Coastline Dynamic in Belitung Timur: A Hydrodynamic and

Sediment Transport Model Approach

Hariyadi

, Pratomo Danar Guruh

, Handoko Eko Yuli

, Froditus Nicolody Ofirla Eflal

Wirasatrya Anindya

, Yusuf Muh

and Hutabarat Johanes

Department of Ocean Engineering, Faculty of Fisheries and Marine Sciences, University of Diponegoro,

50275, Semarang, Indonesia

Geomatics Engineering, Institut Teknologi Sepuluh Nopember, 60111, Surabaya, Indonesia

Keywords: The Coastline Dynamic, Belitung Timur, Hydrodynamic, Sediment Transport.

Abstract: This research developed a three-dimensional hydrodynamic model to simulate the flow and sediment transport

pattern in Belitung Timur coastal area. The hydrodynamic model was formed by sea level variations and river

discharges to generate the simulation of the flow pattern in the research area. Based on this simulation, a

sediment distribution pattern was modelled to understand the accretion and erosion processes in the research

area. The sediment transport model implemented non-cohesive and cohesive sediment classes. The advection-

diffusion algorithm was utilized to get the picture of suspended-sediment transport pattern in water column.

Flux formulations were implemented to understand the erosion and deposition of the sediment. The maximum

current magnitude is 0.3 ms-1 which occurs during spring tide period. The sediment transport rate is 18 x 10-

4 m2s-1 with alteration of the depth is approximately 0.2m up to 0.6m. The sedimentation processes in the

area could modify the coastline morphology and ultimately will affect the boundary definition in this area.

1 INTRODUCTION

The coastline is an area with unique ecosystems

which is interconnected with the beach. A coastal area

is a very dynamic area as well as its coastline

(Mukhtar, et.al, 2018). The coastal area in Belitung

Timur regency is active as many activities located in

this area. The regency contributes great revenue to the

state from the mining sector especially minerals.

Belitung Timur has a potential of a unique natural

resources especially sand, kaolin, quartz, and lead

mining activities (Natasia, et.al, 2016). These mining

activities, apparently, cause various effects on the

environment such as changes in the coastline.

In addition to mining activities, changes of

coastline also caused by the abrasion in the coastal

area because of the dynamics of the ocean. Here, the

hydrodynamics modelling was used to monitor the

alteration of the coastline in Belitung Timur. In this

research, a hydrodynamic model was utilized to

analyze changes in coastline due to the dynamics of

the ocean. The research attempted to investigate the

variations of the shoreline dynamic in Belitung Timur

due to mining activity based on the sediment

distribution pattern.

2 IMPLEMENTATION OF

RESEARCH

2.1 Research Area and Data

The location of this research is on the eastern coastal

area of Belitung Timur, Bangka Belitung province.

The geographical location of the area is 2˚20’00” S

and 108˚00’00” E to 3˚20’00” S and 108˚40’00” E,

which is shown in Fig 1.

The main spatial data used in this research was

derived from Belitung Timur Chart with 1:200,000 in

scale provided by Pushidrosal (2001). The hydro-

oceanographic data used in the research are

bathymetry data, tidal, river discharge, and wind of

Belitung Timur. In addition to these data, cohesive

and non-cohesive sediment samples are also used to

generate the model which sand is the dominant

sediment type in the area.

Hariyadi, ., Guruh, P., Yuli, H., Eﬂal, F., Anindya, W., Muh, Y. and Johanes, H.

Coastline Dynamic in Belitung Timur: A Hydrodynamic and Sediment Transport Model Approach.

DOI: 10.5220/0008848601950199

In Proceedings of the 6th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management (ISOCEEN 2018), pages 195-199

ISBN: 978-989-758-455-8

195

The research utilized Delft3D as a hydrodynamic

modelling software, ArcGIS 10.3 to perform the on-

screen digitation process, Matlab R2014a to support

the data processing, and file format conversion

software.

Figure 1: Belitung Timur Chart (Pushidrosal).

2.2 Methods

The early stages of the data processing in this research

is rectification and on-screen digitation of the

Belitung Timur chart using ArcGIS. This is

performed to produce coastlines in a shapefile (*.shp)

format. The next stage is building a mesh. The

process was accomplished by using RGFGRID

module. The grid used in the research is a structured

grid type, with rectangular shape model.

The mesh is created by merging the grid and

depths data using QUICKIN module. The

interpolation used a triangular irregular network

method. The main parameter of flow generators is

from the water level variation. The open boundaries

condition in this research is generated by water level.

The simulation model was run for 29 days from

November 26 to December 26, 2017 with time frame

that is divided into 4.5 days (warming up), 0.5 days

(spin up), and 24 days (simulation). In this research

used time step 0.5 seconds which considered terms of

stability (CFL - Courant Fredrich Lewy).

3 RESULTS AND DISCUSSION

3.1 Domain Model (Mesh)

The research used 500m × 500m grid for representing

the modelling area. Fig 2 shows the grid used in the

research.

Figure 2: Grids model of the research area.

The result of a depth interpolation process with a

triangular interpolation grid method on entire grid

models can be seen in Fig 3.

Figure 3: Model Domain.

ISOCEEN 2018 - 6th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management

196

3.2 Tide

Tide observation is used as an input parameter of the

model. The tidal power generator and the flow are the

main force for simulating the hydrodynamics

condition in the vicinity area. Based on the tidal

analysis, Belitung Timur water has mixed

semidiurnal dominant tide type.

Figure 4: The Comparison Between Tide Observation and

Model Data.

Fig 4 shows the comparison diagram of the

observation tide and the model data. Data modeling

in the time window has a Mean Absolute Error

(MAE) of 0.004m This indicates that MAE value

obtained is relative small, with error rate belongs to

small classification (Wilmott and Matsuura, 2005).

The Formula 1 shows the calculation of MAE:

𝑀𝐴𝐸 





∑

𝑥

,

𝑥

,



 0.004 𝑚𝑒𝑡𝑒𝑟𝑠





(1)

Based on the statistic tests, the results comply the

requirement. The next process is building sediment

transport model according to the flow model

(Khotimah, 2012).

3.3 Hydrodynamic Modelling

Process modelling of hydrodynamics generate the

conditions of flow and sediment transport modelling

approach of motion dynamics of the sea in Belitung

Timur. In this research generated simulation of the

flow indicated by Fig 5, as follows:

(a) Spring Tide

Figure 5: Patterns of Flow at (a) Spring Tide Period and (b)

Neap Tide Period.

Coastline Dynamic in Belitung Timur: A Hydrodynamic and Sediment Transport Model Approach

197

(b) Neap Tide

Figure 5: Patterns of Flow at (a) Spring Tide Period and (b)

Neap Tide Period (cont.).

The flow pattern was analyzed in two periods

(spring and neap tide periods). During the spring tide

(Fig 5a), the depth average velocity is between

0.05ms

-1

to 0.3ms

-1

. The largest flow velocity occurs

on Selandu Island. The largest velocity of flow also

occurs on Selandu Island in the neap tide period.

Overall flow during this period between from

0.05ms-1 to 0.2ms-1. The dominant flow direction

on both a period is moving from deep sea towards the

land on flood conditions. In contrast to the dominant

ebb tide conditions leads to Northest and Southeast.

Analysis of sediment distribution pattern in this

research based on the condition from magnitude of

the mean total transport, shown in Fig 6.

Figure 6: The Mean Total Transport at Belitung Timur.

Fig 6 shows the largest sediment transport

conditions occur around at Selandu Island

(designated by red box), yet the magnitude of

sediment transport is relative still small conditions,

between 4x10-4 m2s-1 to 8x10-4 m2s-1.

3.4 The Coastline Changes

In order to show the coastline changes in Belitung

Timur, the analysis process was performed by

creating the cross-sections of the seabed at the coastal

area. The comparison is completed by taking pieces

of the transverse cross-section from the beach to the

deep sea areas in 3 conditions: initial, middle, and

finish from simulation condition. Fig 7 and 8 show

the comparison chart of the bed level from some

samples of the transverse cross-section in the

Belitung Timur.

Figure 7: The Cross-Section of North Coastal Area from

Linggang’s River.

ISOCEEN 2018 - 6th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management

198

In Fig 7, the erosion occurs in 10.0m to 25.0m of

the depth from the coastal area. The depth variation

arises in approximately 0.2m to 0.6m deeper than

initial conditions. The coastal area was altered;

however, the alteration is not significant.

Figure 8: The Cross-Section of South Coastal Area from

Linggang’s River.

The sample of the transverse cross-section at

South of Linggang’s River, shown by Fig 8. Notice

that the erosion occurred at a distance 5.0m to 10.0m

from coastal area. The change of the depth ranges

from 0.2m to 0.4m. It is clearly shown that at the

distance of 10.0m to 15.0m from the coastal area, the

activity of erosion and sedimentation is quite

significantly altered from initial condition.

4 CONCLUSION

Based on the results of processing and data analysis,

the coastline changes which occurred in the coastal

area of Belitung Timur because of abrasion. The

magnitude of the changes in the coastline due to

abrasion is maximum 0.6m from the initial condition,

with simulation period is 1 month. The main factors

cause the magnitude of the changes coastline is a

small value of grain size sediment on Belitung Timur,

thus the mainland easily eroded by ocean waves or

current that comes. The mining activities at Belitung

Timur also accelerate the change of shoreline.

REFERENCES

C.J. Willmott, K. Matsuura, 205. Adv MAE and RMSE,

Clim. Res., 30.

M. K. Mukhtar, T. Hariyanto, C. B. Pribadi, 2018. Evaluasi

Perubahan Garis Pantai, POMITS.

M. K. Khotimah, 2012. Validasi Tinggi Gel. Sig., UI.

N. Natasia, M. N Barkah, D. H. Saputra, M. K. Alfadli,

2016. Studi Awal Potensi Bahan Galian Pada Daerah

Kabupaten Belitung Timur, BSC 14.

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