Case StudyJENEBERANG RIVER BASIN, SOUTH SULAWESI , INDONESIA

1.RIVER BASIN2.CALDERA OF MT. BAWAKARAENG3.SEDIMENT CONTROL PLAN4.BILI-BILI DAM5.PROBLEMS OF DOWNSTREAM

AREA OF BILI-BILI DAM

The Jeneberang River System, which has acatchments area of 762.01 km2, originates atcaldera slope of the Mt. Bawakaraeng. Five(5) major sub-basins :1. Bili-Bili Dam Basin : 384.40 km2,

2. Salo Malino : 85.89 km2,3. Salo Kausisi : 37.50 km2,4. Jene Rakikang (42.2 km2),5. Binanga Jajang : 22,7 km2,

1. RIVER BASIN

10 km

A

B

0 5

Jene Berang

Salo Garassi

Binanga Sapaya

Binanga Tokka

Jene Lata

Binanga Jajang

Jene Rakikang

Salo Malino

Jene Berang

Salo B

ulang

Salo Takapala

Salo Malino

Balang Kampala

Binanga Patteteang

119o 55'E119o 50'E119o 45'E119o 40'E119o 35'E119o 30'E119o 25'E

5o 10'S

5o 15'S

5o 20'S

5o 25'S

Jene Berang

KEY MAP

N

Mak

assa

r Stra

it

Bili Bili ReservoirJene Bontomalangere

Bili Bili Dam

Malino

Limbunga

Mangempang

Jonggoa

Bili Bili JenelataKampili

Bayang

Legend:

Macini Sombala

Bontojai

Bulu Karampuang(1407m)

Bulu Bulunta(941m)

BuluBawakaraeng

(2830m)

Bulu Sarongan (2514m)

Bulu Sarobaiya (2560m)

Bulu Baria(2658m)

Makassar

SOUTH SULAWESI

SOUTH EAST SULAWESI

CENTRAL SULAWESI

NORTH SULAWESI

GORONTALO

River

Mountain

Catchment Area

Latest Collapse

Existing Sand Pocket

Existing Sabo Dam

Bridge

Existing Rainfall Gauging Station

Existing Water LevelGauging Station

Existing Rainfall and Water LevelGauging Station

Salo Kausisi

Proposed Rainfall Gauging Station

Proposed Water LevelGauging Station

Proposed VibrationSensor

Figure 1.

Jene

Rak

ikan

g

Bin

anga

Jaj

ang

Salo

Mal

ino

Salo

Kau

sisi

0

500

1,000

1,500

2,000

2,500

3,000

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000

Distance (m)

Rel

ativ

e El

evat

ion

(m)

Daraha Bridge

Bili

Bili

Dam

Mt. Bawakaraeng

Figure 1.

2.1. Natural Condition.Elevation: 2,830 mMt. Bawakaraeng, whose name literallymeans “Mouth of King”, shows large calderaformation.Existing Caldera is surrounded by Mountainranges of Lompobatang and Bawakaraengranging from Elev. 1,800 m to 2,200m. Thecaldera is in process of expansion at present.

2. CALDERA OF MT. BAWAKARAENG

Mt. Bawakaraeng Caldera Wall

Old Lava Form

Mt. Bawakaraeng (Elev.2,830m)

Summit

Jeneberang River

Lompobatang-Bawakaraeng Caldera (as of July, 2005)

2.2. Occurrence of Caldera Collapse

A gigantic caldera-wall collapse occurred onMarch 26, 2004, at the northeast of caldera of Mt.Bawakaraeng (hereinafter the Collapse). Thevolume of collapsed mass is estimated at 200 to300 million m3. The caldera-wall collapse broughttremendous damage to the area, accounting for 32people death and missing, 635 cows losing, manyhouses, elementary school and about 1,500 ha ofagricultural land buried. Total damage wasestimated at about Rp. 22 billion.

2.3. Monitoring of CracksThere are many cracks observed and start settingobservation points at each zone by installation ofwooden pegs as shown in picture below.Pompengan-Jeneberang RBO has installed suchobservation point totally 32 locations (EL.2600-2650m).Each displacement of crack will be observed atleast once in three months as well as rainfall databy using automatic rainfall gauging instrumentinstall by the Pompengan-Jeneberang RBO.

Zone 1,2 and 3

Zone 4

Locations of monitoring pilesfor opening of cracks

For monitoring of open crack,measurement pile and board bar areinstalled and change of intervalsbetween piles and boards aremeasured. And condition of collapsedwall is observed by watching andtaking photos from the fixed points.

H

Crack H2

H1

Crack

Caldera wall

H equal this spacel

Installation for small open crack Applied for open crack with width of less than 20 cm

Installation for crack which may move horizontally and verticallyApplied for open crack with width of 20 cm and more

Installation for crack which has sliding condition Applied for crack 2-4 only

2.4. Potential Collapse of Caldera Ridge WallTo grasp of the Caldera wall slope condition andstability in detail, slope units are divided into three(3) groups, 10 units in the North Caldera, 10 unitsin the East Caldera and 10 units in the SouthCaldera. In each slope unit, slope inventory recordhas prepared. The total unstable volume of thewhole caldera wall slope is estimated to be145,068,000 m3. In east caldera wall is estimatedwith 111,073,000 m3.

• Level I, estimated volume is 20,102,500m3, Ineast Caldera, and partly in the east side of theNorth Caldera.

• Level II ,estimated volume is 24,646,000 m3.• Level III, estimated volume is 27,819,500 m3

• Expansion Portion, which indicates possiblemaximum collapse extent at present condition, isestimated to be 72,500,000m3 in volume.

Level of possibility Collapace

3. Sediment Control Plan3.1. Formulation of Sediment Disaster

Mitigation Plan1) caldera wall collapse (as preliminary sediment

movement),2) debris flow,3) mud flow, and4) gully erosion and surface erosion.

Among these phenomena, there are two types ofconsiderable sediment disasters, namely:1) Sediment disasters directly caused by

preliminary (future collapse) and secondarycollapse,

2) Sediment disasters caused by rainfall such asdebris flow, mud flow, gully/river bank erosion

Sediment disaster mitigation plan should beformulated against both the sediment disasters, andwill be formulated in combination with structuralmeasures and non-structural measures.

3.1. Formulation of Sediment Disaster Mitigation Plan....

Sediment Control Plan against Rainfall• Debris Flow• Mud Flow

Non-structural Measure

Preliminary Caldera CollapseDebris Flow Occurrence

Structural Measure

Non-structural Measure

Sediment Disaster Mitigation Plan

Both the structural and non-structural measures have to cooperatedemonstrating each characterized measures to attain sediment disastermitigation in the Jeneberang River Basin.

3.2 Target Sediment Amounts to be controlled

The amount of sediment deposit in the main riverof Jeneberang was estimated at over 230 millionm3 (JICA estimation in 2006) and 40 % of themstill remained in caldera area. The unstablesediment in the caldera is estimated with 90million m3 as of July 2008. Therefore, 61% ofthe total sediment deposit has already flowed intothe downstream reaches. It volume is estimatedbased on the topographic survey result with 140million m3.

Bed material load Bed load

Suspended load

Wash load

3.3. Concepts of Sediment Transportation System by Structure Measure

It is necessary to analysis sediment transportation system in the basin. It is the way to formulate a sabo facility plan in the Jeneberang River Basin. In general, sediment transportation loads is classified as:

Mountain Stream

Riverbed

Tran

spor

tatio

n Pr

ofile

Sec

tion

Distribution of Sediment

Sediment Source

Regulating Volume

Boulder Slit Dam /Large Conduit Dam

Sabo Dams

Sand Pocket Works

Consolidation Dams

WL SL BL

Sedi

men

t Flo

w S

ectio

nD

ebris

Flo

w S

ectio

n

WL : Wash Load Φ＜0.1 mm

SL : Suspended Load 0.1＜Φ＜1.0 mm

BL : Bed Load 1 mm ＜Φ

Riv

erbe

d/Ba

nkEr

osio

nR

iver

bed/

Bank

Eros

ion

Runoff control volume Storage Volume

Bilibili Dam

Sand Mining

Outflow/Inflow Outflow

SedimentationSedimentation

WL SL BL

BoulderSand

Silt & Clay

Sediment Movement

WL SL BLRegulating Volume Storage Volume

Sand Pocket Works

Inflow

SP-5SP-4

SP-3 SP-2 SP-1

SedimentationSedimentation

Sand Mining

Sand Mining

Sand Mining

WL SL BLStorage Volume

SL

Sub Basin

WL BL

SL

Sub

Basi

n

WL

BLSL

Sub

Basi

n

WL

BL

3.4 Layout of Sediment Control WorksBased on tentative target sediment amount to becontrolled and to be transported at present andfuture topographic conditions along the rivercourses, the propose facility layout plan asillustrated in Figure below, which can be classifiedinto six (6) sediment control works, to reduce thedebris flow occurrence, to stabilize the riverbed, toregulate the debris flow deposit, to control debrisflow direction and to reduce the inflow sediment toBili-Bili reservoir.

Sediment runoff control works

Debris flow control works

Jeneberang Main Stream

Debris flow occurrence control works

Deposition

works with sand mining

Tributaries:- Salo Malino- Salo Bengo- Others

Sediment runoff control works

Deposition Works (Existing Dam)

Caldera

Hill side works

Debris flow occurrence control works

Process of Traditional Stone Terracing

1st

Dry pitching

2nd

Mud layer

3rd

Process

1) Hillside Works and Surface erosion control work .

Outlet of Caldera: Surfaceerosion control work site:dense plantation is required.EL.1000-1500m

EL 1,500m: Surface erosion byrain drop on the deposit ofcaldera: rain drop has accuratesurface erosion process. 2 -3 cmdepth surface erosion during halfhour rainfall observed

Surface soil eroded by rain drop

2) Debris flow occurrence control worksshall be proposed with series of sabo dams atthe exit of a valley, and debris flow directioncontrol works with sabo dams.

Riverbe

d Aug.

2004

Original P

roposed Dams

No.7

-２ No.7

-3

No.7

-4 No.7

-5

No.7

-8 No.7

-７

No.7

-1

Lengkese Village

No.7

-3 No.7

-4

No.7

-5

No.7

-6

No.7

-7

No.7

-8 No.7

-9

No.7

-10

No.7

-1

No.7

-2

Present Rive

rbed Sep.2006

Riverbed Sep. 20061/12～1/13

2 years change

Revised Propose Sabo Dam

Riverbed Aug. 20041/10

Riverbed slope change due to rapid erosion

process

Sabo dam No.7 series in the upper reaches

3) Debris flow control works, and Sediment runoffcontrol works shall be proposed in combinationwith Sabo dams and consolidation dams to restrainunstable riverbed and riverbank profile withpresent riverbed level, to control debris flowdirection, and to accumulate runoff sedimentdeposit at river section from Daraha Bridge sectionto upper reach section of sand pocket No.5 dam.

4) Sediment deposition works and Flow DirectionControl Works which stock the large amount ofgravel and sand material with sand pocket facilities.

Location /Proposed Sabo Facility Recommended Sabo Facility /Structure Type

(1) Upper ReachDebris Flow Occurrence Control worksSeries of Sabo dams (it is necessary toconsider the number of sabo dams /type ofsabo dams based on the results of movementof sediment from caldera)

Combination type of INSEM and concrete type

CSG and ISM type of soil cement was applied to shorten construction Period

(2) Middle Reach(Debris Flow Control Works, Sediment Runoff Control Work) Series of Sabo dams (1 Open type dam, and 5 closed type dam)Series of Consolidation dams withIrrigation intake facility (2 consolidationwith crossing road, and 4 consolidationdams)

Combination type of INSEM and concrete type

Combination of Masonry and concrete type

(3) Sand Pocket Area(Sediment Deposit Area)Rehabilitation of 5 existing sand pocketdamsA series of dispersion dams with irrigationintake facility would be considered

Existing sand pocket dams will be utilized as either sub-dam body or base body of new main dams

Combination of Masonry and concrete type

Sediment Disposal work by machineryexcavation at the edge of reservoir

Machinery excavation both by mining activities and Government at the edge of Reservoir

Lay Out of Sabo Plans

3.6. Sediment Control Effect by Proposed Sabo Facilities

The sediment control facilities has constructed on presentriverbed between upper to middle reaches which alreadypiled up with sediment deposits in order to fix presentriverbed deposit. The facilities will be functioned asfixation of riverbed which means;• to reduce secondary sediment movement from present

sediment deposits,• to reduce lateral erosion of sediment deposits• to control riverbank erosion during flooding time• to stock and regulate the debris flow deposit from upper

stream• to guide sediment flow/sediment flow direction

Source Sediment Restraining

Storage Capacity(Dead Storage)

Initial Riverbed

Source Sediment Restraining

Storage Capacity(Remaining Storage)

Initial Riverbed

Slit/ConduitBase

Slit/Large -Conduit Dam Static Riverbed

Dynamic RiverbedRegulating Storage

Closed-typeStatic Riverbed

Dynamic RiverbedRegulating Storage

Open-type Dam(Blockage-type Dam)

Closed-type Dam(Normal Dam)

KD

-2 KD

-3

KD

-4 CD

-1 CD

-2 CD

-3

Dam

Sub

-dam

Direct Control Sediment Volume

In-direct Control Sediment Volume

Σ Direct Sediment Volumeby Structure Measure

Σ In-direct Sediment Volumeby Riverbed Consolidation Work

+ 20m

+ 6.0km

= 48.43million m3

= 1.56 million m3

KD

-1

+ 10m

7-2

7-3 7

-4 7-5

7-6

7-7

Dam

Sub-d

am

Direct Control Sediment Volume

In-direct Control Sediment Volume

Σ Direct Sediment Volumeby Structure Measure

Σ In-direct Sediment Volumeby Riverbed Consolidation Work

+ 40m

+ 5.0km

= 28.2 million m3

= 1.3 million m3

7-1

+ 20m

Middle Reach Upper Reach

Estimated sediment control volumes of the above proposed facilities are summarized in table below

Location

Direct Control

Sediment Volume

In-direct Control

Sediment Volume

Total Direct and Indirect

Control Sediment Volume

(1) Upper Reach 1.300 28.200 29.500

(2) Middle Reach 1.560 48.430 49.990

Total 2.860 76.630 79.490

(Million m3)

3.7. Implementation of WorksSince the caldera wall collapsed on March2004, the Government of Indonesiacooperating with Government of Japan hadmade efforts to cope the above sedimentproblem in Jeneberang River both structuralmeasures and non-structural measures asshown on figures below.

Bili-Bili Dam and Its Reservoir

Dam type :Main Dam height :Main Dam Crest length :Main Dam Crest width :Main Dam Body volume :Catchment area :Left Wing Dam height :Left Wing Dam Crest length :Left Wing Crest width :

Rock-fill dam73 m750 m10 m2.76 million m3

384.4 km2

42 m646 m10 m1.47 million m3

Gross storage volume :Effective storage volume :Sediment Capacity :Water Utilization Capacity :Design Flood Water Level :Normal Water Level :Low Water Level :Irrigation area (total):Raw Water transmission capacity:

375 million m3

346 million m3

29 million m3

305 million m3

EL.103.0 mEL. 99.5 mEL.65.0 m25,000 ha3.3 m3/s

4. Bili-BiliDam

Three (3) irrigation systems are named as Bili-Bili, Bissua and Kampili, Net total irrigation service areas 23,663 ha.

Municipal and industrial water supply PDAM MakassarPDAM GowaSugar factory in Takalar Regency (PT. Perkebunan Nusantara IV (Persero)

Hydro Power 18 MW

PDAM Makassar owns water treatmentplants with clean water production capacityof 2,340 liter/sec in total and takes 1,250liter/sec from the Jeneberang River, or about53 % of the total water production, whilewater source of PDAM Gowa totallydepends on the water flow of the JeneberangRiver Basin

4.1. Reservoir SedimentationThe cumulative reservoir sedimentation curve since1997shown on following figures and cumulativesedimentation volume had reached 62,744,000 m3 as ofNovember 2008.

Sediment Inflow Volume

Cumulative Sediment Volume

Design Sediment Storage Capacity

-10

0

10

20

30

40

50

60

70

19992001

20042005

20062007 Wet

2007 Dry

2008 Wet

2008 Dry

Res

ervo

ir Se

dim

enta

tion

( x m

illion

m3 )

The annual variation of sedimentation profile of Bili-BiliReservoir based on lowest riverbed elevation of results ofbathymetric survey result is shown on Figure below.

40

50

60

70

80

90

100

110

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Longitudinal Distance from Dam Site (m )

Elev

atio

n (m

)

1997

2008

Nov

2005 Sep

Intak

4.2. Turbidity of Bili-Bili ReservoirThe following graph shows raw water turbidity records before and after the collapse. High turbidity rates occurred during the rainy season in the month of December and January. The maximum turbidity rate declined to 33,000 NTU in 2006 and about 4,000 NTU in 2007.

Rainfall and Turbidity of Bili-bili Dam

10

100

1,000

10,000

100,000

1,000,000

Date

7-M

ar-0

111

-May

-01

15-J

ul-01

18-S

ep-0

122

-Nov

-01

26-J

an-0

21-

Apr-0

25-

Jun-

029-

Aug-

0213

-Oct

-02

17-D

ec-0

220

-Feb

-03

26-A

pr-0

330

-Jun

-03

3-Se

p-03

7-No

v-03

11-J

an-0

416

-Mar

-04

20-M

ay-0

424

-Jul-

0427

-Sep

-04

1-De

c-04

4-Fe

b-05

10-A

pr-0

514

-Jun

-05

18-A

ug-0

522

-Oct

-05

26-D

ec-0

51-

Mar

-06

5-M

ay-0

69-

Jul-0

612

-Sep

-06

16-N

ov-0

620

-Jan

-07

26-M

ar-0

730

-May

-07

3-Au

g-07

7-O

ct-0

711

-Dec

-07

14-F

eb-0

819

-Apr

-08

23-J

un-0

827

-Aug

-08

31-O

ct-0

84-

Jan-

09

Turb

idity

(NTU

)

0

50

100

150

200

250

Rain

fall I

nten

sity (

mm

/day

)

Bili-bili Dam Outlet Daily Rainfall (from Jan. 2001-Nov.2005 based on Malino Rainfall,from Dec. 2005-up to now based on Lengkese Rainfall)

4.3. Characteristics of Reservoir Sediment DepositionThe investigation of sedimentation in reservoir edge in thestate of reservoir water level at EL. 83.29 m was conductedon October 12, 2006 and the following characteristics arefounded.

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

0.0001 0.001 0.01 0.1 1 10

Diameter(mm)

Perse

tage o

f Pass

age(%

)

Reservoir NO1

Reservoir NO2

Reservoir NO3

Fine Material in Caldera

Fine Material in Spoil Bank

As shown in grain distribution of reservoir deposit, content of sediment size is mainly 1mm>φ> 0.075mm (fine sand) and φ< 0.075mm (silt) is less 10 % and classified as bed load material.

4.4. Cause of Reservoir TurbiditySerious muddy water occurred from 2004 and significantreduce at present. The cause of muddy water is originatedfrom very fine soil particle which covered on the sedimentdeposit in the caldera area. Field investigation made onOctober 2006 found the very fine soil exists at temporaryspoil bank in right reservoir edge. The grain distribution issmaller than 0.075mm that classified as wash loadmaterials. This material is same soil which accumulated onthe sediment surface in December 2004.These fine materials on the surface of debris flowmaterials which causes to high turbidity observed severaltime in the caldera area and upper reach of Daraha bridgesite.

Very fine material at inlet structure of Bili-Bili Dam (el.82 m, November 3, 2006)

sedimentaion

Very Fine Material on the surface of debris flow deposit Feb, 2006

Appereance of sand gravel materials after washed away (Mar, 2—0)

Very Fine Material

Debris Flow Deposit

Large-Scale of Sediment Flow Occured (July 2005, Dry Season)

Inlet Bottom, 59.00

LWL, 65.00

NWL, 99.50

SWL, 101.60

DFWL, 103.00

30

40

50

60

70

80

90

100

110

120

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Distance from the Dam (m)

Elev

atio

n (E

L. m

)

Initial River Bed20082018 (10years)

2028 (20years)

2038 (30years)

2048 (40years)

4.5. Prediction of Future Reservoir Sedimentation

Cumulative

Sedimentation

Volume(103m2)

Percentage of Sediment Volume in the Gross Storage

Capacity

Cumulative

Sedimentation in the

Water Utilization Capacity(103m2)

Percentage of

Sediment Volume in the Water Utilization Capacity

Cumulative in the Flood

Control Capacity (103m2)

Percentage of

Sediment Volume in the Flood

Control Capacity

2008 60,959 16% 57,215 19% 1,373 3%

2018(10 years) 98,394 26% 93,000 30% 2,939 7%

2028(20 years) 126,105 34% 119,825 39% 3,936 10%

2038(30 years) 148,623 40% 142,943 47% 3,675 9%

2048(40 years) 168,981 45% 163,778 54% 3,329 8%

Note: Gross Storage Capacity = 375,000,000 m3; Water Utilization Capacity = 305,000,000 m3;

4.6 Reservoir Sediment Management PlanThe measures of Bili-Bili reservoir sediment management might be specified the following stages.1st stage: Occurrence of caldera collapse2nd stage: Reduce sediment inflow to reservoir

Reduction of sediment transportation volume, fine sediment trapping facilities, excess sediment removal both by structural sabo dam watershed improvement by planting conservation work,

3rd Stage: Increase reservoir sedimentation volume and keep dam function. Decrease reservoir capacity in 2048 become 50 % , Maintenance dredging work surrounding intake

4th Stage: Recovering reservoir capacity and functionDry excavation, Construct giant sediment trap at the edge of reservoir, Selectable intake facility5th Stage: Alternative dam construction at Jenelata

46

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4Debris flow mitigation work inupper reaches (structuralmeasure and non-structuralmeasure)

-

Sediment removal work atedge of reservoir (Recoving offlood control function)

2

IP 524 Most UrgentMaintenance Dredging Workfor avoiding possible inletblockade by sediment inflow

Maintenance dredgingsurrounding intake screenduring dry season (mean depth:20-30m)

Improvement of Intake facility

Installation of Giant SedimentTrap

4 Long Term Measure(Recommendation)

Provision of New Dam inJenelata River (Jenelata Dam)Reservoir Capacity: 140 millionm3, Dam Height 48.0 m

3 Urgent Measures to sustainoriginal dam functions

2014 2015

IP 524 Urgent DisasterReduction Project forreduction of sediment outflowfrom Caldera and Upper RiverSection

1

Countermeasure work Main Works Picture / Image of Facility 2012 20132008 2009 2010 2011

Sluice Gate

Operation Room

Siphon Feed PipeScreen

Supply Pipe

Flow

Intake

Flood Control Capacity41,000,000 m3

Excess Volume

Dredging period : Rainy Season (6months)

F/S Study

Installation of selective intake

On-Going Urgent Sediment Control Project

Continued sediment removal work by GOI

On-Going Urgent Sediment Control Project

Installation of Giant Sediment Trap

Detail Examination of Multi-Purpose Dam (F/S, DD,CS)

Intake

TYPICAL SECTIONSCALE B

5. PROBLEMS OF DOWNSTREAM AREA OF BILI-BILI DAM

1. Illegal buildings and high trees hamper water flow (reducing wet area of river section);

2. Solid and liquid waste disposal causes water quality deterioration;

3. Safety of residents who reside in the river area;

4 Excessive sand mining may cause river bed degradation.

48

Flood risk to residents

Reduction of River Flow Capacity

50

Garbage may lead to river degradation and water quality deterioration

Building ruins may decrease river channel capacity for accomodating flood water

Garbage may lead to river degradation and water quality deterioration

Garbage may lead to river degradation and water quality deterioration