Channel migration and meander cutoff in response to high magnitude flood event: a case study from the Meshwa River, North Gujarat, India

摘要

The traces of cutoff meander loops, swamps or shallow lakes provide ideal sites for understanding sedimentation pattern and depositional environment and also provide clues for the reconstruction of the past landscape. It is intriguing to analyze the process of present day meander cutoff for a better correlation with the processes of palaeomeander formation. In the north Gujarat alluvial plains, within the largely internally draining Vatrak river basin, one of its major tributary, Meshwa River, shows fluvial landscape with palaeochannels, meander scar and meander cutoffs features resulting from channel shifting processes. Data has been generated from abandoned channel fill to understand the fluvial dynamics and depositional environment. The river exhibits prominent changes in its course from the year 1971 to 2012 spreading over time span of 41 years. The point bars associated with the meanders have been abandoned and further incised providing scope for facies analysis and depositional environment interpretations. Five episodes of repeated submergence and emergence have been inferred probably related to levee deposits suggesting minor variations in the streamflow conditions. Based on the channel planform analysis and discharge estimations also it can be concluded that the rate of channel migration has varied over the last 40 years. The discharge estimations suggest that the major shift has however been related to a high magnitude flood event in the year 2009 that led to the channel meander cutoff. Variations in the index of channel migration also points towards higher channel migration rate and suggests that the river was in a highly erosive phase cutting its own channel and reworking the floodplain deposits.