Who has not seen a river? And who has then, not been moved by a fierce emotion? The common man sees its life granting blessed form, the government or CWC engineer sees in it as a potential dam project, the hydropower developers a site for hydro project, a farmer his crop vitality, fisher folk, boatspeople and river bed cultivators a source of livelihood, the industry & urban water utilities view it as their personal waste basket, the real estate developer as a potential land grab site, a sand miner as a source of sand and the distraught villager his lifeline. In earlier days, film makers used to see it as site for filming some memorable songs, but these days even that has become a rarity.
Rivers truly are a complex entity that invoke varied emotions and responses!
A river shifts in colour, shape, size, flow pattern of water, silt, nutrients and biota, in fact all its variables seem to change with time and space. The perceptions differ as one moves from mountains to plains to the deltas. The same stream displays a wide variance of characteristics that depend upon the land it flows through and the micro climate along its banks. Rivers many a times seem to mirror the local flavour of the land they flow through. Or is it the local flavour that changes with river flow? Clearly both are interdependent.
Today, as we talk of rivers, their rejuvenation and try to figure out their ecological flow and their health quotient , a good beginning to understand the existing rivers would be their classification modules. What defines a river? Which factors are used for their classification? How do we actually classify our rivers?
As far as the first of these questions is concerned, none of the official agencies have tried to define a river!
Possiby, the first post independence classification of river basins was attempted in 1949 by precuser institute of current Central Water Commission (CWC). Since then various organisations have followed their own methodology and criteria for basin classification and arrived at different numbers.
NIH (National Institute of Hydrology), Roorkee organises our 7 major rivers, that is the Brahmaputra (apparently this includes the Ganga and the Meghna), Godavri, Krishna & Mahanadi (that flow into the Bay of Bengal), and the Indus, Narmada & Tapi (which drain into the Arabian Sea) , along with their tributaries to make up the entire river system in our country. This is clearly problematic and chaotic, since it leaves out vast areas of the country and the rivers that flow through them.
A quick look at the classification based on these 3 aspects –origin, topography and the basin they form.
Based on Origin or Source
Depending on the origin or where they begin their journey from, there are the Himalayan (perennial) rivers that rise from the Himalayas and the Peninsular rivers that originate from the Indian plateau. The Himalayan rivers include the Ganga, the Indus and the Brahmaputra river systems along with their tributaries, which are fed throughout the year by melting ice and rainfall. They are swift, have great erosion capacity and carry huge amounts of silt & sand. They meander along the flat land, create large fertile flood plains in their wake and their banks are dotted by major towns and cities.
The peninsular rivers, on the other hand are more or less dependent on rain. These are gentler in their flow, follow a relatively straighter path, have comparatively less gradient and include Narmada, Tapi, Godavari, Krishna, Cauveri and Mahanadi rivers, among many others.
Based on topography
The Himalayan Rivers flow throughout the year, are prone to flooding and include Indus and the Ganga-Brahmaputra-Meghna.
The Deccan Rivers include the Narmada and Tapi rivers that flow westwards into the Arabian Sea, and the Brahmani, Mahanadi, Godavari, Krishna, Pennar & Cauvery that fall into the Bay of Bengal.
The Coastal Rivers are comparatively small in size and numerous in number, with nearly 600 flowing on the west coast itself.
Rivers of the Inland Drainage Basin are centered in western Rajasthan, parts of Kutch in Gujarat and mostly disappear before they reach the sea as the rainfall here is scarce. Some of them drain into salt lakes or simply get lost in the vast desert sands.
Island Rivers Rivers of our islands: A&N islands & Lakshadip group of islands
The Narmada River System comprises of the Narmada River that represents the traditional boundary between North & South India and which empties into the Arabian Sea in Bharuch district of Gujarat. Tapi river of the Tapi River System rises in the eastern Satpura Range of Madhya Pradesh and then empties into the Gulf of Cambay of the Arabian Sea, Gujarat. Its major tributaries are Purna, Girna , Panzara , Waghur , Bori and Aner rivers.
Also called the Vriddh (Old) Ganga or the Dakshin (South) Ganga, Godavari of the Godavari River System, originates at Trambakeshwar, Maharashtra and empties into the Bay of Bengal. Summers find the river dry, while monsoons widen the river course. Its major tributaries include Indravati, Pranahita, Manjira, Bindusara and Sabari rivers.
The Krishna River System includes Krishna river, one of the longest rivers of the country,that originates at Mahabaleswar, Maharashtra, and meets the sea in the Bay of Bengal at Hamasaladeevi, Andhra Pradesh. Tungabhadra River, formed by Tunga and Bhadra rivers, is one of its principal tributary. Others are Koyna, Bhima, Mallaprabha, Ghataprabha, Yerla, Warna, Dindi, Musi and Dudhganga rivers.
The Kaveri River System has the Kaveri (or Cauvery) river whose source is Talakaveri in the Western Ghats and it flows into the Bay of Bengal. It has many tributaries including Shimsha, Hemavati, Arkavathy, Kapila, Honnuhole, Lakshmana Tirtha, Kabini, Lokapavani, Bhavani, Noyyal and Amaravati. The Mahanadi of the Mahanadi River System, a river of eastern India rises in the Satpura Range and flows east into the Bay of Bengal.
Broader definition: Catchment area size
River basins are widely recognized as a practical hydrological unit. And these can also be grouped, based on the size of their catchment areas (CA). This easy to understand river system classification divides them into the following categories as tabulated below:
CA in sq km
No. of river basins
CA in million sq. Km
% Run off
Major river basin
CA > 20,000
Minor (Coastal areas)
Flow is uncertain & most lost in desert
Major river basins include the perennial Himalayan rivers- Indus, Ganga & Brahmaputra, the 7 river systems of central India, the Sabarmati, the Mahi, Narmada & Tapi on the west coast and the Subarnekha, Brahmani & the Mahanadi on the east coast and the 4 river basins of Godavri, Krishna, Pennar and Cauvery, which takes the total to 14. The medium river basins include 23 east flowing rivers such as Baitarni, Matai & Palar. A few important west flowing rivers are Shetrunji, Bhadra, Vaitarna & Kalinadi. The minor river basins include the numerous, but essentially small streams that flow in the coastal areas. In the East coast, the land width between the sea and the mountains is about 100 km, while in the West coast, it ranges between 10 to 40 km. The desert rivers flow for a distance and then disappear in the desert of Rajasthan or Rann of Kutch, generally without meeting the sea.
A need for details
Under India-WRIS (Water Resources Information System) project too, the river basin has been taken as the basic hydrological unit, but the country has been divided into 6 water resource regions, 25 basins and 101 sub basins, which are an extension of the earlier 20 basins delineated by CWC, as detailed in the ‘River basin Atlas of India’.  The details of the individual catchment area of these 20 river basins is tabulated here:
CA (Sq. Km)
River Length, km
Indus (Upto border)
Barak & others
Brahmani & Baitarni
West flowing rivers from Tapi to Tadri
Many independent rivers
West flowing rivers from Tadri to Kanyakumari
East flowing rivers Between Mahanadi & pennar
East flowing rivers Between Pennar & Kanyakumari
W flowing rivers of Kutch & Saurashtra includes Luni
Area of inland drainage in Rajasthan
Many independent rivers
Minor rivers draining into Myanmar & Bangladesh
Many independent rivers
Note: 1. River Length is only for the main stem of the river, does not include tributaries, etc.
Area of inland drainage in Rajasthan is not given in this reference, it has been arrived at by inference.
Indus basin is constibuted by six main rivers: Sutlej, Beas, Ravi, Chenab, Jhelum and Indus itself. Some tributaries of this system form independent catchment in India (e.g. Tawi river in Chenab basin) as these confluence with the main river only in downstream of the border.
Of course these methods only classify rivers based on their physical & geographical attributes, their drainage area, river length, volume of water carried and tributary details. For a detailed study of a river, what is also needed is its ecological assessment. The methods for river classification may be varied and still evolving, but this information is fundamental to better understand and map the rivers that criss cross across the country.
And definitely a first step to try and understand our rivers!
Above: Hilsa fishers in Bangladesh setting out for their journey Photo: with thanks from Arati Kumar-Rao
In addition to the Gangetic Fisheries Primer, SANDRP will shortly publish a Primer documenting the Impacts of dams on Riverine Fish and Fisher Communities. One of the most profound impacts of dams on fish is blocking migration routes and perhaps no other fish symbolizes this impact as dramatically as the Hilsa: the Silver Queen of the River.
Glimpses of the impacts of dams on Hilsa in South Asia.
Arguably, Hilsa is not just a tasty and healthy fish species that migrates from the sea up the river to spawn. It is a cultural icon that binds Bengalis, whether from West Bengal or Bangladesh, together in their shared love for Ilish Machch. Pohela Baishakh or the new year day’s meal is not complete without Ilish. Though Hilsa is celebrated fervently by the Bengalis, it is prized in all estuaries of South Asia, from Narmada, Mahanadi, Godavari, Cauvery to Indus and Irrawaddy and takes the name of Chaski, Palva, Ilishii, Palla, Pulasa, etc. It is also found at confluence of Tigris and Euprates in Iran, where it is as prized and known as Sbour. The fish flavours several poems, folklore, songs and phraseologies of the entire South Asia. In cultural terms, the significance of Hilsa is comparable only to Salmon and Mahseer.
Tenualosa ilisha, Hilsa or Indian Shad belongs to the sub family Alosinae of Family Clupeidae. Commercially, it is the most important fisheries in the estuaries, especially in the Ganga-Hooghly region.It occurs in marine, estuarine and riverine environments and is found in Indus of Pakistan, Irrawaddy of Myanmar and Indian rivers like Ganga, Bhagirathi, Hooghly, Rupanarayan, Brahmaputra, Godavari, Narmada, Cauvery, Tapti, coastal rivers like Padma, Jamuna, Meghana, Karnafuly and others in Bangladesh. It is seen to migrate up smaller estuaries like Pennar too.
Hilsa, by habitat, is a marine fish but migrates in estuaries and rivers for spawning, normally inhabiting the lower region of the estuaries and the foreshore areas of the sea. Hilsa ascends the rivers for spawning and the spent fish and their progeny migrate down the river towards lower estuaries and coastal areas, moving in shoals. The peak upstream migration of Hilsa in most of the rivers of the country is generally in the monsoons months of July and August and continues upto October or November. The spring spawners that enter the river for spawning in January-March return to the sea during July-August when these are caught in good numbers. The monsoon spawners that enter the river during September- October return to the sea after spawning and these spent fishes are caught in good numbers during January- March. Similarly, the off springs of spring-spawners make journey for the sea from the river during November- January, whereas the off springs of monsoon spawners return to the sea from the river during July- September. (Bhaumik et al, CIFRI, 2012)
Obstruction to undertaking this spawning migration by dams and barrages has been singled out as the primary reasons for the fall of Hilsa fisheries in India as well as Bangladesh. The trade of this commercially important fish species constitutes upto 1.5% of Bangaldesh’s National Gross Domestic Product and about 2 million fishers are estimated to depend on Hilsa fisheries in Gangetic estuaries. Till August 2014, Bangladesh has stopped Hilsa exports to India to contain astronomic price rises in Bangladesh as the costs of the fish are becoming uncontainable due to its cultural importance on one hand and dwindling supply on the other. India has requested Bangladesh to lift the ban of Hilsa export, but it is yet to relent, due to a number of socio-political reasons. 
One of the main reasons for the phenomenal fall of Hilsa in Gangetic delta has been the Farakka Barrage built by India in the 1970’s, just a few kilometers upstream the India –Bangladesh border, to divert water from Ganga into the Hooghly river, to keep the Kolkata Port at the mouth of Hooghly, free of sediments.
Prior to commissioning Farakka Barrage in 1975, there are records of the Hilsa migrating from Bay of Bengal right upto Agra, Kanpur and Delhi covering a distance of about 1400 kms. Maximum abundance was observed at Buxar, near Allahabad, at a distance of about 650 kms from river mouth. Post Farraka, Hilsa is unheard of in Yamuna in Delhi and its yield has dropped to zero in Allahabad, from 91 kg/km in 1960s. Studies as old as those conducted in mid-seventies single out Farakka’s disastrous impacts on Hilsa, illustrating a near 100% decline of Hilsa above the barrage post construction.
An obligatory Fish lock provided in Farakka Barrage is non-functional and tagging experiments reveal that Hilsa cannot move across the barrage due to obstruction of three-tire sluice gates. For more on how Farakka has failed its objective and continues to impact livelihoods: https://sandrp.wordpress.com/2014/11/25/lessons-from-farakka-as-we-plan-more-barrages-on-ganga/
Fishers who live off the Ganges strongly feel the pressure of dams, personified by Farakka. In north India, ‘Farakka’ –the word doesn’t mean a village on the Bangladesh border anymore, but means destruction by dams. The local Hindi dialects have borrowed new phraseology: “Farakka hua, tabse hilsa toh bas bhabis” (Farakka happened, and then Hilsa exist only in imagined future)”. The same phrase repeats up to the Yamuna River! In a recent status survey of Gangetic fisheries almost 75-80% of fishers singled out ‘Farakka’ as the root cause of all their miseries. They actually referred to multiple barrages built on the respective rivers. But destruction had a common name: Farakka.
Bangladesh has been making several serious attempts to revive Hilsa fisheries and implements a strict fishing ban in certain months to avoid fishing “jatkas” or small Hilsa. It has also declared several Hilsa Sanctuaries to protect the fish and is witnessing small and steady improvements in the population. India has hardly taken any steps to protect this specie. IUCN has led a program called Ecosystems for Life: A Bangladesh-India Initiative and Hilsa fisheries is a part of this project. There is also a Norwegian project on Hilsa Aquaculture  ( All prior efforts of Hilsa Aquaculture have failed). However, the primary need to address the giant problem of the Farakka Barrage is being unaddressed. The barrage and reduced freshwater in the downstream is also exacerbating other stressors like sedimentation of the river mouth, high fishing pressure on limited stocks, concentrated pollution, etc.
Hilsa in other Rivers (would taste as sweet!) Hilsa is found not only in Ganges delta but most of the estuaries in India. In all of these places, Hilsa fishery is primarily affected by dams and barrages near the estuaries, blocking spawning migration and reducing freshwater from upstream.
Hilsa in Cauvery: A century of impacts In Tamizh, Hilsa caught at Sea is Kadal Ullam and the one in the River is the Aattu Ullam. Here, the impact of Mettur dam on valuable Hilsa fisheries in the Cauvery has been recorded as early as 1939 in an issue of Current Science, where it is stated: “Unfortunately the effect of the dam (Mettur on Cauvery) on the fisheries below was disastrous. The number of valuable Indian Shad or Hilsa, the most important sea fish ascending the Cauvery for breeding purposes, declined as the high floods which enabled them to ascend the rive no longer occur. The serious decline of fisheries in Cauvery would be evident from the fact that the fishery rental of the river below the dam which used to amount to 80000 Rs. annually has steadily declined since the formation of the dam to about 42,900 rupees.”Puntius species also disappeared in Cauvery post dam, which formed 28% of the landings prior to dam construction.
As per the Report “Fishing the Cauvery: How Mettur Changed it all,” by Ramya Swayamprakash published by SANDRP, It was Sir Aruthur Cotton himself, way back in 1867 who alerted the erstwhile government about the damages wrought by weirs on river fisheries. Immediately, Dr. Francis Day was commissioned to investigate the impact on fisheries and subsequently appointed Inspector-General of Fisheries in India. In his report on the fisheries of India and Burma, Day condemned dams as insurmountable barriers to fish passage; he designed a fish passage which was on the Lower Anicut on the Kollidam. The pass was primarily designed for the Hilsa who could not ascend it, as it was too wide. According to the Madras Fisheries department in 1909, the fish pass did not ensure Hilsa migration because of various practical and technical difficulties; in the first place, the expenses for the construction of a fish pass were not commensurate with the expected results and secondly, sufficient water could not be provided for the efficient working of the pass. Interestingly, Hilsa was sought to be cultivated and exported along the lines of the Salmon in north-western United States. So important was the Hilsa that a stuffed specimen made its way into the exhibits sent to the Great Exhibition from the Bombay Presidency, in 1851!
Today, the Hilsa is unknown on the Cauvery. According to fish biologists, the Hilsa ascended the anicuts on the Cauvery up to Mettur to spawn overcoming the low anicuts. But the coming of the Mettur Dam formed an impassable barrier.
Hilsa in Godavari is known as Pulasa when caught i the river and Vilasa when caught n the sea! Here too, the fish is declining and main reasons are said to be declining water levels and the Dowleswaram Barrage  (Arthur Cotton Barrage). In Andhra villages too Pulasa has a huge cultural significance.
This author made a presentation to the Standing Committee of the Lok Sabha, the lower house of Indian Parliament in June 2012 about the impacts of dam on riverine fish and discussed Hilsa, when an MP from Coastal Godavari district in Andhra Pradesh said, “I know Pulasa! My constituency depends on riverine fisheries like Pulasa, and not marine fisheries, but we end up talking only about marine fish and not river fish and Pulasa and the impacts of upstream projects on livelihoods of river fishers”
In Mahanadi, Orissa, Hilsa has been hit by dams and is recording a declining trend. Paradip recorded about 500 tonnes Hilsa, but prices have increased astronomically.
Hilsa in Narmada, Sardar Sarovar and the proposed Bhadbhut Barrage The narrative of damming the Narmada by the Narmada Valley Projects is one of the most significant stories of an on-going struggle against modifying a river and way of life of her people. Although there are many facets to the story ranging from displacement, false benefits and true costs, forest loss, non-existent rehabilitation and an all-pervasive insensitivity of the government towards weaker communities, the impacts of this project on riverine fisheries have been equally profound. Narmada River system experienced a nearly 70% decline in Hilsa catches in just a decade between 1993 to 2004 ( From 15319 t to 4866 t ) and this decline was prominently recorded from 1998-99 onwards. As per CIFRI, the most stressed species after Sardar Sarovar Project (SSP) construction is the Hilsa and Macrobrachium prawn (Jumbo River Prawn). CIFRI made some prediction about impacts of the dam after 35 years, calling it a ‘critical period’ when fisheries will be nearly lost. Shockingly, these conditions are already being witnessed in Narmada Estuary in Bharuch which records nearly 30% Inland Fish production. More than 12,000 people from 21 villages in Bharuch alone depend on Narmada Estuary for fisheries.
Assessment of impact of commissioning of Sardar Sarovar dam and other projects in 2009 by CIFRI revealed that SSP will retain 96% of the sediment, adversely affecting biological productivity of the downstream including Narmada estuary. However, already the Sardar Sarovar and upstream dams in Narmada Basin have already resulted in retention of about 95% sediment, cutting off the delta from nutrient rich silt. Historical sediment discharge of Narmada was 61 million tonnes and the current sediment discharge (average of last ten years of the study) was found to be 3.23 million tonnes.
According to CIFRI, “While the annual inflow is 23.68 MAF (1981-1990), it will be reduced to 15.9 MAF after 10th year of SSP, to 4.34 MAF at the 30th year and will cease at the 45th year. This freshwater decline will severely affect Hilsa fishery and prestigious fishery contributed by M rosenbergii (Jumbo River Prawn)”. As freshwater declines, there will be “Steep hike in salinity regime with tidal ingress. Fishery not tuned to such enhanced salinity will succumb to such pressure. Mangroves will also be affected and this will impact marine fish production as Mangroves are nurseries of many marine fish.”
Gujarat Government has agreed to release 600 cusecs water from Sardar Sarovar and Bhadbhut Barrage as environmental flows. There is no study as to whether this amount is sufficient for estuarine balance, for ecological needs of Hilsa or other species, for spawning migration, etc. Also, there is no guarantee that Gujarat will release this meagre quantity. Ironically, the minimum flows of 600 cusecs agreed to be released by Gujarat through SSP come to 532. 9 Million Cubic Metre (MCM) water annually and CIFRI’s warning of a sharp fisheries decline at 30th year was for 4.34 MAF or 5353.4 MCM! So, 532.9 MCM released now as minimum flows is barely 10% of a dire scenario predicted at 30th year of commissioning SSP[i]!
It is hardly a wonder that Hilsa is falling sharply in Narmada Estuary and fishers are directly blaming the Sardar Sarovar for this decline.
Last Straw for Narmada Hilsa: Bhadbhut Barrage: Gujarat Government is planning to build Bhadbhut Barrage about 17 kms from Bharuch, directly affecting the Narmada estuary and the Hilsa and Prawn fishery. The Barrage is planned for SEZ and also water sports and is a part of an infeasible scheme known as the Kalpasar project which plans to dam almost all rivers as they meet the Gulf of Khambat.
The Bhadbhut Barrage is being fiercely opposed by fishers in Bharuch because of its serious impacts on their livelihoods and Hilsa fisheries. Public Hearing of Bhadbhut Barrage was held in July 2013, wherein the fisher community staged a walk out, stressing that the EIA had under-reported Hilsa fisheries in the region, number of fishers and their dependence on the Estuary for fish. The walkout took place immediately after Pravin Tandel, the fisherfolks’ local leader, spoke saying the project would “adversely affect the fish catch, especially Hilsa, once it is implemented. Currently, Hisla fetches Rs 1,200 per kg, and is our main source of livelihood.”
Hilsa in the Indus: In the Indus too, Hilsa fisheries, known as Palla are the main stay of local fisher communities. Hilsa fish is a highly contested territory due to declining catches.
Before the construction of the Sukkur Barrage, the Palla used to reach to Multan as per records of 1907. The Sukkur Barrage and then later the Kotri Barrage severely restricted Palla’s range, affecting the fish and its fishers. According to M. R. Quereshi, ex-Director of Marine Fisheries Department of Pakistan, the Palla used to ascend the river (Indus) to spawn in the middle of June but its ascent is now delayed by at least one month owing to late freshets. Kotri Barrage near Hyderabad has severely restricted its breeding range. Like the Cauvery, in Kotri too the fish ladders do not work due to faulty designs and Hilsa is unable to ascend them, consequently prevented from going up to the upper reaches of the river. As a result the Hilsa fishery is being depleted and immediate action is imperative to increase its production. “Failing this, the fish will eventually disappear from the river.”
To conclude, the fate of this silvery fish hangs in a fine balance. Not only does the Hilsa enjoy huge cultural significance, it also supports millions of livelihoods. In the United States, several dams, like the recent Glines Canyon Dam on the Elwha, have been decommissioned for their impacts on migrating fish and dependent communities. Elwha river dams came down in a biggest decommissioning effort because the indigenous Klallam tribe asserted its rights on traditional Salmon fisheries which were blocked by these dams. In Japan too, Arase Dam was decommissioned because of its impact on Ayu fish and fishers.
What has happened in India to the Hilsa fish and fishers is far more serious.
Hilsa has a striking ecological, economic and cultural significance. Till date, ranching or farming of Hilsa has not worked. Till date, fisher communities continue to face conflicts, hardships and risks, go deeper and deeper in the sea to gather a few Hilsa. Till date, dam operations have not changed, nor have the fish passes been designed, built, operated or monitored to help the fish. Till date, none of the fisher communities who suffered colossal losses when a dam affected Hilsa, have been compensated for their loss.
Is it not time to rethink these dams, to help the fish and our fishers?
 Milton, STATUS OF HILSA (Tenualosa ilisha) MANAGEMENT IN THE BAY OF BENGAL: AN ASSESSMENT OF POPULATION RISK AND DATA GAPS FOR MORE EFFECTIVE REGIONAL MANAGEMENT, Report to FAO Bay of Bengal Large Marine Ecosystem Project , 15 February 2010
 CIFRI, River Narmada, Its Environment and Fisheries, 2009
“We enjoy Pushing Rivers Around” –An early Hydraulic engineer in California (from Patrick McCully’s Silenced Rivers, 1996)
“We can tame the mighty rivers. We are an example of human will and endeavor”
-Sutlej Jal Viduyt Nigam Limited, damming the entire Satluj Basin in India.
“A river flowing to the sea is a waste”- a view held by several water resource developers in India
Welcome to Anthropocene ,says James Syvitski, a leading oceanographer, geologist and hydrologist from Colorado University who has been studying subsidence of deltas.
Some scientists are now placing Anthropocene, an era marked with human interference with natural systems, at par with geological epochs like Pleistocene and Holocene. It is manifested in many ways. Rivers and associated systems like deltas and floodplains possibly have had to face the maximum brunt of the Anthropocene.
Cutting edge scientists like Prof. Syvitski who study the changes in our deltaic systems seem to reach to a common conclusion: Delta subsidence is now the main driving force for effective sea level rise for many coastal environments. This subsidence is more influential than sea level rise related to global warming and any deltas are sinking much faster than the sea level is rising.
But why are deltas sinking? What is the main reason behind this subsidence which is eating away land and making millions of people more vulnerable?
It has been established that the main reason behind delta subsidence is drastically reducing sediments reaching the delta.Studies estimate that during the past century, there has been a 94% reduction in Krishna’s sediment reaching the delta, 95% reduction from historic load in Narmada, 80% reduction in Indus, 80% reduction in Cauvery, 96% reduction in Sabarmati, 74% reduction in Mahanadi, 74% reduction in Godavari, 50% reduction Brahmani, etc.,
But why are sediments not reaching the delta?
Almost unanimous agreement between scientists indicates that the reason behind this drastic decline in sediments is sediment retention by dams and reservoirs in the upstream.(Walling and Fang (2003), Vörösmarty et al., 2003; Syvitski et al.,(2005), Erisson et al, (2005), Walling (2008), K Rao et al (2010), H Gupta et al (2012) ). This has been reiterated in IPCC WG II Report, April 2014.
Prof. Syvitski wrote a few words on the issue for SANDRP. He says, “A delta can form only where the sediment volume supplied from a river can overwhelm the local ocean energy (waves, tides, currents). Ocean energy is ceaseless. Engineering of our river systems, largely through the construction of upstream dams and barrages, has reduced this sediment supply. Consequently ocean energy has begun to reduce the size of our deltas, and coastal retreat is presently widespread. Deltas, once the cradle of modern civilizations, are now under threat — some deltas are in peril of lasting only the next 100 years. Sea level is rising due to ocean warming and glacier melting. Incessant mining of groundwater from below a delta’s surface, along with oil and gas extraction, further contribute to our disappearing deltas. At risk are the residences of more than 500 million people, the loss of biodiversity hotspots, major infrastructure (e.g. megacities, ports), and the rice and protein bowls of the world. Every year thousands of people drown due to storm surges and other coastal flooding. Sinking deltas are evidence of the magnitude of the human footprint on our planetary environment. We must learn to do better.” Professor J P Syvitski (U Colorado, Boulder, USA), Chair — International Geosphere-Biosphere Programme (ICSU), Executive Director, the Community Surface Dynamics Modeling System
Large reservoirs trap as much as 80% of the upstream silt. As a result, most rivers are carrying much less sediment, and some rivers (like Krishna, Indus, Nile, and Colorado) transport virtually no sediment! In the last 50 years, the combined annual sediment flux of the large Chinese rivers has been reduced from 1800 million tons (Mt) to about 370 Mtmainly due to frenzied dam building. The impact of dams and reservoirs on sediment retention has been so significant that the resultant reduced sediment load represents a volume of about 730 km3, equivalent to an area of 7300 km2 assuming a 10 m thick bed. Waling (2008) states that about 25 Gt/year of sediment are trapped by large dams each year. IPCC Report (Assessment Report 5, 2014) refers that 34 rivers with drainage basins of 19 million km2 in total show a 75% reduction in sediment discharge over the past 50 years due to reservoir trapping.
Delta Subsidence and Effective Sea Level Rise (ESLR)
While this delta subsidence and sediment retention has several impacts on dense delta population and coastal ecosystems which offer important services, one of the most serious impacts is its direct role in Effective Sea Level Rise. Ericsson and Vorosmarty et al, 2012, concluded that decreased accretion of fluvial sediment resulting from sediment retention and consumptive losses of runoff from irrigation (also due to dams) are the primary determinants of ESLR in nearly 70% of studied deltas.
More and more scientists are concluding that climate related sea level rise has a ‘relatively minor influence on delta conditions’, as compared to anthropogenic reasons. As seen above, there is an almost unanimous agreement that dams are the most important factor influencing contemporary land-ocean sediment fluxes. Globally, greater than 50% of basin-scale sediment flux in regulated basins is potentially trapped in artificial impoundments of approximately 45,000 reservoirs (with dams 15 m high) (Vörösmarty et al., 2003; Syvitski etal., 2005) and sediment delivery to deltas has been reduced or eliminated at all scales.Other reasons for delta subsidence include flow diversion by dams, sediment compaction due to groundwater abstraction, oil and gas exploration and mining, etc,.
Deltas, formed by centuries of accretion of rich sediment, are one of the most fertile and densest populated regions across the world. It is estimated that close to half a billion people live on or near deltas, often in megacities. Although constituting a mere 5% of the total landmass, coastal regions sustain almost three-quarters of the world’s population and yield more than half of global gross domestic product (Vorosmarty et al.,2009).
The direct impacts of ESLR and delta subsidence include inundation of coastal areas, saltwater intrusion into coastal aquifers, increased rates of coastal erosion, an increased exposure to storm surges, etc. These threats have implications for hundreds of millions of people who inhabit the deltaic as well as the ecologically sensitive and important coastal wetland and mangrove forests.
Already, some studies are ringing alarm bells. It is estimated that if no mitigation measures are undertaken and sediment retention continues, then by 2050, more than 8.7 million people and 28,000 km2 of deltaic area in 33 deltas studied including Ganga-Brahmaputra, Indus, Krishna and Godavari could suffer from enhanced inundation and increased coastal erosion. In addition, a larger population and area will be affected due to increased flood risk due to storm surges. Conservative estimates state that delta area vulnerable to flooding could increase by 50% under the current projected values for sea-level rise in the 21st century and this could increase if the capture of sediment upstream persists and continues to prevent the growth of the deltas.
The Intergovernmental Panel on Climate Change (IPCC) projects that sea level will rise by another 21 to 71 cm by 2070, with a best estimate of 44 cm averaged globally. This will further compound impacts of delta subsidence and sediment trapping.
It has been estimated that even in the case of debilitating floods, sediment has not reached rivers in the deltas.In 2007–08 alone Ganges, Mekong, Irrawaddy, Chao Phraya, Brahmani, Mahanadi, Krishna and Godavari flooded with more than 100,000 lives lost and more than a million habitants displaced. Most of the deltas that suffered from floods did not receive a significant input of sediment, and this lack of sediment can be attributed to upstream damming. Some studies demonstrate that storage of sediment-laden water of major flood events leads to huge sediment trapping behind mega dams.
Above: Global distribution of ESLR under baseline for each of the 40 deltas studied by Ericsson et al, 2006.From Ericsson et al, 2006
Fluvial Sediments and Deltas in India
Rivers are not only conduits of water. They are a complex, moving systems carrying sediment, nutrients, organisms, ecosystems, energy, material and cultures in their wake.
There are three kinds of sediments: suspended, bed load and wash load. Here we are referring to mainly the suspended sediments in the rivers. Sediments play a significant role in the river geomorphology, defining the river channel, its shape and structure. Sediment deposits form alluvial floodplains, deltas, levees, beaches, ox bow lakes and lagoons and creeks. The sediment load and composition changes according to the river, the geological landscape it flows in, its length, flow, structure, etc. While much of the sediment is deposited by the river on its banks, the delta of the river is primarily formed of rich sediments. Through this deposition, the river may form distributaries at its mouth, like in case of Ganga, Brahmaputra or Mahanadi systems. Ganga-Brahmaputra Delta, shared by India and Bangladesh is one of the largest delta systems in the world, spanning more than 100,000 km2carrying more than one billion tonnes of sediments annually.
Deltaic populations in shared rivers of India, Bangladesh and Pakistan: Population of Ganga-Brahmaputra-Meghana Delta is more than 147 million people with a population density of more than 200 people per km2 (520 people per square mile), making it one of the most densely populated regions in the world . The Krishna Godavari twin deltas supports 9·26 million people inhabiting the 12,700 km2 area at 729 persons per km2, which is more than double the country’s average. Cauvery delta supports 4.4 million people while the Mahanadi Delta too supports millions. Only two districts of Cuttack and Jagatsinghpur have a population more than 3.7 million. (Census 2011) in addition, the contribution of deltas to economics, food production, transport, ecosystem services etc., is immense, making it a very valuable ecosystem which deserves protection. Indus Delta in Pakistan supports more than 900,000 people.
Deltas in Peril: Impact of damming on deltas in India
1. Krishna-Godavari Delta: In 2010, a team led by K Nageswar Rao of Dept of Geo Engineering, Andhra University, carried out an assessment of the impacts of impoundments on delta shoreline recession in Krishna and Godavari Delta. The study revealed a net erosion of 76 km2 of area along the entire 336-km-long twin delta coast during the 43 years between 1965–2008 with a progressively increasing rate from 1·39 km2 per year 1965 and 1990, to 2·32 km2 per year during 1990–2000 and more or less sustained at 2·25 km2 per year during 2000–2008.
For Krishna, flows as well as suspended sediments in the delta have nearly reached zero. Suspended sediment loads decreased from 9 million tons during 1966–1969 to negligible 0·4 million tons by 2000–2005. Syvitski et al in their 2009 assessment place Krishna in the category of “Deltas in Greater Peril: Virtually no aggradation and/or very high accelerated compaction.”
In the case of the Godavari delta, there has been almost a three-fold reduction in suspended sediment loads from 150·2 million tons during 1970–1979 to 57·2 million tons by 2000–2006. Syvistki et al classify Godavari delta as “Deltas in greater risk: reduction in aggradation where rates no longer exceed relative sea-level rise”. H Gupta et al (2012) suggest that decline in historic sediments of Godavari post damming has been as high as 74%.
Above: Graph indicating decadal sediment and water flow trends at Prakassam Barrage, across Krishna. Dam building also marked. From Rao et al, 2010
According to Dr. Rao, a comparison of data on annual sediment loads recorded along the Krishna and Godavari Rivers shows consistently lower sediment quantities at the locations downstream of dams than at their upstream counterparts, holding dams responsible for sediment retention. Reports based on bathymetric surveys reveal considerable reduction in the storage capacities of reservoirs behind such dams. Authors say: “Sediment retention at the dams is the main reason for the pronounced coastal erosion along the Krishna and Godavari deltas during the past four decades, which is coeval to the hectic dam construction activity in these river basins.”
Impacts of this can be seen in destroyed villages like Uppada in Godavari delta, destruction of Mangrove forests and shoreline. Similarly Krishna delta is losing land at the rate of 82·5 ha per year, leading to destruction of mangrove forests and loss of land.
The study concludes: “If the situation continues, these deltaic regions, which presently sustain large populations might turn out to be even uninhabitable in future, considering conditions elsewhere, such as in southern Iraq, where the farmers downstream of dams across Tigris River in Iraq, Syria and Turkey are being forced to migrate to urban centres as the reduced river flows become overwhelmed by seawater.”
I talked with Dr. Rao and asked him, if his disturbing study had any impacts. He said, no one from the administration has contacted him ever about this issue.
Above: Sediments measured at Sir. Arthur Cotton Barrage across Godavari near the Delta from Rao et al, 2010
A similar study by IWMI concludes: “Coastal erosion in the Krishna Delta progressed over the last 25 years (is) at the average rate of 77.6 ha/ yr, dominating the entire delta coastline and exceeding the deposition rate threefold. The retreat of the Krishna Delta may be explained primarily by the reduced river inflow to the delta (which is three times less at present than 50 years ago) and the associated reduction of sediment load. Both are invariably related to upstream reservoir storage development.”
Krishna Basin Water Disputes Tribunal Award, though mentions dam siltation (it mentions that in 5 decades, Tungabhadra Dam has silted up to 22% of its capacity), does not say anything about flow for flushing sediments or its importance to the delta in Andhra Pradesh, or if the “minimum instream flow” recommended by the Tribunal will address this issue. This is a major limitation of the tribunal, when advanced studies have been conducted on the Krishna River delta condition and its relation to upstream dams has been established beyond doubt. Only at one place does it mention that to reduce siltation of the Almatti Dam, sluice gates should be opened when water is flowing above the crest.
However, the Award states that issues like minimum in stream flows are not decided once for all and it is an evolving process. Let us hope that there is some space to address the issue of shrinking deltas through this.
Above:Decreasing Sediments of Krishna down the years from K Rao et al, 2010
In the upstream Maharashtra, more and more dams are under construction in the Krishna Godavari Basin. One of the proposed dams called Kikvi, at the headwaters of Godavari in Trimbakeshwar was cleared by the Forest Advisory Committee recently. Ironically, the proponent (Water Resources Department, Maharashtra and Nashik Municipal Corporation) justified this dam which will submerge more than 1000 hectares of land, by stating that one more large dam close to Kikvi: Gangapur Dam is heavily silted up. Rather than desilting Gangapur Dam, the administration wants to build one more dam.
Above: Trends in Sediments in Godavari and dam building activity. From K Rao et al
Many dams in Krishna Godavari Basin in Maharashtra have been criticised for not contributing to increasing irrigation.These dams are not only obstructing river flow, but are also acting as sediment traps. Unfortunately, the MoEF is not even considering impacts of sediments while appraising dams. In Karnataka, major projects are being undertaken by fraud, without environmental appraisal, violating Environment laws, similarly in Andhra Pradesh, many projects are being pushed illegally without environmental appraisal and which involve huge corruption.
2. Cauvery Delta: Although detailed studies have not been carried out, there is a clear indication of salt water intrusion and delta erosion in this over developed basin, due to upstream dams. The saline-freshwater boundary map indicates a steady migration inland.
A study by Gupta et al, 2012, indicates that historical sediment flux of Cauvery was 1.59 million tonnes, which is now 0.32 million tonnes (average of 10 years) and hence, there is a whopping 80% reduction in sediment flux of the river.
Unfortunately, the Cauvery Water Disputes Award Tribunal between Karnataka and Tamilnadu does not even mention the word ‘sediment’ in its award. There has been no justification for 10 TMC feet (Thousand Million Cubic feet) water recommended by the Tribunal for Environmental purposes and its possible impact on sediment carrying (or even environment for that matter).
Pennar showed 77% reduction and Mahanadi showed 67% reduction in amount of silt reaching the delta in recent years. (Gupta et al, 2012)
3. Narmada Delta: The west flowing rivers like Narmada and Tapi do not form extensive deltas like the east flowing rivers. Nonetheless, sediments from a huge river like Narmada play an important part in the stability of Narmada delta and villages and ecosystems around it.
Above: From: H. Gupta et al, 2007 and 2012
Gupta et al (2012 and 2007) assessed daily water discharge and suspended sediment load data measured by CWC at two gauging stations, one upstream of the Sardar Sarovar dam (Rajghat), and another downstream of the dam (Garudeshwar).
Historical sediment discharge of Narmada was found to be 61 million tonnes and the current sediment discharge (average of last ten years of the study) was found to be 3.23 million tonnes, indicating a reduction of 95% sediment discharge. The presence of dam reduces 70–90% of coarse and approximately 50% of medium-sized particles on their way downstream, allowing them to settle in the reservoir Comparative studies of average suspended sediment load at various locations on the Narmada River for more than two decades, show overall reduction in suspended sediment load in the river.
The study indicated 96% reduction in suspended silt flux in Sabarmati, 41% reduction in Tapi and 68% in Mahi.
4. Ganga- Brahmaputra Delta: Different studies put different values for individual and combined sediment load of the Ganga Brahmaputra system, which carries one of the highest sediment loads in the world. According to Islam (1999) Ganges and Brahmaputra rivers in Bangladesh transport 316 and 721 million tonnes of sediment annually. Of the total suspended sediment load (i.e. 1037 million tonnes) transported by these rivers, only 525 million tonnes (c. 51% of the total load) is delivered to the coastal area of Bangladesh and the remaining 512 million tonnes are deposited within the lower basin, offsetting the subsidence. Of the deposited load, about 289 million tonnes (about 28% of the total load) is deposited on the floodplains of these rivers. The remaining 223 million tonnes (about 21% of the total load) is deposited within the river channels, resulting in aggradation of the channel bed at an average rate of about 3.9 cm/yr sediment.
Across the 20th Century, Syvitski et al suggest about 30% reduction of silt load in the river system. Gupta et al  suggest that the observed decrease in sediment load could be due to construction of several mega dams in the Ganga basin, closure of Farakka barrage (1974) and diversion of sediments laden water into the Hooghly distributary. They also caution that dams in Ganga and Brahmaputra can worsen the situation.
5. Indus Delta: Inam et al (2007) assessed annual sediment loads of the Indus river at Kotri Barrage (270 km upstream from river mouth) during the last 73 years. The study indicates that annual sediment load of the Indus river has reduced drastically from 193 Mt (between 1931 and 1954) to 13 Mt (between 1993 and 2003). According to them, construction of three large dams on the Indus river, namely Kotri Barrage, Mangla and Terbela led to this situation causing annual water discharge to reduce from 110 km3 to 37 km3, with disastrous impacts on the delta ecosystem and population.
Above: Variation of water and sediment discharge below Kotri Barrage in Indus basin: Inam et al
Inam states : “Currently the Indus river hardly contributes any sediment to the delta or Arabian Sea.The active delta is reduced from 6200 km2 before construction of dams to 1200 km2. The sea water has travelled upstream upto 75 kms, combined loss of freshwater and sediment has resulted in loss of large areas of prime delta agricultural land and submergence of several villages in the coast. This has caused desertification and displacement of several hundred of thousands of local residents. Study of records and bathymetric maps from 1950 indicate widespread coastal retreat…The life on the delta is dependent on availability of freshwater and sediment. Severe reduction of both as a result of dams and barrages and associated structures in the upstream has resulted in pronounced erosion in parts of the delta and reduction in mangroves. Environmental studies to be extended to the entire Indus ecosystem from the mountains to the Arabian sea.”
It is clear that deltas and dependent populations and ecosystems have suffered due to near total ignorance about the impact of dams on sediment and deltas and if immediate action is not taken then, this will impact a huge population and a large eco-region in Indian subcontinent, as elsewhere.
The impacts of nutrient rich sediment retention and flow reduction is not limited to teh delta, but has also affected marine fish production
The issue of impact of a dam on the sediment regime of the river is not being studied or considered at all while conducting Environmental Impact Assessments of projects, appraising the project for options assessment, environmental clearance, cost benefit analysis or through post clearance monitoring and compliance.
Sediment release and sediment transport through rivers is not being raised in trans-boundary river negotiations.
Looking at the severity of the issue and its far reaching impacts on millions of people in India and across the world, there is a need for adopting urgent and strong mitigation measures against sediment trapping in dams.
It has to be remembered that for older dams, older hydropower projects and most irrigation projects, there is no mechanism available to flush the accumulated silt.
Sediment retention also reduces the life of the dam, while starving the river and delta in the downstream of sediment. As per a study by SANDRP in 2006, India may be losing 1.95 Billion Cubic Meters of Storage capacity of its reservoirs annually. This implies that the rivers are losing at least that quantity of sediment annually.
The frantic dam activity in Indian Himalayas at this moment will have a serious impact on Ganga Brahmaputra Delta in India and Bangladesh and Indus Delta in Pakistan. There is an urgent need to, firstly, acknowledge these links, assess the impacts, include them in cost benefit and options assessment, address the issues and implement mitigation measures, where relevant, abandon the projects where impacts are unacceptable projects unviable.
In case of the Ganga Brahmaputra delta, recent studies have indicated that the main source of sediment in the river is the Himalayas. Of the entire sediment load of Ganga catchment (This study assumed it to be 794 million tonnes/year), 80+/-10 % comes from High Himalayas and 20+/-10 % comes from Lesser Himalayas.
Bumper to bumper dam/ hydropower project building is occurring in almost all of the Himalayan states in India, which is poised to make Indian Himalayas most densely dammed region in the world. All of these dams are located in the downstream of the Greater and straddling Lesser Himalayas and can together have a tremendous impact on Ganga’s sediment load. Uttarakhand is planning and building nearly 336 Hydroelectric projects,while Sikkim and Himachal Pradesh too are building hundreds of hydro projects. Arunachal Pradesh intends to dam most of its rives to produce hydropower.
No studies on impact of these projects on sediment regime of the rivers are being carried out for; neither does the MoEF insist that projects will not be cleared unless such studies are carried out. Even Cumulative impact assessments are not assessing this aspect.
Some stark examples:
The Cumulative Impact Assessment Report of the Upper Ganga Basin in Uttarakhand (where more than one hundred dams are planned and under construction back to back) was doen by IIT Roorkee. This cumulative impact assessment did not study any cumulative impacts due to reduced silt load of the river following major dam push.
The Lohit Basin Study done by WAPCOSwhich involves more than 12 dams across the Lohit River, one of the three main segments that form Brahmaputra, does not mention anything about impacts of dams on sediments. The only thing it states is very worrying : “Due to substantial storage capacity, the Demwe Upper reservoir will have high sediment retention capacity and a large proportion of sediments carried by the Lohit River will get settled in the reservoir.”
Siang Basin Study (by RS Envirolinks Pvt Limited), which involves three mega dams across the main stem Siang, completely obliterating free flowing stretches in the river,in addition to 42 hydropower dams, does not mention anything about sediment regime, although being specifically asked to address this issue by the Expert Appraisal Committee, Union Ministry of Environment & Forests (MoEF).
1500 MW Tipaimukh Mega Dam near Bangladesh Border, which has received Environmental Clearance from MoEF does not study the impacts of sediment retention on downstream Bangladesh, and this concern has been raised by the groups in that country. The Environment Management Plan of this project which can submerge 25000 hectares of forests does not even mention the word “sediment”.
The bumper to bumper dam building activity in Himachal Pradesh in Satluj, Beas, Chenab and Ravi rivers will have a major impact on silt load reaching the Indus river Basin and the Indus Delta in Pakistan. However, none of the EIAs or EMPs mention any impact of the dams on the sediment regime of the river.
In conclusion, although the risks of delta subsidence, effective sea level rise and its impact on a huge population and ecosystems has been established, these risks are being entirely ignored in the current governance surrounding rivers and deltas.
National Centre for Sustainable Coastal Management It is unfortunate to see that MoEF’s National Centre for Sustainable Coastal Management, supported by MoEF and World Bank does not allude to this issue or raise it through any publications. In conversation with SANDRP, Director R. Ramesh said that the center may look at these issues in the future. However, its publications on National Assessment of Shoreline Changes on Tamilnadu and Odisha do not mention upstream dams, although robust evidence exist that Cauvery delta and Mahanadi, Brahmani and Baitarni deltas are eroding due to sediment retention. Let us hope this institute will try to highlight the impact of dams on deltas with the seriousness it deserves.
1. Urgently study impacts of sediment retention by dams on delta population and ecosystems: MoEF, Ministry of Rural Development and Urban Development should conduct an in-depth study to understand the scale of the problems and the extent of affected people and ecosystems due to sediment impoundment by upstream dams.
2.Urgently study the optimal level of sediments (and water regime) needed for stabilising deltas and reducing subsidence.
3. Urgently institute a study to assess the extent of sediment and flows needed to be released from upstream dams and feasibility of such releases on regular basis, mimicking the river’s hydrograph. Where dams have sluice gates, these should be opened in monsoons where feasible, to allow sediment flushing. Even in dry and stressed river basins like Colorado in the United States, such high releases for redistributing sediments have been conducted in the 1990s and again in 2013 with proper planning and impact assessment.
4. In Krishna and such other basins, where delta subsidence, coastal erosion and related impacts like salinity intrusion and storm surges has reached serious proportions, specifically problematic dams should be considered for decommissioning.
Environmental Appraisal Process
Study of impact on sedimentation and siltation should be a part of the environmental impact assessment, environmental appraisal and clearance process.
There should be a separate section in EIA for e-flows and sedimentation studies. Similarly such studies should be mandatory part of cumulative impacts, carrying capacity and basin studies.
More dams in basins which support large deltaic populations and those having significant impacts of sediment retention by reservoirs should not be cleared.Let us hope that this chronically neglected issue receives the attention it deserves. Delta subsidence and ESLR due to upstream damming again highlights the complex and interconnected nature of the riverine ecosystem. The environmental governance in India ( as also South Asia) surrounding rivers has been treating rivers with an extremely piecemeal approach. It is clear that with the herculean challeneges we face now, such an approach is no longer affordable.
…especially in the part called Delta, it seems to me that if the Nile no longer floods it, then, for all time to come, the Egyptians will suffer – Herodotus, History, c 442 BC (stated in Patrick McCully’s Silenced Rivers)
International Water Management Institute (IWMI) has recently published a study named Glacier Systems and Seasonal Snow Cover in Six Major Asian River Basins: Hydrological Role under Changing Climate, authored by Oxana S. Savoskul and Vladimir Smakhtin which claims that the hydrological role of the melt-water resources in six major rivers e.g. Indus, Ganges, Brahmaputra, Syr Darya, Amu Darya and Mekong of the Hindukush-Himalayan region (HKH) has been comprehensively assessed for the first time on a basin scale. Reviewing already published studies, this report draws some interesting conclusions regarding the role of glacier and snow meting for six river basins which includes three major rivers basins of India.
The map below shows area of the river basins included in this study. In this report, the term ‘melt-water resources’ has been used to cover glacier systems and seasonal snow cover. This report uses 1961-1990 status of melt-water resources as the baseline and compares with the 2001-2010 using the following characteristics: specific glacier runoff (average depth of annual discharge from glacier-covered area), basin total glacier runoff, shares of renewable and nonrenewable components in glacier runoff, total seasonal surface snowmelt from non-glaciated areas, portion of seasonal snowmelt lost for the recharge of groundwater aquifers, the contribution of glacier runoff and seasonal snowmelt to mean annual flow (MAF).
The authors have used Glacier mass budget-based methods and hydrograph separation techniques which they stated as suitable for basin-scale assessments instead of the temperature-index methods. They say that application of these two methods in semi-distributed models can give the highest currently possible accuracy of +30%. The authors opine that many of the studies done previously had confused between the ‘snowmelt’ and ‘glacier-melt’ because these studies have not dealt with terminologies and methodologies in detail. The report states that there is a scarcity of glacier runoff estimates in peer-reviewed papers, “An analysis of publications on modeling runoff from large- and medium-scale glaciated catchments….. indicates that not many of these dealt with modeling glacier runoff per se. Even fewer report their evaluations of glacier runoff separately from snowmelt, if at all.”
For the three of the six river basins studies and which flow through India, i.e. Indus, Ganges and Brahmaputra the total annual glacier runoff for the period of 1961-1990 was 41 km3,16 km3 and 17 km3 respectively. But in the recent periods of 2001-2010, total glacier runoff was reduced to 36 km3, 15 km3 and 16 km3 respectively for the three basins, see Table 1 for details.
It is clear from the table that while Indus and Brahmaputra basins have similar percentage of area under glaciers and snowmelt, the reduction in the glacier and snow cover area are more pronounced in Indus basin. Besides, in all the three basins the reduction in glacier area is more pronounced that the snow cover area. However, the contribution of glacier melt and also snow melt to run-off is much higher in Indus basin compared to Brahmaputra basin, showing the greater role of precipitation in Brahmaputra basin. Within the Indus basin even though seasonal snow covers 28% of the total area, much than the 2.6% occupied by glaciers during 1961-90, the contribution of two sources to Mean Annual Flow is almost same. But a question arises, has the contribution of glacier melt to the runoff increased in any of the basins in the recent decade? The answer is surprisingly, no.
Table 1: Recent changes in the glaciers and seasonal snow and their contributions to MAF
Part of basin area(%) covered by
Contribution to MAF (%)
For the Ganges basin, the report says that heavy summer precipitation almost solely determines MAF volume for the basin. Maximum seasonal snow area in the Ganges basin makes just 6% of the entire basin area. Similar situation were reported for the Brahmaputra basin, where the lower parts of the basin i.e. Southeastern Tibet and Eastern Himalayas where nearly 75% of the basin’s glaciers are located, witness heavy summer monsoon rains. Regarding Indus basin the report says, “Precipitation in the IndusBasin is more evenly distributed between the seasons, but is highly variable spatially – similar to Brahmaputra and Amu Darya, where annual precipitation in some catchments is tenfold (3,000 mm) of that in the other glacier-covered parts of the basin (300 mm).”
Reviewing already published documents the report states “it appears that the research in High Asia is concerned much more with CC impacts than with objects of the impact. Yet, understanding of the expected basin-scale changes in glacier runoff in response to climate change remains largely unclear.”
The report does an analysis of assessments done on impact of climate change on water availability in Himalayas and concludes that many assessments rely on poorly verified sources. The report refers to the statement made by Cruz et al. (2007) “The current trends of glacier-melts suggest that the Ganga, Indus, Brahmaputra and other rivers that criss-cross the northern Indian plain could likely become seasonal rivers in the near future as a consequence of climate change…,” This statement was admitted as a typing error after publication but even then this has been reiterated as an apocalyptic vision in NGO reports.
Using the Table 2 given below, the report states that glacier contribution is a minor item in the annual river water budgets in the Ganges and Brahmaputra basins. The report says “The impact of climate change was found to be more prominent on seasonal rather than annual water availability.” It is clear from the table that, in the recent decades non-renewable component in all three basins have gone up while renewable and total volume of water from glacier melt have come down. It is also noteworthy that, even though Brahmaputra basin has more area under glacier cover than the Ganges basin (see Table 1), the volume of water from non renewable glacier flow was more in both periods in the Ganges basin. Besides, the percentage of increase in nonrenewable glacier runoff components during 2001-10 is highest among all three basins, signifying that glaciers are melting fastest in Ganga basin.
Table 2: Contribution of renewable and non-renewable components to glacial runoff
Glacier runoff components
Total Glacier runoff (km3)
Total Glacier runoff contribution to MAF (%)
The reports also states, “Glaciers and seasonal snow in CC-impact assessments should be perceived as natural water reservoirs with gradually diminishing storage and flow regulation capacity, both on intra-annual and inter-annual scale. Potential changes of precipitation regime coupled with effects of temperature rise on evapo-transpiration will impact future hydrological regimes of the major rivers much more significantly, affecting both MAF and flow seasonality.”
The authors of this report clear some fog around climate change and Himalayan glacier system and snow-melt. One lacuna of the report is that even though the report discusses glacier run-off it makes no mentions of glacier lakes and glacier lakes induced floods. There are several incidents of glacier lake induced floods happening in the basins discussed. There is evidence to show that in the recent flood devastation in Uttarakhand in India glacial lakes played significant role.
Parag Jyoti Saikia
with inputs from Himanshu Thakkar
South Asia Network on Dams, Rivers and People (www.sandrp.in)
Indus river rises in the southwestern Tibet Autonomous Region of China. Originating in the Tibetan plateau of western China in the vicinity of Lake Mansarovar in Tibet Autonomous Region, the river runs a course through the Ladakh district of Jammu and Kashmir and then enters Pakistan via the Northern Areas (Gilgit-Baltistan), flowing through the North in a southerly direction along the entire length of Pakistan, to merge into the Arabian Sea near the port city of Karachi in Sindh.
The Sub-basin wise generation data of large hydro with installed capacity of the basin in the latest year 2012-13.
Inst Capacity (MW)
The above graph shows the trend line of power generation of Big Hydropower projects for last 28 years in the basin, the trend-line shows diminishing generation from existing hydro power projects of Indus River Basin.
It shows that the per MW generation in 2012-13 (4.28) has dropped by a huge 17.69% from the highest per MW generation (5.2) achieved in the year 1988-89.
All generation figures have been taken from official data of Central Electricity Authority (CEA).
List of other projects (up to 25 MW) under operation (for which latest generation figures not available):