Slum Identification Using High-resolution Satellite Data

Population explosion and rapid urbanisation in India over the past two decades has introduced problems associated with informal settlements. Lack of local authority current and accurate databases complicates any preventative or remedial measures to control the growth of settlements, but integrated remote sensing and GIS allows some understanding of development patterns and level of infrastructure.

Rapid urbanisation has generated the problem of informal settlements in almost every city in India. A rural population migrates to the city in search of employment and, out of sheer necessity, has no alternative but to settle in existent slum areas or to search for new sites of least resistance in which to establish shelter. Such dwellings are usually built in marginal areas such as along natural drainage channels, railway lines, hillsides etc. Informal settlements may be described as inadequate or sub-standard housing areas with lack of basic facilities and services. Planning controls are usually ineffective due to lack of timely information and people having little regard for such things in the absence of any other alternative.

Dehradun State Capital
Dehradun, capital of the newly formed state of Uttaranchal in India, is strategically situated in the Himalayan foothills, with undulating topography and landform and drained by two major seasonal rivers, the Rispana and the Bindal Rao. The problem of informal settlements increased here after Dehradun became the capital in 2000, when new job opportunities presented themselves in both the formal and informal sector. The change in function from institutional to administrative generated new job opportunities, which increased migration, resulting in both planned and unplanned developments inside and outside the city. A study has been carried out to trace the development patterns of informal settlements using IKONOS panchromatic and multi-spectral merged products to determine environmental consequences. Study of development patterns may explain and predict behaviour of informal settlements over time and space, providing insight for preventing environmental degradation and maintaining the urban eco-system.

Identifying Settlements
A general definition of ‘informal settlement’ classifies it as an area in which the social and physical environment is so unhealthy as to constitute a menace to every aspect of wellbeing, physical, mental, social and psychological. It is an area consisting of dwelling units that do not comply with urban standards of housing; it is usually high-density and lacking in proper structures or made up of poorly maintained structures, deprived of basic infrastructure services. The interpretation key adopted to detect informal settlements from IKONOS data includes small size, shape, relatively dark tone, irregular and narrow street pattern. Areas of wasteland such as banks of natural drainage channels, railway-line embankments and road margins are taken as association for identification.

Development Pattern
The pattern of development of informal settlements is linear, mainly following natural drains and railway lines. There is high-density development in marginal areas. In Dehradun most informal settlements have developed along the two natural rivers. A detailed study using high-resolution satellite data identified a total of 113 pockets of informal settlement within Dehradun municipal area. Of these, ninety are situated along seasonal rivers and drainage channels, while 23 are dispersed within the city.

Cause and Effect
Demand for land for housing has raised land prices beyond the affordability of the common urban populace. Migrants from surrounding rural areas began to remain near their place of work by occupying marginal spaces along the natural drainage channels, railway line and major roads. Most people living in these areas are employed in the informal sector, including labourers in the construction industry and household jobs in surrounding planned residential areas. Accessibility and transportation networks play a major role in the pattern of development of informal settlements. Informal settlements have developed towards the left-hand side, as well as in areas near to the bridge towards the right-hand side of the drainage channel: good accessibility. Vacant spaces between the two bridges towards the right-hand side of the drainage channel are potential areas for the development of future informal settlements. Obviously, accessibility and physiographic conditions are the major influencing factor for linear patterns of development of informal settlements.

Living Conditions
A detailed study has been carried out to trace the level of infrastructure in the informal settlements on either side of the drainage channels. The results show that the level of infrastructure is better on the left-hand bank of the river. About 64% of houses on the left bank, and 42% on the right, have available water within 100 metres. About a quarter of the houses are served by the electricity supply on both sides of the river. Sanitation and street lighting conditions are also better on the left bank. About 34% of houses on the left bank and 42% houses on the right of drainage have no proper sanitation facility, while 41% of houses on the left bank and 77% of houses on the right lack proper drainage along the street. Only 57% of houses on the left bank and 27% of houses on the right are served by street lighting. The physical condition of houses is an indicator of socio-economic status of residents. The condition of houses on the left bank of the river is better than that of those on the other side. About 61% of houses on the left side are of permanent structure, of which 3% are in very good condition. This shows that the inhabitants are not economically weak and can pay taxes for basic infrastructure facilities. In contrast, 44% of houses on the right-hand bank of the river are permanent structures but not in very good condition. About 2% of houses on the left side and 7% of houses on the right are temporary structures with brick, mud walls and plastic and iron-sheeting roofs.

Consequences
Poorly developed areas threaten our environment, health and quality of life in numerous ways. The impact of informal settlements upon their environment has been studied under two parameters: the physical environment and the social environment Simply by virtue of their existing and functioning, informal settlements have considerable impacts on ecosystems and other environmental resources which provide societal and environmental benefits. The ecological impact of these settlements spans the local, city and regional scale. There are very clear effects on the quality of ground and surface water. There is pollution of storm-water runoff from upper hills reaching the rivers, as well as underground water contamination. Together these are responsible for deterioration in air and water quality. Further, there is alteration to the natural landscape, and soil erosion. Such developments increase unemployment and concentrate poverty in urban centres. They generate pressure on existing infrastructures and increase traffic congestion. These are areas where the urban poor live in very impoverished conditions with inadequate infrastructure and social amenities. They do not pay any tax for infrastructure facilities and thus bring disparity to the supply of basic facilities.

Final Remarks
Informal settlements have been and remain a problematic aspect of urban growth in India. The issues and problems associated with this pattern of development are serious. The social and economic consequences of such settlements include both positive and negative effects, but impacts upon environmental and natural resources are predominantly adverse. Recommendations to prevent this pattern of development in future and to improve the present scenario include the following.

• Care should be taken to develop ecologically sensitive areas and other incidental spaces simultaneously with development of residential areas.
• Attempts should be made to regulate rapid urbanisation of land along rivers. Land lying along natural drainage channels should be protected and properly developed to maintain and improve water quality, as well as an aesthetically pleasing environment.
• As the economic condition of dwellers improves they should be charged a minimal contribution for basic infrastructure. Land transformation should be monitored and charged to persons of better economic condition.
• High-resolution satellite data could be used to monitor slum and squatter settlements within the city and improved management.

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