Geomorphic and stratigraphic evolution of floodplain lakes in the Central Ganga Plains, India

The floodplains of the mighty river Ganga are centrally located in the Himalayan foreland basin and act as temporary storehouse for sediments eroded and transported from the Himalayan mountains. This fluvial landscape provides sufficient groundwater and fertile lands that support the agricultural activities to sustain the livelihood of a vast population. The Ganga plains exhibit a broad array of geomorphic features associated with the fluvial environment of deposition. The interfluve between the Ganga and Sai rivers in the Central Ganga Plains has been documented to be the oldest geomorphic surface in the region. Narrow meandering loops of streams, stretches of linear lakes representing sinuous abandoned channels and meander cut-offs, small ponds, and oxbow lakes can be observed in the elevated interfluve of both these rivers. The presence of numerous oxbow lakes and small isolated pools as remnants of the abandoned channels is a testimony to a highly active fluvial setting in the past.
In order to understand the evolution of the linear belt of meander cut-offs and oxbows in the Ganga-Sai interfluve, both regional and local scale geomorphic mapping was done using the earth observation satellite imageries and a multi-temporal approach was followed to efficiently trace all the observable geomorphic features in this fluvial setting. The regional scale geomorphic mapping of this interfluve shows a linear paleochannel belt comprised of meander cutoffs and small abandoned channel segments run parallel to the present-day Sai river. A large oxbow lake (Baraila Tal) was selected from this linear belt of cutoffs and excavated at three locations to investigate the chrono-stratigraphic succession of these lakes. Results from the geomorphic analysis suggest that the belt of paleochannel remnants was previously a part of the avulsed channel of Sai river. Three stages of landscape evolution and development of various geomorphic features related to channel migration between the Late Pleistocene and Holocene period in the Ganga-Sai interfluve region in the Central Ganga Plains have been identified. Stratigraphic succession at Baraila Tal shows the presence of micaceous sandy material at the base which suggests that the lake was previously a part of an active fluvial system. This litho-unit is overlain by the finer clayey silt and silty clay deposits which indicate that the depositional environment transformed from a fluvial to a lacustrine system. The proposed evolutionary pathway has been validated using results of stable isotopic data generated from the micro-gastropod shells picked from the lake sediments of Baraila Tal in the Ganga-Sai interfluve.