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