Preventive measures for coastal erosion in cua lo tam quang commune nui thanh district quang nam province

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT THUY LOI UNIVERSITY HOANG THI LINH GIANG PREVENTIVE MEASURES FOR COASTAL EROSION IN CUA LO, TAM QUANG

MINISTRY OF EDUCATION

AND TRAINING

MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT

THUY LOI UNIVERSITY

HOANG THI LINH GIANG

PREVENTIVE MEASURES FOR COASTAL EROSION IN CUA LO, TAM QUANG COMMUNE, NUI THANH DISTRICT,

QUANG NAM PROVINCE

MASTER THESIS

HANOI, 2016

AND TRAINING AND RURAL DEVELOPMENT

THUY LOI UNIVERSITY

HOANG THI LINH GIANG

PREVENTIVE MEASURES FOR COASTAL EROSION IN CUA LO, TAM QUANG COMMUNE, NUI THANH DISTRICT,

QUANG NAM PROVINCE

DECLARATION

I hereby certify the work which is being presented in this thesis entitled, “Preventive measures for coastal erosion in Cua Lo, Tam Quang commune, Nui Thanh District, Quang Nam province.” in partial fulfillment of the requirement for the award of the Master of Coastal Engineering and Management, is an authentic record of my own work carried out under supervision of Assoc Prof Dr Mai Van Cong The matter embodied

in this thesis has been submitted to UNDP in Vietnam and DMC under the framework

of the project “Strengthening Institutional Capacity for Disaster Risk Management in Viet Nam Including Climate Change Related Risks (SCDM Phase II)”

Ha Noi, December, 2016

Hoang Thi Linh Giang

ACKNOWLEDGEMENTS

First of all I would like to acknowledge the sponsors UNDP in Vietnam and DMC under the framework of project “Strengthening Institutional Capacity for Disaster Risk Management in Viet Nam Including Climate Change Related Risks (SCDM Phase II)” for the scholarship support

I owe special words of many thanks to Assoc Prof Dr Mai Van Cong- my supervisor for his concern, guidance, enthusiasm, valuable advice and assistance with so much care

I would like to acknowledge Assoc Prof Dr Tran Thanh Tung and Prof Dr Thieu Quang Tuan who are main co-ordinator of this master program, making value contributions to success in Master course I would like to say thanks to Professor Marcel Stive for his comment on proposed solutions I also want to thank to M.Sc Nguyen Quang Duc Anh from VINWATER for his comments, supports in modeling work and suggestion, M.Sc Le Duc Dung from VASI for his supports in data and model validation

I would like to thanks faculty of Marine and Coastal Engineering of Thuy Loi University for providing support in numerous aspects amid the study

My high appreciation goes to all the lecturers who have taught and provided me with such valuable knowledge to my future career both in Vietnam and in the Netherland;

my colleagues, friends and my classmates for their support and assistance

Finally, I would like to keep the great thanks to my sweet family for their great support and always being source of encouragement, motivation and energy

TABLE OF CONTENTS

DECLARATION i

ACKNOWLEDGEMENTS ii

TABLE OF CONTENTS iii

LIST OF FIGURES vi

LIST OF TABLES ix

INTRODUCTION 1

1 Rationale of this research 1

2 Research objectives 1

3 Focus area 1

4 Research methodology and implementation 2

5 Structure of the thesis 2

CHAPTER I: LITERATURE REVIEW 3

1.1.Overview of erosion and sedimentation 3

1.1.1.Some researches in foreign countries 3

1.1.2.Coastal erosion and shoreline changes researches in Vietnam 5

1.1.3.Recent coastal researches in Quang Nam province 9

1.2.Research method in erosion and sedimentation 12

1.2.1.Method of mapping- remote sensing 12

1.2.2.Questionnaire method 12

1.2.3.Field survey method 13

1.2.4.Modeling method 13

1.2.5.Statistical and synthetic analyzing method 13

CHAPTER II: OVERVIEW OF STUDY AREA 14

2.1.Study area description 14

2.2.Natural conditions 15

2.2.1.Climate condition 15

2.2.1.1.Temperature 15

2.2.1.2.Rainfall regime 15

2.2.1.3.Wind regime 16

2.2.1.4.Wave regime 17

2.2.1.5.Typhoons 19

2.2.1.6.Hydrological regime 20

2.2.2.Geological conditions 22

2.3.Social-economic features 23

2.4.Status of coastal erosion and existing coastal protection measures in study areas 23 2.5.Coastal development 28

CHAPTER III: ANALYSIS OF COASTAL EROSION PROCESS AND SHORELINE CHANGES IN THE STUDY AREA 35

3.1.Causes of coastal erosion in study area 35

3.1.1.Hypothesis 1: Erosion caused by structural properties of the coast 37

3.1.2.Hypothesis 2: Erosion and shoreline changes caused by sea level rise and the extreme boundary conditions of hydrological factors 37

3.1.2.1.Erosion and shoreline changes caused by sea level rise 37

3.1.2.2.Effect of typhoons and storm induced cross-shore erosion 38

3.1.3.Hypothesis 3: Erosion and shoreline changes caused by human activities 41

3.2 Analysis of mechanisms for erosion and shoreline changes in the study area 42

3.2.1 CERC formula 42

3.2.2 Mike model 46

3.2.2.1 Data collection 46

3.2.2.2 Mike 21 model 47

3.2.2.3 Model set up 48

3.2.2.4 Calibration and verification of simulation model 54

3.2.3 Evaluation of the hydrodynamic regime in Cua Lo area 57

3.2.3.1 Hydrodynamic regime of Cua Lo area in winter 58

3.2.3.2 Hydrodynamic regime of Cua Lo area in summer 61

3.2.3.3 Hydrodynamic regime of Cua Lo area in flooding 64

3.2.3.4 Conclusions 66

CHAPTER IV: POSSIBLE ALTERNATIVE COUNTERMEASURES 68

4.1 The common principles of planning countermeasures 68

4.2 Proposed planning countermeasures for study area 68

4.3 Evaluating of planning countermeasures by modeling 77

4.3.1 Extraction locations of the results from Mike 21/3 FM model 77

4.3.2 Hydrodynamic regime and bed level change of Cua Lo area in summer 78

4.3.3 Hydrodynamic regime and bed level change of Cua Lo area in winter 82

4.3.4 Hydrodynamic regime and bed level change of Cua Lo area in flooding 86

4.3.5 Evaluation of possible countermeasures 90

CONCLUSIONS AND RECOMMENDATION 94

1 CONCLUSIONS 94

2 RECOMMENDATION 95

REFERENCES 96

APPENDIXES 100

Appendix 1: Frequency table in Spring, Summer, Autumn, Winter at Ly Son station… .100

Appendix 2: The result of calibration tidal model 104

Appendix 3: The result of verification tidal model 115

Appendix 4: Comparision of bed level change at 5 sections 122

LIST OF FIGURES

Fig.2- 1: Study area 14

Fig.2- 2: Wind rose at Ly Son (1985-2012) 17

Fig.2- 3: Wave roses in March, April and May at Ly Son station 18

Fig.2- 4: Wave roses in Jun, July and August at Ly Son station 18

Fig.2- 5: Wave roses in September, October and November at Ly Son station 19

Fig.2- 6: Wave roses in December, January and February at Ly Son station 19

Fig.2- 7: River system 20

Fig.2- 8: Discharge of Truong Giang river in flood season 21

Fig.2- 9: Existing coastal protection measures in Cua Lo area (Nui Thanh) 24

Fig.2- 10: Geo-textile (Internet &Google Earth) 25

Fig.2- 11: Geo-textile was destroyed in the southern of Cua Lo in 12/2013 25

Fig.2- 12: Approximately 30 m of existing revetments was seriously damage 26

Fig.2- 13: Large concrete blocks were capsized off the ground 26

Fig.2- 14: Tam Hai revetment, Nui Thanh district, Quang Nam provinces were destroyed after only a short time in use (Internet &Google Earth) 26

Fig.2- 15: Waterway in Cua Lo river mouth(Internet &Google Earth) 27

Fig.2- 16: Eroded area in Ba Tinh, Nui Thanh, Quang Nam (Internet &Google Earth) 27

Fig.2- 17: Coastal development (Google Earth) 29

Fig.2- 18: Average erosion rate in Cua Lo 30

Fig.2- 19: Average accretion rate in Cua Lo 31

Fig.2- 20: Accretion-erosion in Cua Lo in the period from 1965 to 2014 33

Fig.3- 1: Main causes and factors causing coastal erosion and shoreline changes 36

Fig.3- 2: Historic tracks of storm events in the vicinity of the research site 39

Fig.3- 3: Historic relevant tracks of storm events in the vicinity of the research site 40

Fig.3- 4: Phu Ninh reservoir (Google Earth) 42

Fig.3- 5: Representative cross sections 44

Fig.3- 6: Extend of large domain model 49

Fig.3- 7: Nested detailed (small) model 50

Fig.3- 8: Bathymetry of large model 51

Fig.3- 9: Bathymetry of small model 51

Fig.3- 10: Boundary conditions of large model 52

Fig.3- 11: The location of water level measuring stations 54

Fig.3- 12: The calibration result of water level at Son Tra station 55

Fig.3- 13: The calibration result of water level at Cua Dai station 55

Fig.3- 14: The verification result of water level at Cua Dai station 56

Fig.3- 15: The distribution of the characteristic waves of Cua Lo area in winter 58

Fig.3- 16: The distribution of total currents (speed and direction) when tide going up of Cua Lo area in winter 59

Fig.3- 17: The distribution of total currents (speed and direction) when tide going down of Cua Lo area in winter 59

Fig.3- 18: Result extracted points from the model 60

Fig.3- 19: Current velocities at points in winter 60

Fig.3- 20: The distribution of the characteristic waves of Cua Lo area in summer 62

Fig.3- 21: The distribution of total currents (speed and direction) when tide going up of Cua Lo area in summer 62

Fig.3- 22: The distribution of total currents (speed and direction) when tide going down of Cua Lo area in summer 63

Fig.3- 23: Current velocities at points in summer 63

Fig.3- 24: Water level of Cua Lo area in flooding 64

Fig.3- 25: The distribution of total currents (speed and direction) in flooding 65

Fig.3- 26: Current velocities at points in flooding 65

Fig.4- 1: Master plan 1 71

Fig.4- 2: Dredging for navigation 72

Fig.4- 3: Master plan 2 74

Fig.4- 4: Extraction locations of the results from Mike 21/3 FM model 77

Fig.4- 5: The distribution of total currents (speed and direction) when tide going up and down in summer of master plan 1 78

Fig.4- 6: The distribution of total currents (speed and direction) when tide going up and down in summer of master plan 2 79

Fig.4- 8: Bed level change in summer of master plan 2 81

Fig.4- 9: The distribution of total currents (speed and direction) when tide going up and down in winter of master plan 1 82

Fig.4- 10: The distribution of total currents (speed and direction) when tide going up and down in winter of master plan 2 83

Fig.4- 11: The distribution of the characteristic wave in winter of master plan 1 84

Fig.4- 12: The distribution of the characteristic wave in winter of master plan 2 84

Fig.4- 13: Bed level change in winter of master plan 1 85

Fig.4- 14: Bed level change in winter of master plan 2 86

Fig.4- 15: The distribution of total currents (speed and direction) in flooding of master plan 1 87

Fig.4- 16: The distribution of total currents (speed and direction in flooding of master plan 2 87

Fig.4- 17: Water level of master plan 1 88

Fig.4- 18: Water level of master plan 2 88

Fig.4- 19: Bed level change of master plan 1 89

Fig.4- 20: Bed level change of master plan 2 90

LIST OF TABLES

Table 2- 1: Statistical wind speed (average and maximum) per month in Ly Son

(1985-2012) 16

Table 2- 2: Wind speed statistics (average and maximum) in the direction of Ly Son (1985-2012) 16

Table 2- 3: Average erosion rate in Cua Lo 30

Table 2- 4: Average accretion rate in Cua Lo 31

Table 3- 1: List of the typical storms in Quang Nam coastal areas 40

Table 3- 2: Cross section 1 44

Table 3- 3: Cross section 2 45

Table 3- 4: CERC calculation results 45

Table 3- 5: Parameters of large model 53

Table 3- 6: The coordinates of measuring stations 54

Table 3- 7: Wave height at Ly Son station in season (1985-2012) 58

Table 4- 1: Ship size calculates the navigation 69

Table 4- 2: Preliminary planning of master plan 1 72

Table 4- 3: Preliminary planning of master plan 2 75

Table 4- 4: Extraction coordinates of the results from Mike 21/3 FM model 77

Table 4- 5: Evaluation possible countermeasures 93

INTRODUCTION

1 Rationale of this research

Coastal erosion and sedimentation become serious at many coastal sections in the Central Vietnam in general and Cua Lo, Tam Quang commune, Nui Thanh district, Quang Nam province in particular This causes many adverse consequences on daily life as well as social economic development, such as house collapsed, public works destroyed, shoreline retreated and crop yields reduced This situation triggers local and central government to urgently seek for a solution to minimize the erosion and sedimentation problems Proposing possible solution for Cua Lo location, Tam Quang commune, Nui Thanh district, Quang Nam province is therefore very important

2 Research objectives

This study comes up with the following objectives:

- Analysis of erosion causes and determination of driving forces that lead to the accretion, erosion of the study area

- Proposing possible solutions for coastal erosion prevention in Cua Lo, Tam Quang commune, Nui Thanh District, Quang Nam province

3 Focus area

- Focus area of this study is a coastal section around the Cua Lo river mouth, belonging toTam Quang commune, Nui Thanh district within the geographical limits

of 15°30'25.15"N - 108°37'44.95"E to 15°28'7.21"N – 108°41'49.72"E

4 Research methodology and implementation

Research methodology and implementation as following:

Research methodology and implementation

5 Structure of the thesis

Besides the introduction, conclusion, recommendation and annexes, the study is consisted 4 chapters as following:

Chapter 1: Literature review

Chapter 2: Overview of study areas

Chapter 3: Analysis of coastal erosion process and shoreline changes in the study area

Chapter 4: Possible alternative counter measures

CHAPTER I: LITERATURE REVIEW

1.1 Overview of erosion and sedimentation

1.1.1 Some researches in foreign countries

Coastal erosion and sedimentation are natural processes; however, they have become anomalous and widespread in the coastal zone of Asia and other countries Zhang et al (2004) confirmed that the erosion is a global problem According to Hegde (2010), most of the coastline in countries around coastal areas was severely eroded The rates

of erosion however, differ with the countries It is well noticed that about 70% of the coastline of the world is eroding In India, which has a long coastline of about 7500

km including islands, 23% of the coast is eroding In USA, the rate of erosion varies from 0.3m to 0.6 m/year Louisiana State in USA is losing coastal land at the rate of one acre for every 24 minutes, according to U.S.Army Corps of Engineers If this is not arrested, some 800,000 acres of land is reported to be lost in next about 40 years and Louisiana shoreline is expected to recede by about 33 miles A US Federal Emergency Management Agency report of year 2000, states that in next 60 years, 25%

of homes and other structures with in 150m of shoreline and the shores of Great Lakes would fall victim to erosion Bilan (1993) reported that the erosion rate in the northern part of Jiangsu province in China is serious and as high as 85 m/year, in Hangzhou bay the rate is 40m/year, while in Tianjin it is 16-56 m/year In Japan loses 160 ha of land every year by erosion If the situation doesn’t change, Japan will be losing 2400 ha after 10 years and 4800 ha after 25 years Shoreline retreat of 2.7m/year has been reported in Mauritius and the coasts of some islands in Fiji have retreated by more than 30m in the past 70 years

Erosion becomes more serious in developing countries such as in Asia, especially Southeast Asia

According to Jarupongsakul (2006), the rate of erosion around the coastal periphery of Thailand is generally from 15 to 25 metres a year But the country’s 2,666.5 kilometer shoreline is under serious threat from coastal erosion, which is occurring at different

rates along shorelines of the Gulf of Thailand and the Andaman Sea About 485 kilometres out of 1653 kilometres in the Gulf of Thailand is severely eroded, while about four percent of the shoreline along the Andaman Sea, or 114 out of 1014 kilometres, is eroding at what is considered a critical rate.The rate of erosion is most alarming along the Gulf of Thailand, from Trat province in the East to Narathiwat province in the South Besides natural factors, the main reason leading to the erosion is due to the increase of the shrimp farm to reduce the presence of mangrove forests Gegar Prasetya (2007) reported that coastal erosion started in the northern coast of Java Island in the 1970s when most of the mangrove forest had been converted to shrimp ponds and other aquaculture activities, and the area was also subjected to unmanaged coastal development, diversion of upland freshwater and river damming in Indonesia Coastal erosion is prevalent throughout many provinces (Bird and Ongkosongo, 1980; Syamsudin et al., 2000; Tjardana, 1995) such as Lampung, Northeast Sumatra, Kalimantan, West Sumatra (Padang), Nusa Tenggara, Papua, South Sulawesi (Nurkin, 1994) and Bali (Prasetya and Black, 2003) Realizing the serious problems, a lot of money was provided by the Indonesian Government to combat coastal erosion from 1996 to 2004, but only for Bali Island in order to protect this valuable coastal tourism base A combination of hard structures and engineering approaches (breakwaters/jetties/revetments) of different shapes that fused functional design and aesthetic values, and soft structures and engineering approaches (beach nourishment) was used They succeeded in stopping coastal erosion on Sanur, Nusa Dua and Tanjong Benoa beaches

According to Othman (1994), nearly 30 percent of the Malaysian coastline is undergoing erosion A study of national shoreline erosion in Malaysia conducted in

1985 showed that more than 1.972km coastline of Peninsular Malaysia has been affected (Chua TE, 1998) Serious erosion areas include half of Kuala Perlis to Sungai Udang, west coast of Johore and northern Kuala Selangor (Abdullah 1992) In addition, 85% of the coastline 39.3km from Sugai Sungai Kerian to Gula has eroded

As reported by Kastl (2011), shoreline in Koh Kong Province - Cambodia migration landwards is 390 m between 1973 and 2011 (10.3 m per year), resulting in the loss of 0.60 km2 of mangrove forests The main reason is due to extensive river sand mining

in all nearby rivers since 2008 and dam construction since 2010 is correlated in time with increased rates of beach barrier migration

1.1.2 Coastal erosion and shoreline changes researches in Vietnam

The coastal zone of Vietnam is more than 3260 km long, extending through the territories of 24 provinces and cities, which include 127 urban and rural districts, 21 towns and 6 cities (Ha Long, Vinh, Hue, Quy Nhon, Nha Trang, Vung Tau) At the coast, a series of interactive processes occur between the land and the sea, between natural and human processes, between the dynamic forces of rivers and the sea, etc Coastal erosion and sedimentation are complicated phenomenon caused by marine dynamics Erosion and sedimentation are due to a combination of many factors Erosion and sedimentation are two sides of an issue The research of erosion and sedimentation must be based on a systematic and integrated evaluation if the factors causing erosion and sedimentation The factors causing coastal and river mouth erosion and sedimentation are closely related with each other and interact with each other in a unified system, which follows the law of nature and closely controlled by man, creating a kinetic balance among them When one or some factors change, other also change to establish a new balance

In recent years, the process of erosion along the coasts has been occured strongly, caused many adverse consequences on human activities in the coastal areas Many houses and public welfare works have been destroyed, lands and crops have been scaled down Especially in the strongly eroded areas: Cat Hai (Hai Phong), Van Ly, Hai Trieu, Hai Hau (Nam Dinh), Ngu Loc, Hau Loc (Thanh Hoa), Canh Duong (Quang Binh), Phan Ri (Binh Thuan), Can Thanh (Ho Chi Minh), Go Cong Dong (Tien Giang), Ho Tau, Dong Hai (Tra Vinh), Ngoc Hien (Bac Lieu), etc Coastal erosion is causing shoreline changes and significantly impacting the environment of

the coastal areas Therefore, the study of preventive measures for coastal erosion is extremely important

According to Pham Huy Tien et al., 2005, coastal erosion has been observed in all coastal provinces of the Central region Here 263 erosion sites have been recorded, of which the smallest site covers 1.4 ha, the largest one covers 262.8 ha The total area of coastal erosion in the period 1990 - 2003 is 8839 ha Observation and records show that in the total 263 erosion sites 284 coastal sections and 10 areas have been completely eroded In the coastal section from Thanh Hoa to Khanh Hoa there is an erosion site in every 6 km The coastal erosion occurs at different rates The areas with irregular, rugged landform, with many bays and peninsulas, bedrock, river mouth areas erosion occurs with small extent, low to medium intensity.Strong and very strong erosion occurs in convex coastal sections facing wind and wave direction,with sand being the main shore-building material There are up to 268 erosion sections composed

of sand, accounting for 93.7% of the total erosion sections.The Central coastline from Thanh Hoa to Binh Thuan is 1765 km long, of which 392 km are being eroded (accounting for 22% of the total coast line).The survey results show that the eroded coastal sections with length over 1000 m account for 41% In the Central region, erosion occurs nearly all over the coast line, in the territories of all coastal provinces, though with different intensity and rate The areas with strongest erosion are concentrated in the coastal zone of the Thanh Hoa, Thua Thien - Hue, Quang Nam, Quang Ngai, Phu Yen

Studies of phenomena close / open estuaries, lagoons just only significant focus area in Tam Giang-Cau Hai (Thua Thien-Hue) area with the phenomenon of open / close Hoa Duan estuary In which, the majority of projects were carried out within the framework

of international cooperation between Vietnam – Netherlands (Cooperation between Water Resources University, Ha Noi and Delft University Technology) In general, the research projects at Tam Giang – Cau Hai Lagoon concentrated in researching nature open/close regime of estuaries, calculate estuaries stability, salt intrusion with different open/close scenarios of estuaries Some research project such as: Tran Thanh Tung et

al (2007); Nghiem Tien Lam (2006); Nghiem Tien Lam et al (2007); Thieu Quang Tuan (2007); Tran Duc Thanh et al (2000, 2002) Sumary, assess the results of

research on erosion, deposition of Vietnam coastline and estuaries was presented by Assoc Nguyen Manh Hung in the monographic: "Coastline and estuaries evolution in Vietnam" (Nguyen Manh Hung, 2010)

In recent years, Central Vietnam has spent thousands of billions to build hundreds of river bank protection embankments But before unexpected developments of the climate, people of central Vietnam have to suffer from hurricanes, severe floods consecutively, along with threatening high tides which caused a series of sea dykes eroded or damaged, with serious impact on the lives of people

In Thua Thien Hue province, many eroded areas have appeared recently with more than tens of kilometers of coastline in the communes of Phu Vang, Quang Dien, Huong Tra towns, threatening the lives and property of people Thousands of cubic meters of soil and vegetation in the coastal areas of Phu Thuan, Phu Hai commune, Thuan An town (Phu Vang district), Vinh Hai, Vinh Hien commune (Phu Loc district), Quang Cong Commune, Quang Ngan (Quang Dien district) and Hai Duong commune (Huong Tra town) were washed away in waves and tides The coastline adjacent to the erosion area is covered with embankments in Genh hamlet (Thai Duong Ha Nam rural, Hai Duong commune), but continue to eroded 10 m deep and 500 m long In Phu Yen province, Provincial People's Committee has signed a decision to proclaim a state of emergency about coastal erosion in Ro hamlet area, Phu Dong Ward (Tuy Hoa City) in the last few years, threatened the lives and properties of dozens of households in the region Local people said when the sea level fluctuated greatly, 5-7 m high waves were common, which destroyed embankments and caused serious erosion, rocks were dumped into the sea, which might be dangerous to local people

In addition, some fishing ports and shipping routes into several ports faced serious sedimentation problems in estuaries in Central Vietnam, i.e: Tam Quan Bac estuary (Hoai Nhon - Binh Dinh), Da Rang river mouth (Phu Yen), Sa Huynh estuary (Duc Pho), My A estuary, Dong Hai estuary, La Gi, Phan Thiet and Nhat Le, etc

The south of Tam Quang estuary (Hoai Nhon- Binh Dinh)

The Tam Quan Bac estuary (Hoai Nhon- Binh Dinh) is where 1.400 ships coming and going, the largest fishing port in Binh Dinh province and one of the busiest ports in Binh Dinh The main navigable channel frequently occur serious accretion, it makes ships difficult to go inside of the harbour and shelter harbor The government of Binh Dinh Province has invested more than 80 billion implementing the construction of safety zone in order to avoid storms in Tam Quan Bac and construction of a breakwater at the southern bank of Tam Quan Bac with 850 meters long

My A estuary is a mouth of small river of Duc Pho district, Quang Ngai province, but

it pays a very important role in social and economic development of the area The changes of My A estuary is very complicated, it causes many difficulty for transportation of fishing boats and ships, and even for the life of local people It has been drastically narrowed over the last decade due to sand and earth deposited at the sea mouth by the river and ocean tides Some 300 boats used to regularly enter and exit My A each day, but now only about 200 small-capacity boats can fit in the narrow lane Each year, when rough seas narrow local waterways, the government has mobilized funds from fishermen to hire dredge the passages However, after each rainy season, the estuaries and channels are filled up again with silt and sand deposits

The conditions are similar at the Sa Huynh Estuary, 20 kilometers south of My A Passages to the Sa Huynh fishing port, which opened in 2008, have been silted while the harbor’s signal light system has also been damaged by sedimentation

The Da Rang River mouth in central coastal Phu Yen Province's Tuy Hoa City has been narrowed as a result of sand encroachment, causing difficulties in the movement

of hundreds of ships In 2012, a fishing ship with a capacity of 165CV and 10 fishermen onboard was caught in shoals at the river mouth Around 50 fishing ships went through the Da Rang River mouth each day and it took each ship between one to two hours to come into the harbour and even between one and two days for big ships

Over past years deposition has occurred in Cua Tung mouth and erosion occurred at

Nu Hoang terrace The development has negatively influenced tourist and fishing activities

In Quang Nam province, the farmers living along the coast are still worried day and night by the threat of collapsing sea embankments About 10,000 households in the city of Hoi An coastal (Quang Nam) are familiar with these situations Many houses here were struck by heavy waves The lives of tens of thousands of people were threatened In particular, 300 m embankment of Cua Dai beach had just collapsed one year ago, costing approximately 100 billion VND Many houses in the area were flooded Meanwhile, in the area of Thu Bon River, located in Hoi An, two embankments of Ngoc Thanh -Cam Pho and Thanh Ha were severely eroded The eroded embankments significantly impacted the lives of people After the flood event, about 10,000 houses in Cam An Ward, Cam Thanh, Cua Dai, Tan Hiep Commune (Cu Lao Cham) had to deal with the effects of erosion

The situation of serious erosion in neighboring coastal estuary in Central Vietnam is becoming an emergency, it has recently been affecting people's daily activities, both social and economic, the national security and the defense in the area

1.1.3 Recent coastal researches in Quang Nam province

Quang Nam coasts composes commonly by slight to medium sand, the low ground surface, so it is easy to be strongly affected by hydrodynamics conditions such as wave, sea level rise The above process caused shoreline erosion, sedimentation, move the channel to the estuary, destroying coastal works, flooding in the coastal areas, estuaries In order to protect the coastline and estuaries, local government has built a system of embankments in the southern bank of the Cua Dai river and the southern bank of Cua Lo ( Truong Giang river), the embankment along the Au Co road (Cua Dai), Tam Thanh embankment, the coastal resorts in Hoi An have also built protection embankments However, some positions of the system of embankments at the beach Hoi An, Cua Lo have been destroyed; south bank embankment system of Cua Dai has caused great erosion for An Luong area, the channel at Cua Lo and Cua Dai still

frequently fluctuate Especially, in recent time, erosion of beach Ba Tinh (Quang Tam, Nui Thanh) become seriously by the exploitation of sand at the beach

Studying and predicting hydrodynamic processes and changes of shoreline, estuary in Quang Nam have been conducted with many different sizes, the most notably which is state level topic KHCN.06.08: "Study the laws and predict trends deposition-erosion coastal areas and estuaries Vietnam" (1996-2000); international cooperation projects Vietnam-India (2002-2003): "Study, predict the erosion-sedimentation in coastal areas

of Vietnam" with key research areas is Hoi An beach, is presided by Le Phuoc Trinh (Oceanographic Institute) Two themes have focused research on the evolution of the process of erosion, sedimentation at the Hoi An estuary The result has set up maps of terrain and shoreline changes for the Hoi An estuary area Based on data collected from themes, scientific researches on the process of hydro-dynamics and terrain changes was announced Ha Noi National University PhD thesis: "Study of natural hazards on the basis of geomorphology method to serve the urban development of coastal Da Nang-Quang Ngai areas" (1999-2000) by Dao Dinh Bac as a team leader has provided documents on natural disasters is erosion and deposition of coastal and estuary in Quang Nam State-level project: "Apply steps 3, 4, 5 integrated coastal management model for Quang Nam province" (2008-2010) by Nguyen Tac An (Institute of Oceanography) presides The study has collected data on the process of hydrodynamic and erosion, sedimentation in coastal areas in Quang Nam, serves coastal integrated management Science and technology research by Vu Minh Cat, et al., (2002-2003): “Study of drainage solutions, prevent erosion and sedimentation of

Vu Gia- Thu Bon estuary” Provincial thesis (2007-2008): "Survey, assess and propose solutions to protect and restore the ecosystem of coastal wetlands in Quang Nam" by Pham Viet Tich chaired, measured 20 sections from Dien Duong to Cua Lo These are very precious data to support for assessing changes in topography in the study area Codes of State- level thesis: KC.09.24 / 06-10 (2008-2010): "Scientific and technical Justifying for integrated management and sustainable development of the coastal NTB meet the strategic objectives of sea economic development " by Bui Hong Long (Institute of Oceanography) host and VAST thesis (2008-2009): "Assess the impact of

protection structures to the environment of coastal estuaries NTB" by Le Dinh Mau (Oceanographic Institute) studying, assessing the current situation and the impact of bank protection works and estuaries in Quang Nam The research results of the project were provided on the current situation of erosion-accretion and changes in terrain as well as the impact of the protection works in Quang Nam Within the framework of international cooperation projects Vietnam - Denmark (2008-2010): "Evaluation of the impact of climate change on natural conditions, environmental and socio-economic development in the Middle Central Vietnam" Institute of Geography (VAST) chaired,

in which Quang Nam is a key research area The goal of the project is to contribute to poverty reduction, environmental protection and community life, including health in the coastal area through the study of climate change, natural disasters and their effects,

as well as the necessary response measures However, projects just only focused research and forecast the climate change and their effects, the process hydrodynamics has not been studied in detail The directly relevant project to the coastal of Quang Nam has been announced e.g Bui Hong Long, Le Dinh Mau (2000); Le Phuoc et al (2001); Le Dinh Mau (2002, 2005, 2006, 2009, 2012); Le Dinh Mau et al (2004); Dinh Thi Hoi et al (2013) In addition, some studies of the hydrodynamics process in Quang Nam to serve the design of protection embankments, estuaries by departments

in Quang Nam conducted at Cua Dai, Cua Lo, Tam Thanh area in recent years e.g Tran Thanh Tung (2004) in which sediment transport and shoreline changes in Cua Dai is computed using UNIBEST model These documents are very important about natural conditions, hydrodynamics for building scientific basis in coast protection, the estuary, serves the planning, sustainable development in coastal zones in Quang Nam Under the combined effects of natural conditions such as geology, topography, river hydrology, the wind, flow, waves, water levels, etc and human activities such as coastal, estuaries protection works, dredging works, mining materials, etc Both processes are closely linked and have a role and impact on the process of erosion and accretion Basic characteristics of erosion and deposition in the coastal area of Quang Nam (Le Phuoc Trinh, 2003; Le Phuoc et al., 2001 and 2003): Focus and drastic in some short coast sections, is popular in the areas where has bank protection works, the

estuary, which was exploit materials (Cua Dai, Cua Lo, Ba Tinh); alternating each other in space and time between erosion-corrosion and accumulation-sedimentation However, erosion is greater than accretion; quite markedly seasonal nature, in which the northeast monsoon caused strong and regular erosion, with southwest wind, erosion and sedimentation only happen in extreme weather conditions such as storms, tropical depressions, etc ;Cua Dai, Cua Lo estuary showed signs of shifting to the south in certain periods (tens of years);

1.2 Research method in erosion and sedimentation

1.2.1 Method of mapping- remote sensing

Comparing maps of the same scale for different time periods is useful in studying of coastline morphological changes by time and coastline and river mouth evolution This method allows us to study the vast areas, synchronously, objectively and give us an overall stage of the coastline evolution in the different time of mapping and photographing

1.2.2 Questionnaire method

This method was the first time applied in studies of present stage of coast erosion along the coastline of Vietnam The method is simple, not time-consuming, inexpensive, and produces timely information Questions in questionnaire notes are often short, clear, and easy to understand and answer The answerers (usually commune officers) only need to have passed at least the secondary school The questions are about the composition of the coast (sand, rock and clay), coastal bathymetry, ranges of erosion, accumulation (width, length), occurring period of erosion, accumulation, and types of applied protection measured etc This method allows us to gain the qualitative and quantitative information for each different erosion, accumulation stretches with small size or occurred in the short time that are omitted by the method of mapping and remote sensing because of low resolution of maps and photos also will be pointed out

1.2.3 Field survey method

This is a necessary and indispensable method which is often used after implementing the first two methods The aim of this method is to check and determine technical information which is not correct or contradiction according to the earlier methods Furthermore, this method has often been applied for the severe eroding stretches to get additional data on geology, geomorphology and sediment transport rates

1.2.4 Modeling method

Mathematical modeling method is one of the most effective methods to simulate the coastline and river mouth evolution

1.2.5 Statistical and synthetic analyzing method

All information obtained by the different methods is used as input for the statistical and synthetic analyzing method The analyzed results are tabulated; from these tables, the places of eroding or accumulation stretch and the accordance important information are noted The research results will be mapped in the evolution diagram with the scale of 1/250000 and after that of 1/100000 and synthesize all the data to find out the patterns, reasons and characteristics of coastline evolution

CHAPTER II: OVERVIEW OF STUDY AREA

2.1 Study area description

Nui Thanh district shares a border with Quang Nam province in the south that was established in 1984 based on Tam Ky district, and the district border Tam Ky city in the North, Binh Son and Tra Bong districts in the South, and Nam Tra Mi district in the East The interest area is Cua Lo, Tam Quang commune, Nui Thanh distrist within

an extent of 15°30'25.15"N - 108°37'44.95"E to 15°28'7.21"N - 108°41'49.72"E

The district has a 37-km coastline section of beautiful beaches, such as Bien Rang, Tam Tien and Tam Hai There are some existing tourism projects actively such as Le Domaine De Tam Hai, Cat Vang Tam Tien, Chu Lai Resort Tam Hai is the only island commune of the district Nowadays, coastal erosion and sedimentation processes have been occurring in a rather complicated manner, causing serious consequences in Cua Lo areas

Fig.2- 1: Study area

Study area

2.2 Natural conditions

2.2.1 Climate condition

Vietnam has a tropical monsoon type of climate Quang Nam in general and Nui Thanh district in particular are located in the East of Truong Son mountain range and Hai Van mountain pass in the South Therefore, this place is the transition between Northern- and Southern-Vietnam climates Beside Nui Thanh district also has its own characteristics in climate because of its topography

Nui Thanh District has 17 communes and towns, including 8 communes adjacent to the sea so influenced by marine and continental climates According to data from local hydrometeorology stations, Nui Thanh district climate has the following characteristics:

2.2.1.1 Temperature

The average annual temperature in the area is around 27.60C The highest in July with average monthly temperatures is 31.60C December and the lowest in January with average monthly temperature is only 22.80C The dry season starts from April and ends in October On days when the southwest wind blows landward (from June to August), the air temperature increases The cold season lasts from the end of December to March next year The temperature variation is diurnal: peak daily temperature generally occurs dry season, a minimum daily temperature generally occurs cold season

2.2.1.2 Rainfall regime

The rainy season lasts from September to December The highest rainfall is October (720 mm) The total average annual rainfall is 2531.5 mm The average number of rainy days in a year is 140 days, the rainfall in October and November accounts for 50.4% of the annual rainfall There are an approximately 140-145 rainy days in a year The months with most rainy days are October, November, December; each has about 20-21 rainy days The months with the least rainy days are March, February, there are 5-6 rainy days in each month

2.5-Table 2- 1: Statistical wind speed (average and maximum) per month in Ly Son (1985-2012)

Table 2- 2: Wind speed statistics (average and maximum) in the direction of Ly Son (1985-2012)

Fig.2- 2: Wind rose at Ly Son (1985-2012)

(Source: “KC09.17/11-15”)

The main wind direction at Quang Nam includes Southeast, Northwest, and Northeast

In winter the prevailing wind direction is northeast and northwest with frequency accounted for over 40% In the months from winter to summer, the southeast and southeast wind direction is the prevailing direction besides northwest and south In the summer period includes the main wind direction is southeast, south direction besides southwest and northwest To the transition months from the summer to the winter, winds from the northwest and west prevail it is clear seen that the wind regime in Ly Son is distinct seasons nature According to statistical calculations see strong winds from level 8 or higher mainly occur in the winter months or at the time of the storm, tropical depression affected area (usually from September to the end of December each year, or may come in January, in February the next year)

Wind regime at Ly Son Island is the basis for calculating and forecasting hydrodynamic processes in coastal areas of Quang Nam

2.2.1.4 Wave regime

Sea waves in general and big waves in storms in particular cause damage to coastal communities and residential surrounding coastal area Waves are the main cause for

the destruction of coastal structure and shoreline erosion Besides the destructive impact directly, wave energy is transmitted through wave-induced currents This is the main factor causing the seabed sediment transport and created the erosion and accretion zone Wave conditions change could lead to beach change due to the different erosion processes: back to the shore, bed erosion, increasing slope Therefore, the study of the wind impact such as wind direction and its factor were extremely important to the coast

According to analysis data from Ly Son Island, NE monsoon starts from October to early March next year, the strongest in December SW monsoon starts from April to August, the strongest in July September and March are monsoon transitional period

Fig.2- 3: Wave roses in March, April and May at Ly Son station

Fig.2- 4: Wave roses in Jun, July and August at Ly Son station

Fig.2- 5: Wave roses in September, October and November at Ly Son station

Fig.2- 6: Wave roses in December, January and February at Ly Son station

(Source: “KC09.17/11-15”)

Overall, in coastal areas of Quang Nam, northeast monsoon period, the dominant wave direction was NE Southwest monsoon period, the dominant wave direction was SE Wave regime at Ly Son Island is the basis for calculating and forecasting hydrodynamic processes in coastal areas of Quang Nam in general and Nui Thanh in particular

2.2.1.5 Typhoons

Typhoons usually occur from September to December, they are most appear in October and November, they usually attach heavy rain caused flooding The annual average typhoon often occur 8-10 typhoons impacting directly or tropical depression

affecting the region Due to unexpected developments of the weather, there are five appearing storms and tropical depressions and they have affected the area very early in May and June

2.2.1.6 Hydrological regime

The local river system includes Tam Ky river, Truong Giang river, Ba Tuc river, Trau river, etc.These rivers originate from the West, Northwest eastward flowing down to the sea through An Hoa river mouth and Cua Lo river mouth The river basins are small, from 50 to 100 km2 The river lengths are from 20 to 40 km, with steep channels, and flow rate varying with the seasons Currently, the rivers are contained in the upstream areas to build water reservoirs such as Phu Ninh reservoir in Tam Ky river, Thai Xuan reservoir in Trau river

Fig.2- 7: River system

(Result of Vietnam Academy for Water Resources)

Fig.2- 8: Discharge of Truong Giang river in flood season

(Result of Vietnam Academy for Water Resources)

In particular the two largest rivers flow through Nui Thanh district are:

Truong Giang river: A river runs alongside the coast of Quang Nam flow to the sea through the Tam Xuan 1 commune, Tam Xuan 2 commune, Tam Anh commune and Tam Tien commune, Tam Hoa commune, Tam Hiep commune and Tam Giang commune, Nui Thanh town connection An Hoa river mouth with Cua Dai river mouth, Hoi An The downstream sections of these rivers are relatively wide

Tam Ky river: the confluence of 10 small springs, derived from the west, flows from west to east and out on to a main line at Xuan Binh - Phu Tho, Tra Tam commune Nui Thanh district, then from the Northwest - Southeast flow through Hoa river mouth A catchment area is about 800 km2

The district's rivers converge to the east created turbulence area, built the dunes and created the pond rammer in Tam Quang commune, Tam Anh Nam commune, Tam Anh Bac commune, Tam Hoa commune, Tam Giang commune, Tam Hai commune, Tam Tien commune Diurnal tide occurred in October about 15 days, and the rest are irregular semidiurnal tide The average water level is 1.2 m, spring tide is from 1.2 to 2

m, neap tide is 0.5 m The average flow speed is 0.2 to 0.3 m/s, the maximum speed is 2.5 m /s Storm surge heights can be up to 1.5 – 3 m

Due to the characteristics of the regional climate, water discharge of rivers varied with season, was remained in upstream and water discharge in downstream was let down

2.2.2 Geological conditions

The study area has two stratigraphic layers:

Early cambria metamorphic rock layer: This was type of crystalline schist with dark gray and bluish This stone was distributed in Northeast cape of An Hoa, Hon Dua island The characteristics of these rocks were similar to rocks of A Vuong layer

Basalt eruptions rock and Pliocene - Pleixtocen volcanic sedimentary rock layer: This was already weathered basalt The upper part has been turned into yellow alit – feralit The thickness of this soil layer was weathered nearly 40 m Under this layer of weathered rock was dark brown laterite rock and it all cohered This laterite layer exposed on the surface in many places due to seawater corroded weathered soils above These rocks were distributed in cape of An Hoa, Hon Dua island With a high degree of weathering, basalt has been classified into Pliocene - Pleixtocen age by geologists (Source: Geological map of Vietnam, continent part, a ratio of 1: 500,000

by Tran Duc Luong, Nguyen Xuan Bao, editor, 1986)

Quarternary deposit rock layer: Pleistocene deposit This sediment distributed narrow strips, extended along rivers, small streams, formed mainly white - gray sandy, dark gray due to it was mix with organic impurities and powdered clay This type was pale yellow sand, it used to be sand dunes, ancient sand dike but today it is affected by wind, waves and it is accumulated and distributed mostly in the area of Tam Hai commune According to Tran Nghi (1997), this sand was derived from here, due to a system of Tam Ky river -Trau river flow out in the time Pleixtocen (Q12-3) The mineral composition is mainly quartz sand, feldspar, mica, urmalin, mud, clay, layered unclear and thickness from 3 - 4 m

2.3 Social-economic features

Founded in 1983, Nui Thanh district at that time was a town with 12 communes After nearly 32 years of construction and development, Nui Thanh district has been gradually urbanized and is on its way towards the fourth grade city in 2020 Nui Thanh District currently has 17 communes and towns with a population of over 140,000 people This district has seaport, airport, national highway 1A, a train station and a North-South rail running across Especially, Nui Thanh is located in key regions of Chu Lai open economic zone and two industrial complexes: Trang Ton and Nam Chu Lai with hundreds of companies

In recent years, along with the development of the country, that the economy of Nui Thanh district has gradually integrate with the national economy has created conditions for development a multi-sector economy and encouraged all sectors and individuals to invest in production and business On May 12.2008, Quang Nam provincial People's Committee issued decision 4219 / QD-Committee approving the overall planning of urban construction Nui Thanh district After more than 6 years of implementing decision

4219 (from 2008-2015), Nui Thanh district has changed, the industrial park and services are formed, attracting investors and creating jobs for local workers local and surrounding areas The residential projects, ecotourism, upgraded roads, concretization, infrastructure systems, electricity, roads, schools and health development are relatively synchronized, creating a new image for the district Nui Thanh

2.4 Status of coastal erosion and existing coastal protection measures in study

areas

Coastal protection and protection in estuary areas have applied at Cua Lo area shown

in Fig.2-9

Fig.2- 9: Existing coastal protection measures in Cua Lo area (Nui Thanh)

(Le Dinh Mau, et al., 2015)

According to the statistics, annually typhoons often occur about 8 to 10 influencing to the district They often occur from August to November, combined with heavy rains, causing floods In the Tam Hai Island Nui Thanh district, there were several positions deepening inland about 50 m during 5 years In Thuan An group, Tam Hai commune is the same of border with sea in 2 directions, and the situation of salt intrusion in a severe way, so 200 households that local organization is going to re-locate other place

In 2009, the system consists of 9 geotextile bags (Geo-textile) had been built to protect the shoreline However, they was completely destroyed by wave after a short time Systems of coast protection forest (forest of casuarinas) were unable to prevent the destruction of the shore by wave action

Fig.2- 10: Geo-textile (Internet &Google Earth)

Fig.2- 11: Geo-textile was destroyed in the southern of Cua Lo in 12/2013

(Le Dinh Mau, et al., 2015)

In 2010, Quang Nam province has invested in the revetment construction in essential places in Tam Hai commune When put into operation in 2012, the phenomenon of erosion was reduced living life of local people is more stable However, the influence

of 13 typhoons in 2013 that a segment revetment in the end of the dikes about 30 m were waves, storm damage and Tam Hai commune has petitioned the province to

reconsider In addition, Tam Hai is about 2.4 km of Thuan An and Binh Trung Village need to build revetments to keep the land without deepening inland about 10m every year, but no social investment funds

Fig.2- 12: Approximately 30 m of

existing revetments was seriously

damage

Fig.2- 13: Large concrete blocks were

capsized off the ground

Fig.2- 14: Tam Hai revetment, Nui Thanh district, Quang Nam provinces were

destroyed after only a short time in use (Internet &Google Earth)

The accumulation of sediment in the north of Cua Lo had been affecting water traffic,

it made transportation more difficult

Fig.2- 15: Waterway in Cua Lo river mouth (Internet &Google Earth)

A rather large area was lost from Ba Tinh to Bai Lang in Tam Quang commune According to local people, Ba Tinh and Bai Lang landmarks are quite beautiful with

100 m white sandy beach that connect to shoreline However, at this moment, the beach has been eroding severely, and some places are vulnerable to landside

Fig.2- 16: Eroded area in Ba Tinh, Nui Thanh, Quang Nam (Internet &Google

Earth)