Study of Spatio Temporal Dynamics of Brahmaputra River Islands, India

The present paper aims to study the spatio temporal dynamics of Brahmaputra river islands and to identify the stable river islands using three decade long multispectral satellite data using Google Earth Engine, a cloud computing platfor. Brahmaputra is the second largest carrier of sediment load in the world. The river has created a thick extensive valley supporting about 27 million people by providing land for agriculture and human habitat. Relationship between channel geomorphology, sediment transport and river flow is related to rate of erosion and deposition which in turn contribute formation of stable river island locally known as chars. Major floods hits river banks almost every year which changes the course of Brahmaputra river drastically affecting the chars profoundly. This makes it crucial to investigate the long term behaviour of chars. For the present study, Landsat-5 and Landsat-8 data ranging from 1988 to 2018 was processed and analysed using vegetation index based knowledge classifier. The study includes assessment of aggradations and degradation of the chars during the study period. The study analyses the changes in area and count of total number of chars and the behaviour of river for three decades. It has been found that approximately 33% of area of river is covered by vegetation island. It is observed that not only the river extent, but also number of chars and total area of chars is increasing consistently over the years. The study shows that approximately 5125 number of islands were created in three decades covering 123,000 hectares of area. Study also showed that nearly 2363 number of chars were stable in the river from past thirty years which covers around 68,000 ha of area, while 3260 islands are stable from twenty years covering 97,000 ha of area and 3859 number of islands are stable from past ten years covering 146,000 ha of area. The newly formed island and age of current island was also determined for each decade. Based on spatio-temporal analysis of islands, the chars which are susceptible to erosion are also identified and mapped.

Keywords : Google Earth Engine, Landsat, River dynamics, NDVI