[Assam] [WaterWatch] Why does river Brahmaputra remain untamed?

Tue Dec 27 09:45:04 EST 2005

Brahmaputra Board, has been a totally useless 
undertaking. They don't have anything to show for 
their decades long existence. But it is to be 
expected from the India which is perfectly 
willing to accept the make-believes of 'process' 
as accomplishments.

We don't need MORE studies. We know 
channelization of Brahmaputra is the only 
salvation for Assam. And it must begin NOW! We 
know it won't be accomplished in a year or two or 
even ten. It wioll have to be an ongoing project 
for a very long time, and not just in 
Assanm--B'desh too; for the good of both nations.

At 6:13 AM -0800 12/27/05, Dilip/Dil Deka wrote:
>Good article with facts and numbers.
>Geologically Brahmaputra is known as a fairly 
>new river though we call it "Burha Luit". Do 
>geologists know how young the river is? Did the 
>river start flowing at the time the Himalayas 
>formed? Or was it a later phenomenon when a 
>water body in Tibet burst its land container? It 
>would be interesting to know.
>
>The essence of the article is in the following 
>two paragraphs. The statistics on embankments 
>and canals that the article gave probably 
>include the truibutaries and as I remember they 
>were all temporary make-shift measures. 
>Multidisciplinary investigation only as 
>suggested by the author  will lead to a better 
>solution. Wasn't the Brahmaputra Board 
>dismantled? Is there talk of a new 
>multidisciplinary organization? Anybody knows?
>Dilip
>
>"Why are we so helpless in containing the spates 
>of Brahmaputra and coping with its flood hazard? 
>Why do our efforts go awry and all civil 
>engineering measures end up in shambles?"
>
>"It will therefore be advisable to embark
>on a comprehensive multidisciplinary investigation of the
>Brahmaputra valley in Assam to provide a 
>rational knowledge-based perspective for the 
>design of flood resilient mitigation measures."
>
>
>
>Chan Mahanta <cmahanta at charter.net> wrote:
>
>At 11:40 AM +0000 12/27/05, waterwatch100 at yahoo.com wrote:
>
>>Why does river Brahmaputra remain untamed?
>>
>>Taking into consideration the reality of the 
>>continuing tectonic movements on active faults, 
>>it should be evident that building of 
>>embankments and drainage channels in upper 
>>Assam would not bring lasting relief from flood 
>>hazards.
>>
>>
>>
>>
>>
>>Come May and the wild river of the east is seized with spells of
>>unrelenting spate, attendant deluge, sediment deposition and
>>erosion. The flood hazard has been ravaging upper Assam unabatedly
>>since time immemorial. Explorers of ancient times – those who
>>established Praagjyotishpur in Kamrup province – must have discerned
>>in this river something very different from all other rivers of the
>>subcontinent, as evident from the singularly masculine name they
>>gave it – `Brahmaputra' or `the son of Brahma'. Despite gigantic
>>efforts and colossal expenditure (> Rs 15,000 million) in building
>>3647 km of embankments, 599 km of drainage channels and 431 km2 area
>>of soil conservation1, Brahmaputra continues to wreck havoc by
>>uncontrollable floods year after year.
>>
>>Records show that catastrophic floods occurred in 1954, 1962, 1966,
>>1972, 1973, 1977, 1978, 1983, 1984, 1987, 1988, 1991, 1993, 1995,
>>1996 and 1998. Upwards of 9600 km2 land, that is 12.21% of the
>>geographic area of Assam, is annually affected by floods. In 1998,
>>the flood which came in 4 frightening waves, deluged 38,200 km2 or
>>48.65% geographic area of the state, putting in peril the lives and
>>properties of 12.5 million people1.
>>
>>Why are we so helpless in containing the spates of Brahmaputra and
>>coping with its flood hazard? Why do our efforts go awry and all
>>civil engineering measures end up in shambles? The answer, in my
>>opinion, lies in our failure to recognize the reality of active
>>faults and continuing crustal movements in this geodynamically
>>restless region. Understandably, the flood coping measures have
>>never been designed to accord with this recognition.
>>
>>Girdled as it is, by the arms of the Eastern Himalayan Syntaxis –
>>the knee-bend of the mountain ranges – the Assam terrane is
>>underthrusting northwards under the Arunachal Himalaya and, less
>>energetically, eastwards beneath the Indo-Myanmarese ranges2,3.
>>There is, therefore, very severe deformation and attendant faulting
>>and thrusting in the terrane caught between the Himalaya–PatkaiNaga
>>ranges and the Meghalaya massif. The drastic reduction of the width
>>of the alluvial plains from 350 to 300 km, respectively, in the
>>flood plains of Sindhu and Ganga to less than 100 km in the
>>Brahmaputra basin is not without significance. Coming of the
>>Meghalaya–Mikir blocks of the Peninsular Indian Shield closer to the
>>Himalaya explains this attenuation of the alluvial domain of the
>>Quaternary foreland basins.
>>
>>The severe deformation of the Assam region is eloquently expressed
>>in its much faulted framework4,5. The E–W trending faults (Dauki
>>Fault, Brahmaputra-Mikir Fault), and the transverse tear faults
>>(Kopili Lineament, Dhubri Fault, Dudhnoi Fault, Chidrang Fault, Um
>>Nagot Lineament) and thrusts (Dapsi Thrust, Barapani Thrust) are
>>among the many that dissect the terrane of the Meghalaya–Mikir
>>blocks. The E–W Dauki and Brahmaputra–Mikir Faults roughly demarcate
>>the southern and northern physiographic limits of the Meghalaya
>>Plateau which is a horst of sorts. The plateau stands as a ~ 2000 m
>>high physiographic eminence against the sunken 3–4 m high (above sea
>>level) Sylhat Plains in Bangladesh.
>>
>>Most of these faults are seismically quite active4 as borne out by
>>the distribution of epicentres in the fault zones, such as the
>>locations of 7 earthquakes of M "  4.5 along the 26.5°
>>
>>The catalogue of earthquakes of magnitude 4.5 and above in the
>>period 1897–1992 shows the higher (87%) seismicity in the Meghalaya-
>>Mikir blocks and adjoining Indo-Myanmarese range and northern
>>Bangladesh plains, compared to near absence in upper Assam and lower
>>seismicity in Arunachal Himalaya6. In the Meghalaya block, the
>>
>western part (Tura region) riven with faults exhibits greater
>seismicity as testified by major earthquakes of 1897, 1923, 1930 and
>1943.
>
>Gowd et al.6, Molnar7 and Gahlaut and Chander8 attribute the higher
>seismicity of the Meghalaya–Mikir blocks to reactivation of what has
>been postulated as a gently dipping shallow thrust or midcrustal
>detachment. I believe that many E–W and transverse faults that
>dissect the block (Figure 2) are active. Compared to the N3° E
>orientation of SHmax in the Meghalaya–Mikir blocks, it is N26° E in
>upper Assam (and N23° E in Peninsular Indian Shield)6.
>
>The NNW–SSE  trending Kopili Lineament of high 
>seismicity thus constitutes the  tectonic 
>boundary between the two stress domains.
>
>Significantly, it was in the belt of this Kopili 
>Lineament that earthquakes have occurred 
>recurrently – one of M 7.2, three of 6.0 £  M < 
>7.0 and several of 4.5 £  M < 6. Doubtless, 
>tectonic movements have been taking place time 
>and again on the faults of the Kopili Lineament. 
>This seismically active Kopili lineament cuts 
>across the Brahmaputra about 35 km NW of 
>Navagaon between Mikir Hills and the 
>prolongation of Meghalaya massif.
>
>Levelling observations9 made three times during 1910–197  indicated
>that the blocks of the Guwahati–Dergaon section have been
>consistently rising – the vertical velocity increasing progressively
>from 0.3 mm/yr to 4.5 to 31 mm/yr at Dergaon (approximately 30 km
>west of Jorhat) implying faster rise of the Mikir block. In the
>Guwahati–Goalpara sector, the eastern side moved in the NNE
>direction and the western part shifted SSW-ward during 1856–1938
>(ref. 9). North of the Dauki Fault, the Meghalaya block has been
>rising at the rate of 0.3 to 0.4 mm/yr (ref. 10).
>
>It is obvious that the block delimited by seismically active faults
>has been rising perceptibly though variably in space and time. The
>uplift of the Meghalaya block is evident in the gorge that the
>otherwise wide Brahmaputra has cut near Guwahati – in the place
>where a N–S lineament traverses the river.
>
>The uplift of the Meghalaya block – through the prolongation of
>which the Brahmaputra has cut its channel – must have caused ponding
>of the river. The continuing movements must be impeding its flow
>with resultant accumulation of sediments in the upstream channel
>(Figure 4). The deposition of great volumes of sediments – occurring
>as islands and bars – in the channel has phenomenally reduced the
>carrying capacity of the Brahmaputra. Flood waters are bound to
>spill over and spread far and wide. The 1897 earthquake of M 8.7 had
>caused not only the ponding of streams but also blockade of the
>Brahmaputra.
>
>According to Oldham11, there was a deluge unrelated to
>rains as a result of a barrier formation across the Brahmaputra,
>downstream of Hathi- mura, accompanied possibly by subsidence of the
>floor under the river. The 15 August 1950 earthquake (M 8.7) had
>likewise drastically affected the gradient of this river, stopping
>the flow temporarily and bringing about flooding and rapid
>accumulation of enormous volume of sediments in the channel.
>
>The lowest water level rose by 3 m as a result 
>of the earthquake, and near Dibrugarh and 
>downstream the channel was silted up 2.5 to 3 m. 
>The scarp13 that one sees north-east of 
>Dibrugarh is probably the
>surface expression of the fault that lifted up the downstream block
>and caused ponding of the Brahmaputra.
>
>Imagine a similar development overtaking the Brahmaputra valley in
>the event of a major earthquake! Taking into consideration the
>reality of the continuing tectonic movements on active faults, it
>should be evident that building of embankments and drainage channels
>in upper Assam would not bring lasting relief from flood hazards.
>The solution lies in channelizing discharge of the order of 48,160
>m3/s (ref. 12) of the Brahmaputra through canals, aqueducts,
>tunnels, etc. across the northward prolongation of the Meghalaya
>block, particularly between Guwahati and Hathimura and other places
>(west of Mikir Hills) where identified active faults cross its
>channel.
>
>The canals would have to be deepened periodically in order
>
>to keep pace with the rate of uplift of the block. Absence of
>channelization of the Brahmaputra in spate would always cause
>ponding, leading to deposition of sediments, reduction in carrying
>capacity and inundation of the flood plain. In my opinion, this is
>what is happening to- day. It will therefore be advisable to embark
>on a comprehensive multidisci-plinary investigation of the
>Brahmaputra valley in Assam to provide a rational knowledge-based
>perspective for the design of flood resilient mitigation measures.
>
>Goswami, S., Souvenir: National Workshop on Geodynamics of North-
>eastern India, Dibrugarh University, Dibrugarh, 1998, pp. 36–41.
>Mukhopadhyay, M. and DasGupta, S., Technophysics, 1988, 149, 299–
>322.
>Acharyya, S. K., Indian J. Geol., 1997, 69, 211–234.
>Nandy, D. R. and DasGupta, S., Phys. Chem. Earth., 1991, 18, 1147–
>1163.
>Kayal, J. R. and De, R., Bull. Seismol. Soc. Am., 1991, 81, 131–138.
>Gowd, T. N., Srirama Rao, S. V. and Chary, K. B., Curr. Sci., 1998,
>74, 75–80.
>Molnar, P., J. Geol. Soc. India, 1987, 30, 13–27.
>Gahalaut, V. K. and Chander, R., Tectonophysics, 1992, 204, 163–174.
>Rajal, B. S. and Madhwal, H. B., Himalayan Geol., 1996, 17, 17–32.
>Chugh, R. S. and Valdiya, K. S., Indian J. Geol., 1989, 61, 1–13.
>Oldham, R. D., Memoir Geol. Surv. India, 1899, 29, 1–379.
>Goswami, Dulal, C., in Flood Studies in India, Geol. Soc. India,
>Bangalore 1998, pp. 53–75.
>Proc. Intern. Symp. Neotectonics of South Asia, Survey of India,
>Dehradun, 1986.
>
>---------------------------------------------------------------------
>-----------
>
>K. S. VALDIYA
>
>Geodynamics Unit,
>
>Jawaharlal Nehru Centre for
>
>Advanced Scientific Research,
>
>Bangalore 560 064, India
>
>
>
>
>
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