Impact of Temporal Variation in Land Use on Surface Run Off: A Case Study of Cochin City, Kerala, India

Abstract

The process of urbanization is unplanned and is at a faster rate in developing countries like India. Urbanization is the process of land use alteration. The growth of urban areas results in significant changes in the physical properties of the land surface. The consequence is increased in area of impervious surface resulting in enhanced surface runoff. Increased surface runoff would eventually result in alteration of the prevailing hydrologic system. The present study is an attempt to quantify the impact of land use changes due to urbanization on surface runoff and thereby to study the emerging challenges it impart on the water management and sustainable development. The study area is Cochin, one of the fast developing second tier metros in India. We estimated the seasonal and yearly runoff volume for the study area using SCS-CN method. In this method, land use as well as soil data were used to estimate the runoff volume. The land use changes for the study area were prepared from Survey of India topographic map as well as satellite data. Recent land use map was generated using high resolution Quick Bird image. Runoff depth and volume was calculated for various land use categories using daily rainfall data for the past three decades. An attempt was also made to study the impact of high resolution land use classification on the run off volume. The significant finding from the study is the observation of approximately 24% increase in the average runoff volume over last forty years. This increase in the runoff volume can be attributed to the considerable increase in less permeable area. The built up area increased at the cost of land that falls mostly in the category of vegetation. Approximately one fourth of the study area comprises of water body. The study shows that over the last four decades, the water body got shrunk due to reclamation during the process of vigorous urbanization. The study thus facilitates to identify significant changes in the temporal characteristics of runoff that may lead to major disturbances in the prevailing hydrologic system.