Climate Change Driven Variations in Future Longshore Sediment Transport Rates along the Coast of Vietnam

Transcription

1 Climate Change Driven Variations in Future Longshore Sediment Transport Rates along the Coast of Vietnam Rev.4 March 2014 Authors : Supott Thammasittirong (AIT) Sutat Weesakul (AIT) Ali Dastgheib (UESCO-IHE) Roshanka Ranasinghe (UESCO-IHE)

2 Executive Summary Introduction This report presents the results of the study on Climate Change driven variations in longshore sediment transport rates along the coast of Vietnam. The project was funded by Ministry of environment and infrastructure of the etherlands. Vietnam has been identified by the International Panel on Climate Change (IPCC, 2007, 2014) as one of the countries that might be most affected by climate change. In particular the Mekong and the Red River deltas, with their extremely high population density in low lying areas, are severely threatened by sea level rise and anticipated increases in the frequency and intensity of typhoons and storms. The coastline of Vietnam is presently severely eroded and mangrove forests are reduced in area and density by severe storms and sea level rise. The coastline of Vietnam is 3,260 kilometers long and consists of 114 river mouths, 48 Bays, 12 lagoons, and 3000 islands. Impacts of changing climate in the coastal zone are already threatening people s livelihoods as well as the ecological system. Out of the many potential climate change (CC) impacts on coasts, the one impact that has received most attention is coastline recession due to sea level rise (SLR), while little or no attention has been given to other potential coastal CC impacts. Recent sutidies has highlighted that other CC impacts may in fact override the SLR impact on coasts (Stive et al., 2009; Ranasinghe and Stive, 2009; Ranasinghe et al., 2013). One such potentially severe CC impact that has not been sufficiently investigated is the coastal response to CC driven variations in offshore wave characteristics. Since longshore sediment transport is a direct function of breaking wave height and direction, assessment of CC on the longshore sediment is now possible for the Vietnamese coast due to a recent study of "Climate Change driven variations in the wave climate along the coast of Vietnam" funded also by Ministry of environment and infrastructure of the etherlands. Changes in longshore sediment transport rates will determine the coastline evolution in medium to long term time scales (i.e years) and spatial scales (i.e km). Objective The main objective of this study is to evaluate the impact of climate change on the large scale longshore sediment transport rates along the coast of Vietnam. Methodology Wave characteristics are the most important input data for the calculation of longshore sediment transport. The previous study on "Climate Change driven variations in the wave climate along the coast of Vietnam" compared the present ( ) and the future ( ) offshore wave climate at several locations along Vietnam coast using downscaled output from two global climate models (ECHAM and GFDL). i

3 In the present study, the and offshore wave climate derived from the aforementioned study are used to determine the nearshore wave climate for both time slices for 22 different coastline sections along the coast of Vietnam (Figure E-1). This was done by using the spectral wave model SWA model. The nearshore wave climate for the present time slice ( ) is used as the input to the GEESIS model to estimate annual average longshore sediment transport at these 22 coastline sections. These model estimates were verified with reported longshore sediment transport rates as far as possible. The verified GEESIS model was then forced with the nearshore wave climate for to estimate future climate change modified longshore sediment transport along the Vietnam coast. Figure E-1 Locations of 22 selected coastal sections along the Vietnam coastline. ii

4 Results The computed results indicate that the volume and direction of longshore sediment transport along the coast of Vietnam is rather variable. For present conditions, the annual average results from ECHAM and GFDL wave climate at 22 costal sections are found to be in the range of 11,000-2,748,000 m 3 /year in total gross transport and 1,400-1,426,000 m 3 /year in net transport in a northerly direction (at coastal section S2, S4 and S18-S21) and 35,000-2,740,000 m 3 /year in net transport in a southerly direction (at coastal section S1, S3, S5-S17 and S22). For future conditions, the annual average results at the 22 costal sections are in the range of 10,000-3,403,000 m 3 /year in total gross transport and 2,000-1,569,000 m 3 /year in net transport in a northerly direction (at coastal section S4, S9, S18-S21) and 500-3,174,000 m 3 /year in net transport in a southerly direction (at coastal section S1-S3, S5-S8, S10-S17 and S22). The estimated results of longshore sediment transport rates for the present ( ) and future ( ) show significant changes in net longshore sediment transport rates along the coast of Vietnam, with upto 0.5 million m 3 /year increase in the net transport rate at some locations. Such large changes in longshore sediment transport rates can lead to significant future variations in the position and orientation of the Vietnamese coastline. The results are summarized in Table E-1. The magnitude of the change and its foreseen effect on the coastline emphasizes the urgent need for detailed coastal morphological studies and quantitative risk assessments at sensitive coastal areas along the coast of Vietnam. This appears to be particularly the case in the vicinity of Danang (coastal sections 17, 18 and 19) due to the large projected future changes in longshore sediment transport direction and magnitude in this area, with an additional 875,000 m 3 of sand being transported away from this area per year. iii

5 Table E.1 Changes in net sediment longshore sediment transport due to climate change at 22 coastal sections along the Vietnam coastline. Coastal section S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S21 S22 Description The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 62%, in the order of 30,000 m3/yr There is no dominant direction of net longshore sediment transport in this section it will remain the same upto 2100 but with more tendency toward the south. The magnitude will decrease with about 7% in order of 1,000 m 3 /year in the southerly direction The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 34%, in the order of 125,000 m3/yr There is no dominant direction of net longshore sediment transport in this section it will remain the same upto 2100 but with more tendency toward the south. The magnitude will decrease with about 28% in order of 2,000 m 3 /year in the southerly direction The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 50%, in the order of 122,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 37%, in the order of 113,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 40%, in the order of 78,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 30%, in the order of 145,000 m3/yr There is no dominant direction of net longshore sediment transport in this section it will remain the same upto 2100 but with more tendency toward the north. The magnitude will increase with about 240% in order of 162,000 m 3 /year in the northerly direction The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 7%, in the order of 80,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 22%, in the order of 155,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 30%, in the order of 176,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 16%, in the order of 434,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 23%, in the order of 131,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 9%, in the order of 170,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 15%, in the order of 105,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 23%, in the order of 460,000 m3/yr The net longshore sediment transport is toward the north at present and will remain towards the north upto The magnitude of net annual transport increases by 45%, in the order of 290,000 m3/yr The net longshore sediment transport is toward the north at present and will remain towards the north upto The magnitude of net annual transport increases by 10%, in the order of 124,000 m3/yr The net longshore sediment transport is toward the north at present and will remain towards the north upto The magnitude of net annual transport increases by 15%, in the order of 170,000 m3/yr The net longshore sediment transport is toward the north at present and will remain towards the north upto The magnitude of net annual transport increases by 20%, in the order of 113,000 m3/yr There is no dominant direction of net longshore sediment transport in this section it will remain the same upto 2100 but with more tendency toward the north. The magnitude will increase by about 60% in order of 5,000 m 3 /year in the northerly direction iv

6 Table of Contents Executive Summary.... i Table of Contents. v List of Tables. vi List of Figures... viii 1 Introduction Background Statement of the Problems Objectives of the Study Scope of the Study Methodology Methods GEESIS Computation of Longshore Sediment Transport for the Coast of... Vietnam 6 3 Results and Discussion Model Calibration Modeling Results of Present Longshore Sediment Transport Rates Modeling Results of Future Longshore Sediment Transport Rates 28 4 Conclusions v

7 List of Tables Table Page Summary characteristics of the 22 coastal sections along the Vietnam 7 coastline Comparison of computed and reported net longshore sediment 18 transport rates at coastal section S1, S19, S20 and S Comparison of computed and reported gross longshore sediment 18 transport rates at coastal section S1, S19, S20 and S Summary of computed net longshore sediment transport rates for 21 present ECHAM wave climate Summary of computed gross longshore sediment transport rates for 22 present ECHAM wave climate Summary of computed net longshore sediment transport rates for 23 present GFDL wave climate Summary of computed gross longshore sediment transport rates for 24 present GFDL wave climate Summary of average net and gross longshore sediment transport rate 25 calculated from GEESIS for present period along Vietnam coast Summary of computed net longshore sediment transport rates for future 30 ECHAM wave climate Summary of computed gross longshore sediment transport rates for future 31 ECHAM wave climate Summary of computed net longshore sediment transport rates for future 32 GFDL wave climate Summary of computed gross longshore sediment transport rates for future 33 GFDL wave climate Summary of average net and gross longshore sediment transport rate 34 calculated from GEESIS for future period along the Vietnam coast vi

8 Table (Cont d) Page Future change in computed average net longshore sediment transport 34 rate from ECHAM and GFDL Future change in computed average gross longshore sediment transport 35 rate from ECHAM and GFDL 4-1 Changes in net sediment longshore sediment transport at 22 coastal 41 sections along the Vietnam coastline due to climate change. vii

9 List of Figures Figure Page Locations at which future CC modified wave climate was obtained Locations of 22 coastal sections along the Vietnam coastline for 8 GEESIS model simulation Wave rose diagrams from ECHAM climate model for the present period 9 ( ) Wave rose diagrams from GFDL climate model for the present period 12 ( ) Locations of the previous research studies area Comparison plots of net longshore sediment transport rates Comparison plots of gross longshore sediment transport rates Computed average net longshore sediment transport rates at locations along Vietnam coast for present wave climate ( ) Computed average gross longshore sediment transport rates at locations along Vietnam coast for present wave climate ( ) Estimates of present and future average net longshore sediment 35 transport rates at 22 costal sections Estimates of present and future average gross longshore sediment 37 transport rates at 22 costal sections Future change in average net longshore sediment transport rates at 38 the 22 costal sections along Vietnam Coast Future change in average gross longshore sediment transport rates at 39 the 22 costal sections along Vietnam Coast viii

10 CHAPTER 1 ITRODUCTIO 1.1 Background Vietnam has been identified by the International Panel on Climate Change (IPCC, 2007, 2014) as one of the countries to be most affected by climate change. In particular the Mekong and the Red River deltas with their extremely high population density in low lying areas are severely threatened by sea level rise and anticipated increases in the frequency and intensity of typhoons and storms. The coastline of Vietnam is 3,260 kilometres long and consists of 114 river mouths, 48 Bays, 12 lagoons, and 3000 islands. About 18 million people, almost a quarter of the total population, live in the coastal districts of Vietnam. Impacts of changing climate in the coastal zone are already threatening people s livelihoods as well as the ecological system. Coastlines are severely eroded and mangrove forests are reduced in area and density by stronger storms and sea level rise. During the last 50 years, the sea level along Vietnam's coastline has risen by approximately 20 cm, while the tropical cyclone frequency has increased by 2.15 events per 50 years. Over the last 50 years, consistent coastal erosion has been observed at 397 sites, covering a total coastline length of 1,000 km, at an average rate of 5-10 m/yr, although at some locations long term erosion rates as large as m/yr have been reported. Most of the coastline in the south has been eroded continuously at a rate of approximately 50 m/year since the early twentieth century (Cat et al., 2006, Mazda, Y. et al., 2002). This massive erosion is mostly due to wave and current action and the vanishing mangrove vegetation. Significant erosion also occurs in the central coastal zone of Vietnam and preventive measures such as sea dykes, revetments, and tree plantations have been implemented in many coastal areas. Of the many potential climate change (CC) impacts on coasts, the one impact that has received most attention is coastline recession due to sea level rise (SLR), while little or no attention has been given to other potential coastal CC impacts. Recent literature has highlighted that other CC impacts may in fact override the SLR impact on coasts (Stive et al., 2009; Ranasinghe and Stive, 2009; Ranasinghe et al., 2013). One such potentially severe CC impact that has not been sufficiently investigated is the coastal response to CC driven variations in offshore wave characteristics. Assessment of this phenomenon is now possible for the Vietnamese coast due to a recent study of "Climate Change driven variations in the wave climate along the coast of Vietnam CCWaves Vietnam" funded via the I&M-IHE MoU. Using state-of-the-art Global climate model output, dynamic downscaling and wave modelling, CCWaves-Vietnam has provided future projections for CC modified average wave conditions along the entire Vietnam coast. 1.2 Statement of the Problems As longshore sediment transport is a direct function of breaking wave height and direction, any future CC driven changes in these wave characteristics will have a profound impact on longshore sediment transport rates, and therefore on coastlines, particularly at medium to long term time scales (i.e years) and medium to large spatial scales (i.e

11 km). For example, persistent alongshore gradients in longshore sediment transport (even small gradients) could result in chronic impacts such as coastline recession (Cowell et al., 2003a, 2003b; Komar, 1998), inlet migration (FitzGerald, 1988), ebb/flood delta depletion/accretion (Oertel, 1972) etc. Most, if not all, of these impacts are generally considered as negative impacts by coastal managers/planners, and thus, over the last 50 years or so, there has been an enormous amount of research effort expended on developing robust methods and tools to accurately predict longshore sediment transport rates for given wave conditions. The one-line longshore transport model (GEESIS) will be used in this study to calculate the present and future longshore sediment transport rates along the entire coast of Vietnam by using the offshore wave conditions determined in the previous CCWaves-Vietnam study. 1.3 Objectives of the Study The main objective of this study is to investigate the broad scale longshore sediment transport rates for the coast of Vietnam and evaluate the effect of climate change on future longshore sediment transport rates using projected average offshore wave conditions determined in the previous CCWaves-Vietnam study. 1.4 Scope of the Study In order to achieve the objectives, the scope of study can be defined as follows: 1) The present ( ) and future ( ) of ECHAM and GFDL wave climate determined in the previous CCWaves-Vietnam study will be used as wave input data in the GEESIS model. 2) The longshore sediment transport rates will be calculated by the GEESIS model at the 22 selected coastal locations along the Vietnam coastline. 2

12 CHAPTER 2 METHODOLOGY 2.1 Methods Wave characteristics are the most important input data for the calculation of longshore sediment transport. The CCWaves-Vietnam study derived the future ( ) CC modified wave climate at 10 more or less equally spaced locations along Vietnam coast (Figure 2.1-1). To achieve this, CCWaves-Vietnam adopted the spectral wave model, MIKE21 SW, which was forced with climate model (ECHAM and GFDL) derived winds for the A2 greenhouse gas (GHG) scenario, dynamically downscaled using CSIRO s (Australia) CCAM stretched grid model for three time slices; , and The A2 scenario is a high end GHG scenario and thus represents a worst case situation. The output consisted of 6 hourly significant wave height, wave period and wave direction for the present (1981 to 2000) and the future (2041 to 2060 and 2060 to 2100). In this study we will first use the above described wave conditions to calculate contemporary longshore sediment transport rates using a process based longshore transport model (GEESIS model) at the nearshore coastal locations corresponding to the above mention 10 offshore wave locations, and verify model results with reported longshore sediment transport rates at these locations (i.e. model validation). Subsequently, projected wave conditions for the time slice will be used in the validated model to derive estimates of future CC modified longshore sediment transport rates at the selected coastal locations along the Vietnam coastline. The main steps of the methodological procedure that will be adopted are summarized below: Step 1: Offshore wave characteristics (~ 50km offshore) will be obtained from the previous CCWaves-Vietnam study for the present ( ) and future ( ) time slices at 10 more or less equally spaced locations along the coast of Vietnam (see Figure 2.1-1). Step 2: The SWA model, which is based on the deep water third generation wave model (WAM model), will be used to transform the offshore wave data to the nearshore wave data which can be used in GEESIS. Step 3: The wave characteristics for the present time slice will be used in GEESIS to obtain annual average longshore sediment transport estimates at 22 selected nearshore locations. These model estimates will then be verified with reported longshore sediment transport rates at or near the selected locations as far as possible. The model will be iteratively calibrated until the best possible match between modelled and reported longshore sediment transport rates is achieved. This will result in a validated GEESIS Model which can then be used confidently to obtain forecasts. 3

13 Step 4: The validated GEESIS model will be forced with nearshore wave characteristics for the future time slice to obtain the rates of potential sediment transport for Step 5: Longshore sediment transport rates predicted for the two time slices will be subjected to a sophisticated statistical analysis to determine areas along the Vietnam coast where CC may result in significant changes in longshore sediment transport rates and subsequent changes in the coastline Figure Locations at which future CC modified wave climate was obtained 4

14 2.2 GEESIS GEESIS, developed by Coastal Engineering Research Center (CERC), US Army Corps of Engineers, is designed to simulate long-term shoreline change on an open coast, as produced by spatial and temporal differences in longshore sand transport (Hanson 1987, 1989; Hanson and Kraus 1989). The name GEESIS is an acronym that stands for GEEralized model for Simulating Shoreline Change. The modeling system is founded on considerable research and applications of shoreline change numerical models. Wave action is the mechanism producing the longshore sand transport, and, in GEESIS, spatial and temporal differences in the transport rate may be caused by such diverse factors as irregular bottom bathymetry, wave diffraction, boundary conditions, line sources and sinks of sand. There are also constraints on transport (such as seawalls and groins). These factors are interrelated and may work in different combinations at different times. The GEESIS model is generalized in that it allows simulation of a wide variety of userspecified offshore wave inputs, initial beach plan shape configurations, coastal structures, and beach fills. Input to the model is the shoreline position, beach profiles and a time series of significant wave height, significant wave period, and the direction. Based on these data, the model calculates wave breaking properties, longshore sediment transport rates, and shoreline positions. The empirical predictive formula for the long-shore sand transport rate used in this model is: Q = (H 2 C g ) b [a 1 sin θ bs a 2 cos θ bs H x ] b (2.1) where H is the wave height (m), C g is the wave group speed given by linear wave theory, b subscript denoting wave breaking condition and θ bs is the angle of breaking waves to the local shoreline and the non-dimensional parameters a 1 and a 2 are given by: k 1 a 1 = 16 ( ρ s ρ 1)(1 p) ( ) and (2.2) a 2 = k 2 8 ( ρ s ρ 1)(1 p) tan β ( ) where k 1 and k 2 are the empirical coefficient which treated as the calibration parameters, ρ s is the density of sand (taken to be 2.65x10 3 kg/m 3 for quartz sand), ρ is the density of water (1.03x10 3 kg/m 3 for sea water), p is the porosity of sand on the bed (taken to be 0.4) and tan β is the average bottom slope from the shoreline to the depth of active longshore sand transport. 5

15 2.3 Computation of Longshore Sediment Transport for the Coast of Vietnam The GEESIS model is applied to compute the longshore sediment transport rates for the coast of Vietnam. The study area covers 22 selected sandy coastal sections starting from the south to the north of Vietnam s coast (S1 to S22) as shown in Figure This model is a one-dimensional model grid system where to the north, south and east of the study domain is the sea, while to the west is the land. In order to employ GEESIS for sediment transport computations, the initial data of coastline position, offshore/nearshore wave and other parameters must be obtained. - Coastline Position The actual coastline shape (position) of each of the 22 coastal sections considered is simplified to a straight coastline (with coastline orientation obtained from Google Earth) with the assumption that there are no changes in coastline position or effects of structures such as groins, offshore breakwaters and revetments within each section. - Wave Data Offshore wave data obtained from the previous CCWaves-Vietnam study at 10 more or less equally spaced locations along the coast of Vietnam (see Figure 2.1-1), were transformed through wave propagation modelling (SWA model). The nearshore positions are located outside the region of breaking waves such that the wave parameters extracted can be applied to calculate longshore sediment transport. The significant wave height, significant wave period and wave direction from two climate models (GFDL and ECHAM) for the present ( ) and future ( ) time slices at the nearest grid points to the 22 coastal sections of the study area provided by SWA model, were be used as input data for GEESIS model. The wave rose diagrams of the significant wave height at each coastline sections for present period during are shown in Figure and 2.3-3, while the results for the future period during are shown in Appendix A. The wave rose diagrams show that along the coast of Vietnam the wave direction is very dominantly from northeast to east corresponding to the northeast monsoon. The wave height and frequency of waves due to the northeast monsoon are also the strongest. - Other input parameters Other input parameters such as mean sediment grin size d50, beach profiles, berm height and depth of closure were obtained from available projects. The summary characteristics of the 22 coastal sections (S1 to S22) are presented in Table

16 Table Summary characteristics of the 22 coastal sections along the Vietnam coastline. Length of coastal Water depth at input Mean sediment Section Coastline orientation section waves grin size d 50 o. (km) (degree) (m) (mm) S S S S S S S S S S S S S S S S S S S S S S

17 Figure Locations of 22 coastal sections along the Vietnam coastline for GEESIS model simulation 8

18 68.61 % Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S Coastal Section S % Coastal Section S % Coastal Section S8 Figure Wave rose diagrams from ECHAM climate model for the present period ( ) 9

19 51.1 Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S % % Coastal Section S13 Coastal Section S14 Figure (cont d) Wave rose diagrams from ECHAM climate model for the present period ( ) 10

20 50.72 % Coastal Section S % Coastal Section S % % Coastal Section S17 Coastal Section S % Coastal Section S % Coastal Section S % % Coastal Section S21 Coastal Section S22 Figure (cont d) Wave rose diagrams from ECHAM climate model for the present period ( ) 11

21 71.72 % % Coastal Section S1 Coastal Section S % Coastal Section S % Coastal Section S % % Coastal Section S5 Coastal Section S % Coastal Section S % Coastal Section S8 Figure Wave rose diagrams from GFDL climate model for the present period ( ) 12

22 50.77 % Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S % % Coastal Section S13 Coastal Section S14 Figure (cont d) Wave rose diagrams from GFDL climate model for the present period ( ) 13

23 50.89 % % Coastal Section S15 Coastal Section S % % Coastal Section S17 Coastal Section S % % Coastal Section S19 Coastal Section S % % Coastal Section S21 Coastal Section S22 Figure (cont d) Wave rose diagrams from GFDL climate model for the present period ( ) 14

24 CHAPTER 3 RESULTS AD DISCUSSIO 3.1 Model Calibration The computed longshore sediment transport rates from this study will be compared with longshore sediment transport rates reported in literature at or near the selected locations for the present time slice ( ). There are various research studies of longshore sediment transport for the coast of Vietnam, but most of them are focused on the central coast of Vietnam, especially at the coast of Thua Thien-Hue province. Estimations of longshore sediment transport rates at some areas along the coast of Vietnam from previous research studies are selected for model calibration and comparison as shown in Figure The results of these previous research studies can be summarized as follows: (1) orthern coast of Vietnam at Hai Hau Beach (am Dinh province) Hung et al. (2006) computes the longshore sediment transport at Hai Hau beach using the program SEDTRA with input wave conditions during The estimated net sediment transport is 63,000 m 3 /year in a southwest direction (which agrees with the enlargement of the sand spit toward the southwest and the southwest overlapping of the bypass bar in the inh Co mouth), while the gross transport is 490,000 m 3 /year. In the present study, the GEESIS model was used for shoreline change simulation at Hai Hau beach with calibration parameters k 1 = 0.80 and k 2 = The best fit between calculated and measured coastline positions for the period from 1912 to 1965 and 2001 to 2005 was determined for model calibration and verification, respectively. (2) Central coast of Vietnam at Thua Thien Hue province and Quang Binh province Tran Quang Tien (2004) calculates the longshore sediment transport in littoral zone of Vietnam Central using the Bijker method, CERC method and the improved method based on the Meyer-Peter formula with 2002 hindcasted waves. The computed results at Thuan An area (Thua Thien Hue province) was found to be in the range of 600,000-1,100,000 m 3 /year in total gross transport and 400, ,000 m 3 /year in net transport in a northwest direction while the net transport at Hai Duong (Thua Thien Hue province) and gu Thuy (Quang Binh province) is about 1,500,000 m 3 /year and 900,000 m 3 /year in a northwest direction, respectively. In the present study, the GEESIS model was used for shoreline change simulation at Thuan An beach with calibration parameters k 1 = 0.75 and k 2 = The result of GEESIS agreed well with recent observed trend along this shoreline. 15

25 Hai Hau Beach gu Thuy Hai Duong Thuan An Beach Tat Channel LEGED Coastal sections of this study area Previous research study area Figure Locations of the previous research studies area 16

26 Lam (2009) evaluates different measurements and calculations of the longshore sediment transport for the coast of Thua Thien Hue done by different authors through the years The most reasonable results (with an agreement with the development of the sand spit and dredge records) is found to be in the range of 600,000-1,600,000 m 3 /year in total gross transport and 300, ,000 m 3 /year in net transport in a northwest direction. (3) Southern coast of Vietnam at Tat channel, near Mekong delta Q.T.Doan et al. (2013) presents the calculation results of littoral sediment transport at Tat channel (Phu Long province) using the LITDRIFT model with input wave condition during 9 years from 1999 to The estimated net sediment transport was found to be in the range of 150, ,000 m 3 /year in a southwest direction. The sediment transports in the present time slice ( ) at or near the above selected locations, which are coastal section S1, S19, S20 and S22, were computed by the GEESIS model. First, the calibration parameters k 1 and k 2 were set equal to the values of previous studies and has finally been adjusted after comparing the computed results of net and gross longshore sediment transport rates between this study and the previous studies. The selected values of the calibration parameters k 1 and k 2 are shown in the following table: Coastal Section k 1 k 2 S S S S The computed results of net and gross longshore sediment transport rates from the GEESIS model at these coastal sections and corresponding reliable estimated values reported in literature are summarized in Table and Table The comparison plots of longshore sediment transport rates between the computed results and the reported values are shown in Figure and The computed results of longshore sediment transport rates seem to vary annually and depend on the wave climate condition (ECHAM or GFDL) and coastline orientation as well. However, there is reasonable quantitative agreement between the computed results and the reported values. Difference in methods and period of computation, coastline orientation and wave climate condition are the main reasons that cause the difference of longshore sediment transport rates between this study and previous studies. For example, at Thuan An beach (located in coastal section S19), the previous study of Tran Quang Tien in 2004 were used hindcast wave in 2002 as input data for the calculation of longshore sediment transport by CERC, Bijker, and Meyer-Peter improved method. While in this 17

27 study, the of ECHAM and GFDL wave climate data were used as input data in GEESIS model to compute longshore sediment transport rate. Thus, the above k 1 and k 2 values were used as calibration coefficients in GEESIS with input ECHAM and GFDL wave climate to calculate annual longshore sediment transport at other coastal sections for the present ( ) and future ( ) time slices. Table Comparison of computed and reported net longshore sediment transport rates at coastal section S1, S19, S20 and S22. Study Area Estimates of Q net (m 3 /yr)* Coastal This study earby area section ECHAM wave GFDL wave Previous study S1 Tat channel 33,000 to 102,000 9,000 to 77, ,000 to 170,000 S19 Thuan An -786,000 to -1,772, ,000 to -1,703, ,000 to -700,000 beach S19 Hai Duong -786,000 to -1,772, ,000 to -1,703,000-1,500,000 S20 qu Thuy -768,000 to -1,725, ,000 to -1,579, ,000 S22 Hai Hau beach -21,000 to 71,000 5,000 to 111,000 63,000 ote: (*) the positive transport direction is southward Table Comparison of computed and reported gross longshore sediment transport rates at coastal section S1, S19, S20 and S22. Study Area Estimates of Q gross (m 3 /yr) Coastal This study earby area Previous study Section ECHAM wave GFDL wave S1 Tat channel 96,380 to 168,000 73,892 to 151,000 /A S19 Thuan An beach 787,000 to 1,772, ,000 to 1,705, ,000 to 1,600,000 S19 Hai Duong 787,000 to 1,772, ,000 to 1,705,000 /A S20 qu Thuy 769,000 to 1,727, ,000 to 1,580,000 /A S22 Hai Hau beach 77,000 to 136,000 53,000 to 152, ,000 18

28 Figure Comparison plots of net longshore sediment transport rates Figure Comparison plots of gross longshore sediment transport rates 19

29 3.2 Modeling Results of Present Longshore Sediment Transport Rates Modeling work of GEESIS was conducted at 22 coastal sections along the coast of Vietnam as shown in Figure The computed annual net and gross longshore sediment transport rates for the present time slice ( ) at the 22 locations are summarized in Table to 3.2-4, while the average annual net and gross longshore sediment transport rates are summarized in Table and shown in Figure to The plots of computed average annual net and gross longshore sediment transport rates at 22 locations are shown in Appendix B. The computed results indicate that the magnitude and direction of longshore sediment transport along the coast of Vietnam is rather variable. The annual average results at 22 costal sections from ECHAM wave climate input data are found to be in the range of 12,000-2,780,000 m 3 /year in total gross transport and 900-1,457,000 m 3 /year in net transport in a northerly direction (at coastal section S2, S4, S9 and S18-S21) and 26,000-2,750,000 m 3 /year in net transport in a southerly direction (at coastal section S1, S3, S5-S8, S10-S17 and S22). While, the results from GFDL wave climate input data are found to be in the range of 11,000-2,748,000 m 3 /year in total gross transport and 1,900-1,390,000 m 3 /year in net transport in a northerly direction (at coastal section S2, S4, S18- S21) and 32,000-2,720,000 m 3 /year in net transport in a southerly direction (at coastal section S1, S3, S5-S17 and S22). Comparison of average computed results of annual longshore sediment transport rates from ECHAM and GFDL at each coastal section for in Figure and show that all of them have similar magnitude and direction, except at S9. There are significant temporal variations in the computed annual longshore sediment transport rates from both ECHAM and GFDL wave climates during as shown in Appendix B. The results from ECHAM wave climate seem to have less fluctuation than the results from GFDL wave climate except during the period

30 Table Summary of computed net longshore sediment transport rates for present ECHAM wave climate. Year et Longshore Sediment Transport Rates for Present ECHAM Wave Climate (m 3 /year) Section1 Section2 Section3 Section4 Section5 Section6 Section7 Section8 Section9 Section10 Section , ,000-5, , , , ,000-7, , , ,128-3, ,000-7, , , , ,000 31, , , , ,000-1, , , , ,000 40, , , ,000 6, ,000 5, , , , ,000 37,000 1,019, , ,000-3, ,000-6, , , , ,000-87, , , , ,000-3, , , , ,000 33,000 1,195, , ,000 1, , , , , , , , , , ,000-2, , , , , , , , ,000-1, ,000-5, , , , , , , , , ,000-4, , , , , , , , , ,000-3, , , , ,000 44,000 1,022, , , ,000-4, , , , ,000 88,000 1,292, , ,000-6, ,000-11, , , , ,000-74, , , ,000 4, , , , , , , , , ,000 1, ,000-1, , , , , ,000 1,397, , ,000-7, ,000-12, , , , , ,000 1,834,000 1,294, , ,000-5, , , , ,000-87, , , ,000-1, ,000-5, , , , ,000 41, , , ,000-1, ,000-3, , , , , , , , ,000-3, ,000-6, , , , , , , ,000 Average 64, ,150-4, , , , ,150-7, , ,800 ote: the positive transport direction is southward Table (cont d) Summary of computed net longshore sediment transport rates for present ECHAM wave climate. Year et Longshore Sediment Transport Rates for Present ECHAM Wave Climate (m 3 /year) Section12 Section13 Section14 Section15 Section16 Section17 Section18 Section19 Section20 Section21 Section ,000 2,767, ,000 1,799, ,000 2,176, ,000-1,156,000-1,135, ,000 16, ,000 1,738, ,000 1,123, ,000 1,339, , , , ,000 16, ,000 2,537, ,000 1,651, ,000 1,970, ,000-1,300,000-1,262, ,000 36, ,000 2,874, ,000 1,818, ,000 2,208, ,000-1,288,000-1,267, ,000 41, ,000 3,013, ,000 1,945, ,000 2,420,000-1,007,000-1,392,000-1,366, ,000 15, ,000 3,406, ,000 2,139, ,000 2,615,000-1,000,000-1,343,000-1,307, ,000 21, ,000 2,730, ,000 1,742, ,000 2,237, ,000-1,291,000-1,271, ,000 15, ,000 2,673, ,000 1,692, ,000 2,165, ,000-1,256,000-1,242, ,000 14, ,000 2,146, ,000 1,374, ,000 1,772, ,000-1,099,000-1,086, ,000 20, ,000 1,804, ,000 1,146, ,000 1,496, , , , ,000-21, ,000 3,011, ,000 1,854, ,000 2,288, ,000-1,294,000-1,252, ,000 41, ,000 3,513, ,000 2,283, ,000 2,716,000-1,122,000-1,772,000-1,725, ,000 58, ,000 2,490, ,000 1,536, ,000 1,968, ,000-1,179,000-1,158, ,000 8, ,000 2,056, ,000 1,335, ,000 1,544, , , , ,000 45, ,000 3,867, ,000 2,469, ,000 2,934,000-1,127,000-1,682,000-1,623, ,000 58, ,054,000 4,292, ,000 2,826,000 1,177,000 3,043, ,000-1,621,000-1,544, ,000 71, ,000 2,644, ,000 1,656, ,000 2,097, ,000-1,295,000-1,284, ,000 24, ,000 2,579, ,000 1,641, ,000 1,984, ,000-1,236,000-1,202, ,000 49, ,000 2,559, ,000 1,630, ,000 2,071, ,000-1,251,000-1,253, ,000 7, ,000 2,383, ,000 1,514, ,000 1,969, ,000-1,088,000-1,105, ,000-11,974 Average 424,600 2,754, ,150 1,758, ,750 2,150, ,050-1,262,500-1,236, ,450 26,372 ote: the positive transport direction is southward 21

31 Table Summary of computed gross longshore sediment transport rates for present ECHAM wave climate. Year Gross Longshore Sediment Transport Rates for Present ECHAM Wave Climate (m 3 /year) Section1 Section2 Section3 Section4 Section5 Section6 Section7 Section8 Section9 Section10 Section ,000 11, ,000 13, , , , , ,000 1,107, , ,380 11, ,000 14, , , , , , , , ,549 10, ,000 12, , , , , ,000 1,046, , ,000 21, ,000 28, , , , , ,000 1,216, , ,000 8, ,000 11, , , , , ,000 1,116, , ,000 15, ,000 19, , , , , ,000 1,308, , ,000 10, ,000 13, , , , , , , , ,000 9, ,000 11, , , , , , , , ,000 10, ,000 13, , , , , , , , ,000 13, ,000 16, , , , , , , , ,000 11, ,000 13, , , , , ,000 1,143, , ,000 11, ,000 13, , , , , ,000 1,371, , ,000 10, ,000 14, , , , , , , , ,000 12, ,000 13, , , , , , , , ,000 10, ,000 12, , , , , ,000 1,441, , ,000 12, ,000 16, , , , , ,000 1,871,000 1,357, ,000 13, ,000 15, , , , , , , , ,000 16, ,000 22, , , , , ,000 1,038, , ,000 7, ,000 8, , , , , , , , ,000 11, ,000 16, , , , , , , ,000 Average 124,346 11, ,300 15, , , , , ,800 1,059, ,550 Table (cont d) Summary of computed gross longshore sediment transport rates for present ECHAM wave climate. Year Gross Longshore Sediment Transport Rates for Present ECHAM Wave Climate (m 3 /year) Section12 Section13 Section14 Section15 Section16 Section17 Section18 Section19 Section20 Section21 Section ,000 2,786, ,000 1,835, ,000 2,192, ,000 1,157,000 1,135, ,000 92, ,000 1,771, ,000 1,187, ,000 1,366, , , , ,000 77, ,000 2,551, ,000 1,678, ,000 1,984, ,000 1,301,000 1,263, ,000 92, ,000 2,925, ,000 1,951, ,000 2,267, ,000 1,288,000 1,268, , , ,000 3,025, ,000 1,967, ,000 2,435,000 1,039,000 1,393,000 1,368, ,000 91, ,000 3,438, ,000 2,197, ,000 2,645,000 1,005,000 1,344,000 1,308, ,000 91, ,000 2,743, ,000 1,765, ,000 2,251, ,000 1,291,000 1,271, ,000 84, ,000 2,690, ,000 1,722, ,000 2,181, ,000 1,256,000 1,242, ,000 79, ,000 2,160, ,000 1,409, ,000 1,787, ,000 1,100,000 1,087, ,000 85, ,000 1,842, ,000 1,205, ,000 1,545, , , , ,000 80, ,000 3,043, ,000 1,915, ,000 2,317, ,000 1,295,000 1,253, , , ,000 3,526, ,000 2,304, ,000 2,729,000 1,205,000 1,772,000 1,727, , , ,000 2,510, ,000 1,576, ,000 1,987, ,000 1,179,000 1,159, ,000 87, ,000 2,094, ,000 1,406, ,000 1,579, , , , ,000 99, ,000 3,876, ,000 2,482, ,000 2,946,000 1,131,000 1,682,000 1,624, , , ,143,000 4,307,000 1,022,000 2,848,000 1,214,000 3,062,000 1,001,000 1,621,000 1,544, , , ,000 2,667, ,000 1,694, ,000 2,120, ,000 1,296,000 1,286, ,000 96, ,000 2,608, ,000 1,702, ,000 2,005, ,000 1,236,000 1,202, ,000 96, ,000 2,568, ,000 1,644, ,000 2,080, ,000 1,253,000 1,253, ,000 78, ,000 2,399, ,000 1,548, ,000 1,982, ,000 1,089,000 1,106, ,000 79,444 Average 611,750 2,776, ,000 1,801, ,150 2,173, ,600 1,263,150 1,237, ,450 94,118 22

32 Table Summary of computed net longshore sediment transport rates for present GFDL wave climate. Year et Longshore Sediment Transport Rates for Present GFDL Wave Climate (m 3 /year) Section1 Section2 Section3 Section4 Section5 Section6 Section7 Section8 Section9 Section10 Section ,000-1, ,000-5, , , , , , , , ,000-2, ,000-7, , , , , ,000 1,978,000 1,452, ,000-8, ,000-13, , , , , ,000 1,695,000 1,238, ,007 4, ,000 2, , , , , ,000 1,325, , ,000-4, ,000-7, , , , , ,000 1,950,000 1,418, ,000-5, ,000-10, , , , ,000-14, , , ,000-3, ,000-8, , , , , , , , ,941 7, ,000 6, , , , , ,000 1,280, , ,000-3, ,000-9, , , , , , , , ,000-4, ,000-8, , , , ,000-18, , , ,845 5, ,000 3, , , , , , , , , ,000-1, , , , , ,000 1,418, , ,000-6, ,000-11, , , , , ,000 1,490,000 1,129, , ,000-5, , , , , , , , ,000-3, ,000-8, , , , , ,000 1,034, , ,000-4, ,000-8, , , , , , , , ,000-1, ,000-4, , , , , ,000 1,773,000 1,290, ,000-4, ,000-8, , , , , ,000 1,626,000 1,172, ,125-7, ,000-11, , , , ,000 59, , , ,210 6, ,000 3, , , , , ,000 1,728,000 1,296,000 Average 40,708-1, ,800-5, , , , , ,500 1,216, ,750 ote: the positive transport direction is southward Table (cont d) Summary of computed net longshore sediment transport rates for present GFDL wave climate. Year et Longshore Sediment Transport Rates for Present GFDL Wave Climate (m 3 /year) Section12 Section13 Section14 Section15 Section16 Section17 Section18 Section19 Section20 Section21 Section ,000 2,292, ,000 1,510, ,000 1,719, ,000-1,100,000-1,045, ,000 43, ,221,000 4,412,000 1,052,000 2,899,000 1,285,000 3,035, ,000-1,691,000-1,562, ,000 96, ,047,000 3,538, ,000 2,433,000 1,143,000 2,456, ,000-1,380,000-1,283, ,000 45, ,000 3,165, ,000 2,023, ,000 2,242, ,000-1,415,000-1,291, ,000 85, ,186,000 4,177,000 1,095,000 2,836,000 1,319,000 2,909, ,000-1,703,000-1,579, ,000 69, ,000 1,621, ,000 1,089, ,000 1,282, , , , ,000 6, ,000 2,177, ,000 1,442, ,000 1,594, ,000-1,075,000-1,010, ,000 31, ,000 3,281, ,000 2,143, ,000 2,492, ,000-1,617,000-1,526, ,000 53, ,000 2,179, ,000 1,517, ,000 1,638, ,000-1,088,000-1,035, ,000 17, ,000 1,637, ,000 1,093, ,000 1,313, , , , ,000 24, ,000 1,877, ,000 1,316, ,000 1,295, ,000-1,018, , ,000 59, ,000 3,394, ,000 2,268, ,000 2,519, ,000-1,509,000-1,417, ,000 45, ,000 2,738, ,000 1,998,000 1,017,000 1,859, ,000-1,252,000-1,189, ,000 42, ,000 1,781, ,000 1,243, ,000 1,321, , , , ,000 11, ,000 2,171, ,000 1,507, ,000 1,513, , , , ,000 5, ,000 1,877, ,000 1,302, ,000 1,419, , , , ,000 17, ,092,000 3,677,000 1,006,000 2,525,000 1,190,000 2,538, ,000-1,536,000-1,425, ,000 70, ,000 3,509, ,000 2,402,000 1,079,000 2,479, ,000-1,307,000-1,233, ,000 39, ,000 1,496, ,000 1,045, ,000 1,163, , , , ,000 9, ,113,000 3,499, ,000 2,371,000 1,157,000 2,329, ,000-1,443,000-1,309, , ,000 Average 717,550 2,724, ,250 1,848, ,750 1,955, ,150-1,208,400-1,132, ,300 44,261 ote: the positive transport direction is southward 23

33 Table Summary of computed gross longshore sediment transport rates for present ECHAM wave climate. Year Gross Longshore Sediment Transport Rates for Present GFDL Wave Climate (m 3 /year) Section1 Section2 Section3 Section4 Section5 Section6 Section7 Section8 Section9 Section10 Section ,000 13, ,000 17, , , , , ,000 1,054, , ,000 17, ,000 21, , , ,000 1,079,000 1,048,000 2,097,000 1,589, ,000 12, ,000 17, , , , , ,000 1,741,000 1,294, ,522 8, ,000 9, , , , , ,000 1,429,000 1,024, ,000 8, ,000 11, , , , , ,000 1,975,000 1,458, ,000 13, ,000 18, , , , , , , , ,000 12, ,000 18, , , , , ,000 1,063, , ,430 10, ,000 10, , , , , ,000 1,315, , ,000 17, ,000 21, , , , , ,000 1,002, , ,000 8, ,000 11, , , , , , , , ,892 10, ,000 11, , , , , ,000 1,038, , ,937 7, ,000 8, , , , , ,000 1,455,000 1,031, ,000 13, ,000 17, , , , , ,000 1,538,000 1,187, ,783 16, ,000 20, , , , , , , , ,000 11, ,000 14, , , , , ,000 1,121, , ,000 10, ,000 13, , , , , , , , ,000 9, ,000 12, , , , , ,000 1,806,000 1,334, ,000 9, ,000 11, , , , , ,000 1,678,000 1,246, ,582 8, ,000 12, , , , , , , , ,062 12, ,000 12, , , , , ,000 1,793,000 1,368,000 Average 109,410 11, ,250 14, , , , , ,050 1,292, ,950 Table (cont d) Summary of computed gross longshore sediment transport rates for present GFDL wave climate. Year Gross Longshore Sediment Transport Rates for Present GFDL Wave Climate (m 3 /year) Section12 Section13 Section14 Section15 Section16 Section17 Section18 Section19 Section20 Section21 Section ,000 2,324, ,000 1,592, ,000 1,747, ,000 1,101,000 1,045, ,000 83, ,360,000 4,435,000 1,158,000 2,941,000 1,391,000 3,059, ,000 1,697,000 1,563, , , ,108,000 3,557,000 1,011,000 2,464,000 1,186,000 2,479, ,000 1,380,000 1,283, ,000 85, ,000 3,207, ,000 2,093, ,000 2,276, ,000 1,415,000 1,293, , , ,230,000 4,188,000 1,125,000 2,853,000 1,345,000 2,923, ,000 1,705,000 1,580, ,000 95, ,000 1,641, ,000 1,123, ,000 1,306, , , , ,000 59, ,000 2,222, ,000 1,528, ,000 1,643, ,000 1,076,000 1,011, ,000 92, ,000 3,299, ,000 2,170, ,000 2,515, ,000 1,618,000 1,527, ,000 98, ,000 2,187, ,000 1,530, ,000 1,649, ,000 1,089,000 1,037, ,000 53, ,000 1,663, ,000 1,140, ,000 1,338, , , , ,000 74, ,000 1,915, ,000 1,381, ,000 1,333, ,000 1,021, , , , ,000 3,405, ,000 2,287, ,000 2,533, ,000 1,509,000 1,419, ,000 85, ,049,000 2,747, ,000 2,024,000 1,063,000 1,872, ,000 1,255,000 1,191, ,000 75, ,000 1,799, ,000 1,272, ,000 1,340, , , , ,000 57, ,000 2,210, ,000 1,571, ,000 1,546, , , , ,000 64, ,000 1,896, ,000 1,337, ,000 1,436, , , , ,000 66, ,139,000 3,694,000 1,040,000 2,551,000 1,223,000 2,562, ,000 1,537,000 1,426, , , ,062,000 3,517, ,000 2,415,000 1,121,000 2,489, ,000 1,308,000 1,233, ,000 79, ,000 1,515, ,000 1,081, ,000 1,188, , , , ,000 67, ,186,000 3,534,000 1,032,000 2,426,000 1,227,000 2,371, ,000 1,444,000 1,311, , ,000 Average 815,050 2,747, ,450 1,888, ,450 1,980, ,200 1,209,700 1,134, ,300 89,541 24

34 Table Summary of average net and gross longshore sediment transport rate calculated from GEESIS for present period along Vietnam coast. Area Average et Sediment Transport Rate * Average Gross Sediment Transport Rate ECHAM ( ) GFDL ( ) ECHAM ( ) GFDL ( ) Section1 64,620 40, , ,410 Section ,916 11,973 11,569 Section3 421, , , ,250 Section4-4,252-5,782 15,039 14,653 Section5 287, , , ,750 Section6 345, , , ,000 Section7 227, , , ,200 Section8 364, , , ,400 Section9-7, , , ,050 Section10 948,150 1,216,350 1,059,000 1,292,600 Section11 564, , , ,950 Section12 424, , , ,050 Section13 2,754,100 2,724,900 2,776,450 2,747,750 Section14 452, , , ,450 Section15 1,758,650 1,848,100 1,801,750 1,888,950 Section16 591, , , ,450 Section17 2,150,600 1,955,750 2,173,000 1,980,250 Section18-884, , , ,200 Section19-1,262,500-1,208,400 1,263,150 1,209,700 Section20-1,236,950-1,132,550 1,237,750 1,134,150 Section21-669, , , ,300 Section22 26,372 44,261 94,118 89,541 ote: (*) the positive transport direction is southward Figure Computed average net longshore sediment transport rates at 22 locations along Vietnam coast for present wave climate ( ) 25

35 Figure (cont d) Computed average net longshore sediment transport rates at 22 locations along Vietnam coast for present wave climate ( ) Figure (cont d) Computed average net longshore sediment transport rates at 22 locations along Vietnam coast for present wave climate ( ) 26

36 Figure Computed average gross longshore sediment transport rates at 22 locations along Vietnam coast for present wave climate ( ) Figure (cont d) Computed average gross longshore sediment transport rates at 22 locations along Vietnam coast for present wave climate ( ) 27

37 Figure (cont d) Computed average gross longshore sediment transport rates at 22 locations along Vietnam coast for present wave climate ( ) 3.3 Modeling Results of Future Longshore Sediment Transport Rates The computed annual net and gross longshore sediment transport rates from ECHAM and GFDL wave climate for the future time slice ( ) at the 22 costal sections along Vietnam coast are summarized in Table to 3.3-4, while the average net and gross longshore sediment transport rates are summarized in Table The estimates of future average net and gross longshore sediment transport rates at these coastal locations compared with the results from present wave climate ( ) are shown in Figure and 3.3-2, respectively. The corresponding plots of computed annual net and gross longshore sediment transport rates are also shown in Appendix C. From Table to 3.3-4, the annual average results at 22 costal sections from future ECHAM wave climate are in the range of 11,000-2,989,000 m 3 /year in total gross transport and 400-1,493,000 m 3 /year in net transport in a northerly direction (at coastal section S4, S9 and S18-S21) and 2,000-2,964,000 m 3 /year in net transport in a southerly direction (at coastal section S1-S3, S5-S8, S10-S17 and S22). While, the results from future GFDL wave climate are found to be in the range of 10,000-3,403,000 m 3 /year in total gross transport and 1,400-1,645,000 m 3 /year in net transport in a northerly direction (at coastal section S2, S4, S9, S18- S21) and 14,000-3,380,000 m 3 /year in net transport in a southerly direction (at coastal section S1, S3, S5-S8, S10-S17 and S22). Future change in net and gross longshore sediment transport rates at the 22 costal sections are summarized in Table to and shown in Figure to Analysis and comparison of simulated results of changes in longshore sediment transport rates due to the present wave climate (1981 to 2000) and future (2081 to 2100) conditions along the coast of Vietnam can be summarized as follows: 28

38 - Direction of computed net longshore sediment transport from ECHAM and GFDL climate wave at most coastal section are mainly from north to south, except coastal section S2, S4, S9, S18, S19, S20 and S21 where the net longshore sediment transport from south to north. - Changes of longshore sediment transport rates between present and future period have both increasing and decreasing trends. For example, there are expected to increase in net and gross longshore sediment transport rate at coastal section S1, S3, S5-S7, S13, S15 and S17-S21; and decrease at coastal section S4, S8, S10-S12, S14 and S16. - The results from ECHAM and GFDL future wave climate provide the same trend (increasing or decreasing) of longshore sediment transport changes for almost all coastal sections (except coastal section S9 in net transport rate and coastal section S22 in gross transport rate). - At coastal section S2, S4, S9 and S22, there are large percentage differences of net longshore sediment transport rates between the two different climate models (GFDL and ECHAM). The large percentage changes between and can also be found at these coastal sections in ECHAM, and at S1 and S9 in GFDL. This is because their coastline orientations are almost perpendicular to the present day ( ) wave direction and therefore present net longshore sediment transport rates are very small (at costal section S2, S4, S9 and S22). 29

39 Table Summary of computed net longshore sediment transport rates for future ECHAM wave climate. Year et Longshore Sediment Transport Rates for Future ECHAM Wave Climate (m 3 /year) Section1 Section2 Section3 Section4 Section5 Section6 Section7 Section8 Section9 Section10 Section ,000 1, ,000-2, , , , , ,000 1,046, , ,000 7, ,000 4, , , , ,000-86, , , ,000-1, ,000-4, , , , , , , , ,000-3, ,000-7, , , , , , , , ,000 12, ,000 10, , , , , ,000 1,329, , ,000 4, ,000 1, , , , , ,000 1,085, , , ,000-2, , , , , , , , ,000 3, , , , , , , , , ,000 5, ,000 3, , , , , ,000 1,299, , , ,000-2, , , ,000 88, , , , ,000 7, ,000 4, , , , , , , , , ,000-2, , , , , , , , ,000 3, ,000 1, , , , ,000 32,000 1,178, , ,000-1, ,000-3, , , , , , , , ,000 2, , , , , ,000-72, , , ,619 3, ,000 1, , , , , , , , ,000-1, ,000-5, , , , ,000-38,000 1,490, , ,000 1, , , , , ,000-86, , , ,000 1, , , , , , , , , ,000 2, ,000-1, , , , , , , ,000 Average 91,331 2, , , , , , , , ,700 ote: the positive transport direction is southward Table (cont d) Summary of computed net longshore sediment transport rates for future ECHAM wave climate. Year et Longshore Sediment Transport Rates for Future ECHAM Wave Climate (m 3 /year) Section12 Section13 Section14 Section15 Section16 Section17 Section18 Section19 Section20 Section21 Section ,000 3,429, ,000 2,103, ,000 2,722,000-1,139,000-1,529,000-1,521, ,000 19, ,000 2,403, ,000 1,493, ,000 1,891, , , , ,000-1, ,000 3,648, ,000 2,200, ,000 3,047,000-1,403,000-1,697,000-1,728, ,000-21, ,000 3,070, ,000 1,884, ,000 2,522,000-1,094,000-1,381,000-1,374, ,000 18, ,000 3,706, ,000 2,289, ,000 2,757, ,000-1,277,000-1,224, ,000 54, ,000 4,122, ,000 2,460, ,000 3,407,000-1,458,000-1,696,000-1,719, ,000-16, ,000 2,408, ,000 1,515, ,000 2,056, ,000-1,118,000-1,155, ,000-35, ,000 1,988, ,000 1,218, ,000 1,640, , , , ,000 7, ,000 4,941, ,000 2,908, ,000 4,042,000-1,696,000-1,965,000-1,973,000-1,042,000-3, ,000 2,618, ,000 1,564, ,000 2,262,000-1,008,000-1,091,000-1,127, ,000-26, ,000 1,911, ,000 1,198, ,000 1,578, , , , ,000-12, ,000 1,788, ,000 1,158, ,000 1,473, , , , ,000-7, ,000 3,498, ,000 2,149, ,000 2,673,000-1,064,000-1,520,000-1,493, ,000 39, ,000 2,872, ,000 1,837, ,000 2,368,000-1,012,000-1,246,000-1,259, ,000-1, ,000 2,705, ,000 1,736, ,000 2,153, ,000-1,267,000-1,255, ,000 15, ,000 2,093, ,000 1,349, ,000 1,724, ,000-1,055,000-1,071, ,000-19, ,000 4,520, ,000 2,817, ,000 3,503,000-1,333,000-1,773,000-1,734, ,000 50, ,000 2,482, ,000 1,562, ,000 1,988, ,000-1,122,000-1,115, ,000 14, ,000 2,946, ,000 1,829, ,000 2,515,000-1,127,000-1,280,000-1,308, ,000-14, ,000 2,130, ,000 1,314, ,000 1,798, ,000-1,140,000-1,165, ,000-23,820 Average 296,750 2,963, ,750 1,829, ,800 2,405,950-1,025,900-1,293,550-1,296, ,850 1,703 ote: the positive transport direction is southward 30

40 Table Summary of computed gross longshore sediment transport rates for future ECHAM wave climate. Year Gross Longshore Sediment Transport Rates for Future ECHAM Wave Climate (m 3 /year) Section1 Section2 Section3 Section4 Section5 Section6 Section7 Section8 Section9 Section10 Section ,000 9, ,000 9, , , , , ,000 1,097, , ,000 16, ,000 19, , , , , , , , ,000 9, ,000 11, , , , , ,000 1,055, , ,000 7, ,000 9, , , , , , , , ,000 17, ,000 17, , , , , ,000 1,442, , ,000 10, ,000 11, , , , , ,000 1,179, , ,000 9, ,000 11, , , , , , , , ,000 13, ,000 15, , , , , , , , ,000 10, ,000 11, , , , , ,000 1,367, , ,000 9, ,000 11, , , , , , , , ,000 14, ,000 15, , , , , , , , ,000 8, ,000 10, , , , , , , , ,000 11, ,000 12, , , , , ,000 1,304, , ,000 4, ,000 6, , , , , , , , ,000 8, ,000 9, , , , , , , , ,938 9, ,000 10, , , , , , , , ,000 10, ,000 13, , , , , ,000 1,552, , ,000 9, ,000 11, , , , , , , , ,000 10, ,000 11, , , , , , , , ,000 11, ,000 13, , , , , , , ,000 Average 141,947 10, ,050 12, , , , , , , ,500 Table (cont d) Summary of computed gross longshore sediment transport rates for future ECHAM wave climate. Year Gross Longshore Sediment Transport Rates for Future ECHAM Wave Climate (m 3 /year) Section12 Section13 Section14 Section15 Section16 Section17 Section18 Section19 Section20 Section21 Section ,000 3,444, ,000 2,125, ,000 2,743,000 1,143,000 1,529,000 1,521, , , ,000 2,462, ,000 1,585, ,000 1,965, , , , ,000 79, ,000 3,661, ,000 2,226, ,000 3,058,000 1,406,000 1,698,000 1,728, ,000 84, ,000 3,083, ,000 1,905, ,000 2,534,000 1,096,000 1,381,000 1,375, ,000 90, ,000 3,746, ,000 2,362, ,000 2,794, ,000 1,277,000 1,224, , , ,000 4,131, ,000 2,474, ,000 3,419,000 1,459,000 1,696,000 1,720, ,000 85, ,000 2,418, ,000 1,530, ,000 2,069, ,000 1,118,000 1,155, ,000 69, ,000 2,040, ,000 1,301, ,000 1,695, , , , ,000 90, ,000 4,957, ,000 2,935, ,000 4,060,000 1,697,000 1,965,000 1,974,000 1,042,000 88, ,000 2,637, ,000 1,596, ,000 2,284,000 1,009,000 1,092,000 1,127, ,000 78, ,000 1,958, ,000 1,276, ,000 1,633, , , , ,000 84, ,000 1,814, ,000 1,201, ,000 1,500, , , , ,000 69, ,000 3,534, ,000 2,212, ,000 2,701,000 1,080,000 1,520,000 1,493, , , ,000 2,882, ,000 1,852, ,000 2,380,000 1,018,000 1,246,000 1,260, ,000 80, ,000 2,730, ,000 1,781, ,000 2,182, ,000 1,267,000 1,257, , , ,000 2,110, ,000 1,376, ,000 1,747, ,000 1,055,000 1,071, ,000 72, ,000 4,536, ,000 2,843, ,000 3,524,000 1,339,000 1,773,000 1,735, , , ,000 2,513, ,000 1,616, ,000 2,021, ,000 1,122,000 1,116, ,000 83, ,000 2,967, ,000 1,864, ,000 2,543,000 1,132,000 1,280,000 1,308, ,000 90, ,000 2,150, ,000 1,350, ,000 1,820, ,000 1,140,000 1,165, ,000 79,155 Average 532,600 2,988, ,550 1,870, ,800 2,433,600 1,031,850 1,293,750 1,296, ,850 88,096 31

41 Table Summary of computed net longshore sediment transport rates for future GFDL wave climate. Year et Longshore Sediment Transport Rates for Future GFDL Wave Climate (m 3 /year) Section1 Section2 Section3 Section4 Section5 Section6 Section7 Section8 Section9 Section10 Section ,000 2, , , , , , ,000 1,897,000 1,398, ,000-4, ,000-8, , , , ,000 65, , , ,000-8, ,000-13, , , , , ,000 1,038, , ,000 1, ,000-1, , , , , ,000 1,107, , , ,000-5, , , , , ,000 1,316, , , ,000-3, , , , ,000-97,000 1,129, , , ,000-3, , , , , , , , ,000-4, ,000-8, , , , ,000-62, , , ,000 6, ,000 4, , , , , ,000 1,455, , ,000 1, , , , , ,000 85,000 2,034,000 1,192, ,000-5, ,000-8, , , , , ,000 1,452, , ,000 1, , , , , , ,000 1,019, , ,000-2, ,000-6, , , , , ,000 1,094, , ,000 2, , , , , , ,000 1,223, , ,000-3, ,000-7, , , , ,000-86, , , ,000-6, ,000-10, , , , , , , , ,000 3, ,000 1, , , , , ,000 1,704,000 1,204, , ,000-1, , , , , ,000 1,362, , ,000-3, ,000-6, , , , ,000 43,000 1,086, , ,098-5, ,000-8, , , ,000 3, , ,000 51,000 Average 74,155-1, ,650-4, , , , ,900-7,350 1,136, ,050 ote: the positive transport direction is southward Table (cont d) Summary of computed net longshore sediment transport rates for future GFDL wave climate. Year et Longshore Sediment Transport Rates for Future GFDL Wave Climate (m 3 /year) Section12 Section13 Section14 Section15 Section16 Section17 Section18 Section19 Section20 Section21 Section ,162,000 4,068,000 1,053,000 2,753,000 1,215,000 2,794, ,000-1,688,000-1,611, ,000 64, ,000 1,946, ,000 1,300, ,000 1,498, , , , ,000-2, ,000 2,602, ,000 1,702, ,000 1,945, ,000-1,166,000-1,141, ,000 24, ,000 4,208, ,000 2,505, ,000 3,486,000-1,553,000-1,877,000-1,900,000-1,012,000-7, ,000 4,398, ,000 2,651, ,000 3,464,000-1,443,000-1,872,000-1,872, ,000-6, ,000 3,681, ,000 2,219, ,000 2,862,000-1,146,000-1,498,000-1,489, ,000 8, ,000 3,283, ,000 1,990, ,000 2,685,000-1,170,000-1,450,000-1,464, ,000-14, ,000 1,829, ,000 1,187, ,000 1,469, , , , ,000-12, ,000 3,853, ,000 2,420, ,000 2,824,000-1,063,000-1,649,000-1,600, ,000 44, ,000 5,961, ,000 3,662,000 1,169,000 4,536,000-1,703,000-2,303,000-2,277,000-1,162,000 34, ,000 4,080, ,000 2,569, ,000 3,080,000-1,156,000-1,679,000-1,645, ,000 40, ,000 2,602, ,000 1,718, ,000 1,970, ,000-1,123,000-1,106, ,000 19, ,000 2,673, ,000 1,778, ,000 1,970, ,000-1,305,000-1,269, ,000 41, ,000 3,909, ,000 2,438, ,000 3,105,000-1,203,000-1,472,000-1,464, ,000 34, ,000 2,643, ,000 1,682, ,000 2,114, ,000-1,184,000-1,194, , ,000 1,642, ,000 1,068, ,000 1,364, , , , ,000-14, ,000 4,435, ,000 2,782,000 1,060,000 3,146,000-1,024,000-1,611,000-1,531, ,000 74, ,000 5,684, ,000 3,264, ,000 4,671,000-1,971,000-2,240,000-2,266,000-1,201,000-7, ,000 3,015, ,000 1,958, ,000 2,326, ,000-1,283,000-1,284, ,000-2, ,000 1,174,000 74, , ,000 1,071, , , , ,000-43,655 Average 493,600 3,384, ,350 2,118, ,100 2,619,000-1,039,950-1,425,700-1,413, ,450 13,618 ote: the positive transport direction is southward 32

42 Table Summary of computed gross longshore sediment transport rates for future GFDL wave climate. Year Gross Longshore Sediment Transport Rates for Future GFDL Wave Climate (m 3 /year) Section1 Section2 Section3 Section4 Section5 Section6 Section7 Section8 Section9 Section10 Section ,000 11, ,000 13, , , ,000 1,096,000 1,110,000 1,956,000 1,514, ,000 9, ,000 12, , , , , , , , ,000 11, ,000 16, , , , , ,000 1,112, , ,000 8, ,000 9, , , , , ,000 1,162, , ,000 13, ,000 15, , , , , ,000 1,365, , ,000 13, ,000 16, , , , , ,000 1,226, , ,000 10, ,000 12, , , , , ,000 1,001, , ,000 9, ,000 13, , , , , , , , ,000 12, ,000 13, , , , , ,000 1,543,000 1,065, ,000 7, ,000 9, , , ,000 1,079,000 1,200,000 2,107,000 1,526, ,000 8, ,000 11, , , , , ,000 1,507,000 1,053, ,000 15, ,000 21, , , , , ,000 1,084, , ,000 9, ,000 12, , , , , ,000 1,168, , ,000 9, ,000 12, , , , , ,000 1,288, , ,000 8, ,000 12, , , , , , , , ,000 8, ,000 12, , , , , , , , ,000 10, ,000 11, , , , , ,000 1,813,000 1,330, ,000 5, ,000 6, , , , ,000 1,003,000 1,436, , ,000 8, ,000 11, , , , , ,000 1,146, , ,312 6, ,000 9, , , , , , , ,000 Average 134,966 9, ,500 12, , , , , ,750 1,219, ,000 Table (cont d) Summary of computed gross longshore sediment transport rates for future GFDL wave climate. Year Gross Longshore Sediment Transport Rates for Future GFDL Wave Climate (m 3 /year) Section12 Section13 Section14 Section15 Section16 Section17 Section18 Section19 Section20 Section21 Section ,298,000 4,082,000 1,133,000 2,773,000 1,278,000 2,808, ,000 1,690,000 1,613, , , ,000 1,966, ,000 1,334, ,000 1,520, , , , ,000 77, ,000 2,627, ,000 1,744, ,000 1,970, ,000 1,167,000 1,143, ,000 77, ,000 4,227, ,000 2,535, ,000 3,512,000 1,558,000 1,878,000 1,900,000 1,012,000 99, ,000 4,409, ,000 2,668, ,000 3,479,000 1,459,000 1,873,000 1,873, ,000 90, ,000 3,706, ,000 2,260, ,000 2,889,000 1,154,000 1,498,000 1,489, ,000 96, ,000 3,295, ,000 2,016, ,000 2,700,000 1,175,000 1,451,000 1,464, ,000 79, ,000 1,843, ,000 1,215, ,000 1,484, , , , ,000 68, ,000 3,877, ,000 2,460, ,000 2,846,000 1,069,000 1,649,000 1,600, , , ,275,000 5,973,000 1,126,000 3,678,000 1,302,000 4,553,000 1,725,000 2,303,000 2,278,000 1,162, , ,000 4,086, ,000 2,581, ,000 3,089,000 1,188,000 1,681,000 1,647, , , ,000 2,620, ,000 1,749, ,000 1,985, ,000 1,123,000 1,106, ,000 70, ,000 2,689, ,000 1,804, ,000 1,990, ,000 1,305,000 1,272, , , ,000 3,924, ,000 2,463, ,000 3,126,000 1,210,000 1,473,000 1,466, , , ,000 2,651, ,000 1,696, ,000 2,123, ,000 1,184,000 1,195, ,000 73, ,000 1,670, ,000 1,115, ,000 1,396, , , , ,000 69, ,047,000 4,485, ,000 2,866,000 1,176,000 3,199,000 1,033,000 1,612,000 1,531, , , ,000 5,694, ,000 3,279, ,000 4,684,000 1,977,000 2,240,000 2,266,000 1,201, , ,000 3,024, ,000 1,974, ,000 2,335, ,000 1,284,000 1,284, ,000 71, ,000 1,202, , , ,000 1,103, , , , ,000 58,757 Average 685,750 3,402, ,050 2,148, ,750 2,639,550 1,052,900 1,426,350 1,414, ,450 92,810 33

43 Table Summary of average net and gross longshore sediment transport rate calculated from GEESIS for future period along the Vietnam coast. Area Average et Sediment Transport Rate * Average Gross Sediment Transport Rate ECHAM ( ) GFDL ( ) Difference ECHAM ( ) GFDL ( ) Difference (m 3 /yr) (m 3 /yr) (m 3 /yr) (%) (m 3 /yr) (m 3 /yr) (m 3 /yr) (%) Section1 91,331 74,155-17, , ,966-6, Section2 2,384-1,351-3, ,633 9, Section3 512, ,650 4, , ,500 3, Section ,428-4, ,218 12, Section5 379, , , ,950 7, Section6 427, ,700 7, , ,800 4, Section7 284, ,900-4, , ,550-5, Section8 249, , , , , , Section9-196,450-7, , , ,750 49, Section10 868,850 1,136, , ,700 1,219, , Section11 442, , , , , , Section12 296, , , , , , Section13 2,963,900 3,384, , ,988,650 3,402, , Section14 357, , , , , , Section15 1,829,150 2,118, , ,870,500 2,148, , Section16 514, , , , , , Section17 2,405,950 2,619, , ,433,600 2,639, , Section18-1,025,900-1,039,950-14, ,031,850 1,052,900 21, Section19-1,293,550-1,425, , ,293,750 1,426, , Section20-1,296,400-1,413, , ,296,950 1,414, , Section21-701, ,450-36, , ,450 36, Section22 1,703 13,618 11, ,096 92,810 4, ote: (*) the positive transport direction is southward Table Future change in computed average net longshore sediment transport rate from ECHAM and GFDL. Area ECHAM Wave Climate GFDL Wave Climate Present ( ) Future ( ) Change Present ( ) Future ( ) (m 3 /yr) (m 3 /yr) (m 3 /yr) (%) (m 3 /yr) (m 3 /yr) (m 3 /yr) (%) Section1 64,620 91,331 26, ,708 74,155 33, Section ,384 3, ,916-1, Section3 421, ,350 91, , , , Section4-4, , ,782-4,428 1, Section5 287, ,000 91, , , , Section6 345, ,050 81, , , , Section7 227, ,000 57, , ,900 98, Section8 364, , , , , , Section9-7, , ,950 2, ,500-7, , Section10 948, ,850-79, ,216,350 1,136,400-79, Section11 564, , , , , , Section12 424, , , , , , Section13 2,754,100 2,963, , ,724,900 3,384, , Section14 452, ,750-94, , , , Section15 1,758,650 1,829,150 70, ,848,100 2,118, , Section16 591, ,800-76, , , , Section17 2,150,600 2,405, , ,955,750 2,619, , Section18-884,050-1,025, , ,150-1,039, , Section19-1,262,500-1,293,550-31, ,208,400-1,425, , Section20-1,236,950-1,296,400-59, ,132,550-1,413, , Section21-669, ,850-32, , , , Section22 26,372 1,703-24, ,261 13,618-30, Change 34

44 Table Future change in computed average gross longshore sediment transport rate from ECHAM and GFDL. Area ECHAM Wave Climate GFDL Wave Climate Present ( ) Future ( ) Change Present ( ) Future ( ) Change (m 3 /yr) (m 3 /yr) (m 3 /yr) (%) (m 3 /yr) (m 3 /yr) (m 3 /yr) (%) Section1 124, ,947 17, , ,966 25, Section2 11,973 10,633-1, ,569 9,930-1, Section3 441, ,050 92, , , , Section4 15,039 12,218-2, ,653 12,673-1, Section5 336, ,850 84, , , , Section6 353, ,050 83, , , , Section7 241, ,050 58, , ,550 98, Section8 518, ,700-56, , ,400-97, Section9 559, ,100 27, , ,750 6, Section10 1,059, ,700-92, ,292,600 1,219,050-73, Section11 740, ,500-91, , , , Section12 611, ,600-79, , , , Section13 2,776,450 2,988, , ,747,750 3,402, , Section14 586, ,550-70, , , , Section15 1,801,750 1,870,500 68, ,888,950 2,148, , Section16 702, ,800-79, , , , Section17 2,173,000 2,433, , ,980,250 2,639, , Section18 900,600 1,031, , ,200 1,052, , Section19 1,263,150 1,293,750 30, ,209,700 1,426, , Section20 1,237,750 1,296,950 59, ,134,150 1,414, , Section21 669, ,850 32, , , , Section22 94,118 88,096-6, ,541 92,810 3, Figure Estimates of present and future average net longshore sediment transport rates at 22 costal sections 35

45 Figure (cont d) Estimates of present and future average net longshore sediment transport rates at 22 costal sections Figure (cont d) Estimates of present and future average net longshore sediment transport rates at 22 costal sections 36

46 Figure Estimates of present and future average gross longshore sediment transport rates at 22 costal sections Figure (cont d) Estimates of present and future average gross longshore sediment transport rates at 22 costal sections 37

47 Figure (cont d) Estimates of present and future average gross longshore sediment transport rates at 22 costal sections Figure Future change in average net longshore sediment transport rates at the 22 costal sections along Vietnam Coast 38

48 Figure Future change in average gross longshore sediment transport rates at the 22 costal sections along Vietnam Coast 39

49 CHAPTER 4 COCLUSIOS 1. The present study has estimated the present and future longshore sediment transport rates at 22 coastal sections along Vietnam coast using a one-line longshore transport model (GEESIS), which has been forced by ECHAM and GFDL wave climates determined in the previous CCWaves-Vietnam study for two time span of and GEESIS model calibration was conducted by applying calibration parameters values for k 1 and k 2 from previous research studies. Calibration parameters k 1 and k 2 with values of and , give moderate and good quantitative agreement between the computed results and the reported values. 3. The computed results indicate that the volume and direction of longshore sediment transport along the coast of Vietnam is rather variable. For present conditions, the annual average results from ECHAM and GFDL wave climate at 22 costal sections are found to be in the range of 11,000-2,748,000 m 3 /year in total gross transport and 1,400-1,426,000 m 3 /year in net transport in a northerly direction (at coastal section S2, S4 and S18-S21) and 35,000-2,740,000 m 3 /year in net transport in a southerly direction (at coastal section S1, S3, S5-S17 and S22). For future conditions, the annual average results at 22 costal sections are in the range of 10,000-3,403,000 m 3 /year in total gross transport and 2,000-1,569,000 m 3 /year in net transport in a northerly direction (at coastal section S4, S9, S18-S21) and 500-3,174,000 m 3 /year in net transport in a southerly direction (at coastal section S1-S3, S5-S8, S10-S17 and S22). 4. For the two time span of and , directions of net longshore sediment transport at almost all coastal sections are the same, except at coastal sections S2, S4, S9 and S22. In these sections the net transport in both time spans are variable in different years but net sediment transport due to climate change effect (time span of ) at S2 and S4 is turning more toward the south and at S9 and S22 is changing more toward the north. 5. The estimated results of longshore sediment transport rates from present ( ) and future ( ) CC modified wave climate show significant changes in net and gross longshore sediment transport rates along the coast of Vietnam. 40

50 Table 4.1 Changes in net sediment longshore sediment transport at 22 coastal sections along the Vietnam coastline due to climate change. Coastal section S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S21 S22 Description The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 62%, in the order of 30,000 m3/yr There is no dominant direction of net longshore sediment transport in this section it will remain the same upto 2100 but with more tendency toward the south. The magnitude will decreases with about 7% in order of 1,000 m 3 /year in the southerly direction The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 34%, in the order of 125,000 m3/yr There is no dominant direction of net longshore sediment transport in this section it will remain the same upto 2100 but with more tendency toward the south. The magnitude will decreases with about 28% in order of 2,000 m 3 /year in the southerly direction The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 50%, in the order of 122,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 37%, in the order of 113,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 40%, in the order of 78,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 30%, in the order of 145,000 m3/yr There is no dominant direction of net longshore sediment transport in this section it will remain the same upto 2100 but with more tendency toward the north. The magnitude will increases with about 240% in order of 162,000 m 3 /year in the northerly direction The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 7%, in the order of 80,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 22%, in the order of 155,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 30%, in the order of 176,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 16%, in the order of 434,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 23%, in the order of 131,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 9%, in the order of 170,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport decreases by 15%, in the order of 105,000 m3/yr The net longshore sediment transport is toward the south at present and will remain towards the south upto The magnitude of net annual transport increases by 23%, in the order of 460,000 m3/yr The net longshore sediment transport is toward the north at present and will remain towards the north upto The magnitude of net annual transport increases by 45%, in the order of 290,000 m3/yr The net longshore sediment transport is toward the north at present and will remain towards the north upto The magnitude of net annual transport increases by 10%, in the order of 124,000 m3/yr The net longshore sediment transport is toward the north at present and will remain towards the north upto The magnitude of net annual transport increases by 15%, in the order of 170,000 m3/yr The net longshore sediment transport is toward the north at present and will remain towards the north upto The magnitude of net annual transport increases by 20%, in the order of 113,000 m3/yr There is no dominant direction of net longshore sediment transport in this section it will remain the same upto 2100 but with more tendency toward the north. The magnitude will increases with about 60% in order of 5,000 m 3 /year in the northerly direction 41

51 REFERECES Cat,.., Tien, P.H., Sam, D.D. &.. Bien., Status of coastal erosion of Vietam and proposed measures for protection. FAO Asia Pacific. Eva-Lena E. and Madeleine H. P., Sediment transport and coastal evolution at Thuan An Inlet, Vietnam. Master Thesis, Lund University. Hung,.M., Dien. D.C., Effects of the storm number 7 (DAMREY) on the sea dyke system of am Dinh Province, J. Mar. Sci. 4 (T6). Lam,.T., Hydrodynamics and morphodynamics of a seasonally force tidal inlet system. Ph.D. Thesis, Delft University of Technology. Mazda, Y., Magi, M., anao, H., Kogo, M., Miyagi, T., Kanazawa,. and Kobashi, D, Coastal Erosion due to longterm human impact on mangrove forests. Wetlands Ecology and Management. Vol. 10: 1-9. Hanson,H. and Kraus,.C., GEESIS: Generalized model for simulating shoreline change. Technical Report CERC U.S. Army Engineer Waterways Experiment Station, Coastal Engineering Research Center, Vicksburg, Mississippi, 185p. Q. T. Doan, Y.C. Chen, T.T. Quach and P.K. Mishra., umerical modeling in shore line evolution prediction: Case study of Tat Dike, Vietnam. International Journal of Earth Sciences and Engineering, Vol.6, pp Tien, T.Q., Use of hindcast wave field by WAM model for calculation of sediment transport in littoral zone of Vietnam Central. The 14th OMISAR Workshop on Ocean Models.Taipei, Taiwan. Young, R.S.; Pilkey, D.H.; Bush, D.M.; and Thieler, E.R., A discussion of the Generalized Model for Simulating Shoreline Change (GEESIS). Journal of Coastal Research, 11(3),

52 Appendix A Result of Present Longshore Sediment Transport Rates 43

53 66.94 % % Coastal Section S1 Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S5 Coastal Section S Coastal Section S % Coastal Section S8 Figure A-1 Wave rose diagrams from ECHAM climate model for the future period ( ) 44

54 49.98 % % Coastal Section S9 Coastal Section S % Coastal Section S Coastal Section S % Coastal Section S13 Coastal Section S14 Figure A-1 (cont d) Wave rose diagrams from ECHAM climate model for the future period ( ) 45

55 49.82 % Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S21 Coastal Section S22 Figure A-1 (cont d) Wave rose diagrams from ECHAM climate model for the future period ( ) 46

56 66.91 % % Coastal Section S1 Coastal Section S % Coastal Section S % Coastal Section S % % Coastal Section S5 Coastal Section S % Coastal Section S Coastal Section S8 Figure A-2 Wave rose diagrams from GFDL climate model for the future period ( ) 47

57 47.80 % Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S % % Coastal Section S13 Coastal Section S14 Figure A-2 (cont d) Wave rose diagrams from GFDL climate model for the future period ( ) 48

58 50.10 % Coastal Section S % Coastal Section S Coastal Section S % Coastal Section S % Coastal Section S % Coastal Section S % % Coastal Section S21 Coastal Section S22 Figure A-2 (cont d) Wave rose diagrams from GFDL climate model for the future period ( ) 49

59 Appendix B Result of Present Longshore Sediment Transport Rates 50

60 Figure B-1 Computed annual net longshore sediment transport rates for present wave climate ( ) 51

61 Figure B-1 (cont d) Computed annual net longshore sediment transport rates for present wave climate ( ) 52

62 Figure B-1 (cont d) Computed annual net longshore sediment transport rates for present wave climate ( ) 53

63 Figure B-1 (cont d) Computed annual net longshore sediment transport rates for present wave climate ( ) 54

64 Figure B-1 (cont d) Computed annual net longshore sediment transport rates for present wave climate ( ) Figure B-2 Computed annual gross longshore sediment transport rates for present wave climate ( ) 55

65 Figure B-2 (cont d) Computed annual gross longshore sediment transport rates for present wave climate ( ) 56

66 Figure B-2 (cont d) Computed annual gross longshore sediment transport rates for present wave climate ( ) 57

67 Figure B-2 (cont d) Computed annual gross longshore sediment transport rates for present wave climate ( ) 58

68 Figure B-2 (cont d) Computed annual gross longshore sediment transport rates for present wave climate ( ) 59

69 Appendix C Result of Future Longshore Sediment Transport Rates 60

70 Figure C-1 Computed annual net longshore sediment transport rates for present ( ) and future wave climate ( ) 61

71 Figure C-1 (cont d) Computed annual net longshore sediment transport rates for present ( ) and future wave climate ( ) 62

72 Figure C-1 (cont d) Computed annual net longshore sediment transport rates for present ( ) and future wave climate ( ) 63

73 Figure C-1 (cont d) Computed annual net longshore sediment transport rates for present ( ) and future wave climate ( ) 64

74 Figure C-1 (cont d) Computed annual net longshore sediment transport rates for present ( ) and future wave climate ( ) Figure C-2 Computed annual gross longshore sediment transport rates for present ( ) and future wave climate ( ) 65

75 Figure C-2 (cont d) Computed annual gross longshore sediment transport rates for present ( ) and future wave climate ( ) 66

76 Figure C-2 (cont d) Computed annual gross longshore sediment transport rates for present ( ) and future wave climate ( ) 67

77 Figure C-2 (cont d) Computed annual gross longshore sediment transport rates for present ( ) and future wave climate ( ) 68

78 Figure C-2 (cont d) Computed annual gross longshore sediment transport rates for present ( ) and future wave climate ( ) 69