The Narmada alluvial fan is one of the world's largest, with an axial
length of 23 km. The architecture is dominated by debris-flow deposits
(Gms facies). Matrix support, a clay content of 3% and clast contact
indicate that the clast-support mechanism resulted from a combination
of buoyancy and dispersive pressure. The other facies include gravel/s
and-couplet facies (GSh), planar cross-stratified gravel facies (Gp(1)
and Gp(2)), sand-sheet facies (Sm), and trough cross-stratified sand
facies (St). Gms, GSh and Sm facies are debris-flow and sheet-flow dep
osits that aggraded the fan, whereas Gp(1) and St are channel bars and
channel fills that dominated the fan between major flood events. The
fan is characterised by subrounded to rounded clasts. The rounding is
due to the elongated catchment area upstream of the fan apex, as clast
s are rounded during prolonged bed load transport and are temporarily
arrested upstream of the fan apex as channel bars. These clasts are re
mobilized and entrained in debris-flows on the fan during events of an
omalous discharge (storm events). The basalt clasts show a progressive
fail in maximum clast size from 150 cm to 10 cm away from the fan ape
x. The Narmada river exhibits discharges of up to 60,000 m(3)/s, but,
due to reconfinement of the feeder channel resulting from tectonic rea
ctivation of pre-existing lineaments during the Late Pleistocene, this
does not aggrade the fan. Tectonism has influenced the location of th
e depositional site, has provided the necessary physiographic contrast
, and has played an important role in the erosion of the fan, whereas
climate-controlled primary and secondary processes have determined the
nature of alluvial architecture.