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River channel shifting involves the lateral migration of an alluvial river channel across its floodplain. High planform dynamics are a distinctive feature of the Koshi river, particularly in the lower stretches as a result of recurring floods. In this research, the dynamics of channel planform and shifting through systematic analysis and interpretation of diverse channel configurations using multidate Landsat TM 5 images (1999 and 2009) and Sentinel-2A image (2019) of the Koshi River from Chatara to the Nepal-India border has been studied. Remote sensing techniques and GIS environment was used for change analysis based on the satellite imageries. The channel shifting was determined by assessing and estimating the transient changes in the planform from the temporal satellite data. The results indicated that the Koshi River is highly braided over the stretch of 48 km south from Chatara. It can be easily visualized that the southern section of the river has more river stretch and braiding than the northern section. Between 1999 and 2019, the area of the water channel is reduced by 24.08 km2 whereas, the channel bars have increased by 68.08 km2. The river was observed having experienced a clear shift of the channel toward the west in recent years. The average annual rate of shifting was estimated to be 21.6 m year−1 towards the west and 0.8 m year−1 towards the east, with the overall expansion of the river flood plains. This study can be utilized for developing integrated sustainable river and land management plans in the Koshi basin and support future researches on relevant topics.
Baniya et al. (Wed,) studied this question.