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Figure 1
ed as "old river floodplain remains".
1.2.1 Subdivision of the upper river floodplain into
lithologic units
Using differences in landscape patterns and spectral
signatures the upper river floodplain is subdivided
into two lothologic units: sandy deposits and sandy-
silty deposits.
Sandy deposits: The meandering area along the
Ganges River can be expected to consist of sandy
materials deposited at flood times by fast flowing
water (fig. 2) . These areas appear white on band-5
(visible) and light-grey on band-7 (near-infrared)
of the 1975 images, which corresponds to the fact
that sand and silt reflect high amounts of energy in
the electromagnetic spectrum.
Silty-sandy deposits under a clay mantle: In the
areas further away from the Ganges riverbank, the
basins appear uniform dark on the band-7 and light
in colour on the band-5 images (fig. 2). Vegetation
covered straight and curved ridges are clearly seen
with their light colours occurring through dark co
loured basins on band-7 and with their dark colours
occurring through light coloured basins on band-5
images. A uniform dark appearance of basins on near
infrared images suggests that they are covered by a
clay mantle. This kind of clay mantle is often
observed in floodplains where basins formed, long
abandoned by the river and flooded again by very
slow moving water. The basins under the clay mantle
possibly consist of silty-sandy materials, depos
ited in a transition zone with decreasing water
velocity.
1.2.2 Subdi
litho
The "embroi
floodplain
5 images (f
nation of v
ges River
Northwest a
basins and
contain fin
A sharp cor
of areas on
ed a subdi
under a cla
Silty dep
on the banc