Changes of Coastlines Caused by Abration using Multitemporal

Satellite Images: Case Study - Coastal of Gianyar District, Bali

Teguh Hariyanto

, Cherie Bhekti Pribadi

, Akbar Kurniawan

and Mutia Kamalia Muktar

Geomatics Engineering Department, Faculty of Civil, Environment, and Geo Engineering, Institut Teknologi Sepuluh

Nopember Surabaya Indonesia

Keywords: Coastlines, Multitemporal Satelite Images, Gianyar, Bali

Abstract: The beach was a transitional area between land and sea. In Gianyar Regency, Bali stretches the sea along the

southern island of Bali which is an area that is directly adjacent to the coastal area. Of course, this is

inseparable from the dynamics of changes in the physical coast caused by land erosion by sea water (abrasion)

and the presence of sediment transport from the land (accretion) which generally highlight the changes in

shoreline. For this reason, research is needed to determine the magnitude of changes have occurred along the

coastline in 2002 to 2017 resulting in a map of shoreline changes. This research using the ratio interpretation

methods on the SWIR channel and green on Landsat 7 and Landsat 8 imagery plus classification, it can be

used to identify the coastline and analyze the magnitude of the changes that occur.

1 INTRODUCTION

Coastline is an area which has several separate

ecosystems between one ecosystem and another

ecosystem having interconnected and various

functions that are sometimes mutually beneficial or

harmful. Therefore, the coastal area is an area which

has dynamic movement as well as the coastline.

The southeast coast along the coast in Gianyar

Regency has a significant change due to impact of

these two aspect. Erosion of the beach has an impact

to collapse of shores on beach and stalls which

become a resting place for recreation to the beaches

in Gianyar Regency, Bali.

Classification of coastal areas in Indonesia can be

more easily recognized by using remote sensing

methods with temporal and spatial processes. Remote

sensing technology is very supportive in

identification and assessment of resources in coastal

areas and coastline changes, because it has the

advantage of being able to cover large areas with high

spatial resolution, as well as providing many choices

of remote sensing satellites which have good

accuracy in identifying objects on the surface of the

earth.(Hariyanto,2017)

Landsat satellites have the ability to detect

coastline changes using band ratio methods

(Vreugdenhil, C. B. 1999), therefore this study uses

Landsat satellites to determine the coastline changes

in 2002 and 2017 in Gianyar Regency, Bali

2 METHODS

The location of this study is located in Gianyar

Regency, Bali located between 115o13'29” BT –

115

22’23” BT and 8

18’48 ”LS - 8

38’58

"LS.Administratively, boundaries are as follows:

North Side : Bangli Regency

East Side : Klungkung Regency

South Side : Denpasar City and Badung Strait

West Side : Badung Regency

Hariyanto, T., Pribadi, C., Kurniawan, A. and Muktar, M.

Changes of Coastlines Caused by Abration using Multitemporal Satellite Images: Case Study - Coastal of Gianyar District, Bali.

DOI: 10.5220/0008373200330037

In Proceedings of the 6th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management (ISOCEEN 2018), pages 33-37

ISBN: 978-989-758-455-8

Figure 1: Study Area

3 DATA ACQUISITION

The data used in this study are Landsat 7 ETM+ C1

L1TP acquisition date of May 22th 2002, Landsat 8

OLI / TIRS C1 L1TP acquisition date of October 29th

2017, boundary administration of Gianyar regency,

boundary administration district in Gianyar regency,

ground truth of land cover in Gianyar regency was

obtained from measurements to the field, map of

Indonesian environment coast of gianyar regency,

tidal data in Gianyar regency in 2002 and 2017.

4 DATA PROCESSING

4.1 Band Merging

Combining Landsat 7 and Landsat 8 satellite imagery

combine separate bands into one file. Band combined

are blue, green, red and SWIR-1 bands. In this case,

band combined there are 4 bands, namely band 1, 2,

3 and 5 for Landsat 7 satellite imagery, and band

combined there are 4 bands, namely band 2, 3, 4 and

6 for Landsat 8 satellite imagery.

4.2 Sub-setting Image

The case study used is the beach along Gianyar

Regency, Bali. Subsetting image uses a subset of

vectors from the boundaries of Sukawati sub-district,

Blahbatuh sub-district, and Gianyar sub-district.

4.3 Land and Sea Masking

Band Ratio serves to separate the land and sea

regions. The formula used to identify coastlines

covered by sand and soil is a green band divided by a

SWIR-1 band. In this case, the band ratio on Landsat

7 satellite imagery uses a band 2 divided by band 5.

Whereas on satellite imagery Landsat 8 uses band 3

divided by band 6.

4.4 Raster Conversion to Vector

Changing the identified image of land and sea into

vector shapes (.shp) by using Raster to Polyline and

Raster to Polygon tools so that it will produce

coastlines from each image.

4.5 Supervised Classification

This classification to see land cover changes around

the coast. This classification starts with how to make

ROI from the pixels of each class, namely vegetation,

settlements, water bodies, and road bodies. Then the

classification is done with the supervised

classification: maximum likelihood tool, which will

form polygons from the classification results of each

class.

4.6 Accuracy Test

Accuracy test uses omission matrix and commission

which aims to find out whether the classification

process is accurate or not. If the results are above 85%

then tolerance has accepted. Accuracy testing is done

by making an omission table and a commission that

compares the results of the interpretation image with

field test results, then generate overall accuracy.

4.7 Spatial Analysis

Analyzing shoreline changes due to the abrasion of

Gianyar Regency, Bali in 2002 and 2017.

4.8 Map of Coastlines Change in 2002

to 2017

From the results of the image overlay, then the map

lay-outing process is carried out. The resulting map is

a map of shoreline changes due to abrasion in the

Gianyar Regency region, Bali from 2002 to 2017

which has been corrected with tidal data.

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

4.9 Calculation of Coastlines Change

Area in 2002 to 2017

This area calculation is used to determine how much

shoreline changes due to abrasion.

5 RESULT AND DISCUSSION

5.1 Land and Sea Masking

Coastlines change due to abrasion in Gianyar

Regency can be known through Landsat 7 and

Landsat 8 satellite imagery using band ratio method.

Band ratio is used to separate land and sea, so as to

produce coastlines from the image. This method uses

the value of the surface reflectance on radiometric

corrected images.

In this study, the two images used are L1TP levels

which has been orthorectified and radiometric

corrected using GCP from GLS2000 and DEM data

which include SRTM, NED, CDED, DTED, GTOPO

30, and GIMP (USGS, 2017).

The formula used in this method is a green band

divided by the SWIR-1 band, this formula can detect

sand-covered coastlines and land (Alesheikh, 2007)

where in this case study, beach in Gianyar Regency

was a beach covered with sand and soil. The formula

on Landsat 7 uses band 2 divided by band 5 and

Landsat 8 uses band 3 divided by band 6. The

following is the result of using the band ratio formula

on Landsat 7 and 8 satellite images:

Figure 2. Results of Landsat 7 Image Band Ratio

Figure 3: Results of Landsat 8 Image Band Ratio

Figure 4 tell us that Landsat 7 produces a land area

that is in solid gray, and an area of the sea colored in

gray dots. Meanwhile, in Figure 5 tell us that Landsat

8 produces a land area that is black and area of the sea

colored in white. From this process, a clear coastline

can be produced.

5.2 Raster to Vector Conversion

Raster to vector conversion is used to obtain

coastlines that can be calculated and overlayed so it

will be easier to analyze coastline changes due to

abrasion and make a map of coastline changes due to

abrasion. Result of raster to vector conversion on

Landsat 7 and 8 satellite imagery can be seen in the

following figure :

Figure 4: Landsat 7 Coastline Vector in 2002

Changes of Coastlines Caused by Abration using Multitemporal Satellite Images: Case Study - Coastal of Gianyar District, Bali

Figure 5: Landsat 8 Coastline Vector in 2017

Figure 6 tell us that coastline vector from Landsat

7 satellite imagery in 2002, and Figure 7 tell us that

coastline vector from Landsat 8 satellite imagery in

2017.

5.3 Coastline Changes

Coastline changes due to abrasion in Gianyar regency

can be known through Landsat 7 satellite imagery in

2002 and Landsat 8 satellite imagery in 2017 using

band ratio method which is converted into a vector,

so that extensive abrasion can be known. Image

processing results show the abrasion area that occurs

on coast of Gianyar Regency which is presented in

the following table:

Table 1. Changes in Area Due to Abrasion

District Sub-District Village

Abrassion

Area

(km

)

Gianyar

Sukawati

Ketewel 0,065

Sukawati 0,025

Saba 0,015

Blahbatuh

Pering 0,006

Keramas 0,007

Medahan 0,011

Gianyar

Lebih 0,026

Tulikup 0,040

Total

0,195

The results of processing Landsat 7 satellite

imagery in 2002 and Landsat 8 satellite imagery in

2017 show that the abrasion area that occurred quite

large from 2002 to 2017 of 0.195 km2. The village

that was most affected by abrasion is Ketewel Village

of 0.065 km2 Tulikup Village of 0.040 km2, Lebih

Village of 0.026 km2, Sukawati Village of 0.025

km2, Saba Village of 0.015 km2, Medahan Village of

0.011 km2, Keramas Village 0.007 km2, and the most

slightly exposed to abrasion is Pering Village of 0.006

km2. Coastline changes due to abrasion occur purely

due to natural factors, namely the beach located in

high seas zone.

Coastline from satellite imagery also takes into

account natural factors, one of which is the tide. Map

of the coastline changes of Gianyar Regency in 2002-

2017 has been corrected from the calculation of the

tides. The following is a tidal correction calculation:

Table 2. Tidal calculations

Acquisitio

n Date

Tim

HHW

(m)

d (m) m (m)

(m)

(o)

(m)

22 May

2002

10:1

1,391

11,06

384,20

0,32

1,64

0,19

October

2017

10:2

1,476

11,39

412,87

0,08

1,58

0,05

Coastline is carried out by take a point on the

coastline which is assumed that the condition of

seawater has experienced the same increase, after that

it can be calculated the slope of the coast which will

result in a distance of coastline shifting from tidal

correction (x). Highest High Water Level (HHWL) is

obtained from the tidal calculation using the least

square method, the depth value (d) is obtained from

the contour contained in Gianyar Regency, Beach

Environment Map which is corrected with the tidal

reading value when recording the image (η) and the

HHWL value. Coastline in 2002 obtained from

Landsat 7 were drawn ashore in the amount of 0.199

m and coastline in 2017 which is obtained from

Landsat 8 is drawn towards the land of 0.051 m.

6 CONCLUSION

Based on results of this study, there are several things

can be concluded in this study, Landsat 7 and 8

satellite imagery carried out by band ratio method, a

map of the Gianyar Regency coastline changes can be

made in 2002-2017. The results of the processing of

Landsat 7 and 8 satellite imagery show that the

abrasion area that occurred quite large from 2002 to

2017 was 0.195 km2. The village that was most

affected by abrasion is Ketewel Village of 0.065 km2

Tulikup Village of 0.040 km2, Lebih Village of 0.026

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

km2, Sukawati Village of 0.025 km2, Saba Village of

0.015 km2, Medahan Village of 0.011 km2, Keramas

Village 0.007 km2, and the most slightly affected

abrasion is Pering Village of 0.006 km2.

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Changes of Coastlines Caused by Abration using Multitemporal Satellite Images: Case Study - Coastal of Gianyar District, Bali