Arusha City Council Tanzania Strategic Cities Project
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UNITED REPUBLIC OF TANZANIA PRESIDENT‘S OFFICE REGIONAL ADMINISTRATION AND LOCAL GOVERNMENT ARUSHA CITY COUNCIL TANZANIA STRATEGIC CITIES PROJECT (TSCP) SECOND ADDITIONAL FINANCING (AF2) (IDA CREDIT NO. 5947-TZ) The Provision of Consultancy Services for Study and Design of Storm Water Drainage System and Preparation of Drainage & Sanitation Development Plan (DSDP) for Arusha City for a period of 2020-2040 CONTRACT No. LGA/003/2018-2019/C/07 FINAL DSDP REPORT March, 2020 Table of Contents LIST OF TABLES ......................................................................................................................... V LIST OF FIGURES ..................................................................................................................... VII ABBREVIATIONS: ...................................................................................................................... X EXECUTIVE SUMMARY ......................................................................................................... XII SECTION 1: INTRODUCTION .................................................................................................. 24 1.1 BACKGROUND INFORMATION ......................................................................................... 24 1.2 JUSTIFICATION FOR THE ASSIGNMENT ........................ ERROR! BOOKMARK NOT DEFINED. 1.3 OUTLINE OF THE PROJECT ................................................................................................ 25 1.3.1 Project Objectives ....................................................................................................... 25 1.3.2 Study Areas................................................................................................................. 25 1.4 PROJECT SCOPE AND DELIVERABLE .......................... ERROR! BOOKMARK NOT DEFINED. 1.4.1 Scope of the project .................................................................................................... 31 1.4.2 Deliverables ................................................................................................................ 32 SECTION 2: ASSESSMENT OF EXISTING SITUATION ....................................................... 34 2.1. SUMMARY OF BASELINE CONDITIONS ....................... ERROR! BOOKMARK NOT DEFINED. 2.1.1 Climatic condition. ..................................................................................................... 34 2.1.2 Topography ................................................................................................................. 34 2.1.3 River Basin ................................................................................................................. 34 2.1.4 Territory and climate description ............................................................................... 35 2.1.5 Settlements.................................................................................................................. 36 2.1.6 Water Supply, Sanitation and Drainage System in Arusha City ................................ 38 SECTION 3. STORM WATER MANAGEMENT MEASURES ............................................... 57 3.1. FLOOD CONTROL AND STORM WATER DRAINAGE ...... ERROR! BOOKMARK NOT DEFINED. 3.2. FLOODING CONTROL MEASURES ................................ ERROR! BOOKMARK NOT DEFINED. 3.2.1. Storm water Drainage Design Strategy ................................................................... 58 3.2.2. Hydrological Design Criteria .................................................................................. 59 3.2.3. Considerations from Urban Master Plan - Managing Storm Water by 2035 ......... 60 3.2.4. Rainfall data ............................................................................................................ 61 3.2.5. Rainfall Runoff Modelling ...................................................................................... 64 3.2.6. New IDF Curve for Arusha City ............................................................................. 66 3.2.7. Climate Change In Arusha ...................................................................................... 67 3.2.8. Catchment Delineation............................................................................................ 70 3.2.9. Flood Risk and Vulnerability Mapping ................................................................... 76 3.2.10. Hydraulic Analysis .................................................................................................. 81 3.2.11. Hydraulic Modeling ................................................................................................ 86 HEC-RAS Model ........................................................................................................... 86 3.2.12. Multi Criteria Analysis for Drainage Interventions ................................................ 87 i 3.3. STRUCTURAL MEASURES FOR STORM WATER DRAINAGE .................... ERROR! BOOKMARK NOT DEFINED. 3.3.1 Causes of flooding in Arusha CC. .............................................................................. 92 3.3.2 Demolition and reconstruction of existing insufficient capacity major drains ........... 94 3.3.3 Roads and Paving ..................................................................................................... 103 3.3.4 Expansion and banks protection of the main flow channels .................................... 105 3.3.5 Cleaning and repairing of the existing minor drains ................................................ 106 3.3.6 Projects implementation – phasing on drainage works ............................................ 107 SECTION 4: NON-STRUCTURAL STORM WATER MANAGEMENT .............................. 109 4.1. EARLY WARNING SYSTEMS .......................................................................................... 109 4.2. SUSTAINABLE URBAN DRAINAGE SYSTEMS .................................................................. 111 4.3. PROPOSED NON-STRUCTURAL DRAINAGE MEASURES FOR ARUSHA CITY .................... 114 4.3.1. EARLY WARNING SYSTEM .......................................................................................... 114 4.3.2. Emergency response Plan ..................................................................................... 114 4.3.3. Systems in Informal Settlements .......................................................................... 115 4.3.4. Land use management policies and practices ....................................................... 117 4.3.5. The vulnerability-based approach ......................................................................... 118 4.3.6. Enforcement of the existing laws, regulations ...................................................... 118 SECTION 5: INSTITUTIONAL STORM WATER MANAGEMENT .................................... 120 5.1. MAJOR PROBLEMS IN DRAINAGE SYSTEM MANAGEMENT ............................................ 120 5.1.1. Lack of knowledge. ............................................................................................... 120 5.1.2. Lack of coordination between sector stakeholders. .............................................. 120 5.1.3. Missed storm water management decentralization. .............................................. 120 5.1.4. Failure to take the populations‘ expectations into account. .................................. 121 5.1.5. Limited local capacities for financing investment. ............................................... 121 5.1.6. Failure to comply with best construction practice. ............................................... 121 5.2. REVIEW OF INSTITUTIONAL MEASURES FOR DRAINAGE SYSTEM MANAGEMENT.......... 121 5.2.1. Existing Situation .................................................................................................. 121 5.2.2. Operation and maintenance for the proposed Drainage System ........................... 122 5.2.3. The Disaster Management .................................................................................... 123 5.3. PROPOSED INSTITUTIONAL MEASURES FOR DRAINAGE SYSTEM MANAGEMENT .......... 124 SECTION 6. PROPOSED STRUCTURAL MEASURES FOR SANITATION ....................... 126 6.1. Construction of waste water treatment plants. .......................................................... 126 6.2. Proposed new waste water treatment plants ............................................................. 127 6.2.1. Waste Water Flow Projection ............................................................................... 127 6.2.2. Trunk Main Sewer pipe ........................................................................................ 138 6.2.3. The design of conventional gravity sewers is based on the following design criteria: 139 6.2.4. The formula of design parameters ........................................................................ 140 6.3. New faecal sludge treatment plants .......................................................................... 142 6.4. Constructed wetlands ................................................................................................ 146 ii 6.4.1. Treatment description and criteria ........................................................................ 147 6.5. Planted Drying Beds (PDBs) .................................................................................... 148 6.5.1. Design consideration of the planted drying beds .................................................. 148 6.5.2. Expected output ...................................................................................................