Master thesis: Applying genesis model in researching Nha Trang coastline evolution

I hereby declare that is the research work by myself under the supervisions of Assoc Prof Dr Tran Thanh Tung and Dr Nguyen Quang Chien 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 results of my thesis have not been published by me to any courses or any awards.

Ha Noi, January 2016

Vu Duy Toan

1 would like to thank to my daily supervisors Dr Nguyen Quang Chien and Assoc prof.Dr Tran Thanh Tung for sharing their knowledge, providing their useful feedback, guidance, the time invested in me, advice and discussion we had during my thesis work.

Furthermore, I would like to thank to my family, showing their interest and ‘unconditional support

CHAPTER I OVERVIEW OF SHORELINE EVOLUTION AND MULATION USING ONE-LINE MODE!

1.1 §ome issues worth considering in coastline evolution study 1 1.2 Process study shoreline changes in the world and current research trends 1.3, Numerical modeling of coastline evolution 3 1.3.1 Basie Assumption of shoreline change modeling 3 1.32 Litpack model 5 1.3.3, Unibest model 6 1.34, Genesis model 8 1.3.6 Conelusion la CHAPTER II ANALYSIS NHÀ TRANG COASTLINE EVOLUTION,

2.1, Overview of the study area 4 2.2, Data for shoreline and beach monitoring I 2.2.1, Climatology Is

2.2.2 Hydrodynamics Is 2.2.3, Geology and Geomorphology 19 2.24, Wave characteristies 19 22.5 Sediment Transport Regime in Nha Trang 20 2.3, Analysis Nha Trang coastline evolution 2 2.4, Conclusion 24 CHAPTER 3 APPLY OF ONE-LINE MODEL TO STUDY NHA TRANG COASTLINE EVOLUTION.

3.1 SWAN MODEL.

3.12 SWAN model setup 30 3.2 GENESIS MODEL 2 3.2.1, Basic theory of Genesis model 2 3.22 Setup Genesis model 7 CHAPTER 4 PROPOSE ORIENTED SOLUTIONS TO STABILIZE NHA TRANG BEACH << neserereirrrrrrrirrrrrrrrrroouSổ) 4,1 Scenarios simulated with protective structure 56 4.1.1, Scenarios Nha Trang coastline evolution without protective structure for 1 year, 5 years, 10 years 56 4.1.2, Scenarios Nha Trang coastline evolution with protective structure for 1 year, 5 years, 10 years 58 4.2, Scenarios simulated with beach nourishment 61

REFERENCES APPENDICES

LIST OF FIGURES

Figure 1.1 Nha Trang coast (Source: Google earth) ix Figure 1.2 Conceptual framework of Nha Trang Coastline evolution study xii Figure 1.3 Input and output file structure of GENESIS 8 Figure 1.4 Calculation diagram of Genesis model 10 Figure 2.1 The discharge from Cai River in the year of 2013 as well as the mean rainfall in Nha Trang in the years 1995 ~ 2014 16 Figure 2.2 The variation of the wind magnitude and ditection for September during the years of 2002 ~ 2011, ie during the southwest monsoon 7 Figure 23 The variation of the wind magnitude and direction for November during the years of 2002 — 2011, ie during the northeast monsoon, 7 Figure 2.4 The tidal level variation in the south of Nha Trang bay in the year of 2013 measured at Institute of Oceanography Tide Station in Nha Trang 18 Figure 2.5 Wave rose offshore Nha Trang 20 Figure 2.6 Nha Trang shoreline over years from 2003 ~ 2015 23 Figure 3.1 Computational domain of Swan model 31 Figure 3.2 Wave height boundary condition for Swan model 3 Figure 3.3 Wave period boundary condition for Swan model 33 Figure 3.4 Wave direction boundary condition for Swan model 33

igure 3.5 The location of two points use for calibration in Swan model 35

Figure 3.6, Wave height of Swan model & Wavewatch III data at Continental shelf 109.5, 12.5) (From January to December, 2013) 37 Figure 37 Wave Period of Swan model & Wavewatch III data at Continental shelf

109.5, 12.5) (From January to December, 2013) 37 Figure 3.8, Wave Period of Swan model & Wavewatch IT data at Continental shelf

109.5, 12.5) (From January to December, 2013) 38

Figure 3.9 Wave height of Swan model & Wavewatch III data at Continental shelf 2

(109.5, 12.0) (From January to December, 2013) 38 Figure 3.10 Wave period of Swan model & Wavewatch III data at Continental shelf 2

(109.5, 12.0) (From January to December, 2013) 39

Figure 3.11 Wave Direction of Swan model & Wavewatch III data at Continental shelf 2 (109.5, 12.0) (From January to December, 2013) 39 Figure 3.12, Wave height of Swan model & Wavewatch IIT data at Continental shelf 1 (109.5, 12.5) (une to August, 2014) 40 Figure 3.13, Wave period of Swan model & Wavewatch III data at Continental shelf 1 (109.5, 12.5) (From June to August, 2014) 40 Figure 3.14, Wave height of Swan model & Wavewatch III data at Continental shelf 2 (109.5, 12.0) (From June to August, 2014) 41 Figure 3.15, Wave height of Swan model & Wavewatch III data at Continental shelf 2 (109.5, 12.0) (From June to August, 2014) 41 Figure 3.19 Extract wave data points as boundary conditions for Genesis model 48 Figure 3.21 Wave height for genesis boundary condition sọ Figure 3.22 Wave Period for Genesis boundary condition SI Figure 3.23 Wave Direction for Genesis boundary condition 51 Figure 3.24, Measured and predicted shoreline positions using different transport

parameters (12/2013) 33

Figure 3.25 Comparison of shoreline in model and measured data for 27/06/2014 55 Figure 4.1 Nha Trang coastline evolution without protective structure over years 56 Figure 4.2 Nha Trang shoreline position over ten years 38 Figure 4.4, Result of Scenario with three Breakwaters over 10 years 9 Figure 44 Nha Trang coastline evolution after nourishment over years 2

LIST OF TABLES

‘Table 2.1, Statistic storms directly influence to Khanh Hoa Province ‘Table 3.1 The default setting in SWAN and selection for model setting ‘Table 3.2: Parameters used for model calibration.

Table 4.1, Shoreline change after 1 year without protective structure ‘Table 42 Shoreline change after 5 years without protective structure Table 4.3, Shoreline change after 10 years without protective structure

Table 4.4 Shoreline change after 1 year after building three breakwaters, Table 45, Shoreline change ater 5 years after building thre breakwaters ‘Table 4.6, Shoreline change after 10 years after building three breakwaters

1 would like to thank to my daily supervisors Dr Nguyen Quang Chien and Assoc prof.Dr Tran Thanh Tung for sharing their knowledge, providing their useful feedback, guidance, the time invested in me, advice and discussion we had during my thesis work.

Furthermore, I would like to thank to my family, showing their interest and ‘unconditional support

INTRODUCTION Study area

Nha Trang is a coastal city and capital of Khanh Hoa province The study area is located at the vicinity of Cai River, the north is Cai River and at the south of study area isa breakwater of military por.

Nha Trang is one of the most beautiful bays in the world, one of tourist centers, famous resort in the country and the world with many’ beautiful landscapes, blue sea, many of the most typical ecosystems the coral reefs, many beautiful sandy beaches With marine tourism criteria at present the world is: Sun, Sea, Sand (38), the Nha Trang Bay meets these criteria above, Nha Trang has many beautiful beaches, the beach along Tran Phu Street with a length of about 7 kilometers is the most famous beach.

Nowadays the city experiences new possibilities to earn capital as tourists are drawn to the atea, Many people come for the appealing weather, but the long and central located sandy beach is also making it an attractive place for leisure,

Figure 1.1 Nha Trang coast (Source: Google earth)

1 Motivation

‘Viet Nam has 3260 km coastline, 89 river mouths and more than 3000 islands Along the coastline are 29 provinces and cities A number of seaports, oil refinery plants, fishing areas and aquaculture zones greatly contributes to the economic development of the coastal and estuarine areas.

Beside advantages and huge potential, annually we have to deal with beach erosion, estuarine deposition and the Government had to invest thousands of billions VND to consolidate, upgrade sea dykes and to build coastal structure protection

Coastline evolution process is very complicated, which varies in space and time The process is strongly related to nearshore hydrodynamic condition including tidal circulation, wind wave, wave-induced currents combined with storm surge Especially it becomes more and more complicated and stronger duc to climate change and sea level rise On the other hand, due to the continuity of the longshore sediment transport, the coastal protection in this region will again cause erosion in other regions Therefore, it is necessary to perform coastline evolution prediction based on the bathymetry, meteorology, nearshore hydrodynamic for coastal zone planning with the ‘ims of sustainable development and national defense

2, Research Seope

Nha Trang beach section (300 m at the vicinity of Cai River),

3 Research objective

= The study aims to estimate Nha Trang coastline evolution using Genesis model, = Propose alternative solutions to protect Nha Trang Coast.

4 Research content

~ Analysis on the coastline evolution of Nha Trang coast.

~ Modelling wave propagation from deep water to shallow water using Swan model,

= The rationale and usability of Genesis model, a one-line numerical model, for coastline evolution and coastal erosion.

~ Applying Genesis model to predict shoreline changes for the background scenario after | year, 5 years, and 10 years

~ Proposal of preliminary soluti 1 to protect Nha Trang coast.

~ Applying Genesis model to predict shoreline changes with the presence of structure after 1 year, 5 years, and 10 years.

5 Literature review

Recently, some researches relevant to the coastline evolution and hydrodynamic in the area of Nha Trang has been performed.

Le Thanh Binh and Duong Hai Thuan, “The Shoreline Evolution of the Nha Trang Beach, Khanh Hoa, Vietnam’, 2015 Binh and Thuan (2015) showed that strong

erosion phenomenon occurred at the area bebind the groin during the northeast

‘monsoon and revealed foot of the embankments along the beach,

Le Thanh Binh and others, ‘Some Preliminary Results on Studying the Shoreline Evolution of Nha Trang Bay Using Video-Camera’, Binh et al (2014) indicated that the monitoring technique on shoreline change in Nha Trang beach is very signi int

and it obviously illustrates a good (endency and general picture on seasonal evolution of shoreline change in Nha Trang beach,

Nguyễn Trang Việt etal, vestigation of Erosion Mechanism on Nha Trang Coast,

Viet Nam’, 2015 Viet etal (2014) showed thatthe erosion ofthe coast in recent year relating to the degeneration of a river mouth sand spit, In particular, the erosion is caused by waves which are generated by northeast monsoon resulting in longshore sediment transport directed from north to south, Moreover, shoreline retreat or monsoon season were calculated from wind data,

Nguyễn Thành Luân, Nguyễn Hoàng Son and Trần Thanh Ting, 'Nghiên Cứu Biến

động Vùng Cửa Sông Cái, Nha Trang qua Các Tư Liệu Viễn Thám (giai đoạn 1999

-2013)", 455 (2014) Luan et al (2014) used remote sensing technique to analyze

coastline evolution and indicated that the coastline evolution in this area is due to certain parameters like wind, wave, seasonal river discharge, and water level

Nguyễn Trung Việt et aL, “Seasonal Evolution of Shoreline Changes in Nha Trang Bay, Vietnam’, 2016 Viet et al (2016) showed that coastline evolution due to both human and nature has major effects on the future of tourism development Moreover, the beach will be affected by potential increase in the frequency of typhoons,

Research methods

~ Numerical Modeling

«Using Swan model to propagate wave from deep water to shallow water ® The use of Genesis model to predict coastline evolution

= Documentary Analysis: collecting basic data and previous research results about natural characteristics, hydrodynamic and coastline dynamics of Nha Trang.

Dacia] => Dawa >| Gani) FP | (Cleo eran)

Figure 1.2 Conceptual framework of Nha Trang Coastline evolution study

CHAPTER I OVERVIEW OF SHORELINE EVOLUTION AND SIMULATION USING ONE-LINE MODELS.

1.1, Some issues worth considering in coastline evolution study Coastline evolution mainly includes the following issues:

- Coastal deposition, erosion causing coastline change (marine transgression, marine degradation);

The proce: of rising, lowering of local the beach elevation:

~ Coastline evolution process under the impact of the coastal and river constructions ‘These processes are considered in the whole period from the past, present to future In this thesis report, the term evolution refers to the future development of the coastline 1.2 Process study shoreline changes in the world and current research trends ‘The breaking waves and surf in the nearshore combining with various horizontal and vertical patterns of nearshore currents effectively transport beach sediments ‘Sometimes this transport result only in a local rearrangement of sand into bars and troughs or into series of rhythmic embayment cut into the beach At other times there are extensive longshore displacements of sediments, possibly moving hundreds of thousands of cubic meters of sand along the coast each year, Longshore sediment transport is among the most important nearshore processes that control beach

morphology, and determines in large part whether shores erode, acerete, or remain

stable, An understanding of longshore sediment transport is essential to sound coastal engineering design practice.

Currents associated with nearshore cell circulation generally act to produce only a local rearrangement of beach sediments, The rip currents of the circulation can be important in the eross-shore transports of sand, but there is minimal net displacement cf beach sediment along the coast More important to the longshore movement of sediments are wave breaking obliquely to the coast and the longshore currents they generate, which may flow along an extended length of beach, The resulting movement ‘of beach sediment along the coast is referred to as littoral transport or longshore

sediment transports, whereas the actual volumes of sand involved in the transport are termed the littoral drift This longshore movement of beach sediment is of particular importance in that the transport can either be interrupted by the construction of Jetties and breakwaters (structures that block all or a portion of the longshore sediment

transport), or can be captured by inlets and submarine canyons In the ease of a jetty,

the result is a buildup of the beach along the up drift side of the structures and erosion of the beach down drift of the structures The impacts pose problems to the adjacent beach communities, as well as threaten the usefulness of the adjacent navigable

The litioral transport can also result from the currents generated by alongshore gradients in breaking wave height, commonly called diffraction currents This

transport is manifested as a movement of beach sediments toward the structures which

creates these diffraction currents (such as jetties, long groins and headlands) The result is transport in the “upwave" direction on the downdrift side of the structure This, in turn, can ereate a buildup of sediment on the immediate, downdift side of the structure or contribute to the creation of the crenulated-shaped shoreline on the downdrift side of a headland,

Also in recent times, the World and Asian countries attach great importance to the study of changes in the estuary and the coast of the Netherlands, the US, UK, Belgium, Japan, Thailand, Singapore Concurrent to the research, many construction works on estuaries and coasts have also been built, which have great effect on the development of economic and national security of the countries above Another important topic of coastal and estuarine search is the prediction of coastal sediment transport, which hhas been developed and matured, as represented by research

cientists to the United States, Japan, and the

“The main trends in research developments and coast estuaries in the world today are:

‘*Modemization of the survey means to obtain results which are well

documented, helping to assess the status of being realistic and provide the exact,

parameters for the mathematical model

«Improving the mathematical description of he process and methods

*Cary out field research, in conjunction with laboratory experiments using hydraulic models

+ Full data warchousing and advanced techniques in data retrieval and processing.

1.3 Numerical modeling of coastline evolution 13.1, Basie Assumption of shoreline change modeling

A common observation is that the beach profile maintains an average shape that is characteristic of the particular coast, apart from times of extreme change as produced by storms For example, steep beaches remain steep and gently sloping beaches remain ‘gentle in a comparative sense and in the long term Although seasonal changes in wave climate cause the position of the shoreline to move shoreward and seaward in a cyclical manner, with corresponding change in shape and average slope of the profile, the deviation from an average beach slope over the total active profile is relatively small Pelnard ~ Considere (1956) originated a mathematical theory of shoreline

response fo wave action under the assumption that the beach profile moves parallel to

itself, ie, that it translates shoreward and seaward without changing shape in the course of eroding and accreting He also by waves obliquely incident to a beach with a ‘groin installed in a movable-bed physical model

If the profile shape does not change, any point on it is sufficient to specify the location Of the entire profile with respect to a baseline,

‘Thus, one contour line can be used to describe change in the beach plan shape and volume as the beach erodes and accretes This contour line is conveniently taken as the readily observed shoreline, and the model is therefore called the “shoreline change” or ‘shoreline response” model Sometimes the terminology “one-line” model, a shortening of the phrase “one-contour line” model, is used with reference to the single contour line.

‘A second geometrical — type assumption is that sand is transported alongshore between two well ~ defined limiting elevations on the profile The shoreward limit is located at the top of the active berm, and the seaward limit is located where no significant depth changes occur, the so-called depth of profile closure Restriction of profile movement

between these two limits provides the simplest way to specify the perimeter of beach cross-sectional area by which changes in volume, leading to shoreline change, can be computed,

‘The model also requires predictive expressions for the total longshore sand transport rate, For open-coast beaches, the transport rate is a fun n of the breaking wave height and direction alongshore Since the transport rate is parameterized in terms of breaking wave quantities, the detailed structure of the nearshore current pattern does not directly enter.

Finally, itis assumed that there is a clear long-term trend in shoreline behavior This ‘must be the case in order (o predict a steady signal of shoreline change from among the ‘noise” in the beach system produced by storm, seasonal changes in waves, tidal fluctuations, and other cyclical and random events In essence, the assumption of a clear trend implies that the wave action producing longshore sand transport and boundary conditions are the major factors controlling long-term beach change This assumption is usually well satisfied at engineering projects involving groins, jet and detached breakwaters, which introduce biases in the transport rate

‘Standard assumptions of shoreline change modeling are: = The beach profile shape constant;

~ The shorewatd and seaward limits of profile are constant; ~ Sand is transported alongshore by the action of breaking waves: ~ The detailed structure ofthe nearshore circulation is ignored; ~ There isa long-term trend in shoreline evolution,

Curently, powerful advances in ocean dynamics research, measurement equipment and ealeulation technique has allowed us to simulate the process of evolution of the coastline via computer programs which solve complicated math equations on the physical phenomena involved, Mathematical model with its special abilities and increasing popularity has proved to be superior to other research methods through short implementation time, flexibly in changing simulation scenarios, and high resolution of results, Of course, due to the limitations in modeling, the exactness of

equations and completeness of data input, the solution obtained from the mathematical model is not absolute accurate, especially in quantitative terms If the mathematical model is combined with other methods it is adequate to give us more reliable foreca sting results

‘There have been a lot of mathematical models with th cations that aresoftware appl ‘well-known scientific institutions in the world of ocean dynamics and over time they are increasingly complete and advanced Bruun’ original model (1962) solely account for the rising water levels due to climate change and tectonic subsidence activities to predict changes in the coastline The more modem computer programs such as GENESIS (US Navy shore CERC combined with Lund university), UNIBEST by the Institute of Hydraulics Delft - Netherlands, LITPACK by Danish Hydraulic Institute

besides the massive model 2D & 3D has provided users the abi

such as estuaries MIKE Danish, Dutch Delft 3D, CEDAS Wy to predict the morphology of coastal are

US and other models in the UK, Japan however a full introduction on such models is outside the scope of this thesis report.

‘The following section introduces a few powerful mathematical models being widely used in the world and introduced into Vietnam with the purpos

the coastal zone The models are: GENESIS, UNIBEST and LITPACK.

se to predict changes in

1.3.2 Litpack model

4) Introduction of LITPACK model

LITPACK (within the MIKE software suite) is the abbreviation for Littoral Processes and Coastline Kinet

Institute (DH) ~

movement under the action of waves and currents, coastal sediment, shoreline changes

- Centre of Water and Environment - Danish Hydraulic

a the software program modeling of non-cohesive sediment

and the development of soil on relatively flat coastline ‘The sub-modules of the program include:

~ LITSTP: for calculating the movement of non-cohesive sediment under the action of,

‘waves and currents;

~ LITDRIFT: for calculating longshore and coastal sediments; ITLINE: for calculating shoreline changes;

~ LITPROF: for calculating eross-shore sediment transport: - LITTREN: for calculating sedimentation in the stream (canals) b) Module LITLINE ~ Scope and rationale usability

@ General introduction

LITLINE module is a software program which calculates shoreline changes with the input wave data is imported by time series On the other hand, this model was based on the theory of one line (one-line theory), the cross-sectional area of the coast as surgery

does not change in the course of erosion/accretion Therefore, only the coast

morphology is described by the shoreline position (coastline position) The one-line theory is presented in this section is applicable to other software programs (UNIBE: GENESIS),

LITLINE has the following applications

+ Study shoreline changes under the influence of natural Factors + Study the shoreline under the influence ofthe coastal structures

+ Research shoreline restoration measures by beach nourishment method

1.3.3 Unibest model 4) General overview

UNIBEST software (Uniform Beach sediment Transport - sediment movement coasts are) is built and developed by Hydraulic Institute Delft - Netherlands (WL - Delft Hydraulics) This software aims to establish a more complete studies and calculated longshore sediment transport as well as study of relationships morphology between soil dynamics coast to coast surface shape (shoreline evolution),

UNIBEST process consists of two modules:

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UNIBEST-TC: for calculating sediment transport and shoreline developments under the effect of wave, tidal current and wind;

~ UNIBEST-CL+: for calculating shoreline evolution due to differences sediment transport Longshore sediment transport is considered the effects of runoff and tidal waves, UNIBEST-CL + module consists of wo sub-modules:

+A sub module for calculating the longshore sediment transport (the LT module):

+ A sub module for calculating shoreline development (the CL module).

‘The longshore sediment transport is calculated by module LT Sediment will be the input data for the module to calculate CL shoreline changes, which takes into account the form of coastal structures like: embankment, groins, offshore breakwaters or a combination of these structures.

+b) Sub module UNIBEST LT

This sub module was established to calculate Longshore current due to wave and tidal, thereby calculating longshore transport with any beach profile.

‘Surf zone dynamics is calculated through wave models which allow modeling of random waves propagating from deep to shallow water, Longshore and cross-shore sediment transport are estimated by many different formulas with specific conditions Computer programs may require data input regarding the wave field and tidal regime, and allow calculation of total sediment transport in the year, in season or only in a

©) Sub-module UNIBEST CL

‘The CL sub-module is set to calculate shoreline changes due to differences overload long shore for coastlines near the road are in theory a (single line theory) The boundary conditions and different initial conditions are included, offering various situations of coastline evolution,

In addition, this model has the ability to calculate the coastal structures with different

types of structures such as: permeable or impermeable groins, seawalls and

embankments, sea dikes, breakwater, estuarine regulation structures, artificial beach nourishment systems or beach replenishment projects The effects of wave diffraction behind structures are also included in the model.

1.3.4 Genesis model a) GENESIS

GENESIS is a coastal shoreline and beach topography response model developed by

Hanson and Kraus (1989) for the US Army Corp of Engineers GENESIS is an abbreviation for Generalized Model for Simulating Shoreline Change, a software

program to calculate the shoreline changes for a long time at the coast The study area

of the model in the spatial range (1-100) km and time period (1-100) months

GENESIS vrutexr

Figure 1.3 Input and output file structure of GENESIS

GENESIS calculates coastline evolution as a result of the change of longshore sediment transport over time and space, in which consider including the shoreline change due to the effects of beach replenishment, due to sediment sources from the

river or coastal structures.

GENESIS is capable of caleul:

cease construction works exist, The ability of the model are as follows:

ing the shoreline changes for natural coasts and in the

‘The number and type of buildings arbitrary combination with other forms of work such as soldering, wave direction dyke, detached breakwater, pier and beach replei ishment projects ashore.

~ Structural forms of conventional groins or T-, Y-shaped groins.

~ As to the diffracted wave after breakwaters, dikes and embankments nozzle line direction

Calculation for a large domain surrounding the study area,

Waves input consists of deep water wave height, period and wave direction, ~ The data series of different waves.

~ Sediment transport generated by obliquely-oriented waves or unevenly distributed "waves heights along the coast

~ Wave overtopping through offshore breakwater.

Besides that, GENESIS has some disadvantages: there are certain restrictions, such as: ~ Neglect reflected waves from structures,

- Shoreline Offshore Reach Breakwater, Shore do not untouchable offshore breakwater

~ Some small limited about distance, shape, structure direction, Small limited number of distance, shape and orientation of the building.

~ Neglect the change of tidal water level

~ Limited of shoreline evolution theory calculation The main limitations of the theoretical calculations shoreline changes.

Diagram of the model calculations are summarized in Figure 1.4, which notes that the input wave data can from an external program such as RCPWAVE or directly by

Breaking | | Shoreline evolution Long shore Sediment wave Ay, ‘Transport Q, Họ, Oj T

Figure 1.4 Calculation diagram of Genesis model 1.3.5 Comparision of three one-line models

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Table 1 Wave in evaluated models

Waves GENESIS Toternal wave modal Ỹ Coupled spectral wave model Ỹ

Table 2 Structures in evaluated models

GENESIS |LITPACK | UNIBEST

‘Detached breakwater transmission Y N NA “Time dependent breakwater transmission Y N NA ‘Water level dependent wave transmission Y N NA Wave reflection from structures N N N Wave diffraction around structures Y Y Y

in

Table 3 Boundary conditions for evaluated models

GENESIS LIPACK UNIBBST

‘Moving boundary Y N N Pinned boundary Y Y Ỹ

Gated boundary Ÿ N N Constant shoreline angle N N Ỹ Constant transport rae N N ¥

Variable wansport rate N N Ỹ

Table 4 Inlet features in evaluated models

GENESIS JLHPACK | UNIBEST Tiet Bypassing within the grid N

Tale shoalTeatare sediment balance N N

Tnlet shoal dredging N N N

Table 5 Variable parameters in evaluated models

GENESIS JLHPACK | UNIBEST

Variable depth of closure N Y NA ‘Variable empirical transport coefficients N NA NA Variable resolution grid alongshore N N N

Time and space-varying soureesink Ỹ Ỹ Ỹ

Variable eross-shore profile N Y NA Variable grain size N Y NA

Table 6 Other included processes, modules, or features in evaluated models, GENESIS [LITPACK | UNIBEST Direct provision or changing Hide level Y Y Y Tidalfother non-LST cunentx Y Y Y Offlhore contour Y Y NA Wind-driven transport N N Y Regional contour Y NA NA

Results indicate that all models represent the same major processes driving shoreline change with many small variations in approaches or capabilities The major differences in capabilities noted are listed below:

* UNIBEST and LITPACK include a more rigorous calculation method for longshore transport, Calculations are conducted on a 2D grid (eross-shore and

+ UNIBEST applies a curvilinear grid instead of linear GENESIS address the

same issue through addition of a regional contour LITPACK does not include cither option.

* UNIBEST does not calculate diffraction internally,

1.3.6 Conclusion

By analyzing the features of the model on the show, with regional authors conducted

the study, the use of model Genesis shoreline changes are fully in line with the

objectives of the research that the author set out.

3

CHAPTER II ANALYSIS NHÀ TRANG COASTLINE EVOLUTION

2.1, OVERVIEW OF THE STUDY AREA,

Nha Trang is a coastal city and a c¢ ter of politics, fonomy, culture, science and technology and tourism in the province of Khanh Hoa, Vietnam Before becoming the land of Vietnam, la Trang belongs to Champa The ruins of the Cham remain in parts of Nha Trang Nha Trang is known as the peat! of the South China Sea, the green jewel because of the value of nature, beauty and its climate

Nha Trang is located in the central province of Khanh Hoa North borders Ninh Hoa Dien Khanh district on the west, the east adjacent 10

Nha Trang has a total land area of 252, 6 km*, with 27 administrative unit’s basis: 19 ‘wards and 08 municipalities with a total population of over 393218 (as of 31/12/2010) Nha Trang has many geographical advantages, which is convenient for road, rail, air,

sea domestic and international, is the gateway to the South Central and Central

Highlands should Nha Trang has many conditions to expand exchanges and development

Nha Trang terrain with elevations quite complex ranging from 0 to 900 m above sea level is divided into three topographical regions Coastal plains and along Cai covers about 81,3 km? accounting for 32.33% of the whole city; transition zone and Tow hills with a slope of 30 to 150 mainly in the west and southeast, or on small islands aecount for 36.24% of the atea, mountainous terrain is steep on both ends 150 distributed in North - South of the city, on Hon Tre island and some islands accounted for 31.43% of the rock city.

Storm characteristic

According to the statistical results from the National Centre for Hydro -Meteorological Forecasting showed: Since 1998 - 2016 the total number of hurricanes affecting to Nha Trang is 11 storm, However, most of the storms are very small and do

4

"not cause serious consequences to the Nha Trang The storm had the biggest influence is super typhoon Hai Yan storm in 2013 with 24 levels The storms directly influencing Khanh Hoa Province from 1998 to date are presented in the table below:

‘Table 2.1 Statistic storms directly influence to Khanh Hoa Province

Year Storm Date Storm level

2011 | “Tropical Depression TWENTYFIVE | 04-0512 lô 2012 ‘Tropical storm GAEMI 02~0610 ụ 2013 | $aprTyphoon-SHAIYAN 0= 13/1 24 204 ‘Tropical Sam SINLAKU 26- 30/11 B

Base on storm data in the table 2.1 showed that only Super Typhoon ~ 5 HaiYan affect directly to Nha Trang with highest level This storm makes beach cross section profile significantly change.

2.2, DATA FOR SHORELINE BEACH MONITORING

2.2.1 Climatology

In Nha Trang the year divided two seasons, the dry season and the wet season, The

precipitation is around 1,500 millimeters per year The dry season usually occurs in the

month of January until August, Between the years of 1995 - 2004 the mean precipitation was 8.40 millimeters in February, which makes it the driest month of the

15

year The months September to December is the wet season, with the most precipitation appearing in the November, which has a mean value of 386 millimeters of rain during the time period 1995 = 2004 (Mau, 2004).

The large amount of rainfall coincides well with the time of year when the northeast monsoon is taking place, ie, in the months of October to March (Lefebvre et al, 2014), The large amount of rainfall also leads to a higher river discharge through Cai River A larger volume of water being transported in the river generates a larger force, ‘Which in turn manage to transport a greater amount of grains through the river and out to the sea (Mau, 2014),

Figure 2 1 The discharge from Cai River in the year of 2013 as well as the mean rainfall in Nha Trang in the years 1995 ~ 2014

Nha Trang is affected by 10 monsoons, the northeast monsoon and the southwest ‘monsoon The northeast monsoon is the strongest one and is most dominant in the ‘months November and January In the years 1988 to 2007 the maximum recorded wind velocity was measured to be 28 nvs in November 1988 The southwest monsoon is most dominant in the month of June to September The maximum recorded wind

velocity between the years of 1988 0 2007 was recorded to be 16 mvs and occurred in

September 1992 (Mau, 2014) Figure 22 and Figure 2.3 show the magnitude and direction of the winds in the months September and November, which represent the months of the southwest and northeast monsoons, respectivi , during the years 2002

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= 2011 The weather data, ie the precipitation and the wind data, have been measured

at the meteorology station in Nha Trang at the latitude 12°13” and longitude 109°12"

Figure 2.2 The variation of the wind magnitude and direction for September duri the years of 2002 ~ 2011, ic, during the southwest monsoon,

Figure 2.3 The variation of the wind magnitude and direction for November during the years of 2002 ~ 2011, ie during the northeast monsoon.

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“The temperature in Nha Trang is fairly constant throughout the years It only varies slightly between the higher temperature of 29 degrees Celsius during the summer months of June, July and August and the mean temperature of 24 degrees Celsius occurring during the winter months of December and January (Mau, 2014).

2.2.2, Hydrodynamics

‘The wave climate at Nha Trang coincide with the wind patterns and monsoons During the northeast monsoon, strong waves are entering from the northeast, while during the southwest monsoon, weaker waves enters from the southeast Water bodies can also be affected by the gravitation force that the earth experience from the sun and moon, Depending on the location, the difference in water level could range from almost none

to several meters (U.S Atmy Corps of Engineers, 1984) Diurnal tide means that the

water body experience one high and two low tides per day As the lunar day is not

equal to a sun day, each tide is occurring in a delay of approximately S0 minutes per

day The largest tide is called the spring tide and occurs when the sun and moon is linear and thus exert its force in the same direction When being perpendicular to each other the tide is at its lowest point, called neap tide (Pinet, 1998), Nha Trang experiences a mix of the diurnal tide and the semi-diurnal tide In Nha Trang the spring tide can reach 2.5 meters and the neap tide can be as low as 0.4 meters (Bui et al., 2014) The tidal level for the year of 2013 can be seen in Figure 2.4.

‘Water level {mios kl a gs

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Figure 2.4 The tidal level variation in the south of Nha Trang bay in the year of 2013‘measured at Institute of Oceanography Tide Station in Nha Trang

2.2.3 Geology and Geomorphology

‘The main contributor to sediment in the Nha Trang bay is the Cai River It deposits sediment in the bay and forms ridges there and thus the sediment is said to have terrigenous background, Only 2% of the material on the beach at Nha Trang is made up from biogenous material that contains a lot of caleium carbonate like shells, corals ete, The situation is different when looking in small bays that are sheltered on the island in the bay, where the calcium carbonate content in the sediment reaches a much higher level, due to the higher distance to the river mouth (Inman, 1966).

“The sand in the bay has some differences in the appearance Most of the sediment discharge from the river Cai is made up of sand (Mau, 2014) and this sand is light in

colour and have irregular surfaces (Inman, 1966) Only a minor part if the sand is

made up from the darker and slightly more reddish sand.

‘The city of Nha Trang is built on old beach ridges which have coarse sand Below this

layer of approximately 10 meters, another layer of more silty sand is located It is believed to be the remains of the beach existing prior to the modem beach of Nha “Trang (Inman, 1966).

2.2.4 Wave characteristics

‘The wave data collection at deep water from Marine Department and the US National

Atmospheric Administration (NOAA) from 1997 to 2010 showed the offshore wave

climate pattern of Nha Trang From October last year to April next year, is the leading Wave northeast direction, with the most intense in the months of November, December and January Wave height is so large, from 2 m to over 4 m From April to September, ‘wave direction is mainly southwest, wave height from 0.3 m to 3 m change Due to offshore wave has southwest direction so wave does not propagate directly into the bay

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Offshore wave pattern of | Offshore wave pattern of | Offshore wawe pattem Nha Trang in January (data | Nha Trang in June (data | Nha Trang during several

1997 - 2010) 1997 - 2010) years (1997 ~ 2010)

Figure 2.5 Wave rose offshore Nha Trang

Overall, during the northeast monsoon, east and northeast waves dominate, Northeast ‘monsoon impact on Nha Trang region strongest in the month X, XI, XM, Land II, its effects can to IV The swell waves which cause a strong impact on bank of Nha Trang Bay are those from the East.

In Nha Trang bay need to consider to swells due to storm, though the storm is far not come directly to in Khanh Hoa, especially on stage at the Cai River flood and high tide period,

2.2.5, Sediment Transport Regime in Nha Trang

The flow, and thereby also the transport of sediment, is mostly dependent the wave climates inside the bay The wave climates are in turn affected by the Tocal winds, the ‘monsoons and the bathymetry of the bay (Mau, 2014).

The flow from Cai varies to a great extent due to the uneven occurrence of precipitation, large amount of rainfall leads to larger flow and little precipitation leads

to lower flow As the sediment is transported by the water, the amount of sediment

reaching the bay varies with the precipitation The sediments reaching the bay area to some extent settled inside the bay while some, normally finer particles, are transported seaward or sediments are transported further south down the coast and are deposited in

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for example Cam Ranh, a city about 40 kilometers from Nha Trang When there is little or low wind speed, the freshwater from the river floats on top of the seawater due to the difference in density, Thus the sediment have lower tendency to settle and the beach will have less nourishing of sand, (Inman, 1966).

‘Waves contain energy and can thus transport sediment As the waves are higher in the

northeast monsoon the tendency to transport sediment, and also heavier sediment, is thus higher then The waves create stronger currents which ereate stronger longshore ‘currents and the sediment transport increases The islands in the area also play a role in hhow the transportation is affected By being an obstacle to the Southeast Sea, the sediment is not affected by offshore drift to the full extent, The islands also affect the wave climate by causing the wave to diffract along its contours and waves are

reflected against the islands Thereby, the islands ereate a more complex wave climate

(Inman, 1966).

The tide present in the bay can also transport sediment in the erosshore direction as the sea level alters and a tidal current is generated, But as the current is relatively small compared to the currents created by the wave motion, it has only a litte impact of the

{transport of the bay The small current can mostly transport very fine material and thus

the low transport has little impact on the evolution of the beach.

Between the islands and the mainland the wind affects the water by ereating a str current with a high velocity that prevents the particles from settling easily, especially the fine particles coming from the river That would likely be one of the factors explaining the relatively deep passage of 24 meters between the Hon Tre Island and the mainland (Inman, 1966)

‘There is two rivers entering Nha Trang bay, the rivers Cai and Tac Cai is entering the bay in the center of the bay, while Tac River mouth is situated in the south of the bay and thereby only contributes minor to the freshwater flow into the bay Sediments follow with the water flow and Cai yearly transport 80.38 million tons of sediment into the bay, most of it entering the bay when the flow is high in the winter months On the other hand, Tac only transport 0.26 million tons of sediment per year to the bay

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(Nguyen et al, 2013) According to Inman (1966), Cai brings 195,000 cubic meters sediment per year to the outlet of which sand is estimated to be approximately 63% of that load (Inman, 1966).

2.3, ANALYSIS NHA TRANG COASTLINE EVOLUTION,

To get an understanding of how Nha Trang beach has evolved during the recent years, the program Google Earth was used, The program used satellite images, which provides a plan view of the chosen area Satellite image between the years 2003 ~ 2015 were available over the beach of Nha Trang To see changes of shoreline, selected years were digitalized The shorelines for several years were then plotted and visualized in a graph The graph sketched with a distance of $ km, By presenting shorelines from several years in the same graph, trends for the shoreline evolution could be seen, Shoreline data is selected for the different years, which allows us to assess changes in the coast of Nha Trang over the years.

The shoreline is not fixed, but has a natural tendency to change and adapt to new conditions, both naturally and anthropogenically Shorelines can be either accreted or eroded

‘When a beach is exposed to higher wave than normal, sediment from the beach will be transported out into deeper part of the sea with the cross shore current The seasons of the year also have a clear relationship to the condition of the beach Long shore currents can also influence the natural variation of the complete shoreline orientation, Depending on the strength and angle of the incoming wave, which vary with the seasons, the shoreline position may fluctuate, With waves coming from the Nonh

dire ion, the shoreline might retreat in the south part and accrete in the north part If

‘waves instead come from the south direction, the reverse will occur, This makes the shoreline to naturally shift in gradient from a plan view Moreover, sea level rise occurs gradually around the world, which threaten to have adverse effects on the coast.

Figure 2.6 Nha Trang shoreline over years from 2003 ~ 2015

Coastal structures affect the long shore sediment transport which is the most common cause of causing coastal erosion The presence of coastal structures will cause a variety of effects involve the following:

= Trapping the sand at the downstream of the structures causes the lack of

sediment supply for vicinity location,

= Sediment transport from nearshore to deeper water.

Before 2003, when there was no cape front border posts (Pham Van Dong street), the northem and southern coastline of Cai River was accreted even tend to be filling up

the Cai River mouth Once, this was poured rock promontory stretching out (2006)

until now, the southern cape shoreline park area, north of the bridge Tran Phu starting

to erosion Faced with such erosion, the city built the embankment before the temple

nests, this building disrupted, and causing imbalance in the coastal sediment Entails,

is sand eroded estuary and sand fades sure the door first.

2B

In addition, the hardening embankment south coast estuaries have cụt the sediment exchange between the stream and river banks So under the influence of the flood season the river flow was pushed closer to the shore line of the South, cause erosion in the south of Cai River Mouth,

2.4, CONCLUSION

Nha Trang coast lies in area with moderate climate conditions, less affected by extreme weather conditions: wind, rain, water level fluctuation, waves, currents, and storm However, the coast of Nha Trang has a relatively large impact on people building the system as bank protection, reclamation,

In terms of natural factors: the coast of Nha Trang influenced mainly by waves coming

from the NE and E (NE monsoon period) and less affected by the waves towards SE

(SW monsoon period) Northern coastal strip is influenced mainly by the wave direction E, south shoreline strongly affected both NE and E 2 wave direction, wave direction NE particularly this is also the waves have a higher frequency of the wave E, Erosion and sedimentation in the Cai estuary Nha Trang directly related to the

operation of the northeast monsoon, which acts to redistribute sediment in the estuary,

dunes exist as underground, underground sand.

CHAPTER 3 APPLY OF ONE-LINE MODEL TO STUDY NHÀ TRANG COASTLINE EVOLUTION

In this chapter, Swan model was setup for Nha Trang area, simulate wave propagate

from deep water to shallow water to extract wave data using for Genesis boundary

condition, Genesis was used to calculate shoreline change over several years 3 SWAN MODEL.

BULL Basic theory of SWAN model

n ‘The SWAN (Simulating Waves Nearshore) model is a third-generation numeri

Wave model to compute random, short-crested, wind-generated waves in coastal

regions with shallow water and ambient currents, Physical processes in SWAN include wave shoaling, refraction, nonlinear interactions, depth-induced breaking, 'wave-curenL interaction, and bottom friction and whitecapping dissipation SWAN đoes not account for diffraction or reflections due to bottom scattering SWAN is driven by local winds and wave input through boundary conditions, and waves are modulated by tidal currents The numerical scheme is implicit, unconditionally stable and not subject to aCourant eriteria

Action Balance Equation

Inthe presence of ambient current, the action density is conserved while the energy density is not The action density N(Ø, 6) is equal to the energy density E(Ø, 6) divided by the relative angular frequency ơ, Le N(o, 6) = E(Ø, Vo SWAN solves for the

evolution of the wave spectrum by using the action density spectrum The governing equation for Cartesian coordinatesis

ệ h 2 yŸ

cN+ GN+Ể cN+ = 3.1Nes EN ae ty : GB)

where x, y are horizontal Cartesian coordinates, t, is time, Ð is the propagation direction of each wave component, cạ, cy, cạ, cụ stand for the propagation velocity in race, G-space, 0-apace respectively § is the source term in terms of which include the effects of generation, dissipation, and nonlinear ‘wave-wave interaction The first term on the left-hand side of Eq (3.1) is the rate of

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change of action density in time, the second and third terms are propagation of action in physical space, The fourth and fifth terms show the shifting of the relative frequency and the refraction due to variations in depth and currents,

‘The propagation velocity is taken from linear wave theory (Whitham, 1974, 2

Dingemans, 1997) Based on the dispersion relation ø2 = gktanhkh, the group „ Vhete k is wave number, velocity without current velocity is calculated by,

is water depth, g is gravitational acceleration, and cg0 is dependent on x,y and ø:

Finally, the group velocity with current velocity in terms of x, y, ø and Øis expressed by (Bretherton and Garrett, 1969):

Cela, y, 0,0) =eg0(,y,ø)+ Ủy cos0% Uy sind (32)

OU, Uy, Em".

-l& - 2} incon + Sin ngu

Sin (ø.) = A + BE(ø, 8) an

‘The expression for A from Cavaleri and Malanotte-Rizzoli (1981) is used with a filter to climinate wave growth at frequencies lower than the Pierson-Moskowitz frequency

In which Ay is the wind direction, H is the filter and ø,„, is the peak frequency of the fully developed state according to Pierson and Moskowitz (1964)

Although the specified wind speed in SWAN is U10, the speed at 10m elevation,

the friction velocity Us is used in computation, Us is obtained by:

a-mo{o0ast [ant seø-ø)- ly 6.13)pel ee

In which cụ, is the phase speed, p, and py are the density of air and water respectively,

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