TEMPORAL SHIFT OF BAGMATI RIVER OVER 25 YEARS USING LANDSAT

Abstract. Bagmati River has been a terrific boon in different aspects like natural, cultural, ecological, etc. However, the river has been in a critical situation with the shift in its quality and quantity during these years. Since the changes are slow-growing, actual shifts are barely noticed. While the in-situ analysis and experimentation become costly, the analysis of Landsat images acquired with the application of Remote Sensing (RS) and Geographic Information System (GIS) provides an inexpensive technique in estimating and mapping such temporal shift in the river. Concerning the case, this study modelled the temporal changes of the Bagmati River within 25 years (1991–2016) using the multi-temporal Landsat images. We adopted the Normalized Difference Water Index (NDWI for the unsupervised extraction of the water feature and monitoring the changes. A model was developed in Arc-GIS by discerning the river, and the difference was determined for 25 years. The result indicated a major temporal shift in the river channel with a decreasing trend from 1991 to 2016. Over 25 years, the river loss almost one-third of its original water-flow channel with a severe sweep in the south-western portion of the study area. With this precise information, a field-based study can be undertaken either to analyse the damage caused by the river in those particular portions or to assess the factors affecting the river shift. Hence, we strongly recommend employing the cost-effective methods, RS and GIS, for detecting, analysing and monitoring the shifts and changes in the rivers and lakes over a while.