DCOM Volume I

Volume I: Design of Water Supply Projects

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TABLE OF CONTENTS

#	Title	Page
1	CHAPTER ONE: INTRODUCTION	1
2	CHAPTER TWO: PROJECT PLANNING	17
3	CHAPTER THREE: WATER SOURCES ANALYSIS	35
4	CHAPTER FOUR: WATER DEMAND ASSESSMENT	56
5	CHAPTER FIVE: PIPELINES DESIGN	76
6	CHAPTER SIX: PUMPING SYSTEMS	91
7	CHAPTER SEVEN: WATER TREATMENT	96
8	CHAPTER EIGHT: TREATMENT OF WATERS WITH SPECIAL CONTAMINANTS	148
9	CHAPTER NINE: DESIGN OF WATER STRUCTURES	159
10	CHAPTER TEN: APPLICATION SOFTWARE	203
11	CHAPTER ELEVEN: METERING	208
12	CHAPTER TWELVE: DESIGN STANDARDS AND SPECIFICATIONS	217
13	CHAPTER THIRTEEN: ROLE OF STAKEHOLDERS IN DESIGN OF WATER SUPPLY PROJECTS	228
14	APENDICES: APPENDICES	231

Chapter #	Chapter Title	Page
i	LIST OF SPECIAL COMMITTEE MEMBERS	V
1	CHAPTER ONE: INTRODUCTION	1
1.1	Global Considerations on Water Supply and Sanitation	1
1.1.1	Global Considerations on Water Supply and Sanitation	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	13
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
Example	Example	Example
Example	Example	Example
Example	Example	Example
Example	Example	Example

• 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 Managemen