O-Level Geography Chapter 1 Topography of Pakistan Indus Plain

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Indus Plain

The Indus Plain is divided into two regions; the Upper Indus Plain and the Lower Indus Plain. The Upper Indus Plain extends from areas below Kashmir and Lesser Himalayas to Mithankot. The Lower Indus Plain extends from Mithankot to the Indus Delta.

Features:

• Upper Indus Plain In the upper Indus plain there are doabs (a doab is a land between two rivers) e.g. Bari Doab
• Bars (alluvial terraces) are also present, which are 7-12m high e.g. the Nilli and Ganji Bars.
• The rivers keep on changing their course slightly (meanders).
• There are levees along the river bed, which help contain the river.
• Active flood plains are present alongside the river; these are low lying areas of flat land, which are annually flooded in the rainy season. The active flood plain is made up of new alluvium
• The old flood plains are also present. They are flat areas, which are higher than active flood plains. They are made up of old alluvium, which had been deposited a decade ago. They’re flooded after a decade or so, when strong monsoon winds combine with the heavy melting of snow and ice in the glaciers of the Northern Mountains.
• Piedmont plains are found at the foothills of the Himalayas in the Salt Range. They are formed by the deposition of material by hill torrents, when they lose their speed. Kirak Hills exist between the River Chenab and Jhelum.

Lower Indus Plain

• The Lower Indus Plain principally differs from the Upper Indus Plain due to presence of a tidal delta (the Indus Delta) and also because in the Lower Indus Plain only one river that is, the river Indus, flows.
• Indus delta exists in some of the southern parts of the Lower Indus Plain. A delta is a low lying triangular area which has alluvial deposits.
• the river divides into distributaries before entering a larger body of water (in this case the Arabian Sea). The delta exists because of the deposition of material carried by the river. This happens because when the river enters into the sea, it loses its speed and thus also loses its ability to hold this material, which is therefore deposited at the mouth of the river.
• In the lower Indus Plain, we may find limestone ridges which are known as cuestas, a few examples being; Rohri and Gango Takar Cusetas.
• Oxbow lakes are also present in the lower Indus plain.
• Active and Old Flood Plains are also present, but a doab and alluvial terraces are absent. Meanders however are present too.
• Piedmont Plains are present at the foothills of Kirthar and Sulaiman Mountain ranges.
• Part of the Indus plain that extends into Balochistan is known as the Kachi Sibi Plain. Both these plains have rolling sand dunes (Thal and Thar deserts), flat plain areas, have some low lying hills, oxbow lakes and meanders etc.
• The main differences are the number of tributaries and distributaries (delta) in both the plains,
• The Upper Indus Plain is also a bit higher than the low lying Lower Indus Plain. Considering the altitude of these two plains, we see that it decreases from North towards the South generally.

Drainage of Indus Plain

The Lower Indus plain is drained by the River Indus mainly flowing in the North-South direction. Meanders and oxbow lakes also exist. Piedmont plains exist in-between the river Indus and Sulaiman and Kirthar Mountain ranges. In the Upper Indus plain, River Indus and its Eastern tributaries flow in North- South direction. Tributaries are Jhelum, Chenab, Ravi and Sutlej. Meanders and oxbow lakes also exist.

Meanders zigzag pattern of rivers is called Meander.

• Oxbow Lake Crescent shaped part separated from a curve of Meander is known as ox-bow Lake. it is a temporary feature.
• Levees Natural increase of land near river banks is called levees. This is because of the deposition of sediments alongside the river banks.( Embankment walls are artificially man-made walls alongside the river bank).

Active Flood Plain:

It is a flat plain on both sides of a river, which suffers annual floods during the rainy season. It is around 2-3m above the level of a river. It is around 10-20km long. The river always changes its position, thus meanders have come into existence. Abandoned (dry) and braided channels are also visible in the dry season. Meanders, oxbow lakes and embankments of a river can be seen as well. Soils of loam and silt (Alluvial Soils), which are good for farming, are present in both the UIP and LIP.

Old flood Plain:

It is higher than active flood plain around 5m higher than river level. It is around 10-20m long. It is made up of old alluvium. Evidence of meanders and of levees is present in these plains. Oxbow lake depressions can also be seen. The old flood plains are present in both UIP and LIP. 

Bars (Alluvial Terraces)

These are flat areas which are only found in the Upper Indus plain. They are 7-12m high and last for 25-35km. They are made up of areas of silt and clay. In Pakistan all the bars have a south west direction.

Scarp

Scarp is a slope,, which separates the old flood plain from the bar upland. It is around 20m long and 11m high above the river level. It is made when old alluvium on the bar upland is eroded, thus, leaving a slope which connects both old flood plain and the bar upland.

Rivers and Doabs of UIP / LIP

CHAJ doab lies between CHEnab and Jhelum rivers.

RACHNA lies between RAvi and CHENAb rivers.

BARI doab lies between BEAs and RavI rivers.