Supporting Report

Supporting Report (C) Natural Condition and Landsliding Management Plan PREPARATORY SURVEY FOR THE PROJECT ON DISASTER PREVENTION AND MITIGATION MEASURES FOR THE ITAJAI RIVER BASIN FINAL REPORT VOLUME III : SUPPORTING REPORT ANNEX C : NATURAL CONDITION AND LANDSLIDE MANAGEMENT Table of Contents Page CHAPTER 1 Introduction ........................................................................................................... C-1 1.1 Coverage ....................................................................................................................... C-1 1.2 Constitution ................................................................................................................... C-1 1.2.1 General ................................................................................................................. C-1 1.2.2 Introduction .......................................................................................................... C-1 1.2.3 Master Plan .......................................................................................................... C-1 1.2.4 Feasibility Study................................................................................................... C-1 CHAPTER 2 Regional Topography, Geology, Pedology, and Vegetation .................................. C-2 2.1 Topography ................................................................................................................... C-2 2.2 Geology ......................................................................................................................... C-7 2.2.1 General ............................................................................................................... C-7 2.2.2 Sub-river Basins of the Three Upstream Tributaries (Itajai do Norte, Itajai do Oeste, Itajai do Sul) .................................................................................................. C-8 2.2.3 Sub-river Basins of Itajai-Acu, Benedito, Itajai-Mirim, and Luiz Alves ........... C-10 2.2.4 Geological Characteristics of Sub-river Basins ................................................. C-12 2.3 Pedology ..................................................................................................................... C-13 2.4 Vegetation ................................................................................................................... C-18 CHAPTER 3 Status of Landslide and Sediment Discharge ...................................................... C-21 3.1 Landslide ..................................................................................................................... C-21 3.1.1 Status and Restoration Works ...................................................................... C-21 3.1.2 Landslide Movement Types and Their Characteristics ................................ C-25 3.1.3 Characteristics of Landslide on Each Municipality ................................... C-31 3.2 Sediment Discharge .................................................................................................... C-33 3.2.1 Status and Restoration Works ...................................................................... C-33 3.2.2 Method of Analysis ...................................................................................... C-34 3.2.3 Result of Calculation ................................................................................... C-34 3.3 Risk Assessment and Risk Mapping for Landslide and Sediment Discharge ............. C-35 3.3.1 Procedure of Risk Assessment and Risk Mapping....................................... C-35 3.3.2 Identification of Potential Landslide Location............................................. C-36 i 3.3.3 Selection of Priority landslide Risk Sites ..................................................... C-36 3.3.4 Calculation of Potential Annual Loss .......................................................... C-36 3.3.5 Risk Mapping ............................................................................................... C-38 CHAPTER 4 Needs and Basic Policy for Formulation of the Master Plan for Landslide Management .................................................................................................... C-42 4.1 Basic Principle and Approach ..................................................................................... C-42 4.1.1 Principle ....................................................................................................... C-42 4.1.2 Approach ...................................................................................................... C-42 4.2 Needs for Landslide Management .............................................................................. C-42 4.3 Basic Policy for Landslide Management .................................................................... C-46 4.3.1 General ......................................................................................................... C-46 4.3.2 Non-Structural Measure ............................................................................... C-47 4.3.3 Structural Measure ....................................................................................... C-48 CHAPTER 5 Master Plan for Landslide Management ................................................. C-50 5.1 General ........................................................................................................................ C-50 5.2 Non-Structural Measure .............................................................................................. C-50 5.2.1 Installation of Early Warning System for Landslide and Flash Flood ......... C-50 5.2.2 Technical Enhancement Plan for Landslide Management ......................... C-54 5.3 Structural Measure for Landslide ................................................................................ C-54 5.3.1 Priority and Plan of Structural Measures for Landslide ...................................... C54 5.4 Mitigation Measures for Sediment Yield .................................................................... C-58 5.5 Mitigation of Flash Flood ........................................................................................... C-59 5.6 Capacity Building for Structural Measure and Support for Private Self-reliantEffort ......................................................................................................... C-62 5.6.1 Capacity Building for Structural Measures ........................................................ C-62 5.6.2 Support for Private Self-reliant Effort ................................................................ C-62 5.7 Sustainable Maintenance ............................................................................................. C-62 5.7.1 Maintenance of Structural Measures .................................................................. C-62 5.7.2 Maintenance for Landslide Flashflood Early Warning System ......................... C-63 CHAPTER 6 Engineering Geology on Selected Structural Measuer Sites ...................... C-64 6.1 Oeste Dam ................................................................................................................. C-64 6.2 Sul Dam ...................................................................................................................... C-69 6.3 Itajai Mirim Upstream Gate ........................................................................................ C-74 6.4 Itajai Mirim Downstream Gate ................................................................................... C-79 6.5 Structural Measures for Landslides ............................................................................. C-83 6.5.1 Site for Structural Measures for Landslide and Engineering Geological Investigations .............................................................................................................. C-83 6.5.2 Engineering Geology on Selected Structural Measure Sites .............................. C-87 CHAPTER 7 Feasibility Study of Structural Measure for Landslide ................................ C-117 7.1 Landslide Type and Selection of Type for Measure .................................................. C-117 7.2 Criteria Applied for the Feasibility Design ............................................................... C-118 7.2.1 Classification of Landslide Type ..................................................................... C-118 ii 7.2.2 Selection of Measure against Mountainside Collapse ...................................... C-119 7.2.3 Selection of Measure against Valley side Slope Collapse ............................... C-120 7.2.4 Selection of Measure against River Bank Collapse ......................................... C-120 7.2.5 Selection of Measures against Slide ................................................................. C-124 7.3 Feasibility Design on Structural Measure for the Selected Sites .............................. C-127 CHAPTER 8 Feasibility Study for Early Warning System for Landslide and Flash Flood ........ C137 8.1 General .................................................................................................................... C-137 8.2 Rainfall Monitoring, Data Communication, and Repository .................................... C-137 8.3 Criteria of Rainfall Index for Attention/Alarm ......................................................... C-138 8.4 Management of Information, Calculation of Rainfall Index ..................................... C-138 8.5 Evacuation Order

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