study of the sedimentation trend in the prospective …

36 BULLETIN OF THE MARINE GEOLOGYVolume 24 No. 1, June 2009

STUDY OF THE SEDIMENTATION TREND IN THE PROSPECTIVE AREA OF PORT OF MARINE CENTER, CIREBON BASED ON REMOTE SENSING DATA

by :

Undang Hernawan 1)

(Manuscript received December 02, 2008)

ABSTRACT

A coastal zone is the interface between the land and water that influenced by both ofthem. Coastal dynamic is influenced by many factors from land and sea, such as sedimentationand current. In order to support marine facility, Marine Geological Institute (MGI) plan to builda port. The prospective area is behind MGI office at Cirebon. This study use multi temporalremote sensing data in order to observe trend of coastline change around MGI.

Based on the interpretation of the data, there are sedimentation around the MGI water andabrasion due to the presence of Kejawanan’s jetty and Kalijaga River. The result also shows thatthe current in this region is moving from southeast to northwest. The presence of the Kejawanan’sjetty stymies the movement of sediment. The sediment which is normally moving to the north ofthe jetty is then trapped on the south side of the structure, so that the sediment precipitates in thisregion and makes it as the active region of sedimentation and accretion. The presence mangroveconduces to support sedimentation speed and accretion at this region, because of his function asthe catchment area. Abrasion occurs in the eastern part of MGI office at the Kalijaga river mouthwithin the bay. The Kalijaga River mouth is predicted to be the primary source of sedimentation inthis area.

The coastline change caused by sedimentation will be continuing as long as it is supplied bythe sediment. The direction of the sedimentation is parallel to the jetty and it forms ellipsoid, withthe sedimentation/accretion region is behind MGI office. The abrasion area is found in KalijagaRiver mouth and a small area beside Kalijaga River. In order to build a port, we have to considerthis sedimentation process. One of the alternatives to build the port is to make a quay pile modelwhich gives way the current to pass through the other side of the port. Another alternative is tobuild the port as a pond model but it needs accuracy in building the mouth of jetty to minimize thesedimentation process.

Keyword : sedimentation, Cirebon, remote sensing

SARI

Pantai/pesisir merupakan wilayah antara daratan dan lautan yang masih dipengaruhi olehkeduanya. Dinamika pantai dipengaruhi oleh faktor-faktor dari daratan dan lautan sepertisedimentasi dan arus. Untuk menunjang “marine facility center” Puslitbang Geologi Kelautan

1. Marine Geological Institute, Jl. Dr. Junjunan No. 236 Bandung

37BULLETIN OF THE MARINE GEOLOGYVolume 24 No. 1, June 2009

(P3GL) bermaksud untuk membangun pelabuhan. Daerah yang prospektif adalah di belakangkantor P3GL, Cirebon. Studi ini menggunakan data citra satelit multi temporal, yang bergunauntuk melihat arah perkembangan dan perubahan garis pantai di belakang kantor P3GL dansekitarnya.

Berdasarkan interpretasi data citra, di daerah studi ditemukan adanya daerah akresi/sedimentasi dan daerah abrasi yang disebabkan oleh adanya dermaga Kejawanan dan adanyasungai Kalijaga. Hasil studi juga menunjukkan arah arus umumnya bergerak dari tenggaramenuju barat laut. Keberadaan jetty Kejawanan menyebabkan aliran arus dan sedimen terhenti.Sedimen yang seharusnya bergerak ke arah utama menjadi terhalang dan terjebak di bagianselatan jetty, sehingga mengendap di daerah ini. Keadaan ini menyebabkan daerah ini menjadidaerah sedimentasi yang aktif (akresi). Keberadaan mangrove pada daerah ini juga menambahkecepatan sedimentasi di daerah ini, karena berfungsi sebagai daerah tangkapan sedimen. Abrasiterjadi di sebelah timur P3GL, tepatnya pada daerah lengkungan teluk dan di mulut sungaiKalijaga. Daerah mulut sungai Kalijaga diprediksi sebagai sumber sedimen pada daerah ini.

Perubahan garis pantai yang disebabkan oleh sedimentasi akan terus berlangsung di daerahini, selama adanya pasokan sedimen. Sedimentasi ini akan berlangsung sampai arahnya sejajardengan jetty Kejawanan dan akan membentuk ellipsoid, dengan daerah sedimentasi berada disekitar jetty dan belakang P3GL sementara daerah abrasi berada di sungai Kalijaga dan daerahsebelahnya. Karena itu, pembangunan pelabuhan P3GL sebaiknya memperhatikan kondisi ini.Salah satu alternatifnya adalah dengan membuat pelabuhan model tiang pancang yangmemungkinkan arus dan sedimen untuk bergerak ke sisi sebelahnya. Alternatif lain adalah dalambentuk kolam pelabuhan, tetapi harus tepat memperhatikan mulut pelabuhan untukmeminimalkan sedimentasi yang terjadi.

Kata kunci : sedimentasi, Cirebon, citra satelit

INTRODUCTIONThe term "coastal zone" means the

coastal waters (including the lands thereinand thereunder) and the adjacentshorelands (including the waters thereinand thereunder), strongly influenced byeach and in proximity to the coastlines ofthe several coastal states, and includesislands, transitional and intertidal areas,salt marshes, wetlands, andbeaches.(http://mapping2.../glossary.html). Coastal dynamic isinfluenced by many factors from land andsea, such as sedimentation and current.Human activities in the land/uppercoarse still can influence to coastaldynamic, such as transporting suspendedmaterial to the coast and it is precipitatedas sedimentation (Dahuri et al, 2004).

These zones are important because amajority of the world's population inhabitsuch zones. Coastal zones are continuallychanging because of the dynamicinteraction between the oceans and theland. Waves and winds along the coast areboth eroding rock and depositingsediment on a continuous basis, and ratesof erosion and deposition varyconsiderably from day to day along suchzones. The energy reaching the coast canbecome high during storms, and suchhigh energies make coastal zones areas ofhigh vulnerability to natural hazards.(http://www.tulane.edu/~sanelson/geol204/coastalzones.html)

Marine Geological Institute (MGI)plans to build a port in order to supportthe marine facilities. One of the factorsthat influence the jetty is sedimentation on


this area. MGI office is located betweenKalijaga River in the southeast that supplysediment and Kejawanan’s jetty in thenorth that changes current direction.

Consequently, stabilization of thecoastline is one of the most importantconsiderations when highway facilitiesare located in the coastal zone. It is alsonecessary to determine the dominantgeomorphic processes of the coastline.This type of information may be obtainedfrom borings, soil surveys, analysis ofaerial photographs, and fieldreconnaissance. Because coastlines mayhave significant temporal variability, it isnecessary to obtain sufficient historicaldata to identify either this variability orlong-term trends. (http://www.fhwa.dot.gov/.../hec25.cfm)

Remote sensing technology is anaccurate technology which record theearth continuously, real time, and up todate, so relatively accurate for describingreal condition on the earth and capable todetect environmental changes on long-term trends. One of remote sensing data isLandsat Thematic Mapper (TM) formiddle resolution and Quickbird imageryfor high resolution. Desiderating of usingof remote sensing technology is todescribe sedimentation process base oncoastal line change on long-term andpredict trends of the sedimentation in thenext time.

METHODThe material for this study is Landsat

TM imagery that acquired in 1995, 2000and Quickbird imagery that acquired inMarch 2002 (rainy season), acquiring June2002 (dry season) and 2006. The softwarefor data processing is Erdas Imagine,Ermapper and MapInfo.

The method is comparison betweenmulti-temporal imagery that shows

environmental changes and its impact tosedimentation and coastal line changes.The interpretation of general current hasbeen done also by analysis of turbidityand suspended material. Landsat TMimagery can show turbidity andsuspended material in band 1, 2 and 3which used in this interpretation.

RESULT AND ANALYSISFigure 1 show Quickbird imagery of

Cirebon’s coastal zone area, exactlybehind MGI Office. MGI office locatedbetween Kalijaga River in the southeastand Kejawanan Jetty in the north.

A coastline is not static. As wavesapproach shore and feel the bottom, waterpiles up and breakers form. Primarilythese waves, breaking at an angle to thecoastline, are what generate a "longshorecurrent" that parallels to the shore. Importantly, the longshore current is notonly moves water in the surf zone, but it isalso moves the sediment parallel to thecoastline. The longshore current and theresulting transport of sediment is only oneof the dynamic processes that constantlyalters the coastline. As waves repeatedlyhit the shore, water moves onto the beachand then retreats in a continuous cycle. However, the waves are not all that moveson the coastline. In fact, the sediment onthe shore is also always on the move. Great energy is expended on the beach aswaves crash against the coastline. Thisenergy allows the water to transportsediment. The grains are lifted as thewaves in the swash zone move onto thebeach, and then the grains are depositedagain as the water retreats. As long as thewaves hit the coastline straight on (i.e., thewave crests are parallel to the coastline),the sand grains will be picked up andredeposited in the same general area. Inthis case, no real net movement of sand


occurs in the swash zone. However,waves generally do not form parallel tothe coastline, and thus, usually approachthe shore at an angle. Consequently,beach sand will have a net movement upor down the beach, depending on thedirection of incoming waves. This netmovement of the beach sand is known as“beach drift”. (http://www.earthscape.org/t1/vip01/vip01c.html). Figure 2 shows a generaldirection of current base on Landsat TMImagery.

The direction of the current dependson season, tide condition. Based on the

TM imagery, the general direction ofcurrent in study area is coming fromsoutheast toward northwest. This TMimagery acquired in dry season. Generaldirection in rainy season is opposite withthe dry season, i.e. toward southeast. Theaverage speed is 0,17 m/s. The wave inthe study derived from wind data. Winddirection that affected to wave is comefrom east with average direction 10 – 15knot. (Novico, 2006) As the wavesapproach the coast at an angle a currentdevelops which moves parallel to theshore (longshore current). Beachsediments move along with this current

Figure 1. Quickbird imagery of the study area


(longshore drift) (http://physics.uwstout.edu/IntroGeo/shorelines.htm). So, the major effect thatinfluence to the beach is from east-southeast.

The other factor that affect to thecoastline is beach structure. Structuressuch as jetty, piers or groins can alter thenormal course of beach drift. Jetties like inthe north of MGI office cause waverefraction, and alters the flow of thelongshore current, it does cause sedimentto be redistributed along the coastline. Sediment is trapped by the breakwater,and the waves become focused on anotherpart of the beach, not protected by the

breakwater, where they can causesignificant erosion. Similarly, becausegroins and jetties trap sediment, areas inthe downdrift direction are not resuppliedwith sediment, and beaches becomenarrower in the downdrift direction.(http://www.tulane.edu/.../coastalzones.htm). Figure 3. showsgeneral structure on the beach and itsimpact to the sediment movement.

The coastal zone behind MGI office isalso influencing by many factors such asexisting of Kejawanan’s jetty in the northof MGI and Kalijaga River in the southeastof MGI. Figure 4 shows the coastal linechange in this area based on imagery data.

Figure 2. General current of the study area


Generally, the coastal line has movedforward (accretion) along the coast line,except an area in the southeast of MGIbeside Kalijaga River. The biggestaccretion has been found besideKejawanan’s jetty, i.e. 400 m during 1995 –2006, that means, the average ofsedimentation is 26.3 m/year. Theaccretion behind MGI has an average of1.5 – 3.5 m/year. The abrasion area isfound in the mouth of Kalijaga River andin a small area at the basin behind KalijagaRiver.

The longshore current influences tocoastal line changes and sedimentationprocess, because this current moves thesuspended material and precipitates inother area. The direction of longshoretransport is directly related to thedirection of wave approach and the angleof the wave crest to the shore. Thelongshore current is the flow of waterparallel to the coastline that is driven by

the longshore component of the wave-induced thrust as it enters the surf zone.The longshore currents are responsible forthe downdrift movement of sediments inthe nearshore zone. The longshoresediment transport is influenced by thewave height, period, direction ofapproach, and the beach slope (AASHTO2004). The sediment that is carried withthe longshore current is called longshoreor littoral transport. (http://www.fhwa.dot.gov/engineering/hydraulics/hydrology/hec25.cfm)

In this area, current moves fromsoutheast to northwest and take thesediment material from the southeast.Figure 5a shows Quickbird imagery ofKalijaga River mouth in 2002 at the rainyseason that supply the sediment materialto this area; Figure 5b shows Quickbirdimagery 2006 in dry season that showsabrasion in this area.

Figure 3. General structure on the beach and its impact to the sediment movement


In rainy season, Kalijaga River takesmany sediment flows and it isprecipitated at the mouth of river.Another rill that just adrift on rainy seasonalso takes the sediment and it supplies tothis region but in small amount.Meanwhile on dry season, the influence ofmarine factor even greater than the river

flow, so that the sediment particle thoseare precipitated before in the mouth ofKalijaga River is flowing towardsnorthwest, MGI beach region, as aprospective area for the port. This regionundergoes abrasion. Abrasion in thisregion has an average of 20 m/yearsbetween years 2002 – 2006. Commonly, it

Figure 4. Coastal line change based on imagery from 1995 – 2006 Data source: a,b. Landsat TM (www.zulu.nasa.gov), c. Quickbird 2002, d. Quickbird 2006 (Google earth)


Figure 5. Quickbird Imagery at rainy and dry season

Figure 5. Sketch of the coastal line change beside jetty area(Modified from http://www.earthscape.org/t1/vip01/vip01c.html)


can be said that the sedimentation mainsource is come from Kalijaga River.

Mangroves grow up along thecoastline at this region, particularlybehind MGI office and besideKejawanan’s jetty, except a small area inthe northeast at the bay region besideKalijaga River that constitute abrasionregion. The presence of mangroveconduces to support sedimentationprocess in this region, because ofmangrove functions as catchment areaand place descent of sediment particles(sedimentation).

Jetty structure in the north of studyarea gives a major effect to coastlinechanges. The jetty is interfering with themovement of sediment down current. Assand moves toward the north, it is trappedby the jetty. As a result, sand accumulateson the south side of the structure. However, sand that would normallymoves to the north of the jetty is thentrapped on the south side of the structure. Figure 5 shows the sketch of coastal linechange beside jetty area.

PredictionCondition of waters behind MGI office

(prospective ports planning) constitutecalm region because the longshore currentthat move toward northwest will bestymied by Kejawanan’s jetty in thenorthwest. This situation causesprospective area of port planning untiljetty area constitute as sedimentation area.

This sedimentation process caused bysedimentation will be continuing as longas it is supplied by the sediment. In thewaters around of prospective port area,the sedimentation process will becontinuing. Sedimentation is estimateduntil equal with Kejawanan’s jetty evenexceeds it. Similarity with this place, thesedimentation process behind MGI office

will follow Kejawanan jetty location inellipsoid forms. Meanwhile erosion/abrasion is happening in the eastern partof MGI beside Kalijaga's river and atKalijaga's estuary. The presence ofmangrove in this region really determinescoastline changing preferably on erosionregion that can prevent and or reduceerosion. On the accretion region, thepresence of mangrove conduces tosupport sedimentation process.

Based on the sedimentation conditionthat exists in the prospective area,building a port have to consider of thissedimentation. One of the alternatives tobuild the port is to make a quay pilemodel which gives way the current topass through the other side of the port.The long of port model goes away towardmean exceed long of Kejawanan jetty.Another alternative is to build the port asa pond model but it needs accuracy inbuilding the mouth of jetty to minimizethe sedimentation process.

CONCLUSIONThe water behind MGI office area is an

active sedimentation area. Thesedimentation main source is predictedcome from Kalijaga River. The direction ofthe sedimentation is parallel to the jettyand its forms ellipsoid, with thesedimentation/accretion region is behindMGI office and the abrasion area inKalijaga River mouth and a small areabeside Kalijaga River. One of thealternatives to build the port is to make aquay pile model which gives way thecurrent to pass through the other side ofthe port. Another alternative is to buildthe port as a pond model but it needsaccuracy in building the mouth of jetty tominimize the sedimentation process.


ACKNOWLEDGEMENTThe author wish to thank Ir. Subaktian

Lubis, MSc, the director of MarineGeological Institute who has encourageme in preparing and publishing thismanuscript. The author also thank Mr.Franto as a Chief Scientist of the team whosupport me to study the material.

REFERENCESDahuri, R., Jacob, R., S.P. Ginting, dan M.J.

Sitepu. 2004. PengelolaanSumberdaya Wilayah Pesisir danLautan Secara Terpadu. PranadyaPramita. Jakarta.

http://mapping2.orr.noaa.gov/portal/calcasieu/calc_html/resources/glossary.html

https://zulu.ssc.nasa.gov/mrsid/

http://www.earth.google.com

http://www.earthscape.org/t1/vip01/vip01c.html

http://www.fhwa.dot.gov/engineering/hydraulics/hydrology/hec25.cfm

http://www.tulane.edu/~sanelson/geol204/coastalzones.html

Novico, Franto, Kris Budiono, PurnomoRahardjo, Yogi Noviadi, NineuYayu, Undang Hernawan. FauziBudi P. 2006. Pengembangan PusatPenelitian Dan PengembanganGeologi Kelautan Cirebon SebagaiMarine Center Tahap II. PusatPengembangan Geologi Kelautan.Bandung.

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