Sustainable Urban Drainage Systems (SUDS) â is it the answer to the problem ..... systems consisting of five drainage basins, large natural drains, storm water ...
MSc. Water Resources Technology and Management
CE5WEMb – Water and Environment Management
Sustainable Urban Drainage Systems (SUDS) – is it the answer to the problem of urban flash floods in New Delhi, India.
By Rohit Kumar Das (ID: 1208953)
University of Birmingham College of Engineering and Physical Sciences School of Civil Engineering Edgbaston Birmingham B15 2TT United Kingdom Date of Submission: 24-04-2012
Executive Summary: India has witnessed rapid economic growth and urbanisation over the past two decades. The economic activities and a boom in high technology and services sector has led to a demand for work, leisure, and living spaces fuelling a construction boom in cities like New Delhi, Mumbai and Bangalore. The construction of large office complexes, shopping malls, roads, pavements, parking lots and high-rise apartment buildings have led to an increase in paved surfaces. According to Carmon and Shamir (2010), increase in paved surfaces in a city leads to instances of urban flash floods and decreases the percolation of rainwater into the water table. Construction of high rise apartments also leads to increased abstraction of groundwater to an unsustainable level. The increased instances of urban flash floods causes water logging in the slums which are usually located in low-lying areas - leading to a potential health and safety hazard. New Delhi and adjoining areas of Noida, Ghaziabad, Gurgaon and Faridabad have witnessed severe flash floods during the annual monsoon rains over the last few years. Flooded streets, overflowing drains and waterlogged slums have become increasingly common. The costs of damage to roads and infrastructure and the invisible social costs arising out of loss of livelihood and the cost of treatment due to water-borne diseases are enormous and these problems threatens to turn fast growing megalopolises like New Delhi into unhealthy cities of contradictions and inequality (United Nations, 2011a). This report presents a systemic view of the demographic, economic, social and environmental facets of the problem and suggests a paradigm shift in the management of storm water and drainage. Even though the problem is not endemic to New Delhi, the city has been chosen for this project as a case because among all Indian cities, New Delhi receives the maximum number of rural migrants every year owing to its proximity to predominantly rural states of Uttar Pradesh, Haryana and Rajasthan (UNDP, 2009). It is worth mentioning in this context that both Uttar Pradesh and Rajasthan rank very low in the Human Development Index (HDI) among Indian states (UNDP, 2007). Also, New Delhi and adjoining areas have witnessed an unprecedented housing and construction boom over the last few years. Moreover, New Delhi also serves as a model of development for other Indian cities which too are growing at a rapid rate. This report also highlights that the provision of sustainable storm water and drainage management in cities is an important yet hitherto neglected feature of urban development in India. The current drainage practices are based on myopic and symptomatic approaches – storm water is routed through open or covered drains and finally discharged into the river Yamuna with minimal or no treatment. Also, the government and civic authorities undertake forced evictions and demolition of the slums (The Hindu, 2011) from time to time as a measure to clear the low lying areas which add to the clogging of the storm water channels. Unfortunately, such methods result in merely shifting the problem. This report highlights the need for a multi-faceted approach and suggests certain Best Management Practices to manage storm water by treating it as a resource rather than a nuisance. The report concludes that while rapid urbanisation is an inevitable process and that people will continue to migrate from villages to cities, the future presents a challenge to manage storm water effectively in order to make future cities vibrant and healthy. By implementing the BMPs cited in the report and involving community participation, the problems of urban flash floods, water supply, sanitation and drainage in New Delhi can be addressed in an effective manner.
Contents 1. Rising Cities of Tomorrow – Contrasts and Contradictions…….…..1 2. Delhi – A City of Jinx….………………………...………………….3 3. A Problem of Plenty and Plenty of Problems………………….........6 4. Think Global, Act Local…………………………………………….9 5. For the People, By the People……………………………………....13 6. To Conclude……………………………………………...…………16
References……………………………………………………………i
1. Rising Cities of Tomorrow – Contrasts and Contradictions: Human civilisation reached a silent but significant milestone sometime around 2008 when for the first time in recorded history, there were more people living in urban areas than rural areas. More than half the human population (3.3 Billion) live in cities and urban areas and this figure is projected to increase to upto 5 billion by 2030 and majority of these urban dwellers will be in Asian countries like China and India (United Nations, 2011a). This is best illustrated by the graph created using the gapminder tool as shown in figure 1.1 below:
Figure 1.1 – Showing the growth of Urban population growth in China, India, Brazil, United Kingdom, United States of America and Bangladesh. [Source: www.gapminder.com] The rapid economic growth of India and China over the last 3 decades is seen as the primary driver for this massive influx of people from rural to urban areas. In India, the economic liberalisation and subsequent industrialisation and growth of tertiary economic sectors such as banking, finance, information technology, consulting and retail since 1991 has led to a massive change in urban demographics due to large scale migration from rural to urban areas. More and more cities are emerging as major hubs of education, healthcare, commerce and industry and the capital city of New Delhi along with Mumbai and Kolkata feature in the top 10 urban agglomerations as per United Nations (2011b) as shown in table 1.1 below:
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Table 1.1 – Top 10 Urban Agglomerations in 2011 (Source: United Nations, 2011c) Rank Population Country Urban agglomeration order (millions) 1 Japan Tokyo 37.22 2 India Delhi 22.65 3 Mexico Ciudad de México (Mexico City) 20.45 4 United States of America New York-Newark 20.35 5 China Shanghai 20.21 6 Brazil São Paulo 19.92 7 India Mumbai (Bombay) 19.74 8 China Beijing 15.59 9 Bangladesh Dhaka 15.39 10 India Kolkata (Calcutta) 14.40 Throughout human history, industrialisation and economic growth has led to growth in urban population. Most of the highly industrialised countries have a high urban population. However, the growth pattern followed by China, India and Brazil is not same as the one followed by USA and UK and other OECD countries (Organisation for Economic Cooperation and Development) in the earlier part of the twentieth century. Figure 1.2 below shows a gapminder plot between GDP (Gross Domestic Produce) per capita (in US Dollars, inflation adjusted, purchasing power parity) and urban population (1960-2008).
Figure 1.2 – Plot between Income per person and urban population in China, India, Brazil, South Korea, South Africa, the United Kingdom and USA (1960-2008) [Source: www.gapminder.com] From the above figure, it may be inferred that the urbanisation in the highly industrialised countries like USA, the United Kingdom, Japan and South Korea was gradual and and it was driven by an urban ‘pull’ – urban centres attracted affluent people from rural areas. In contrast, the urbanisation in China, India and other newly industrialised countries is due to a rural ‘push’. This can been seen from the graph from the steeper slopes for India and China indicate that the increase in urban population in India and China did not lead to substantial rise in per capita income during the period 1960 to 2008. 2
2. Delhi – The City of Jinx: According to Datta (2006), urbanisation in India is a product of demographic explosion and poverty induced rural-urban migration. The big cities attained inordinately large population size leading to a virtual collapse in the urban services and followed by basic problems in the field of housing, creation of slums/shanty towns, water, infrastructure, transport and leading to a general degradation of quality of life. Moreover, Ahluwalia (2002) states that recent globalisation and liberal economic policies have led to rapid economic activities and spurt in demand for infrastructure office complexes, retail spaces, housing and transportation in urban India and a massive construction boom followed. It may be mentioned that the construction boom created a demand for labour which was fulfilled by cheap labour from rural areas. Also, the rural migrant population, already subject to poverty, migrate to the cities readily in search of better opportunities. They are largely employed in the unorganised sector and receive no pension or housing benefits. And they usually settle in unauthorised settlements or slums or ‘Jhuggi-Jhopri’ (JJ) clusters. According to United Nations (2006), a slum is defined as a run-down area of a city characterised by sub-standard housing and squalor and lacking in tenure security. The United Nations (2011a) also state that cities like New Delhi and Bangalore are moving straight from agriculture based to high-technology and services provision without any significant manufacturing transition to speak of, contrary to the established historical pattern. Unconventional or not, though, these economic transitions come as a major socio-economic challenge for urban areas, insofar as they have been unable to generate sufficient number of durable job opportunities in the manufacturing or services sectors that could provide gainful employment to the people migrating from the rural areas. Since construction work is mostly temporary and job opportunities are sporadic and seasonal, these people remain in a vicious cycle of urban poverty and lack of opportunities and are forced to remain in slums. This results in creation of new slum and JJ clusters around newly developed areas. As per the latest reports of the Delhi Urban Shelter Improvement Board (2011), the area under JJ clusters is over 7 square kilometers spread across 700 settlements. Figure 2.1 below shows a typical JJ cluster in New Delhi.
Figure 2.1 – A typical JJ cluster in New Delhi (Source: www.tehelka.com, www.firstpost.com) On the other hand, the new and rapidly growing tertiary sectors like information technology, consulting, retail, banking and finance have led to the construction of roads, buildings and other structures. According to the latest reports of the Delhi Development Authority, the total built up area of New Delhi and adjoining areas is over 700 sq. km and this is expected to rise exponentially in the coming years. Figure 2.2 below shows the urban land cover in New Delhi and adjoining areas of Noida, Ghaziabad, Gurgaon and Faridabad: 3
Figure 2.2 – Showing urban land cover [Source: Sudhira, 2011] The per capita cement consumption for National Capital Region of Delhi is recorded to be the highest in the country (Financial Times, 2004) and is predicted to increase in the future. Per capita cement consumption is an indicator of the level of construction activity. The result can be seen in figure 2.3 below which shows an urban sprawl in South Delhi with the Qutub Minar in background.
Figure 2.3 – Photograph showing unplanned organic growth of buildings in South Delhi. [Source: www.flickriver.com]
In the above photograph, it can be seen that the buildings are constructed densely and the growth is largely organic with little or no central planning. Many areas of New Delhi are being constructed in this manner because the size of the land holdings is small and normally individuals undertake the construction with little or no architectural and urban planning considerations. However, in stark contrast, many areas are also being constructed as per modern urban planning principles as shown in figure 2.4 below: 4
Figure 2.4 – Showing new construction in Dwarka sub-city in New Delhi [Source: www. forum.skyscraperpage.com/showthread.php?t=117135] It can be seen in the above photograph that most of the buildings are large multi-storeyed residential complexes with little or no green cover between the buildings. Wide roads and parking lots are built around such apartment complexes to provide access and parking facilities to the residents of these apartment complexes. Water supply is either through municipal agencies like DJB (Delhi Jal Board) or through abstraction of groundwater through boreholes constructed by the builders. It maybe worth mentioning in this context that according to Sengupta and Romani (2011), the legal system for groundwater management in India falls within a complex, multilayered framework of constitutional and statutory provisions at the central and state levels. The 1998 National Water Policy (NWP) and the 2002 amended version do not have statutory status and thus cannot be legally enforced. Also, there is inadequete institutional, technical and financial capacity to ensure equitable access to groundwater and to prevent abstraction of ground water to unsustainable levels. In the light of the above, it is highly likely that these new townships will continue to draw groundwater and without any limits, chances of wastage are extemely high. The combined effects of these new township have a damaging effect on underground aquifers – the recharge of aquifers is hampered due to increase in paved surfaces and unlimited abstraction leading to a withdrawal rate exceeding the replenishment rate. If unchecked, this could lead to a serious problem of depletion of groundwater reserves. According to the Economic Survey of Delhi (2005-06), the decreasing groundwater level in Delhi has become a matter of serious concern. At some places in south and south west Delhi, the water level has gone down to 20-30m below the ground level. The quality of underground water is detiriorating and in several places, it has been found to be unfit for human consumption. Also, nitrate and fluoride concentrations have been found to exceed permissible WHO standards. The Central Pollution Control Board (2008) has reported that the groundwater table in Delhi has decreased by 4m over the last few decades. 5
3. A Problem of Plenty and Plenty of Problems: New Delhi and adjoining areas under the National Capital Region receives an average annual rainfall of about 714mm (WMO, 2012) of which over 75% is received in the months of July, August and September which is also known as the Monsoon season. Figure 3.1 below shows the average annual rainfall data for New Delhi.
Figure 3.1 – Climatological information for New Delhi [Source: Indian Meterological Department, 2012] As a result, the city receives enormous amount of rainfall in three months and the rest of the year is relatively dry. According to the City Developmen Plan – Delhi under the Jawaharlal Nehru Urban Renewal Mission (2009), The storm water management situation in Delhi is a complex situation owing to the combination of a number of natural and man-made drainage systems consisting of five drainage basins, large natural drains, storm water drains along the roads and combined sewer cum storm water drains (sometimes as a bypass arrangement for blocked sewer lines). However, most of the water collected through different drainage systems finally gets discharged into the river Yamuna. More often, this discharge undergoes little or no treatment and adds to the pollution of river Yamuna. Due to lack of solid waste management systems, open drains have become receptacles of garbage till they are completely filled up, leading to overflow of sullage and storm water. Consequently, in the rainy season, the drains are unable to take the flow and spill over flooding the roads. It appears that a comprehensive overview of the situation is lacking and only piecemeal solutions have been attempted at different points of development of the city. Figure 3.2 below shows an instance of flash floods occuring in New Delhi during the monsoons. 6
Figure 3.3 – Urban flash flood in New Delhi, September 11, 2009 [Source: The Hindu, 2009] It can be seen from the above photograph that the excess storm water flows out of the drains which do not have the capacity to convey large volumes of storm runoff. The runoff normally flows to the low lying areas and creates stagnant pools of water. Many of the slums are located in low lying areas which lack even basic drainage services. The stagnant pools of water become breeding grounds of mosquitoes. According to Gupta (2009), an increase in the number of malaria cases have been reported immediately after the monsoon rains. Much of these cases are reported from private hospitals and nursing homes and smaller clinics. The official figures of malaria according to National Vector Borne Disease Control Programme (2012) and the National Institute of Malaria Research (2012) are much lower. Gupta (2009) states that the main reason behind the low official figures is that the official report only takes into account the cases that are admitted to the government hospitals and do not take into account the actual number of malaria incidents. However, according to the National Vector Borne Disease Control Programme (2012), Haphazard and unplanned growth of towns has resulted in creation of “urban slum” with poor housing and sanitary conditions promoting vector mosquito breeding potential for malaria, filaria and dengue fever/ Dengue haemorrhagic fever. Due to population pressure all cities are expanding and parallel cities have come up and epidemic situations prevail in Gurgaon, Navi Mumbai and Noida. This seems like the newly developed cities are sitting on a malaria and dengue epidemic time bomb waiting to explode at any moment. Even though the number of deaths reported currently is low and the diseases have not yet attained epidemic proportions, it may be mentioned that malaria and other mosquito borne diseases lead to significant loss of income for the lower strata of the society. Oarno and Cairncross (1991) state that drainage construction is an effective mosquito control measure. It is cheaper than application of 7
insecticides and does not have to be repeated regularly. In many cases, drainage construction is cheaper than a year’s supply of insecticides and unlike chemical insecticides, improved drainage has no detrimental effect on the environment; on the contrary, it constitutes an environmental improvement. Moreover, the danger of mosquitos’ developing resistance to insecticides does not apply in this case. According to Oarno and Cairncross (1991), although deaths due to drowning in floods or burial beneath landslides or collapsing homes are perhaps the most dramatic signs of the suffering that drainage can help to alleviate, less noticeable and tangible are the greater impacts of the toll of disease and disability due to standing water. The ‘faecal-oral’ diseases which include the well-known water related diseases like diarrhoea, typhoid and cholera are often responsible for more child mortality than any other disease are acquired by consumption of contaminated food and water. Surface water becomes contaminated with these pathogens from sources such as blocked sewers and overflowing septic tanks and open defecation. This contaminated surface water also pollutes the shallow aquifers which serve as the source for the hand-pumps which are main source of drinking water for many of these inhabitants. Figure 3.4 below shows the typical scenario in an informal urban settlement and the sources of water contamination and water pollution.
Figure 3.3 – Stagnant water and disease transmission in urban slums: Health consequences of poor drainage. [Source: Oarno and Carincross (1991)] 8
4. Think Global, Act Local: The complex problems cited in the earlier sections are actually the symptoms and not the disease and the solution lies in treating the disease in a comprehensive and effective manner. The multi-faceted nature of the problem demands a multi-faceted solution and more importantly, a change in paradigm and mind-set. This part of the report suggests some fundamental changes in the way storm water is managed in order to create a vibrant, sustainable, equitable and green New Delhi of tomorrow an image of which is represented by the photograph shown in figure 4.1 below:
Figure 4.1 – Skyline at Connaught Place, New Delhi [Source: www.wikipedia.com, 2012] The crux of the problem lies in the fact that stormwater has been traditionally treated as a nuisance and broadly, the aim of urban drainage design and implementation has been to get rid of it as quickly as possible. The history of stormwater management has continued to evolve since the industrial revolution and the subsequent urbanisation that took place in USA, Europe and other industrialised countries. From being seen as a destructive force, to a pollution source it is now being widely seen as a valuable resource. This evolution is a result of the increasing understanding of the effects of anthropogenic activities on hydrology – both surface as well as ground water. According to Carmon and Shamir (2010), new approaches to stormwater management have evolved contemporaneously across the world since 1970s without much communication between the scientists and researchers. Although the original motivation and objectives for carrying out the research for developing these new stormwater management principles were different in each case, all of them adopted sustainable development as the ultimate goal. Researchers and urban planners in Australia pioneered this new method and the Water Sensitive Urban Design Research Group (1989) was among the earliest to initiate research in this area. The primary objective of these research activities was to protect the groundwater aquifers from depletion due to insufficient percolation as a result of increase in amount of impervious paved surface. Many other researchers like Fletcher et. al. (2004) have carried out research on the lines of flood protection and urban runoff on a regional and national scale. 9
In the United States of America, the driving force behind the formulation of new stormwater management systems has been the protection of water quality in the streams and lakes from the stormwater runoff from urban areas since 1970 (USEPA, 1999). This new methodology is known as Low Impact Development (LID) and was pioneered by the Prince George’s County (1999) in Maryland. The main requirement of LID is that the hydrological response (in terms of runoff volume) should be kept as it were before the development and the urban planner has full freedom to choose the means for achieving this objective. Of late, LID has been adopted by the USEPA (2007) as a primary planning approach for runoff management in order to protect and restore water quality in streams and lakes. Also, according to USEPA (2000), the implementation of LID Best Management Practices in comparison to conventional development practices in 17 locations has resulted in savings of 15-80% in costs of construction and project management. Researchers in Japan have conducted extensive research with the objective of flood protection and urban stream restoration. Herath et al. (1993) and Musiake et al. (1999) have conducted longitudinal field studies on the regulating effects of retention, detention and infiltration on the volume of urban runoff. The Government of British Columbia (2002), Canada adopted an approach to stormwater management known as ‘ADAPT’ – Agree that stormwater is a resource; Design for the complete spectrum of rainfall events; Act on a priority basis in at-risk catchment basins; Plan at four levels – regional, watershed, neighbourhood and site; Test solutions and reduce costs by adaptive management. In the United Kingdom, the focus was primarily on sustainable design for urban drainage (CIRIA, 2004; Butler and Parkinson, 1997). Subsequently, the scope was widened and according to CIRIA (2006), the objectives covered sustainable water and wastewater management in relation to land use, urban planning and drainage while taking into account the social, economic and environmental aspects of flooding and urban stormwater management. Researchers in Israel like Carmon and Shamir (1999), Carmon et al. (1997) and Kronaveter et al. (2001) began with a single objective in mind – conservation of Israel’s coastal aquifer, emphasising on on-site infiltration in individual building lots – both public and private. It was concluded that the loss in groundwater reserves could be reduced significantly by simple means of connecting impervious surfaces to pervious surfaces to allow infiltration into aquifers. Thus, it is seen that the global trend in stormwater management has evolved significantly over time and more recently, efforts have been focussed on finding sustainable and environmentally friendly stormwater management techniques. Traditional mind-set of treating stormwater as a nuisance has been discarded and a new mind-set of treating stormwater as a valuable resource is taking shape all over the world. On a positive note, the urban drainage in New Delhi is not yet massively centralised and there is a lot of scope to incorporate these sustainable principles in the urban drainage in New Delhi. And moreover, successful implementation of these practices in New Delhi will spurt similar efforts in other Indian cities which too are rapidly growing and are facing similar problems. 10
For formally planned colonies and settlement, the principal objective of stormwater management can be the one followed by the LID best management practices – the hydrological response in terms of runoff and percolation be kept similar to the predevelopment levels while giving the urban planner/architect the freedom to choose the methods and techniques. The process of incorporating SUDS and LID Best Management Practices into urban development maybe initiated through a policy of rewarding those developers who implement them through indirect financial or other benefits and imposing punitive measures on those who fail to implement them. Several BMPs have been developed throughout the world for providing sustainable drainage. Some of them are briefly described below: Filter strips and swales (CIRIA, 2012): Filter strips and grassed swales are vegetated surface features that drain stormwater evenly off impermeable areas like roads, parking lots and building clusters. Swales are long shallow channels and filter strips are gently sloping areas of ground and both provide opportunities for slow conveyance and infiltration (where appropriate). Both these techniques mimic the natural drainage patterns by allowing rainwater to run in sheets through vegetation, slowing and filtering the flow. Swales also can be designed for a combination of conveyance, infiltration, detention and treatment of runoff. Both swales and filter strips are effective in removing pollutants from the runoff from roads and parking lots by trapping organic and mineral particles and then incorporating these trapped particles into the soil. Figure 4.2 below shows a swale and a filter strip.
Figure 4.2 – Cross Section of a Swale and a Filter Strip [CIRIA, 2012] Permeable Surfaces and Filter Drains (CIRIA, 2012): Filter drains and permeable surfaces are devices that have a volume of permeable material below ground to absorb and percolate surface water to increase infiltration of rain and stormwater. Permeable surfaces can include grass (if the area will not be trafficked), reinforced grass, gravelled grass, solid paving blocks with large vertical holes filled with gravel, solid paving blocks with gaps between individual units, porous paving blocks with a system of voids within units, porous asphalt and continuous surfaces with an inherent system of voids. Currently, concrete paving blocks are a preferred choice for constructing parking lots and walkways due to the lower cost and faster execution and this offers an opportunity to effectively implement permeable surfaces. 11
Infiltration Devices (CIRIA, 2012): Infiltration devices drain water directly into the ground. They may be used at source or the runoff can be conveyed in a pipe or swale to the infiltration area. They include soakways, infiltration trenches, infiltration basins as well as swales, filter drains and ponds. Infiltration devices can be integrated into and form a part of the landscaped areas. Soakways and infiltration trenches are completely below ground and water should not appear on the surface. Infiltration basins and swales designed for infiltration store water on the ground surface, but are dry except in periods of heavy rainfall. Figure 4.3 shows various infiltration devices.
Figure 4.3 – Cross-section of soakways and infiltration basins. In addition to the above, numerous other alternatives can be formulated while taking into account the local soil conditions, availability of space and other constraints. In this context, it may be mentioned that implementing these BMPs has an added benefit of reduced construction cost. Grassed swales were used in lieu of RCC drains in the township of 4X300 MW Rosa Thermal Power Project, Shahjahanpur, Uttar Pradesh and this resulted in net savings of about INR 8, 000,000/- (equivalent to £0.8 Millions). By including the principles of sustainable urban drainage in the curriculum of architecture and urban development, organising training programmes for practicing architects and increasing awareness about the benefits of implementing the BMPs to the developers and investors and all other stakeholders which include residents, local authorities, city and town councils, municipal authorities and urban planners and by making statutory provisions in urban planning policies, thereby making it legally binding for planners and developers to implement SUDS in their development, the problems of increased urban runoff, depletion of groundwater reserves and diffused pollution of water bodies can be mitigated to a great extent.
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5. For the People, By the People: In the slums and informal urban settlements, the traditional top-down approach will not yield the desired results because these settlements are constructed in an organic and unplanned manner. The size of the land holdings is small and there is no fixed tenancy – which means that the residents have no legal right over the land and may be evicted forcibly. According to Chandrasekhar and Mukhopadhyay (2008), there are large differences among the urban poor in modes of livelihood and access to resources. Contrary to popular perception, not all slum dwellers are poor. According to Sengupta (2009), a survey of nine slums in Howrah, Kolkata revealed that almost two-thirds of slum dwellers were above the poverty line. In such a scenario, a bottom – up approach in which community participation is mobilised and combined with technical and financial support from local governments can help achieve the combined goals of providing potable water, sanitation and drainage to the urban poor. Oarno and Cairncross (1991) have formulated several low – cost drainage designs for use in informal urban settlements, some of which have been successfully implemented in the city of San Salvador in Brazil. The drainage problems of an individual neighbourhood are a part of a hierarchy of problems related to the drainage network of the whole city and corresponding with the hierarchy of drains which compose it. These drains may range from major canals or large trunk sewers which college water from large areas of the city down to the small ditches or drainpipes that run along the roadside or serve individual properties. In the case of unplanned urban settlements or slums, closed drains may be built after careful considerations where there is lack of available space and open drains maybe constructed wherever possible. In case of open drains, the unlined channels are the cheapest to construct and maintain using untrained labour. Another low – cost measure is to lay turf or sow fast growing local grass on the slopes of the open drains to protect the slopes from scouring action of the water. For larger drains, the channels may be lined using local burnt bricks or stones or construction debris while keeping in mind to provide weep holes at regular intervals to prevent the lining from being ruptured due to excess pore water pressure from the confined soil. Figure 5.1 below shows the cross section of unlined, partially lined and lined drains.
Figure 5.1 – Cross-section of unlined partially lined and lined drains [Source: Oarno & Cairncross, 1991] 13
Oarno and Cairncross (1991) suggest that in very narrow streets where heavy vehicles do not pass and space is at a premium, the road itself may be designed to function as a stormwater drain. This is possible only if the slope is less than 5% and if the road has a surface such as compacted gravel or stone to protect it from erosion. Alternatively, drainage channels may be provided with removable covers with holes or botches to enable rainwater to enter and to make it easier to remove. The latter approach can also be used with a series of prefabricated channel elements laid out as shown in figure 5.2 of a stepped drain used in the city of San Salvador in Brazil.
Figure 5.2 – Pre-fabricated covered drain design [Source: Oarno and Cairncross, 1991] According to Oarno and Cairncross (1991), the smallest channels, less than 300mm deep, do not need weepholes and can be conveniently lined with brick or with precast concrete elements. The elements should weigh less than 50 kg so that they can be carried and laid in place by two persons without any machinery. Precast channels should be preferably laid on a bed of compacted sand, 50mm thick. A single channel size can be adapted for larger flows by laying it deeper and building the sides with masonry. Prefabricated elements have the advantage over masonry or in situ concrete linings in that they can be laid relatively quickly. Masonry drains take a long time to build and concrete poured in place requires several days to set. Meanwhile, local traffic is disrupted and the fresh masonry or concrete can be ruined by a sudden downpour. Moreover, if drains are constructed in the dry season to avoid an unexpected downpour, there may be a shortage of water to cure the concrete in place. In a covered workshop, such difficulties can be overcome and strict quality control can be enforced in the preparation of the precast concrete units.
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Community participation in these areas can be initiated to use local manpower and resources while urban planners and engineers can offer technical assistance and knowhow to implement these projects. The various steps or activities involved in constructing drains are listed below.
Excavation and earthwork. Transport of soil, water, sand and cement. Manual compaction of soil or sand. Preparation of prefabricated elements. Carriage of prefabricated elements. Safe storage of prefabricated drain elements. Laying in position of the prefabricated elements. Finishing and planting for embankments. Providing food and water to the volunteers.
It may be mentioned that while building a drainage system is a complicated activity requiring engineering skills, the individual tasks are simple and can be done by the community. The only task in the list mentioned above which requires specialised skills is in the preparation of prefabricated drain elements and the procurement of cement, sand and aggregate for the same. Government and Non – Government agencies can help fill in the gap in the technical and financial area of the activity and local community leaders can provide the necessary impetus. Also, the stormwater can be routed to specially designed detention tanks to store the water which can be used to provide drinking water to the inhabitants. Moreover, the precast concrete elements can be easily removed and relocated in case the informal settlement/slum is evicted due to change in urban land use regulation. Improvement in drainage, water supply and sanitation will lead to an improvement in livelihood, education and living standards of the community. The problems of drainage and sanitation in urban slums are different from those of the planned urban settlements and they require a different approach. Direct involvement of the residents is perhaps the best method as they are the biggest stakeholders and improved drainage will result in direct benefits for them – in terms of reduced infant mortality rates, reduced instances of malaria and other water borne diseases and healthier living conditions.
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6. To Conclude: The problems posed by the rapid growth of cities and their social and environmental impacts are largely non-linear in nature and their solutions require an integrated and systemic approach. While there is no lack of technical expertise or the resources to implement sustainable urban drainage systems in New Delhi, there is a deficit of systemic mind-set and a traditional approach to view stormwater as a nuisance. The symptoms of the problem have manifested themselves in the face of flash floods, waterborne and water related diseases, groundwater depletion and contamination and high pollution levels in the river Yamuna. Implementation of the BMPs of the principles of Sustainable Urban Drainage Systems can help tackle the threat posed by the mismanagement of urban stormwater runoff and also regenerate the fast depleting groundwater aquifers. Also, by involving community participation, the BMPs for informal settlements can be implemented effectively. This report concludes that while the task of creating a healthy and sustainable New Delhi of tomorrow is enormous, it is not impossible and if timely action is not taken, the problem will spiral out of control and will lead to a situation of water stress and a potential health and disease epidemic – a direct threat to social stability and economic growth. With a change in approach, a shift in paradigm and a systemic view in implementing SUDS, the problems posed by rapid urban growth in New Delhi can surely be mitigated to create a healthy, vibrant and sustainable megalopolis of future.
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