■ J DecemDer 1973 
761 
27 March 1975 
BAN 0-5 BAN D _ 7 
\ 
Figure 2 M u It itemporal - multispectral Landsat images from the Delta . area ot Bangladesh 
10 January 1974 
BAND _ 7 
BAND.5 
1.2.2 Subdivision of the lower river floodplain into 
lithologic units 
The "embroidery floodplain" pattern of the lower 
floodplain (fig. 4b), which can be seen on all band- 
5 images (fig.2) might have developed by the combi 
nation of very slow moving flood waters of the Gan 
ges River in the North, the Kumar River in the 
Northwest and the Arialkhan River in the South. The 
basins and ridges of the lower river floodplain may 
contain finer materials such as silt, clay and loam. 
A sharp contrast produced by dark and grey colours 
of areas on the 1975 near-infrared images has allow 
ed a subdivision into two units: silty deposits 
under a clay mantle and silty-loamy deposits. 
Silty deposits under a clay mantle: As can be seen 
on the band-7 image, the clay mantle in the upper- 
river floodplain also extends somewhat into the 
lower river floodplain area (fig. 2). Here the 
crests of ridges coming out with light colours 
through the dark coloured clay mantle produce an 
embroidery pattern which is clearly recognizable. 
This pattern permits to trace the boundary between 
lower and upper floodplain under the clay mantle. 
The same boundary is seen on all band-5 images. The 
light coloured ridges visible on both band-5 and 
band-7 images are an indication that silty deposits 
might lay under the clay mantle. 
Silty-loamy deposits: Apart from the dark colour 
ed clay mantle area, the lower river floodplain 
appears light-grey on band-5 and slightly darker on 
band-7 (fig. 2) . The same light-grey colour of the 
floodplain can also be seen on the 1973 band-5 
image. This suggests the presence of sand or silt