Question

about plain of ganga

Answer 1

The Ganga plain is a major part of the great plains of north India which comprise the Rajasthan plain, the Punjab plain and the Ganga plain and have been formed through the process of alleviation by the Satluj, the Ganga and the Bhramaputra drainage systems during late Tertiary and Quaternary periods.

In fact, the great plains are in the form of a transitional belt between the Himalayas in the north and the Deccan plateau in the south covering an area of more than 7,77,000km from Rajasthan to West Bengal. The Great Plains run for a distance of 2400km from West to East and have a width of 480km in the West and 144km in the east

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Answer 2

Location of Ganga Plain:

The Ganga plain is a major part of the Great Plains of north India which comprise the Rajasthan plain, the Punjab plain and the Ganga plain and have been formed through the process of alluviation by the Satluj, the Ganga and the Brahmaputra drainage sys­tems during late Tertiary and Quaternary periods.

In fact, the great plains are in the form of a transitional belt between the Himalayas in the north and the Deccan plateau in the south covering an area of more than 7,77,000 km2 from Rajasthan to West Bengal. The Great Plains run for a distance of 2400 km from west to east and have a width of480 km in the west and 144 km in the east.

Geological Formation of Ganga Plain:

Lithologically, the Ganga plain is characterized by Quaternary alluvia with varying combinations of clay, silt, sand and gravels. It is, thus, evident that lithologically the Ganga plain is monotonous except some variations in the northern part where the Bhabars of the Himalayas grade into the plains and in the southern part.

In fact, ‘alluvium is one continuous and conformable series of fluviatile and subaerial deposits, mainly composed of unconsolidated beds of clay, sand, gravel, and their mixture in varying proportion’. The basement of alluvial depos­its and their exact thickness could not be ascertained inspite of several attempts.

According to Oldham the thickness of alluvium ranges between 4000-6000m whereas Glennie’s estimate of alluvium depth comes to about 2000m. Ganga alluvia are classified into khadar and bhangar. Khadar represents alluvial depos­its in the riverine tracts or the flood plains of the rivers where the constituents of khadar i.e., silt, caly and sand, are renewed almost every year due to alluviation fol­lowed by floods.

On the other hand, bhangar represents older alluvium of relatively higher lands which are not submerged under water during floods. The Bhabar and Tarai regions contain gravel deposits comprising coarse sands, pebbles and cobbles with clay and silt.

‘One distinctive character of the bhangar is the formation of kankarpans (hardpans) in the sub-soil zone through capillary action owing to the alternating calcareous sand and clay beds here as also elsewhere in the zone of seasonal rainfall, which adds to soil moisture reten­tion in the subsoil zone’.

D.C. Dassarma and S. Biswas (1971-72) estab­lished the following stratigraphic successions of the Quaternary alluvium deposits resting over the Vindhyan basement in the alluvial-filled Belan basin (Allahabad district, U.P.) from below upward:

(i) Gravel-mottled clay formation,

(ii) Red brown gravel-sand formation,

(iii) Yellow silt formation,

(iv) Caliche formation,

(v) Buried soil layer,

(vi) Aeolian sand formation, and

(vii) Modern soil horizon.

The sequence of older and newer alluvia is repeated throughout upper, middle and lower Ganga plains but ‘there is conspicuous absence of older allu­vium in the delta region, which is quite extensive in the northern parts of the region’.

Physiographic Regions of Ganga Plain:

Geomorphologically, the entire Ganga plain is monotonous as no significant bold reliefs of mountain­ous and dissected plateau regions are found. Extensive flood plains, natural levees, sharp meanders, ox-box lakes, gullied riparian tracts, braided channels, bluffs etc. are the only morphological features of the Ganga plain.

Though the entire Ganga plain exhibits geomorphological homogeneity but it is divided into three regions following R.L. Singh (1971) viz.:

(1) Upper Ganga plain,

(2) Middle Ganga plain, and

(3) Lower Ganga plain.

(1) Upper Ganga Plain:

Upper Ganga Plain lies between the Yamuna valley in the west and 100m contour in the east cover­ing an area of 1,49, 029 km2 of Uttar Pradesh. The drainage of the area comprises two drainage systems of the Ganga and the Yamuna (It may be mentioned that the Yamuna is also a tributary of the Ganga and hence the upper Ganga plain is drained by a single drainage system i.e. the Ganga drainage system).

Most of the streams adopt parallel courses and join the master streams at acute angles. Extremely low channel gradi­ent because of almost level plain country makes the rivers sluggish and their erosive power is markedly reduced. The drainage pattern is pinnate but the overall pattern is dendritic. Significant rivers are the Yamuna, the Ganga, the Ramganga, the Gomati, the Ghaghra and their numerous tributaries.

Though linear erosion is very limited but the areal erosion in the form of soil erosion is more wide­spread in the Ganga plain. Soil erosion is the most common widespread geo-environmental problem of the major catchment areas of big rivers in Uttar Pradesh, Micropedogenic erosional processes are the primary and basic mechanism responsible for the soil loss.