DCOM Volume I

Volume I: Design of Water Supply Projects

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TABLE OF CONTENTS

LIST OF SPECIAL COMMITTEE MEMBERS v CHAPTER ONE 1 INTRODUCTION 1 1.1 Global Considerations on Water Supply and Sanitation 1 1.1.1 Sustainable Development Goals (SDGs) 1 1.1.2 Climate Change and Resilience to Climate Change 2 1.1.3 Public Private Partnership in Water Supply and Sanitation Projects in Developing Countries 3 1.1.4 International Water Law 4 1.2 Development Agenda and Water and Sanitation Sector in Tanzania 5 1.2.1 National Water Policy 7 1.2.2 Legal and Institutional Framework for Water Supply and Sanitation Services 8 1.2.3 Coverage and Access to Water Supply Services 9 1.2.4 Policy Environment for Water and Sanitation Services in Tanzania 9 1.2.5 Major Stakeholders in Water Supply and Sanitation Projects 10 1.2.6 Water Supply and Sanitation Public Private Partnership in Tanzania 11 1.3 Rationale for Preparation of the Fourth Edition DCOM Manual 12 1.4 About the Fourth Edition of the DCOM Manual 13 1.5 Organisation of the 4th edition of the DCOM Manual 14 1.6 Purpose of this Volume 14 1.7 References 15 CHAPTER TWO 17 PROJECT PLANNING 17 2.1 Planning Considerations for Water Supply Projects 17 2.2 Project Planning Steps 18 2.3 Pump Protection 18 2.3.1 Initiation 18 2.3.1.1 Community Assessment Steps 20 2.3.1.2 Methods of conducting community assessment 20 2.3.1.2.1 Comprehensive community assessment 20 2.3.1.2.2 Strategic community assessment 20 2.3.2 Pre-feasibility Study 21 2.3.3 Feasibility Study 21 2.3.3.1 Water Supply Projects Ranking and Technology Selection Criteria 22 2.3.3.1.1 Ranking of Projects 22 2.3.3.1.2 Choice of Technology 23 2.3.4 Preliminary and Detailed Design 23 2.3.4.1 Detailed Engineering Drawings 24 2.3.4.2 Detailed estimates of capital costs 24 2.3.4.3 Detailed estimates of recurrent costs 24 2.3.4.4 Anticipated revenue 25 2.3.4.5 Detailed design report 25 2.3.4.6 Project write-up to be submitted to potential financiers 25 2.3.5 Project Phasing 25 2.3.6 Procurement 26 2.3.6.1 2.2.6.1 Preparation of Tender Documents 26 2.3.6.2 Tendering process 27 2.3.7 Implementation/Construction Stage 27 2.3.7.1 Contract Management 27 2.3.7.2 Contract supervision and administration 27 2.3.8 Operation and Maintenance Stage 28 2.3.9 Performance Monitoring 28 2.4 Consulting the Integrated Water Resources Management and Development (IWRMD) Plans 28 2.4.1 Status of Development and Implementation of IWRMD Plans 29 2.4.2 Components of IWRMD Plans 30 2.5 Consult Guidelines for Preparation of Water Safety Plans - Resilient to Climate Change 30 2.6 Environmental and Social Impact Assessment Compliance 30 2.6.1 Procedures for Conducting ESIA in Tanzania 31 2.6.2 Strategic Environmental and Social Assessment (SESA) Compliance 31 2.7 Potential Impacts of Climate Change on Water Supply Projects 32 2.8 Participation of Community Based Water Supply Organizations (CBWSO) in Various Planning Stages 32 2.9 References 32 CHAPTER THREE 35 WATER SOURCES ANALYSIS 35 3.1 Availability of Water Resources in Tanzania Mainland 35 3.2 Water Sources Available in Tanzania Mainland 38 3.2.1 Rainwater and fog harvesting 39 3.2.2 Surface Water 39 3.2.2.1 Rivers or streams 39 3.2.2.2 Impoundments 39 3.2.2.3 Springs 39 3.2.2.4 Lakes 39 3.2.2.5 Dams 40 3.2.3 Groundwater 40 3.2.3.1 Infiltration galleries/wells 40 3.2.3.2 Well 40 3.2.3.3 Classification of wells based on the aquifer tapped 41 3.2.3.3.1 Shallow wells 41 3.2.3.3.2 Deep wells 41 3.2.3.3.3 Artesian wells 41 3.3 Quality Suitability of Water Sources for Water Supply Projects 42 3.4 Pilot Testing of Water Sources for Establishment of Appropriate Treatment 42 3.5 General Considerations for Selection of Water Sources 42 3.5.1 Adequacy and reliability 42 3.5.2 Quality of water sources 43 3.5.3 Technical Requirements 43 3.5.4 Cost implications to develop a water source 43 3.5.5 Protection of water sources 43 3.5.6 Legal and management requirements 44 3.5.7 Distance of water supply source 44 3.5.8 Topography of the project area and its surroundings 44 3.5.9 Elevation of a source of water supply 44 3.6 Determination of water source yield 44 3.6.1 Rainwater and fog harvesting 45 3.6.1.1 Rainwater harvesting 45 3.6.1.1.1 Types of rainwater harvesting 45 3.6.1.1.2 Components of rainwater harvesting system 46 3.6.1.1.3 Estimation of the yield 47 3.6.2 Hydrological Analysis of Surface Waters 47 3.7 Other considerations for various water sources 55 3.7.1 Water permits Considerations 55 3.7.2 Conservation of water sources 55 3.8 References 55 CHAPTER FOUR 56 WATER DEMAND ASSESSMENT 56 4.1 Water Demand Assessment 56 4.2 General Factors Affecting Water Demand Assessment 57 4.3 Determination of Water Demand for Different Uses 58 Step 7. Establish Net Water Demand 67 Step 9: Establish Operational water consumption 67 Step 10: Establish System water losses 68 Step 11 Establish Non-Revenue Water 69 4.4 Variations in Water Consumption 70 4.4.1 Definitions 70 4.4.2 Variation in the Rate of Consumption 71 4.4.2.1 Diurnal variation in demand 71 4.4.3 Peak Factors 72 4.4.4 Predicting Demand 74 4.4.5 Design Demand 75 4.5 References 75 CHAPTER FIVE 76 PIPELINES DESIGN 76 5.1 Design Requirements of pipelines 76 5.2 Types of pipelines 76 5.3 Security considerations for pipelines 76 5.3.1 Methods of water transmission and distribution 76 5.3.2 Gravity flow 77 5.3.3 Pumping with storage 77 5.3.4 Direct pumping to the distribution system 77 5.4 Pipeline Hydraulics Assessment 77 5.4.1 Pressure 77 5.4.2 Determination of Head Losses 77 5.5 Water supply transmission system 79 5.5.1 Determination of Transmission Pipe Size 79 5.5.2 Maximum Pressure 79 5.6 Distribution system 80 5.6.1 Branched System 80 5.6.2 Looped System 81 5.7 Pipe network analysis 82 5.7.1 Network analysis by Conventional method (Hardy Cross) 82 5.7.2 Network Analysis by Computer Software 82 5.7.2.1 EPANET Software 82 5.7.3 Pipeline design criteria 85 5.8 Pipeline materials selection 86 5.8.1 Considerations in Selecting Pipeline Materials 86 5.8.1.1 Flow Characteristics 86 5.8.1.2 Pipe Strength 86 5.8.1.3 Durability 87 5.8.1.4 Type of Soil 87 5.8.1.5 Availability 87 5.8.1.6 Cost of Pipes 87 5.8.2 Types of Pipe Materials Available 87 5.8.2.1 Galvanized Iron (GI) Pipes 87 5.8.2.2 Plastic Pipes 87 5.9 Appurtenances for transmission and distribution mains 88 5.9.1 Valves 89 5.9.1.1 Isolation Valves 89 5.9.1.2 Check Valves 89 5.9.1.3 Float Valves 89 5.9.1.4 Air Release Valves 89 5.9.1.5 Pressure Reducing Valves 89 5.9.1.6 Washout valves 89 5.9.2 Fittings 89 5.10 References 90 CHAPTER SIX 91 PUMPING SYSTEMS 91 6.1 Introduction 91 6.2 Rationale 91 6.3 Common Types of Pumps used in water supply 91 6.4 Pumping System Setup 91 6.5 Source of Pumping Power 92 6.6 Pumping system design pump selection 92 6.7 Pump Protection 95 6.8 References 95 CHAPTER SEVEN 96 WATER TREATMENT 96 7.1 Introduction 96 7.1.1 Classification of the qualities of water sources found in Tanzania according to the complexity of its treatment 96 7.1.2 Classification of Unit Operations to achieve water treatment levels 99 7.2 Recommended overall design approach for treatment plant components 99 7.3 Documents and websites consulted and those which are hyper-linked to the DCOM Manual 100 7.4 Water treatment design considerations 100 7.5 Water treatment levels and units 101 7.5.1 Pre-treatment 101 7.5.1.1 Scum and Floating Materials Skimmer 101 7.5.1.2 Screening or straining 101 7.5.1.3 Grit Removal 103 7.5.1.3.1 Design criteria 103 7.5.1.4 Sand Traps 105 7.5.1.5 Pre-chlorination 107 7.5.1.6 Water pre-conditioning (pH adjustment) 108 7.5.2 Primary Treatment 108 7.5.2.1 Sedimentation 108 7.5.2.2 Primary Filtration 114 7.5.2.2.1 Slow Sand Filtration 114 7.5.2.2.2 Rapid Gravity Sand Filtration 117 7.5.2.2.3 Comparison between Slow Sand Filters and Rapid Sand Filters 118 7.5.2.2.4 Other Types of Filters 119 7.5.2.3 Floatation 124 7.5.2.3.1 Dissolved-Air Floatation 124 7.5.2.3.2 Electrolytic Floatation 125 7.5.2.3.3 Dispersed-Air Floatation 125 7.5.2.4 Aeration 125 7.5.2.4.1 Falling Water Aerators 126 7.5.2.4.2 Spray Aerators 127 7.5.3 Secondary Treatment 130 7.5.3.1 Clarification 130 7.5.3.2 Coagulation 130 7.5.3.3 Flocculation 131 7.5.3.4 Filtration 131 7.5.4 Tertiary Treatment 132 7.5.4.1 Disinfection 132 7.5.4.1.1 Disinfection Methods 132 7.5.4.1.2 Chlorinators 132 7.5.4.1.3 Design considerations for chlorinators 133 7.5.4.2 Ozonation 133 7.5.4.3 Water softening 134 7.5.4.3.1 Methods of Softening 135 7.5.4.4 Defluoridation of Water 139 7.5.4.4.1 Fluorides 139 7.5.4.4.2 Defluoridation 139 7.5.4.5 Water Conditioning 141 7.5.5 Management of Water Treatment Sludge 141 7.5.5.1 Treatment of Water Treatment Sludge 141 7.5.5.1.1 Sludge Thickening 141 7.5.5.1.2 Sludge Dewatering 143 7.5.5.1.3 Sludge Drying Beds 144 7.5.5.1.4 Sludge Lagoons 144 7.5.5.1.5 Mechanical Sludge Dewatering 145 7.5.5.1.6 Backwash Water Recovery 145 7.5.5.1.7 Waste from Slow Sand Filters 146 7.5.5.2 Disposal of sludge 147 7.6 References 147 CHAPTER EIGHT 148 TREATMENT OF WATERS WITH SPECIAL CONTAMINANTS 148 8.1 Natural Organic Matter 148 8.2 Arsenic 149 8.3 Radioactive 149 8.4 Fluoride removal from drinking water 149 8.5 Toxic Cyanobacteria in Drinking Water 150 8.6 Available methods for removal of special water contaminants 152 8.7 Desalination 152 8.7.1 Additive method 152 8.7.2 Adsorption methods 153 8.7.3 Capacitive deionization (CDI) 153 8.7.4 Membrane Filtration 154 8.7.5 Reverse Osmosis 156 8.8 References 158 CHAPTER NINE 159 DESIGN OF WATER STRUCTURES 159 9.1 Sizing and Locating Water Structures 159 9.1.1 Tanks 159 9.1.1.1 Storage tanks 159 9.1.1.2 Sedimentation/Settling Tanks 160 9.1.1.3 Break Pressure Tanks 161 9.1.2 Water Intakes 162 9.1.3 Dams 164 9.1.3.1 Engineering Classification of Dams 164 9.1.3.2 Size classification of dams 164 9.1.3.3 Feasibility and geotechnical investigations 166 9.1.3.4 Hydrological analysis of the catchment 167 9.1.4 Geotechnical Investigation 169 9.1.4.1 Design of dams 170 9.1.5 Boreholes 173 9.1.5.1 Groundwater prospecting 179 9.1.5.2 Drilling 182 9.1.5.3 Siting of Well/Borehole 182 9.1.5.4 Well design 183 9.1.5.5 Pumping Tests 183 9.1.5.6 Groundwater quality 187 9.1.6 Water points and Service connections 190 9.1.7 Common Types of Water Points 191 9.1.8 Minimum Technical Requirements of Water Points 191 9.1.9 Criteria for Design of Water Point/Kiosks 191 9.1.10 Location Considerations for Water Points 192 9.1.11 Technical Tips to Improve Water Points 193 9.1.11.1 Rainwater harvesting 196 9.1.11.2 Fog harvesting 200 9.2 Structural Design of Concrete 201 9.2.1 Structural requirements 201 9.2.2 Methods 201 9.2.2.1 Working Stress Method 201 9.2.2.2 Ultimate Load Method 201 9.2.2.3 Limit State Method 201 9.3 References 201 CHAPTER TEN 203 APPLICATION SOFTWARE 203 10.1 Application Software Contexts 203 10.2 Recommended Application Software 203 10.2.1 Distribution Network Design Software 203 10.2.1.1 Epanet 203 10.2.1.2 AutoCAD 204 10.2.1.3 WaterCAD 204 10.2.1.4 WaterGEMS 204 10.2.1.5 KY PIPES 204 10.2.1.6 GeoNode 204 10.2.1.7 AutoStudio 204 10.2.1.8 InfoWater 205 10.2.1.9 GIS Software 205 10.2.1.10 MS Project 205 10.2.2 Operation and Maintenance Software 205 10.2.2.1 MS Project 205 10.2.2.2 Excel 205 10.2.2.3 EDAMS 206 10.2.3 Water Quality 206 10.2.3.1 WaterCAD 206 10.3 Supervisory, Control and Data Acquisition (SCADA) Systems 206 10.4 References 207 CHAPTER ELEVEN 208 METERING 208 11.1 Introduction 208 11.2 Types of Water Meters 208 11.3 Prepaid Meters 208 11.4 Types of Prepaid water models commonly used in Tanzania 209 11.5 Importance of Prepaid Water Metering 210 11.6 Design Considerations for Prepaid Water Meters 210 11.7 Design considerations for prepaid public standpipes 211 11.8 Design consideration for individual domestic customer 212 11.9 Design consideration for Commercial and Institutional Customers 212 11.10 Importance of integrating Prepaid with Post paid revenue management 212 11.11 Selection Criteria for Prepaid water meters 212 11.12 References 214 11.13 Internet Links: 216 CHAPTER TWELVE 217 DESIGN STANDARDS AND SPECIFICATIONS 217 12.1 Design Standards 217 12.2 Specifications 218 12.3 Materials 218 12.3.1 Building Materials 218 12.3.2 Materials Testing 219 12.3.2.1 Aggregates 219 12.3.2.2 Water 221 12.3.2.3 Cement 221 12.3.2.4 Concrete Works 221 12.3.2.5 Steel 222 12.4 Soil Test 222 12.4.1 Methodology of conducting Soil Investigation for borehole and test pit 222 12.4.2 Soil Investigation for dams 223 12.4.3 Suitability of soil materials for dam construction 223 12.4.4 Determination of In-Situ Bearing Capacity of the Soil 224 12.5 References: 227 CHAPTER THIRTEEN 228 ROLE OF STAKEHOLDERS IN DESIGN OF WATER SUPPLY PROJECTS 228 13.1 Types of Stakeholders 228 13.2 Roles of stakeholders 228 13.3 References 230 APPENDIX A: CLIMATE CHANGE AND RESILIENCE TO CLIMATE CHANGE 232 APPENDIX B: MINIMUM WATER FLOW REQUIREMENT FOR FIRE FIGHTING 237 APPENDIX C: EXAMPLE: ESTIMATING THE CAPACITY OF TANK 239 APPENDIX D: STRUCTURAL DESIGN OF CONCRETE 241 APPENDIX E: SUPPLY PUMPING SYSTEMS 251 APPENDIX F: SOURCE OF PUMPING POWER 263 APPENDIX G: ADDITIONAL DETAILS OF VARIOUS UNIT OPRATIONS 275 APPENDIX H: METHODS FOR DISINFECTING WATER 281 APPENDIX I: MEASUREMENTS OF WATER HARDNESS 287 APPENDIX J: BASIC STATISTICS USED IN ESTIMATION OF DESIGN OF FLOOD EVENTS 289 APPENDIX K: DAMS DETAIL DESIGN 294 APPENDIX L: STANDARD DRAWINGS 306 APPENDIX M: SELECTED INTAKE DESIGNS. 307 SUBJECT INDEX 309