Chapter 3 Drainage

Drainage Systems In India

The drainage system of an area refers to its river network. Rivers, flowing from higher elevations, converge to form a main river that eventually drains into larger water bodies like seas or oceans. A drainage basin is the area drained by a single river system. An elevated landform, known as a water divide, separates adjacent drainage basins.

India's drainage systems are primarily shaped by its relief features, leading to a classification of rivers into two main groups:

• Himalayan Rivers: These are mostly perennial, meaning they have water throughout the year, fed by both rainfall and melting snow. They originate north of the Himalayan ranges, have long courses, perform significant erosion in their upper reaches, and form meanders, ox-bow lakes, and deltas in their lower courses.
• Peninsular Rivers: Many of these rivers are seasonal, their flow dependent on rainfall. They have shorter and shallower courses compared to Himalayan rivers. While some originate in central highlands and flow west, most rise in the Western Ghats and flow east into the Bay of Bengal, forming deltas.

The Indus River System

Originating in Tibet near Lake Mansarowar, the Indus river flows west, entering India in Ladakh. It is joined by tributaries like the Zaskar, Nubra, Shyok, and Hunza in Kashmir. After flowing through Baltistan and Gilgit, it emerges at Attock. In Pakistan, it is joined by the Satluj, Beas, Ravi, Chenab, and Jhelum near Mithankot before emptying into the Arabian Sea. The Indus basin is largely in Pakistan, with a smaller portion in India. India utilizes about 20% of the Indus water system for irrigation in Punjab, Haryana, and parts of Rajasthan.

The Ganga River System

The Ganga originates as the Bhagirathi from the Gangotri Glacier and merges with the Alaknanda at Devaprayag. Emerging onto the plains at Haridwar, it is joined by Himalayan tributaries like the Yamuna (rising from Yamunotri Glacier and meeting Ganga at Allahabad), Ghaghara, Gandak, and Kosi (originating in the Nepal Himalaya). These rivers often cause floods but enrich the soil. Peninsular tributaries include the Chambal, Betwa, and Son. The Ganga flows east to Farakka in West Bengal, where it bifurcates. The Bhagirathi-Hooghly distributary flows south to the Bay of Bengal, while the main stream enters Bangladesh, joins the Brahmaputra, and flows as the Meghna into the Bay of Bengal, forming the vast Sundarban Delta.

The Brahmaputra River System

Rising in Tibet east of Lake Mansarowar, the Brahmaputra is slightly longer than the Indus but mostly flows outside India. It flows east parallel to the Himalayas, takes a "U" turn at Namcha Barwa, and enters India in Arunachal Pradesh through a gorge, where it's called Dihang. Joined by Dibang, Lohit, and other tributaries in Assam, it forms the Brahmaputra. Known as Tsang Po in Tibet and Jamuna in Bangladesh, it carries less water and silt in Tibet but carries significant water and silt in Assam due to high rainfall. It features braided channels and numerous riverine islands. Floods are common in Assam and Bangladesh due to the river's overflow.

The Himalayan Rivers

These rivers are characterized by their long courses, perennial nature, significant erosional and depositional activities, and the formation of deltas. The three major Himalayan river systems are the Indus, Ganga, and Brahmaputra, each with numerous tributaries that contribute to their vast drainage basins.

The Peninsular Rivers

The Western Ghats act as the primary water divide for Peninsular India. Most major rivers like the Mahanadi, Godavari, Krishna, and Kaveri flow eastwards into the Bay of Bengal, forming deltas. The Narmada and Tapi are notable exceptions, flowing westwards through rift valleys into the Arabian Sea, forming estuaries instead of deltas. Peninsular river basins are generally smaller than those of the Himalayan rivers.

The Narmada Basin

Originating from the Amarkantak hills in Madhya Pradesh, the Narmada flows west through a rift valley, creating picturesque locations like the Marble Rocks and Dhuadhar Falls. Its tributaries are short and mostly join at right angles. The basin covers parts of Madhya Pradesh and Gujarat.

The Tapi Basin

Rising in the Satpura ranges, the Tapi also flows through a rift valley, parallel to the Narmada but is shorter. Its basin includes parts of Madhya Pradesh, Gujarat, and Maharashtra. The narrow western coastal plains mean west-flowing rivers are short, with notable examples being the Sabarmati, Mahi, Bharathpuzha, and Periyar.

The Godavari Basin

The Godavari, the longest Peninsular river (approx. 1500 km), rises in Maharashtra and drains into the Bay of Bengal. Its basin is the largest among Peninsular rivers, covering parts of Maharashtra, Madhya Pradesh, Odisha, and Andhra Pradesh. Known as the 'Dakshin Ganga', its major tributaries include Purna, Wardha, Pranhita, Manjra, Wainganga, and Penganga.

The Mahanadi Basin

Originating in the highlands of Chhattisgarh, the Mahanadi flows through Odisha to the Bay of Bengal. Its length is about 860 km, and its basin is shared by Maharashtra, Chhattisgarh, Jharkhand, and Odisha.

The Krishna Basin

Rising near Mahabaleshwar, the Krishna flows for about 1400 km to the Bay of Bengal. Its tributaries include Tungabhadra, Koyana, Ghatprabha, Musi, and Bhima. The basin covers Maharashtra, Karnataka, and Andhra Pradesh.

The Kaveri Basin

The Kaveri originates in the Brahmagiri range of the Western Ghats and flows into the Bay of Bengal in Tamil Nadu. Its length is about 760 km, with tributaries like Amravati, Bhavani, Hemavati, and Kabini. The basin covers parts of Karnataka, Kerala, and Tamil Nadu. It forms the Shivasamudram Falls, a source of hydroelectric power.

Lakes

India has numerous lakes, varying in size and characteristics. Most are freshwater lakes, often of glacial origin in the Himalayas (e.g., Wular Lake in J&K is the largest freshwater lake, formed by tectonic activity; Dal, Nainital are others). Lakes can also form from wind action, river deposition (ox-bow lakes, lagoons like Chilika, Pulicat, Kolleru), or human activities like dam construction (e.g., Guru Gobind Sagar). Seasonal lakes exist in semi-arid regions (e.g., Sambhar lake in Rajasthan, a salt-water lake used for salt production). Lakes regulate river flow, prevent floods, help in power generation, moderate climate, maintain ecosystems, and are vital for tourism and recreation.

Role Of Rivers In The Economy

Rivers are fundamental to human civilization and the economy. Riverbanks have historically attracted settlements that grew into cities. Rivers provide essential resources for irrigation, navigation, and hydropower generation, which are particularly crucial for India's agriculture-dependent economy. They also support fishing and tourism.

River Pollution

Increasing demands for water from domestic, municipal, industrial, and agricultural sectors lead to excessive water withdrawal, reducing river volumes. The dumping of untreated sewage and industrial effluents further pollutes rivers, diminishing their self-cleansing capacity. Rising pollution levels, especially in rivers like the Ganga, have prompted government action through initiatives like the Ganga Action Plan (1985) and the National River Conservation Plan (NRCP) (1995) to improve water quality.

Exercise

The chapter's exercises focus on understanding India's river systems and lakes. They include identifying the location of lakes (Wular, Sambhar, etc.), sources of rivers (Narmada, Indus, Ganga, etc.), and distinguishing between Peninsular river types (longest, rift valley flow). Students are asked to differentiate between Himalayan and Peninsular rivers, compare east and west-flowing Peninsular rivers, and explain the economic importance of rivers. Map skills involve locating major rivers and lakes on an outline map of India, and a crossword puzzle reinforces knowledge of river names and related features.