Abstract:
Analyses of a fluvial sedimentary sequence from the lower reaches of the Narmada
River establish a record of rhythmic cycles of sediment facies that represent floods
during the late Holocene. The south-west Indian monsoon strongly influences the
study area, and heavy rainfall or cyclones which originate from either the Bay of
Bengal or the Arabian Sea, also affect the region. Optically stimulated luminescence
dating places the 8 m thick sediment sequence in the climate transition phase which
ranges from the Medieval Warm Period to the Little Ice Age. Multi-proxy analyses
including high-resolution granulometry, magnetic susceptibility, ferromagnetic mineral
concentration, facies major oxide geochemistry, and micro-fossil records (from two
sedimentary units) are used to study these late Holocene flood events. The latter are
characterised by multiple sediment facies, depositional events, changes in channel
morphology, and distinctive flood signatures. Integration of these records enables to
identify two distinct aggradations viz. phase I and phase II, as well as a relative change
in channel morphology. The study describes 11 flooding events and their imprints over
multi-proxy records. Historic documents and instrumental records from the town of
Bharuch referring to floods, movement of channel sand, channel shallowing, and the
dysfunction of the ancient port of Bharuch further validate the inferences drawn from
the sedimentary sequence. The study exemplifies the need to use high resolution and
multi-proxy studies to interpret paleoflood records and climate signatures in order to
build archives of monsoonal rivers.
