NON STRUCTURAL MEASURES FOR INTEGRATED WATER RESOURCES AND FLOOD MANAGEMENT FOR SEMARANG

Oky Subrata and William M Putuhena Reseach Center for Water Resources, Ministri of Public Work

(Jl. Ir, H. Juanda 193 Bandung, Indonesia)Email : okysubrata@gmail.com

Semarang city of Central Java province, Indonesia suffer from flooding cause of land-use change,high rainfall conditions and inadequate drainage system and high tides. Impact of floodings becomemore severe with the trend of urbanization and industrial growth. To overcome this problem, TheGovernment of Indonesia build Jatibarang Dam on the upper water catchment areas of the Garang Riveras the flood control in the framework of structural measures that is a part in flood management.Measures of flood control shall be successful if supported by non-structural methods through IntegratedWater Resources and Flood Management Project which includes watershed and disaster management.Watershed Management Activities consist of Erosion Control and Satellite Image Analysis to monitor landuse change and The Disaster Management activities consist of Development of Flood MonitoringFacilities, Development of Flood Hazard Map.

Analysis of flood monitoring results indicate that Garang catchment required hydrological gaugingfacilities, the flood monitoring center, the telemetry gauging stations, the data transmission system, andthe sirens and patrol cars for flood dissemination. Flood simulation Analysis for the 25-years returnperiod resulted in a reduction of inundation due to construction of the Dam of Jatibarang 10.18%.Sediment analyses show sediment control require a land planning regulations, making check dams andreforestation in some locations. The results were deducted from comparison of SPOT5 Satellite Image in1998 and 2008 showing a change in the condition of the land forest was reduced by 23%. The mixedfarm was reduced by 43%, and paddy field was reduced by 34%.

Keyword : Non Structural Measures, Flood Management, Hazard Map.

1. Introduction

Semarang City, the capital ofCentral Java Province, haspopulation of 1,740,000 as of 2013(1).The city and its surrounding areassuffer almost every year from floodsin the rainy season and fromshortage of water supply in the dryseason. The problem on watershortage will aggravate further inthe future due to the recent trendof population concentration to theurban area.Causes of flooding in the

area is due to the landuse change inupper catchments area, excessiverainfall in city area withinadequate drainage system and hightide during full moon.Degradation of protected areacapacity is causing fatal impact tohuman life. Floods in the rainyseason may trigger slope failure andextreme droughts may occur in thedry season. What happened in January1990 is an example of improper

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watershed management. The citySemarang at that time was seriouslydamaged by flash flood causing 47dead, destroying 25 houses, anddamaging 126 houses and 15 publicfacilities. Approximately 145 ha ofsettlement area flooded by twometers water elevation for threehours. Although the flash flood hadcaused a lot of damage, change ofland-use at Mt. Ungaran even showedan increase and development contraryto environmental principles resumed.Obviously, the community ownedprotected area (55%) had become verycritical.In addition, many investigationsalso identify serious landsubsidence in city area. Suchcondition shall increase thesusceptibility to flooding. Furthermore, land subsidence in the coastalarea of the City has progressed inthe past decade and will continuemore due to the excess groundwaterexploitation by the industrialsector. In order to suppress thepreset land subsidence, where annualrate observed from October 1997 toMay 2000 at 3 to 10 cm, theindustrial water source changedfrom groundwater to rivercompulsory.To mitigate these chronic problemsand to enhance the economicdevelopment and stabilization ofpeople’s livelihood, appropriatemeasures are indispensable forSemarang City and its surroundingareas. The city, provincial andcentral governments have implementedmany counter-measures regardingflood control, but up to presentdate, these efforts have beenunyielding, and lately there seems

to be a tendency of only partial andun-comprehensive concern.Up to present date, the dynamicdevelopment has changed Semaranginto a densely populated city. Moreand more settlement becomeintervening variable the open publicgreen space provided as protectedarea. The lack of constructions planof a new drainage system had ignoredthe basic principles of function ofthe two canals built during theDutch occupation.As has been mention above floods inSemarang city, occur due to land-usechange in upper catchments area.Damage to a river catchments due tochange of land-use in upper streamareas may increase land erosion,surface flow, river discharge andsediment transport causing negativeimpact to the river sectiondownstream such as decrease ofeffective dam life time generated bysedimentation.Attempts ofcontrolling sedimentation flow indams that could be done byimplementing a strategy startingwith decreasing land erosion byintroducing reforestation in rivercatchments areas, reducing surfaceflow, and extending flowconcentration time by combiningsediment and water quality control.To optimize these efforts aregulation is required on decidingappropriate location planning sothat control of land erosion andsurface flow to be a minimum.The problem of flood in Semarang isnever ending and has occurred sincethe Dutch occupation. If the Dutchhad constructed the East and WestFlood Canals, the Indonesiangovernment through a long tediousprocess has decided to construct the

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Jatibarang Reservoir as a method offlood control. The benefits of Jatibarang Reservoir

construction:a) Availability of electricity

generator with with capacity of1.5 MW.

b) Availability of raw water 1.05m3/sec for Semarang city.

c) Conservation areas in the upstreamd) Flood Control for Kali Garang/West

Canal with 50 years returnperiods.

e) Increasing a recreational area.f) Availability good environment

alongsideKali-Garang.Measures of flood control shall besuccessful if supported by non-structural methods, i.e.comprehensive watershed management,land-use complying to naturalcondition, control of erosion,control of flood prone area, , floodmonitoring and flood warning system,flood plain control and lawenforcement.1.1. ObjectivesThe objectives of the non-structuralmeasures management are as follows:a) To mitigate the damages inflicted

by the extraordinary flood thatexceeds the design flood level ofthe structural flood mitigationmeasures along K. Semarang,downstream of Simongan weir byproviding necessary and timelyflood information to the localpeople and government authoritiesconcerned with flood warning anddefensive activities.

b) To ensure the effectiveness andsafe operation of the existingflood control facilities withinKali Garang and Kali SemarangDrainage area.

c) To control landuse condition.

1.2. Project location

The Kali Garang catchments covers anarea of 10.000 ha, Kali Kripik 3.400ha, and Kali Kreyo 7.000 ha.

Figure.1. Location of Project area.

2. Materials and MethodsCharacteristic of Integrated FloodManagement (IFM) is considering ariver areas as a dynamic system thatis interaction between river bodyand land by which one principle isrisk management.(WMO & Global WaterPatnership ). Characteristics of IFMare as follows: Integration–particularly in terms

of institutional arrangements. Flood management should be

intertwined with droughtmanagement through the effectiveuse of floodwater

Measures to change the runoffregime should consider effectsholistically (e.g. link between

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deforestation, urbanisation,runoff and landslides)

All floods should be “managed” andnot just the ones up to a certaindesign standard.

2.1. Flood Monitoring FacilitiesThe facilities would involve thehydrological gauging facilities, theflood monitoring center, thetelemetry gauging stations, the datatransmission system, and the sirensand patrol cars for flooddissemination.

HidrologicalGauging Facility

Dam Monitoring Facility

Flood Monitoring

Telecommunication FacilityTransmittal of Flood

Information

Flood Monitoring/Command Center

Flood Warning SirenPatrol Car

Dissemination of Flood to Relevant Agencies and

Local Community

Figure 2. Flow Design for warningsystem.

2.2. Flood Hazard MapReasonable solution in this fieldintroduces Flood Directive ([FloodDirective, 2007]). Two stepsapproach is required to identifyflood hazard and flood risk. Firststep include assessment ofpreliminary flood risk based on thehistorical floods which havesignificant adverse impacts on humanhealth, the environment, culturalheritage and economic activity andfor which the likelihood of similarfuture events is still relevant. Onthe basis of a preliminary flood

risk assessment each country willidentify those areas for which theyconclude that potential significantflood risks exist or might beconsidered likely to occur. And forthese areas flood hazard maps andflood risk maps should be prepared.By flood hazard, it is generallyunderstand the likelihood of a floodhappening in a certain place at acertain time.Information abouthazard is presented on maps. As aminimum, they include the borders ofthe area at risk of a “referenceflood” - generally a flood of adefined probability ofoccurrence.Apart from the linesmarking out the range of floods,risk maps often include informationon the depth and velocity of thewater. Flood risk maps for terrainssituated on riversides are developedin many countries, based on modelanalyses or historical floods.Operationally, flood hazard map isdefined as a map that provides withgeographical information that isessential for local residents toconduct “safe and smooth evacuation.Usually, when floods comes,residents are not aware of possibleflooding at their home; are notwilling to move even when danger iscoming close; do not know how toreact to warnings; do not know whereto evacuate. Also, flood response(civil defense) officials areimmersed with (mis)information andcry for help because they may notknow what are actually happening inthe field. It is expected that floodhazard map is a tool to mitigaterecurrent tragedies by addressinglack and/or confusion of essentialinformation for evacuation. Floodhazard map is a tool to helpresident to be preliminarily

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prepared for flooding; to be alertwhen flood occurs; to safelyevacuate in emergency(Kenzo Hiroki,…. )Historical information (humanmemory, chronicles etc.), These areextremely important sources ofinformation about where thesephenomena have occurred in the past,and what their extent was. Withtoday’s increased mobility, however,people are not always sources ofinformation that can allow us toidentify catastrophes from long ago.They include data concerning thespeed of the phenomenon’s course,the extent of potential flood areas,and describe warning system forinhabitants and owners of propertyat risk.

2.3. Erosion ControlThe method adopted to estimate soilerosion in a land in this study isUniversal Soil Loss Equation (USLE).This equation computes the potentialsoil loss as a function soilerodibility, rainfall erosivity, andtopographical factor. Actual erosionis when human intervention is takinginto account. The general USLEequation is

A = R.K.L.S.C.PA = Soil loss (annual average) in ton/ha. R = Rainfall erosivity K = Soil erodibility L = Length of slope factorS = Slope factorC = Vegetation factorP = Conservation practice

2.4. Satellite Image Analysis

The compilation of land-use mapsusing satellite images (SPOT 5) isdevided into several stages ofimplementation, namely, preparation,satellite image processing,interpretation and satellite imageclassification, data cleaning aswell as attribute editing. Recordingof remote sensing data by satellitesensor can be based on reflection orobject electromagnetic radiation onground surface. The satellite issituated at remote distance from theearth station, but data recorded bysatellite are transmitted at theinstant to the earth station. These raw data can make use ofsatellite remote sensing datathrough data digital processing .These data are processed to returndata/pictures of objects on groundsurface relevant with actualconditions and not interfered byother data. The process of digitalsatellite remote sensing images canbe classified as follows: a. Data pre-processing comprising

radiometric and geometriccorrection.

b. Image re-construction, that is,image recovery because ofdisruption of data transmissionfrom the remote sensing satelliteto earth station.

c. Image cleaning improving the imagequality so that the images can beused for further implementation ofdigital processing or visualinterpretation.

d. Object classification referring tothe detection of class or type ofobject at different image.

3. Result3.1. Flood Monitoring FacilitiesAim of the establishment is thesehydrological stations can provide

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the hydrological data required forthe support of flood forecasting andearly warning, so that lossestriggered by floods commonlyoccurring in the Garang catchmentcan be minimized.Analysis for daily rainfalls duringfour flood occurrences werecollected from the stations Mijan,Gunungpati, Sumurjurang, Susukan,Ungaran and Medono. Distances amongthe stations are depicted on Table1.

Table 1. Distances among RainfallStations in km

Nam e M ijan GunungpatiSum urjurang Susukan Ungaran M edonoM ijan 0 6.63 10.04 11.44 13.26 9.88

Gunungpati 6.63 0 3.88 5.18 7.09 5.99Sum urjurang 10.04 3.88 0 1.43 3.4 6.38Susukan 11.44 5.18 1.43 0 2.14 7.39Ungaran 13.26 7.09 3.4 2.14 0 9.01M edono 9.88 5.99 6.38 7.39 9.01 0

Four flood occurrences weredocumented, namely :1. 20-21 January 1990, peak

discharge recorded at Simongan549 m3/s, with maximum rainfallconcentrated at Gunungpati andminimum rainfall at Simongan,whereas minimum rainfall forGarang sub-catchment was observeat Susukan. The distribution ofstorms could be categorized ashomogeneous since the differencebetween maximum and minimum wassmall.

2. 26 January 1990; peak dischargerecorded at Simongan 1104 m3/s,with maximum rainfallconcentrated at Medono and Mijan,whereas minimum rainfall wasfocused at Simongan. The minimumrainfall for Garang-SimonganCatchment was at Susukan andSumurbarang. The distribution ofstorms could be categorized ashomogeneous since the difference

between maximum and minimum wassmall.

3. 29 January 1993; peak dischargerecorded at Simongan 976 m3/s,with maximum rainfall wasconcentrated at Medono andSimongan and the depression(minimum rainfall) at Susukan.The distribution of storms iscategorized as non homogeneous asdiscrepancy of maximum (232 mm)and minimum (59 mm) was large.

4. 22 January 2002; peak dischargerecorded at Simongan 893 m3/s,with concentration of maximumrainfall at Medono and Ungaran,and depression (minimum rainfall)at Simongan,. Distribution ofstorms can be classified ashomogeneous since differencebetween maximum and minimum wassmall.

The water level and rainfallstations are needed especially formonitoring flood peak record atdownstream of K. Garang. Due tounsufficient flood data formonitoring disaster management, thenew hydrological stations whichconsist of water level and rainfallstations become very important formonitoring flood peak discharge flowto Jatibarang dam and downstream ofGarang River. This dam is planned tobe in the Kreo River, one of the K.Garang’s tributary. The new gaugingand rainfall stations which isproposed in K. Garang catchment.

3.2. Development of Flood HazardMap

This data may help in identifyingareas at risk of flash floods. Thestandard procedure for marking outsuch areas is a combination ofhydrological and hydraulic modelling

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with GIS spatial analyses. Digitalmaps (spatial databases), ifavailable, facilitate not only themarking out of areas at risk, butalso analyses of who and what is indanger. These analyses are worthverifying and adding to. Localexperiences can be used to this end,if possible, to inscribe on the mapthe extent of historical floods.This can be enhanced together withlocal services, and even withresidents of a chosen location.Modeling of river flow need to besimulated and calibrated todetermine the condition andcharacteristics of flooding in thefield. The calibration model is thefirst step to be done becauseresults of the calibration processwill be used to assess the accuracyof model to the naturalcharacteristics, in this case floodsevents (inundation and water level)to be simulated. If theschematization model complies withthe conditions in the field , nextstep can proceed to the stage ofestablishment of scenario, but ifnot, corrections are to be made onparameters of model used. In thiscase, simulations in the Kali Garangare performed in three scenarios,namely: 1) Existing conditions, where

condition of rivers in actualstate had not been studied suchas the construction ofJatibarang dam and heightening ofembankment.

2) Condition after construction ofthe Jatibarang dam in KaliKreo.

3) Condition due to construction ofthe Jatibarang dam combined withthe heightening of embankmentstarting at the confluence of

Kali Kreo, Kali Kripik and KaliGarang Hulu.

For the case of floods in the KaliGarang, was determined that floodevents used to calibrate the modelwill be the Q25 flood discharge.According to these conditions, itcan be concluded if calibration(base case) done for modelparameters (initial conditions androughness of channel) has beenappropriate, and able to generatewater flow conditions in accordancewith field conditions. Overlandsimulation results of Q 25th SOBEKare combined with results of fieldobservations where largest floodevent occurred in 1990, especiallyin Desa Sampangan, indicated arunoff of Q25 more than 50 km.This demonstrates the accuracy ofmodel to the natural characteristicsof simulated flood events(inundation and water level).

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Figure 3. simulation results of 25years return period flood (existingcondition and DAM contruction).

3.3. Erosion ControlBased on the erosion control activities using year data 2008, itcan be evaluated as follows:a) Sub Catchment Garang Hilir: with 2

recharging wells, then wouldreduce the critical area into 881ha or 36 % (decreasing criticalland 2%)

b) Sub Catchment Garang Hulu: withpublic forest 125 ha, city forest25 ha, public forest enrichment100 ha, 1 gully plug, 2 controldam and 2 recharging well, thenwould reduce the critical landinto 3,178 ha or 57,7% (decreasingcritical land 7.98%)

c) Sub Catchment Kreo: with publicforest 75 ha, and 3 rechargingwells, and 1gully plug, then wouldreduce the critical land into3,549 ha or 56.497% from the totalsub Catchment Kreo (decreasingcritical land 5,22%).

d) Sub Catchment Kripik with publicforest 75 ha, city forest 25 ha,public forest enrichment 25 ha,and 1 recharging well, then wouldreduce the critical land into2,175 ha or 60.58% (decreasingcritical land 4,48%).

3.4. Satellite Image AnalysisLand-use maps can be used asreference in the establishment ofland-use plans required indevelopment activities, so that moreaccurate zoning can be done. Land-use maps can also be applied inflood models for indication of land-use composition approptiate forflood control. These models mayindicate areas prove to floods,

disadvantages probably occuring,land conversion value, and immensityof area.

7000 0 7000 M eters

G rg_lu.shpG edungHutanJalanKebun/PerkebunanPerm ukim anRum putSaw ahSem ak B elukarSungai/D anau/W aduk/S itu/Telaga/K olamTanah K osongTegalan/Ladang

N

Figure 4. Land-use in Garangcatchment based on imageinterpretation result.

4. Discussion4.1. Flood Monitoring FacilitiesBased on the references, the projectreports, some information from BalaiPengelolaan DAS and siteinvestigation, there are only a fewhydrological stations available inK. Garang catchment. These are dueto the equipment of the hydrologicalstations and environment conditions.The new water level and rainfallstations are needed especially formonitoring flood peak record atupstream and downstream of K.Garang. Due to insufficient flooddata for monitoring disastermanagement, the new hydrologicalstations which consist of waterlevel and rainfall stations becomevery important not only formonitoring flood peak discharge flowto Jatibarang dam but also formonitoring flood at downstream ofGarang River. The dam is planned to

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be built in the Kreo River, one ofthe K. Garang’s tributary.

JATIBARANG DAMJATIBARANG DAMJATIBARANG DAMJATIBARANG DAMJATIBARANG DAMJATIBARANG DAMJATIBARANG DAMJATIBARANG DAMJATIBARANG DAM

1. Pramuka1. Pramuka1. Pramuka1. Pramuka1. Pramuka1. Pramuka1. Pramuka1. Pramuka1. Pramuka

2. Kreo 2. Kreo 2. Kreo 2. Kreo 2. Kreo 2. Kreo 2. Kreo 2. Kreo 2. Kreo MundinganMundinganMundinganMundinganMundinganMundinganMundinganMundinganMundingan

3. u/s Confluence3. u/s Confluence3. u/s Confluence3. u/s Confluence3. u/s Confluence3. u/s Confluence3. u/s Confluence3. u/s Confluence3. u/s ConfluenceKreo kripikKreo kripikKreo kripikKreo kripikKreo kripikKreo kripikKreo kripikKreo kripikKreo kripik

5. Up Stream5. Up Stream5. Up Stream5. Up Stream5. Up Stream5. Up Stream5. Up Stream5. Up Stream5. Up StreamSimonganSimonganSimonganSimonganSimonganSimonganSimonganSimonganSimongan

4. u/s Confluence4. u/s Confluence4. u/s Confluence4. u/s Confluence4. u/s Confluence4. u/s Confluence4. u/s Confluence4. u/s Confluence4. u/s ConfluenceGarang KreoGarang KreoGarang KreoGarang KreoGarang KreoGarang KreoGarang KreoGarang KreoGarang Kreo

6. River Mouth6. River Mouth6. River Mouth6. River Mouth6. River Mouth6. River Mouth6. River Mouth6. River Mouth6. River Mouth

MedonoMedonoMedonoMedonoMedonoMedonoMedonoMedonoMedono

121212121212121212

GilisariGilisariGilisariGilisariGilisariGilisariGilisariGilisariGilisariMijenMijenMijenMijenMijenMijenMijenMijenMijen

101010101010101010

GonoharjoGonoharjoGonoharjoGonoharjoGonoharjoGonoharjoGonoharjoGonoharjoGonoharjo

888888888

999999999

PonganganPonganganPonganganPonganganPonganganPonganganPonganganPonganganPongangan

Gn.PatiGn.PatiGn.PatiGn.PatiGn.PatiGn.PatiGn.PatiGn.PatiGn.Pati

555555555

666666666

SumurSumurSumurSumurSumurSumurSumurSumurSumurJ urangJ urangJ urangJurangJurangJurangJurangJurangJurang

J atibarangJ atibarangJ atibarangJ atibarangJ atibarangJatibarangJatibarangJatibarangJ atibarang777777777

SimonganSimonganSimonganSimonganSimonganSimonganSimonganSimonganSimongan111111111111111111

222222222

LempuyanganLempuyanganLempuyanganLempuyanganLempuyanganLempuyanganLempuyanganLempuyanganLempuyangan

Nyat NyonoNyat NyonoNyat NyonoNyat NyonoNyat NyonoNyat NyonoNyat NyonoNyat NyonoNyat Nyono

333333333KarangjatiKarangjatiKarangjatiKarangjatiKarangjatiKarangjatiKarangjatiKarangjatiKarangjati

444444444

SrondolSrondolSrondolSrondolSrondolSrondolSrondolSrondolSrondol111111111

LEGENDLEGENDLEGENDLEGENDLEGENDLEGENDLEGENDLEGENDLEGEND

0 2,5

kilometers

Rainfall StaRainfall StaRainfall StaRainfall StaRainfall StaRainfall StaRainfall StaRainfall StaRainfall StaClimate StaClimate StaClimate StaClimate StaClimate StaClimate StaClimate StaClimate StaClimate Sta

Water Level StaWater Level StaWater Level StaWater Level StaWater Level StaWater Level StaWater Level StaWater Level StaWater Level Sta

Master Station

BBWSPJ

Master StationMaster StationMaster StationMaster StationMaster StationMaster StationMaster StationMaster StationMaster Station

110

Figure 5. Plan of Flood MonitoringFasilities and Proposed New

Hydrological Stations.

4.2. Development Flood Hazard MapBy flood hazard, we generallyunderstand the likelihood of a floodhappening in a certain place at acertain time.Information abouthazard is presented on maps. As aminimum, they include the borders ofthe area at risk of a “reference

flood” - generally a flood of adefined probability of occurrence.Flood routing in the Garang Riverwas carried out to observe floodslikely to happen in order for thenecessary evacuation measures to betaken. Flood routing is done inexisting condition at various floodevent return periods. Simulationresults of the 1D-2D model with 25return period show that largestflood had occurred in upstreamGarang River due to the meetingpoint of flood from the upstream andtidal flow from the downstream.Floods because of tidal flowoccurred also on the right sectionof the Garang watershed, althoughnot of the extent and waterdepthcompared with the floods in theGarang River.Base on the three scenarios forflood simulation, evaluation anddiscussion is carried out to createa Flood Hazard Map for Garangwatershed.Analysis of Flood HazardMap show the diffrences of floodinundation with various returnperiods for 3 specified scenario(see Table 2).

Table 2. Flood inundation with various return periods for 3 specifiedscenario.

ReturnPeriods Scenario inundation

(ha)ReducingArea (%)

Q - 10years Existing Condition 1274

Existing Condition+ Jatibarang DAM 1058 16.95

Existing Condition+ Jatibarang DAM+Dike 555 56.44

Q - 25years Existing Condition 2043

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Existing Condition+ Jatibarang DAM 1835 10.18

Existing Condition+ Jatibarang DAM+Dike 771 62.26

Q - 50years Existing Condition 2303

Existing Condition+ Jatibarang DAM 1889 17.98

Existing Condition+ Jatibarang DAM+Dike 962 58.23

4.3. Erosion ControlThis evaluation concludes that thereare still critical lands in KaliGarang. In sub Catchment GarangHilir 36%; sub Catchment Garang Hulu57,7%, sub Catchment Kreo 56,49%;and sub Catchment Kripik 60,58%.Therefore still work to be done tocontrol the erosion by publicforest, public forest enrichment,city forest, control dam, gully plugand recharging well in thesettlement area.Result analysis can be explainedthat in general erosion in studyarea is classified as very light asindicated by the 82.015 km2 (49,81 %)of total area of 191,6 km2.Approximately 44.20 km2 (23 %) isclassified as lightly eroded, 31.08km2 (16,22 %) moderate, 22.59 km2(11.79 %) heavily eroded, and only11.7 km2 (6,11 %) very heavilyeroded. Total erosion indicatesapproximately 2,076,591 ton/year orabout 108 ton/ha/year.Erosion in Garang catchment can alsobe indicated by thickness of erosionshowing the thickness of erodedtopsoil. This study, however doesnot take into account the erosiondeposited from other grids. Thecalculation of erosion thickness isonly related to the thickness ofsoil eroded at one certain grid. In

order to determine erosion thicknessand with soil density of about 1.2ton/m3, average thickness of erosionin the entire Garang catchment wasdetermined as 9,03 mm/year

4.4. Satellite Image AnalysisLand cover data available is fromthe year of 1998 (Bakosurtanal),resulted the rate of land-use: Land-use in Garang-Pajangan is dominatedby Non irigated dry field (24.9%),rice fields (29,60%), forests(10.4%), settlement area (11.5%) andothers 23,6%.Land classsification determined byinterpretation result 1998 and 2008differs in amount, therefore someclasses are combined based onsimilarity.The SPOT 5 image map for GarangCatchment, established in 2008,resulted the rate of land-use:a) Land-use in the Jatibarang Dam

catchment is dominated byplantations (36,55%), rice fields(29,84%), forests (20,73%),settlement area (10,54%) andothers 2,34%.

b) Garang Pajangan althoughdominated by plantations(38.45%), is showing a largerrate for settlement area(20.54%). Rice fields are

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covering an area of 19.54%, andforests (8%), where others13,44%.

Table 3 depicts land-use changes inGarang catchment for the period1998-2008. For example, forest areadecreased with 23.01% in 2008,settlement increased with 87,11%,mixed crop farming decreased with43,31%, plantation increased with31,17%, and rice fields decreasedwith 34,09%.Table 3. Land-use changes In Garang

Catchment.

Land Use

WideArea

Different (Ha)

Percentage

Forest 460.17 23.01Settlement -1920.62 -87.11Mixed crop farm 1409.52 43.31

Estate -1887.53 -31.17Rice field 1937.84 34.095. Conclusion

Measures of flood control shall besuccessful if supported by non-structural methods throughIntegrated Water Resources and FloodManagement Project which includes

watershed and disaster management.Flood simulation on 25 years returnperiod using 3rd scenario (ExistingCondition+ Jatibarang DAM+Dike) showthe highest flood reduction is 62 %than previous. Total erosionindicates approximately 2,076,591ton/year or about 108 ton/ha/year.Therefore still work to be done tocontrol the erosion by publicforest, public forest enrichment,city forest, control dam, gully plugand recharging well in thesettlement area. Land-use changesthat occurred in Garang catchmentindicated that almost all major landchanges of above 20% from 1998 usingmap analysis. It needs to befollowed up with the strengtheningof laws against land use in thefuture.Acknowledgements

This research was funded by JICALOAN IP – 534through the CTIConsultant and Research Center forWater Resources, Ministry of PublicWorks action.

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