annex no.3 assessment of wonogiri reservoir sedimentation · table 2.1.1 number of days of power...

Annex No.3 Assessment of Wonogiri Reservoir Sedimentation

i

120THE STUDY ON COUNTERMEASURES FOR SEDIMENTATION

IN THE WONOGIRI MULTIPURPOSE DAM RESERVOIR

IN THE REPUBLIC OF INDONESIA

FINAL REPORT

SUPPORTING REPORT I

Annex No.3 Assessment of Wonogiri Reservoir Sedimentation

Table of Contents

Page

CHAPTER 1 WONOGIRI MULTIPURPOSE DAM...................................................................3-1 1.1 Principal Feature of Wonogiri Multipurpose Dam .........................................................3-1 1.2 Performance of Wonogiri Dam Reservoir Operation .....................................................3-1

1.2.1 Reservoir Operation ........................................................................................3-1 1.2.2 Flood Control ..................................................................................................3-4 1.2.3 Wonogiri Irrigation System.............................................................................3-7 1.2.4 Power Generation at the Wonogiri Hydropower Station.................................3-8 1.2.5 Operation and Maintenance ............................................................................3-8

CHAPTER 2 GARBAGE PROBLEMS AT WATER INTAKE....................................................3-9

2.1 Garbage Problems ..........................................................................................................3-9 2.2 Garbage from the Keduang River ................................................................................3-11

2.2.1 Garbage from the Keduang River .................................................................3-11 2.2.2 Results of Garbage Survey............................................................................3-12

CHAPTER 3 CURRENT STATUS OF THE WONOGIRI RESERVOIR SEDIMENTATION ..............................................................................................3-13

3.1 Previous Monitoring Studies on the Wonogiri Reservoir Sedimentation.....................3-13 3.1.1 PBS in 1989 ..................................................................................................3-13 3.1.2 Gadjah Mada University in 1985 and 1990 ..................................................3-14 3.1.3 PT CMA in 1993 ...........................................................................................3-14 3.1.4 Comparison of Estimated Wonogiri Reservoir Capacity ..............................3-16

ii

3.1.5 Comparison of Average Erosion Rate (Depth) in the Wonogiri Watershed......................................................................................................3-16

3.2 Current Status of the Wonogiri Reservoir Sedimentation ............................................3-17 3.2.1 Reservoir Sections and Profiles in 1980-2004 ..............................................3-18 3.2.2 Reservoir Sedimentation Survey in 2004 by PBS.........................................3-21 3.2.3 Current Wonogiri Reservoir Conditions in 2004 and 2005...........................3-22

CHAPTER 4 RESULTS OF GEOLOGICAL INVESTIGATIONS ...........................................3-27

4.1 Drilling Works..............................................................................................................3-27 4.2 Geological Sections......................................................................................................3-27

CHAPTER 5 MONITORING ON SEDIMENTATION IN FRONT OF INTAKE ....................3-33

5.1 Method of Monitoring..................................................................................................3-33 5.2 Result of Monitoring ....................................................................................................3-34 5.3 Topographic Survey at Intake Forebay on October 2006.............................................3-35 5.4 Preliminary Analysis on Sedimentation at Intake ........................................................3-35

5.4.1 Sediment Inflow from the Keduang River ....................................................3-35 5.4.2 Topographic Feature at Intake.......................................................................3-35 5.4.3 Suction Effect of Intake ................................................................................3-36

List of Table

Table 1.1.1 Principal Features of Wonogiri Multipurpose Dam and Reservoir.........................3-1 Table 1.2.1 Estimated Large Floods into Wonogiri Reservoir...................................................3-6 Table 1.2.2 Present Irrigation Area of Wonogiri Irrigation Project ...........................................3-7 Table 1.2.3 Mean Monthly Discharges at Colo Weir in 1986-2005 ..........................................3-7 Table 2.1.1 Number of Days of Power Stoppage due to Trash Rack Cleaning at

Wonogiri Power Station..........................................................................................3-9 Table 3.1.1 Estimated Annual Wonogiri Reservoir Sediment Inflows by Tributary ...............3-14 Table 3.1.2 Estimated Sediment Deposits in the Wonogiri Reservoir .....................................3-14 Table 3.1.3 Wonogiri Reservoir Capacity Loss by Storage Zone between 1980 and

1993 ......................................................................................................................3-15 Table 3.1.4 Comparison of Average Erosion Rates by Past Studies........................................3-17 Table 3.2.1 Estimated Wonogiri Reservoir Storage based on DEM........................................3-24 Table 3.2.2 Wonogiri Reservoir Capacity Loss by Storage Zone between 1980 and

2005 ......................................................................................................................3-24 Table 4.1.1 Results of Drilling Works .....................................................................................3-27 Table 4.1.2 Grain Size Distribution of Sediments ...................................................................3-28

iii

List of Figure

Figure 1.1.1 Allocation of Storage Capacity and Water Levels of Wonogiri Dam .....................3.1 Figure 1.2.1 Wonogiri Reservoir Water Level Hydrograph in 1983-2005..................................3-2 Figure 1.2.2 Estimated Mean Monthly Inflow into Wonogiri Reservoir (1983-2005) ...............3-3 Figure 1.2.3 Mean Monthly Outflow from Wonogiri Reservoir in 1983-2005...........................3-3 Figure 1.2.4 Estimated Monthly Wonogiri Reservoir Inflow in 1983-2004 ...............................3-4 Figure 1.2.5 Typical Flood Control Operation of Wonogiri Dam...............................................3-4 Figure 1.2.6 Location of Upper Solo River Improvement Project in 1994.................................3-5 Figure 1.2.7 Design Flood Discharge Distribution for Upper Solo River Improvement

Project.....................................................................................................................3-5 Figure 1.2.8 Actual Flood Operations of Wonogiri Reservoir ....................................................3-6 Figure 2.2.1 Location Map of Garbage Survey.........................................................................3-11 Figure 2.2.2 Result of Garbage Survey from November 2006 to January 2007.......................3-12 Figure 3.1.1 Location Map of Cross Sections for Sedimentation Survey.................................3-13 Figure 3.1.2 1993-year Reservoir Contour Map Reproduced by PBS......................................3-15 Figure 3.1.3 Projection of Wonogiri Reservoir Sedimentation by Past Monitoring

Studies ..................................................................................................................3-16 Figure 3.1.4 Illustration of Average Erosion Rate over the Watershed .....................................3-17 Figure 3.2.1 Location Map of Cross Sections for Reservoir Sedimentation Survey in

2004 and 2005 ......................................................................................................3-18 Figure 3.2.2 Reservoir Sections in 1980-2004..........................................................................3-19 Figure 3.2.3 Reservoir Profiles in 1980-2004...........................................................................3-20 Figure 3.2.4 Location Map of Data Points by PBS Survey in 2004 .........................................3-21 Figure 3.2.5 Location Map of Data Points by JICA Survey in 2005 ........................................3-22 Figure 3.2.6 Reservoir Contour Map in 1993 ...........................................................................3-23 Figure 3.2.7 Reservoir Contour Map in 2004 ...........................................................................3-23 Figure 3.2.8 Change of Wonogiri Reservoir Capacity by Storage Zone between 1980

and 2005 ...............................................................................................................3-24 Figure 3.2.9 Wonogiri Dam Reservoir Elevation-Capacity Curves in 1980, 1993 and

2005 ......................................................................................................................3-25 Figure 3.2.10 Keduang Reservoir Elevation-Capacity Curves in 2005 ......................................3-25 Figure 3.2.11 3D View of Wonogiri Dam Reservoir Sedimentation ..........................................3-26 Figure 4.1.1 Location Map of Drilling Works...........................................................................3-27 Figure 4.1.2 Percentage of Sediments Composition in the Wonogiri Reservoir.......................3-28 Figure 4.1.3 Grain Size Distribution of Drilling Cores.............................................................3-29 Figure 4.1.4 Composition of Surface Sediment Materials in Wonogiri Reservoir and

Five (5) Major Tributaries ....................................................................................3-30 Figure 4.2.1 Geological Sections in Wonogiri Reservoir(Keduang River and Solo

iv

River) ....................................................................................................................3-31 Figure 4.2.2 Geological Sections in Wonogiri Reservoir (Tirtomoyo River and Temon

River) ....................................................................................................................3-32 Figure 5.1.1 Monitoring Locations in the Forebay of Intake ....................................................3-33 Figure 5.2.1 Comparison of Sediment Levels in front of Intake...............................................3-34 Figure 5.4.1 Relations among Sedimentation Level, Inflow Velocity, Shear

Velocity(U*) and Critical Shear Velocity (U*c) ...................................................3-36 Figure 5.4.2 Shear Velocity around Intake................................................................................3-37

Attachment

Attachment 1 Monitoring Result of the Garbage Survey .........................................................A1-1 Attachment 2 Reservoir Sections in 1980-2004.......................................................................A2-1 Attachment 3 Result of Sediment Monitoring Forebay of Intake ...........................................A3-1 Attachment 4 Topographic Map of Intake Forebay on October 2006......................................A4-1 Attachment 5 Calculation on Bed Load Transportation in the Intake ......................................A5-1

The Study on Countermeasures for Sedimentation Final Report in the Wonogiri Multipurpose Dam Reservoir Supporting Report Annex No.3

Nippon Koei Co.,Ltd. 3-1 July 2007 Yachiyo Engineering Co.,Ltd.

CHAPTER 1 WONOGIRI MULTIPURPOSE DAM

1.1 Principal Feature of Wonogiri Multipurpose Dam

The principal feature of the Wonogiri Multipurpose Dam Reservoir is summarized in Table 1.1.1 below and the allocation of the storage capacity and designated water levels are also shown in Figure 1.1.1 below.

Table 1.1.1 Principal Features of Wonogiri Multipurpose Dam and Reservoir

Dam type Rockfilll Normal Water Level EL. 136.0 mDam height 40 m Design Flood Level EL. 138.3 mCrest length 830m Extra Flood Water Level EL. 139.1 m

Embankment volume 1,223,300 m3 Spillway (Radial gate) 7.5 m x 7.8 m x 4 nos.

Catchment area 1,350 km2 Crest height EL. 131.0 mReservoir area 90 km2 Flood inflow discharge 4,000 m3/sGross storage capacity 735 x 106 m3 Flood outflow discharge 400 m3/sActive storage capacity 615 x 106 m3 Design flood discharge 5,100 m3/sFlood control storage capacity 220 x 106 m3 PMF 9,600 m3/s

Irrigation & hydro power storage capacity 440 x 106 m3 Installed capacity 12.4 MW

Sediment storage capacity 120 x 106 m3 Design head 20.4 mSediment deposit level EL. 127.0 m Max. discharge 75 m3/sLimited water level in flood during flood season EL. 135.3 m Annual energy output 50,000 MWh

Source: PBS

Flo

od

Cont

rol

220 x

10

6 m

3

Flood FloodNon-flood

DecMay

Flood Control220 x 106 m3

Irrigation &Hydropower395 x 106 m3

Flood Control175 x 106 m3

Irrigation &Hydropower440 x 106 m3

Nov

Crest of Dam142.0 m Extra Flood W.L.　EL. 139.1 m

Design Flood WL.　EL. 138.3 m

Normal H.W.L EL. 136.0 m

Control W.L.　EL. 135.3 m

Sediment StorageCapacity　120 x106 m3

LWL EL. 127.0 m

Irriga

tion &

Hyd

ropo

wer

440

x 1

06 m

3

Allocation of Storage Capacity Designated Water Levels Source: PBS

Figure 1.1.1 Allocation of Storage Capacity and Water Levels of Wonogiri Dam

1.2 Performance of Wonogiri Dam Reservoir Operation

1.2.1 Reservoir Operation

The mean annual inflow volume of approximately 1.23 billion m3 in 1983-2005 (see Figure 1.2.2 in the next page) exceeds the reservoir volume of 735 million m3 at the design flood water level of EL. 138.3 m. The reservoir water level hydrograph in



1983-2005 is presented below.

126

128

130

132

134

136

138

Jan-

83

Apr

-83

Jul-8

3

Oct

-83

Jan-

84

Apr

-84

Jul-8

4

Oct

-84

Jan-

85

Apr

-85

Jul-8

5

Oct

-85

Jan-

86

Apr

-86

Jul-8

6

Oct

-86

Jan-

87

Apr

-87

Jul-8

7

Oct

-87

Jan-

88

Apr

-88

Jul-8

8

Oct

-88

Jan-

89

RW

L (E

l. m

)

CWL 135.3(Dec.1-Apr.15), NHWL 136.0 (Apr.16-Nov.30)

LWL 127.0m

126

128

130

132

134

136

138

Jan-

89

Apr

-89

Jul-8

9

Oct

-89

Jan-

90

Apr

-90

Jul-9

0

Oct

-90

Jan-

91

Apr

-91

Jul-9

1

Oct

-91

Jan-

92

Apr

-92

Jul-9

2

Oct

-92

Jan-

93

Apr

-93

Jul-9

3

Oct

-93

Jan-

94

Apr

-94

Jul-9

4

Oct

-94

Jan-

95

RW

L (E

l. m

)

LWL 127.0m


126

128

130

132

134

136

138

Jan-

95

Apr

-95

Jul-9

5

Oct

-95

Jan-

96

Apr

-96

Jul-9

6

Oct

-96

Jan-

97

Apr

-97

Jul-9

7

Oct

-97

Jan-

98

Apr

-98

Jul-9

8

Oct

-98

Jan-

99

Apr

-99

Jul-9

9

Oct

-99

Jan-

00

Apr

-00

Jul-0

0

Oct

-00

Jan-

01

RW

L (E

l. m

)

LWL 127.0m


126

128

130

132

134

136

138

Jan-

01

Apr

-01

Jul-0

1

Oct

-01

Jan-

02

Apr

-02

Jul-0

2

Oct

-02

Jan-

03

Apr

-03

Jul-0

3

Oct

-03

Jan-

04

Apr

-04

Jul-0

4

Oct

-04

Jan-

05

Apr

-05

Jul-0

5

Oct

-05

Jan-

06

RW

L (E

l. m

)

LWL 127.0m


Source: Wonogiri Reservoir Operation Record obtained from PJT-1 and PLTA Wonogiri

Figure 1.2.1 Wonogiri Reservoir Water Level Hydrograph in 1983-2005

Figure above shows the annual sequence that water storage during the wet season and followed by irrigation and hydropower generation releases during the dry season. Because of the progress of sedimentation in front of the intake, the Wonogiri reservoir has been operated since 1996 not to lower the El. 130.0 m (except in 2003 when the dredging of sediments at the intake was made under the JICA Grant Aid Program).

Figure below shows the estimated mean monthly inflow into the Wonogiri reservoir in 1983-2005. Mean monthly inflow of 110.8 m3/s (268 million m3) is the highest in February, and August becomes the lowest of 2.3 m3/s (6 million m3). The estimated runoff coefficient is 0.46 and its annual runoff depth is 912 mm.



0

50

100

150

200

250

300

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep Oct

Nov

Dec

Mea

n M

onth

ly In

flow

(Mil.

m3)

Source: JICA Study Team

Figure 1.2.2 Estimated Mean Monthly Inflow into Wonogiri Reservoir (1983-2005)

Figure 1.2.3 below shows the mean monthly outflow from the Wonogiri reservoir in 1983-2005. The outflow comprises the water release through spillway and hydropower generation. As shown, the mean annual water release from spillway (spillout) is around 18% of the total outflow volume or 210 million m3. The remaining volume (82% or 932 million m3) is used for hydropower generation.

0

50

100

150

200

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Mon

thly

Out

flow

(Mil.

m3)

SpillwayTurbine

0

20

40

60

80

100

Jan

Feb

Mar

Apr

May Jun

Jul

Aug

Sep Oct

Nov

Dec

Mon

thly

Out

flow

(m3/

s)

SpillwayTurbine

Source: Wonogiri Reservoir Operation Records obtained from PJT-1 and PLTA Wonogiri

Figure 1.2.3 Mean Monthly Outflow from Wonogiri Reservoir in 1983-2005

It is noted that the excessive water release from the spillway in the beginning of wet season unusually occurred in November only in 1998 and in December only in 1995 respectively. Figure below shows the monthly inflow into Wonogiri reservoir in 1983-2004 in terms of the hydrological year basis November to October. Severe drought occurred in 1989/90, 1996/97, 2003/2004 and 2004/2005. The most severe one occurred in 1996/97, when the Wonogiri reservoir water level could not reach NHWL El. 136.0 m.



The Wonogiri dam experienced consecutive three-year droughts in 2002/03 to 2004/05. In the last two years, no water release through spillway has been practiced.

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

1983

/84

1984

/85

1985

/86

1986

/87

1987

/88

1988

/89

1989

/90

1990

/91

1991

/92

1992

/93

1993

/94

1994

/95

1995

/96

1996

/97

1997

/98

1998

/99

1999

/00

2000

/01

2001

/02

2002

/03

2003

/04

2004

/05

Dam

Inflo

w V

olum

e (M

il. m

3 )

Hydrological Year: From November to October

Mean Annual: 1,231 million m3


Figure 1.2.4 Estimated Monthly Wonogiri Reservoir Inflow in 1983-2004

1.2.2 Flood Control

The reservoir water level is controlled not to exceed the Control Water Level (El.135.3 m) during the flood season from December 1st to April 15th for eliminating the possibility of overtopping of a Probable Maximum Flood (PMF) on the dam crest. The reservoir provides 220 million m3 of flood control capacity to regulate the standard highest flood discharge (SHFD) with peak discharge of 4,000 m3/s to the constant outflow of 400 m3/s (see Figure 1.2.5 in the next page). The peak outflow discharge is 1,170 m3/s for the design discharge of 5,100 m3/s for spillway, which is equivalent to 1.2 times a 100-year probable flood, and 1,360 m3/s for PMF of 9,600 m3/s. Since the completion of the Wonogiri Dam in 1980, no flooding events have so far occurred in Surakarta, largest city in the Bengawan Solo River Basin. The Wonogiri Dam has much contributed to social welfare in the basin and has greatly benefited the people in the downstream area.

Dam Operation for Standard Highest Flood Dischrge (4,000m3/sec)

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

0 24 48 72 96 120Time(hr)

Dis

char

ge (m

3/s)

130.0

131.0

132.0

133.0

134.0

135.0

136.0

137.0

138.0

139.0

140.0

Res

ervo

ir W

ater

Lev

el (E

L.m

)

Inflow Outflow RWL

InflowStandard Highest Flood Discharge (4,000m3/s)

Outflow (400m3/s)

Source: Detailed Design Report on Wonogiri Multipurpose Dam Project, 1978

Figure 1.2.5 Typical Flood Control Operation of Wonogiri Dam



The Upper Solo River Improvement Project was completed in 1994. The objective river stretch is of around 53 km from Nguter to Jurug bridges. The location map of the Project is presented in Figure 1.2.6 below.

Source: Completion Report for Upper Solo River Improvement Project, 1994

Figure 1.2.6 Location of Upper Solo River Improvement Project in 1994

The Nguter bridge is located downstream of the Colo weir and the Jurug brigde is located about 5 km downstream of Surakarta city. The catchment area of Bengawan Solo at Jurug is around 3,220 km2. The river stretch was improved against the 10-year flood incorporating significant flood control effect of the Wonogiri Dam. Seven short-cut channels in total 13 km long were constructed. Design flood discharge distribution along the stretch is illustrated in Figure 1.2.7 below.

Figure1.2.7 Design Flood Discharge Distribution for Upper Solo River Improvement Project

Jurug Bridge

Nguter



Large flood inflows into the reservoir were estimated based on the hourly basis reservoir operation records of 1983-2004. The estimated large flood inflows are listed below.

Table 1.2.1 Estimated Large Floods into Wonogiri Reservoir

Year Occurrence Date Peak Discharge (m3/sec)

Inflow Volume (million m3)

1983 April 14 to 18 2,660 80.8 1984 January 4 to 5 1,650 52.3 1985 March 6 to 9 2,720 223.0 1988 February 4 to 6 2,880 130.3 1991 February 9 to 12 1,210 94.0 1992 February 12 to 15 1,210 109.6 1994 March 7 to 10 1,760 106.1 1998 December 22 to 26 1,350 37.2 2000 February 3 to 7 1,600 26.1 2003 January 2 to 5 1,010 104.9 2004 December 3 to 4 1,330 32.0


As seen in the table above, the Wonogiri reservoir experienced the largest flood with peak discharge of 2,880 m3/sec on February 5, 1988, followed by the 1985 year flood of 2,720 m3/sec. Large flood inflows exceeding 2,000 m3/s have occurred in 1980s.

The figures below shows actual flood operations of Wonogiri reservoir.

06 - 09 Mar. 1985

0

500

1,000

1,500

2,000

2,500

3,000

6:00

18:0

0

6:00

18:0

0

6:00

18:0

0

6:00

18:0

0

6:00

Inflo

w (m

3 /s)

InflowSpillway

Total Outflow

04 - 06 Feb. 1988

0

500

1,000

1,500

2,000

2,500

3,000

0:00

12:0

0

0:00

12:0

0

0:00

12:0

0

0:00

12:0

0

0:00

Inflo

w (m

3 /s)

Inflow

Spillway

Total Outflow


Figure 1.2.8 Actual Flood Operations of Wonogiri Reservoir



1.2.3 Wonogiri Irrigation System

Immediately after completion of the Wonogiri Irrigation Project in 1986, the water supply to the Wonogiri irrigation system was commenced. Irrigation water is taken from the Colo intake weir located about 13 km downstream of the Wonogiri Dam. The Wonogiri irrigation system comprises 94 km long main canal and 105 km long secondary canal. Water released from the Wonogiri dam is taken to the West and East main canals at the Colo intake. At present, the irrigation area has been extended from 24,000 ha in the original plan to 29,330 ha where triple or double cropping farming is being practiced. The present irrigation area of Wonogiri irrigation system is as follows:

Table 1.2.2 Present Irrigation Area of Wonogiri Irrigation Project

(Unit: ha) East Main Canal West Main Canal Office

Surface Pumping-up Sub-Total Surface Pumping-

up Sub-Total Total

1 Wonogiri 0 0 0 440 250 690 6902 Sukoharjo 2,860 300 3,160 3,610 200 3,810 6,9703 Kartosuro 490 100 590 0 0 0 5904 Bekonang 5,110 350 5,460 0 0 0 5,4605 Klaten 0 0 0 3,640 0 3,640 3,6406 Karranganyar 1,770 350 2,120 0 0 0 2,1207 Sragen Hulu 5,970 400 6,372 0 0 0 6,3708 Sragen Hilir 3,290 200 3,494 0 0 0 3,490

Total 19,490 1,700 21,190 7,690 450 8,140 29,330

Source : Balai PSDA Bengawan Solo Wilayah Surakarta

Mean monthly discharge at the Colo intake in 1986-2005 are presented in the table below. Table 1.2.3 Mean Monthly Discharges at Colo Weir in 1986-2005

(unit : m3/sec) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Release for maintenance flow

30.7 51.4 54.7 32.0 4.8 3.3 3.2 3.2 4.5 6.8 11.8 17.8

Left canal intake 2.4 2.8 2.5 3.1 3.3 3.5 3.4 3.2 3.4 2.7 2.3 2.7

Right canal intake 15.2 13.8 15.7 16.5 16.9 15.7 16.0 15.6 17.0 15.5 14.4 16.6

Total Inflow at Colo 48.3 70.2 74.0 54.1 26.2 23.3 23.3 22.5 25.6 26.0 29.0 35.5

Source: Balai PSDA Bengawan Solo Wilayah Surakarta

Colo Intake Weir



1.2.4 Power Generation at the Wonogiri Hydropower Station

The power house is located just downstream of the Wonogiri Dam. It accommodates the generating equipment with an installed capacity of 12.4 MW to produce annual energy output of 55,000 MWh. The maximum discharge for power generation is 75 m3/s. In the dry season of May-November, around 50-60 million m3 of the stored water in reservoir is used for power generation. In terms of a mean monthly discharge, they

are around 20-25 m3/sec. Power generation is of no consumptive water use. Thus the majority of released water through power generation is then used for irrigation water taken at the Colo weir. The lowest reservoir water level for power generation is currently set El. 130 m due to the sediment deposits in front of power intake.

1.2.5 Operation and Maintenance

PJT I Bengawan Solo was established on March, 2003 based on the Presidential Decree No. 129/2000. With this, the operation and maintenance of the Wonogiri Dam was transferred to PJT I Bengawan Solo branch from PBS. The main revenue of PJT I Bengawan Solo is water charge for hydropower generation (PLN) and municipal/industrial water use (PDAM and industrial water utility). The Wonogiri Dam is mainly managed by these revenues.

Wonogiri Power Station



CHAPTER 2 GARBAGE PROBLEMS AT WATER INTAKE

2.1 Garbage Problems

The intake supplies the reservoir water to the power station and for irrigation releases. The considerable quantity of vegetative debris and garbage washes into the intake forebay area at the beginning of the wet season. Partial blockage of the power intake by garbage frequently occurs. Approximately 20 days per rainy season the intake trash racks are blocked by vegetative debris causing the hydraulic head across the turbines to drop and the turbines to shut down. The trash racks are then cleaned by force of divers. Table below gives the record of power stoppage in 1996-2002 due to cleaning at the Wonogiri power station.

Table 2.1.1 Number of Days of Power Stoppage due to Trash Rack Cleaning at Wonogiri Power Station

Year Days of Power Stoppage 1996 39 1997 19 1998 21 1999 7 2000 34 2001 16 2002 10 2003 6

Source: PLTA Wonogiri

The sediment deposited in the forebay consist of very fine grained materials (wash load). No sands in the deposits. No wear (abrasion) or related problems have occurred with the power turbines and no parts of the turbines have been replaced since operation began in the mid 1980s. This indicates that only very fine sediment materials such as clay and silt have passed through the turbines. According to the Wonogiri power station (PLTA Wonogiri), there is a clearance of 200 mm at the power turbines that might be enough to pass through the sediment materials.

Photos below the debris and garbage at the intake, and latest debris flushing through the spillway conducted on December 29, 2004 at RWL El. 133.4 m. The volume of debris that was gathered in front of the spillway is roughly estimated to be 1,250 m3 (= 2,250 m3 in area x 0.5 m in depth). In the flushing, 3 gates were fully opened respectively. The flushing duration was around 50 minutes.



Photo: Removed vegetative debris and garbage at intake (December 29, 2004)

Photo: Debris flushing on December 29, 2004

Photo: Debris removal in January, 2004

Photo: Debris flushing on December 29, 2004



2.2 Garbage from the Keduang River

2.2.1 Garbage Survey in the Keduang River

In the Study, garbage survey was carried out to estimate the garbage volume conveyed from the Keduang River in the period of November 2006 to February 2007. The garbage trap made of bamboo was installed on the existing check dam on the Keduang River as shown in Figure 2.2.1. During the garbage survey, water level at 800 m upstream of the garbage trap in the Keduang River was periodically observed with intervals of hourly in flood period and 2 times per day in non-flood period.


Figure 2.2.1 Location Map of Garbage Survey

Installation of garbage trap by bamboos Broken garbage trap by flood

Garbage taking Garbage burning after measurement of volume

Location of Garbage Survey (Check Dam No.1 in Keduang River)

WL Gauge Station



2.2.2 Results of Garbage Survey

As shown in the photos, the conveyed garbage from the Keduang River was mainly composed of organic materials such as bushes, branches and harvested crops as same as the deposited garbage around the Intake. The volume of trapped garbage with discharge from November 2006 to January 2007 is shown in Figure 2.2.2 below. Monitoring result of the garbage survey is presented and attached in Annex 1. The volume of trapped garbage is 36 m3 in November, 120 m3 in December, 97 m3 in January Totally 253 m3 of garbage was trapped. Floods at the beginning of wet season convey larger quantity garbage into the Wonogiri reservoir. As the reservoir water level is the lowest at the beginning of wet season, garbage from the Keduang River is likely to reach the intake forebay.

Monitoring of Garbage in Keduagn River(November 2006)

05

10152025303540

2006/11/14 2006/11/19 2006/11/24 2006/11/29

Balk

Vol

ume(

m3)

0100200300400500600700800

Dis

char

ge(m

3/s)

Garbage Vol.(m3)Q (m3/sec)

Monitoring of Garbage in Keduagn River(December 2006)

05

10152025303540

2006/12/1 2006/12/11 2006/12/21 2006/12/31

Balk

Vol

ume(

m3)

0100200300400500600700800

Dis

char

ge(m

3/s)


Monitoring of Garbage in Keduagn River (January 2007)

05

10152025303540

2007/1/1 2007/1/11 2007/1/21 2007/1/31

Balk

Vol

ume(

m3)

0100200300400500600700800

Dis

char

ge(m

3/s)



Figure 2.2.2 Result of Garbage Survey from November 2006 to January 2007



Source: JICA Study Team Figure 3.1.1 Location Map of Cross Sections for Sedimentation Survey

CHAPTER 3 CURRENT STATUS OF THE WONOGIRI RESERVOIR SEDIMENTATION

3.1 Previous Monitoring Studies on the Wonogiri Reservoir Sedimentation

A number of studies to evaluate the reservoir sedimentation have been so far completed by PBS since the completion of Wonogiri Dam in 1981. The most recent study before the current Study was by PT Citra Mandala Agritrans (PT CMA) in 1993. This section summarizes the results of the earlier studies. Major studies were by: • Gadjah Mada University, Yogyakarta, 1985 & 1990. • Bengawan Solo River Basin Development Project (PBS),1986,1987 & 1989. • PT Citra Mandala Agritrans (PT CMA), 1993 These studies used one of following three methods to assess the sedimentation of Wonogiri reservoir: i) Bed profiles were surveyed across

the reservoir at set locations (see Figure 3.1.1 on the right). The new reservoir capacity was then determined by computing the volume between adjacent profiles. The total volume of sediment trapped in the reservoir was the difference between the original (pre-reservoir 1:10,000 scale map in 1980 with 2 m contour intervals as the initial condition) and newly computed capacities (by Gadja Mada University).

ii) Reservoir sediment inflow computed from suspended and bed load sediment transport measurements in the six tributaries entering the reservoir (by PBS).

iii) A contour map was drawn from profiles surveyed at the Figure 3.1.1 set locations. A 500 m by 1,000 m grid was superimposed over the map. Areas and volumes of individual grid blocks for the full range of water levels were computed using the “cubic spline method”. The total reservoir area and capacity was the sum of the values of all the individual blocks. Areas and capacities were given for incremental water levels of 0.01 m from El 127.0 to 138.5 m (by PT CMA).

Main results of these studies are briefed below.

3.1.1 PBS in 1989

PBS estimated the sediment inflow into the Wonogiri based on the sediment measurements in the major six tributaries as follows:



Table 3.1.1 Estimated Annual Wonogiri Reservoir Sediment Inflows by Tributary (Unit: 1,000 ton/year)

River 1981 1982 1983 1984 1985 1986 1987 1988 Tirtomoyo 951 1,048 757 1,103 751 958 740 617Keduang 299 - 398 395 357 461 94 30Solo - 283 343 564 282 478 248 257Alang 54 22 224 150 66 35 123 38Temon 44 33 61 81 102 51 27 35Wuryantoro 3 2 4 24 15 5 6 3Total 4,046 1,389 1,787 2,317 1,574 1,988 1,239 949Accumulated 4,046 5,435 7,222 9,539 11,113 13,101 14,340 15,289

Total Volume (103 m3) 2,549 3,424 4,550 6,010 7,001 8,254 9,034 9,632

Source: Monitoring Reports by PBS

As shown above, the total sediment volume into the Wonogiri reservoir in 1981-1988 was estimated 9.63 million m3. Thus the annual average sediment inflow was estimated around 1.2 million m3/year.

3.1.2 Gadjah Mada University in 1985 and 1990

The Wonogiri reservoir capacity estimates of Gadjah Mada University were conducted both in 1985 and 1990. These estimates were based on the reservoir bed cross-sectional profiles across the reservoir at the pre-determined locations as shown in Figure 3.1.1. Both surveys were made by echo sounding. The estimated sediment deposits (loss of storage volume below El. 138 m) were around 86.2 million m3 in 1981-1985 and 156.4 million m3 in 1980-1990, respectively as listed below. The estimated annual average sediment deposition is around 15.6 million m3/year in 1981-1990.

Table 3.1.2 Estimated Sediment Deposits in the Wonogiri Reservoir (Unit: m3)

Elevation Range below El. 127 m below El. 138 m Storage 123,590,000 718,044,000

1981-1985 41,476,804 86,165,2801985-1990 31,654,637 74,245,7501981-1990 68,184,603 156,389,980

Source: Gadja Mada University Faculty of Geology (GMU), 1985 and 1990, Monitoring Soil Erosion in Upper Solo by Monitoring Sedimentation in Wonogiri Reservoir

3.1.3 PT CMA in 1993

For 1993, PT CMA produced a reservoir contour map from the surveyed profiles and used this to compute the reservoir capacity. Only a rough copy of PT CMA contour map was available. The map was originally at an approximate scale of 1:30,000 with 5 m contour intervals. Figure 3.1.2 in the next page shows a contour map re-produced by PBS. From the change of H-V curves, a significant reduction in reservoir capacity due to sedimentation occurred between 1981 and 1993. The loss of storage capacity to due sedimentation below El. 138 m is 240 million m3 and the annual loss of capacity below El. 138 m is 18.5 million m3/year.

The loss of capacity due sedimentation by storage zone between 1980 and 1993 is summarized below.



Table 3.1.3 Wonogiri Reservoir Capacity Loss by Storage Zone between 1980 and 1993 Reservoir Capacity (million m3) Capacity Lost due to SedimentationReservoir Zone in 1980 in 1993 Value (million m3) of Original (%)

Flood Control Storage (El. 135.3 – 138.3 m) 220 160 60 27

Effective Storage (El. 127.0 – 136.0 m) 440 306 134 30

Dead Storage (below El. 127.0 m) 120 56 64 53

Total Volume 780 522 258 - Source: JICA Study Team

- 6000

- 7000

- 8000

- 9000

- 10000

- 5000

- 4000

- 0000

- 3000

- 2000

- 13000

- 1000

- 11000

- 12000

- 14000

140.00

135.00

130.00

130.00

130.00

135.00

130.00

125.

00

140.0

0

135.00

135.0

0

125.00

125.00 140.00

125.00

135.00

130.00

135.00

DEPARTEMEN PEKERJAAN UMUMDIREKTORAT JENDERAL PENGAIRAN

PROYEK INDUK PENGEMBANGANWILAYAH SUNGAI BENGAWAN SOLO

PETA CONTOUR SEDIMENWADUK WONOGIRI

KETERANGAN GAMBAR :

SUMBER DATA :

125.

00

130.00135.00

135.00140.00

140.00150.00

160.00170.00180.00

190.00

200.00

205.00

190.00

180.00

170.0

0

150.00

125.

0013

0 .00

135 .

00

125.

0013

0 .00

135.

00

140.00

140.0013

5 .0 0

130.

00

120.00

PARKI NG AREA

120.

00

160.00

136.00

136.

00

136.00

136.00136.00

136.

00

TAHUN 1993

140.00150.00

160.00170.00180.00

190.00

200.00

205.00

190.00

180.0

017

0.00

150.00

MAIN DAM

CH

UTE

WAY

POWER

INTA

KE

GAT

E S

HAF

T

SUR

GE

TAN

K13

6.00

100.

00

PL U

N GE

PO

OL

106 .

0 0

106 .

0 0

117.

500

117.50

0

125 .

00

130.

00

135.

00

125 .

00

130.

00

135.

00

140.00

140.0

013

5.00

130.

00

120.00

SUB DAM

PARKING AREA

120.

00

HOUSE

142.000

142.000

160.0

0

136.

00

K. Leber

K. Keduwang

K. Gesin

g

K. Tirtomoyo

K. Beling

K. Parak

K. Alan

g

K. Ngrowo

K. Bendungan

K. Sambilengkung

S. B

enga

K. Wurya

ntoro

K. N

glengkong

K. Kopen

K. Dukuh

wan

So l

o

S. Be Solo

S. BengaSolo

wan

wannga

Source: PBS Figure 3.1.2 1993-year Reservoir Contour Map Reproduced by PBS



3.1.4 Comparison of Estimated Wonogiri Reservoir Capacity

Figure 3.1.3 below shows the comparison of estimated Wonogiri reservoir capacities and linear projections for future sedimentation by the past monitoring studies. As predicted above , capacity of Wonogiri reservoir is expected to decrease to around 330 million m3 applied by the estimate of Gadja Mada University (15.6 million m3/year in 1980-1988) and to 270 million m3 by PT. CMA (18.5 million m3/year in 1981-1993). By both projections, the Wonogiri reservoir would lose about 55-63% of its capacity around by year 2005.

The detailed results of these studies are not presented herein because poor procedures were used to compute the sediment deposition, for the following reasons. i) Determination of reservoir capacity by summing the computed volumes between

adjacent profiles probably gives inaccurate results in a reservoir with many bays as in the Wonogiri. The more accurate procedure for a reservoir such as Wonogiri is to collect more survey data than that obtained from only the Figure 3.1.1 sections to enable a detailed contour map to be produced. The reservoir capacity is then the sum of the volumes computed between incremental contour intervals.

ii) The accurate estimation of sediment inflow to a reservoir using sediment transport measurements in tributary rivers requires the collection of extensive field measurements over many years with the emphasis on measurements during short-duration flood events. Such intensive measurement was not conducted.

iii) The PT CMA results might be of low reliability due to large grid size of 500 m x 1,000 m.

In summary, the results of all the reservoir studies in the past are considered more or less inaccurate, and particularly the PT CMA results. The capacity estimate of PT CMA (1993) was reevaluated later under the Study by use of the re-produced reservoir contour map.

3.1.5 Comparison of Average Erosion Rate (Depth) in the Wonogiri Watershed

An erosion rate is estimated as illustrated below. The erosion rates are estimated for the past three studies as summarized below.

Historical Change of Storage Capacity of WonogiriReservoir

0

100

200

300

400

500

600

700

800

1980 1985 1990 1995 2000 2005Year

Stor

age

Cap

acity

(mil.

m3)

PBS

GMU

PT CMA


Figure 3.1.3 Projection of Wonogiri Reservoir Sedimentation by Past Monitoring Studies



Average ErosionRate (Depth) : E

R

(mm/year)

Catchment Area: A (km2)Watershed BoundaryAverage Sediment Inflow

into Wonogiri Reservoir:SW (m3/year)

ER = (mm)

SWA x 10 3


Figure 3.1.4 Illustration of Average Erosion Rate over the Watershed

Table 3.1.4 Comparison of Average Erosion Rates by Past Studies

Past Study Average Sediment

Deposition (million m3/year)

Average Erosion Rate

(mm/year)

Example: Erosion Depth in 100 years

(cm) PBS in 1989 1.2 0.9 9UGM in 1985 & 1990 15.6 11.6 116PT CMA in 1993 18.5 13.7 137


3.2 Current Status of the Wonogiri Reservoir Sedimentation

An echo sounding survey with GPS on the Wonogiri reservoir was undertaken in two times from October to November 2004 (before entering the wet season) and June to July 2005 (after the wet season) under the current Study in order to estimate the current status of the Wonogiri reservoir sedimentation as well as incremental sediment deposit in the wet season in 2004/2005. Figure 3.2.1 below shows the location of cross sections for reservoir sedimentation survey. As seen, 35 supplementary cross sections was added to the pre-set 64 sections in 1985, 1990 and 1993 to enable more accurate contour map of the reservoir bed.




Figure 3.2.1 Location Map of Cross Sections for Reservoir Sedimentation Survey in 2004 and 2005

3.2.1 Reservoir Sections and Profiles in 1980-2004

Longitudinal and cross-sectional profiles in the reservoir and principal tributaries are developed. These profiles show the 1980, 1993 and 2004 reservoir bed conditions. The location of cross sections is already given (see Figure 3.2.1 above). Figures below are the cross-sectional and longitudinal profiles of major tributaries. All reservoir sections in each river are attached in Annex 2.

9,125,000 N

1L

1R2L

2R3L

3R

W6R 4R

L3R

K1R/L3L

K1L

L4R

L4LL5R

L5L

K2L

K2R

K3L

K3R

K4R

K4LK5L

K5R

K6L

K6R

K7LK7R

L1R

L1L

L2R

L2L

G2R

G2LG1RG1L

T2L

T2RT3R

T3L T4R

T4L T5R

T5LT6R

T6L T7L

T7R T8R

T8L

T9R

T9L

W6L

W7R W7L

W5L

W5R

4/5L

W4RW1L

W1RW2L

W2R

W3L

W3R

N8L

N8RN9L

N9R N6LN7L

N7RN6R 7L

7R

B0R

B0L/B1LN1R

N1LN2L

N3L N2R

N3R

N4/5L

N4RN5R 9R

9L

B1R/B6L

B6R

B7R

B7L

B2R

B2L B3RB3L B4R

B4LB5R

B5L

10L 10R

11L11R

12R12L

B8R

B8L

13R14R

15R15L14L

13LA1L

A1RA2L

A3LA4L

A2R

A3RA4R

Existing Survey Line in 1985, 1990 and 1993

Supplimentary Survey Line in 2004

Keduang

Tirtomoyo

Temon

Bengawan SoloAlang

Wuryantoro



Tirtomoyo (T2)

115

120

125

130

135

140

0 250 500 750 1000 1250 1500 1750 2000 2250 2500

Distance (m)

Ele

vation (EL.m

)

1980

1984

1990

1993

2004

Keduang (K2)

115

120

125

130

135

140

0 250 500 750 1000 1250 1500 1750 2000 2250 2500

Distance (m)

Ele

vation (EL.m

) 1980

1984

1990

1993

2000

2004

Bengawan Solo (8)

115

120

125

130

135

140

0 250 500 750 1000 1250 1500 1750 2000 2250 2500Distance (m)

Ele

vation (EL.m

)

1980

1984

1990

1993

2004

Bengawan Solo (4)

115

120

125

130

135

140

0 250 500 750 1000 1250 1500 1750 2000 2250 2500

Distance (m)

Ele

vation (EL.m

)

19801984199019932004

N

Wonogiri Dam

Solo River


Figure 3.2.2 Reservoir Sections in 1980-2004



Bengawan Solo River

110

120

130

140

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000Distance (m)

Ele

vatio

n (m

)

El-2004El-1993El-1990El-1984El-1980

31 24

5 6

78

9 10 11

1213

14 15

Wonogiri Dam

NWL 136.0

LWL 127.0

Keduang River

110

120

130

140

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000

Distance (m)

Ele

vatio

n (m

)El-2004El-1993El-1990El-1984El-1980

k1k3 k4 k5 k6k2

k7 NWL 136.0

LWL 127.0

Wonogiri Dam

Tirtomoyo River

110

120

130

140

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000

Distance (m)

Ele

vatio

n (m

)

El-2004El-1993El-1990El-1984El-1980

T2T3 T4

T5 T6 T7 T8 T9

T1

Tirtomoyo ConfluenceNWL 136.0

LWL 127.0

Wonogiri Dam

Temon River

110

120

130

140

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000Distance (m)

Ele

vatio

n (m

)

El-2004El-1993El-1990El-1984El-1980

B1 B2 B3B4 B5

B0

Temon Confluence

NWL 136.0

LWL 127.0

Wonogiri Dam

Alang River

110

120

130

140

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000Distance (m)

Ele

vatio

n (m

)

El-2004El-1993El-1990El-1984El-1980

A1 A2 A3 A4

Alang ConfluenceC fl

NWL 136.0

LWL 127.0

Wonogiri Dam


Figure 3.2.3 Reservoir Profiles in 1980-2004



3.2.2 Reservoir Sedimentation Survey in 2004 by PBS

PBS carried out the reservoir sedimentation survey independently subletting the sub-contractor. The survey was made in July to September 2004. However the final report was completed in May 2005. The eco soundings were made as many locations as possible to increase the density of data points so that an accurate reservoir topographic map can be produced. Totally around 100,000 points with an interval of around 10 m were surveyed. The location map of data points is shown below. Very unfortunately, the survey was made only within the reservoir water surface at the time of survey (below the reservoir water level El. 132 m). The perimeter (ground surface) survey from the water’s edge to the maximum reservoir area was not conducted.


Figure 3.2.4 Location Map of Data Points by PBS Survey in 2004

In order to increase an accuracy of reservoir topographic mapping in 2005, data points were added under the Study, mainly for several reservoir profile directions as shown in Figure 3.2.5 below.




Figure 3.2.5 Location Map of Data Points by JICA Survey in 2005 3.2.3 Current Wonogiri Reservoir Conditions in 2004 and 2005

The current reservoir capacity was estimated based on the contour mapping of reservoir bed and DEM (Digital Elevation Method) as given below. Past sedimentation survey results in 1993 was re-assessed by means of the same procedure.

The result of reservoir sedimentation survey by PBS in 2004 was very useful for cross-checking the survey results in 2004 undertaken by the current Study. Finally the contour map from the 2004 survey result was modified incorporating with the PBS survey results in 2004. Figures below show the reservoir contour maps in 1993 and 2004.

Echo Sounding Survey

Contour Map of Sedimentation

Preparation of DEM (10 m x 10 m)

H-A and H-V Curves




Figure 3.2.6 Reservoir Contour Map in 1993


Figure 3.2.7 Reservoir Contour Map in 2004



Elevation-area-capacity relationships of Wonogiri reservoir for 1980, 1993, 2004 and 2005 were developed by use of DEM (around 900,000 meshes in total) as shown in Figure 3.2.9 in next page. Table below presents the estimated Wonogiri storage capacity.

Table 3.2.1 Estimated Wonogiri Reservoir Storage based on DEM Reservoir Capacity

(million m3) Sediment Deposit

(million m3) Reservoir Zone 1980 1993 2004 2005 1993 2005

below El. 127.0 m (DWL) 114 69 58 58 45 (39%) 56 (49%)

below 136 m （NHWL） 547 468 435 433 79 (14%) 114 (21%)

below 138.3 m （DFWL） 730 650 618 616 80 (11%) 114 (16%)


As seen above, approximately 114 million m3, or 16% of the total capacity 730 million m3 was lost due to sedimentation in 1980-2005. The estimated current loss of capacity due to sedimentation in the three storage zones between 1980 and 2005 is summarized below.

Table 3.2.2 Wonogiri Reservoir Capacity Loss by Storage Zone between 1980 and 2005 Reservoir Capacity

(million m3) Capacity Lost due to

Sedimentation Reservoir Zone 1980 2005 Value

(million m3) of Original

(%) Flood Control Storage (El. 135.3 – 138.3 m) 232 230 2 0.9

Effective Storage (El. 127.0 – 136.0 m) 433 375 58 13.4

Dead Storage (below El. 127.0 m) 114 58 56 49.1


As shown above, around 13% of the original effective storage zone (between El. 127.0 m and El. 136.0 m) has been filled with sediment deposits by 2005. In other words, around 87% of the original effective storage zone is still usable. Historical change of each reservoir zone is illustrated below.

0

100

200

300

400

500

1980 1993 2005

Year

Res

ervo

ir C

apac

ity (m

il. m

3)

Flood Control Storage Effective Storage Dead Storage


Figure 3.2.8 Change of Wonogiri Reservoir Capacity by Storage Zone between 1980 and 2005

Three dimensional views of the topography on the Wonogiri reservoir bed were produced from the contour line data before construction of the dam in 1980 and in 2004 as presented in Figure 3.2.11 in the next page.

0

20

40

60

80

100

1980 1993 2005

Year

Res

ervo

ir C

apac

ity (

%)

Flood Control Storage Effective Storage Dead Storage



Wonogiri Dam Reservoir H-V curve

115

120

125

130

135

140

0 100 200 300 400 500 600 700 800

Storage Capacity (mil. m3)

Elev

atio

n (E

L.m

)Control W.L 135.30 m

D.F.W.L 138.30 m

N.H.W.L 136.00 m

L.W.L 127.00 m

1980

1993

2005


Figure 3.2.9 Wonogiri Dam Reservoir Elevation-Capacity Curves in 1980, 1993 and 2005

Keduang Reservoir H-V curve

115

120

125

130

135

140

0 5 10 15 20 25 30 35 40 45 50

Storage Capacity (mil. m3)

Elev

atio

n (E

L.m

)

Control W.L 135.30 m

D.F.W.L 138.30 m

N.H.W.L 136.00 m

L.W.L 127.00 m

2005


Figure 3.2.10 Keduang Reservoir Elevation-Capacity Curves in 2005




Figure 3.2.11 3D View of Wonogiri Dam Reservoir Sedimentation



CHAPTER 4 RESULTS OF GEOLOGICAL INVESTIGATIONS

4.1 Drilling Works

A drilling survey was carried to clarify geological condition in the reservoir area in the first phase of the Study in 2004. Standard penetration test with core sampling were performed at 12 drilling holes as presented in the location map Figure 4.1.1. Results of drilling works are summarized in Table 4.1.1 below. The grain size distributions of each drilling hole is presented in the Table 4.1.2 and Figure 4.1.3. The sediment deposited in the Wonogiri reservoir consists of very fine grained materials (wash load) with 87% of total volume as presented in the Figure 4.1.2. Almost no sands are composed in the deposits.

Table 4.1.1 Results of Drilling Works

Geological condition (m)

Drilling No

Name of River

Length (m)

Sediments after the dam was

completed

Original river

deposit, Terrace deposit

Base rock (rock type) Remarks

BH-1 Solo 15 0.0-2.5 2.5-15.0 (tuffaceaous sand) 2.5-4.0 Organic soil BH-2 Solo 16 0.0-2.0 2.0-8.0 8.0-16.0 (tuffaceaous sand) 2.0-5.0 Organic soil BH-3 Temon 9 0.0-7.6 7.6－9.0 BH-4 Solo 12 0.0-3.6 3.6-9.2 9.2-12.0 (tuff) BH-5 Tirutomoyo 12 0.0-1.5 1.5-12.0 (tuffaceous sand) 1.5-3.0 Organic soil BH-6 Tirutomoyo 13 0.0-3.5 3.5-13.0 (tuff) BH-7 Solo 13 0.0-0.8 0.8-1.5 1.5-12.0 (tuff)

BH-8 Solo 14 0.0-2.02.0-14.0 (lappili tuff, tuffaceous sand)

BH-9 Solo 13 0.0-1.7 1.7-13.0 (lapilli tuff) BH-10 Solo 23 0.0-3.2 3.2-23.0 (lappili tuff) BH-11 Keduwang 25 0.0-17.5 17.5-25.0 BH-12 Keduwang 17 0.0-8.0 8.0-17.0 (tuff breccia)


N

BH-9

Location of Drilling

BH-10 BH-11

BH-12 BH-8

BH-7

BH-5BH-4

BH-3

BH-2

BH-1

BH-6


Figure 4.1.1 Location Map of Drilling Works



Table 4.1.2 Grain Size Distribution of Sediments Gravel

0.24-1.3 1.3-5 5-16 16-31 31-75 75-250 250-850 850-2000 2000-9500(m) (m) (%) (%) (%) (%) (%) (%) (%) (%) (%)

BH-1 2.5 0.20-0.40 64.0 2.5 8.5 11.0 8.8 3.8 1.0 0.5 0.00.60-0.80 66.0 6.0 10.0 6.0 7.7 3.1 0.6 0.4 0.11.55-1.75 62.5 6.5 11.0 6.5 5.6 2.8 2.8 1.4 0.9

BH-2 2 0.30-0.50 65.6 4.4 11.0 9.0 7.1 2.0 0.9 0.0 0.00.60-0.80 60.7 8.3 16.0 8.0 4.7 1.2 1.0 0.0 0.01.50-1.70 46.5 5.5 10.0 6.0 9.6 17.3 4.1 0.8 0.2

BH-3 7.6 0.30-0.50 61.5 5.5 9.5 7.5 9.1 6.3 0.4 0.2 0.00.70-0.90 49.5 4.5 8.0 7.0 9.2 17.4 3.5 0.8 0.11.50-1.70 73.7 4.3 8.0 5.0 5.7 2.1 0.4 0.8 0.12.00-2.50 73.6 5.4 9.0 4.5 4.4 2.2 0.4 0.3 0.25.00-5.50 66.4 4.1 7.5 7.5 6.4 7.8 0.3 0.1 0.0

BH-4 3.6 0.20-0.40 42.4 2.6 4.0 3.0 8.8 22.8 11.9 3.8 0.70.65-0.90 46.8 4.2 6.0 5.5 8.8 15.3 10.3 3.0 0.01.50-1.70 74.8 5.2 3.0 5.0 5.3 3.3 1.0 1.9 0.52.00-2.50 61.5 6.5 7.0 3.5 6.0 10.6 3.9 0.9 0.2

BH-5 1.5 0.25-0.45 61.3 3.7 6.0 4.0 5.3 12.0 6.3 1.3 0.20.75-1.00 68.2 3.8 5.0 3.5 4.5 9.6 4.4 0.6 0.31.20-1.50 37.0 2.5 4.5 4.0 6.4 30.6 14.2 0.6 0.1

BH-6 3.5 0.30-0.50 14.2 1.8 5.0 7.0 11.1 16.1 34.3 9.8 0.70.60-0.80 29.7 5.8 7.5 6.0 9.8 18.7 15.8 5.7 1.01.50-1.70 37.6 3.9 4.5 4.0 5.5 8.1 25.1 10.5 0.82.00-2.50 24.5 2.5 4.0 2.0 6.3 27.0 25.7 6.0 2.0

BH-7 0.8 0.15-0.35 79.8 3.2 3.5 1.5 3.8 4.4 2.1 1.4 0.30.55-0.75 70.0 6.0 6.0 4.0 3.2 4.7 3.0 1.8 1.3

BH-8 2 0.30-0.50 84.2 3.3 3.5 2.0 4.8 1.6 0.5 0.2 0.00.60-0.80 43.9 7.1 7.0 9.0 12.7 15.1 4.7 0.4 0.11.50-1.70 81.4 5.6 5.0 5.0 1.2 1.2 0.5 0.2 0.0

BH-9 1.7 0.30-0.50 77.2 4.8 7.0 7.0 3.0 0.6 0.3 0.1 0.00.70-0.95 79.6 5.9 7.5 4.0 2.1 0.4 0.3 0.1 0.01.50-1.70 86.9 3.1 4.0 2.0 2.7 0.9 0.3 0.1 0.0

BH-10 3.2 0.40-0.60 28.9 6.1 9.0 9.0 14.2 27.7 5.1 0.0 0.00.60-0.80 50.4 11.6 16.0 12.0 9.0 0.8 0.2 0.0 0.01.45-1.70 43.7 9.8 16.5 14.0 11.9 3.5 0.5 0.0 0.02.00-2.50 34.1 12.9 19.0 16.0 12.2 4.3 1.5 0.0 0.0

BH-11 17.5 0.30-0.50 52.3 10.7 12.0 13.5 10.8 0.5 0.1 0.1 0.00.60-0.80 44.1 11.4 22.5 12.0 7.5 2.5 0.0 0.0 0.01.50-1.70 51.1 13.9 20.0 7.0 5.8 2.0 0.2 0.0 0.02.00-2.50 19.2 5.8 9.0 8.0 14.0 34.3 9.3 0.4 0.05.00-5.50 20.0 7.5 11.5 8.0 14.9 27.0 10.6 0.5 0.08.00-8.50 32.5 11.5 24.0 14.0 11.1 5.6 1.2 0.0 0.0

11.00-11.50 38.2 8.4 15.5 16.0 17.6 4.0 0.3 0.2 0.014.00-14.50 46.3 14.2 22.5 10.0 5.7 0.8 0.4 0.0 0.017.00-17.50 44.9 23.1 20.0 7.0 3.9 0.7 0.2 0.2 0.0

BH-12 8 0.30-0.50 47.1 6.4 8.5 7.0 12.7 15.7 2.4 0.2 0.00.70-0.90 61.4 5.6 14.0 8.5 7.3 2.4 0.6 0.2 0.01.70-2.00 61.4 4.6 16.0 12.0 4.9 0.7 0.3 0.2 0.02.50-3.00 51.5 7.5 17.0 14.5 7.7 1.2 0.4 0.2 0.05.50-6.00 54.9 4.1 8.0 7.0 7.6 9.5 7.2 1.7 0.0

Depth ofSediment

SamplingDepth

Grain size (μm)Boring

No.Clay Silt Sand


FINESAND13%

SILT22%

CLAY65%


Figure 4.1.2 Percentage of Sediments Composition in the Wonogiri Reservoir

4.2 Geological Sections

The longitudinal geological sections in the reservoir along Keduang, Tirtomoyo, Temon, Solo Rivers are presented in Figure 4.2.1. The character of sediment material component of main tributaries in the Wonogiri dam catchment area is described below. ･ Sediment materials in the reservoir derived from the Keduang River are composed

mainly of silt and clay, which are inferred to have been transported as suspended load. ･ Sediment of the reservoir from the Alang River, Solo River, Temon River and

Tirtomoyo River gradually become finer downstream ward and form sandy to clayey fore-set bed in the vicinity of the upstream end of the reservoir. Transportation analysis of the sediment from these rivers needs to consider tractional load in addition to suspended load.



BH-1

0% 50% 100%

0.20-0.40

0.60-0.80

1.55-1.75

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-2

0% 50% 100%

0.30-0.50

0.60-0.80

1.50-1.70

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-9

0% 50% 100%

0.30-0.50

0.70-0.95

1.50-1.70

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-10

0% 50% 100%

0.40-0.60

0.60-0.80

1.45-1.70

2.00-2.50

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-5

0% 20% 40% 60% 80% 100%

0.25-0.45

0.75-1.00

1.20-1.50

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-6

0% 50% 100%

0.30-0.50

0.60-0.80

1.50-1.70

2.00-2.50

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-7

0% 50% 100%

0.15-0.35

0.55-0.75

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-8

0% 50% 100%

0.30-0.50

0.60-0.80

1.50-1.70

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-3

0% 20% 40% 60% 80% 100%

0.30-0.50

0.70-0.90

1.50-1.70

2.00-2.50

5.00-5.50

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-4

0% 50% 100%

0.20-0.40

0.65-0.90

1.50-1.70

2.00-2.50

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-11

0% 20% 40% 60% 80% 100%

0.30-0.50

1.50-1.70

5.00-5.50

11.00-11.50

17.00-17.50

Sampling

Depth (m) 0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500

BH-12

0% 20% 40% 60% 80% 100%

0.30-0.50

0.70-0.90

1.70-2.00

2.50-3.00

5.50-6.00

Sampling

Depth (m)0.24-1.31.3-55-1616-3131-7575-250250-850850-20002000-9500


Figure 4.1.3 Grain Size Distribution of Drilling Cores



Source:JICA Study Team

Note: Sediment materials were sampled in the section of the boring core between 0.2 m - 0.6 m in depth and test pitting samples of 0.5 m in depth.

Figure 4.1.4 Composition of Surface Sediment Materials in Wonogiri Reservoir and Five (5) Major Tributaries

LEGEND

500,00

0 E

495,00

0 E

490,00

0 E

485,00

0 E

9,135,000 N

9,130,000 N

9,125,000 N

9,120,000 N

9,130,000 N

9,135,000 N

9,125,000 N

9,120,000 N

500,00

0 E

495,0

00 E

485,0

00 E

7°52’30” S

１11°

00’00” E

490,00

0 E

1L

1R

2L

2R

3L

3R

W6R 4R

L3R

K1R/L3L

K1L

L4R

L4L

L5R

L5L

K2L

K2R

K3L

K3R

K4R

K4L

K5L

K5R

K6L

K6R

K7LK7R

L1R

L1L

L2R

L2L

G2R

G2LG1R

G1L

T2L

T2R

T3R

T3L

T4R

T4L

T5R

T5L T6R

T6LT7L

T7RT8R

T8L

T9R

T9L

W6L

W7R W7L

W5L

W5R

4/5L

W4R

W1L

W1R

W2L

W2R

W3L

W3R

N8L

N8R

N9L

N9R N6L

N7L

N7R

N6R 7L

7R

B0R

B0L/B1LN1R

N1L

N2L

N3L

N2R

N3R

N4/5L

N4RN5R

9R

9L

B1R/B6L

B6R

B7R

B7L

B2R

B2L

B3R

B3L B4R

B4L

B5R

B5L

10L

10R

11L

11R

12R

12L

B8R

B8L

13R

14R 15R

15L14L

13LA1L

A1R

A2L

A3L

A4L

A2R

A3R

A4R9,115,000 N

8°00’00” S

A5L

A5RA6L

A7L

A6R

A7R

16R

16L

17R

17L

B6R

B7R

B8R

B8L

B7L

B6L

T8aR

T8aL

T10R T11R

T11LT10L

K8R

K9R

K10R

K8L

K9L

K10L

W8L

W9L

W10L

W8R

W9R

W10R

EXISTING SURVEY LINE IN 1993 (Re Survey)

NEW SURVEY LINE FOR CONTOURING

CROSS-SECTIONAL SURVEY for 6 Rivers

BH9 L=13m

BH8 L=14m

BH7 L=13m

BH4 L=12m

BH3 L=9m

BH2 L=16m

BH11 L=25m

BH12 L=17m

BH10 L=12m

BH5 L=12m

SU-4

BH1 L=12m

BH-6 L=13m

BH10 L=23m

Keduwang R.

Tirtomoyo R.

Temon R.

Bengawan Solo

Alang R.

AdBed-1

34%

56%

5% 5%

AdBed-2

61%

35%

2%

2%

AdBed-1

1%

73%

10%

16%

AdBed-1

61%

34%

2%

3%

SdBed-2

68%

27%

3%

2%

AdBed-1

5%

80%

8%7%

BdBed-1

65%

28%

4%

3%

BdBed-2

63%

32%

3%

2%

BdBed-3

0%

67%

12%

21%

TdBed-1

76%

22%

1%

1%

TdBed-2(0.2m-1.5m)

65%

30%

3%

2%

TdBed-3

2%

80%

10%8%

KdBed-1

73%

23%

3%

1%

KdBed-2

79%

19%

1%

1%

KdBed-3

85%

12%

2%

1%

sandsilt

gravelclay

BH-1(0.2m-0.4m)

0%

5%

28%

67%

BH-2(0.3m-0.5m)

0%

3%

27%

70%

BH-3(0.3m-0.5m)

0%

7%

26%

67%

BH-4(0.2m-0.4m)

0%

39%

15%

46%

BH-5(0.25m-0.45m)

0%20%

15%65%

BH-6(0.3m-0.5m)

0%

61%23%

16%

BH-7(0.15m-0.35m)

0%

8%

9%

83%

BH-8(0.3m-0.5m)0%

2%

10%

88%

BH-9(0.3m-0.5m)0%

1%

17%

82%

BH-10(0.4m-0.6m)

0%

33%

32%

35%

BH-11(0.3m-0.5m)

0%

1%

36%

63%BH-12(0.3m-0.5m)

0% 18%

28%54%

TdBed-2(0.0m-0.2m)

1%

73%

16%

10%



100

110

120

130

140

150

0 5 10 15Distance Upstream of Dam (km)

Ave

rage

Riv

er B

ed E

leva

tion

(m)

Original Surface (1980)

2004 lowest

Ked

uwan

g B

r.C

heck

Dam

1

BH-11BH-12

MudSand

Assumed surface ofbasal conglomerate

Borehole

Projectedborehole

HWL 136m

LWL 127 m

0% 20% 40% 60% 80% 100%

0% 20% 40% 60% 80% 100%

Gravel

0.24-1.3μm 1.3-5μm 5-16μm 16-31μm 31-75μm 75-250μm 250-850μm 850-2000μm 2000-9500μm

Clay Silt Sand

110

120

130

140

0 5 10 15 20 25Distance Upstream of Dam(km)

(EL.

m)

S1S2

S3

S4S5

S6

NWL 136.0m

LWL 127.0m

S7

S8 S9 S10S11

S12

S13 S14S15

B-2(2002)

MudSand

Borehole

Foreset Plane

Projectedborehole

BH-7

BH-8BH-9

BH-1BH-20% 20% 40% 60% 80% 100%

BH-4

0% 20% 40% 60% 80% 100%

0% 20% 40% 60% 80% 100%

0% 20% 40% 60% 80% 100%

?

0% 20% 40% 60% 80% 100%

0% 20% 40% 60% 80% 100%

Gravel


Clay Silt Sand


Figure 4.2.1 Geological Sections in Wonogiri Reservoir (Keduang River and Solo River)

Keduang River

Bengawan Solo River



110

120

130

140

0 5 10 15 20 25

Distance Upstream of Dam (km)

Ave

rage

Riv

er B

ed E

leva

tion

(m)

2000 survey

1993 survey

1980 mapping

2004 survey

Tirtomoyo RiverSolo River

S1

S2S3

S4 S5

T1

T2T3

T4T5 T6

T7

T9T8

B-2(2002)

BH-9BH-8

BH-7

BH-5

BH-6

Mud

Sandy soil

borehole

Foreset Slope

Projectedborehole

Foreset Slope

NWL 136.0m

LWL 127.0m

0% 20% 40% 60% 80% 100%

0% 20% 40% 60% 80% 100%

Gravel


Clay Silt Sand

110

120

130

140

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000Distance (m)

Ele

vatio

n (m

)

El-2004El-1993El-1990El-1984El-1980

Temon RiverSolo River

NWL 136.0m

LWL 127.0m ?

Mud

Sandy soil

0% 20% 40% 60% 80% 100%

BH-3


Figure 4.2.2 Geological Sections in Wonogiri Reservoir (Tirtomoyo River and Temon River)

Tirtomoyo River

Temon River



CHAPTER 5 MONITORING ON SEDIMENTATION IN FRONT OF INTAKE

5.1 Method of Monitoring

The intake structure of the dam has been seriously affected by sediment inflow from the Keduang River. After completion of the Project for Urgent Countermeasures for Sedimentation in the Wonogiri dam reservoir in March 2004, PBS has been being monitoring periodically sediment levels on the approach channel to the water intake. The method of monitoring is outlined below.

Area : Approach channel and the forebay of the intake (see Figure 5.1.1 below) (20 m (W) x 120 m (L) by 3 sections with an interval of 5 m)

Method : Echo Sounder (RAYTHEON COMPANY) Schedule : Monthly basis

n

Axis Ⅲ

Axis Ⅱ

Axis Ⅰ

Bench mark

45m

Section 1

Section 2

Section 3

Section 4

Section 5

Section *

*

Section *

*

Section *

*

Section *

*

Section *

*

Section *

*

Section *

*

Section *

*

Floating Log Boom

Bench mark

Intake Gaute

Intake

5m

10m

10m


Figure 5.1.1 Monitoring Locations in the Forebay of Intake

Intake after Completion in 1980 Monitoring Survey in May 2005



River bed conditions around Intake on Driest Season: RWL was approx. EL. 127.0 m

5.2 Result of Monitoring

The result of sedimentation monitoring to date is summarized in Annex-3. Figure 5.2.1 below shows the comparison of sediment levels on the approach channel just in front of and 10 m upstream of the intake. It is appeared that: i) Sediment level was EL. 123.7 m in front of trash lack in July 2005. ii) Sediment level rose by 2.1 m from October 2004 to July 2005 during the wet season. iii) Opening space between the sediment level and top of the intake is approximately 3.3

m in July 2005. iv) Sediment levels were stable during the dry

season from May 2004 to October 2004. v) During the succeeding wet season, sediment

levels increased by around 3 m from November 2004 to February 2005.

vi) However, sediment levels were almost stable from March to May 2005.

vii) Stable slope of sediment deposits might be approximately 1/20-1/30 from the longitudinal sediment profiles.

120

125

130

135

2004

/01/

01

2004

/03/

31

2004

/06/

29

2004

/09/

27

2004

/12/

26

2005

/03/

26

2005

/06/

24

2005

/09/

22

2005

/12/

21

2006

/03/

21

2006

/06/

19

2006

/09/

17

2006

/12/

16

Sed

imen

t Lev

el (E

L.m

)

In front of Intake 10 m upstream from Intake

L.W.L 127.0 m

N.W.L 136.0 m

Wet Season Wet Season Wet SeasonWet Season


Figure 5.2.1 Comparison of Sediment Levels in front of Intake

Echo Sounder



5.3 Topographic Survey at Intake Forebay on October 2006

A leveling survey was conducted by PJT-1 in the surrounding area of the intake on October 2006, while the reservoir water level dropped below EL.130.0 m in the end of dry season and sediment deposits around the intake were appeared on the ground.

The method of monitoring is outlined below. Survey Period : October 2006 Survey Area : 250 m x 400 m in forebay of intake and spillway Interval : approx. 10 m Method : leveling

The obtained contour map is presented in Annex-4

5.4 Preliminary Analysis on Sedimentation at Intake

5.4.1 Sediment Inflow from the Keduang River

The Keduang River is the primary cause of the current sedimentation problems in front of the intake because it enters the reservoir close to the dam.

There are two hydraulic mechanisms of sediment inflow from the Keduang River. • At the beginning of the wet season (the reservoir is around at the low water level),

extremely high turbid water due to the Keduang flood directly flows into the intake forebay area along the low water channel which is naturally formed along the dam.

• In the middle and later stage of wet season, turbid water penetrates into the reservoir as a density (muddy) current. From the result of water quality monitoring in the Study, it is appeared that the density current reaches the intake.

Photos: Keduang River within Wonogiri Reservoir

5.4.2 Topographic Feature at Intake

Topographic feature on sedimentation at the intake are described below: • Sediments have already been deposited on the approach channel (cut-off channel) to

the intake because the sediment levels has already risen over LWL El. 127 m.

Keduang River

Keduang River



• Therefore the existing approach channel connecting the intake and original river can not function due to almost full sedimentation up to LWL.

5.4.3 Suction Effect of Intake

The inlet of the intake is designed as bellmouth (11.6 m (W) x 11.0 m(H)) to secure the smooth stream line and reduce the head loss at the inlet. As a brief quantitative analysis, the suction effect of the intake was examined below.

(1) Sediment Level and Shear Velocity:

The relations among sediment level and inflow velocity, shear velocity (U*) and critical shear velocity (U*c) at the inlet are analyzed and summarized in Figure 5.4.1 below. The basic conditions, formulas and calculation results is attached in Annex 5. In this analysis, the objective discharges are applied 75 m3/s for the maximum power discharge and 30 m3/s for the average.

116

117

118

119

120

121

122

123

124

125

126

0.00 2.00 4.00 6.00 8.00

Velocity (m/s)

Sedi

men

t Lev

el (E

l.m)

Maximum Average

116

117

118

119

120

121

122

123

124

125

126

0.00 0.05 0.10 0.15 0.20

U*c [Shear Velocity (m/s)]

Sedi

men

t Lev

el (E

l.m

Maximum Average

U*c(d=5mm)

U*c(d=1mm)

U*c(d=0.1mm)

U*c(d=0.01mm)

Note) Iwagaki formula is applied for the calculation of the critical shear velocity (U*c),.


Figure 5.4.1 Relations among Sedimentation Level, Inflow Velocity, Shear Velocity(U*) and Critical Shear Velocity (U*c)

As the sediment level is higher, the inflow velocity and U* become larger. Considering as a smallest case, however, immediately after construction of the intake, the inflow velocity was around 0.24 m/s for the average power discharge with the sediment level of El.116.0 m. On the other hand, focused on the critical shear velocity (U*c), it can be estimated as 0.009 m/s against the sediment deposits at the intake, D60 of which is assumed 0.01 mm.

The relation above indicates that inflow velocity is usually faster than the critical shear velocity. If there is no obstruction, the sediment deposits in front of the intake can be washed into the inlet by the suction effect at the intake. In fact, however, there are some obstructions as i) garbage blocking at the trash lack, ii) consolidation of sediment deposits, and iii) characteristics of re-suspension and repose angle of a cohesive sediments. As the results, the suction effect of the intake cannot function well and sediment level has risen up to EL.124 m as of July 2005.

(2) Sediment Velocity along the Longitudinal Section of the Intake:

The shear velocity along the longitudinal section on the approach channel is shown in Figure 5.3.2 below. As seen, in front of the intake, the shear velocity is very low due to wider section. At the inlet, the shear velocity depends on the sediment level as mentioned



above. In the original condition, the shear velocity was approx. 0.01 m/s at the inlet, but at present, it has increased to 0.04 m/s which is almost the same as that of the inside of intake tunnel.

Shear Velocity around Intake

0.000

0.020

0.040

0.060

0.080

0.100

-40.0 -30.0 -20.0 -10.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0

Distance (m)

Shea

r Vel

ocity

(m/s

) Original ConditionAfter Sediment Deposits (2003)

Intake

Deposit Line（Aug.2003）


Figure 5.4.2 Shear Velocity around Intake

annex no.3 assessment of wonogiri reservoir sedimentation · table 2.1.1 number of days of power...

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