Assessment of relationship of braiding intensities with stream power and bank erosion rate through Plan Form Index (PFI) method: a study on selected reaches of the upstream of Ganga river near Malda district, West Bengal, India

Abstract

River bank erosion is a hazardous and common phenomenon in diara region near Malda district of North East India during monsoon and post monsoon periods of every year. The left bank of Ganga river is texturally very weak along diara region of Malda district. The present work explores relations between stream power, braiding intensities and bank erosion in certain stretches of upstream of the Ganga river near Malda district of West Bengal in India. In the present study, we have tried to do a quantitative assessment of channel braiding process of the Ganga river by applying the Plan Form approach and equivalent measurement of stream power. A comparative study of discrete years has been done through braiding index to understand morphological behaviour of the channel. Beside its stream power of the selected stretches of the study area is estimated and compared with braiding intensity and bank erosion. This paper presents the dynamic behaviour of the channel pattern of the Ganga river system in Malda district over a time span of 40 years. This procedure addresses the selection of input parameters from digital satellite images comprising scenes for the years 1975, 1995 and 2015 with specific dates, from Rajmahal in Jharkhand district to Farakka barrage in Malda district. To obtain Plan Form Indices for the entire study area, required parameters were extracting through using GIS techniques. Stream power is measured through analyzing latest flood records and satellite images. The present study concluded that a wide spread and continuous braiding process has occurred in the study area due to aggradations of riverbed and temporal declination of stream power.