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

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,

MINISTRY OF EDUCATION

AND TRAINING

VIETNAM ACADEMY OF 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

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

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

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

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

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

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

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

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

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

- 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 longitudinal 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

Semi-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

south-southwest 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; Middle-Upper 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

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