Storm Drainage: An engineering guide to the low-cost evaluation of system performance

Millions of slum residents across the world suffer the hazards and misery of frequent flooding of their streets and homes, which may result in savings of a lifetime being washed away in a few hours, damaged property, loss of work and time, and higher risks of diarrhoea, worm infection and other health problems. This manual is written to help engineers, aid and agency workers understand drainage problems more clearly in the developing world, so that they can work towards finding practical solutions. It focuses on three questions of particular relevance to low-income urban areas in developing countries: what is drainage performance? how can we evaluate a drainage system, to access how best to improve its performance? what are the effects of solids in drains upon performance? This manual is the outcome of two-and-a-half years of fieldwork in the city of Indore, in Madhya Pradesh, India and can be used as a practical aid by municipal engineers, consulting engineers and engineering instructors and students, as well as development and aid workers involved in drainage systems.

Table of Contents:
Acknowledgements ix 1 Introduction 1 Drainage and surface water drainage 1 Surface water drainage and public health 1 The purpose of the manual 2 Who this manual is for 3 The structure of the manual 3 Origins of the manual 3 2 Drainage systems, flooding, and performance 5 Wet weather processes: what happens when it rains? 5 Rainfall becomes runoff 5 Runoff transports solids 9 Runoff enters the drain 10 Runoff flows through the drain 10 Flooding takes place 11 Flood waters are contaminated 12 Dry weather processes: solids deposition and drain maintenance 12 Solids deposition 12 Drain cleaning 15 Community perceptions of flooding 16 Priority 16 Predictability 16 Expectations 17 Drainage performance and evaluation 17 3 Factors that affect performance 19 Types of drainage system 19 Major and minor drainage 19 Types of minor drainage systems 19 Hydraulic capacity 21 Frequency of flooding 21 Depth of flooding 25 Area of flooding 25 Duration of flooding 28 Street grading 28 Inlets 29 Catchment surface and storage 30 Effect on runoff volume 30 Effect on timing of flow 31 Annexe 3-A: Derivation of frequency and capacity relationships 33 Annexe 3-B: Performance aspects of inlets 35 4 Drainage evaluation: general approaches 38 System-wide evaluation 38 Gather background data 40 Perform field work 41 Analyse the data 42 Write up the findings 44 Evaluating a specific catchment 45 Gather background data 45 Perform field work 46 Analyse the data 46 Write up the findings 47 5 Studying the catchment 48 Topographic survey 48 Level of accuracy 48 Data to collect 49 Analysis 49 Defining a catchment 51 Surface cover survey 52 6 Assessing flooding as a problem 54 Resident surveys 54 Avoid 'leading' questions 55 Ask more than one person 56 Try to be specific 56 Retrospective flood surveys in Indore 57 Direct observation 57 Resident gauges 59 Chalk gauges 59 Electronic level gauging 62 Summary 63 7 Flow estimation 65 Catchment area and cover type 65 Rainfall intensity 66 Using IDF curves to estimate flows 67 Limitations of IDF curves and simplified methods 69 Annexe 7-A: How to develop IDF curves 71 Developing curves from continuous data 71 Developing curves from limited data 72 vi 8 Assessing drainage capacity 81 Concepts of capacity 81 Three types of capacity estimation 82 Examples of the three levels of analysis 84 Design capacity 84 As-built capacity 85 Actual capacity 85 Drainage network surveys 86 Level of network analysis 87 Annexe 8-A: Using software for drainage analysis and design 88 Introduction 88 Classification and characteristics of software 89 Choosing between packages 92 Why invest in a software package? 93 What are the pitfalls to avoid? 93 9 Drainage network structural survey 94 Conduit measurements 94 Dimensions 94 Levels 95 Condition of conduits 100 Open conduits 100 Closed conduits 100 Condition of inlets 105 10 Maintenance surveys 106 Drain solids surveys 106 Visual observation 106 Solids levels 106 Solids build-up surveys 107 Solids sampling and size distribution 110 Inlet solids surveys 112 Blockage of inlet mouths 112 Solids levels 113 Drain cleaning observation 113 Removing solids from the drain 115 From the drain to safe disposal 115 Solid waste monitoring 116 11 Studying drainage systems in action 118 What to look for in wet weather 119 Catchment and subcatchment boundaries 119 The nature of flooding in flood-prone areas 119 The hydraulic performance of the total drainage system 119 The surface flow routes followed by runoff during floods 120 The nuisance, hazard, and damage of flooding 120 How to manage wet weather tasks 120 Organizing a team 120 Organizing specific tasks 121 Summary 125 12 Summary and conclusions 126 Themes of preceding chapters 126 Why flooding matters 126 Performance 126 Factors that affect performance 126 General approaches to drainage evaluation 127 Studying the catchment 128 Assessing flooding as a problem 128 Estimating flows from runoff 128 Assessing drainage capacity 129 Drainage network structural survey 129 Maintenance survey 129 Studying drainage systems in action 129 Final conclusions 130 Implications for improving system performance 130 Implications for improving drainage design 130 13 References 132