NCERT-aligned Class 11 Geography topic. Every item is anchored to a real location on India's map — built for boards (CBSE, ICSE, state) and UPSC aspirants.
How do hydrologists define a DRAINAGE SYSTEM + a DRAINAGE BASIN?
A DRAINAGE SYSTEM is the network of streams, rivulets + rivers that together convey rainwater + groundwater discharge from a region toward the sea (or a lake or interior sink). Each system has its own GEOGRAPHIC FOOTPRINT — known as the DRAINAGE BASIN or CATCHMENT — defined as the total land area whose surface water flows into that particular river. Drainage basins are bounded by WATERSHEDS (ridges separating basins). India's major basins: Indus, Ganga-Brahmaputra-Meghna (combined), Mahanadi, Godavari, Krishna, Kaveri, Narmada, Tapi, west-flowing peninsular rivers, east-flowing peninsular rivers.
What is a watershed?
The boundary line separating one drainage basin from another — usually a ridge or upland.
Difference between drainage basin and watershed?
Drainage basin = the AREA drained by a river; Watershed = the BOUNDARY between two basins. ("Basin is bigger; watershed is the rim.")
What does the term RIVER SYSTEM mean in hydrology?
A RIVER SYSTEM consists of the main (trunk) river + every WATERCOURSE that feeds INTO it (tributaries) + every channel that flows OUT of it (distributaries, especially in deltas). The system gathers water from a wider DRAINAGE BASIN — the total land area that drains to that river — + delivers it to the sea, a lake, or sometimes inland into the desert. Major Indian examples: the INDUS system (Indus + Jhelum + Chenab + Ravi + Beas + Sutlej); the GANGA system (Ganga + Yamuna + Ghaghara + Gandak + Kosi etc.); the BRAHMAPUTRA system; the GODAVARI + KRISHNA + KAVERI + MAHANADI peninsular systems.
Two principal drainage classifications in India?
(i) On the basis of relief: Himalayan vs Peninsular; (ii) on the basis of size: major (>20,000 sq km), medium (2,000-20,000), minor (<2,000).
Are Himalayan rivers perennial or seasonal?
PERENNIAL — fed by both monsoon rainfall AND glacial melt; flow throughout the year.
Are Peninsular rivers perennial or seasonal?
Mostly SEASONAL — depend on monsoon rainfall; flow reduces drastically in dry season.
Which rivers are antecedent (older than Himalayas)?
Indus, Sutlej, Brahmaputra — they originated BEFORE the Himalayan uplift; cut deep gorges as the mountains rose.
What stage are Himalayan rivers in?
YOUTHFUL stage — fast-flowing, deep V-shaped valleys, gorges, waterfalls, rapids; intense erosional activity.
What stage are Peninsular rivers in?
MATURE stage — broad shallow valleys; meanders, ox-bow lakes, mostly fixed courses.
Drainage development of Peninsular rivers?
Have very long courses with non-perennial flow; flow with established gradients; mostly graded channels.
Why do most peninsular rivers flow east?
General slope of the Peninsular plateau is from west to east — Western Ghats are higher than Eastern Ghats.
This topic is part of the NCERT Class 11 Geography syllabus, drawn from the chapter Ch 3: Drainage System. Content is cross-referenced against the latest NCERT textbook editions + standard reference works.
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