thach Han and Huong estuaries.
Morphodynamic factors also caused coastal erosion and aggradation
in the study areas.
4.2 Morphological change evaluation
The evaluation of morphological changes, especially modern
morphology, is the major component of applied geomorphology. In
order to determine the morphological evolution tendency of estuary,
it is necessary to analyze geomorphological characteristics,
morphological evolution history and specify ancient shorelines in the
study areas.
4.2.1 Morphological changes in the Ma estuary
The morphological features of Ma estuary had been changed
spatially and temporally. Evidences of late Pleistocene ancient
coastal zone existed in Yen Thai, Yen Lac communes (Yen Dinh
district) and Xuan Lai, Xuan Yen communes (Tho Xuan district).
According to those evidences, mainland of Thanh Hoa floodplain
was landward further to the modern coast and lied in Tho Xuan, Yen
Dinh and Trieu Son districts. During middle Holocene, ancient
shoreline stretched from Van Loc commune (Hau Loc district) to
Hoang Dat, Hoang Duc, Hoang Dai communes (Hoang Hoa district),
Quang Phu, Quang Nhan communes (Quang Xuong district). In the
modern age from 1965 to present, the shoreline has changed
relatively complicated (Table 4.2).

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Figure 4.5. Shoreline changes of Ma estuary
Table 4.2. Coast status of Ma estuary

North of Hoi rivermouth
South of Hoi rivermouth
Rate of change
Rate of change
Period
Status
(m/y)
(m/y)
Status
Conclusion
Conclusion
Maximum Average
Maximum Average
1965Slightly
slightly
(-)
10.8
3.1
(+)
12.1
4
1975
retreat
advance
1975Moderate
Slightly
(-)
18.7
4.2
(-)

10.5
3.5
1990
retreat
retreat
1990slightly
slightly
(+)
6.2
3.2
(+)
10.7
2
2001
advance
advance
2001Slightly
slightly
(-)
7.23
3.75
(+)
14.2
1
2017
retreat
advance

Note: advance/retreat/mixed
Generally, the shoreline of Ma estuary had advanced and move

seaward at relatively high rate. During late Pleistocene to middle
Holocene, the estuary advanced seaward up to few tens’ kilometers.
From late Holocene, the estuary gained more than 20km seaward.
Evaluation of modern morphological changes of Hoi and Lach
Truong rivermouths were energetic, thus showing the movement
trend of the shoreline in near future (Figure 4.5).
17


4.2.2 Morphological changes of Thach Han estuary
The estuary of Thach Han river was initiated since late
Pleistocene according to research results on local geomorphology
and geological settings. In late Pleistocene, the mainland lied distant
from modern shoreline, while local subsidence promoted marine
transgression deep into the mainland and the majority of Thach Han
estuary submerged. In late Holocene, uplifting activities and marine
regression took place and formed coastal plains. From 1952 to
present, the estuary has changed diversely as shown in Table 4.4.
Table 4.4.. Coast status of Thach Han estuary
Period

Cua Viet coastal zone
Interior of Cua
Northern
Southern
Viet
coast
coast
rivermouth

1952-1965

(+)

1965-1979

(-)

1979-1989

(-)

1989-1999

(+)

1999-2017

(+)

Unstable
coast,
alternative
Overview
shoreline
retreat/
advance

Morphological evolution

Shoreline retreat/advance
alternatively, tend to be stable
(-)
(+/-)
southward. Minor change in
rivermouth.
Prodominent shoreline retreat on
northern coast, alternative
retreat/advance on southern
(+)
(+/-)
coast, relatively stable. Change
reduced southward. Prodominent
erosion inside channel. Minor
change in rivermouth
Prodominent shoreline retreat,
slight alternative retreat/advance
(-)
(+/-)
inside channel. Significant
change in rivermouth.
Advanced shoreline, significant
(+)
(+/-)
change inside channel. Unstable
rivermouth.
Moderage shoreline advance,
alternative shoreline
(+)
(+/-)

advance/retreat inside channel.
Significant change in
rivermouth.
Unstable
Northern coast had experienced
Unstable
coast,
significant changes, exceed
channel,
alternative
southern coast. Coastal stability
alternative
shoreline
enhanced southward. Significant
shoreline
retreat/
change
retreat/ advance
advance
in-channel in rivermouth.

Note: advance/retreat/mixed
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Since late Pleistocene to present, the morphology of Thach Han
estuary had experienced consideratble changes, mainland advanced
seaward for tens kilometers. Modern coastal morphological change
are shoreline retreat landward on the northern coast of Cua Viet
rivermouth, and relative stable on the southern coast.

Figure 4.9. Morphological changes of Thach Han estuary (Cua Viet
rivermouth)
4.2.3 Morphological changes of Huong estuary
Morphological changes in Huong estuary took place from late
Pleistocene to present at a vigorous pace. In late Pleistocene,
mainland of Thua Thien-Hue lied remotely inland from modern
coast, as in Huong Tra, Huong Thuy, Phu Loc districts and west of
Hue city. Uplifting movement and marine regression since late
Holocene had resulted a modern coastal strandplain. In the modern
period from 1965 to present, Huong estuary has experienced some
diverse transformation as shown in Table 4.6.
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Table 4.6. Coast status of Thuan An estuary
Period

North of
Thuan An
rivermouth

1965-1978

(-)

1978-1989
1989-1994
1994-1999
11/1999

(-/+)
(+/-)
(+/-)
(-)

1999-2005

(+)

2005-2010

(-)

Overview

Less stable

Location
South of
Inside Thuan Change evaluation
Thuan An
An rivermouth
rivermouth
Unstable coast,
(-)
(+/-)
predominant
erosion
(-)

(+/-)
Less stable coast
(-/+)
(+/-)
Less stable coast
(+/-)
(-/+)
Less stable coast
(-)
(-)
Rapid erosion
Relatively stable
(+/-)
(+/-)
coast
(-/+)
(+/-)
Less stable coast
Thuan An
rivermouth was less
Morphological stable, undergone
changes due to
influence from
economic
alluvial-marine
Less stable
movements,
morphodynamic
less stable
factors, mineral

exploitation and
river regulation

Note: coastal erosion/coastal deposition/mixed
The morphology of Huong estuary had been modified rapidly
since late Pleistocene to present, mainland had progradated tens
kilometers seaward. Recently, marine transgression occurred in
Thuan An rivermouth and nurtured coastal erosion for the last 52
years (1965-2017). Total morphological change area in Thuan An
rivermouth was approximately 8.12km2, mostly on the coast of Hai
Duong – Thuan An, Tam Giang – Thanh Lam lagoonal coast and
riverine of Huong river (Figure 4.14).
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Figure 4.14: Shoreline movement probability of Huong estuary
(Thuan An rivermouth)
4.3 Suggestions for reasonable use of territorial resources
4.3.1 Exploitation, reasonable use and preservation of natural
resources
The detail and concrete plans for the coastal estuaries of Ma,
Thach Han and Huong rivers, based on the shoreline change
probability toward natural disaster mitigation and risk reduction are
crucial and necessary. Besides, the study areas are rich on deposit
placers and require a master projection for mineral exploitation.
4.3.2 Coastal floodway maintenance
Coastal floodway maintenance should be calculated by
integrating morphological evolution domain in the detail maps of
socio-economic development plans of each particular region.
4.3.3 Effiency exploitation and management of waterways

Research results on the morphological changes of river channels
could be used as basic scientific platform to propose planning
direction and measuarement toward effiency use of waterways.
4.3.4 Marine tourism
Decision makers can propose ideal concrete plan or projection
toward natural hazard mitigation via using study results on
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geomorphology and morphological changes of those coastal
estuaries, thus promote sustainable marine economic development of
the northern central Vietnam.
CONCLUSIONS
The morphology of coastal estuaries in northern central Vietnam
initiated and developed in the extreme and diverse settings of
internal-external morphodynamic factors and anthropogenic
processes. Neotectonic and modern tectonic movements with the
tectonic fault systems played a crucial role, which controlled and
dominated the development and transformation of estuaries’
morphology in the study areas.
Geomorphological maps scaled at 1:50.000 of the coastal
estuaries of Ma, Thach Han and Huong rivers had been established
using homogeneous landform classification by fusion methodology
of conventional geomorphological methods, high resolution remote
sensing techniques and GIS techlonogies.
The coastal estuaries of Ma, Thach Han and Huong rivers were
classified as delta and liman types and developed since middle-late
Pleistocene to present. The delta of Ma estuaries consisted of 3
alluvial landforms, 3 marine landforms and 7 heterogenous
landforms. The liman type of Thach Han estuary developed 4 marine

landforms, 6 alluvial landforms and 7 heterogeneous landforms.
Similar landform classification for Huong river was 4, 4 and 9 units
of marine, alluvial and heterogeneous provenances.
Ancient shorelines in late Pleistocene, middle Holocene of coastal
estuaries in northern central Vietnam had been reconstructed by the
analysis of geomorphological and Quaternary geological evidences.
Shorelines of modern era were also deliniated by using fusion
methodology of remote sensing data, thematic maps and GIS
22


technologies for each estuary (Ma estuary from 1965-2017; Thach
Han and Huong estuaries from 1952-2017).
There were 3 phases of morphological transformation in both
three estuaries: late Pleistocene – middle Holocene, middle Holocene
– late Holocene, and late Holocene to present. Abrasion terraces and
denudation, denudation-erosion hills developed in middle-late
Pleistocene were abundant to the west of study areas. Alluvial,
marine deposition landforms and alluvial-marine landforms
developed in early-middle Holocene widespreaded and accounted for
the majority of study areas. Other heterogenous landforms such as
marine, alluvial-marine, marine-bog, lagoonal developed in late
Holocene to present were distributed in the rivermouth and coastal
zone of the study areas.
Modern morphodynamic processes such as erosion and deposition
are the dominant factors for the morphological change of coastal
estuaries in northern central Vietnam. Deposition takes place mostly
in Ma estuaries, caused aggradation, while erosion dominances in
Thach Han and Huong estuaries and caused marine transgression.
The coastal estuaries in northern central Vietnam are

advantageous for economic development in tourism, transportation,
aquaculture and deposit placer exploitation. As the consequence, it is
necessary to establish a master plan for reasonable use of territorial
resources based on the outcomes of modern morphological change
study, toward sustainable socio-economic development and
environmental protection of the northern central Vietnam.

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