Semarang is a coastal city that has been suffered by rob flood for at least 25 years. One of main factors causes rob flood in Semarang is land subsidence. Land subsidence occurs in Semarang is a complex problem because the rate of land subsidence is different in places and changes in the development of time. Therefore it is necessary to monitor the land subsidence rate in Semarang. The aim of this research are to check the newest elevation of Bench Marks in coastal area of Semarang, to monitor land subsidence rate in coastal area of Semarang, To make

elevation and land subsidence contour map in coastal area of Semarang.  

The result of this research shows that bench marks which are above MSL +100 m in height are stable enough. The closer to the sea, the faster land subsidence occurs. Soil type in coastal area of Semarang which is included young-soft soil type makes it still undergoes compression / consolidation.  More over, coastal area of Semarang which is the center of the city activity such as Industry, buildings, reclamation, crowded transportation, and many artisian well has made land subsidence happens faste

Wirasatriya, Anindya

English

Semarang is a coastal city that has been suffered by rob flood for at least 25 years. One of main factors causes rob flood in Semarang is land subsidence. Land subsidence occurs in Semarang is a complex problem because the rate of land subsidence is different in places and changes in the development of time. Therefore it is necessary to monitor the land subsidence rate in Semarang. The aim of this research are to check the newest elevation of Bench Marks in coastal area of Semarang, to monitor land subsidence rate in coastal area of Semarang, To make elevation and land subsidence contour map in coastal area of Semarang. 

The result of this research shows that bench marks which are above MSL + 100 m in height are stable enough. The closer to the sea, the faster land subsidence occurs. Soil type in coastal area of Semarang which is included young-soft soil type makes it still undergoes compression / consolidation.  More over, coastal area of Semarang which is the center of the city activity such as industry, buildings, reclamation, crowded transportation, and many artisian well has made land subsidence happens faster.



Key Words : Bench Marks Elevation, Land Subsidence, Semaran

Diponegoro University Institutional Repository

INTERNATIONAL CONFERENCE Geomatics, Fisheries and Marine Science for a Better Future and Prosperity ____________________________________Semarang, Indonesia, October 21st – 22nd  2008 FISHERIES and MARINE SCIENCE 330 THE STUDY OF  LAND SUBSIDENCE RATE AT COASTAL AREA OF SEMARANG CITY, INDONESIA   Anindya Wirasatriya Oceanography Study Programme, Diponegoro University, Indonesia   Abstrak  Semarang is a coastal city that has been suffered by rob flood for at least 25 years. One of main factors causes rob flood in Semarang is land subsidence. Land subsidence occurs in Semarang is a complex problem because the rate of land subsidence is different in places and changes in the development of time. Therefore it is necessary to monitor the land subsidence rate in Semarang. The aim of this research are to check the newest elevation of Bench Marks in coastal area of Semarang, to monitor land subsidence rate in coastal area of Semarang, To make elevation and land subsidence contour map in coastal area of Semarang.  The result of this research shows that bench marks which are above MSL + 100 m in height are stable enough. The closer to the sea, the faster land subsidence occurs. Soil type in coastal area of Semarang which is included young-soft soil type makes it still undergoes compression / consolidation.  More over, coastal area of Semarang which is the center of the city activity such as industry, buildings, reclamation, crowded transportation, and many artisian well has made land subsidence happens faster.  Key Words : Bench Marks Elevation, Land Subsidence, Semarang  1. INTRODUCTION In the last 25 years, Semarang City that lies at coastal area of Central Java has suffered “rob” flood, flood caused by the raising sea level at high tide. This kind of flood inundated many places in Semarang City. In May 2005, there are at least 14  village were inundated by “rob” flood with the width of puddle area was 2.418 Ha. One factor causes “rob” flood is sea level rise. The sea level rise rate that recorded at Tide Observation Station Tanjung Mas Harbor, Semarang was 5,43 cm/year (Wirasatriya, 2005)   Based on the previous research of Wirasatriya (2005), the dominant factor causes sea level rise in Semarang City was land subsidence. At the other side there was also global warming factor that caused sea level rise  in whole part of the world but this global factor only caused sea level rise in Semarang about 2,65 mm/year. The value of land subsidence that happened in Semarang varied among one place INTERNATIONAL CONFERENCE Geomatics, Fisheries and Marine Science for a Better Future and Prosperity ____________________________________Semarang, Indonesia, October 21st – 22nd  2008 FISHERIES and MARINE SCIENCE 331 with others. Generally closer to coastal area the faster land subsidence occurres. Sutanta and Hobma (2002) stated that it would be very difficult to determine the value of land subsidence in Semarang since there would be a different value in different place and  different time. This complexity aroses from the dynamics of natural phenomena and human intervention, which in turn make it difficult to find the most probable scenario of land subsidence in the area. Therefore  it is very important to observe the land subsidence in Semarang coastal area periodically.  Based on Wirasatriya (2005) in order to observe land subsidence in Semarang coastal area, it is necessary to measure the elevation of many Bench Marks (BM) in Semarang each year. By knowing those BMs elevation each year, the value of land subsidence in many places in Semarang will be monitored. The aim of this research are : 1. To check the newest elevation of Bench Marks in coastal area of Semarang. 2. To monitor land subsidence rate in coastal area of Semarang. 3. To make elevation and land subsidence contour map in coastal area of Semarang  2. RESEARCH METHOD  This was descriptive research that had explorative character. According to Arikunto (1993) this kind of research was performed to descript the situation or status of a phenomenon. Thus the final result of this research  give the description of elevation and land subsidence in coastal area of Semarang.  The research was done in June 2006. The procedure of this research was divided into 3 step, i.e. : preparation step, leveling measurement step and data analysis step. The preparation step were preparing the equipments , searching  for the related literature and  secondary data like previous elevation data, Semarang map, etc.  The measuring step used leveling method to observe the elevation of BMs in coastal area of Semarang. TTG 449 which is the most stable BM was used as a reference point of measurement. TTG 449 is located in front of the “Ada” store in Srondol which has  221,004 m of elevation from mean sea level (MSL) (later the elevation value will be noted as MSL + 221,004 m). According to Muhrozi et al INTERNATIONAL CONFERENCE Geomatics, Fisheries and Marine Science for a Better Future and Prosperity ____________________________________Semarang, Indonesia, October 21st – 22nd  2008 FISHERIES and MARINE SCIENCE 332 (1997) TTG points is gained from List Book of reference points from BAKOSURTANAL, the responsible institution for surveying and mapping data in Indonesia.  The elevation measurement  followed this stripe : 1. “Go” stripe : Starting from srondol, Jl. Setia Budi, Jl. Gombel Lama, Jatingaleh, Kaliwiru, Jl. Sultan Agung, Taman Diponegoro Elisabeth, Jl. Diponegoro, Siranda, Simpang Lima, Jl. Gajah Mada, Jl Pemuda, Johar Post Office, Jl. Ronggowarsito and finished in Tanjung Emas Harbour. 2. ”Back” stripe : Starting from Tanjung Emas Harbour, Jl. Ronggo Warsito, Johar Post Ofice, Jl Imam Bonjol, Tugu Muda, Kali sari, Jl S Parman, Taman Diponegoro Elisabeth, Jl Sultan Agung, Kaliwiru, Jatingaleh,  Gombel , Jl Setia Budi, and finished in  Srondol. The bench marks that were measured for the elevation were : 1. “Go and Back” Stripe : a. TTG 449 in front of ADA Store  Srondol b. DTK 348 in forked road of  Jl Setia budi and Jl Kyai Mojo c. DTK 346 in forked road of Jl Setiabudi and Jl Gombel Lama d. BM Gombel in Jl Gombel Lama e. TTG 447 at the clock monument at Kaliwiru f. DTK 341 in front of AKPOL g. DTK 340 at  Diponegoro park near Elisabeth Hospital h. Go back to TTG 449 passing the same BM. 2. Circle stripe : a. DTK 340 at Diponegoro park near Elisabeth Hospital b. BM 6 Pelabuhan in front of  Siranda Hotel c. DTK 002 at simpang lima field d. DTK 335 at Jl Gajah mada e. BM Sub-District Border in front of Johar Post Office f. BM Tidal Observation Station at Tanjung Emas Harbour Semarang g. BM Drip in front of Johar Post Office h. TTG 446 at Tugu Muda Park i. DTK 338 at the crossroad of Jl Ngaglik lama, Jl Rinjani and Jl S Parman INTERNATIONAL CONFERENCE Geomatics, Fisheries and Marine Science for a Better Future and Prosperity ____________________________________Semarang, Indonesia, October 21st – 22nd  2008 FISHERIES and MARINE SCIENCE 333 j. BM Kop A Yani 16 in front of Gajah Mungkur Sub-District office k. DTK 014 in front of Gajah Mungkur Sub-District office l. DTK 340 at Diponegoro park near Elisabeth Hospital BM elevation data gained were compared with the previous elevation data to analyze the value of land subsidence. More over the value of land subsidence was also compared with the previous data to know the change of subsidence rate. The elevation and subsidence rate data were input for making elevation contour map and land subsidence contour map in coastal area of Semarang.  3. RESULT AND DISCUSSION Result  The elevation of BMs in Coastal area of Semarang are shown in table 1, Based on the leveling measurement from TTG 449 as a reference point. Table 1. BM elevation in Semarang City  BM Name Location Coordinate Position Elevation ( m from MSL) LS BT Sep 02 Sep 05 Jun 06 TTG - 449 Srondol  07003’43,4”  110024’49,1” 221,004 221,004 221,004 DTK - 348 Srondol 07003’06,8” 110025’01,7” 232,418 232,418 232,418 DTK - 346 Gombel 07002’39,1” 110025’17,1”  - 247,639 247,639 BM 5 Gombel 07002’23,7” 110025’15,9” 222,492 222,487 - BM Gombel Gombel 07002’01,7” 110025’01,4”  - 167,068 167,068 TTG - 447 Kaliwiru  07001’24,4”  110025’14,4” - 105,250 105,250 DTK - 341 Akpol 07000’56,1” 110025’07,1” 100,102 99,996 99,996 KopYani 15 Diponegoro Park 07000’28,2” 110024’58,0” 90,120 89,991 - DTK - 340 Diponegoro Park 07000’28,2” 110024’58,1” 90,365 90,237 90,235 DTK 339 Siranda 07000’03,7” 110025’06,3” - 58,671 58,669 BM 6 .Pel.  Siranda 06059’52,8” 110025’06,1”  - 34,211 34,207 DTK-002 Simpang lima  06059’26,4”  110025’19,6” - 3,647 3,604 DTK-335 Jl Gajah Mada 06058’44,3” 110025’15,4  - 2,566 - BM. Kec. 1 Johar 06058’09,6” 110025’28,4”  - 1,420 - BM. Kec. 2 Kalisari 06059’46,4” 110024’28,7” - - 38,430 BM. Drip Johar 06058’10,5” 110025’27,4”  - 1,110 1,053 TTG-446 Tugu Muda 06059’01,6” 110024’34,3” 4,7145 4,512 4,467 DTK - 338 Ngaglik Lama  06059’49,4”  110024’25,0” 43,121 42,945 42,934 KopYani 16 Gajah Mungkur  07000’16,5”  110024’23,0” 91,070 90,925 90,927 DTK - 014 Gajah Mungkur  07000’16,5”  110024’32,8” 91,532 91,385 91,338 BM 7 TPKS Harbour 06056’52,5” 110025’33,6” - 1,242 1,171 BM 6 TPKS Harbour 06056’46,5” 110025’38,8” - 1,507 1,434 BM.I SPPII1 Harbour 06056’41,5” 110025’39,3” - 2,989 2,931 BM 8 TPKS Harbour 06056’31,7” 110025’28,4” - 0,965 0,880 INTERNATIONAL CONFERENCE Geomatics, Fisheries and Marine Science for a Better Future and Prosperity ____________________________________Semarang, Indonesia, October 21st – 22nd  2008 FISHERIES and MARINE SCIENCE 334  Land subsidence rate was known based on elevation data in September 2005 and Jun 2006 as shown in table 2 Table 2. Land subsidence rate of BMs in Semarang   BM name Location Coordinate Position Average Subsidence rate (cm/thn) LS BT TTG – 449 Srondol  07003’43,4”  110024’49,1” 0 DTK – 348 Srondol 07003’06,8” 110025’01,7” 0 DTK – 346 Gombel 07002’39,1” 110025’17,1” 0 BM 5 Gombel 07002’23,7” 110025’15,9” - BM Gombel Gombel 07002’01,7” 110025’01,4” 0 TTG – 447 Kaliwiru  07001’24,4”  110025’14,4” 0 DTK – 341 Akpol 07000’56,1” 110025’07,1” 0 KopYani 15 Diponegoro Park 07000’28,2” 110024’58,0” - DTK – 340 Diponegoro Park 07000’28,2” 110024’58,1” 0,267 DTK 339 Siranda 07000’03,7” 110025’06,3” 0,267 BM 6 .Pel.  Siranda 06059’52,8” 110025’06,1” 0,533 DTK-002 Simpang lima  06059’26,4”  110025’19,6” 5,733 DTK-335 Jl Gajah Mada 06058’44,3” 110025’15,4 - BM. Kec. 1 Johar 06058’09,6” 110025’28,4” - BM. Kec. 2 Kalisari 06059’46,4” 110024’28,7” - BM. Drip Johar 06058’10,5” 110025’27,4” 7,6 TTG-446 Tugu Muda 06059’01,6” 110024’34,3” 6,0 DTK – 338 Ngaglik Lama  06059’49,4”  110024’25,0” 1,467 KopYani 16 Gajah Mungkur  07000’16,5”  110024’23,0” 0 DTK – 014 Gajah Mungkur  07000’16,5”  110024’32,8” 6,267 BM 7 TPKS Harbour 06056’52,5” 110025’33,6” 9,467 BM 6 TPKS Harbour 06056’46,5” 110025’38,8” 9,733 BM.I SPPII1 Harbour 06056’41,5” 110025’39,3” 7,733 BM 8 TPKS Harbour 06056’31,7” 110025’28,4” 11,333   The linear trend assumption was used in determining the land subsidence rate. Sutanta and Hobma (2002) explained that it was very hard to determine the most accurate scenario for land subsidence in Semarang since the dynamic of natural factor and human intervention. A simplicity had been made to determine it. It was the land subsidence was assumed following linier trend and using the newest data as a base of subsidence forecasting.  Elevation and land subsidence contour map in Semarang is shown in figure 1 and 2 below INTERNATIONAL CONFERENCE Geomatics, Fisheries and Marine Science for a Better Future and Prosperity ____________________________________Semarang, Indonesia, October 21st – 22nd  2008 FISHERIES and MARINE SCIENCE 335 110.4 110.42 110.44-7.06-7.04-7.02-7-6.98-6.96 September 2005 110.4 110.42 110.44-7.06-7.04-7.02-7-6.98-6.96 Jun 2006  Fig 1. Elevation Contour Map of Semarang (in M + MSL) 1 km U U 1 km INTERNATIONAL CONFERENCE Geomatics, Fisheries and Marine Science for a Better Future and Prosperity ____________________________________Semarang, Indonesia, October 21st – 22nd  2008 FISHERIES and MARINE SCIENCE 336 110.4 110.42 110.44-7.06-7.04-7.02-7-6.98-6.96  Fig 2. Land Subsidence Contour Map of Semarang (in cm/tahun)  Discussion  According to table 1 and 2; figure 1 and 2, Bench marks which are above MSL + 100 m in height were stable enough. The closer to the sea, the faster land subsidence occurs. Based on Wirasatriya (2005) soil type in coastal area of Semarang which included young-soft soil type makes it still underwent compression / consolidation.  More over, coastal area of Semarang which is the center of the city U 1 km INTERNATIONAL CONFERENCE Geomatics, Fisheries and Marine Science for a Better Future and Prosperity ____________________________________Semarang, Indonesia, October 21st – 22nd  2008 FISHERIES and MARINE SCIENCE 337 activity such as industry, buildings, reclamation, crowded transportation, and many artisian well has made land subsidence happens faster. Based on Suhandini (2004) in http://www.landpolicy.org, the land subsidence rate depended on the burden on the land. The heavier burden, the faster land subsidence happens. It was observed in Semarang that because of 5 tons burden, it would be lower the land about 0,0102 m -0,4098 m. Suripin (2002) had found the correlation between the land subsidence rate and the height of pilling and also between the land subsidence rate and the reduction of under ground water elevation. Those correlation are shown at equations below : Y = 0,159 X2,5069  R2 = 0,9954 Y = Land Subsidence rate (m) X = Pilling Height (m) S = 6,5267 SU0,6394 (R2 = 0,9904) S = Land Subsidence Rate (m) SU = The reduction of under ground water (m)  A research team from Mineral Engineering Faculty, Bandung Institute of Technology stated that the reduction of under ground water elevation in Semarang caused the degradation of the land about 0,6 – 1,2 cm/year in rate (Suripin, 2002). Data from Geology and Environment Management Agency (1999) showed that the amount of artisian well pipes increased fast in Semarang. In 1982 there were 127 pipes noted and they sucked under ground water about 13,49 million m3. In 1998, there were 776 pipes noted and it caused 35,64 million m3 of under ground water is sucked. There fore it is necessary to make an effective rule to control the under ground water sucking.    The fastest land subsidence occurs in Tanjung Emas Harbour (Pelabuhan Tanjung Emas). It reached more than 10 cm/year. Tanjung Emas harbor has very crowded industry activity where in that area is located many large factories. Those large factories are also have artisian well to supply their water demand. More over, loading and unloading activity of trailer truck that bring tons of cargo and the existing of north main street with its traffic add to the burden of soil in Tanjung Emas Harbor. Therefore it is important to manage the human activity at coastal area of Semarang City in order to prevent the worsening of land subsidence.     INTERNATIONAL CONFERENCE Geomatics, Fisheries and Marine Science for a Better Future and Prosperity ____________________________________Semarang, Indonesia, October 21st – 22nd  2008 FISHERIES and MARINE SCIENCE 338 4. CONCLUSIONS   The conclusion of this research are : 1. Areas at Semarang city where have elevation above 100 m + MSL are stable enough and do not undergo land subsidence 2. The closer to the sea, the faster land subsidence occurs and the fastest land subsidence occurs in Tanjung Emas Harbour (Pelabuhan Tanjung Emas).  REFERENCES Arikunto, S. 1993. Research Procedure : A Practice Approach, Rineka Cipta, Jakarta BAPPEDA Semarang. 2000. The Coastal and Sea Area Profile of Semarang City. BAPPEDA. Semarang http://www.landpolicy.org. Semarang, A city that Ignores Land Use Management  and Environment. Browsing on 26 June 2004 Muhrozi; S Pranoto dan Nasrullah. 1997. Study on Determining Land Subsidence at the Lower Land of Semarang. Civil Engineering , Diponegoro University, Semarang Suripin, 2002. Model Development of Ground Water Abstraction and Land Subsidence Potential Maps at The North Coast of Semarang Based On GIS. Civil Engineriing Study Program. Engineriing Faculty Diponegoro University. Semarang. 32 p Sutanta, H dan TW Hobma. 2002. Preliminary Assessment of The Impact of Land Subsidence and Sea Level Rise in Semarang, Central Java, Indonesia. Proceeding PORSEC. Bali Wirasatriya, A. 2005. Sudy of Sea Level Rise as a Basis of Rob Flood Problem Solving at Coastal Area of Semarang. Thesis : Coastal Resources management, Diponegoro University, Semarang        

THE STUDY OF  LAND SUBSIDENCE RATE AT COASTAL AREA OF SEMARANG CITY, INDONESIA

THE STUDY OF  LAND SUBSIDENCE RATE AT COASTAL AREA OF

SEMARANG CITY, INDONESIA

http://eprints.undip.ac.id/51177/1/paper.pdf

THE STUDY OF LAND SUBSIDENCE RATE AT COASTAL AREA OF SEMARANG CITY, INDONESIA

Abstract

Similar works

Full text

Available Versions

Diponegoro University Institutional Repository

Diponegoro University Institutional Repository