Urban Water Cycle Processes and Interactions

Effective management of urban water should be based on a scientific understanding of the impact of human activity on both the urban hydrological cycle – including its processes and interactions – and the environment itself. Such anthropogenic impacts, which vary broadly in time and space, need to be quantified with respect to local climate, urban development, cultural, environmental and religious practices, and other socio-economic factors.

Urban Water Cycle Processes and Interactions represents the fruit of a project by UNESCO’s International Hydrological Programme on this topic. The volume begins by introducing the urban water cycle concept and the need for integrated or total management. It then explores in detail the manifold hydrological components of the cycle, the diverse elements of urban infrastructure and water services, and the various effects of urbanization on the environment – from the atmosphere and surface waters to wetlands, soils and groundwater, as well as biodiversity. A concluding series of recommendations for effective urban water management summarize the important findings set forth here.

Urban Water Series - UNESCO-IHP Volumes

Following from the Sixth Phase of UNESCO’s International Hydrological Programme (2002–2007), the Urban Water Series – UNESCO-IHP addresses fundamental issues related to the role of water in cities and the effects of urbanization on the hydrological cycle and water resources. Focusing on the development of integrated approaches to sustainable urban water management, the Series should inform the work of urban water management practitioners, policy-makers and educators throughout the world.

1 Urban water cycle 1

1.1 Introduction 1

1.2 Urban water cycle concept 3

1.3 Total management of the urban water cycle 7

2 Urban water cycle hydrologic components 9

2.1 Water sources 10

2.1.1 Municipal water supply 10

2.1.2 Precipitation 10

2.1.2.1 Climatic aspects 10

2.1.2.2 Urban precipitation 11

2.2 Hydrologic abstractions 12

2.2.1 Interception 13

2.2.2 Depression storage 13

2.2.3 Evaporation and evapotranspiration 13

2.2.4 Infiltration 14

2.2.5 Lumped hydrologic abstractions 14

2.3 Water storage 15

2.3.1 Soil moisture 15

2.3.2 Urban groundwater 15

2.4 Interflow and groundwater flow 16

2.5 Stormwater runoff 16

2.6 Natural drainage: urban streams, rivers and lakes 17

2.7 Needs for urban water infrastructure 18

3 Urban water infrastructure 19

3.1 Demands on water services in urban areas 19

3.2 Water supply 21

3.2.1 Overview of situation in developing countries 23

3.2.1.1 Middle East and North Africa (MENA) 23

3.2.1.2 Sub-Saharan Africa (SSA) 24

3.2.1.3 East, South and South-East Asia (ESSA) 24

3.2.2 Historical development 24

3.2.3 Water demand 25

3.2.3.1 Water supply standards: quantity 27

3.2.3.2 Water supply standards: quality 28

3.2.4 Water supply sources 29

3.2.4.1 Conjunctive use of sources and artificial recharge 30

3.2.4.2 Supplementary sources of water 30

3.2.4.3 Water shortage 32

3.2.5 Example of improving the water supply in the Tehran Metropolitan Area 32

3.2.6 Drinking water treatment 33

3.2.6.1 Emerging technologies 33

3.2.6.2 Desalination 33

3.2.6.3 Disinfection 35

3.2.7 Water distribution systems 36

3.2.8 Drinking water supplies in developing countries 36

3.3 Urban drainage 37

3.3.1 Flooding in urban areas 39

3.3.1.1 Local (pluvial) flooding 40

3.3.1.2 Urban (fluvial) floods 41

3.3.2 Stormwater 42

3.3.2.1 Stormwater characterization 44

3.3.2.2 Stormwater management 45

3.3.2.3 Special considerations for drainage in cold climates 48

3.3.3 Combined sewer overflows 48

3.3.3.1 CSO characterization 48

3.3.3.2 CSO control and treatment 49

3.4 Wastewater and sanitation 50

3.4.1 Problem definition 50

3.4.2 Technological development 52

3.4.3 Ecological sanitation 53

3.4.4 Basic demands on wastewater management systems 54

3.4.5 Wastewater characterization 55

3.4.6 Wastewater systems without separation of wastewaters at the source 56

3.4.6.1 Centralized systems 56

3.4.6.2 Distributed (local) systems 57

3.4.7 Systems with separation of wastewaters at the source 58

3.4.8 Wastewater treatment technologies for developing countries 59

3.4.9 Case study of water pollution control in the Tehran Metropolitan Area 60

3.4.10 Water and wastewater reuse 61

3.4.10.1 NEWater in Singapore 62

3.4.10.2 Shinjuku water recycling centre, Tokyo, Japan 62

3.4.10.3 Wetlands with fish production in Calcutta, India 63

3.4.10.4 Reuse of (untreated) sewage for agricultural irrigation in the Mezquital Valley (Mexico City sewage disposal) 63

3.4.10.5 Reuse of stormwater and greywater in Sydney, Australia 64

3.4.11 Closing observations on wastewater management in developing countries 64

4 Impacts of urbanization on the environment 67

4.1 Overview 67

4.2 General characterization of urbanization effects 68

4.2.1 Increased ground imperviousness 68

4.2.2 Changes in runoff conveyance networks 69

4.2.2.1 Construction of runoff conveyance networks 70

4.2.2.2 Canalization of urban streams and rivers 70

4.2.2.3 Interfering transport infrastructures 71

4.2.3 Increased water consumption 71

4.2.4 Timescales of urbanization effects 72

4.2.5 Types of receiving waters and spatial scales 72

4.3 Urbanization effects on the atmosphere 73

4.3.1 Thermal effects (urban heat island phenomenon) 74

4.3.2 Urban air pollution 74

4.3.3 Combined impacts 75

4.4 Urbanization effects on surface waters 75

4.4.1 Physical effects 76

4.4.1.1 Urbanization effects on flows 76

4.4.1.2 Urbanization effects on sediment regime: erosion and siltation 76

4.4.1.3 Modification of the thermal regime of receiving waters 77

4.4.1.4 Density stratification of receiving water bodies 77

4.4.1.5 Combined physical effects 78

4.4.2 Chemical effects 79

4.4.2.1 Dissolved oxygen reduction 79

4.4.2.2 Nutrient enrichment and eutrophication 79

4.4.2.3 Toxicity 80

4.4.3 Microbiological effects 81

4.4.3.1 Waterborne pathogens 81

4.4.3.2 Indicators of microbiological pollution 85

4.4.4 Combined effects on surface waters 86

4.4.5 Examples of urbanization effects on specific types of receiving waters 87

4.4.5.1 Rivers 87

4.4.5.2 Lakes and reservoirs 89

4.5 Urbanization effects on wetlands 91

4.6 Urbanization effects on soils 94

4.6.1 Erosion 94

4.6.2 Transport of pollutants in soils 95

4.6.3 Changes in water quality during percolation through soils 96

4.6.4 Effects of sludge disposal on soils 96

4.6.4.1 Sludge production 97

4.6.4.2 Sludge quality 97

4.6.4.3 Biosolids (sludge) application on land 98

4.6.4.4 Sludge disposal 98

4.6.4.5 New chemicals of concern in sludge 99

4.7 Urban impacts on groundwater 99

4.7.1 Unintentional discharges into groundwater aquifers 100

4.7.2 Intentional discharges into groundwater aquifers 102

4.7.3 Impacts on aquifers 103

4.8 Urban impacts on biota: loss of biodiversity 103

4.8.1 General structure of water bodies and their biota 103

4.8.2 Properties of the water bodies affecting flora and fauna 103

4.8.3 Effects of alterations of urban water bodies on biota 104

4.8.3.1 Rivers 104

4.8.3.2 Lakes and reservoirs 106

5 Summary 109

References 113

Index 127