Res­cue Facts from Drown­ing

The Economic Times - - Breaking Ideas - Jayanta Bandy­opad­hyay & Ni­lan­jan Ghosh

There is a wide­spread pub­lic per­cep­tion in In­dia that the struc­tural in­ter­ven­tions in the Ti­betan Plateau by China on the Yar­lungTsangpo, a tribu­tary of the Brahma­pu­tra, will greatly re­duce the flow of the Brahma­pu­tra in down­stream North-East (N-E) In­dia.

State­ments of Chi­nese in­ter­ven­tions on the Yar­lung be­ing dan­ger­ous for In­dia have the po­ten­tial of gen­er­at­ing new points of con­tention in China-In­dia hy­dropol­i­tics. The con­tentions have been fur­ther in­ten­si­fied by the re­cent op­er­a­tional­i­sa­tion of the Zangmu hy­dro-power project on the Yar­lung. This project is ex­pected to pro­duce 2.5 bil­lion KWH of elec­tric­ity an­nu­ally. In 2016, five more hy­dropro­jects are pro­posed to be com­pleted on the river.

Un­doubt­edly, an es­ti­mated hy­dropower po­ten­tial of 114,000 MW of the Yar­lung is very lu­cra­tive for China in the con­text of mit­i­ga­tion of green­house gas (GHG) emis­sions. De­spite a lot of clam­our about such projects, hardly has there been an ob­jec­tive, sci­en­tific anal­y­sis of the is­sues. This has led to sen­sa­tional myths and claims, which de­serve to be re­viewed. The down­stream im­pacts of hy­dro-power and wa­ter trans­fer projects are quite dif­fer­ent and should be dis­tin­guished. The se­ries of projects un­der­taken by China on the Yar­lung and its trib­u­taries is re­port­edly for hy­dro-power gen­era- tion, which does not re­duce the to­tal flow but changes its hy­dro­graph (flow pat­tern). The im­pacts on the hy­dro­graphs of the Brahma­pu­tra will be gen­er­ated not merely from the hy­dro-projects on Yar­lung, but also from the down­stream projects on the same river Siang/Di­hang and the Dibang or the Luhit, all of which flow through In­dia.

As a trans-Hi­malayan tribu­tary, the Yar­lung is sub­stan­tially fed by snow and glacial melts, in ad­di­tion to rain­fall in semi-arid Ti­bet. A very large com­po­nent of the to­tal an­nual flow of the Brahma­pu­tra is gen­er­ated in the south­ern as­pect of the Hi­malaya in Bhutan and In­dia by trib­u­taries from the Buri Di­hing into the Teesta.

The to­tal an­nual out­flow of the Yar­lung from China is es­ti­mated to be about 31 bil­lion cu­bic me­tres (BCM), while the an­nual flow of the Brahma­pu­tra at Ba­hadurabad, the gaug­ing sta­tion near the end of the sub-basin in Bangladesh, is about 606 BCM. Thus, the con­tri­bu­tion of Ti­bet in the to­tal flow of the Brahma­pu­tra can be taken as about 5%.

Fur­ther, while the peak flows at Nuxia and Tsela Dzong, a mea­sur­ing sta­tion at the great bend of the Yar­lung in the Ti­betan plateau, are about 5,000 and 10,000 cumecs, the peak flow at Ba­hadurabad is ap­prox­i­mately 50,000 cumecs. The lean sea­son flow in Nuxia is to the tune of 500 cumecs, while the lean flow at Ba­hadurabad is about 5000 cumecs.

Th­ese fig­ures do not sup­port the lin­ear al­ge­braic think­ing that the flow in a river is pro­por­tional to its length in­side a country, as is per­ceived pop­u­larly -- given that out of the Brahma­pu­tra’s length of 2,880 km, 1,625 km in Ti­bet flows as the Yar­lung Tsangpo.

An­other point of con­cern re­lates to the im­pact of the projects on the sed­i­ment flow. The sed­i­ments of­fer im­mense ecosys­tem ser­vices for the down­stream economies of In­dia’s N-E states, and Bangladesh. The sed­i­ment flow to the down­stream will be im­pacted by all the hun­dreds of hy­dro-power projects on the river and trib­u­taries.

Most of th­ese are in In­dia. The projects around Zangmu in Ti­bet will also af­fect the flow of sed­i­ments, though sed­i­ment ex­clu­sion tech­nol­ogy has im­proved man­i­fold lately. Fur­ther, the ac­tual sed­i­ment flow into the Brahma­pu­tra will also be di­rectly linked with hy­dro-power projects on the Di­hang, the Dibang and the Luhit, in In­dia up­stream of the Sadiya. This is par­tic­u­larly due to the in­tense mon­soon pre­cip­i­ta­tion on the south­ern as­pect of the Hi­malaya.

While Nuxia (Ti­bet) on the Yar­lung re­ceives around 350 mm of rain­fall dur­ing mon­soon, as the Yar­lung crosses the Hi­malayan crest line and reaches the south­ern as­pect with the names of Siang and Di­hang, the an­nual pre­cip­i­ta­tion in Pasighat goes up to about 4500 mm. The flow vol­ume and dis­charge in the Yar­lung is not suf­fi­cient to gen­er­ate and trans­port a large sed­i­ment load.

More­over, the an­nual sus­pended sed­i­ment load near Nuxia has been mea­sured to be around 30 mil­lion met­ric tonnes, quite small as com­pared to the 735 mil­lion met­ric tonnes at Ba­hadurabad. How­ever, in case of hy­dro-power projects in the south­ern as­pect, sed­i­mentex­clud­ing tech­nol­ogy can play a sig­nif­i­cant role. With low wa­ter and sed­i­ment con­tri­bu­tion as com­pared to the south­ern as­pect, a wa­ter trans­fer project in the north­ern as­pect -even if con­structed at great eco­nomic and en­ergy cost -- can­not have se­ri­ous im­pacts down­stream. So, the dis­tinc­tion needs to be made not on the ba­sis of whether a project is Chi­nese or In­dian, but whether the project is on the north­ern or south­ern as­pect of the Hi­malaya. The cur­rent work­ing hy­poth­e­sis does not re­flect this sci­en­tific re­al­ity.

Bandy­opad­hyay is ex-pro­fes­sor, IIM Cal­cutta. Ghosh is se­nior eco­nomic ad­vi­sor, World Wide Fund for Na­ture, New Delhi

No moles in this moun­tain: Yar­lung-Tsangpo river, Ti­bet

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