Part VI — Physical Geography of Bihar
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Chapter 6: Rivers, Plains, Climate, and Natural Resources
6.1 Physiographic Divisions
Bihar lies almost entirely within the middle Gangetic plain, a vast alluvial tract formed by the Ganga and its tributaries. The state is conventionally divided into two broad physiographic zones by the Ganga, which flows west to east through the middle of the state: North Bihar (Trans-Gangetic plain), a flat, low-lying, flood-prone tract fed by fast-flowing Himalayan-origin rivers; and South Bihar (Cis-Gangetic plain), a comparatively higher, more stable plain fed by slower-moving, rain-fed rivers originating in the Chotanagpur Plateau region (now largely in Jharkhand). A small hilly tract in the extreme south (Rajgir hills, Kaimur range spurs) provides Bihar's only significant relief above the plains.
6.2 The River Systems of Bihar
The Ganga is Bihar's principal river, entering the state near Buxar in the west and exiting near Rajmahal (in present-day Jharkhand) in the east, dividing the state into its northern and southern halves. Its major tributaries define Bihar's river geography:
North Bihar (Himalayan-origin) rivers: the Gandak, originating in Nepal, notorious for its shifting course and flood potential; the Kosi, often called the "Sorrow of Bihar" for its extreme flood-proneness and history of dramatically shifting its course across North Bihar over centuries (a westward shift of over 100 km within recorded history); the Bagmati, also flood-prone, flowing through the Mithila region; and the Ghaghara (Sarayu), forming part of Bihar's western boundary with Uttar Pradesh in places.
South Bihar (Peninsular/Plateau-origin) rivers: the Son, Bihar's largest south-bank tributary of the Ganga, regulated by the Indrapuri Barrage; the Punpun; and the Falgu, a seasonal river at Gaya famous for its association with Hindu funerary rites (Pind Daan) at the Vishnupad Temple, where the river famously flows partly underground for much of the year.
6.3 Climate
Bihar has a subtropical, monsoon-influenced climate with three broad seasons: summer (March–June, hot and dry, with maximum temperatures often exceeding 40°C in districts like Gaya and Bhojpur), the monsoon season (June–October, bringing the bulk of annual rainfall via the southwest monsoon), and winter (November–February, mild but with occasional cold waves, particularly affecting North Bihar due to proximity to the Himalayan foothills). Average annual rainfall varies across the state, generally decreasing from northeast to southwest, with North Bihar receiving comparatively higher rainfall than the southern districts.
6.4 Floods — Bihar's Defining Natural Hazard
Bihar is India's most flood-prone state by proportion of its geographical area affected, with roughly three-quarters of North Bihar's land area vulnerable to periodic flooding. This vulnerability stems from the combination of low-gradient, silt-choked river channels, the steep drop in elevation as Himalayan rivers enter the plains (causing them to deposit sediment and shift course unpredictably), and heavy monsoon and glacial-melt discharge from Nepal's catchment areas. The Kosi's history of course changes has made flood management — through embankments, barrages (such as the Kosi Barrage at Bhimnagar, near the Nepal border), and more recent proposals for high dams within Nepal — a persistent and politically significant policy challenge for the state.
6.5 Soil Types
Bihar's soils are predominantly alluvial, deposited by its river systems, and are broadly classified into newer alluvium (Khadar), found in low-lying areas closer to riverbeds and renewed annually by flood-deposited silt, and older alluvium (Bhangar), found on slightly elevated terraces less affected by annual flooding. These alluvial soils, particularly in North Bihar, are highly fertile and support the state's predominantly agrarian economy, discussed further in the next chapter.
6.6 Forests and Natural Resources
Bihar's forest cover is comparatively limited (among the lowest forest-cover percentages of Indian states), concentrated mainly in the southern districts bordering Jharkhand (Kaimur, Rohtas) and in the Himalayan foothill districts of the northwest (West Champaran, home to the Valmiki Tiger Reserve, Bihar's only tiger reserve and part of the Valmiki National Park). Mineral resources are limited following Jharkhand's separation, which took most of undivided Bihar's mineral-rich Chota Nagpur tracts; present-day Bihar's mineral profile is dominated by minor minerals (sand, stone, mica in small quantities) rather than the coal and iron ore that now belong to Jharkhand.
6.7 Practice Set — Physical Geography (25 MCQs)
- Bihar lies almost entirely within which physiographic region?
(a) The Deccan Plateau (b) The middle Gangetic plain (c) The Thar Desert (d) The Western Ghats - Which river divides Bihar into North and South Bihar?
(a) Son (b) Kosi (c) Ganga (d) Gandak - Which river is popularly called the "Sorrow of Bihar" due to its extreme flood-proneness and shifting course?
(a) Gandak (b) Kosi (c) Bagmati (d) Son - The Kosi river originates in which country?
(a) India (b) Nepal (c) Bhutan (d) China - Which river is Bihar's largest south-bank tributary of the Ganga?
(a) Son (b) Punpun (c) Falgu (d) Bagmati - The Falgu river, associated with Pind Daan rites at Gaya, is notable for:
(a) Being the largest river in Bihar (b) Flowing partly underground for much of the year (c) Never drying up at any point (d) Originating in Nepal - The Indrapuri Barrage regulates which river?
(a) Kosi (b) Son (c) Gandak (d) Bagmati - The Kosi Barrage, a key flood-management structure, is located at:
(a) Patna (b) Bhimnagar (c) Gaya (d) Muzaffarpur - Bihar's climate is best classified as:
(a) Arid desert (b) Subtropical, monsoon-influenced (c) Equatorial (d) Mediterranean - Bihar's rainfall generally varies across the state in which pattern?
(a) Uniform everywhere (b) Decreasing from northeast to southwest (c) Increasing from north to south (d) Highest in the extreme south only - Newer alluvium, renewed annually by flood-deposited silt, is known as:
(a) Bhangar (b) Khadar (c) Laterite (d) Black cotton soil - Older alluvium, found on slightly elevated terraces, is known as:
(a) Khadar (b) Bhangar (c) Regur (d) Red soil - Bihar's only tiger reserve is located in which district?
(a) Gaya (b) West Champaran (c) Rohtas (d) Bhagalpur - The Valmiki Tiger Reserve is part of which larger protected area?
(a) Valmiki National Park (b) Kaimur Wildlife Sanctuary (c) Bhimbandh Wildlife Sanctuary (d) Gautam Buddha Wildlife Sanctuary - Jharkhand's separation from Bihar in 2000 primarily affected Bihar's:
(a) River systems entirely (b) Mineral and forest resource base (c) Agricultural soil quality (d) Climate patterns - Which of the following rivers is NOT a Himalayan-origin (North Bihar) river?
(a) Gandak (b) Kosi (c) Son (d) Bagmati - Roughly what proportion of North Bihar's land area is considered flood-vulnerable?
(a) About one-quarter (b) About one-half (c) About three-quarters (d) Effectively none - Bihar's forest cover, compared to other Indian states, is:
(a) Among the highest (b) Among the lowest (c) Exactly average (d) Not measurable - The Ghaghara (Sarayu) river forms part of Bihar's boundary with:
(a) Nepal (b) Uttar Pradesh (c) Jharkhand (d) West Bengal - Bihar's two broad physiographic zones, divided by the Ganga, are known as:
(a) North Bihar and South Bihar (b) Eastern Bihar and Western Bihar (c) Upper Bihar and Lower Bihar (d) Coastal Bihar and Inland Bihar - The steep drop in elevation as Himalayan rivers enter Bihar's plains primarily causes:
(a) Rivers to dry up completely (b) Sediment deposition and unpredictable course shifts (c) Permanent river straightening (d) No effect on river behaviour - Which season in Bihar brings the bulk of the state's annual rainfall?
(a) Summer (March–June) (b) Monsoon (June–October) (c) Winter (November–February) (d) Rainfall is evenly spread year-round - Bihar's hilly tract in the extreme south, providing its only significant relief above the plains, includes spurs of the:
(a) Kaimur range (b) Himalayan range directly (c) Aravalli range (d) Vindhya range's core, not a spur - The Kosi river's historical course shift across North Bihar has been documented as extending over:
(a) A few hundred metres (b) Over 100 km westward (c) Less than 1 km (d) It has never shifted course - Present-day Bihar's mineral profile, after Jharkhand's separation, is dominated by:
(a) Coal and iron ore (b) Minor minerals such as sand, stone, and small quantities of mica (c) Gold and diamonds (d) Petroleum reserves
Answer Key
1.(b)
2.(c)
3.(b)
4.(b)
5.(a)
6.(b)
7.(b)
8.(b)
9.(b)
10.(b)
11.(b)
12.(b)
13.(b)
14.(a)
15.(b)
16.(c)
17.(c)
18.(b)
19.(b)
20.(a)
21.(b)
22.(b)
23.(a)
24.(b) 25.(b)