A GIS STUDY TO ASSESS THE IMPACT OF URBANISATION ON RUNOFF

Abstract

The process of modernisation of villages and elimination of disparities, between such villages, towns and cities where desired facilities, amenities and basic needs of life, such as houses to live in, power, water, hospitals, schools, transport, communication, recreation, roads and such other social infrastructure are made available and where there is a density of population of not less than 1000 per square mile and total population exceeds 5000 and where the most of the people adopt a non-agricultural way of life is known as urbanisation ( Rashmi, 1978). Urban growth have direct impact on the land system and which in turn influences the air and water as well as the mankind. The objective of the present study is to study the growth of urbanisation in Roorkee and surrounding areas, and to assess the impact of urbanisation on runoff using remote sensing and GIS. For studying the pattern of urbanisation and its impacts, remote sensing, aerial photography and other technologies can provide the necessary data base. GIS is extremely useful for spatial and non-spatial data handling, transformation, manipulation, analysis and modelling, necessary for presenting the useful results in required form. Survey of India toposheets for the years 1926 and 1970, aerial photographs of year 1964, IRS IC PAN imagery of year 2000 were analyzed for various land use/land cover classes, common in the above data. Changes in urban features were assessed by digitizing the above data base in ARC/INFO GIS and employing various overlay and other operations. To study the impact of urbanisation, runoff estimation for the years 1970 and 2000 was done by using well-known rational hydrological model. iii The results showed that the physical expansion of urban area has occurred in Roorkee town which resulted in decrease of agricultural land in last 74 years (year 1926 to year 2000). There is an increase in urban area of 14.97 km2 (12.17%) and decrease in agricultural land of 17.37 km2 (14.13%) from year 1926 to year 2000. Similarly, increase in metalled road was observed to about 67 km (i.e. new roads and conversion of unmetalled to metalled roads) in a period of 74 years. The pre-monsoon and post-monsoon runoff values were computed to be 7.22 m3/s, 14.88 m3/s respectively for the year 1970, and 8.46 m3/s and 20.11 m3/s respectively for the year 2000. Because of urban land-use and land cover changes, an increase in runoff was also observed during a period of 30 years. IRS PAN data at 5.8 m spatial resolution was found to be extremely useful for identifying road network and other minor features on the ground. GIS technology is not only helpful to assess the growth in urban features but also it can be used to determine the type and nature of changes.