Planform Pattern of the Lower Teesta River After the Gazaldoba Barrage

Abstract

River planform means the overview of river channel pattern type as well as its configuration. The lower Teesta in West Bengal as braided river is characterised by wide, relatively shallow, multiple channels in which the flow divides and rejoins around bars and islands. In the recent time large number of dam constructions on the river Teesta largely impact on the natural channel pattern of the river. The present study focuses on the quantification of the river planform of the river Teesta after Gazaldoba barrage using satellite images of the discrete years (1997, 1990, 1999, 2008) in the GIS environments. The fundamental objective is to establish the relationships between the causes behind the present changes compare to the past with the quantified values of Planform Index. The result found that the PFI values gradually decreasing trend in the recent time. PFI value less than 4 is highly braided where more than 19 low braided. The maximum value is more than 27 in the narrowed down channel near the Teesta Domohani Bridge where the value is less than 1.6 in several reaches of the recent river. But Channel sinuosity has not increased as much after the barrage construction but the bars and islands are developed much more in the river after barrage as PFI study shows that the number of multiple channels increased. On the other hand from the hydrological data it is evident that the Gazaldoba barrage is not solely responsible for the present channel palnform changes but the other upstream factors are. Thus the river Teesta planform pattern has been changed from low braided to highly braided after the human induced changes in the river.