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

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

Ha Noi, January 2016

Vu Duy Toan

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

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

‘unconditional support

2.1, Overview of the study area 42.2, Data for shoreline and beach monitoring I2.2.1, Climatology Is

2.2.2 Hydrodynamics Is2.2.3, Geology and Geomorphology 192.24, Wave characteristies 1922.5 Sediment Transport Regime in Nha Trang 202.3, Analysis Nha Trang coastline evolution 22.4, Conclusion 24CHAPTER 3 APPLY OF ONE-LINE MODEL TO STUDY NHA TRANGCOASTLINE EVOLUTION.

3.1 SWAN MODEL

3.12 SWAN model setup 303.2 GENESIS MODEL 23.2.1, Basic theory of Genesis model 23.22 Setup Genesis model 7CHAPTER 4 PROPOSE ORIENTED SOLUTIONS TO STABILIZE NHA.TRANG BEACH << neserereirrrrrrrirrrrrrrrrroouSổ)4,1 Scenarios simulated with protective structure 564.1.1, Scenarios Nha Trang coastline evolution without protective structure for 1year, 5 years, 10 years 564.1.2, Scenarios Nha Trang coastline evolution with protective structure for 1year, 5 years, 10 years 584.2, Scenarios simulated with beach nourishment 61

CONCLUSION.

REFERENCES

APPENDICES

LIST OF FIGURES

Figure 1.1 Nha Trang coast (Source: Google earth) ixFigure 1.2 Conceptual framework of Nha Trang Coastline evolution study xiiFigure 1.3 Input and output file structure of GENESIS 8Figure 1.4 Calculation diagram of Genesis model 10Figure 2.1 The discharge from Cai River in the year of 2013 as well as the meanrainfall in Nha Trang in the years 1995 ~ 2014 16Figure 2.2 The variation of the wind magnitude and ditection for September duringthe years of 2002 ~ 2011, ie during the southwest monsoon 7Figure 23 The variation of the wind magnitude and direction for November duringthe years of 2002 — 2011, ie during the northeast monsoon, 7Figure 2.4 The tidal level variation in the south of Nha Trang bay in the year of 2013measured at Institute of Oceanography Tide Station in Nha Trang 18Figure 2.5 Wave rose offshore Nha Trang 20Figure 2.6 Nha Trang shoreline over years from 2003 ~ 2015 23Figure 3.1 Computational domain of Swan model 31Figure 3.2 Wave height boundary condition for Swan model 3Figure 3.3 Wave period boundary condition for Swan model 33Figure 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 shelf109.5, 12.5) (From January to December, 2013) 37Figure 37 Wave Period of Swan model & Wavewatch III data at Continental shelf109.5, 12.5) (From January to December, 2013) 37Figure 3.8, Wave Period of Swan model & Wavewatch IT data at Continental shelf109.5, 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) 38Figure 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 Continentalshelf 2 (109.5, 12.0) (From January to December, 2013) 39Figure 3.12, Wave height of Swan model & Wavewatch IIT data at Continental shelf 1(109.5, 12.5) (une to August, 2014) 40Figure 3.13, Wave period of Swan model & Wavewatch III data at Continental shelf 1(109.5, 12.5) (From June to August, 2014) 40Figure 3.14, Wave height of Swan model & Wavewatch III data at Continental shelf 2(109.5, 12.0) (From June to August, 2014) 41Figure 3.15, Wave height of Swan model & Wavewatch III data at Continental shelf 2(109.5, 12.0) (From June to August, 2014) 41Figure 3.19 Extract wave data points as boundary conditions for Genesis model 48Figure 3.21 Wave height for genesis boundary condition sọFigure 3.22 Wave Period for Genesis boundary condition SIFigure 3.23 Wave Direction for Genesis boundary condition 51Figure 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 55Figure 4.1 Nha Trang coastline evolution without protective structure over years 56Figure 4.2 Nha Trang shoreline position over ten years 38Figure 4.4, Result of Scenario with three Breakwaters over 10 years 9Figure 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

15

32

36Table 3.3 Root mean square percentage error with different cases for Nha Trangshoreline

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

s4

3737370

60

61

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

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

‘unconditional support

Study area

Nha Trang is a coastal city and capital of Khanh Hoa province The study area islocated at the vicinity of Cai River, the north is Cai River and at the south of studyarea 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 NhaTrang Bay meets these criteria above, Nha Trang has many beautiful beaches, thebeach along Tran Phu Street with a length of about 7 kilometers is the most famousbeach

Nowadays the city experiences new possibilities to earn capital as tourists are drawn tothe atea, Many people come for the appealing weather, but the long and central locatedsandy 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 Alongthe 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 toconsolidate, upgrade sea dykes and to build coastal structure protection

Coastline evolution process is very complicated, which varies in space and time Theprocess is strongly related to nearshore hydrodynamic condition including tidalcirculation, wind wave, wave-induced currents combined with storm surge Especially

it becomes more and more complicated and stronger duc to climate change and sealevel 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 thebathymetry, 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, forcoastline evolution and coastal erosion.

~ Applying Genesis model to predict shoreline changes for the background scenarioafter | 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 structureafter 1 year, 5 years, and 10 years

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 ShorelineEvolution of Nha Trang Bay Using Video-Camera’, Binh et al (2014) indicated thatthe 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 yearrelating to the degeneration of a river mouth sand spit, In particular, the erosion iscaused by waves which are generated by northeast monsoon resulting in longshoresediment transport directed from north to south, Moreover, shoreline retreat ormonsoon 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 tocertain parameters like wind, wave, seasonal river discharge, and water level

Nguyễn Trung Việt et aL, “Seasonal Evolution of Shoreline Changes in Nha TrangBay, Vietnam’, 2016 Viet et al (2016) showed that coastline evolution due to bothhuman 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 aboutnatural 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, marinedegradation);

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 Inthis 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 andvertical patterns of nearshore currents effectively transport beach sediments

‘Sometimes this transport result only in a local rearrangement of sand into bars andtroughs or into series of rhythmic embayment cut into the beach At other times thereare extensive longshore displacements of sediments, possibly moving hundreds ofthousands of cubic meters of sand along the coast each year, Longshore sedimenttransport 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 coastalengineering design practice

Currents associated with nearshore cell circulation generally act to produce only alocal rearrangement of beach sediments, The rip currents of the circulation can beimportant 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 ofsediments are wave breaking obliquely to the coast and the longshore currents theygenerate, 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 aretermed the littoral drift This longshore movement of beach sediment is of particularimportance in that the transport can either be interrupted by the construction of Jettiesand 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 adjacentbeach communities, as well as threaten the usefulness of the adjacent navigable

waterways

The litioral transport can also result from the currents generated by alongshoregradients 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) Theresult is transport in the “upwave" direction on the downdrift side of the structureThis, in turn, can ereate a buildup of sediment on the immediate, downdift side of thestructure or contribute to the creation of the crenulated-shaped shoreline on thedowndrift side of a headland,

Also in recent times, the World and Asian countries attach great importance to thestudy 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 onestuaries 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 ofcoastal and estuarine search is the prediction of coastal sediment transport, whichhhas been developed and matured, as represented by research

therlands,

cientists to the UnitedStates, 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 usinghydraulic 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 ischaracteristic 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 waveclimate cause the position of the shoreline to move shoreward and seaward in acyclical 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 relativelysmall 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 thecourse 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 andvolume as the beach erodes and accretes This contour line is conveniently taken as thereadily observed shoreline, and the model is therefore called the “shoreline change” or

‘shoreline response” model Sometimes the terminology “one-line” model, ashortening of the phrase “one-contour line” model, is used with reference to the singlecontour line

‘A second geometrical — type assumption is that sand is transported alongshore betweentwo well ~ defined limiting elevations on the profile The shoreward limit is located atthe top of the active berm, and the seaward limit is located where no significant depthchanges 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 beachcross-sectional area by which changes in volume, leading to shoreline change, can becomputed,

‘The model also requires predictive expressions for the total longshore sand transportrate, For open-coast beaches, the transport rate is a fun n of the breaking waveheight and direction alongshore Since the transport rate is parameterized in terms ofbreaking wave quantities, the detailed structure of the nearshore current pattern doesnot 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, tidalfluctuations, and other cyclical and random events In essence, the assumption of aclear trend implies that the wave action producing longshore sand transport andboundary conditions are the major factors controlling long-term beach change Thisassumption is usually well satisfied at engineering projects involving groins, jetand 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 equipmentand ealeulation technique has allowed us to simulate the process of evolution of thecoastline via computer programs which solve complicated math equations on thephysical phenomena involved, Mathematical model with its special abilities andincreasing popularity has proved to be superior to other research methods throughshort implementation time, flexibly in changing simulation scenarios, and highresolution of results, Of course, due to the limitations in modeling, the exactness of

equations and completeness of data input, the solution obtained from the mathematicalmodel is not absolute accurate, especially in quantitative terms If the mathematicalmodel is combined with other methods it is adequate to give us more reliableforeca 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 theyare increasingly complete and advanced Bruun’ original model (1962) solely accountfor the rising water levels due to climate change and tectonic subsidence activities topredict changes in the coastline The more modem computer programs such asGENESIS (US Navy shore CERC combined with Lund university), UNIBEST by theInstitute 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 themorphology 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 widelyused 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 Processesand 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 theinput wave data is imported by time series On the other hand, this model was based onthe 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-linetheory 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 coastsare) is built and developed by Hydraulic Institute Delft - Netherlands (WL - DelftHydraulics) This software aims to establish a more complete studies and calculatedlongshore sediment transport as well as study of relationships morphology betweensoil dynamics coast to coast surface shape (shoreline evolution),

UNIBEST process consists of two modules:

6

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

~ UNIBEST-CL+: for calculating shoreline evolution due to differences sedimenttransport Longshore sediment transport is considered the effects of runoff and tidalwaves, 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 theinput data for the module to calculate CL shoreline changes, which takes into accountthe form of coastal structures like: embankment, groins, offshore breakwaters or acombination 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 ofrandom waves propagating from deep to shallow water, Longshore and cross-shoresediment 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

storm

©) Sub-module UNIBEST CL

‘The CL sub-module is set to calculate shoreline changes due to differences overloadlong shore for coastlines near the road are in theory a (single line theory) Theboundary conditions and different initial conditions are included, offering varioussituations 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 beachnourishment systems or beach replenishment projects The effects of wave diffractionbehind 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 longshoresediment transport over time and space, in which consider including the shorelinechange 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 worksuch as soldering, wave direction dyke, detached breakwater, pier and beachreplei ishment projects ashore.

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

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

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 offshorebreakwater

~ 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 thetheoretical calculations shoreline changes

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

Hi6iT Di

Protection structures,boundary condition

Breaking | | Shoreline evolution Long shore Sediment

wave Ay, ‘Transport Q,

Họ, Oj T

Figure 1.4 Calculation diagram of Genesis model1.3.5 Comparision of three one-line models

10

Table 1 Wave in evaluated models

Waves GENESISToternal wave modal Ỹ

Coupled spectral wave model Ỹ

Table 2 Structures in evaluated models

GENESIS |LITPACK | UNIBEST

Breakwaters Y Y Y

Beach fill Y Y YĐiffracũng groin Y Y Y

‘Detached breakwater transmission Y N NA

“Time dependent breakwater transmission Y N NA

‘Water level dependent wave transmission Y N NAWave reflection from structures N N NWave 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 | UNIBESTTiet 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 NAVariable grain size N Y NA

Table 6 Other included processes, modules, or features in evaluated models,

GENESIS [LITPACK | UNIBESTDirect provision or changing Hide level Y Y YTidalfother non-LST cunentx Y Y YOfflhore contour Y Y NAWind-driven transport N N YRegional contour Y NA NA

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

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

vertical)

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

same issue through addition of a regional contour LITPACK does not includecither 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 andtechnology and tourism in the province of Khanh Hoa, Vietnam Before becoming theland of Vietnam, la Trang belongs to Champa The ruins of the Cham remain inparts of Nha Trang Nha Trang is known as the peat! of the South China Sea, the greenjewel 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 anddevelopment

Nha Trang terrain with elevations quite complex ranging from 0 to 900 m above sealevel is divided into three topographical regions Coastal plains and along Cai coversabout 81,3 km? accounting for 32.33% of the whole city; transition zone and Tow hillswith a slope of 30 to 150 mainly in the west and southeast, or on small islands aecountfor 36.24% of the atea, mountainous terrain is steep on both ends 150 distributed inNorth - South of the city, on Hon Tre island and some islands accounted for 31.43% ofthe 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 hurricanesaffecting 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 influencingKhanh 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 affectdirectly to Nha Trang with highest level This storm makes beach cross section profilesignificantly 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 meanprecipitation 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 mostprecipitation 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 northeastmonsoon 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 CaiRiver 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 ~ 2014Nha 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 recordedwind 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 anddirection of the winds in the months September and November, which represent themonths of the southwest and northeast monsoons, respectivi , during the years 2002

16

= 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,

Wind RoseNovember 2002-2011

NNE 8-12 ms

NE =4-8 mvs

20-4 mvsENE

SSE

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 variesslightly between the higher temperature of 29 degrees Celsius during the summermonths of June, July and August and the mean temperature of 24 degrees Celsiusoccurring 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 Duringthe northeast monsoon, strong waves are entering from the northeast, while during thesouthwest monsoon, weaker waves enters from the southeast Water bodies can also beaffected 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 islinear and thus exert its force in the same direction When being perpendicular to eachother the tide is at its lowest point, called neap tide (Pinet, 1998), Nha Trangexperiences a mix of the diurnal tide and the semi-diurnal tide In Nha Trang thespring tide can reach 2.5 meters and the neap tide can be as low as 0.4 meters (Bui etal., 2014) The tidal level for the year of 2013 can be seen in Figure 2.4

‘Water level {mi os kl a gs

2 4

Time

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 depositssediment in the bay and forms ridges there and thus the sediment is said to haveterrigenous 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, coralsete, The situation is different when looking in small bays that are sheltered on theisland in the bay, where the calcium carbonate content in the sediment reaches a muchhigher 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 sedimentdischarge 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 isbelieved 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 leadingWave northeast direction, with the most intense in the months of November, Decemberand 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 tooffshore wave has southwest direction so wave does not propagate directly into thebay

19

Offshore wave pattern of | Offshore wave pattern of | Offshore wawe pattemNha 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, itseffects can to IV The swell waves which cause a strong impact on bank of Nha TrangBay are those from the East

In Nha Trang bay need to consider to swells due to storm, though the storm is far notcome directly to in Khanh Hoa, especially on stage at the Cai River flood and high tideperiod,

2.2.5, Sediment Transport Regime in Nha Trang

The flow, and thereby also the transport of sediment, is mostly dependent the waveclimates 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 ofprecipitation, 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 tosome extent settled inside the bay while some, normally finer particles, are transportedseaward or sediments are transported further south down the coast and are deposited in

20

for example Cam Ranh, a city about 40 kilometers from Nha Trang When there islittle 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 thebeach 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, isthus 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 inhhow the transportation is affected By being an obstacle to the Southeast Sea, thesediment is not affected by offshore drift to the full extent, The islands also affect thewave 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 thesea level alters and a tidal current is generated, But as the current is relatively smallcompared 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 strcurrent with a high velocity that prevents the particles from settling easily, especiallythe fine particles coming from the river That would likely be one of the factorsexplaining the relatively deep passage of 24 meters between the Hon Tre Island andthe mainland (Inman, 1966)

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

21

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

of

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, whichprovides 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 andvisualized in a graph The graph sketched with a distance of $ km, By presentingshorelines from several years in the same graph, trends for the shoreline evolutioncould be seen, Shoreline data is selected for the different years, which allows us toassess 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 newconditions, both naturally and anthropogenically Shorelines can be either accreted oreroded

‘When a beach is exposed to higher wave than normal, sediment from the beach will betransported out into deeper part of the sea with the cross shore current The seasons ofthe year also have a clear relationship to the condition of the beach Long shorecurrents can also influence the natural variation of the complete shoreline orientation,Depending on the strength and angle of the incoming wave, which vary with theseasons, 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 theshoreline to naturally shift in gradient from a plan view Moreover, sea level riseoccurs 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 commoncause 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), thenorthem 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 sedimentexchange between the stream and river banks So under the influence of the floodseason the river flow was pushed closer to the shore line of the South, cause erosion inthe south of Cai River Mouth,

2.4, CONCLUSION

Nha Trang coast lies in area with moderate climate conditions, less affected byextreme weather conditions: wind, rain, water level fluctuation, waves, currents, andstorm However, the coast of Nha Trang has a relatively large impact on peoplebuilding 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 wavedirection E, south shoreline strongly affected both NE and E 2 wave direction, wavedirection 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 SWANinclude wave shoaling, refraction, nonlinear interactions, depth-induced breaking,'wave-curenL interaction, and bottom friction and whitecapping dissipation SWANđoes not account for diffraction or reflections due to bottom scattering SWAN isdriven by local winds and wave input through boundary conditions, and waves aremodulated by tidal currents The numerical scheme is implicit, unconditionally stableand 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 governingequation for Cartesian coordinatesis

ệ h 2 yŸcN+ GN+Ể cN+ = 3.1Nes EN ae ty : GB)

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 relativefrequency and the refraction due to variations in depth and currents,

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

2Dingemans, 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)

Then,

3) 64)

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 tocliminate wave growth at frequencies lower than the Pierson-Moskowitz frequency(Tolman, 19922),

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,

27