Bihar is situated between 24° 20' 10" North & 27° 31' 15" North latitudes and 83° 19' 50'' East & 88° 17' 40'' East longitudes. It is 483 Km long (East to West) and 345 Km wide (North to South). Bihar is 12th largest state in India having total area of 94,163 Sq. km.
Bihar is situated between the humid, West Bengal (West) and the sub-humid, Uttar Pradesh (in East) . Hence Bihar has transitional climate between humid and and sub-humid.
Bihar is divided into three physiographic regions:-
- Shiwalik Ranges and Terai Region
- The ganga Plains
- Southern Plateau Region
Shiwalik Ranges and Terai Region
The extension of of Shiwalik Ranges and it's Terai Region are found in North-western part of Western Champaran in Bihar. It is spread in 932 sq. Km. This region represents Tertiary Rock System in Bihar. It is further subdivided into three parts:-
Ramnagar Doon
This is the southern most part of Terai Region and spread into 214 sq. Km area. The highest altitude in this region is about 240 metres.
Someshwar Ranges
This is an extension of Shiwalik Ranges in Bihar and i is the Northern most part of Bihar running over 75 sq. Km and the maximum altitude of the Range is 874 metre, which is also the highest point in Bihar.
It extends from Triveni Canal (in the West) to Bhikhnathori(in the East).
It ha many passes, which are formed due to flow of rivers coming from Nepal. Some of the important passes are Someshwar, Bhikhnathori and Marawat Pass. These passes form route for Nepal from Bihar.
Doon Valley/Harha Valley
This region lies between Ramnagar Doon and Someshwar Ranges. Harha river passes through this valley, because of which, it is also known as Harha Valley.
It is spread in 643 sq. Km. The elevation of this region is higher than the Northern plain of Bihar but it is also plain.
Also Read: Geological Structure of Bihar
The Ganga Plains
This extends from Nepal in the North to Chhotanagpur plateau in southern Bihar. It is spread in 450000 sq. Km, which is about 50% of the total geographical area of Bihar. This is formed by continuous flow of Ganga and it's it's tributaries for millions of years which brought and still bringing alluvial fans and deposited in the trough between the Himalayas and the Peninsular India. It is divided into two parts:-
- The Northern Plains of Bihar
- The Southern Plains of Bihar
The Northern Plains of Bihar
This region extends from Nepal to ganga river and are formed due to deposition of alluvium brought by the Northern tributaries of Ganga in Bihar i.e. Ghaghara, Gandak, Bagmati, Burhi Gandhak, Koshi, Mahananda etc. It also represent the Quaternary Rock system in Bihar.
The revers in Northern plains of Bihar divide it in many Doabs, but the important Doabs in Northern plains are :-
- Ghaghra-Gandak Doab
- Gandak-Koshi Doab
- Koshi-Mahananda Doab
The Northern Plains are down sloping from Nepal in North towards the Ganga river. Gradient of slope is more in this plain than the Southern part of Bihar,. Which results into more erosion due to increased Kinetic Energy which helps in increasing carrying capacity of the rivers in this region. Which is also supported large amount outflow of water from Nepal into India. These rivers generally bring floods in Northern Bihar especially Madhubani, Supaul, Araria, Madhepura, Saharasa, Khagaria, Darbhanga etc.
This region is mainly plain and same everywhere but still differ due to differences in flow of rivers. Koshi, Gandak and Ganga Basin differ from each other significantly.
The Northern part bordering Nepal is swampy in nature while middle part is quite elevated while near Southern bank of Ganga many interesting fluvial landforms are found which are as follows:-
- Diara
- Chaur/Chharan Lake
Diara
These are formed by rivers, when it found hard bedrock in the way of their flow, which lead to formations of two branches of the river and again both branches aligned with each other. Hence a standalone land surface is formed between both the branches of the river.
The Diara region is highly fertile due to the presence new alluvium (Khadar) and availability of water is sufficient .
Example:- Raghopur Diara.
Chaur /Chharan Lake
These are standalone lakes, found in Northern plains. These are formed due to drying of branches of rivers in summer season. These branches are formed in Rainy when excess water come in main channel of the river then it tends ot form branches which cut down from the main channel during summer due to decreased flow in hte main channel of the river.
Southern Plains of Bihar
This region quite complex in terms of physiographical features as it also have some hills coming out of the surface almost in every districts especially in the Southern parts of the district. It is formed due to outpouring of Batholith. Some important examples are Gaya Hills (266 metre), Rajgir Hills (466 metre), Kharagapur (510 metre), Barabar Hills and Giriak Hills.
The Western part of Southern Plains is much wider than the Eastern part. The slope of the Southern plain is quite gentler than the Northern plains. It's slope is about 6cm/Km from South to North towards Ganga Basin. Which results into formation of numerous swamps near southern bank of Ganga from Badh (Patna) to Bhagalpur. These Swamps in Bihar known as 'Tal'.
Example:- Mokama Tal
This plain is made up of Sandy soil formed out of older alluvium (Bhangar) brought by Peninsular Rivers like Son, Punpun, Phalgu, Kiul, Ajay etc. This soil absorb water very readily but still the ground water level in this part is sufficient.
This region faces droughts almost after every 2-3 year. Which results into uncertainty of crops (especially Paddy cultivation) in this region.
Rivers of Southern Plains divide it into three parts:-
- Ganga-Son Doab :- Kaimur, Rohtas, Buxar and Bhojpur
- Plains of Magadh:- Central Part
- Plains of Ang:- Eastern Part
Southern Plateau Region.
This is found in the southern flanks of Bihar between Southern Plain and Chhotanagpur Plateau of Jharkhand. basically it is located between Kaimur in the West to Banka in the East.
This region is blessed with many conical Hills which are made of batholith, like Pretshila, Ramshila and Jethian Hills etc.
It is made up of hard rocks like Gneiss, Schist and Granite etc. This region is rich in minerals and almost all mineral resources of Bihar are found from this region itself.
This can be further divided into two parts:-
Western Part
Extention of Chhotanagpur Plateau in Bihar. It is spread in Kaimur, Rohtas Aurangabad, Gaya, Nawada and some parts of Jamui.
Eastern Part
This is an extension of Rajmahal Hills (Oldest Part in Bihar). It extends from Bhagalpur, Munger, Banka, and some parts of Jamui.