Shoreline Changes Due to Breakwater around Navigation Channel of

Belawan Port

Chairunnisa, Siti Nur Atiah and Rizki Wahyuni

Civil Engineering Department, Universitas Jenderal Achmad Yani, Cimahi, West Java, Indonesia

Keywords: Shoreline, Breakwater, Belawan Port.

Abstract: Shoreline change is caused by longshore sediment transport which is the effect of nearshore wave induced

current. Other causes are physical condition and coastal geomorphology such as bathymetry contour and

coastal protection structure. This paper studies shoreline change in Belawan Port which is located in North

Sumatra, Indonesia. In study area, breakwater is proposed to protect the navigation channel of Belawan Port

from sedimentation problem. The objective of this study is to predict shoreline change around Belawan Port

due to the existence of breakwater by using one-line model, GENESIS. GENESIS is used for predicting the

behaviour of shorelines in response to coastal engineering and/or beach replenishment activities that may

affect long shore sediment transport. The input of the model are bathymetry contour and shoreline position,

waves characteristics (height, period and direction), median sediment diameter (d50), and structure position

and its estimate permeability. The output of the model is the change of shoreline position after a period of

time. Shoreline change around Belawan Port has been analysed under the effects of existing breakwater.

The existence of breakwater can change the natural balance of sediment transport and affect the shoreline

change that occurred.

1 INTRODUCTION

Shoreline change is a natural process which caused

by sediment transport. Sediment can be transported

by current (gravity-, wind-, wave-, tide- and density-

driven currents), by the oscillatory water motion

itself (wave-related transport) or by a combination of

currents and short waves, while in coastal waters the

sediment transport processes are strongly affected by

the high-frequency waves which generally act as

sediment stirring agents; the sediments are then

transported by the mean current (Rijn, 1993).

Shoreline change is primarily driven by the gradients

in total longshore sediment transport and by the

cross-shore transport owing to variability in incident

wave energy (Idier, et.al, 2018). Longshore and

cross-shore sediment transport leads to shoreline

changes, and an accurate prediction of sediment

transport is possible only if the wave and current

hydrodynamics of the coastal area is well understood

(Balas, et.al, 2011).

The development of coastal structures

significantly affects the natural balance of sediment

transport and may cause erosion and accretion in the

coastal areas. The main problems in coastal structure

development is determine sediment movement

patterns or shoreline change patterns that have been

happened or will happen to certain period of time.

By knowing the pattern that happened then the

optimal coastal structure development will be

achieved (Pranoto, 2007).

Shoreline changes due to coastal structures

existence is studied by many researchers. Vaidya et

al. (2015) studied shoreline response to coastal

structure, the result showed there was deposition on

the up drift side and erosion on the down drift side

of the groin, the effect of the increased length of the

groin beyond surf zone is almost negligible, and

since a longer groin traps most of the sand it results

in more erosion on the down drift side. Balas et al.

(2011) observed erosion between two existing

coastal structure, groin and breakwater, which

happen because this groin disturbs the sediment

transport that feeds the beach, and based on

numerical study that to prevent the erosion it is

necessary to remove the previously constructed

groin.

Mathematical modelling of shoreline change is

very useful for understanding and predicting the

long-term evolution of the sandy beaches due to the

Chairunnisa, ., Atiah, S. and Wahyuni, R.

Shoreline Changes Due to Breakwater around Navigation Channel of Belawan Port.

DOI: 10.5220/0008374000550059

In Proceedings of the 6th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management (ISOCEEN 2018), pages 55-59

ISBN: 978-989-758-455-8

construction of these coastal structures. This paper

study the shoreline changes due to breakwater

around navigation channel of Belawan Port, so the

effect of this structure in the future can be estimated.

2 STUDY AREA

Belawan Port is located in North Sumatera,

Indonesia. Its mathematical coordinates are 03°47’

North Latitude and 98°42’ East Longitude. The

location of Belawan Port is very strategic, adjacent

to the Malacca Strait which is an international

navigation lane. As the gateway to the economy of

the North Sumatra region, Belawan Port must

increase port services in the form of facilities and

equipment.

Figure 1: Belawan Port Location.

One of the keys to the development of Belawan

Port is the improvement of navigation channel

capacity, which can be done with several

development scenarios such as increasing the width

of the navigation channel and its depth, or by

determining the location of a new channel. However,

considering the natural condition of Belawan port is

located in the mouth of two rivers and open water,

so naturally it has problems with the hydraulic and

environmental aspects which have the potential to

cause sedimentation. Thus, the planned development

scenario must be able to respond to these natural

phenomena. The sedimentation phenomenon is a

consequence of the existence of Belawan Port, so

that sedimentation behaviour needs to be well

recognized so that port development can be carried

out optimally.

Figure 2 present a scenario that proposed for

Belawan Port development with considering the

sedimentation phenomenon. In the scenario, a new

location of navigation channel is proposed with -14

m LWS depth, 140 m width, and 1: 6 slope. To

prevent sedimentation, the Belawan river was

diverted, and the breakwater is proposed to be built

in the left and right of the navigation channel from

shore area until -10 m depth. The length of the

breakwater is about 9-10 km.

Figure 2: Belawan Port Development Scenario.

In addition to the phenomenon of sedimentation

in Belawan, there have been significant shoreline

changes around the Port of Belawan. This can be

observed by comparing the shoreline on 1984

satellite imagery with 2018 (Figure 3). In a period of

34 years there has been considerable erosion and

accretion. Erosion occurred on the coast to the right

of Belawan port which reached ± 200 m, while

accretion occurred on the coast to the left of

Belawan Port which reached ± 100 m. The amount

of erosion and accretion that occurs, shows that the

shore around Belawan Port are quite dynamic.

Considering the length of the proposed breakwater is

quite long, 9-10 km, it certainly will have an effect

on the balance of the natural sediment transport in

that location, so that it needs further analysis.

Figure 3: Belawan Shoreline Position in 1984 and 2018.

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

3 METHODOLOGY

Generally, this study is carried out following the

stage of data collection, literature study, data

analysis, simulation, and evaluation. The flow chart

can be seen in Figure 4.

Figure 4: Flow Chart of Study.

Data collection includes the information of

coastal area (shoreline position), bathymetry

contour, global map, wind data (velocity and

direction), sediment size, and other related data.

Analysis is conducted for wind data. Wind data is

analysed statistically to get the dominant wind event

at study area, and to forecast wave event using

hindcasting analysis. The result of hindcasting

analysis is time series of wave height and wave

period. Wave time series, shoreline position, median

sediment diameter (d50), and structure position and

its estimate permeability, will be used as the input

for shoreline change simulation with GENESIS.

Furthermore, shoreline change due to breakwater

around navigation channel of Belawan Port can be

predicted.

3.1 Shoreline Changes Model

GENESIS (generalized model for simulating

shoreline) is numerical modelling system that is

designed to simulate long-term shoreline change at

coastal engineering projects (Hanson, 1989). This

model can estimate the value of long shore transport

rate and shoreline changes due to sediment transport

without or with a coastal structure for a certain

period. The simulating steps can be seen in Figure 5.

Figure 5: Simulating Step by GENESIS.

The calculation process is carried out by

predicting longshore transport based on the shape of

the beach face, while shoreline forecasting will be

calculated by considering longshore transport aspect

that occurs. The longshore transport rate (Q) has a

unit of m3/year, because the movement is parallel to

the coast so there are two alternative movements, the

right and left relative to an observer standing on the

beach facing the sea. Left movement is Qlt, and right

movement is Qrt, so that obtained gross sediment

transport rate (gross), Qg = Qlt + Qrt and level of net

transport (net), | Qn | = Qlt – Qrt.

Qg values are used to predict siltation levels in an

open water channel, Qn is used for protected groove

designs and estimates of coastal erosion, and Qlt and

Qrt for the design of sediment build up behind a

coastal structure that withstand sediment movement.

In the calculation of the Genesis model, longshore

transport calculations are carried out using the result

of equation modification from the equation:

Q (+) = ½ (Qg + Qn) (1)

Q (-) = ½ (Qg – Qn) (2)

The results of the modified equation are written

in the following equation:



),a(



































tan416,1

cos

2sin

416118

(3)

Where:

H = wave height

Cg = speed of wave motion (based on wave

theory linear)

Shoreline Changes Due to Breakwater around Navigation Channel of Belawan Port

a = 1 - sand porosity in the coastal area

ρs = sand density

ρ = density of water

θb = the angle of breaking waves is measured

from the local coastline

k1 = approach coefficients form the relationship

between transport values and long shore energy

k2 = coefficient of comparison between beach

slope and breaking wave height

tan β = slope of the coastline along the surf

zone area until the longshore sand transport

4 RESULT AND DISCUSSION

4.1 Wind and Wave Condition

The wind events in 1992-2001 at Belawan Port

showed in Table 1.

Table 1: Percentage of Wind Events in 1992 – 2001.

Percentage of Wind Events

Direction

Wind Velocity (knot)

<10 15-10 15-20 20-25 >25 Total

North 3.621 0.405 0.037 0.001 0.003 4.07

Northeast 13.099 2.106 0.082 0.017 0.004 15.31

East 3.543 0.749 0.064 0.003 0.003 4.36

Southeast 2.113 0.182 0.028 0.012 0.000 2.33

South 3.144 0.084 0.019 0.009 0.001 3.26

Southwest 5.252 0.113 0.036 0.013 0.004 5.42

West 6.054 0.14 0.015 0.006 0.003 6.22

Northwest 3.841 0.233 0.036 0.004 0.003 4.12

Percentage of wind events 45.08

Percentage of calm 54.92

Total 100

The wind event in the port of Belawan is

45.08%, with the dominant wind coming from the

Northeast which is 15.31%, while the calm condition

(no wind) is 54.92%.

Wave data is obtained from wind data analysis,

hindcasting. The result of hindcasting is wave height

and wave period. The wave events in 1992-2001 at

Belawan Port showed in Table 2.

Table 2: Percentage of Wave Events 1992-2001.

Percentage of Wave Events

Direction

Wave Height (m)

<0.25

0.25-

0.5

0.5-

0.75

0.75-1 1-1.5 Total

North 2.65 0.53 0.08 0.01 0 3.27

Northeast 7.95 3.39 1.49 0.53 0.10 13.47

East 2.26 0.78 0.29 0.11 0.07 3.51

Southeast 1.32 0.27 0.10 0.03 0.00 1.72

Northwest 3.06 0.45 0.10 0.02 0.00 3.63

Percentage of wave events 25.60

Percentage of calm 74.40

Total 100

The wave event in Belawan port is 25.6% with

the dominant wave coming from the Northeast

which is 13.47%, while the calm condition (no

wave) is 74.4%.

4.2 Shoreline Change Prediction

Shoreline change prediction has been analysed by

GENESIS, in two conditions, without and with

breakwater, based on the development scenario that

proposed. The length of shoreline which analysed is

nearly 9900 m, with grid interval is 100 m. The

initial shoreline that simulated is based on shoreline

in 2008. The result of simulation without breakwater

will be compared to shoreline in 2018 to obtain the

best calibration coefficient (K1 and K2). The median

sediment diameter (d50) is 0.086 mm, which is

obtained from survey result. The wave parameters

that used in this simulation are the result of

hindcasting analysis from 10 years of wind data,

1992-2001. The beach slope is 0.005, and the

permeability of breakwater is assumed 0.8.

Figure 6: Belawan Shoreline Position in 2008.

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

Figure 7: Simulation Grid.

Figure 8 show the prediction of shoreline position in

2018, and Figure 9 show the erosion and accretion

which occurred and caused shoreline change.

Figure 8: The Prediction of Shoreline Position in 2018.

Figure 9: The Prediction of Shoreline Change in 2018.

The first simulation (without breakwater) is

proposed to obtain the calibration coefficients with

comparing accretion and erosion from simulation

result with accretion and erosion that observed from

satellite images (Google Earth). The best calibration

coefficient K1 and K2 are 0.08 and 0.4. From the

simulation result, there is erosion and accretion in

some place which cause shoreline change. The

average erosion is -6.8 m and the average accretion

is 7 m.

From Figure 9, it showed the effect of

breakwater existence (breakwater position are in

grid 39 and 45). Inside navigation channel, the

existence of breakwater can decrease accretion. The

breakwater existence doesn’t change the pattern of

accretion and erosion that occurred, but it decreases

the amount of accretion and erosion. In the left side

of breakwater position, the decreasing of accretion

and erosion is bigger than the right side. Considering

the incoming wave direction and the layout of

breakwater, breakwater might protect the shore from

the East wave that effect in decreasing accretion and

erosion. The East wave is not the dominant event,

but it has medium amplitude.

5 CONCLUSION

Shoreline position can change due to sediment

transport, longshore and cross-shore. In this study,

shoreline change due to longshore sediment

transport has been simulated by GENESIS. The

existence of breakwater can change the natural

balance of sediment transport and effect the

shoreline change that occurred. In this study, the

breakwater has 9-10 km length, as a long structure, it

also protects the shore from incoming wave which

effect decreasing the amount of accretion and

erosion.

In this study, the analysis of longshore sediment

transport is caused by longshore current which is

wave-driven current, and not consider the effect of

another current (gravity-, wind-, tide- and density-

driven currents). For further study it is suggested to

analyse the longshore sediment transport which is

caused by mean-current, and also consider sediment

input from the river in order to have more accurate

result.

REFERENCES

A. M. Vaidya, S.K. Kori, M.D. Kudale, 2015. Shoreline

Response, Aquatic Procedia 4, 333 – 340

H. Hanson, N.C. Kraus, 1989. GENESIS, Report 1,

Technical Report CERC-89-19.

L. Balas, A. Inan, and E. Yılmaz, 2011. JCR, SI 64, 460-

463

Robinet, D. Idier, B. Castelle, V., 2018. Marieu, Shoreline

Change Model, Environmental Modelling & Software

Vol. 109, 1-16.

S. Pranoto, Perubahan Garis Pantai, 2007. Berkala Ilmiah

Teknik Keairan Vol. 13.

Van Rijn, L., C., 1993. Sand Transport Formula. URL

http://www.leovanrijn-sediment.com/

Shoreline Changes Due to Breakwater around Navigation Channel of Belawan Port