Application of xbeach model to study sedimentation of lach van river mouth

Declaration I hereby declare that is the research work by myself under the supervisions of Dr Nguyen Quang Chien and Assoc Prof Dr 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, June 2018 Nguyen Quoc Anh i Acknowledgements I would like to express my sincere thanks to professors and lectures at Department of Marine and Coastal Engineering of Thuy Loi University and professors and lecturers of the Niche programme for supporting me throughout my study progress Finally, I would like to express my special appreciation to my friends and colleagues for their support, encourage and advices The deepest thanks are expressed to my family member and Hang Iu Chun for their unconditional loves ii TABLE OF CONTENT LIST OF FIGURES v LIST OF TABLES vii ABSTRACT CHAPTER INTRODUCTION 1.1 Research scope 1.2 Research Objective 1.3 Research content 1.4 Literature review 1.5 Research methods CHAPTER COMPUTING METHOD 2.1 Numerical method 2.1.1 Overview of One-dimensional modelling 2.1.2 One-line Model 2.1.3 Some limitations in considering changes in bottom topography when using One-dimensional model 10 2.1.4 Overview of multi-dimensional hydrodynamic modelling 10 2.1.5 Solution procedure 12 2.1.6 Modeling seabed change 14 2.1.7 Some limitations in considering changes in bottom topography when using multi-dimensional model: 16 2.2 Computing sediment transport 17 2.2.1 Soulsby–Van Rijn equation (1997) 17 2.2.2 Some problems need to consider when research sediment transport 19 2.2.3 Formulation in Delft3D model 20 2.3 Computing method of X-beach model 23 2.3.1 The Coordinate system and Grid setup 23 2.3.2 The short wave action balance 25 2.3.3 Wave breaking 26 2.3.4 The bottom friction element: 26 2.3.5 Shallow water equations: 27 iii 2.3.6 Bed shear stress equations 28 2.3.7 Wind equations 29 2.3.8 Bottom updating equations 30 2.4 Selecting a Model for Lach Van river mouth 31 CHAPTER DATA COLLECTION 33 3.1 Bathymetry data 34 3.2 Coastline identification 35 3.3 Wave Data 36 3.4 Wind Data 38 3.5 Tide and surge 39 3.6 Sediment data 40 CHAPTER PROPOSED MODELING STUDY AND EXPECTED ISSUES 41 4.1 Sediment transport process 41 4.2 Grid setup 42 4.3 Model calibration 44 4.4 Modelling scenarios 46 4.5 Wave simulation in big domain 46 4.6 Hydrodynamic and morphological simulation in small domain 48 4.7 Result for ESE wave scenario 49 4.8 Result for ENE wave scenario 54 4.9 Discussion 57 CONCLUSIONS AND RECOMMENDATIONS 60 REFERENCE 61 iv LIST OF FIGURES Figure1 Schematization of XBeach model Figure Element volume on equilibrium beach profile Figure 2 Change in shoreline positions after simulations (upper) and (lower) in comparison with observed data Figure Example of a curvilinear grid (Delft3D-FLOW User Manual, 2014) 13 Figure Mapping of physical space to computational space (Delft3D-FLOW User Manual, 2014) 13 Figure Difference grid in x,y space (Ahmad, S 1999) 14 Figure Flow diagram of “online” morphodynamic model setup (Roelvink, 2006) 16 Figure The staggered grid showing the upwind method of setting bed load sediment transport components at velocity points (G.R Lesser et al., 2004) 22 Figure Grid staggering, 3D view and top view (Delft3D-FLOW User Manual, 2014) 22 Figure Rectangular/ Curvilinear coordinate system of XBeach (Xbeach manual, 2015) 23 Figure 10 Principle sketch of the relevant wave processes (Xbeach manual, 2015) 24 Figure Depth contours digitized from nautical chart (Chien 2017) 34 Figure Beach profile constructed from various bathymetry data source (measured in Vietnamese technical guideline for sea dike design STRM30, and GEBCO) (Chien N.Q, and Tung T.T, 2018) 35 Figure 3 The position of points extracted wave in model WaveWatch 37 Figure Wave roses of the periods Feb-2005 – Jan-2011 (left) and Feb-2011 – Jan-2017 (right) (Chien N.Q, and Tung T.T, 2018) 38 Figure Relationship between wave height and peak period; separation between wind seas and swells is indicated (Color shades shows density of the data points.) (Chien and Tung 2018) 39 Figure Typical astronomic tidal level of Dien Chau (Chien 2017) 39 Figure Location of the study area, with basic modes of sediment transport (Chien and Tung 2018) 41 Figure Layout of the modeling domain 43 Figure Jonswap wave spectrum for Hm0 = 1.28 m and 0.76 m 44 Figure 4 Computed wave field in big domain for the case of ENE waves 47 v Figure Computed wave field in big domain for the case of ESE waves 47 Figure Bathymetry of the small domain 48 Figure 4.7: Wave field of the small domain, ESE wave scenario 50 Figure 4.8: Flow field near the river mouth, ESE wave scenario 51 Figure 4.9: Sediment transport near the river mouth, ESE wave scenario 52 Figure 4.10: Seabed elevation change near the river mouth, ESE wave scenario 53 Figure 4.11: Wave field of the small domain, ENE wave scenario 54 Figure 4.12: Flow field near the river mouth, ENE wave scenario 55 Figure 4.13: Sediment transport near the river mouth, ENE wave scenario 56 Figure 4.14: Seabed elevation change near the river mouth, ENE wave scenario 57 vi LIST OF TABLES Table Extreme water level for location 19°01’N, 105°37’E 40 Table Parameters of the big domain model 45 Table Comparison between simulated result and observed data 45 Table Parameters of the small domain model 49 Table 4 The comparison of results 58 vii ABSTRACT The deposition at the river mouth is a phenomenon interested in recent times on the world Because, it obstructs the economic activities, transportation of people living in the vicinity Nowadays, scientists have done a lot of research to find out the cause of sedimentation at the river mouth They have carried out fieldwork and research methods on the model The advantage of modeling is less costly to invest Besides, updating situation changes and making status prediction by an image is very quickly and easily in interpreting the information With simple studies of the 1D model, researchers have produced results on shoreline dynamics, areas of flooding, etc However, recent studies using 2D models have made research results more meaningful This is due to the advantages in studying the topography development, which based on the parameters of wind and sand There are many models used in the world (Delft, Swan and XBeach) In the framework of the thesis, a Xbeach model is used to simulate the bottom evolution of Lach Van river mouth in Dien Chau district, Nghe An province Parameters and results of the model will be tested with actual measurement data at the Hon Ngu station; finally, the resulting of the bottom topography is stated through the sediment transport in here By using Xbeach model, the author wants to convey the advantages and disadvantages of the model, the ability to apply for specific conditions CHAPTER INTRODUCTION Status of Lach Van river mouth: Lach Van river mouth is located at (18.98°N, 105.62°E), belonging to Dien Chau District, Nghe An province, Vietnam This is a small and narrow river mouth (the mean width approximates 500 m), which is a final point of Bung river (a small river) This area is a anchorage of 500 fishing boats, The anchoring system for avoiding storms is built in 2003 The river mouth has a part of navigation value, although not worthy, because the river is 48 km long Predicting the morphological change of Lach Van river mouth when the natural and human factors affect to study area This position is an intersection of a small river and sea The river was named Bung and is being deposited at the river mouth The two side of the river mouth is a bow-shaped beach of 24km in length and blocked by two rock headlands However, the deposition of Lach Van estuary has been complicated and has had a great impact on the activities of the fishing fleet of Dien Chau district According to a report in the Lao Dong newspaper [article posted on 18/4/2016], "Lach Van river mouth increasingly exhausted, large fishing boats can not go in and small boats only travel at high tide This has made it difficult for fishermen; many fishing vessels have been stranded "Normally, the water level must be from 1.6 to 1.8 m, but now the water level is just 1.2 m" This topography situation is still occurring in 2017 with the serious level of deposition The cause of evolution in Lach Van river mouth: According to the survey from different sources from 2003 to 2009, the analysis showed that the river mouth area has accretion - erosion situations With this river mouth, the main reason for sedimentation is due to the waves that cause the longshore currents carrying sediment to the bottom sea Through the collection and processing of data, particularly data wave, stream sediment moves from north to south with a total measurement about 105 m3/year Figure 4.12: Flow field near the river mouth, ENE wave scenario The change of wind direction hardly affects to the flow velocity in the river The average flow speed in the river and at narrow area is still the same, around 0.1 m/s and 0.2 m/s, respectively Nevertheless, there seems to be a turbulence happening in the river mouth with the velocity vary from 0.05 to 0.15 m/s In addition, the wave velocity tends to rise at the nearshore, compared to the middle of the bay 55 Figure 4.13: Sediment transport near the river mouth, ENE wave scenario A huge load of sediment transport with shoreward direction and distribute along with the coastline, especially from the river mouth to the southern part The typical rate is in the order of 10-5 m2/s/m 56 Figure 4.14: Seabed elevation change near the river mouth, ENE wave scenario The deposition occurs on a large scale Visually, the accretion forms sand dunes, which are distributed along the bottom contours The sedimentation rate increases as the distance approaches the shore The rate of seabed elevation per day (∆zb) begins to rise from 0.001 m/day at a distance of 1,000 m offshore At the nearshore locations, the change of seabed elevation is ranging from 0.003 to 0.004 m/day However, there are some erosion points taken place simultaneously Rate of erosion in this area is ranging from −0.003 to −0.002 m/day 4.9 Discussion From two results above we can see that, the river mouth tends to accreted with both scenarios of wind direction (ESE and ENE) However, the degree of intensity is very different 57 Table 4 Summary of results ESE wave Wave field - The highest root-mean-square wave height in the domain is about 0.4 m - The highest root-mean-square wave height in the domain is about 0.9 m - The average flow speed in the river is about 0.1 m/s, and about 0.2 m/s at narrow sections - - At the river mouth, the interference between from the river and the sea is so quite small (velocity < 0.05 m/s) The average flow speed in the river and at narrow area is still the same, around 0.1 m/s and 0.2 m/s, respectively - Have a turbulence happening in the river mouth with the velocity vary from 0.05 to 0.15 m/s - The wave velocity tends to rise at the nearshore, compared to the middle of the bay Flow field - Along the coast, the flow velocity is quite small, usually < 0.1 m/s - The sediment transport takes place in the nearshore zone with typical rate in the order of 10-6 m3/s/m - The typical rate is in the order of 10-5 m3/s/m The quantity of sediment in ENE wave larger than 10 times the volume of sediment in the wave ESE - The direction is mainly shoreward - Sediment distributes along with the coastline, especially from the river mouth to the southern part - The coastline is accreted and mostly along the shoreline - The deposition occurs on a large scale - The variation of seabed elevation per day is increased by ∆zb , which is typically under 0.001 m - The rate of seabed elevation per day (∆zb) begins to rise from 0,001 m at a distance of 1,000 m offshore - Most of highly accreted locations are placed in the southern area of river mouth - - There are few erosion points and rate of erosion in this area is ranging from −0.003 to −0.002 m/day At the nearshore locations, the change of seabed elevation is ranging from 0.003 m to 0.004 m - There are many erosion points taken place simultaneously Rate of erosion in this area is ranging from −0.003 to −0.002 m/day Sediment transport Seabed level ENE wave 58 We can draw that the ENE wave effect is stronger than ESE Indeed, the results show that the ENE wave causes wider variation in the bottom (from 1000 m back to shoreline) Based on the results of simulation in 24 h of the model, the seabed level change is calculated According to the wave roses of the period 2011-2017, the wave frequency of these two directions is mostly balanced, i.e ENE ~ 33%; ESE ~ 29% (figure: 3.4) So the change of seabed level for one year equals the result of ENE multiplied by 120 times (= 365 x 33%) and plus the ESE multiplied 105 times (= 365 x 29%) Calculation shows that the seabed level change at the river mouth fluctuates from 22 to 46 cm/year The area rising remarkably is similar to the topography in the ENE wave scenario This result is significantly bigger than the result of one-line model (about 10 cm/year) in the study by Chien and Tung (2018) [15] The alternating pattern between accretion and erosion occurs in simulation results The absence of clear identification of these erosion zones is due to many causes Firstly, the model does not have a function to put sediment transport from the river to the sea Besides, the input data of the river flow is restricted Therefore, due to the lack of interaction between the river flow and tide, the hydrodynamic is not truly reproduced at the river mouth Finally, this model is setup with a mean sea level Thus, the sediment transport is not effected by the tidal current 59 CONCLUSIONS AND RECOMMENDATIONS At the Lach Van river mouth, sediment deposition is happening The main reason leads to deposition may be due to waves which generate the longshore currents to carry sediment [15] In this MSc thesis report, the author uses a 2-D numerical model to study the sediment deposition rate By using the bathymetry data from SRTM30 source, and NOAA WaveWatch offshore wave data, with other data from study by Chien and Tung (2018) [15], the Xbeach model is set up The model is composed of two nested domains First the wave model is calibrated in the big domain, and the simulated results is different from the observed data, mostly in wave direction In terms of wave height, calculated results are often larger in NE monsoon and smaller in SE monsoon From the calculation result in big domain, the wave condition is extracted as boundary for the small domain Morphological changes of seabed are calculated in this small domain for typical two conditions, ENE (incoming wave height Hrms = 0.75 m), and ESE (Hrms = 0.44 m) The Xbeach model is appropriate for the current problem and available data of the study The dominant factor of sediment deposition is due to wave The result is comparable to study by Chien and Tung (2018) [15] There are many potentials to improve and continue development about a solution of this study Firstly, field survey work for measuring the cross section of the beach along the shoreline, identifying the grain size, collecting sample of sediment is necessary Secondly, the data of available offshore waves (from 2015 to 2016) can be supplied with the wave data collected in Hon Ngu station It allows to accurately evaluate the characteristics of wave climate 60 REFERENCE [1] P.T Huong and V.T Ca (2008) “Analysis on the dynamic parameters influencing the morphology of Da Rang river mouth”, Journal of Water Resources and Environmental Engineering, No 23, 76-86 [2] Deltares (2011) Delft3D-FLOW: user manual [3] D A Edmonds and R L Slingerland (2007) “Mechanics of river mouth bar formation: Implications for the morphodynamics of delta distributary networks” J Geophys Res., 112, F02034 [4] A Dastgheib; J.A Roelvink; Z.B Wang; (2008) “Long-term process-based morphological modeling of the Marsdiep Tidal Basin” Marine Geology 256(1), 90–100 [5] W Nardin and S Fagherazzi (2012) “The effect of wind waves on the development of river mouth bars” Geophysical Research Letters, 39, L12607 [6] J.H Nienhuis; A.D Ashton; W Nardin; S Fagherazzi and L Giosan (2016) “Alongshore sediment bypassing as a control on river mouth morphodynamics” Journal of Geophysical Research: Earth Surface, 121, 664–683 [7] M.D Hurst, A Barkwith, M.A Ellis, C.W Thomas and A.B Murray (2015) “Exploring the sensitivities of crenulate bay shorelines to wave climates using a new vector-based one-line model” Journal Geophysical Research: Earth Surface, 120, 2586–2608 [8] D Roelvink and D.J Walstra (2005) “Keeping it simple by using complex models” Advances in Hydro-science and engineering, volume VI [9] N.X Hien, D.N Tien, N.T Sao (2012) “Tính tốn phân tích xu bồi tụ, xói lở cửa Đáy”, tr [10] T.V Bon (2012) “Một số kết điều tra nghiên cứu đánh giá biến động hình thái cửa sơng Nhật Lệ - Quảng Bình phục vụ cơng tác quy hoạch khai thác bền vững” Địa kỹ thuật, 2, 23–27 61 [11] V.T Thuy, N.T Hung, V.Đ Cuong (2014) “Hiện trạng nguyên nhân biến động hình thái khu vực cửa sông Ninh Cơ qua tài liệu đo đạc” Water Resources and Environmental Sciences, 47, 33–39 [12] L.D Thanh, V.M Cat, N.B Quy (2015) “Diễn biến cửa sông ven biển miền Trung giải pháp ổn định” Publishing House for Construction [13] T.T Tung, M J F Stive, J.V.D Graaff, J R Walstra (2008) “Morphological stability of tidal inlets using process-based modelling” International Conference on Coastal Engineering, 2182–2194 [14] V.M Cat, P.Q Son (2015) “Ứng dụng công nghệ viễn thám GIS nghiên cứu diễn biến bờ biển Nam Định giai đoạn 1912 – 2013” Water Resources and Environmental Sciences, 50, 56–64 [15] N.Q Chien, T.T Tung (2018) “Recent Sedimentation of a Mesotidal WaveDominated River Mouth: Lach Van, Vietnam” Journal of coastal research SI81, 7pp (in press) [16] J.A Roelvink, (2006) “Coastal morphodynamic evolution techniques” Coastal Eng., 53:277 - 287 [17] R Soulsby (1997) “Dynamics of Marine Sands (Thomas Telford, London)” [18] D Roelvink and A Reniers (2011) “A guide to modeling coastal morphology” World Scientific Singapore [19] Hung N.M (2015) Coastline and River Mouth Evolution in Vietnam Vietnam Publishing House for Science and Technology [20] G.R Lesser et al (2004) “Development and validation of a three-dimensional morphological model” Coastal Engineering 51, P 883–915 [21] Hung (2002) The South China Sea: Meteorology, Oceanography and Dynamics Vietnam National University Publisher: Hanoi 62 SOCIALIST REPUBLIC OF VIETNAM Independence - Freedom - Happiness EXPLANATORY STATEMENT OF EDITED THESIS Student name: Nguyen Quoc Anh; Class: Niche B; Student code: 1481580203001 Major code: Coastal Engineering and Management Master thesis: Application of XBeach Model to Study Sedimentation of Lach Van River Mouth I Modifications in the thesis at the request of the Council: Regarding the number of the formulas: - The comment of Council: Lack of number label for formulas - Responding: The author agrees with the comment of Council and added it Regarding the checking the units: - Dr Nguyen Thi The Nguyen comments: In results for ESE and ENE wave scenarios (p 58), the unit of total sediment transport not write in 10-6 (m2/s) - Responding: The author agrees with the comment of Council and edited to in 10-6 (m3/s/m) Regarding the checking the results of sediment: - Dr Tran Van Sung comments: In figure 3.4 (p 38) the frequency of wave in ENE direction is 33% and in ESE direction is 29% Why did the author take the values of two directions is 50% to calculate in one year? 63 - Responding: Yes, the author has some mistakes in results of the change of seabed level for one year when take the frequency equal 50% for two directions Thus, the author edited the frequency to calculate in this part into: ENE ~ 33%; ESE ~ 29% The new results are updated in this thesis (p 59) Regarding the comparison, the results of modelling between to ESE and ENE wave directions: - Dr Nguyen Kim Cuong comments: In table 4.4 (p 58), why did the author compare the difference in the table when use different boundary conditions of wave height for ESE and ENE wave? - Responding: In opinion of the author, I just want to diagnose the bigger of morphology evolution due to ENE wave direction compared to ESE wave direction However, my expression is unclear when using a word “Comparison” in title of the data table 4.4 Thus, I corrected the word to “Summary” Regarding the correcting objectives of the study: - Dr Nguyen Thi The Nguyen comments: The second point of "Research objective" is not proper Normally the "scenario set-up" is not research objective but rather a step for conducting research Anyway this second "objective" (Propose scenarios to predict evolution of topography at the Lach Van river mouth) can be merged to the first one (simulate geomorphological evolution) - Responding: The author agrees with the comment of Council and corrected second object into: “Propose scenarios to simulate the geomorphologic change and predict bathymetry evolution of Lach Van river mouth using the XBeach 2D model” Regarding the type of wave height using in the part of model calibration: - Dr Nguyen Kim Cuong comments: What kind of wave height the author used in the part of model calibration? If author should use significant wave height instead of RMS wave height in the thesis? 64 - Responding: In producing the table 4.2 (p.45) the output wave heights (Hrms) are converted into significant wave heights (Hs) to compare with observed data: Hs = Hrms * 1.416 The conversion formula is added to the MSc thesis report Regarding the choosing two main wave directions: - Dr Nguyen Kim Cuong comments: Why did the author choose two main directions: ENE and ESE for his simulation? - Responding: There are two scenarios depending on wave directions, which have highest frequency and longest interval in a year: ENE, ESE equal about 33% and 29%, respectively Regarding the model setup: - Prof.Dr Vu Minh Cat comments: Explain the steps to setup the model and boundary conditions and how the simulated results change, if changing grid cell size? - Responding: As described in the section 4.2 (p 42), I used a nested grid system Big domain has an offshore boundary, which crosses the location of NOAA wave data Thus, the calculation of wave height in domain is proceeded The boundary condition at offshore line of small domain is chosen from calculation results of big domain The author does not use one grid for all domain because the gird size should to change with each task which the domain undertakes It means that the big domain with the mission of wave height calculation has the grid size usually larger than others, which used to calculate the bathymetry evolution in the small domain If the grid size is made smaller, i.e the grid is smoothed, the results will be more detailed but the running time will be longer 65 Regarding the time of wave data in calibration part: - Assoc.Prof.Dr Nghiem Tien Lam comments: The author calibrates the data obtained at NOAA station with the data observed at Hon Ngu station However, the time zone between two stations are different Thus, the author needs to convert time zone to same period - Responding: The author agrees with the comment of Council and corrected it I checked original files for four calibration scenarios in the PC: • The case 2006061318 This is the case using wave data 18:00 GMT on 13-Jul-2006 This should correspond to Hon Ngu wave data at 1:00 GMT+7 local time on 14-Jul2006 But this data is not available (no visual observation at night) The existing model simulation is not correct Therefore, I adjust the simulation time, using WaveWatch data at 12:00 GMT on 13Jul-2006 (roughly corresponding to Hon Ngu wave data at 19:00 GMT+7 local time on 13-Jul-2006) In the jonswap.txt (Xbeach input) the wave parameters are modified accordingly: Hm0 fp mainang gammajsp s fnyq = = = = = = 0.71 0.187 123.8 3.3 20.0000 1.0000 66 The output result of XBeach model is compared to wave record obtained at Hon Ngu gauging station • The case 2006061718 This is the case using wave data 18:00 GMT on 17-Jul-2006 This should correspond to Hon Ngu wave data at 1:00 GMT+7 local time on 18-Jul2006 But this data is not available (no visual observation at night) The existing model simulation is not correct Therefore, I adjust the simulation time, using WaveWatch data at 12:00 GMT on 17Jul-2006 (roughly corresponding to Hon Ngu wave data at 19:00 GMT+7 local time on 17-Jul-2006) In the jonswap.txt (XBeach input) the wave parameters are modified accordingly, and the output result of XBeach model is compared to wave record obtained at Hon Ngu gauging station • The case 2006120312 This is the case using wave data 12:00 GMT on 03-Dec-2006 This should correspond to Hon Ngu wave data at 19:00 GMT+7 local time on 03-Dec2006 The existing model simulation is not correct 67 In the jonswap.txt (XBeach input) the wave parameters are modified accordingly, and the output result of XBeach model is compared to wave record obtained at Hon Ngu gauging station • The case 2006120912 This is the case using wave data 12:00 GMT on 09-Dec-2006 This should correspond to Hon Ngu wave data at 19:00 GMT+7 local time on 09-Dec2006 In the jonswap.txt (XBeach input) the wave parameters are modified accordingly, and the output result of XBeach model is compared to wave record obtained at Hon Ngu gauging station The data table is then updated in table 4.2 (p 45) (updated numbers are displayed in bold font) Date Time 2006-06-13 12:00 2006-06-17 12:00 2006-12-03 12:00 2006-12-09 12:00 Bound.cond 0.55m, 5.68 s, 126.8° 0.69m, 4.5 s, 120.04° 1.91m, 6.8 s, 58° 2.07m, 6.6 s, 55° 68 Simulated Observed 0.350.52 m 0.75 m, 114°121° S 0.500.69 m 0.75 m, 110°117° SE 1.0 m, 1.662.05 m NW 46°67° 0.75 m, 1.772.21 m NE 47°65° II Council confirmed the proposal students have edited essays in the opinion of the Council: ………………………………………………………………………………………… … ……………………………………………………………………………………… …… , Day … Month .year 20 SUPERVISOR STUDENT Dr.Nguyen Quang Chien Nguyen Quoc Anh SUPERVISOR CHAIRMAN OF COMMITTE Assoc.Prof.Dr Assoc.Prof.Dr Tran Thanh Tung Nghiem Tien Lam 69 ... Numerical Modeling: the use of XBeach model to predict morphography evolution • Consulting experts Conceptual framework of the study sedimentation of Lach Van river mouth: Figure1 Schematization of XBeach. .. INTRODUCTION Status of Lach Van river mouth: Lach Van river mouth is located at (18.98°N, 105.62°E), belonging to Dien Chau District, Nghe An province, Vietnam This is a small and narrow river mouth (the... framework of the thesis, a Xbeach model is used to simulate the bottom evolution of Lach Van river mouth in Dien Chau district, Nghe An province Parameters and results of the model will be tested with