FINAL REPORT VOLUME-IV SUPPORTING REPORT IIBAKOSURTANAL Badan Koordinasi Survey dan Pemetaan Nasional National Coordination Agency for Surveys and Mapping ... COD Kebutuhan Oksigen

THE STUDY ON

COUNTERMEASURES FOR SEDIMENTATIONIN

THE WONOGIRI MULTIPURPOSE DAM RESERVOIRIN

THE REPUBLIC OF INDONESIA

FINAL REPORT

JAPAN INTERNATIONAL COOPERATION AGENCY

NIPPON KOEI CO.,LTDYACHIYO ENGINEERING CO.,LTD

JULY 2007

VOLUME-IV SUPPORTING REPORT II

Directorate General of Water ResourcesMinistry of Public WorksThe Republic of Indonesia

FINAL REPORT

Composition of Reports

VOLUME-I EXECUTIVE SUMMARY

VOLUME-II MAIN REPORT Part I : Master Plan Study Part II : Feasibility Study

VOLUME-III SUPPORTING REPORT I Annex No.1 Hydrology No.2 Geological Condition No.3 Assessment of Wonogiri Reservoir Sedimentation No.4 Reservoir Sedimentation Analysis No.5 Verification Test for Hydro-Suction System for Sediment Removal No.6 Turbidity Analysis for Downstream Reaches, Solo River Estuary

and Colo Weir

VOLUME-IV SUPPORTING REPORT II Annex No.7 Preliminary Design and Technical Evaluation on Structural

Sediment Management Alternatives No.8 Environmental and Social Considerations (IEE and EIA) No.9 Watershed Conservation and Management

VOLUME-V SUPPORTING REPORT III Annex No.10 Social Survey No.11 Institutional Study for Watershed Management No.12 Cost Estimate No.13 GIS User’s Manual No.14 GIS Training No.15 Dam Safety Analysis No.16 News Letters No.17 Minutes of Meetings

VOLUME-VI DATA BOOK No.1 Meteorological and Hydrological Data No.2 Water Quality and Turbidity

VOLUME-VII PHOTO BOOK

EXCHANGE RATE The exchange rate used in this Study is:

Master Plan Study US Dollar (US$) 1.00 = Indonesia Rupiah (Rp.) 10,035 = Japanese Yen (Y) 119.63 as of December 2005

Feasibility Study US Dollar (US$) 1.00 = Indonesia Rupiah (Rp.) 9,050 = Japanese Yen (Y) 118.92 as of December 2006

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Abbreviation (1/3)

Abbreviation Indonesian EnglishADB Bank Pembangunan Asia Asian Development BankAMDAL Analisis Mengenai Dampak Lingkungan Environmental Impact AnalysisAPBD Anggaran Pendapatan dan Belanja Daerah Provincial Government Development Budget (Provincial Budget)APBN Anggaran Pendapatan dan Belanja Negara Central Government Development Budget (National Budget)BAKOSURTANAL Badan Koordinasi Survey dan Pemetaan Nasional National Coordination Agency for Surveys and MappingBalai PSDA Balai Pengelolaan Sumber Daya Air Regional Office of Water Resources ManagementBalai PDAS Balai Pengelolaan Daerah Aliran Sungai Regional Office of Watershed ManagementBAPEDAL Badan Pengendalian Dampak Lingkungan Environmental Impact Management AgencyBAPEDALDA Badan Pengendalian Dampak Lingkungan Daerah Propinsi Provincial Office of Environmental Impact Management Agency

BAPEEDA Badan Perencanaan Pembangunan DaerahTingkat I Regional Development Planning Agency of ProvinceBAPPENAS Badan Perencanaan Pembangunan Nasional National Development Planning AgencyBB BB Brachiaria BrizanthaBBI Balai Benih Induk Seed Production enterBBLH Biro Bina Lingkungan Hidup Bureau of Environmental GuidanceB-C - Net Present ValueBD - Brachiaria DecumbensBIMAS Bimbingan Masal Mass Guideline for Agricultural DivelopmentBKPH Bagian Kesatuan Pemangkuan Hutan Forest Administration Sub-unitBMG Badan Meteorologi dan Geofisika Meteorological and Geophysical AgencyBOD - Biochemical Oxygen DemandBP2TPDAS Balai Penelitian dan Pengembangan Teknologi Pengolohan

Daerah Aliran SungaiWatershed Management Technology Centera, Ministry of Forestry

BPDAS Solo Balai Pengeloloan Daerah Aliran Sungai Solo Solo River Management Office of Ministry of ForestryBPKH Balai Pemantapan Kawasan Hutan Forest Area Consolidation BureauBPPHH Balai Pengendalian Peredaran Hasil Hutan Forestation Result of Agricultural Extension OfficeBPS Biro Pusat Statistik Central Bureau of StatisticsBPTP Terpadu Balai Pengkajian Teknologi Pertanion Integrated Agricultural Technology Assessment CenterBPTPH Balai Proteksi Tanaman Pangan dan Hortikultura Provincial Plant Protection CenterCd CadmiumCDMP - Comprehensive Developmant and Management Plan Study for Bengawan Solo

River Basin under Lower Solo River Improvement ProjectCOD Kebutuhan Oksigen untuk proses kimia Chemical Oxygen DemandCr Khrom ChromiumCu - CopperCWL Tinggi Muka Air Kendali Control Water LevelDAS Daerah Aliran Sungai Watershed, CatchmentDEM - Digital Elevation MethodDEPDAGRI Departemen Dalam Negeri Ministry of Home AffairsDEPHUT Departemen Kehutanan Ministry of ForestryDEPKES Departemen Kesehatan Ministry of HealthDEPTAN Departemen Pertanian Ministry of AgricultureDFWL Tingi Muka Air Banjir Rencana Design Flood Water LevelDG Direktorat Jendral Directorate GeneralDGLWM Direktorat Jendral Pengelolaan Lahan dan Air Directorate General for Land and Water ManagementDGWR Direktorat Jenderal Sumber Daya Air Directorate General of Water ResourcesDHF - Dengue Hemorrhagic FeverDinas LHKP Dinas Lingkungan Hidup, Kehutanan dan Pertambangan Environment, Forestry and Mining Services of kabupaten WonogiriDIP Daftar Isian Proyek Approved Project BudgetDIPERTA Dinas Pertanian Tanaman Pangan Daerah Propinsi Jawa Provincial Agricultural Service of Central JavaDO Oksigen Terlarut Dissolved OxygenDPRD Dewan Perwakilan Rakyat Daerah Regional House of RepresentativesDPU Departemen Pekerjaan Umum Ministry of Public WorksEFWL Tinggi Muka Air Banjir Ekstra Extra Flood Water LevelEIA Analisis Dampak Lingkungan Environmental Impact AssessmentEIRR - Economic Internal Rate of ReturnEU Uni Eropa European UnionFAO Badan Pangan Dunia United Nations Development Programme /Food and Agriculture OrganizationFORDA Litbang Departemen Kehutanan Forestry Research & Development AgencyGDP - Gross Domestic ProductGIS Sistem Informasi Geografis Geological Information SystemGMU Universitas Gadjah Mada Gadjah Mada University

A-1

Abbreviation (2/3)

Abbreviation Indonesian EnglishGNKPA Gerakan Nasional Kemitraan Penyelamatan Air National Movement of the Partnership for Water PreservationGNP Pendapatan Nasional Gross National ProductGOI Pemerintah Indonesia Government of IndonesiaGOJ Pemerintah Jepang Government of JapanGPS Sistem Posisi Global Global Position SystemGRDP Produk Domestik Regional Bruto Gross Regional Domestic ProductGERHAN Gerakan Nasional Rehabilitasi Hutan dan Lahan National Movement for Forest & Land RehabilitationH-A - Relation between reservoir water level and reservoir surface areaH-V - Relation between reservoir water level and reservoir capacity volumeHKTI Himpunan Kerukunan Tani Indonesia Farmer's AssociationHPI Indek Kemiskinan Human Poverty IndexIBRD (WB) Bank Dunia International Bank of Reconstruction and Development (Work Bank)IEE Pengkajian Pendahuluan Lingkungan Initial Environmental ExaminationIPAIR Iuran Pelayanan Irigasi Irrigation Service FeeIPEDA Iuran Pen Bangunan Daerah Village Land Tax，Provincial Development TaxISPA Infeksi Saluran Pernafasan Atas Upper Respiratory NasopharynxJAMALI Sistem Interkoneksi Jawa-Madura-Bali Java-Madura-Bali power generation systemJBIC - Japan Bank of International CooperationJICA - Japan International Cooperation AgencyJIS Standar Industri Jepang Japanese Industrial StandardsJPY, Yen Yen Japanese YenK2TA Kelompok Konservasi Tanah dan Air Soil and Water Conservation Farmer GroupKBD Kebun Bibit Desa Seeding Garden VillageKCI - Polassium ChlorideKESBANLINMAS Badan Kesatuan Bangsa dan Perlingdungan Masyarakat National Unity and Society Protection BoardKIMPRASWIL Departemen Pemukiman dan Prasarana Wilayah Ministry of Housing and Regional InfrastructureKPH Kesatuan Pemangkuan Hutan Forest Administration UnitKT Kelompok Tani Farmers' Group at Village LevelKUD Koperasi Unit Desa Village Cooperative UnitLHKP Wonogiri Lingkungan Hidup, Kehutanan dan Pertambangan Forestry Sub-services of Wonogiri Human Environment, Forestry and Mining

Services OfficeLKMD Lembaga Ketahanan Masyarakat Desa Village Social Activities Group, Village Welfare InstitutionLPTP NGO (Lembaga Pengembangan Teknologi Perdesaan) -LSM Lembaga Swadaya Masarahkat Nongovernmental Organization (NGO)LWL Tinggi Muka Air Rendah Low Water LevelM&E Pemantauan dan Evaluasi Monitoring and EvaluationMOU Nota Kesepahaman Memorandum of UnderstandingMT I Musim Tanam I Cropping Season IMT II Musim Tanam II Cropping Season IIMT III Musim Tanam III Cropping Season IIINGO Lembaga Swadaya Masyarakat Non Governmental OrganizationNHWL Tinggi Muka Air Normal Normal High Water LevelNO2 Nitrit Nitrogen DioxideNO3 Nitrat Nitrogen TrioxideNTU - Nephelometric Turbidity UnitO&M, O/M Operasi dan Pemeliharaan Operation and MaintenanceOtonomi daerah Otonomi Daerah -OECF - Overseas Economic Cooperation FundOTCA Lembaga Kerjasama Teknis Luar Negei Overseas Technical Cooperation AgencyP4K Pembinaan Peningkatan Pendapatan Petani-Nelayan Kecil Farmer Groups of Small-Scale FarmersPb - LeadPBS Proyek Bengawan Solo Bengawan Solo River Basin Development ProjectP2AT Proyek Pengembangan Air Tanah Groundwater Development ProjectP3A, HIPPA Perkumpulan Petani Pemakai Air, Himpunan Petani Water User's Association (WUA)PABBS Proyek Penyediaan Air Baku Bengawan Solo Bengawan Solo River Water Supply ProjectPBS Proyek Bengawan Solo Bengawan Solo River Basin Development OfficePCM Pertemuan Konsultasi Masyarakat Public Consaltaiton MeetingPDAM Perusahaan Daerah Air Minum Regional Drinking Water Supply CompanyPDAS Pengelolaan Daerah Aliran sungai Watershed ManagementPDRB Produk Domestik Regional Bruto Product Domestic Regional BruttoPerum Perusahaan Umum Public Corporation

A-2

Abbreviation (3/3)

Abbreviation Indonesian EnglishPERSEPSI NGO (Perhimpunan untuk Studi dan Pengembangan

Ekonomi dan Sosial)-

pH Nilai Keasaman pH valuePHBM Pengololaan Hutan Bersama Masyarakat Community Participated Forest ManagementPJP Pembangunan Jangka Panjang Twenty-Five Year Long Term Development PlanPIPWS Bengawan Proyek Induk Pengembangan Wilayah Sungai Bengawan Bengawan Solo River Basin Development OfficePJT Perum Jasa Tirta Public Water Service CorporationPKL Penyuluh Kuhutanan Lapangan Field Forestry Extension WorkerPKSDABS Proyek Pengembangan Konservasi Sumber Daya Air

Bengawan SoloBengawan Solo River Water Resources Conservation Development Project

PLTA Wonogiri Pusat Listrik Tenaga Air Wonogiri Wonogiri Power StationPMF Banjir Maksimum yang mungkin terjadi Probable Maximum FloodPO4 - Phosphoric TetroxidePPL Penyuluh Pertanian Lapangan Field Extension Workersppm Seper juta parts per millionPPTPA Penitia Pelaksana Tata Pengaturan Air River Basin Water Resources Management CommitteePRA Analisa Partisipatori Pedesaan Participatory Rural AppraisalPROPENAS Program Pembangunan National Five-Year National Development ProgramPSAPBBS Proyek Pengelolaan Sumber Air dan Pengendalian Banjir

Bengawan SoloBengawan Solo River Water Resources Management and Flood Control Project

PSDA Pekerjaan Umum Sumber Daya Air Water Resource ManagementPT CMA PT Citra Mandala Agritrans -PTPA Panitia Tata Pengaturan Air -PU Pekerjaan Umum Ministry of Public WorksREI - Rain Erosivity IndexRENSTRA Rencana Strategis Strategic PlanREPEDA Rancangan Peraturan Daerah Annual PlanRp. Rupiah Indonesian RupiahRPH Resort Pemangkuan Hutan Field Unit of KPHRTL Rencana Tindak Lanjut Field Technical Planning in Upper Solo Watershed Protection Project in

Wonogiri WatershedRTT Rencana Teknis Tahunan Yearly Technical Planning in Upper Solo Watershed Protection Project in

Wonogiri WatershedRUTRK-RDTRK Rencana Umum/Detail tata Ruang Kota General City Site Plan, Detailed City Site PlanRWL Muka Air Waduk Reservoir Water LevelSBRLKT Sub Balai Rehabilitasi Lahan dan Konservasi Tanah Sub Unit for Land Rehabilitation and Soil ConservationSCF Faktor Konversi Standar Standard Conversion FactorSDR Nisbah Pengantaran Sedimen Sediment Delivery RatioSEA Penilaian Lingkungan Strategis Strategic Environmental AssessmentSFC Perum Perhutani State Forest CorporationSHFD Debit banjir tertinggi standar Standard Highest Flood DischargeSI - Stress IndexSS Padatan Tersuspensi Suspended SolidSWOT Kekuatan, Kelemahan, Kesempatan, Ancaman Strength, Weakness, Opportunity, ThreatTDS Total Padatan Terlarut Total Dissolved SolidTIU Unit Pelaksana Teknis Technical Implementation UnitTOR Kerangka Acuan Kerja Terms of ReferenceTSS Total Padatan Tersuspensi Total Suspended SolidUKL Upaya Kelola Lingkungan Environmental Management EffortsUNDP/FAO Badan Pangan Dunia United Nations Development Programme /Food and Agriculture OrganizationUPL Upaya Pemantau Lingkungan Environmental Monitoring EffortsUPR Unit Pembenihan Rakyat Community Nursery UnitUPTD Unit Pelaksana Teknis Daerah Local Technical Implementation UnitUS$, USD Dollar Amerika US dollarUSAID - US Agency for International DevelopmentUSLE Persamaan Kehilangan Tanah Umum Universal Soil Loss EquationVAP Rencana Kerja Desa Village Action PlanWC3 Komite Koordinasi Konservasi DAS Watershed Conservation Coordinating CommitteeWKPP Wilayah Kerja Penyuluhan Pertanian Working Area of Agricultural ExtensionWM Pengelolaan Daerah Aliran sungai (DAS) Watershed ManagementWRM Pengelolaan Sumber Daya Air (SDA) Water Resource ManagementZn Seng Zinc

A-3

Annex No.7 Preliminary Design and

Technical Evaluation on Structural Sediment

Management Alternatives

i

THE STUDY ON COUNTERMEASURES FOR SEDIMENTATION

IN THE WONOGIRI MULTIPURPOSE DAM RESERVOIR

IN THE REPUBLIC OF INDONESIA

FINAL REPORT

SUPPROTING REPORT

Annex No.7: Preliminary Design and Technical Evaluation on Structural Sediment Management Alternatives

Table of Contents

Page

CHAPTER 1 BASIC CONDITION FOR CONSIDERING COUNTERMEASURES ...............7-1

1.1 Basic Conditions for Preliminary Design ......................................................................7-1 1.2 Restricting Conditions of Flood Control......................................................................7-12 1.3 Features of Sedimentation............................................................................................7-13

CHAPTER 2 ALTERNATIVES OF COUNTERMEASURES FOR SEDIMENTATION ........7-16

2.1 Preliminary Alignment of Conceivable Alternative Structures....................................7-16 2.2 Alternatives for Reducing Sediment Deposition within the Reservoir ........................7-18

2.2.1 Keduang River Sediment Bypass..................................................................7-18 2.2.2 Sediment Sluicing by New Gates .................................................................7-36 2.2.3 Sediment Storage Reservoir with New Gates ...............................................7-49 2.2.4 Sluicing from Existing Outlet .......................................................................7-60 2.2.5 Sediment Storage Dam .................................................................................7-67 2.2.6 Dry Excavation .............................................................................................7-72 2.2.7 Hydraulic Dredging ......................................................................................7-73 2.2.8 Dam Heightning............................................................................................7-75 2.2.9 Sediment Trapping Dam (Periodic Excavation Dam)...................................7-77 2.2.10 Modification of Reservoir Operation Rule ...................................................7-79

2.3 Alternatives to Keep Proper Function of Intake ..........................................................7-80 2.3.1 Modification of Existing Intake ....................................................................7-80 2.3.2 Relocation of Intake......................................................................................7-83 2.3.3 Debris Trapping Structure at Intake ..............................................................7-86 2.3.4 Debris Trapping structure on Keduang River Mouth....................................7-88 2.3.5 Regular Maintenance Dredging at Intake .....................................................7-91 2.3.6 Garbage Trapping Structure at Intake ...........................................................7-92

ii

2.3.7 Hydro-suction Sediment Removal System (New Sediment Removal System) .........................................................................................................7-94

2.4 Summary of Countermeasures ...................................................................................7-100 CHAPTER 3 FEASIBILITY DESIGN OF SEDIMENT STORAGE RESERVOIR ...............7-105

3.1 Design Condition and Criteria ...................................................................................7-105 3.2 New Spillway.............................................................................................................7-105

3.2.1 Layout Plan of New Spillway .....................................................................7-106 3.2.2 Design .........................................................................................................7-106

3.3 Closure Dike .............................................................................................................. 7-111 3.4 Overflow Dike............................................................................................................7-112

List of Tables

Table 1.1.1 Principal Feature of Wonogiri Multipurpose Dam and Reservoir ........................7-1 Table 1.1.2 Design Flood and Discharge from Spillway.........................................................7-6 Table 1.1.3 Design Flood Discharge (m3/s)...........................................................................7-10 Table 1.1.4 Peak Discharge ...................................................................................................7-11 Table 2.2.1 Two Type of Concept for Sediment Flushing .....................................................7-18 Table 2.2.2 Merits and Demerits of Sediment Bypassing .....................................................7-18 Table 2.2.3 Dimension of Facility .........................................................................................7-19 Table 2.2.4 Comparison of Bypass Cut Discharge................................................................7-23 Table 2.2.5 Sediment Balance of Sediment Bypass ..............................................................7-24 Table 2.2.6 Discharge of Bypass Flow..................................................................................7-30 Table 2.2.7 Dimension of Facility .........................................................................................7-30 Table 2.2.8 Horseshoe Section of Bypass Flow ....................................................................7-31 Table 2.2.9 Comparison of Bypass Route .............................................................................7-34 Table 2.2.10 Facility Plan........................................................................................................7-37 Table 2.2.11 Sediment Balance of Sediment Sluicing by New Gate.......................................7-39 Table 2.2.12 Sediment Discharge from New Gates.................................................................7-49 Table 2.2.13 Facility Plan........................................................................................................7-50 Table 2.2.14 Estimated Mean Monthly Inflow from Keduang River......................................7-51 Table 2.2.15 Reservoir Capacity-Elevation Curve ..................................................................7-52 Table 2.2.16 Effectiveness of Sediment Flushing ...................................................................7-55 Table 2.2.17 Sediment Balance of Sediment Storage Reservoir with New Gates...................7-56 Table 2.2.18 Sediment Balance of Sediment Sluicing from Existing Intake...........................7-62 Table 2.2.19 Dimension of Sediment Storage Dam in Keduang River ...................................7-67 Table 2.2.20 Facility Plan........................................................................................................7-70 Table 2.2.21 Dredging Work and Cost ....................................................................................7-74 Table 2.2.22 Estimated Sediment Volume...............................................................................7-74 Table 2.2.23 Affected Living Area by Dam Heightening........................................................7-76

iii

Table 2.3.1 Facility Plan........................................................................................................7-81 Table 2.3.2 Facility Plan........................................................................................................7-83 Table 2.3.3 Dimension of Facilities.......................................................................................7-88 Table 2.3.4 Dimension of Debris Trapping Structure............................................................7-89 Table 2.3.5 Sediment Removal at the Front of Intake on Regular Maintenance...................7-92 Table 2.3.6 Summary of Suction in Flooding Time ..............................................................7-96 Table 2.3.7 Stress Index.........................................................................................................7-97 Table 2.3.8 Summary of Constant .........................................................................................7-98 Table 2.3.9 Summary of Suction in Power Plant Operation Time ........................................7-98 Table 2.3.10 Summary of Suction Operation ..........................................................................7-98 Table 2.4.1 Alternatives for Sediment Removal in Dam Reservoir (1/2) ...........................7-101 Table 2.4.2 Alternatives for Sediment Removal in Dam Reservoir (2/2) ...........................7-102 Table 2.4.3 Alternatives for Sediment of Intake..................................................................7-103 Table 2.4.4 Evaluation of Alternatives for Reducing Deposition Within the Reservoir......7-104 Table 2.4.5 Evaluation of Alternatives to Keep Proper Function of Intake.........................7-104 Table 3.1.1 Design Condition and Criteria ..........................................................................7-105 Table 3.2.1 Trajectory of Jet Water......................................................................................7-110 Table 3.2.2 Main Quantity of New Spillway.......................................................................7-110 Table 3.3.1 Main Quantity of Closure Dike ........................................................................ 7-111 Table 3.4.1 Main Quantity of Overflow Dike .....................................................................7-113

List of Figures

Figure 1.1.1 Allocation of Storage Capacity and Water levels of Wonogiri Dam ....................7-2 Figure 1.1.2 General Layout of Wonogiri Dam ........................................................................7-3 Figure 1.1.3 Profile and Typical Section of Wonogiri Dam......................................................7-4 Figure 1.1.4 Plan and Profile of Spillway.................................................................................7-7 Figure 1.1.5 Plan and Profile of Intake .....................................................................................7-9 Figure 1.2.1 Wonogiri Dam Operation Record .....................................................................7-14 Figure 2.1.1 Countermeasures for Sedimentation Issues in Wonogiri Reservoir....................7-17 Figure 2.1.2 Conceivable Countermeasures for Whole Reservoir Sedimentation..................7-17 Figure 2.2.1 Illustrates of Layout and alignment of Bypass Channel .....................................7-19 Figure 2.2.2 Alignment and Structure of Bypass Channel ....................................................7-20 Figure 2.2.3 Plan and Profile of Diverting Weir .....................................................................7-21 Figure 2.2.4 Design Discharge of Bypass Channel.................................................................7-22 Figure 2.2.5 Comparison of Bypass Cut Discharge................................................................7-22 Figure 2.2.6 Velocity Distribution...........................................................................................7-24 Figure 2.2.7 Sedimentation at Keduang..................................................................................7-24 Figure 2.2.8 Sedimentation at Whole Reservoir .....................................................................7-25 Figure 2.2.9 Velocity Vector at Whole Reservoir....................................................................7-26 Figure 2.2.10 Result of Reservoir Sedimentation Analysis (Case: Sediment Bypassing) ........7-27 Figure 2.2.11 Proposed Bypass Routes.....................................................................................7-28

iv

Figure 2.2.12 Sediment Discharge from Bypass Channel ........................................................7-29 Figure 2.2.13 Outflow Discharge of Bypass Flow....................................................................7-29 Figure 2.2.14 Profile of Diverting Weir and Inlet of Bypass Channel ......................................7-31 Figure 2.2.15 Typical Cross Section of Bypass Channel ..........................................................7-31 Figure 2.2.16 Longitudinal Section of Bypass Channel .........................................................7-32 Figure 2.2.17 Design Discharge of Bypass Channel.................................................................7-33 Figure 2.2.18 Current State of Proposed Bypass Route............................................................7-35 Figure 2.2.19 Image of Profile of Conceivable Sediment Sluicing Facility .............................7-37 Figure 2.2.20 Location of Proposed Sediment Sluicing Facility ..............................................7-38 Figure 2.2.21 Location of Sluicing Gate...................................................................................7-38 Figure 2.2.22 Velocity...............................................................................................................7-39 Figure 2.2.23 Sedimentation .....................................................................................................7-39 Figure 2.2.24 Layout Plan of New Sediment Sluicing Gate .....................................................7-40 Figure 2.2.25 Profiles of Dam Axis and New Spillway............................................................7-41 Figure 2.2.26 Sedimentation at Whole Reservoir .....................................................................7-42 Figure 2.2.27 Velocity Vector at Whole Reservoir....................................................................7-43 Figure 2.2.28 Result of Reservoir Sedimentation Analysis (Case: Sediment Sluicing by New Gate) ............................................................7-44 Figure 2.2.29 Image of Sediment Flushing...............................................................................7-45 Figure 2.2.30 Discharge Ability of Flushing Gate ....................................................................7-47 Figure 2.2.31 SS Concentration of Keduang River (21, Nov., 2004 – 15, May, 2005) ............7-48 Figure 2.2.32 Relation of Design Discharge and Sediment Discharge .....................................7-48 Figure 2.2.33 Sediment Discharge from New Gates.................................................................7-49 Figure 2.2.34 Location of Sediment Storage Reservoir with New Gates .................................7-51 Figure 2.2.35 Reservoir Capacity-Elevation Curve ..................................................................7-52 Figure 2.2.36 Layout Plan of Sediment Flushing Facility and Closure Dike ...........................7-53 Figure 2.2.37 Alignment and Structure of Closure Dike ..........................................................7-54 Figure 2.2.38 Discharge of Flushing Gate ................................................................................7-55 Figure 2.2.39 Velocity...............................................................................................................7-56 Figure 2.2.40 Sedimentation .....................................................................................................7-56 Figure 2.2.41 Sedimentation of Whole Reservoir at Sediment Storage Reservoir with

New Gates ..........................................................................................................7-57 Figure 2.2.42 Velocity Vector of Whole Reservoir at Sediment Storage Reservoir..................7-58 Figure 2.2.43 Result of Reservoir Sedimentation Analysis (Case: Sediment Storage Reservoir with New Gates) ........................................7-59 Figure 2.2.44 Image of Sediment Flushing by Hollow Jet Valve .............................................7-61 Figure 2.2.45 Velocity...............................................................................................................7-63 Figure 2.2.46 Sedimentation .....................................................................................................7-63 Figure 2.2.47 Sedimentation of Whole Reservoir at Sediment Sluicing from Existing

Intake ..................................................................................................................7-64 Figure 2.2.48 Velocity Vector of Whole Reservoir at Sediment Sluicing from Existing

Intake ..................................................................................................................7-65

v

Figure 2.2.49 Result of Reservoir Sedimentation Analysis (Case: Sediment Sluicing from Existing Intake) ................................................7-66 Figure 2.2.50 Planning of Sediment Storage Dam....................................................................7-69 Figure 2.2.51 Longitudinal Profile of Sediment storage Dam..................................................7-69 Figure 2.2.52 Typical Cross Section of Sediment Storage Dam...............................................7-71 Figure 2.2.53 Sediment Storage Dam System ..........................................................................7-71 Figure 2.2.54 Profile of Sediment Trapping Dam.....................................................................7-72 Figure 2.2.55 Layout of Dry Excavation Areas ........................................................................7-73 Figure 2.2.56 Illustration of Periodic Excavation of Sediment Trapping Dam.........................7-73 Figure 2.2.57 Elevation-Capacity Curve of Wonogiri Reservoir ..............................................7-76 Figure 2.2.58 Inundation Area Due to Dam Heightening .........................................................7-76 Figure 2.2.59 Typical Cross Section of Dam Heightening .......................................................7-77 Figure 2.2.60 Profile of Sand Trapping Dam............................................................................7-78 Figure 2.2.61 Illustration of Periodic Excavation of Sediment Trapping Dam (1/2)................7-78 Figure 2.2.62 Illustration of Periodic Excavation of Sediment Trapping Dam (2/2)................7-78 Figure 2.2.63 Freeboard of Wonogiri Dam...............................................................................7-79 Figure 2.3.1 Modification of Existing Intake..........................................................................7-82 Figure 2.3.2 Alignment and Profile of Relocation of Intake...................................................7-84 Figure 2.3.3 Structure of Relocation Intake ............................................................................7-85 Figure 2.3.4 Debris Trapping Structure Around Intake...........................................................7-86 Figure 2.3.5 Debris Trapping Structure at Intake....................................................................7-87 Figure 2.3.6 Debris Trapping Structure at Keduang River .....................................................7-90 Figure 2.3.7 Regular Maintenance Dredging..........................................................................7-91 Figure 2.3.8 Garbage Trapping Structure Surrounding Intake................................................7-93 Figure 2.3.9 Cross Section of Garbage Trapping Structure ....................................................7-93 Figure 2.3.10 Detailed Cross Section of Garbage Trapping Structure......................................7-93 Figure 2.3.11 Suction Area .......................................................................................................7-95 Figure 2.3.12 Critical Flow and Density...................................................................................7-96 Figure 2.3.13 Density and Volumetric Consistency..................................................................7-96 Figure 2.3.14 Volumetric Concentration and Critical Flow Velocity........................................7-97 Figure 2.3.15 Plan of Hydro-suction Sediment Removal System ............................................7-99 Figure 3.1.1 General Plan of Sediment Storage Reservoir with New Gates.............................F-1 Figure 3.1.2 Design Water Level for Design of New Spillway ............................................7-105 Figure 3.2.1 Plan of New Spillway ...........................................................................................F-2 Figure 3.2.2 Profile of New Spillway .......................................................................................F-3 Figure 3.2.3 H-Q Curve of New Gates .................................................................................7-107 Figure 3.2.4 Width Water Depth Curve of New Gates..........................................................7-107 Figure 3.2.5 New Gates and Typical Cross Section of Spillway ............................................F-4 Figure 3.2.6 H-Q Curve of Training Channel .......................................................................7-108 Figure 3.2.7 Trajectory of Jet Water......................................................................................7-109 Figure 3.2.8 Trajectory of Falling Jet Water .........................................................................7-110 Figure 3.3.1 Plan and Structure of Closure Dike ......................................................................F-5

vi

Figure 3.4.1 Plan and Section of Overflow Dike ......................................................................F-6 Figure 3.4.2 H-Q Curve of Overflow Dike...........................................................................7-112 Figure 3.4.3 Plan and Section of Connecting Conduit..............................................................F-7

Attachments

Attachment 1 Quantity Calculation (New Spillway) ............................................................7-A1-1 Attachment 2 Quantity Calculation (Closure DIke)..............................................................7-A2-1

The Study on Countermeasures for Sedimentation Final Report in the Wonogiri Multipurpose Dam Reservoir Supporting Report Annex No.7

Nippon Koei Co.,Ltd. 7-1 July 2007 Yachiyo Engineering Co.,Ltd.

CHAPTER 1 BASIC CONDITION FOR CONSIDERING COUNTERMEASURES

1.1 Basic Conditions for Preliminary Design

In accordance with dam design and reservoir operation rule, restricting conditions for countermeasures of sedimentation in view of flood control and water utilization shall be considered in this section.

(1) Principal Feature of the Wonogiri Dam

The principal features of the Wonogiri dam and reservoir are shown in Table 1.1.1 and the allocation of the storage capacity of the dam and designated water levels are shown in Figure 1.1.1

Figure 1.1.2 shows the general layout of the Wonogiri dam, and Figure 1.1.3 shows the profile and typical cross section of dam.

Table 1.1.1 Principal Features of Wonogiri Multipurpose Dam and Reservoir

Dam type Rockfilll Normal Water Level EL. 136.0 m

Dam height 40 m Design Flood Level EL. 138.3 m

Crest length 830 m 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 Overflow Crest Height EL. 131.0 m

Reservoir area 90 km2 Flood inflow discharge 4,000 m3/s

Gross storage capacity 735 x 106 m3 Design discharge at flooding 400 m3/s

Active storage capacity 615 x 106 m3 Design flood discharge 5,100 m3/s

Flood control storage capacity 220 x 106 m3 PMF(Provable maximum flood)

9,600 m3/s

Irrigation & hydro power storage capacity

440 x 106 m3 Power plant installed capacity

12.4 MW

Sediment storage capacity 120 x 106 m3 Design head 20.4 m

Sediment deposit level EL. 127.0 m Max. discharge 75 m3/s

Source: PBS



Source: PBS

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



(2) Design Concept

1) Reservoir

Wonogiri reservoir was designed to have total storage of 735 million m3 at maximum flood water level of EL.138.3 m (lake surface area : 87 km2). Normal high water level and low water level were set at EL.136.0 m and EL.127.0 m respectively, between which 440 million m3 was secured as an active storage for the use of irrigation water supply, power generation and etc. As flood control capacity, about 220 million m3 was provided above the elevation of 135.3 m which would have to be maintained during flood season. Below low water level, storage capacity of 120 million m3 was prepared for sedimentation which is estimated as total volume of it for 100-years.

Operation rule of reservoir was established so that it should be recovered full storage by every May and successively release water to meet irrigation demand. Water released is to be utilized first for power generation and then for irrigation at the Colo weir 13 km downstream from dam.

At the end of every rainy season, water level should be recovered to normal water level not to obstacle the water utilization for irrigation.

If any surplus water exists, mostly wet season, it will be used for power generation being added to required irrigation released.

Average discharge during dry season (Jun to September: maximum irrigation period) is 27. 5m3/sec, whereas during rainy season 20.7 m3/sec on average is discharged including surplus water for power generation.

2) Dam

Dam to be constructed at the site immediately downstream of confluence of east tributary of the Kuduang River was designed of a central core type rockfill dam. Due to topographic condition of the dam site, a low sub dam had to be provided with on the right bank ridge.

Height of the dam rises 40. 0m above the base rock and top of crest was set at EL.142.0 m at which the dam had a free board of 2.9 m even above the extra ordinary flood water level and of 6.0 m above the normal high water level. Total crest length is 834 m. Total embankment volume was estimated at 1.8 million m3.

3) Spillway

Spillway was designed of overflow weir with radial gates and chuteway with flip bucket end and with plunge pool on the left bank adjacent to the main dam.

It has effective width of overflow weir of 30 m ([email protected] m), rectangular reinforced concrete chuteway width of 30m to 20m and total chuteway length of 360 m, and 51 m long plunge pool at the downstream end.

Four number of roller gates, 7.5 m wide and 7.8 m high were provided with overflow crest.

This spillway was designed to accommodate extra ordinary flood and to evacuate the discharge 1,360 m3/s at the maximum water level of EL.139.1 m.

Spillway was also designed to regulate the floods under such rule as whenever the



reservoir water level was lower than EL.138.2 m, the discharge from spillway should be maintained a constant outflow of 400 m3/sec, while the water level rises above EL.138.2 m, free overflow should be allowed by fully opening of crest gates until the reservoir surface went down to EL.135.3 m, i.e. the control water level during flood season.

Table 1.1.2 shows the design flood, design discharge and water level coincided with flood

Design flood hydrograph is shown in figure 1.1.4.

Table 1.1.2 Design Flood and Discharge from Spillway Flood discharge Maximum inflow

(m3/sec) Maximum outflow

(m3/sec) Water level

(EL. m) Basic highest flood discharge (S.H.F.D)

4,500 400 138.3

Design flood discharge for spillway

5,200 1,170

Extra ordinary flood 9,600 1,360 139.1

Source: PBS



4) Intake and Waterway

Horizontal Inlet of bell-mouth type with Intake gate is finally selected as intake structure. The bottom elevation of inlet is set at EL.116.00 m. Inlet structure has two square parts of 5.5 m wide each and inclined steal trash-rack at the entrance. A semicircular intake tunnel has an inside diameter of 5.5 m and connects the inlet structure to the gate operating shaft for accommodating the maximum discharge of 75 m3/s.

In order to prevent the air suction into the waterway, the minimum water depth at entrance should be deeper than 1.5 times the diameter of tunnel.

As illustrated below this design standard is followed in the current design.

Hmin=8.5m 1.5D=1.5×5.5=8.25m ∴ Hmin > 1.5D Wave height at Intake when the reservoir water level sticks to the low water level(WL.127.00m) can be estimated from the following SMB formula. Ht = 0.00086 V 1.1 F 0.45 Where the fetch is taken to 1,700 m, then the wave height is 66 centimeters.

Intake facilities to take the surface water of reservoir are not provided in the Wonogiri dam, since these facilities are suited to regions with chilly weather such as in the northern part of Japan.

Hmin>1.5D

LWL 127.00m

EL 118.50m

116.00m D=5.50m



(3) Flood Control Plan

1) Master Plan

Flood control plan is composed of flood control at Wonogiri dam and Improvement plan of downstream of the Solo River.

In case peak inflow at Dam site is below design flood inflow of 4,000 m3/s, most of the inflow is controlled in the reservoir and 400 m3/s outflow is discharged from dam.

Due to these flood control, flood flow at downstream is decreased to approximately 2,000 m3/s at Surakarta.

Capacity of flow at downstream of the Solo River was only 500 m3/s, and river improvement works were implemented to increase the capacity of flow from 500 m3/s to 2,000 m3/s.

Design flood adopted in the flood control plan was (SHFD) standard hydrograph of flood discharge, whose occurrence probability is 60-years at Wonogiri dam site and 40-years at Surakarta.

Design flood discharge is shown in following table at respective control points.

Table 1.1.3 Design Flood Discharge（m3/s)

Condition of river Dam site Surakarta Ngawi Current discharge 4,000 2,160 1,890 Before flood control at dam 4,000 5,300 4,900 After flood control at dam 400 2,000 2,830

Source: PBS

2) Flood Control at Reservoir

The reservoir water level is controlled not to exceed the control water level (EL135.3 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. 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 1982, no flooding has 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.

Flood discharge adopted in the design stage are as shown below.

For estimate of abnormal flood discharge for dam design, the probable maximum flood analysis was introduced.



Table 1.1.4 Peak Discharge Flood Discharge (m3/sec) Remarks

Dry season diversion 350 20-year flood Diversion 3,100 20-year flood Standard highest flood (SHFD) 4,000 60-year flood Spillway Design 5,100 1.2 times 100-year flood Extra ordinary 9,600 Probable maximum flood

Source: PBS

3) Run-off Records

Monthly mean run-off data for the period from 1953/54 to 1972/75 were used for the Dam design report prepared by JICA F/S team on October 1975.

Observed run-off data at Wonogiri for the period from 1975/76 to 2003/4 are supplemented in the above data.

Average annual run-off at the Wonogiri dam site is newly estimated at about 31.73/sec in yearly mean. 12.7 m3/sec in driest year and 56.4 m3/sec in the wettest year in the dam design stage.

(4) Wonogiri Irrigation System

Immediately after completion of the Wonogiri Irrigation Project in 1983, 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. At present, the irrigation area has been extended from 24,000 ha in the original plan to 30,000 ha where triple cropping farming is being practiced.

(5) Power Generation at the Wonogiri Hydropower Station

The powerhouse 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.

(6) Freeboard by the 1978 Detailed Design

According to the Completion Report of Wonogiri Multipurpose Dam Project, the crest elevation of the impervious core zone of Wonogiri dam is El. 141.0 m as illustrated below.

The freeboard of 1.9 m as shown above, given by the difference between the crest of impervious core (El. 141.0 m) and the Extra Flood Water Level (El. 139.1 m), was originally allocated for additional allowance against water wave by the concurrent wind

Core Crest El. 141.0 m

Extra Flood (PMF) Water Level El. 139.1 m

Dam Crest El. 142.0 m

Impervious Core

Freeboard1.9 m



at the occurrence of PMF.

As mentioned in Section 3.1, the freeboard of 1.9 m was provided to prevent rising of the reservoir water surface from overtopping the impervious core zone of the embankment due to wave action that might coincide with the occurrence of PMF.

The wave height (Ht) due to wave action is usually estimated by the following equation (S.M.B. method): Ht = 0.00086 x V1.1 x F 0.45 where, Ht: Wave height (m) V: Mean wind velocity (m/sec) F: Fetch distance (m) According to the design report in 1978, the wave height (Ht) was estimated to be 1.76 m applying that the mean wind velocity (V) and fetch distance (F) were assumed 20 m/sec and 15,000 m. This means that the crest of the impervious core zone should be higher than El. 140.86 m (= El. 139.10 m + 1.76 m). As a result the crest elevation of the impervious core zone was decided El. 141.0 m.

(7) Geological Data

Although it was confirmed that the dominat geological formation covering the wonogiri damsite was alternation of tuff and tuff breccia, volcanic breccia was detected as the base mass under the left abutment, volcanic breccia presumably forms the base formation in the whole area of damsite.

There exists unconformity in geological epoch ; volcanic breccia belongs to Pliocene while tuff and tuff breccia to Miocene.

Andesite mass was found in the volcanic breccia at the center of the left ridge, of which thickness is about 20 m. Since the reliability as foundation of structure seems better than volcanic breccia, spillway weir shall be located on the andesite mass. The existence of andesite and consolidated volcanic breccia suggests that the rock to be excavated from forebay is able to be used as material of dam embankment and other uses.

(Dm site)

Relatively low elevation ridge is extend on the right bank of the dam. hence width of dam become comparatively long as 1,440 m. Earth covering of the surface soil is thick, and foundation rock exist in depth approximately 15 m from surface of the ground. At the portion of left side of the dam, abutment rises about 100 m high from riverbed with hard rock. Earth covering on foundation rock is approximately 5-10 m.

1.2 Restricting Conditions of Flood Control

(1) Safety Discharge from Dam

Flood control plan of Wonogiri dam is that most of flood flow under 4,000 m3/s at dam site is controlled to be 400 m3/s discharge from dam. As gate type is adopted for flood control, 400 m3/s of flood flow as the fixed release-rate operation shall be discharged at flooding by operating the flood control gates. Hence in case of releasing reservoir water for countermeasure of sedimentation as a water flow utilization method, maximum discharge shall be regulated under 400 m3/s of safety discharge.

(2) Available Water Flow for Sediment Removal (Flushing/Sluicing)



In case of lowering water level under normal water level for utilization of water use capacity, it deemed difficult to utilize the water flow for sediment removal. Figure 1.2.1 shows the actual reservoir operation of Wonogiri dam. According to the figure, about during eight (8) years from dam completion of 1983 to 1991, normal water level had been kept under EL.136.0 m water level, which is normal reservoir operation rule. While, from 1991 up to now, water level have been pulled up to EL.137.0 m except draught years, which had been breached thedam operation rule. In rainy season at the beginning of November to December, spill out flow from existing spillway had conducted to flood control at the water level being low. As the flow out for sediment removal, it is consider using this out flow. Annual average volume of spill out flow is estimated about 200 million m3, which is available to use for sediment flushing.

(3) Restricting Conditions from Water Utilization

1) Probable Draw Down of Reservoir Water Level

In Wonogiri dam, 440 million m3 of water- use capacity at dry season is planned to store to utilize for irrigation and power. To meet such requirement, water level of EL.136.0 m should be kept at the end of rainy season. Therefore it is unable to lower water level at dry season. On the other hand, limited water level of EL.135.3 m during flood season had been designated for flooding. Figure 1.2.1 shows the actual reservoir operation. According to the figure, the month being lowest water level is obviously identified at November - December, which is the end of dry-season and the beginning of wet season. Therefore, from the beginning of rainy season, it is deemed effective to use inflow water for sediment flushing. However on actual dam reservoir operation, as reservoir storage turn-over rate is few as 2-4 times, water level was set more than limit water level EL.135.3 m.

2) Probable Flow Water Utilization

In case of drawing down the water level of water-use capacity under than Normal water level, it is deemed difficult to use inflow for sediment flushing/removal.

1.3 Features of Sedimentation

Features of sedimentation in the Wonogiri reservoir considered from the result of field surveys are as follows:

(1) Topographical Condition

Most of the sediment in the reservoir deposited near the dam had been caused by discharge from the Keduang River. The Wonogiri reservoir is primary separated the Keduang River portion and the Solo River portion including other rivers, and the Keduang River occupies one-third (1/3) of Wonogiri dam Uppermost basin, whereas capacity of the reservoir of the Keduang River portion is presumed to occupy only no more than one-thirtieth (1/30) of reservoir, and that outlet of the Keduang River is very near to the dam compared with the main upstream tributaries. From these condition, portion of the Keduang River had been filled with sediment rapidly.



Source: PBS

Figure 1.2.1 Wonogiri Dam Operation Record



(2) Facility Planning

1) Location of Outlet Facilities

Outlet facilities are gathered at left side of the dam, which is the portion of the Solo River. Therefore discharge of the Keduang River had run to the right side of dam at first, and then turned it direction to left side after hitting the dam body, running in front of dam to outlet facilities. On the way to the outlet facilities, massive sediment included in the discharge of the Keduang River had subsided and accumulated at the front of the dam. And sedimentation was presumed to proceed to the portion of the Solo River in front of outlet facilities by discharge from the Keduang River.

2) State of Intake

Intake facilities for irrigation and power generation is laid on with it foundation height EL.116.0 m, which is 11.0 m below planned sediment deposit elevation on dam plan. This is the only facility that sediment might be able to flow out to down stream at below EL.131.0 m of spillway weir overtopping height. This inlet was constructed by ditching the natural ground whose elevation is approximately EL.126.0 m at the right side and EL.129.0 m at left side on average. This topographical condition formed the reservoir of the Keduang River into looking like a vase, whose rim is EL.126.0 m and the bottom of it was approximately EL.110.0 m, original Keduang riverbed This condition contributed to the sedimentation of the reservoir of the Keduang River portion, consequently at and around of Intake had been surrounded by sediment. Sediment deposited on the original ground table EL.126.0 m of right side and EL.129.0 m of left side, had dropped into the ditch of Intake at EL.116.0 m and accumulated at the front of Intake. When trashrack furnished on the Intake surface was covered with garbage, sedimentation was proceeding on the Intake, consequently it might be clogging from lower portion. However intake has some attractive force to flush sediment, clogging of inlet could be eliminated by removing the trash. According to the interview with power plant office, activity of trash remove has been conducted at least twice a year Jun and December by themselves since 1993.

3) State of Spillway

Overtopping portion of spillway weir is set at EL.131.0 m. Sediment flushing can not be conducted until the sediment rises to more than same elevation.



CHAPTER 2 ALTERNATIVES OF COUNTERMEASURES FOR SEDIMENTATION

2.1 Preliminary Alignment of Conceivable Alternative Structures Consequently, the sedimentation problems of the Wonogiri reservoir had become quite serious in view of the following points, requiring the urgent countermeasures to solve them:

a) Sediment deposit at and around intake structure b) Decrease of effective storage volume c) High sediment yield in watershed of the Wonogiri dam and its inflow into the

Wonogiri reservoir This Study will propose the following three (3) countermeasures to improve the above 3 problems on Sedimentation of the Wonogiri reservoir:

i) Countermeasure to keep proper function of intake structure ii) Countermeasure to remove/control sediment from the reservoir iii) Countermeasures to conserve watershed above the Wonogiri dam

(1) Countermeasures to Keep Proper Function of Intake Structure The following alternative countermeasures are conceivable as those to cope with sediment deposit at and around Intake structure in the Wonogiri reservoir.

a) Sediment removal from existing intake structure and its surrounding places i) Introduction of new sediment removal system utilizing a difference

between water levels ii) Conventional dredging using dredger

b) New construction of intake structure to enable to keep proper function of intake structure even in case it is completely filled with sediments. iii) Construction of Intake tower with higher intake level than that of existing

one iv) Replacement of intake structure on left bank of the dam

c) Garbage Prevention into the front of Inlet v) Double screen

(2) Sediment Removal from the Reservoir Considering the sediment inflow characteristics of the tributaries in the Wonogiri dam catchment (uppermost Solo River basin) that are obtained from the available information, the countermeasures for the whole reservoir sedimentation will be formulated by dividing the dam catchment into the Keduang River basin and Solo mainstream basin as shown in Figure 2.1.1. To formulate the countermeasure for the entire reservoir sedimentation, the following components will be examined in this Study:

i) Keduang River sediment bypass ii) Sediment sluicing by new gates iii) Sediment storage reservoir with new gates in the reservoir iv) Sediment sluicing by existing outlets v) Sediment storage dam vi) Dredging vii) Check dam on each tributary and dry excavation

This Study will propose the countermeasures for the sedimentation problems of the entire reservoir by combining the above components.

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