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Impacts of Tipaimukh projects on rivers and economy of Bangladesh!

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by Enamul Hoque

UNIQUE climatic and geomorphic/hydrologic features of the boro rice include continuous irrigation or inundation of land during growing season. On the contrary, during maturing stage, the boro crops require the land to be dry so that the paddy stalks carrying maturing rice do not get rotten. Generally boro crops are harvested in mid to late April. March to May is most likely three of the drier and hotter months of the year in Bangladesh and this natural dryness and hot weather help the rice to mature properly. The other feature of the area is that flash floods during mid to late April and May due to downpour in the Shillong Plateau causes widespread damage of the boro crops. As mentioned above, a one foot rise in the water depth in the rivers generally inundates approximately 10 per cent of the rice crops. A one meter rise in depth of water could inundate 25 to 30 per cent of the boro crops completely under water. To prevent these damages, the farmers congregate together in a commune manner to harvest the crops. Migrant rice worker from lower Meghna such as greater Comilla, Dhaka, Noakhali, Faridpur and even from Barisal area come to this Haor areas to work on harvesting and processing this boro rice. These workers work as exchange worker in which cash is not transacted rather these migrant workers get share of the rice harvested from the farmers.

The floods in Surma Basins or the Haor Basins come in two stages. One flood comes during the early summer or late spring during the months of April to May. This flood is exclusively due to the sudden and high intensity micro-burst related rainfall in the southern slopes of the Tura Range. This rainfall is basically orographic and damages the boro rice and winter crops. Even though this weather pattern exists within the upper watershed of the Barak, due to the dense forests and high water holding capacity of the under hedges including leaf litters in that regions, runoff from the upper Barak does not contribute to the early flood. The second flood arrives during the monsoon time. Due to high frequency sustained rainfall of more than 6,000mm within the southern slopes of the Tura Range, the contribution to the damaging flood is mostly due to this rainfall in Meghalaya. Any development and watershed modelling should consider this fact.

The Surma trough’s other uniqueness is that the haors and the arable lands around haor areas require full flood and drying of the land to maintain the ecological and hydrological balance. The flooding generally remove the undesirable and toxic chemicals left over by the farming, fish droppings and the natural wastes left over by the millions of migratory birds. In addition, the aquatic plants, periphytons, bacteria, fungus and algae or other microbes require flushing every year. The flooding especially the early flood cleans the river beds and banks to a level so that the fish fries and spawning fish can make their nest for the hatchlings. The flooding also provides the young fish ample space for play and movement including their uninterrupted travel during their migration downstream. In winter or dry months it is also essential that the land remain dry for a period of time and the lake water level go below certain depth so that water temperature rises for some photobioreaction to occur.

Tipaimukh dam

INDIA has initiated study from 1952 to formulate flood control in Cachar Valley and to build a dam on the Barak which will provide power and water for irrigation during lean months. Until the early 1990s India could not find any suitable location for the dam. In 1995, the then prime minister Atal Behari Vajpayee, during his visit to north-eastern India, declared that 50,000 megawatts of hydro-electricity should be generated in the north-eastern states. The Tipaimukh dam project gained new momentum. In the 14th Joint River Commission meeting, India brought the issue of the dam all of a sudden. In fact, in a Joint River Commission record of decision contained the following text: ‘With regard to the flood problem of Sylhet, Cachar and adjoining areas, the Commission should jointly examine the scope of the Indian scheme of storage dam on Barak River at Tipaimukh and study expeditiously the potential flood control and other benefits in Bangladesh and report the progress to the Commission at its next meeting.’ This text was not recommended by the joint technical committee constituted by the commission. It is not clear whether the committee ever studied the flood benefits of the project for Bangladesh because the Tipaimukh issue completely disappeared from the agenda of the subsequent JRC meetings. As mentioned earlier, flood control in Bangladesh due to this dam will be minimal due to the fact that majority of the flood flow comes from Meghalaya.

Tipaimukh Dam as proposed will have the following facts:

Location : Lat 24o14’N, Long 93o1’E

Height : 161m

Length : 390m

Area : 29,150 hectare

Design flood discharge : 16,964 m3/sec

Average annual yield : 12.5 billion m3

Dependable yield (90%) : 8.1 billion m3

Power generation : 1500 MW but dependable is 412 MW

The approximate location of the dam is about 500 metre downstream of the confluence of the Barak and the Tuvai and 190 kilometres upstream of the Bangladesh border. The dam is planned to be a rock-fill dam with a central clay core to act as impermeable barrier to water seepage. The height and capacity of the spillway(s) are also not known.

No data has been provided to Bangladesh to assess the construction time schedule and reservoir filling process. It is estimated that this dam may require five to seven years to build. During this time, it is not clear how the floodwater will be diverted, i.e. whether there will be a diversion channel to connect to the Barak downstream of the dam or the water will be diverted to Assam for irrigation. Should India decide to fill the reservoir without releasing water, Bangladesh will not get a drop of water during the two years of reservoir filling times. The reservoir filling time may run from one and a half to two years’ timeframe depending on the weather conditions at those times. This may bring catastrophic economic disaster to Bangladesh.

The location of the dam is in seismically active area that includes a fault named Taithu Fault. The dam is located adjacent to and near the location of the meeting point of the Eurasian Plate, Indian Plate, and Burmese Plate. There are complex movements of plates at this site due to differential movement of these plates. The plate movement includes subsidence, lateral movement, and thrusts. These complex movements have created a mosaic of active, yet shallow faults that can and have triggered very large catastrophic earthquakes. The faults include the Arakan-Youma, Dauki, and Disang Faults. The mountains and sharp turns of the stream channels in this part of the subcontinent carry the telltale signs of these complex phenomena. The likelihood of occurrence of a major earthquake of magnitude 7.6 in next 25 to 30 years in this the region is between 40 and 60 per cent. Probability of occurrence of Magnitude 8.7 earthquake with its epicentre at the Shillong Plateau is perhaps 2 to 5 per cent within next 200 years, assuming the events are random and can be described with a simple binomial probability model. Any major or significnt earthquake can cause dam burst. In such case, river channels and sedimentation patterns in the northeast region may be subject to major disruptions following a severe seismic event. During past earthquakes, instances of ground liquefaction, landslides, rapid subsidence, collapse of river banks, and changes to river courses have been documented (District Gazetteer, 1917).

Recently the Manipur government of India signed a contract to build this dam and the hydroelectric project. The original design called for a barrage at Phulertal to divert water to Assam for irrigation purpose. At this point no information has been delineated to the people of Bangladesh. Bangladesh Government also not disclosing any information that might have been given to the respective Ministry. Only a senior level team of Bangladeshi legislators and few hand-picked experts made a helicopter tour of the site of the dam but they could not land at the site due to prevailing weather conditions. No report of the team except interviews of some participants was available at this time. Another development that worth mentioning here that during a prime minister-level meeting in Bangladesh, Manmohan Singh mentioned that India would not do anything at the Tipaimukh dam that will harm Bangladesh. This statement, however, does not assure that India will not build this dam without talking to Bangladesh. Besides, there is no mention of who is going to study the adverse effect and benefit ratio due to the dam. It is now a known fact, based on worldwide data, that there is not a single large dam that does not do significant harm to the downstream. In fact, most dams failed to fulfil the long-term benefit and brought environmental and economic disaster to the riparian citizens. In the north-western US and other parts, the US government has initiated a decommissioning of dams to revive the original environmental and ecological conditions.

Bangladesh is worried whether the Tipaimukh project will become another havoc and economic devastation like the Farakka Barrage (Asafuddowlah, 1994) in bilateral relations between the two countries. There had been strains in relations between the two neighbours for 30 years over the sharing of the waters of the Ganges River (Khondker, 2003). ‘Bangladesh’s concern is magnified due to the fact that the concern expressed by the indigenous people of the Manipur were sidelined, the government of Bangladesh was not informed about the project despite international norms requiring consultation with lower riparian countries. India had earlier promised to provide Bangladesh with the Detailed Project Report (DPR) and Environmental Impact Study of the Downstream area due to the construction and operation of the Tipaimukh Project before going for its implementation. This information could be used to review the project to verify and mitigate any ill effect and dispel the lower riparian neighbour’s concern. But unfortunately, NEEPCO completed the DPR, solicited international bids, prepared short list and proceeded with the construction, but yet to provide Bangladesh with the promised DPR’ ( Khondker, 2009). It appears that India is playing hard with arrogance to sideline the issues of Bangladesh and the indigenous communities in Manipur and Mizoram while conceiving the project.

It is also understood that India may build a barrage at Phulertal to divert water to Assam for irrigation. The detailed of the diversion barrage is also unknown to Bangladesh. Other unknowns that could impact in adverse manner with regard to proposed Tipaimukh Dam to Bangladesh included the following:

Reservoir operation rules

Rate of dam impoundment in the first two years

Rate of flow impoundment in a normal flooding year

Release of water through spillway in an sudden flood event

Water to be released through the turbine outlets

Water diversion plans through barrage(s) and other means

Dam risks and Safety

Preliminary reports indicate that in full operation, the dam will release water during winter time to raise the water surface by about 1.5 to 2.0 metre at location downstream of Amalshid. This rise in water level will cause widespread inundation of boro rice within the haor basin and along the Meghna floodplain. Approximately 30 percent of the arable land will undergo permanent inundation giving rise to unhealthy and ecologically disastrous swamps. This effect assumes that India will not divert any water out of the Tipaimukh dam or its reservoirs in upstream of the dam or immediately downstream of the dam. During the flooding time or monsoon time unpredictable flood an inundation of the land will occur frequently.

To be continued

Enamul Hoque, P.E., D.GE, F.ASCE is a civil engineer who currently resides in Chandler, Arizona, USA. He owns a civil engineering consulting company and provides services in geotechnical, environmental, materials testing and land and river restoration work.




Source : http://banglawire.com/blog/2011/12/24/impacts-of-tipaimukh-projects-on-rivers-and-economy-of-bangladesh/


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