The Indian government’s recent decisionto go ahead with the plan of constructing a dam at Tipaimukh on the river Barak has touched off intense debates, both in Bangladesh and India, on its merit. Dr M Monirul Qader Mirza debunks the Indian government’s argument in favour of the Tipaimukh project in an essay serialised in three parts.

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BANGLADESH and India share basins of 54 international rivers. The waters of these rivers play an important economic role for agriculture, urban and rural water supplies and navigation sectors. Among the shared rivers between the two countries, until recently, the Ganges was the most debated because of withdrawals of its waters at the Farakka Barrage point and 90 other points above of it. Thus far, Brahmaputra and the Meghna/Barak have remained virgin in terms of water impoundments and withdrawal/transfer. However, this is no more the case. India’s recent decision to go ahead with the plan of building a dam at Tipaimukh on the river Barak has ignited heated debates on its merit in India and Bangladesh.    



allacy 2: Tipaimukh will reduce extreme flooding in Bangladesh   THIS is not as simple as stated by India in the ‘Indo-Bangladesh Task Force Report on Flood Management 1990.’ ‘The storage will moderate the floods in the Cachar district of Assam and Sylhet and Dhaka districts of Bangladesh and provide these areas much awaited relief from floods besides reducing the chances of obstructing the drainage of the main Padma (Ganga) in the event of synchronisation of the flood flows and backing up of Meghna as it happened in 1988’ (p 14). Bangladesh countered the Indian claim by arguing that the ‘updated Indian proposal provides gated spillway for all the dams and claim benefits “to a significant measure” from Dihang dam “to a large extent” from the Subansiri dam and “to vast areas in India and Bangladesh” from the Tipaimukh dam for flood moderation. The above Indian claims are not substantiated by facts and figures’ (p 26).   Bangladesh further stated, ‘The Indian proposal of constructing a dam at Tipaimukh will also not help in flood moderation in Bangladesh as the Meghna basin within Bangladesh is a saucer shaped land mass consisting of a large number of beels and haors. The soil moisture deficiency is comparatively less than in other areas of Bangladesh. The average pre-monsoon precipitation is above 900mm and after meeting the soil moisture deficiency it partly goes to depression storages in the different beels and haors in the area. Sometimes pre-monsoon precipitation also causes early flash floods’ (p 26).   ‘The intensity and duration of monsoon rainfall is of high magnitude in the Sylhet area. The average being of the order of 4000mm. Above 70-80% of the monsoon precipitation goes to direct runoff which causes heavy flood almost every year in the area. The estimated runoff depth is of the order of 3m. As such the Indian proposal of constructing dam at Tipaimukh will not help flood moderation in Bangladesh as the monsoon precipitation in Sylhet basin is enough to cause floods in Bangladesh’ (p 26).   India countered Bangladesh’s argument by insisting that the ‘Tipaimukh reservoir having 9.00 milliard cum. as its live storage will be very effective in absorbing high floods in the valley and protecting the Cacher and Sylhet areas from the flood-ravages. The Tipaimukh reservoir will moderate the floods generated by heavy precipitation over a catchment of 12,758 Sq.km which otherwise would continue to ravage the downstream areas in an uncontrolled manner. Areas of both the countries will get considerable relief from the flood menace after the Tipaimukh reservoir comes up’ (p 61).   The limitation of 9 milliard cubic meters of live storage for flood moderation and hydropower generation is explained below.   Initially, the main purpose of such dam construction in the Meghna/Barak basin was ‘flood control’. However, over the years, its purposes were shifted to ‘hydropower generation’ and ‘irrigation’. A multi-purpose dam has to encounter many problems to optimise its operation to serve all the purposes (could be opposing) efficiently. For example, in order to mitigate downstream flood problems, the storage behind the Tipaimukh dam should be maintained at the lowest level possible at the beginning of the monsoon. If this is the case, then power generation from the dam will have to be compromised. To maximise power generation, water levels (therefore the storage volume) must be maintained at the highest possible levels. This will have limited impact on flood moderation. Therefore, experts are concerned over the stated flood-control benefit of the Tipaimukh dam in extreme conditions, as its main purpose is to generate electricity.   Moreover, there are also other concerns. After a detention from a heavy rainfall event, generated runoff water should be released through the spillway as quickly as possible, within the capacity of the downstream channel to maintain safety of the dam itself. Firsthand examples exist in our neighbourhood. In 2000 the south-western region of Bangladesh was suddenly engulfed by waters arriving from the neighbouring India. The source of the flood waters was the water released from a string of dams in West Bengal, where the capacity of the dams was exceeded due to the sudden onrush of runoff from the catchment areas. Similar incidents were experienced in other parts of the world as well. ‘During the El Niño of 1983, climate and hydrologic forecasts failed to predict abnormally heavy spring runoff in the Rocky Mountains. Dam operators along the Colorado River maintained high water storage levels, failing to prepare for the potential of the flooding. By the time operators began to react, water was bypassing the dams via their spillways and wreaking havoc throughout the system. Ultimately, the Glen Canyon dam in Arizona was heavily impacted with flood flows eroding large volumes of rock from within the canyon walls that support the dam. Fortunately, the flooding peaked and control was regained before the dam was breached’ (http: //science.jrank.org, 2009). As the northeast region of India is very prone to rainfall with long rainy seasons, such events will likely happen in the near future and bring about havoc in the downstream areas of the Barak/Meghna basin in India and Bangladesh.   The reservoir simulation study downstream of the Tipaimukh shows that it would withstand 100-year floods. It should be noted that large floods are often designated as a ‘one-hundred-year flood’ but a 100-year flood does not mean that such a flood occurs once every 100 years. Instead it signifies that there is a one in one-hundred (or 1%) chance of such a flood occurring in a given year, with two exceptions: Sonaimukh and Badarpurghat would be 0.75m and 0.65m above the danger levels, respectively. However, the data used for the calculation the 100-year flood for the Tipaimukh Dam is significantly dated. In its letter of clearance, dated October 24, 2008, the Ministry of Environment and Forests, the government of India asked the authorities concerned to update the peak flood estimation for the project. The MEF stated, ‘Peak flood estimation by frequency method, utilising a short series of 16 years (1966-1981), when the observed peak is 9100 cumec will lead to a significant increase 1 in 100-year flood estimated as 4931 cumec only. Flood frequency study has to be carried out utilising the data from 1966 to 2007 and got vetted by CWC.’ Although the MEF urged NEEPCO to update flood analysis, recently it has released the environmental impact assessment report for general public without any revisions.   Considering a 100-year flood from a short record of only 16 years is an unusual hydrologic practice. Without update of the hydrological assessment and related design parameters, the project will introduce significant risks for the population living in the downstream areas. Any increase in volume of 100-year flood means higher flood depths in the downstream areas of the dam in India and Bangladesh.   To be continuedDr M Monirul Qader Mirza is a water resources engineer and an adjunct professor with the Department of Physical and Environmental Sciences, University of Toronto at Scarborough, Canada.