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