The term Drainage describes the river systemof an area.The area drained by a single river system iscalled a drainage basin.Any elevated area, such as a mountain or anupland which separates two drainage basins,is known as a water divide.
A drainage system is the pattern formed by the streams, rivers, and lakes in a particulardrainage basin. They are governed by the topography of the land, whether a particularregion is dominated by hard or soft rocks, and the gradient of the land.Dendritic drainage systems are the most common form of drainage system. In adendritic system, there are many contributing streams (analogous to the twigs of a tree),which are then joined together into the tributaries of the main river (the branches and thetrunk of the tree, respectively). They develop where the river channel follows the slope ofthe terrain.The geometry of a trellis drainage system is similar to that of a common garden trellisused to grow vines. As the river flows along a strike valley, smaller tributaries feed into itfrom the steep slopes on the sides of mountains. These tributaries enter the main river atapproximately 90 degree angles, causing a trellis-like appearance of the drainagesystem. Trellis drainage is characteristic of folded mountains.Rectangular drainage develops on rocks that are of approximately uniform resistance toerosion, but which have two directions of jointing at approximately right angles. The jointsare usually less resistant to erosion than the bulk rock so erosion tends to preferentiallyopen the joints and streams eventually develop along the joints. The result is a streamsystem in which streams consist mainly of straight line segments with right angle bendsand tributaries join larger streams at right angles.In a Radial drainage system, the streams radiate outwards from a central high point.Volcanos usually display excellent radial drainage. Other geological features on whichradial drainage commonly develops are domes and laccoliths. On these features thedrainage may exhibit a combination of radial and annular patterns.
Himalayan RiversNature of flow – Himalayan rivers are Perennial asreceive water from rainfall as well as snow melting.Catchment area - Very large basinsErosion - Deep valleys and gorges in the Himalayadue to intensive erosionNature of the course - Meandering course and shiftingbeds in the Great plainsOther features - V-shaped valleys, high waterfalls andhuge delta.Penisular RiversNature of flow - Seasonal dependent on rainfall aloneCatchment area – have shorter and shallowercourses as compared to Himalayan riversErosion - Shallow graded valleys with little erosionNature of the course - Straight and linear course.Other features - Shallow valleys, small waterfalls,delta and estuaries
The Indus River System –Rises in Tibet , near Lake Mansarowar, enters India in the Ladakh district of Jammu andKashmir.Tributaries in Kashmir are Zaskar, Nubra, Shyok and Hunza. Flows through Baltistan andGilgit, emerges from the mountains at Attock.Satluj, Beas, Ravi, Chenab and Jhelum join together to enter the Indus near Mithnakot inPakistan, eventually reaches Arabian sea, east of Karachi.Total length 2900 km. one of the longest rivers of the world.Drainage basin covers, states of Jammu and Kashmir, Himachal Pradesh, Punjab andthe rest is in Pakistan.
The Ganga River System –Bhagirathi is joined by Alaknanda at Devprayag in Uttranchal to form Ganga. At Haridwarthe Ganga emerges from the mountains on to the plains.Tributaries from the Himalayas – Yamuna, Ghaghara, Gandak and Kosi Himalaya.Chambal, Betwa and Son come from the Peninsular uplands.The Ganga flows eastwards till Farakka in West Bengal. This is the northernmost point ofthe Ganga delta. The river bifurcates here : Bhagirathi-Hooghly flows southwards.Mainstream flows southwards into Bangladesh and is joined by the Brahmaputra. Here it isknows as Meghna, finally flows into the Bay of Bengal before forming the Sunderban delta.Length of Ganga is 2500 km. The plains from Ambala to Sunderbans is nearly 1800 km butthe fall in the slope is hardly 300 metres, resulting in large meanders.
The Brahmaputra River System –Rises in Tiber east of Mansarowar lake, flows eastwardsparallel to the Himalayas, reaching Namcha Barwa (7757 m),it takes a ‘U’ turn and enters India in ArunachalPradesh.Is called Dihang, joined by Dibang, Lohit, Kenula and manyother tributaries to form the Brahmaputra in Assam.In India it passes through a region of high rainfall, carries alarge volume of water and considerable amount of silt, has abraided channel, forms many riverine islands.During the rainy season, the river overflows its banks, causingwidespread devastation due to floods in Assam andBangladesh.
An estuary is a partly enclosed coastal body ofbrackish water with one or more rivers orstreams flowing into it, and with a freeconnection to the open sea.Estuaries form a transition zone between riverenvironments and ocean environments andare subject to both marine influences, such astides, waves, and the influx of saline water;and riverine influences, such as flows of freshwater and sediment. The inflows of both seawater and fresh water provide high levels ofnutrients in both the water column andsediment, making estuaries among the mostproductive natural habitats in the worldA river delta is a landform that is formed at themouth of a river, where the river flows into anocean, sea, estuary, lake, or reservoir. Deltasare formed from the deposition of thesediment carried by the river as the flowleaves the mouth of the river. Over longperiods of time, this deposition builds thecharacteristic geographic pattern of a riverdelta.
The Peninsular River –The main water divide inPeninsular India is formed bythe Western Ghats.West flowing riverNarmada and Tapi are thewest flowing rivers ofpeninsular IndiaThese rivers make estuariesat their mouthThese rivers drain intoArabian seaEast flowing riverMahanadi, Godavari, Krishnaand Kaveri are the eastflowing rivers of peninsularIndiaThese rivers make deltas attheir mouthThese rivers drain into Bay ofBengalDrainage basins arecomparatively small in size
The Narmada Basin –Rises in the Amarkantak hills in Madhya Pradesh, flows west in a rift valley, creates manypicturesque locations.‘Marble rocks’, near Jabalpur and the ‘Dhuadhar falls’ are some of the notable ones.Narmada basin covers parts of Madhya Pradesh and Gujarat.
The Tapi Basin –Rises in the Satpura ranges, in the Betul district of Madhya Pradesh. Flows in a rift valleyparallel to the Narmada, but it is much shorter in length. Basin covers parts of MadhyaPrdesh, Gujarat and Maharashtra.
The Godavari Basin –Largest Peninsular river, rises from the slopes of the Western Ghats in the Nashik districtof Maharashtra.Length about 1500 km, drains into the Bay of Bengal, largest drainage basin amongstpeninsular river, covers parts of Maharashtra, Madhya Pradesh, Orissa and AndhraPradesh.Tributaries – Purna, Wardha, Pranhita, Manjra, Wainganga and the Painganga.Becouse of its length and area it covers, is also known as ‘Dakshin Ganga’.
The Mahanadi Basin –Rises in the highlands of ChattisgarhFlows through Orissa to reach Bay of Bengal, length about 860 km.Drainage basin is shared by Maharashtra, Chhattisgarh, Jharkhand and Orissa.
The Krishna Basin –Rises from a spring near Mahabaleshwar, flows for about 1400 km, reaches the Bay ofBengal.Tributaries – Tungabhadra, Koyana, Ghatprabha, Musi and the Bhima Drainage basin isshared by Maharashtra, Karnataka and Andhra Pradesh.
The Kaveri Basin –Rises in the Brahmagri range of the Western Ghats, reaches the Bay of Bengal in southof Cuddalore, in Tamil Nadu.Total length is about 760 km, drrains parts of Karnataka, Kerala and Tamil Nadu.Tributaries are Amravati, Bhavani, Hemavati and Kabini.
LakesLakes differ from each other in size and characterstics. Most lakes are permanent, somecontain water only during the rainy season, some of the lakes are the result of the actionof glaciers and ice sheets, some are formed by wind, river action and human activities.Meandering river forms cut-offs that later develop into ox-bow lakes. Spits and bars fromlagoons in the coastal areas, e.g. the Chilika Lake, the Puliket lake, the Kolleru Lake.Lakes in the region of inland drainage are sometimes seasonal, the Sambhar lake inRajasthan is a salt water lake.
Most of the fresh water lakes are in the Himalayan region. They are of glacial origin. TheWular lake (the largest freshwater lake in India) in Jammu and Kashmir is the result oftectonic activity. Dal Lake, Bhimtal, Nainital, Loktak and Barapani are some otherimportant fresh water lakes.The damming of the rivers for the generation of hydel power has also led to the formationof Lakes such as Guru Gobind Sagar (Bhakra Nangal Project).
Importance of Lakes –Helps to regulate the flow of a river, preventsflooding during heavy rainfall and during the dryseason helps to maintain even flow of water, canbe used for developing hydel power, moderate theclimate of the surroundings, maintain the aquaticecosystem, enhance natural beauty, helps developtourism and provide recreation.Role of Rivers in the EconomyWater from the rivers is a basic natural resourceThe river banks have attracted settlers fromancient times, many have developed as big citiesUsing rivers for irrigation, navigation, hydro-powergeneration is of special significance
River PollutionThe growing domestic, municipal, industrial andagricultural demand for water from rivers naturallyaffects the quality of water. As a result, more andmore water is being drained out of the riversreducing their volume. On the other hand, a heavyload of untreated sewage and industrial effluents areemptied into the rivers. This affects not only thequality of water but also the self-cleansing capacityof the river. But the increasing urbanization andindustrialization do not allow it to happen and thepollution level of many rivers has been rising.Concern over rising pollution in our rivers led to thelaunching of various action plans to clean the rivers.