A morphology-independent methodology to assess erosion, accretion and lateral migration of an alluvial channel using geospatial tools: a study on the Raidak-I river of Himalayan Foothills

Channel migration is a significant geomorphological process in the floodplain region. Human intervention in the form of engineering constructions (bridges, embankment, etc.) regarded as another dominant issue which is pulverizing the ways of natural channel adjustment as well as channel behavior. In the study, the channel adjustment in terms of lateral migration is lucidly illustrated with the application of modern tools of geoinformatics, i.e., the techniques of RS and GIS. At present, RS and GIS are capable of detecting as well as representing the channel changes over space and time. The Raidak-I river is a meandering course stretching for about 81.9 km through alluvial plains of Cooch Behar and Alipurduar districts of West Bengal. To study erosion–accretion and lateral migration of Raidak-I river, sequential changes in the position of bank line have been studied with the help of USGS satellite data for the year 1972, 1978, 1990, 1996, 2002, 2009 and 2016. Using Arc GIS10.1 software and Arc GIS extension tools, bank centerline, the average length of migration of channel, shape area migration of the channel and different segments-wise erosion and accretion were assessed. The river bank line shifting due to bank erosion has been carried out considering various time spans, i.e., 1972–1978, 1978–1990, 1990–1996, 1996–2002, 2002–2009 and 2009–2016. The average migration of channel, shape area migration of channel and erosion–deposition decreased from 1972 to 2016 except during the period 1990–1996. Such changes in meander morphology of the Raidak-I river have made the channel more dynamic in the Himalayan foothill region.