DECLARATION Thereby declare that is the research work by myself under the supervisions of Dr. Nguyen Quang Chien and Assoc. Tran Thanh Tung. The results and conclusions of the thesis are fidelity, which are not copied from any sources and any forms.
The reference documents relevant sources, the thesis has cited and recorded as prescribed, The matter embodied in this thesis has not been submitted by me for the award of any other degree or diploma. Hanoi, 15 May 2018 Author Pham Hoai Thuong ACKNOWLEDGEMENTS First of all, Ï would like to express my special thanks to my supervisors Dr. Nguyen Quang Chien and Assoc. Tran Thanh Tung for their patience, enthusiasm and immense knowledge, without them my research study would not have been succeeded, I sincerely thank all the lecturers who taught me in the program especially the lecturers from the Faculty of Marine and Coastal Engineering of Thuyloi University for their useful and interesting lectures, also would like to acknowledge Prof.
Marcel Stive and Assoc. Henk Jan Verhagen for their support and inspiration when I was studying in the Netherlands. Finally, Lam deeply grateful to my family for their great care and encouragement. CONTENTS LIST OF TABLES LIST OF FIGURES.
INTRODUCTION 4 Problem definition 4 Research Objectives and Research Questions 4 Approach and Methodology 'CHAPERI: LITERATURE REVIEW 1.1 The characteristics of mangrove spet 1.2 The mechanism ofwave attenuation through mangroves forest 13. SWAN-VEG Model 1.4 Some studies about wave attenuation by mangrove forest in Vietnam CHAPTER 2: STUDY AREA, 21 Location 22. The reality of mangroves forest. 23 State of the dyke system 24.1 Topography 242 Wind 243 Wave.7 Rain fall 25 24,8 Sunny hour 25 2.11 Bed characteristic 26 CHAPTER 3: WAVE ATTENUATION THROUGH MANGROVES FOREST 2? 31 Selection of appropriate types of mangroves and vegetation parameters, 27 32 Determine bed elevation to plant mangroves 29 33 Scenario selection 34 ‘Computational domain and bathymetry.
35 Hydro-meteorologie condition for normal case 3. Water level 36 Hydro-meteorologic condition for storm case 3.1 Design return period 3.2 Design water level.3 Oflshore wave parameters.1 Wavepropagation using Swan 2D model 38 3.2 Results of wave attenuation by mangrove forest 40 3.8 Comparison with an empirical formula 50 CHAPTER 4: IMPACT OF CLIMATE CHANGE TO MANGROVE FOREST AND WAVE ATTENUATION IN CLIMATE CHANGE SCENARIOS, 53 4.1 Impact of climate change and other factors to the development of mangrove forest 53 4.12 Rise in surface temperature s4 4.13 Storm and extreme weather events 35 4.2 Wave attenuation through mangrove forest in Climate change scenatios.1 Input data, 56 422 Results 58 CONCLUSIONS AND RECOMMENDATIONS 60 + Conclusions. 61 ANNEX 6 ‘AnnexI: SWAN 2D input file 65 Annex 1.1: SWAN 2D input file in Scenario 1 65 Annex 1.2: SWAN 2D input file in Scenario 2 66 Annex 1.3: SWAN 2D input in Scenario3 6 ‘Annex 2: SWAN-VEG inpot file 68 Annex 2.1: Example of SWAN-VEG input file in normal condi mn, SE monsoon 68 ‘Annex 2.2: Example of SWAN-VEG input ile in normal condition, NE monsoon 69 Annex 2.3: Example of SWAN-VEG input file in Storm condition. 70 Annex 3 : Hs, Kt, R in Scenariol,2,3 with 5-year-old tree and 9-year-old tre.1: Hs in scenario 1,2,3 with 5-year-old tree and 9-year-old ee 00.2: Kt in scenario 1,2,3 with S-year-old tree and 9-yearold tee.3: R in seenatio 1,2,3 with 5-year-old tee and 9-year-old tree 16 ‘Annex 4: Hs in scenatios in which density of mangrove forest varies +9 ‘Annex 5: Hs in Scenarios with and without efimate change 83 ‘Annex 6: Some photos from the field tip 85 LIST OF TABLES Table 0.1 Disuibution and area of mangroves [orests in Vietnam, 3 ‘Table 0.2 Mangroves forest in front of the dyke 4 Table 1.1 Some studies about wave attenuation by mangrove Forest im Vietnam.1 Characteristic ofthe sea dykes and revetments.2 Characteristics of tide along Vietnamese coast 2 Table 3.1 Parameters of K, obovata 28 Table 32 Parameters of S.3 Exposed time in a day in some assumed bed elevation, 30 ‘Table 3.4 Input data in SWAN Simulation 3 Table 35 Statistical offshore wave data a4 Table 3.6 Wind and wave parameters in Van Ly Station 38 Table 3.7 Wave properties at nearshore locations (A and B) 40 ‘Table 3.8 Representative diameters of wave attenuation corresponding with SCN1.9 Representative diameters of wave attenuation corresponding with survival rate 46 Table 3.10 Representive diameters of wave attenuation corresponding with width of mangrove forest 47 Table 3.11 Representative diameters of wave attenuation corresponding with width of mangrove forest 49 Table 3.12 Comparison results of wave height behind mangrove to Bao’study.1 Sea level rise in location from Hon Dau to Deo Ngang according to the scenarios of climate change and sea level rise 37 Table 4.2 Water level in Scenarios 58 ‘Table 4.3 Wave height behind mangrove forest and wave attenuation coefficient .59 LIST OF FIGURES Figure 01 Tracks of Global Tropical Cyclones since records began 1958-2015 (Source: seawapa.org) Figure 02 Map of Vietnamese Provinces (Source: Wikipedia) 3 Figure 0.3 Approach ofthe research 7 Figure 1.1 Sonneratia caseolaris 9 Figure 1.2 Kandelia obovata 9 Figure 1.3 Schematic diagram of the mecha sm by which mangrove forests reduce wave enersyl2] 10 Figure 1.4 Schematiz jon of SWAN-VEG model [10] 12 Figure 1.5 Schematization of mangroves is SWAN-VEG.1 Map of Hau Loc (source Google Map) 16 Figure 2.3 Mangroves area in Han Loc District from 1990 to 2015 18 Figure 2.4 Topography of study area 21 Figure 2.5 Water level in study area.6 Tracks of storms in East Sea Figure 2.7 Monthly average temperature Figure 3.1 Illustration for calculation exposed time corresponding to the bed elevation 29 Figure 3.2 Relationship between bed elevation and exposed time in Hau Loc beach .3 Cross section in 1D model 33 Figure 3.4 Wave rose from offshore in Thanh Hoa from 2006 to 2017 3 Figure 3.5 Relationship between wave height and wave period 35 Figure 36 Design water level in Hau Loe ~Thanh Hoà 37 Figure 3.7 Distribution of wave height in scenario SCN1 38 Figure 3.8 Distribution ofwave height in scenario SCN2 39 Figure 3.9 Distribution of wave height in scenario SCN3 29 Figure 3.10 Wave height in mangrove forest in 3 scenarios dị Figure 3.11 Wave height in mangrove forest in scenario 3 ái Figure 3.12 Wave height in mangrove forest in scenatio 2 2 Figure 3.13 Wave height in mangrove forest in scenario 1 “2 Figure 3.14 Kt in normal condition 44 Figure 3.15 Ktin storm condition 44 Figure 3.16 R in normal condition 44 Figure 3.17 Rin storm condition 44 Figure 3.18 Wave attenuation by mangrove forest corresponding to some survival rates 46 Figure 3.19 Relationship between survival rate and wave attenuation 46 Figure 3.20 Wave attenuation by mangrove forest corresponding to several width of the forest 47 Figure 3.21Relationship between width of mangrove forest and wave attenuation ecofficient 48 Figure 3.22 Wave attenuation by mangrove forest corresponding to some density of mangrove forest.23 Relationship between density of mangrove forest and wave attenuation coefficient s0 Figure 4.1 Four scenarios of generalized mangrove response relative SLR[24].2 Wave height behind mangrove forest in some scenarios with and without climate change: 38 INTRODUCTION ‘ Problem definition Vietnam located in the most affected region by storms in the world, Increasing in frequency and intensity of extreme weather phenomena such as floods, storms and tsunamis which is the consequence of global climate change causes a lot of di and threatens the lives and property of the inhabitants in particularly in coastal regions in recent years, Tracks of Global Tropical Cyclones since records began 1958-2015 pear Figure 0.1 Tracks of Global Tropical Cyclones since records began 1958-2015 source: seawapa.org) Finding out the solutions to mitigate disasters and adapt to climate change is an urgent problem.
A lot of recent studi in the world have pointed out that mangrove forests play an important role in riverbanks and coastlines protection and climate regulation, It is considered a multi-objective and sustainable solution for disaster mitigation and climate change adaptation, Fortunately, Vietnam has along coastline and suitable conditions for mangrove development. Inthe past, the inhabitants living in the coastal areas already were aware of the importance of mangroves belts from the experiences of real life. From the early twentieth century, coastal inhabitants planted mangroves species, such as Soneratia caseolaris and Kendelia obovarata in the northern part to protect dykes in the coastal areas and river mouths. Some fragments of dykes were still the same after a medium storm (Beaufort 6 to 8).
In July 1996 when No. 2 typhoon (Frankie) with wind velocities from 103 + 117kmíh occurred in Thai Binh, the sea dykes inThai Thuy Commune (in Thai Binh Province) were not damaged due to having the protection of the mangroves fences. In contrast, the dyke system in Tien Hai Commune was much damaged as a result of the deforestation of the mangroves to make shrimp ponds. 4 typhoon (Wukong) with wind forces of Beaufort 10 landed on Thách Ha Commune (Ha Tỉnh Province), where the dyke system along Nghen River was still the same because in this location mangroves had been planted in 9 rural communes.
If mangroves defenses had not existed, the Dong Mon dyke would have broken and Ha Tỉnh ‘Town would have been flooded and the consequences would have been severe. The local people in Hau Loc Commune (Thanh Hoa Province) recognized the important role of mangroves in wave attenuation from the experiences of 2typhoons, No. 7 in 2005 and No, Sin 2007. The fragments of the dyke which had been protected by mangroves were not destroyed by strong waves; While the fragments of the dyke without the protection of mangroves were broken because waves attach directly to the surface of the dyke [1].
From these examples, itis clear that the mangrove forest is an effective solution to maintain and strengthen the dyke system lying behind. Awareness about the importance of mangroves has risen in recent years. The government has been implementing many programs of mangrove forestation in the coastal provinces. According to the Ministry of Agriculture and Rural Development, the total area of mangrove forests of Vietnam in 2010 was 209,741 ba.
The distribution ‘of mangrove forests is shown in Table 0.1 Distribution and area of mangroves forests in Vietnam. ‘Number Region "Tidal marsh Area, Percentage tha) tha) (%) 1 | Quang Ninh and Northern Delta 122,335 37.7 | North Central Region 30974 1385 608 HH | South Central Region 13,068 2 1530 IV |SowhwestRegion 31484 41,666 51.13 V_ | Cu Long Delta 373301 128,537 34.43 Total | Vietnam 621162 20941 3817 Figure 0.2 Map of Vietnamese Provinces (Source: Wikipedia) ‘Table 0.2 Mangroves foresLin front of the dyke ‘Number Region Length | Dyke with foreshore | Dyke with ofthe | suitable for mangrove | foreshore not dyke | forest development | suitable for system [With | Without | mangrove đem) | mangrove | mangrove | forest (km) (km) | development (km) 1 | Quang - Ninh and 8a 286 301 Northern Delta 1 | North Central Region 338 49 Bs 14 Vv | Cau Long Delta 1.1, it can be seen that the proportion of the area of mangroves forests accounts only more than 30 percent of the area of tidal marshes. The proportion of North Central Region is smallest, about 6 percent. Besides, from Table 0.2, itis clear that most of the tidal marshes in front of the dyke system have suitable conditions for planting mangroves but lacking mangroves belts.
Consequently, strengthening and building mangroves belts in front of dyke system is one of the primary tasks in flood prevention and disaster mitigation. The questions are how to plan mangroves to protect dyke system and to calculate the quantitative effect of reduction wave height after having mangroves belts.