Urban Hydroinformatics: Data, Models and Decision Support for Integrated Urban Water Management available in Paperback
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The Imperative for Urban Water Management
1.1 GLOBAL URBAN WATER ISSUES
The need to address urban water issues becomes all the more urgent as migration to urban areas increases the pressure on the infrastructure and services provided. According to UN reports, the global population growth forecasts are sending out an alarming signal to governments and city managers for them to address some of the most essential urban infrastructural aspects in order to avoid catastrophic consequences of urbanisation. During the 20th century the world's urban population grew from 220 million to 2.8 billion, and is estimated to double during the first 30 years of the 21st century. In 2030 81% of the world's urban population will live in developing countries. The largest migration pressures will come in the 18 megacities (with populations in excess of 10 million) situated in coastal areas. About 75% of people residing in low-lying areas are in Asia, and the most vulnerable are the poor. Slums (or 'informal' urban areas) are growing at the same rate as urban growth. It is expected that most of the growth will occur in developing countries, particularly in regions already under water stress, and where there is limited access to safe drinking water and adequate sanitation facilities. In 2008 50% of the world's population lived in urban areas; this is estimated to change to about 60% in the year 2030, with 95% of the increase taking place in informal urban areas of developing countries in Africa and Asia.
Over the last 20 years there has been a seed change in the water industry of many countries from unregulated national monopolies to regulated decentralised utilities. But the public utilities in developing countries do not perform well due to low motivation, poor management, inadequate cost recovery and political interference.
Regulation has assumed increasing importance in Europe. For example, the EC Urban Waste Water Treatment Directive (CEC, 1991) concerns the collection, treatment and discharge of urban wastewater and the treatment and discharge of wastewater from certain industrial sectors. Its aim is to protect the environment from any adverse effects due to the discharge of such waters.
Similarly, the EC Drinking Water Directive (CEC, 1998) is intended to protect human health by laying down health and purity requirements which must be met by drinking water within the European Community. It applies to all water intended for human consumption apart from natural mineral waters and waters which are medicinal products.
A third directive, the EC Water Framework Directive (CEC, 2000) requires member states to identify all the river basins lying within their national territory and to assign them to individual river basin districts. A competent authority had to be designated for each of the river basin districts by 2004. In addition, member states have to produce a management plan for each river basin including an economic analysis of water use. These directives are discussed further below.
Whereas developed countries are forging ahead with their regulatory regimes to improve the management of their river basins (or watersheds), taking into account urban as well as rural water usage, developing countries are struggling to manage their urban water resources. For them, urban water issues are particularly urgent because the state of urban water assets in these countries is very poor, and available resources are extremely limited. Some of the most vulnerable and essential water-related services impacted by urban population growth are the growing demand for water supply and distribution, the collection and treatment of an increasing amount of wastewater, the drainage of excess stormwater runoff, the maintenance of the quality of surface waters adjacent to and downstream of urban areas, and the management of groundwater beneath urban areas.
Better management of urban water systems is of major concern in helping to meet the Millennium Development Goals (MDGs) (United Nations, 2009), especially in providing an improved urban environment affecting Goal 1: Eradicating extreme poverty and hunger, Goal 4: Reducing child mortality, and Goal 7: Ensuring environmental sustainability (especially targets 9, 10 and 11). Almost one billion people are at risk because they do not have access to safe drinking water. This limits their health and exacerbates their poverty. In addition two billion people are without effective sanitation, which again constrains their development and leads to an ongoing degradation of their environment. Furthermore, climate change appears to be generating a greater frequency of damaging floods and droughts in different parts of the world. Whereas in many cases these disasters are basin wide, particular urban areas have been subject to torrential rain and to inundation from rivers and major urban streams.
1.2 WATER ISSUES IN SOME MAJOR CITIES
In order to appreciate some of the problems faced by some of the major cities consider the following:
Bangkok has a metropolitan area of 1,568.7 km2 and a population in excess of 12 million. It is situated in the flat deltaic plain of the Chao Phraya River. The city is at an average height of about 2 m above sea level, and is vulnerable to intense rainfalls during the rainy season between May and November; daily rainfalls in excess of 400 mm are not unknown. Flooding in the city is caused by rainfall directly on the urban area or by the overtopping of embankments along the Chao Phraya River due to high water levels from flood flows upstream or high surges originating from storms in the Gulf of Siam. The duration of annual flooding has been reduced to a matter of days rather than weeks through the installation of huge pumping stations that discharge flood water from the city to the river. Flood management in the city has been exacerbated by overabstraction of water from aquifers below the city for water supply purposes which has lead to extensive and severe land subsidence within the city boundaries. This was as much as 15 cm per year in some parts of the city. Fortunately this has been remedied by the construction of a large pipe line conveying water to the city centre from the Chao Phraya to the north. Further difficulties with flooding are generated through the large demand for land for development, which has lead to many natural drainage channels being filled in. Another issue concerns the difficulties in flushing the remaining klongs (or canals) to reduce the pollution caused by wastewater discharges from housing and industry, and in removing the refuse that is regularly dumped in them. See Figure 1.1.
Jakarta, the capital city of Indonesia, is another case in point. With a population in excess of 8.5 million (23 million in Greater Jakarta) and an area of 665 km2, Jakarta is situated on the north-west coast of Java on a low lying plain with about 40% of the city below high tide level. There are a number of small rivers flowing through the city from hills to the east. These rivers are prone to flash floods generated by tropical storms on the hills to the east where rapid development has lead to deforestation. Flooding in the city is exacerbated by high tides that inundate the coastal districts. Major flooding occurred in 1996 and 2007 when 70% of the city was inundated with water up to 4 m deep. Like Bangkok the drainage channels are used for garbage disposal and squatters line the banks; see Figure 1.2. Added to this there is a growing sedimentation problem in the rivers. Less than a quarter of the population is properly served by water supply and drainage facilities: most rely on rivers, lakes and private water vendors. Wastewater treatment is negligible, and there are difficulties in flushing and maintaining the drainage channels and canals. Raising funds through property and land taxes has proved difficult because of problems in identifying owners of property.
Dhaka is the most densely populated city in the world, with more than 12 million people in the Metropolitan area of 1463 km2. It is the only city in Bangladesh with a water-borne sewage system, but this serves only 25% of the population while another 30% are served with septic tanks. Only two-thirds of households in Dhaka are served by the city water supply system, which was introduced originally in 1874. More than 9.7 million tonnes of solid waste are produced in Dhaka city each year. The city is flat and close to sea level, which makes it susceptible to flooding during the monsoon season due to heavy rainfall and cyclones; see Figure 1.3.
The capital of the United Kingdom, Greater London has a population in excess of 12 million, and covers an area of approximately 1570 km2. Water supply is from the River Thames, the River Lea, and some underground resources. There is a ring main with a number of contributing potable water treatment works. The pipes are largely cast iron and are deteriorating significantly, which contributes to a reasonably high leakage rate.
During the 19th century the British parliament authorized the development of a modern, combined sewerage system for London to counter the obnoxious smell from wastewater and to alleviate numerous cholera outbreaks. Intercepting sewers were constructed along the lines of the rivers draining into the River Thames. The flow was mainly under gravity, but pumping stations were built to raise the sewage from the north of the Thames to a major treatment works at Beckton, (now serving 3.4 million people), and similarly from the south of the Thames to Crossness (receiving sewage from about 2 million people); see Figure 1.4. In addition, the Mogden treatment works now serves 1.8 million people. Further major improvements were made both to the sewerage systems and the treatment works in the 20th century. Yet the regular expansion of the population living in London and redevelopment has placed increased pressure on the system, which has limited capacity. Flooding therefore does occur with an unacceptable frequency in some areas. The plan now is to build one or more tunnels for storage and transfer of sewage, with a single tunnel being 35 km long and up to 9 m in diameter. Called the Thames Tideway scheme, it forms one of the city's most ambitious wastewater projects since its first sanitation system in the mid-19th century. 32 million cubic metres of untreated sewage is discharged annually into the river; so the tunnel will improve the capacity of London's sewerage system, help prevent sewage discharge into the River Thames, and allow more wastewater to be treated to a higher standard.
Chicago is the third largest city in the USA with more than 9.5 million people in the Metropolitan area of 18,684.2 km2. The city is built on marsh land adjacent to Lake Michigan; see Figure 1.5. With over 1000 mm of rainfall and more than 1000 mm of snowfall, the urban area is prone to flooding. Initially, the wastewater drainage in the city was designed to discharge directly to the Chicago River, which turned out to be ineffective in transporting sewage away from the city. In the late 19th century the flow in the Chicago River was reversed to take wastewater away from Lake Michigan. But matters became worse as the urban area expanded and there were regular major flood events in the metropolitan area. In the last half of the 20th century a major deep tunnel system 176 km long that had been planned as early as 1834 was constructed. The tunnel and surface storage lakes were intended to hold the raw sewage for treatment and diversion to the Chicago River. Drilling for the tunnel was completed in 2005. Fish have returned to the Chicago River though pollution levels are still high. This tunnel has effectively limited the discharge of raw sewage into the Chicago River and enabled its restoration.
Shanghai has over 20 million people in an area of 6,218 km2. A highly advanced and modern city it is constructed near the coast and has a sizeable lake above it which drains through the city to the sea. The low lying nature of the urban area has lead to the construction of polder areas with associated pumping to keep water levels low, especially during high rainfall events. Flooding generally occurs with rainfall in excess of 35 mm/hr.
1.2.7 Belo Horizonte
Belo Horizonte (BH) is the capital of the State of Minas Gerais (Brazil), which in economic terms (gross product) is the third among the 26 Brazilian states. The city lies at 20° South latitude and 44° West longitude and has an altitude of 750 to 1,300 metres. It is located in a mountainous region of tropical soils that originated from the decomposition of metamorphic rock. Tropical highland weather predominates in this area, with an average yearly rainfall of 1,500 mm and an average yearly temperature of 21°C. BH has 2,227,400 inhabitants with a population density of 6,900 inhabitants/km2.
In Belo Horizonte as well as throughout the BH metropolitan area, a separated sewerage system has been adopted, although illicit inter-connections between the wastewater and stormwater networks prevail, resulting in heavily polluted receiving bodies in the urban area and in the Velhas River downstream of the city. Another source of water pollution by wastewater is the lack of interceptor pipelines (Figure 1.7) as part of the main sewerage system.
1.3 PROBLEMS FACED BY MEGA CITIES
In general, the problems with water that are faced by mega cities all over the world are similar. Many cities are situated on the coast or on a major river or lake. They can be highly prone to flooding both through rainfall directly on the urban area, which may generate large amounts of excess runoff that exceeds the capacity of the existing drainage system, and through overbank flows from rivers or spillage from an adjacent lake, or inundation from coastal surges combined with high astronomic tides. Besides the resulting flooding of parts of the urban area, there can be contamination of the flood water due to the flushing of wastewater drainage systems, damage to water distribution systems, mud slides generated on unstable hill slopes, rising groundwater levels due to recharge, and so on. The city authorities have therefore to identify the risks their city faces from flooding, to take action to reduce these risks, to provide adequate forecasting and warning facilities of flood events, and to plan for the restoration of the social and economic life of the community following a disaster.
Each city has the need to sustain its growing population through the provision of adequate fresh water supplies that are normally distributed through pipe networks operating under pressure. The sources for water supply are best located outside the city, preferably from groundwater aquifers, or from rivers upstream of the city. Reservoirs are often used to provide temporary storage of water. In each case some treatment may be required before the potable water is distributed. Correspondingly, there needs to be a means of collecting the wastewater that is produced by domestic, public and industrial use of the potable water. Such wastewater collection is often combined with the drainage of stormwater from the urban area, though there is an increasing trend to keep the collection of wastewater and stormwater separate. What is of primary concern to many cities is to provide some treatment at least of the wastewater component in order to remove harmful pollutants, such as solids, nitrogen and phosphorus compounds, heavy metals and particular bacteria, including e-coli, before returning the effluent to the environment.
With the rapid growth of urban areas in many parts of the world, water engineers face ongoing challenges to extend the services they provide, in particular, water supply and distribution, wastewater collection and storm drainage, in such a way that they do not prejudice future developments. What is more, the artificial nature and construction of the distribution and collection networks implies that they deteriorate in time and therefore need both regular maintenance and eventual renewal or rehabilitation. In particular, the rehabilitation of existing water and wastewater treatment plants and distribution, wastewater and storm drainage networks today should be designed in such a way that expected rehabilitation works needed to cater for urbanization in the future are not made more difficult than necessary. In particular, the discounted costs of investment in and maintenance of urban water services over a period of time into the future should be minimized.
Excerpted from "Urban Hydroinformatics"
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Table of Contents
Contents: The Imperative for Urban Water Management; Urban Water Systems; Hydroinformatics; Data Management; Modelling Paradigms; Decision Support Systems; Involving Society in Urban Water Management; Asset Management; Water Distribution systems; Collection Systems; Wastewater Treatment Management of Water Quality in Integrated Drainage Systems; Urban Flood Risk Management; Management of Urban Water in Developing Countries; Future of Urban Water Management; Glossary; Index