Sea Level Change and Its Impact To The Coastal Area of Semarang City, Central Java

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L A L U A T I K D A R F I R M A N H A K I M

GRADUATE SCHOOL

BOGOR AGRICULTURAL UNIVERSITY BOGOR

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I, Lalu Atikdar Firman Hakim states that thesis entitled:

SEA LEVEL CHANGE AND ITS IMPAT TO SUBMERGENCE AREA IN COASTAL AREA OF SEMARANG CITY,

CENTRAL JAVA

is result of my own work under supervision of supervisory committee during the period April 2011 – June 2012 and it has not been published. The content of this thesis has been examined by the advising committee and an external examiner.

Bogor, July 2012

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ABSTRACT

LALU ATIKDAR FIRMAN HAKIM. Sea Level Change and Its Impact To Submergence Area In Coastal Area of Semarang City, Central Java.

Under the supervision of VINCENTIUS PAULUS SIREGAR and IBNU SOFIAN.

Sea level changing along the time with Mean Sea Level (MSL) shows increasing trend. Semarang City that facing subsidence also impacted by the change of sea level in term of sea level rise and tides. The recorded and reconstructed data (from CSIRO) shows that global sea level rose to 6.83 cm by Dec-2009. Regional sea level change data from University of Colorado also shows the increasing trend of sea level. Three months (Dec-2011 to Feb-2012) realistic tides model that has been generated using FVCOM shows the highest level of the sea surface was 0.473 m while measured sea level in coastal water area of Semarang City by 2010 was 94.669 cm. Measured sea level has to be corrected because the area where it measured experiencing land subsidence. Correction result shows isostatic mean sea level in 2010 was 52.070 cm. Subsidence rate in the location where sea level has measured (Tanjung Mas) can be estimate with the deviation between mean sea level data from tide gauge that experiencing subsidence and isostatic sea level. The result of estimation shows subsidence rate in Tanjung Mas is 7.1 cm/year. The impact of sea level change until 2011 has been formed 1,043.527 Ha of submergence area. Projection in the future shows that in next ten years submergence area will reach ± 3,627 Ha while in next 15 years submergence area will reach ± 4,364 Ha and in next 20 years submergence area will reach ± 4,641 Ha. When spring tides occur, the impact of sea level change will getting worst because area with altitude up to 0.47 from submergence area will be inundated by seawater.

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ABSTRAK

LALU ATIKDAR FIRMAN HAKIM. Perubahan Paras Muka Laut dan Dampaknya Terhadap Genangan di Daratan Pesisir Kota Semarang, Jawa Tengah. Dibawah Bimbingan VINCENTIUS PAULUS SIREGAR and IBNU SOFIAN.

Paras muka laut terus berubah seiring dengan waktu dimana tinggi paras muka laut rata-rata (MSL) menunjukkan adanya kenaikan dari waktu ke waktu. Kota Semarang yang juga dilaporkan mengalami penurunan muka tanah juga telah terkena dampak dari kenaikan paras muka laut dan pasang surut. Data hasil perekaman dan rekonstruksi dari CSIRO menunjukkan bahwa paras muka laut secara global telah meningkat ke level 6.83 cm di atas 0 pada Desember 2009. Data paras muka laut regional perairan Indonesia dari Universitas Colorado juga menunjukkan pola yang sama yaitu kenaikan paras muka laut dari waktu ke waktu. Dengan menggunakan software FVCOM, model pasang surut selama tiga bulan (Dec-2011 to Feb-2012) juga telah dibuat. Selama rentang waktu tersebut nilai pasang tertinggi yang didapatkan adalah 0.473 m. Nilai rata-rata paras muka laut hasil pengukuran langsung di Kota Semarang pada tahun 2010 adalah 94.669 cm. Nilai ini harus dikoreksi karena stasiun pasang surut dilaporkan telah mengalami penurunan. Hasil koreksi menunjukkan nilai isostatic paras muka laut pada tahun 2010 adalah 52.070 cm. Penurunan muka tanah pada stasiun pengukuran pasang surut dapat diestimasi kemudian dengan menghitung deviasi antara nilai hasil pengukuran dengan nilai isostatic paras muka laut. Rata-rata tahunan penurunan muka tanah yang didapatkan adalah 7.1 cm/tahun. Dampak dari kenaikan paras muka laut pada 2011 adalah adanya 1,043.527 Ha daratan yang tergenang permanen. Hasil proyeksi juga menunjukkan bahwa pada 10 tahun mendatang daratan yang tergenang permanen akan mencapai ± 3,627 Ha, pada 15 tahun ke depan daratan tergenang permanen yang terbentuk akan mencapai ± 4,364 Ha dan pada 20 tahun yang akan datang akan mencapai ± 4,641 Ha. Ketika pasang tertinggi terjadi, dampak dari perubahan paras muka laut akan bertambah buruk karena daerah-daerah dengan ketinggian hingga 0.47 m dari daratan yang tergenang permanen juga akan dibanjiri oleh air laut.

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S U M M A R Y

LALU ATIKDAR FIRMAN HAKIM. Sea Level Change and Its Impact To Submergence Area in The Coastal Area of Semarang City, Central Java.

Under the supervision of VINCENTIUS PAULUS SIREGAR and IBNU SOFIAN.

Since the middle of 19th century, sea level has been rising, primarily as a result of human-induced climate change. During the 20th century, sea level rose about 15-20 centimeters (roughly 1.5 to 2.0 mm/year), with the rate at the end of the century greater than over the early part of the century. Satellite measurements of sea level that taken over the past decade indicate that the rate of increase has jumped to about 3.1 mm/year, which is significantly higher than the average rate for the 20th century. Projections show that the rate of sea level rise is likely to increase during the 21st century, although there is considerable controversy about the level of the increases.

Most of the world’s coastal cities were established during the last few millennia, a period when global sea level has been near constant. Semarang city is one of the cities that founded and established before 19th century where nowadays some part of the land area of Semarang city itself always been flooding. The location of Semarang city is directly heading Java Sea with approximately 21 km of coastline length from east border to west. Coastline of Semarang city has change from 21 km in 2005 to 22.71 km in 2006. Most of coastal and water catchment area in Semarang City is low-lying area and much of it are a subject of inundation during peak tide and rainy season periods. These natural hazards represent a special challenging problem for communities in the coastal regions of Semarang city.

This research was focused on the prediction of sea level change and its impact to coastal area in term of flood. There are two kind of flood that caused by sea level rise i.e. submergence (permanent flood) and inundation (non-permanent flood). Submergence area was analyzed by analyzing regional mean sea level and inundation area was analyzed by combining the highest level of regional mean sea level change and local sea level change (tides).

There area so many factors that affecting sea level change where one of the majority factors is global warming. Global warming is the rise in average global surface temperature caused primarily by the build-up of human-produced greenhouses gases, mostly carbon dioxide and methane, which trap heat in the lower levels of the atmosphere (Lindsay, 2010). Global warming is the majoring factor of global climate change where global climate change is a change in the long-term weather patterns that characterize the regions of the world. Global warming occurs majoring as the effect of the increasing of glass house gasses (especially carbon dioxide) in the atmosphere that can absorb emitted infrared radiation by Earth and release that energy into the atmosphere rather than allowing it to escape to the space. As their atmospheric concentration has increased, the amount of energy "trapped" by these gases has led to higher temperatures. One of the most common energy/light reflectance is infrared where infrared can’t escape to the space by green houses gasses blocked. It makes earth temperature increasing and affecting weather characteristic and pattern in an area or even in the world whether it temperature, wind, and/or precipitation.

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wind, and/or precipitation of a region (Merritts et al. 1998). The sun influences weather, where the sun heats the earth's atmosphere and its surface causing air and water to move around the planet. The result can be as simple as a slight breeze or as complex as the formation of a tornado. Some of the sun's incoming long wave radiation is reflected back to space by aerosols. In addition, some of the sun's energy that has entered Earth's atmosphere is reflected into space by the Earth’s surface (the reflectivity of Earth's surface is called albedo). Both of these reflective processes have a cooling affect on the planet.

Actually, sea level had been changing whole the time even there is no occurences of unnatural phenomenon. The change is called tides, the change in sea level a the impat of meteorological phenomenon.

Knowledge of the tides and their patterns dates back to at least 2300 BC in the ruins of coastal cities along the Gulf of Cambay in India. Here archaeologists have uncovered evidence of tidal docks, structures that allow boats to enter at high tide and, by means of a gate, trap the water and keep the boat afloat when the tide recedes. Indian religious texts from 300 400 BC suggest a link between the tides and the phases of the moon, a highly advanced claim for its time. Because tides may rise and fall in excess of 30 feet (10 meters) in this region, they obviously played an important role in the culture and commerce of these ancient people (Sawicki, 2005).

Several notable scholars advanced theories of the tides (including Galileo) but the first complete and fundamental correct explanation was published in 1687 by Sir Isaac Newton in his Principia. In his theory, Newton introduced the Law of Gravitation which states that the gravitational attraction between two planetary bodies is the product of their masses divided by the square of their distance, times the gravitational constant. Differences in gravity at different points on Earth’s surface cause vertical and horizontal forces but the vertical forces are much too small to generated using FVCOM (Finite-Volume Coastal Ocean Model). DTM (Digital Terrain Model) data as the survey result of City Planning Agency of Semarang City in 2008 were used to generate the submergence and inundated area. The RBI (Indonesian topographic) map combined with satellite images and field survey data were used as the base map to obtain several thematic maps that related to flood analysis and loss hazard estimation. Loss estimation involves the calculation of the vulnerable area with the landuse damage, road network and water channel. The estimation is only limited to the tangible damage or physical direct damage caused by tidal flood.

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The result of correction found that isostatic mean sea level in 2010 was 52.070 cm with 2.54+0.6 cm/year of regional rising value.

This research was not measure subsidence rate, it can be estimated by the deviation between mean sea level data from tide gauge that experiencing subsidence and isostatic sea level. The result of estimation shows subsidence rate in Tanjung Mas area (location where tide gauge located) is 7.1 cm/year. This result is not so differ with latest research result (Abidin, 2010) that found the rate of subsidence in same area was 7.5 cm/year from October to December 2008.

As the impact of Sea level change (regional sea level rise and tides), submergence area that formed in 2011 was 1,043.527 Ha and predicted increase 4.4 times by spring tides. Seawater also covered ±149 km of road and ±67 km water channel, so that those facilities can run it function normally. Future projection shows that in next ten years submergence area will reach ± 3,627 Ha while in next 15 years submergence area will reach ± 4,364 Ha and in next 20 years submergence area will reach ± 4,641 Ha. When spring tides occur, the impact of sea level change will getting worst because area with altitude up to 0.47 from submergence area will be inundated by seawater.

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1. It is prohibited to cite all of part of this thesis without referring to and mentioning the sources;

a. Citation only permitted for the sake of education, research, scientific writing, report writing, critical writing or reviewing scientific problem.

b. Citation does not inflict the name and honor of Bogor Agricultural University.

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L A L U A T I K D A R F I R M A N H A K I M

A thesis submitted for the degree Master of Science in Information Technology for Natural Resources Management Program Study

GRADUATE SCHOOL

BOGOR AGRICULTURAL UNIVERSITY BOGOR

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Name : Lalu Atikdar Firman Hakim

Student ID : G 051090091

Study Program : Master of Science in Information Technology for Natural

Resource Management

Approved by,

Advisory Board

Dr. Ir. Vincentius P. Siregar, DEA. Supervisor

Dr. Ir. Ibnu Sofian, M.Eng. Co-Supervisor

Endorsed by,

Program Coordinator

Dr. Ir. Hartrisari Hardjomidjojo, DEA

Dean of Graduate School

Dr. Ir. Dahrul Syah, M.Agr.Sc.

Date of Examination: Date of Graduation:

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ACKNOWLEDGEMENTS

Alhamdulillahi Robbil ‘Alamiin, Praise be to ALLAH SWT The Greatest,

Lord of the Worlds, The All-Wise. Grateful for all of Your grace, I could

finish my thesis after passing all of the obstacles.

"Whenever ALLAH decides

to create something ALLAH has only to say, ‘Exist,’ and it come into existence.

All glory belongs to the Ones in Whose hands is the control of all things. To

Him you will all return."

(QS 36:82-83)

I would like to express my gratitude first to my supervisors: Dr. Ir.

Vincentius P. Siregar, DEA. and Dr. Ir. Ibnu Sofian, M.Eng. for their

assistance, comment, encouragement, and patience in guiding me to

completing my thesis. My gratitude also goes to Dr. Antonius B.W. for his

question, remark, correction and all of his input as the external examiner and

lecturer. To the M.Sc. in IT for Natural Resources Management program

coordinator, Dr. Ir. Haritasi Hardjomidjodjo, DEA, and all staff in

MIT-Biotrop, my gratitude also goes to them.

Sincerely thank is also extended to Ir. M. Helmi, M.Si and all friends in

Semarang for data sharing and survey guidance. To all of my colleagues,

friends, and all MIT students, there are too numerous to thank individually,

but thank’s guys.

Last but not least, to my lovely parents, brother, sister, cousin, auntie, uncle,

fiancée, and all of my family, thank you for always supporting me and being

there for me. I specially dedicated this thesis for you all.

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CURRICULUM VITAE

The author was born on March 30th 1980 in Mataram, West Nusa

Tenggara as the oldest of three children. In 2003, the author

enrolled bachelor degree in Department of Marine Science and

Technology, Bogor Agriculture University and was graduated in

2008 with final research entitle ”Determination of marine tourism

potential zone in south coast of Lombok island, NTB, using

Geographical Information System (GIS)”. In September 2009, the author registered

in Graduate School of Bogor Agricultural University at Master of Science in

Information Technology for Natural Resources Management program. His M.Sc.

thesis entitled “Sea Level Change And Its Impact to Submergence Area in Semarang

City (Central Java) Coastal Area”. He was worked for some company in different

timescale as contracted staff and never been awarded by any kind scholarship during

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LIST OF FIGURES

Figure 2.1. Global temperature change (a) Land and Ocean (b)

Hemispheric………...

Figure 2.2. The increasing of global

temperature.………..

Figure 2.3. Sun-earth-moon system affecting spring tide (a) and neap tide (b)..

Figure 2.4. Daily inequality of tides .………..

Figure 2.5. Building and construction distribution over Semarang city in (a)

red in 1600, green is increasing until 1741, violet is increasing

until 1880, blue is increasing until 1927 and (b) yellow is

increasing until 2009………...

Figure 2.6. Ground water abstraction and registered drilled wells development

in Semarang City………

Figure 3.1. Research location...………...

Figure 3.2. Flowchart for daily sea level change modeling using FVCOM…...

Figure 3.3. Flowchart for terrain model of Semarang City coastal area………

Figure 3.4. Flowchart for landuse and infrastructure mapping..….…………....

Figure 3.5. Research framework……….

Figure 4.1. Sea level dynamic in Semarang city based on the day when spring

tide is occur ………...………..

Figure 4.2. Sea level variation at spring tide………..

Figure 4.3. Sea level variation at ebb tide………..

Figure 4.4. Trend of regional sea level around Indonesia (data from

University of Colorado)………...

Figure 4.5. Monthly average of global mean sea level pattern based on tide

gauge recorded and/or reconstructed data (data from

CSIRO)……….………...

Figure 4.6. Monthly average of global mean sea level pattern based on data of

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Figure 4.7. Recent submergence area………

Figure 4.8. Various adaptation strategies in submergence area (a) plastic bed

cover is permanent flooded bedroom, (b) car try to passing road

that was transformed to submergence area, (c) working activity in

submergence area, (d) fishing activity in former warehouse of an

industry………...

Figure 4.9. Comparison of projected and calculated previous maximum

flooded area………….……….

Figure 4.10. Projecting submergence area in next 10, 15 and 20 years from

now………...………...

Figure 4.11. Projecting inundated area in next 10, 15 and 20 years from

now………...………... 37

42

43

47

48

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LIST OF TABLES

Table 2.1. Principal body tide constituents.………

Table 2.2. Contribution to SLR………...………...

Table 4.1. Result of regional sea level change data processing……….

Table 4.2. Global rising average from tide gauge and satellite in specific time

scale………..

Table 4.3. Real sea level height in Semarang City………...

Table 4.4. Real sea level height in Semarang City and it deviation from tide

gauge data………..

Table 4.5. Properties that affecting by sea level rises and spring

tide……….………….

Table 4.6. Properties that affecting by sea level rises in next 10, 15 and 20

years……….…………..

Table 4.7. Properties that affecting by sea level rises and spring tide in next

10, 15 and 20 years..…....………... Page

10

13

35

38

39

40

45

49

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Background

Since the middle of 19th century, sea level has been rising, primarily as a result

of human-induced climate change. During the 20th century, sea level rose about

15-20 centimeters (roughly 1.5 to 2.0 mm/year), with the rate at the end of the

century greater than over the early part of the century. Satellite measurements

taken over the past decade indicate that the rate of increase has jumped to about

3.1 mm/year, which is significantly higher than the average rate for the 20th

century. Projections suggest that the rate of sea level rise is likely to increase

during the 21st century, although there is considerable controversy about the size

of the increases.

Most of the world’s coastal cities were established during the last few

millennia, a period when global sea level has been near constant. Semarang city is

one of the cities that founded and established before 19th century where nowadays

some part of the land area of Semarang city itself always been flooding. The

location of Semarang municipality is directly heading Java Sea with

approximately 21 km of coastline length from east border to west. Coastline of

Semarang city is always changes along the time from 21 km in 2005 to 22.71 km

in 2006. Most of boundary between land and water (coastal and water catchment

area) is low-lying area and much of it is a subject of inundation during peak tide

and rainy season periods. These natural hazards represent a special challenging

problem for communities, large and small, in the coastal regions of Semarang city.

As population densities continue to increase in Semarang city, the flood hazard

unfortunately is increasing as well due to global sea level rise combined with

locally high rates of land subsidence in the area. In some areas, the combination of

sea level rise and land subsidence is doubly significant effect for flooding. High

rainy season that have not caused significant flooding in the past will begin to do

so, and with greater frequency as sea level, will give continues effect which is

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Data, information, and prediction about sea level change and land subsidence

in Semarang City is very important in correlation with development aspects, urban

planning, facilities and infrastructure development plan, environmental

preservation, ground water mining and controlling, sea water intrusion control,

and civil prevention from the impact of those both phenomenon (mitigation plan).

Therefore, systematic and continuous monitoring is highly needed and must be

notice by planner because coastal planning and development not only looking

toward the future but also underscores the present need for emergency planning

and effective response measures when coastal inundation is imminent. Flood

hazard mitigation at a minimum requires an understanding of the land and

bay-ocean processes that contribute to it in complex and often unpredictable ways.

Objectives

The objective of this research is to identify and measure the rate of sea level

change in Semarang city coastal region and its effect as the basic information for

public generally and for planner and government especially about their living area

and the area that will be developed either structurally or spatially. This research

also predicted the impact of sea level change in specific time as the overview for

future condition.

Outputs

Through integrating of modeling, remote sensing and geographical information

system method, several outputs that has been gained are:

1. Sea level change pattern in the specific time scale.

2. Map informing the effect of sea level change to the land area.

3. Map of study area as the result of future projection that informing the effect of

sea level change to the land area in specific year in the future

4. Sea level change phenomenon and its effect to submergence and inundated

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I I . L I T E R A T U R E R E V I E W

2.1 Global Warming

Global warming is the rise in average global surface temperature caused

primarily by the build-up of human-produced greenhouses gases, mostly carbon

dioxide and methane, which trap heat in the lower levels of the atmosphere

(Lindsay, 2010). Global warming is the majoring factor of global climate change

where global climate change is a change in the long-term weather patterns that

characterize the regions of the world. Global warming occurs majoring as the

effect of the increasing of glass house gasses (especially carbon dioxide) in the

atmosphere that can absorb emitted infrared radiation by Earth and release that

energy into the atmosphere rather than allowing it to escape to the space. As their

atmospheric concentration has increased, the amount of energy "trapped" by these

gases has led to higher temperatures. One of the most common energy/light

reflectance is infrared where infrared can’t escape to the space by green houses

gasses blocked. It makes earth temperature increasing and affecting weather

characteristic and pattern in an area or even in the world whether it temperature,

wind, and/or precipitation.

(a) (b)

Source: NASA GISS, 2012 Figure 2.1. Global temperature change (a) Land and Ocean (b) Hemispheric

Temperature in land is different with temperature in the water/ocean so that

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GISS, since the first data recorded and/or reconstructed, mean temperature change

in land area was increased with the amount ± 1.4 °C per 5 years and in ocean was

increased with the amount ± 0.7 °C per 5 years or land area has double increasing

value than ocean (Figure 4.1 (a)). The warmer of land area can be because land

properties (soil, rock, sand etc.) is better conductor and can preserve heat that it

received than water properties even both object receive the same heat.

Data from NASA GISS also shows hemispheric temperature has been change

and linearly increase where the increasing in northern hemisphere is different with

southern hemisphere. Since the first year data record until 2010, the 5 years mean

of increasing in northern hemisphere was ± 1.25 °C and was ± 0.85 °C in southern

hemisphere (Figure 4.1 (b)). It can possibly caused by the land area in northern

hemisphere is larger than southern part so that human air pollution that can

trapped emitted energy (which is one of majoring factor in global warming) in

northern part is higher than in the southern part. That possibility can be supported

by data from World Bank (2011) that shows the air pollution contribution of each

country.

Developed countries are the countries with the highest contribution of CO2

emissions. In 2006, China contributed 6.103x106 tons of CO2 emissions or 21.5%

of total CO2 emissions. United states contributed 5.752x106 tons of CO2 emissions

or 20.2% of total CO2 emissions. Russia contributed 5.5 % of total CO2 emissions;

India contributed 5.3%, Japan contributed 4.6%, Germany contributed 2.8%,

United Kingdom contributed 2.0%, Canada contributed 1.9%, while South Korea

and Italy has the same contribution with 1.7% of total CO2 emissions per country.

Those top ten countries with the highest CO2 emissions are located in northern

from northern hemisphere is the countries with the highest contribution (exclude

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emission, top ten most polluted cities by particulate matter, and ten countries with

highest carbon dioxide emission/capita can be seen completely in Appendix 1.

2.2 Global Climate Change

Global climate change is a change in the long-term weather patterns that

characterize the regions of the world. The term "weather" refers to the short-term

(daily) changes in temperature, wind, and/or precipitation of a region (Merritts et al. 1998). The sun influences weather, where the sun heats the earth's atmosphere and its surface causing air and water to move around the planet. The result can be

as simple as a slight breeze or as complex as the formation of a tornado. Some of

the sun's incoming long wave radiation is reflected back to space by aerosols. In

addition, some of the sun's energy that has entered Earth's atmosphere is reflected

into space by the Earth’s surface (the reflectivity of Earth's surface is called

albedo). Both of these reflective processes have a cooling affect on the planet.

The greenhouse effect is a warming process that balances Earth's cooling

processes. During this process, sunlight passes through Earth's atmosphere as

short-wave radiation. In atmosphere some of long wave radiation is absorbed by

certain gases (called greenhouse gases). Greenhouse gases include carbon dioxide

(CO2), chlorofluorocarbons (CFC's), methane (CH4), nitrous oxide (N20),

tropospheric ozone (O3), and water vapor. Each molecule of greenhouse gas

becomes energized by the long wave radiation. The energized molecules of gasses

then emit heat energy in all directions. By emitting heat energy toward Earth,

greenhouse gases increase Earth's temperature (Dasgupta and Meisner, 2009).

The greenhouse effect is a natural occurrence that maintains Earth's average

temperature at approximately 60 degrees Fahrenheit. The greenhouse effect is a

necessary phenomenon that keeps all Earth's heat from escaping to the outer

atmosphere. Without the greenhouse effect, temperatures on Earth would be much

lower than they are now, and the existence of life on this planet would not be

possible. However, too many greenhouse gases in Earth's atmosphere could

increase the greenhouse effect. This could result an increases in mean global

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When weather patterns for an area change in one direction over long periods

of time, they can result in a net climate change for that area (the key concept in

climate change is time). The real threat of climate change lies in how rapidly the

change occurs. For example, over the past 120 years, the mean global temperature

appears to have risen 2 to 8 degrees Celsius. These temperatures changes are

depicted in the graph below from the IPCC (2001).

Figure 2.2. The increasing of global temperature

The geological record, the physical evidence of the results of processes that

have occurred on Earth since it was formed, provides evidence of climate changes

similar in magnitude to those in the above graph. This means during the history of

the earth, there have been changes in global temperatures similar in size to these

changes (Schlesinger, 1991). However, the past changes occurred at much slower

rates, and thus they were spread out over long periods of time. The slow rate of

change allowed most species enough time to adapt to the new climate. The current

and predicted rates of temperature change, on the other hand, may be harmful to

ecosystems. This is because these rates of temperature change are much faster

than those of Earth's past. Many species of plants, animals, and microorganisms

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2.3 Tides

Knowledge of the tides and their patterns dates back to at least 2300 BC in the

ruins of coastal cities along the Gulf of Cambay in India. Here archaeologists have

uncovered evidence of tidal docks, structures that allow boats to enter at high tide

and, by means of a gate, trap the water and keep the boat afloat when the tide

recedes. Indian religious texts from 300 400 BC suggest a link between the tides

and the phases of the moon, a highly advanced claim for its time. Because tides

may rise and fall in excess of 30 feet (10 meters) in this region, they obviously

played an important role in the culture and commerce of these ancient people

(Sawicki, 2005).

Several notable scholars advanced theories of the tides (including Galileo) but

the first complete and fundamental correct explanation was published in 1687 by

Sir Isaac Newton (1642 1727) in his Principia. In his theory, Newton introduced

the Law of Gravitation which states that the gravitational attraction between two

planetary bodies is the product of their masses divided by the square of their

distance, times the gravitational constant.

Differences in gravity at different points on Earth’s surface cause vertical and

horizontal forces but the vertical forces are much too small to generate tides. The

tide causing forces result from the horizontal forces acting along the surface of

the Earth (i.e., tangential to the surface), causing motions of water towards points

directly beneath and on the opposite side of the Moon (and Sun).

2.3.1. Origin of the tides

In oceanography, tides are commonly defined as the periodic variations in sea

level that occur as a result of the gravitational forces of the Sun and the Moon.

Tides are a planetary phenomenon, caused by the gravitational attraction of other

planetary bodies on Earth (Sun and Moon). The force of this attraction creates a

very predictable rise and fall of sea level as the Earth rotates on its axis. When

sea level is at its greatest height, the tide is said to be high and when sea level is

at its lowest extent, the tide is said to be low. High tides bring water far up on

the shore, combines with high wave action, these high tides may damage homes

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of the beach.

The moon is the primary factor controlling the temporal rhythm and height of

tides. The moon produces two tidal bulges somewhere on the Earth through the

effects of gravitational attraction. The height of these tidal bulges is controlled

by the moon’s gravitational force and the Earth’s gravity pulling the water back

toward the Earth. At the location on the Earth closest to the moon, seawater is

drawn toward the moon because of the greater strength of gravitational attraction.

On the opposite side of the Earth, another tidal bulge is produced away from the

moon. However, this bulge is due to the fact that at this point on the Earth the

force of the moon’s gravity is at its weakest. Considering this information, any

given point on the Earth’s surface should experience two tidal crests and two

tidal troughs during each tidal period.

The second factor controlling tides on the Earth’s surface is the sun’s gravity.

The height of the average solar tide is about 50 % the average lunar tide. At

certain times during the moon’s revolution around the Earth, the direction of its

gravitational attraction is aligned with the suns. During these times the two tides

producing bodies act together to create the highest and lowest tides of the year.

These spring tides occur every 14 15 days during full and new moons (Roos,

1997).

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2.3.2. Tides Constituent

In most estuaries and seas, a periodic rise and fall of the water can be

observed, it is known as the vertical astronomical tides. The highest level of

tides called High Water level (HW) and the lowest level is called the Low Water

level (LW), whereas the difference between HW and LW is called tidal range.

When the vertical movement of the water level is measured for about one day,

than it can be observed that the second HW and LW differ from first HW and

LW. This difference in HW’s and LW’s is called the daily inequality.

Figure 2.4. Daily inequality of tides

When the water level is measured in “A” location and the wave move

horizontally, a periodic rise and fall of water level can be observed also. So,

associated with vertical movement of the water surface, there is also horizontal

movement of the water particles. In tidal analysis, the tidal signal (the observed

water level versus time) is decomposed into its constituents. Tidal constituent

generally can be distinguish into three main groups, and completely can be seen

(28)

Table 2.1. Principal body tide constituents

Tidal Constituent Period Vertical amplitude (mm)

2.4.1.Eustatic and Isostatic Sea Level Change

There are two kinds of sea levels change: eustatic and isostatic sea level change.

Eustatic sea level change is general or global sea level change, change in seawater

volume globally which is caused by factor like global warming. Isostatic sea level

change is change of sea level at specific site as the sum of sea level rise plus local

(29)

Many observations show that the ocean has been changing over the last

several decades. One aspect of these changing is the warming of ocean, resulting

in increase of ocean volume through thermal expansion. There has also been

addition of water from glacier and ice sheets and changes in storage of water on

or in the land (e.g. retention of water in man-made dams and extraction of water

from aquifers). These together result in changes in sea level

2.4.2.Factors Contributing Sea Level Rise

Since the concern about human-induced global warming in the 1980s was

emerged, sea-level rise and its impacts on the coastal areas have attracted

considerable concern. The large and growing concentration of people and assets

in coastal areas imply to the height of potential impacts. It is estimated that at

least 600 million people live within 10m of sea level in 2010, and these

populations are growing more rapidly than global trends. Populated deltaic areas

and many coastal cities are highly threatened by small rises in sea level. While in

global terms relatively small in number, the very existence of small-island nation

states makes them vulnerable to rises in sea level of the order of 1m (Nisholls et.

al., 2011).

The recent report of the Intergovernmental Panel on Climate Change (IPCC)

estimates that in response to rising temperatures (1.0°-3.5°C higher than 1990

levels in 2100), sea level will have risen from 15 to 95 cm by the year 2100.

IPCC AR4 Report (IPCC, 2007) identifies several major factors that currently

contribute to sea level rise. These are:

1. Ocean Thermal Expansion

Instrumental records shows that the world’s oceans have warmed since 1955,

accounting over this period for more than 80% of the changes in the energy

content of the Earth’s climate system. Further records also shows that during the

period of 1961 to 2003, ocean layer between 0 to 3000 m. has absorbed average

heating rate of 0.2 Watts/m2 (per unit area of the Earth’s surface). During 1993

to 2003, the corresponding rate of warming in the 0 to 700 m ocean layer was

higher, about 0.5 ± 0.18 W/m2. Therefore, between 1961 to 2003, the period

1993 to 2003 had much higher rates of warming, especially in the upper 700 m

(30)

2. Change in Glaciers and Icecaps

During the 20th century, glaciers and ice caps have experienced huge mass

losses. These losses (excluding those around the ice sheets of Greenland and

Antarctica) are estimated to have contributed 0.50 ± 0.18 mm/yr in sea level

equivalent (SLE) between 1961 and 2003, and 0.77 ± 0.22 mm/yr between 1991

and 2003.

3. Glacial melt from the Greenland and Antarctica ice sheets (GIS)

Whether the Greenland and Antarctic ice sheets had been growing or

shrinking over time scales of longer than a decade is not well established from

observations. Lack of agreement standard between techniques and the small

number of estimates preclude assignment of best estimates or statistically tight

error bounds for changes in ice sheet mass balances. However, acceleration of

outlet glaciers draining from the interior has been observed in both the

Greenland and Antarctic ice sheets.

According to the IPCC AR4 (IPCC, 2007), it is very likely (> 90%

probability) that the Greenland Ice Sheet shrunk from 1993 to 2003. An

assessment of the data suggests a mass balance for the Greenland Ice Sheet of –

50 to –100 Gigatons/year (a shrinkage contributing to rising global sea levels of

0.14 to 0.28 mm/yr) from 1993 to 2003, with even larger losses in 2005. The

estimated range in mass balance for the GIS from 1961 to 2003 is between a

growth of 25 Gt/yr and shrinkage of 60 Gt/yr (or –0.07 to +0.17 mm/yr SLE).

There are even greater uncertainties for Antarctica Ice Sheet (AIS). Again

according to the IPCC AR4 assessment of all the data yields an estimate for the

overall AIS mass balance ranging from growth of 100 Gt/yr to shrinkage of 200

Gt/yr (or –0.27 to +0.56 mm/yr of SLE) from 1961 to 2003, and from +50 to –

200 Gt/yr (or –0.14 to +0.55 mm/yr of SLE) from 1993 to 2003.

4. Smaller contribution from snow on land and permafrost

Snow cover has decreased in most regions, especially in spring. Satellite

observations of the Northern Hemisphere snow cover from 1966 to 2005 show a

decrease in every month except in November and December, with a stepwise

drop of 5% in the annual mean in the late 1980s. In the Southern Hemisphere,

(31)

the past 40 years or more. Decreases in the snow pack have also been

documented in several regions worldwide based upon annual time series of

mountain snow water equivalent and snow depth.

Permafrost and seasonally frozen ground in most regions display large

changes in recent decades. Temperature increases at the top of the permafrost

layer of up to 3°C since the 1980s have been reported. Permafrost warming has

also been observed with variable magnitudes in the Canadian Arctic, Siberia, the

Tibetan Plateau and Europe. The permafrost base has been thawing at a rate

ranging from 0.04 m/yr in Alaska to 0.02 m/yr on the Tibetan Plateau.

The complete summary that shows contribution of each parameter majority to

sea level rise based on upon observations as compared to model can be seen in

table 2.2.

Table 2.2. Contribution to SLR (Sea Level Rise)

Sea Level Rise (mm/year)

1961-2003 1993-2003

Source of SLR Observed Modeled Observed Modeled

Thermal expansion 0.42 + 0.12 1.5 + 0.7

(32)

2.5 Sea Level Change Phenomenon in Indonesia

Climate change has and will continue to impact Indonesia where one of the

impacts is sea level change in term of rising. All Indonesia’s coastal area will be

impacted by sea level rise with different scale of impact because the rate of

increase varies with locations (Sofian in ICCRS, 2009). A recent mapping

vulnerability assessment shows that the western and eastern areas of Java Island

(including Jakarta) are at particular threat to droughts, floods, landslides, and

sea-level rise.

Jakarta as one of the most densely populated areas in Southeast Asia is at high

risk of climate impacts because it is frequently exposed to significant flooding and

subsided. The wet season in Jakarta has become wetter, mean sea level rising by

the time, and therefore the city experiences more flooding, which is compounded

by clogged drainage and the fact that major part of the city is at or near sea level.

Previous floods as the combination from all of those factors have occurred in

Jakarta where major flood events in 1996 and 2007 submerged 5,000 hectares of

land with losses from infrastructure damage and state revenue estimated at

US$572 million. These two floods also killed at least 85 people and forced about

350,000 people from their homes (WWF, 2009). More specific, the impact of sea

level change also threaten human life because peak tide has reached it usual peak

tide level. Governor of DKI Jakarta in KOMPAS (2011) states that peak tide has

reached 2.5 meters or 30 cm higher than it normal so that tidal flood inundated

some area in North part of Jakarta. Clear example can be seen in Pantai Muara

and it surrounding area that has been inundated up to 80 cm by this occurrence.

Banjarmasin City as the capital of South Kalimantan Province with 72 km2

area of land where some part of land is low lying area and it City crossing by

Barito river that becomes ship route to reach Java Sea also impacted by sea level

change. When level of ebb tide is lower than normal, ship can come in/out from

Banjarmasin. The impact of sea level rise for specific time period also has been

projected by Susandi et.al. In 2010 sea level will be emerge area that lower than

0.37 m (land area loss around 0.53 km2), in 2050 will emerge land area that lower

than 0.48 m (land area loss around 1.039 km2), and will emerge land area that

(33)

the economic loss of each land area loss where in 2010 the economic losses will

reach $0.03x106, in 2050 economic losses will reach $0.14x106, and in 2100

economic loss will reach $0.69x106.

2.6 Land Subsidence

Land subsidence is a gradual settling or sudden sinking of the Earth’s surface

owing to subsurface movement of earth Materials. Land subsidence is merely the

surface symptom of a variety of subsurface displacement mechanisms. Not all of

these mechanisms are well understood. Subsidence processes are hiding below

ground, their development to the point of surface deformation may involve long

periods of time, and for at least some mechanisms, significant evidence may lie

outside the area directly beneath the surface subsidence. Furthermore, at some

sites more than one condition favorable to subsidence occurrence may be present

and require consideration in analyzing causal mechanisms and devising remedial

procedures (USGS, 2000).

Subsidence is a familiar accompaniment of a variety of natural events that

comprise the geologic history of many areas. For practical reasons geologic

processes that are accompanied by subsidence have been examined for evidence

that the range in their rates of progress extends into a time frame that may produce

damaging effects in terms of man’s time scale. The processes investigated are

those that remove or withdrawal subsurface materials to produce void space or

significant volume reduction-solution, underground erosion, lateral flow, and

compaction-or, in the case of tectonic activity, deep-seated downward

displacement. For all of these naturally occurring geologic processes, examples of

related surface subsidence have been found, though some are rare (Allen, 1970).

The incidence of subsidence is greater where some of these geologic processes are

set in motion or accelerated by man’s engineering activities that involve

excavation, loading, or changes in the ground-water regime.

The term "subsidence" is used because it representing the sinking in a broad

sense to include both slows downwarping and the collapse of discrete segments of

the ground surface. Displacement is principally downward, although the

(34)

term is not restricted on the basis of size of area affected, rate of displacement, or

causal mechanism.

Land subsidence in Semarang city had been occurring with northern part of its

city as the main region of subsided. There are three major factors that causing land

subsidence in Semarang City i.e.; geological structure of soil, groundwater

withdrawal, and building/construction load.

Geologically, Semarang has three main lithologies, namely, volcanic rock,

sedimentary rock, and alluvial deposits. According to Sukhyar (2003), the basement of Semarang consists of Tertiary Claystone of the Kalibiuk Formation.

Overlying this Formation is the Notopuro Formation, which consists of

Quaternary volcanic material. Those two formations crop out in the southern part

of the Semarang area. The northern part of the Semarang area is covered by Kali

Garang deltaic alluvium up to a depth of 80 to 100 m in the coastal area. Aquifers

are found at depths ranging from 30 to 80 m in this alluvium. Van Bemmelen

(1949) reported that the shoreline of Semarang progresses relatively quick toward

the sea, namely about 2 km in 2.5 centuries or about 8 m/year. That “new” land

area is located in northern part of Semarang City (deltaic area) is composed by

very young alluvium with high compressibility. Alluvium, as the upset soil layer

in coastal area of Semarang City is not stabile and its density can be easily

changed. The instability of soil layers in deltaic area will easily change the pattern

of soil layer and without human factor it can causing land subsidence.

As development started to continue, there are some impacts that occur in

Semarang City, one of them is land conversion. Swamp forest, agriculture area

and human non-infrastructure use had been converting into houses, building and

infrastructure. In 1660, the first area that was converted into human uses (building

and infrastructure) is the area that nowadays known as Tanjung Mas harbor area.

Around 600 years ago, Tanjung Mas harbor area is not land area but it known as

the area that covered by seawater completely. Deltaic sedimentation, river deposit,

and sediment cover from tides process formed this land area so that the soil layer

in that area is still young. To supported Tanjung Mas harbor area as the central

area of development, the buffer area of Tanjung Mas also converted and becomes

(35)

Ha and it increased to 109.78 Ha (44.70%) in 1880. In 1927, the building area

expanded toward southern part of Semarang City with the increasing to348.14 Ha

and in 2009, building and infrastructure has covered all part of coastal area with

total area reach 37,984.41 Ha (more than 100 times than in 1927). Semarang City

especially coastal area, with very young unstable alluvium soil layer and can be

decrease without human factor, since 1660 started experience land subsidence

which also caused by building load as the impact of development. The illustration

of building and construction distribution increased over Semarang city, especially

coastal area, can be seen in Figure 2.5.

(a) _(b)

Source: Interpretation of ALOS AVNIR-2 images and Helmi (2010) Figure 2.5. Building and construction distribution over Semarang city in (a) red in

1600, green is increasing until 1741, violet is increasing until 1880, blue is increasing until 1927 and (b) yellow is increasing until 2009

Development with the expansion in number and area of building and

infrastructure has been encouraged the increasing of population through

urbanization. Peoples started moved to the area near facilities (office building,

hospital, road, school, etc.) where all of facilities were centralized built in deltaic

area (had been knowing also as Semarang Bawah). As the effect of increasing

population, the needs of water also increase. Groundwater is one of the water

source that can be easily access by peoples and cheaper than other sources.

Peoples and industries started utilize ground water as their main water source.

When groundwater in the upper layer was not enough to supply human and

(36)

alternative. It can fulfill human and industries need of groundwater but in contrary

the side effect of groundwater pumping in instable soil layer like Semarang City

(especially Semarang Bawah) costly the decreasing of ground water level and

increasing the speed of subsided. Marsudi (2001) also found the similar things on

his research where tremendous amount of groundwater pumping in Semarang City

that exceed it aquifer capacity has led the occurrence of land subsidence. Figure

2.6. below shows the increasing amount of groundwater pumping in Semarang

city where it amount is increasing sharply since early 1990s, the era that has been

known as early industrial era in Semarang City (Abidin et.al., 2011).

Source: Murdohardono in Abidin et.al. (2011) Figure 2.6. Ground water abstraction and registered drilled wells development in

Semarang City

There area several former land subsidence research in Semarang i.e.;

I. Marsudi (2001) conducted land subsidence prediction research in Semarang

from geological point of view. Based on the (1-D) consolidation model, the

result of land subsidence prediction from his research conclude that for the

year of 2013 the ranges of subsidence will be between 87 to 190 cm from

annual condition. He also concluded that the amounts of land subsidence

become larger toward north-northeast direction and increases toward coastal

(37)

II. Kuehn et.al in 2009 conducted land subsidence research in Semarang using

Persistent Interferometery Scattered (PSI) technique. Persistent Scatterer

Interferometry technique (PSI) has been applied to improve land subsidence

mapping because former maps show an overall distribution of land

subsidence, but are inaccurate in detail. PSI measures ground motion using

SAR satellite images. For the PSI processing, 35 radar satellite images

acquired between 2002 and 2006 have been selected. Derived land subsidence

rates vary from fractions of 1 mm per year to values of 10 cm per year and

even beyond. Classification and visualization of the ground motion data

illustrate the boundary between mainly stable ground in the south of Semarang

and increasingly land-subsidence-affected land towards the coast (Kuehn et.al,

2009).

III. Abidin et.al in 2008 and 2009 conducted land subsidence investigation using

GPS survey method. By studying the characteristics and rate of change in the

height components of the coordinates from survey to survey, the land

subsidence characteristics can be derived. In order to achieve level of accuracy

the GPS static survey method based on dual-frequency carrier phase data

processing should be implemented, with stringent measurement and data

processing strategies. GPS surveys for studying land subsidence in Semarang

have been conducted on 7-13 July 2008 and 5-11 June 2009. The number of

observed points was 48 at first survey and 52 points at second survey. Results

from GPS show that land subsidence in Semarang has spatial variations,

ranging from 0.8 to 13.5 cm/year with the mean of 5.9 cm/year. Northern

region of Semarang city exhibits higher rates of subsidence compare to its

(38)

(39)

I I I . M A T E R I A L S A N D M E T H O D

3.1 Research Location and Time

Semarang city is the capital city of Central Java Province, which located in

North Coast of Java lane and connecting two biggest cities in Indonesia, Jakarta

and Surabaya. Geographically, Semarang city is located between 1090 35’ to 1100

50’ E and 60 50’ to 70 10’ S with total area around 373.70 km2 (BAPPEDA, 2005).

The borders of Semarang city administratively are:

North part: Java Sea

South part: Semarang region

East part: Demak region and Grobogan region

West part: Kendal region

Semarang is a coastal urban area situated on the lowland part/coastal area of

Central Java province. As a provincial capital city, Semarang has developed and

grown as a big city on Central Java. The residential growth and industrial

expanses in Semarang City contribute to the land subsidence and flooding.

Semarang has three different types of flooding. These are referred to as: banjir lokal (locally flooding), banjir kiriman (river flooding) and banjir rob (tidal flooding). Local and river flooding occur due to high rainfall intensity combined

with insufficient urban drainage system. Local flooding in particular places, like

in Tawang and Kaligawe, have been identified to be due to the drainage

malfunction and stoppage, as well as improper places for waste disposal.

Subsidences, which occur in Semarang, also increase the effect of flood that

seasonally happened in this city.

This research was conducted in IT (Information and Technology) for NRM

(Natural Resources Management) Research Laboratory (SEAMEO-BIOTROP

Bogor), Geomathics Research Geospatial Information Agency (Cibinong, Bogor),

and coastal area of Semarang City itself. The research was ran on October 2011

until March 2012. Research location can be seen in Figure 3.1, where the study

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Figure 3.1. Research location

3.2 Data Used

This research used several different data. Those data are consisting of

landcover data, satellite images, sea level data, and bathymetry data. Each data

has different function and by combining the result of all data analysis, the goal of

the research can be achieve. Complete main and supporting data that used in this

research are:

(a) Coastline data from National Geophysical Data Center (NGDC)-NOAA

which can be accessed at http://www.ngdc.noaa.gov/mgg/shorelines/

shorelines.html. This coastline data has been accessed in October 2011.

(b) Bathymetry data as the projection of TOPEX with 30arcsecond of spatial

resolution (around 1 km) that has been accessed in October 2011. This data

can be accessed at http://topex.ucsd.edu/WWW_html/srtm30_ plus.html.

(c) Height points as the result of topographic and terrestrial survey from

(41)

(d) Topographic map (RBI) in scale of 1:25.000, produced by the National

Mapping and Coordination Survey Agency (BAKOSURTANAL). The RBI

map is map that released in 2002.

(e) Multispectral image (ALOS AVNIR-2), on June 17, 2009.

(f) BMKG’s tidal gauge annual report data of Semarang city.

(g) Data of global sea level rise from 1880 to 2009. This data has obtained from

CSIRO (http://www.cmar.csiro.au/sea level/sl_data_cmar.html) in December

2011.

(h) Regional sea level time series data in Indonesian area. This data has

obtained in December 2011 from http://sealevel.colorado.edu/

content/regional-sea-level-time-series.

(i) Result of observation at the potential inundation areas and interview to the

local resident. The interview has been conducted in February 2012.

3.3 Material Used

hardware that used in this research while software that used to for data collecting,

processing, and analyzing is divided into opensource and licensed software.

3.4 General Method

The research has been conducted using combination of spatial and numerical

modeling, remote sensing, and geographic information system. There are several

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3.4.1. Measuring Daily Sea Level Change

One of the important factor affecting sea level change is tidal. Tidal level can

be estimate using tides harmonic analyst where on of tools that can deriving

realistic tide model is FVCOM (Finite Volume Coastal Ocean Model).

FVCOM has incorporated the Foreman tidal forecasting program (Chens,

2006) to compute realistic tidal elevation data for the initial conditions and on

the open boundary. It needs coastline and bathymetry as the data to build

boundary of study area. Unstructured triangular mesh has to generate as the

basic data to obtain tidal harmonic data as the input for the model. Up to six tidal

harmonic constituents can be included in the model. The six included tidal

constituents are: 1) S2 tide (period = 12 hours); 2) M2 tide (period = 12.42

hours); 3) N2 tide (period=12.66hours); 4) K1 tide (period = 23.94 hours); 5) P1

tide (period = 24.06 hours), and O1 tide (period = 25.82 hours).

The tidal forcing at the open boundary can be specified by either

amplitude/phase of each tidal constituent. The harmonic analysis is carried out

by using a least square fitting. In the second case, true clock time must be

specified and the results can be analyzed directly using Foreman’s harmonic

analysis program. All of data input must be in the same directory and format so

that model can be run. UNIX programing was used to obtain the result of the

model while some license software was used to displaying the result.

The general step of realistic tidal modeling using FVCOM can be seen in

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Figure 3.2. Flowchart for daily sea level change modeling using FVCOM

Global and regional sea level rise as the other factor that causing sea level

change is taken from research institution. In this research, data of global sea

level rise was acquired from CSIRO, regional sea level change was acquired

from University of Colorado, and local sea level change was acquired from

Coastline Bathymetry

Editing Coordinate Transformation

Geoprocessing (Merge)

Extraction Extraction

Input data

UNIX Programing

Coordinate Transformation Coordinate Transformation

Format Conversion

Grid Generation - Create boundary - Define Resolution - Build Mesh

- Mesh Quality Control - Interpolate bathymetri based

on mesh pattern

UNIX Programing

(44)

BMKG Semarang. BMKG’s data is not corrected yet because tide gauge is

located in unstable soil which sinking linearly. To obtain real sea level,

BMKG’s data must be corrected with average of regional sea level change. The

period of data from BMKG and regional sea level change (from University of

Colorado) must be the same to obtained the correct result. Real sea level can be

calculated as given:

(1)

where is real sea level, SL is recent sea level from BMKG and Sreg is

average of regional sea level change.

3.4.2.Estimating Land Subsidence

This research estimating land subsidence level by calculating the deviation

from sea level which was recorded using tide gauge by BMKG in Semarang

City and isostatic sea level.

Isostatic sea level is obtained by add up yearly sea level value in first

recorded year with yearly change of regional sea level. By this calculation, the

isostatic sea level in next year can be calculated. Land subsidence level can be

calculated then by calculating the average of deviation in last year of data

recorded by BMKG and isostatic sea level in same year.

(2)

where is yearly land subsidence level, SLly is sea level in last year data

recorded from BMKG and SLr is real sea level value in the same year with SLly

and n is time period (year).

submergence area can be drawn easily based on height pattern of the research

(45)

Figure 3.3. Flowchart for terrain model of Semarang City coastal area

3.4.4.Landuse and Infrastructure Mapping

Landuse and infrastructure is the properties that related to human activity. It

change along the time whether it getting better or worse. In Semarang City, it

seems to be worse because the fact nowadays some of infrastructure has been

covered by water permanently and can’t be used anymore as it function. One

factors that causing its worse is flooding. Analyzing the change as the effect of

flooding, landuse and infrastructure map is needed and it will be easily to

analyzed if the format of map is in digital format.

To create digital landuse and infrastructure map, there are two sources that

can be used i.e. printed rupabumi map of Semarang City that has been released

by BAKOSURTANAL in 2002 and digital satellite images that derived from

ALOS-AVNIR in 2009 with 10 m of spatial resolution. The format of both data

source is different, one is digital and the other one is in analog format. To

convert analog map to be digital, it must be scanned, registered and digitized

where the result of digitizing is used as the baseline for correcting satellite image

geometrically. Once it corrected, it can be used to updating digital map as

digitizing result from 2002’s printed map. The steps of landuse and

infrastructure mapping in this research can be seen in Figure 3.4. 2008 Terrestrial Survey Result

Semarang City Public Work Office

Subsidence Point Survey

Interpolate/Gridding Interpolate/Gridding

Subsided area Digital Elevation Modeling

(DEM)

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Figure 3.4. Flowchart for landuse and infrastructure Mapping

3.4.5. Ground Truth

Ground truth or field survey in this research in intended to refers of a

process in which form on a satellite image, result of data processing and

analysis is compared to what is in the reality (at the present time) in order to

verify the contents of the form on the image and result of analysis. Field survey

also intends to collect some other information, which will use in this research,

which cannot be derived from other sources and must be taken directly in the

research location.

Data that collected from ground majority truth will be used as reference for

infrastructure updating. Ground truth also utilized to comparing the result of

projection and previous occurrence of inundation. Preliminary result of data

processing was consulted to the expert as part of the research. All of that has

been conducted so that the final result will not be so differ from it reality. 2009 ALOS-AVNIR Images Printed Rupabumi 1:25.000

Geometric Correction Scanning

Registration

On Screen Digitizing Creating Color Composite Image

Landuse & Infrastructure Mapping

Field Survey

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Figure 3.5. Research framework Spring Tide Sea Level Rise from

BMKG

Highest Sea Level

Semarang City Terrain Model

Recent Landuse and Infrastructure Map

Inundation

Model and Previous

Occurrence comparison Analysis

Expert Consultation

Final Result