Drainage Systems in India

Correct answer: A. Separating two river basins

The direct answer is option A, separating two river basins. A water divide is a highland, ridge, or elevated area that separates the flow of rainwater into two different drainage basins. A drainage basin is the area from which a river and its tributaries collect water. For example, water falling on one side of a ridge may flow into one river system, while water falling on the other side flows into another system. Thus the main work of a water divide is to mark the boundary between two drainage areas. Option A is correct because it describes this exact function. Option B, joining a river to the sea, is not the work of a divide; a river channel carries water towards a lake or sea. Option C, forming distributaries in a delta, happens near a river mouth when the main channel divides, not on a water divide. Option D, making a lake salty, is unrelated to drainage boundaries and depends on evaporation, minerals, and water balance. Remember that a divide divides water flow, not joins it. Exam cue: high ridge plus two directions of runoff means water divide.

Correct answer: B. Erosion

In the upper course the slope is steep so erosion is stronger. Exam tip: connect upper course with valley formation.

Correct answer: A. Deposition

In the lower course river speed decreases and sediments are deposited. Exam tip: connect lower course with deltas and flood plains.

Correct answer: A. By a river depositing alluvium during floods

During floods a river spreads alluvium over nearby land. Exam tip: connect flood plains with deposition.

Correct answer: B. At the mouth of a river

A delta forms at a river mouth due to sediment deposition. Exam tip: connect delta with the final part of a river.

Correct answer: A. Sea tides

Sea tides have greater influence in an estuary. Exam tip: remember Narmada and Tapi as examples.

Correct answer: B. Untreated wastewater and waste

Direct answer: Option B is correct. River pollution commonly occurs when untreated sewage, wastewater, industrial discharge, plastics, or other waste enters a river. ‘Untreated’ means the harmful material has not been cleaned or processed before release. The step-by-step chain is: human activity produces waste; waste enters the river; pollutants change water quality and may harm aquatic life and human health. Option A is wrong because properly treated clean water is not normally a pollution source. Option B directly names untreated wastewater and waste, so it is correct. Option C is wrong because protecting forests generally reduces erosion and supports cleaner water. Option D is wrong because rainwater harvesting conserves water and does not normally pollute a river. Memory cue: untreated waste entering water means pollution.

Correct answer: B. Releasing sewage only after treatment

Sewage and other wastewater may contain germs, harmful chemicals, and large amounts of organic matter. If it enters a river without treatment, it can lower water quality, harm aquatic organisms, spread disease, and make the water unsafe for people. Treatment removes or reduces many pollutants before the water is released. Preventing waste at the source and monitoring discharge are also useful parts of river protection.

Option B is correct because sewage should be treated before it is discharged into a river. Throwing rubbish directly into the water increases pollution, while unplanned construction can damage banks and natural drainage. Stopping a river’s flow does not remove pollutants and can create other environmental problems. Thus, treatment is the most suitable measure among the given choices.

Correct answer: A. By providing irrigation water and fertile soil

The direct answer is A, by providing irrigation water and fertile soil. Rivers are important to agriculture in two main ways. First, their water can be carried through canals, wells, pipelines or other irrigation systems to fields when rainfall is insufficient. Second, rivers deposit fine alluvial soil on floodplains and in deltas. This soil often contains useful mineral material and can support good crop growth when managed properly. Option B is impossible and harmful because rivers do not help farming by drying the sea. Option C concerns coral formations, not the normal agricultural role of rivers. Option D is unrelated: rivers do not help agriculture by lowering the Himalaya. Thus A gives both correct benefits—water and fertile alluvium. Floods can sometimes damage crops, so river benefits must be managed with embankments, planning and conservation, but the basic answer remains A. Memory cue: rivers bring water and alluvium; both support farming.

Correct answer: A. Availability of water and fertile land

River valleys provide water and farmland so they attract settlements. Exam tip: study rivers with human life.

Correct answer: A. Krishna

Krishna flows eastward into the Bay of Bengal. Exam tip: group Krishna with Godavari and Cauvery.

Correct answer: C. Narmada

The Narmada is a major west-flowing Peninsular river. It flows across central India and drains into the Arabian Sea. Godavari, Mahanadi, and Cauvery generally flow eastward into the Bay of Bengal. Exam tip: remember Narmada and Tapi as the major west-flowing Peninsular rivers.

Correct answer: D. Godavari

Godavari belongs to the Peninsular river system. Exam tip: remember Ganga tributaries in a separate list.

Correct answer: D. Cauvery

The direct answer is option D, Cauvery. The Indus drainage system includes the Indus and its major tributaries such as Jhelum, Chenab, Ravi, Beas, and Sutlej. These rivers mainly drain the northwestern part of the Indian subcontinent and ultimately belong to the Indus system. Jhelum in option A is one of the important tributaries of the Indus. Chenab in option B is also an Indus tributary, formed by the meeting of the Chandra and Bhaga rivers. Ravi in option C is another important tributary of the Indus. Cauvery in option D is different: it is a peninsular river of southern India, rises in Karnataka, flows generally eastward, and enters the Bay of Bengal. Therefore it does not belong to the Indus system. The question asks which river does not belong, so select the one from another drainage system. Memory cue: Jhelum, Chenab, Ravi, Beas and Sutlej are Indus-system names; Cauvery is a southern peninsular river.

Correct answer: A. Mangrove forests

Direct answer: Option A, mangrove forests, is correct. The Ganga and Brahmaputra deposit enormous amounts of sediment and form a vast delta at the head of the Bay of Bengal. Its tidal, muddy, saline, and frequently waterlogged environment supports mangroves. The best-known part is the Sundarbans, famous for dense mangrove vegetation and tidal channels. Option A therefore matches both the delta environment and the famous vegetation. Option B, cactus forests, are associated with dry desert or semi-desert conditions, not tidal delta wetlands. Option C, deodar forests, are mountain conifer forests found in high Himalayan areas. Option D, grass deserts, is not the characteristic vegetation of this humid, tidal delta. Memory cue: Sundarbans means Ganga–Brahmaputra delta and mangroves.

Correct answer: A. Alluvium

A river carries alluvium and deposits it in plains. Exam tip: connect alluvium with fertile soil.

Correct answer: A. Slope of land

Rivers generally flow from higher to lower areas according to slope. Exam tip: remember slope with flow direction.

Correct answer: A. Most rivers flow over old hard landmass

Peninsular rivers flow over old hard plateau regions. Exam tip: connect Peninsular rivers with old landmass.

Correct answer: B. Rivers are long and perennial

Himalayan rivers are long and carry water throughout the year. Exam tip: connect Himalayan rivers with perennial nature.

Correct answer: A. Source, tributaries, direction and mouth

A river system includes the whole course and branches of a river. Exam tip: study a river from source to mouth.

Correct answer: A. Due to erosion and deposition processes

Bends may develop due to erosion and deposition along river banks. Exam tip: treat river course as dynamic.

Correct answer: A. Alluvial soil

After floods a river may leave alluvial soil useful for farming. Exam tip: remember the link between flood plains and fertile soil.

Correct answer: A. It shows which sea or bay the river joins

River direction helps identify its final water body. Exam tip: remember flow direction and mouth together.

Correct answer: A. In the upper course where slope is steep

Waterfalls can form in the upper course due to steep slope. Exam tip: connect waterfalls with erosion and steep gradient.

Correct answer: A. They help supply water to fields

Rivers are an important source of irrigation water for agriculture. Exam tip: connect river importance with agricultural production.