Tipaimukh Dam
Impoundment, flow, and EIA
THIS paper will mainly deal with probable Environmental Impact Assessment (EIA) as a result of construction of Tipaimukh Dam. In early nineties a study was undertaken by the government with experts to ascertain the relationship between release of water from the dam during floods and dry season with water levels in rivers in the lower riparian Bangladesh.
The Mathematical Model (MM) conducted between 1993 and 1995 has the following findings:
During floods, water level will decrease by 1.6m; in dry season (Feb) water level will increase about 4 times, to a depth of 1.7m and for dambreak Sylhet area will be flooded to a depth of 1.0m. The data and study date back nearly 16 years. Assumptions made at that time may need change/modification.
Analysis of impoundment and flows
High flow: The flood flow will need further analysis on the basis of new data to ascertain the magnitude of flood level. Flood level will rise rather than decrease.
Low flow: In February at Amalshid water flow will increase by over 4 times with increase in quantity by 60% leading to rise of water level by 1.7m. It appears unrealistic; the study conducted some 16 years ago needs re-evaluation based on new data. Our surmise is, Water level will reduce.
Dambreak: Assumption in MM was unobstructed for flow from the dam to Bangladesh. Sylhet Area will be flooded to a depth of 1.0m if there occurs a dam failure. In it there is no mention of the quantity for the area. It is stated that in this process a volume of 10x109m3 (10 billion m3) of water was involved, and flooded to a depth of 1m. Actual depth and area flooded will be larger as Tipaimukh reservoir holds a volume of 15x109m3 water.
Dambreak occurs for catastrophic hydrological events or severe earthquakes (both are natural events). Massive weight of 15x109m3 of water and weight of dam and other superstructures together about 2 crore tons may accentuate seismic acceleration and earthquake, causing tremendous pressure which combined with water and wind pressures may cause cracking to ultimate failure of the dam. The dam is situated in the seismically most active earthquake-prone zone in India where many catastrophic earthquakes occurred, including two of 8.5 in Richer scale. During dam failure a massive flood wave, a wall of water, would travel downstream to reach Sylhet border in 48 hours or so.
Adverse impacts and EIA
The adverse impacts are sadly pervasive in almost all sectors and sub-sectors of economy and environment and some social issues.
It is learnt that India prepared an EIA which was terminating just at our border. As per international convention EIA should be prepared taking full cognisance of adverse impacts in lower riparian country. Damages to economy and environment that will be caused, should be identified and mitigation measures suggested and expressed in both physical and, more importantly, monetary terms. This is to identify who will bear the cost of mitigation of economic damages and losses and environmental decay and degradation etc. Conventionally as per environmental rule "polluters pay" the cost of cleaning, redressing, correcting and ameliorating the damages caused.
EIA study prepared by India must be available to Bangladesh. Since Bangladesh is sadly excluded in their EIA, we need to prepare our own EIA for Surma-Kushyara-Meghna basins, singly or jointly with India.
Low and high flow impacts
Navigation will suffer -- industries will be affected.
Pollution and environmental decay will be all pervasive due to low water in the whole river system where channels, haors and baors criss-cross in a magical maze.
Agricultural crop production will be impeded for both high and low flow, causing economic loss and despondency to farm populace.
Fishery and fishermen will be economically affected. For all dam projects fishery diminishes in rivers and fishermen lose jobs which pose a major concern for the people and the government.
As the time will pass environmental pollution and degradation will turn worse, and in future, viciously it may be irreversible and beyond redemption.
Slowly and surely cool and congenial environment will turn hotter and hostile, harbinger of a dreadful and apprehensive climate change in the whole Sylhet area.
Massive damage to bio-diversity, flora and fauna will occur, some facing extinction.
Beneficial sediment for increasing soil fertility will be impeded as dam releases clear water.
All dams in the world have adverse impacts upstream, at dam site and downstream areas. There is no dam in the world, free of adverse impacts. Larger the dam, harsher is the problem.
Mitigation measures
Damages caused by environmental degradation will be colossal, but for all damages caused, mitigation measures must be worked out and listed and database. One will have to think how to repair the damage caused to almost all sectors of economy and bring some remedy and relief.
All damages -- economic, environmental and social -- must be quantified and expressed in monetary terms and total cost involved will be presented to the authority with request to provide funds for correction and re-building.
The norm in environmental rule such as "Polluters Pay", should be applied.
With bi-lateral diplomacy tacitly the upper riparian may be asked/requested to pay or at least share the cost of mitigation measures. It is up to the government to find out alternative options like joint fund between the disputing parties.
Concluding remarks
Impoundment and reservoir capacity: The reservoir has a capacity of 15 billion m3 of water. Of this there will remain a certain percent as dead storage. Storage is reserved for continuous release to flow over turbines to generate hydro-electricity and the water is allowed to flow downstream. We must know the rate of flow over turbines and its combined release in downstream channel. There will be mandatory continuous release as ecological flow. Agreed equitable and fair share that will be allowed to flow to Bangladesh must be negotiated now and settled.
Low flow: For low season average level, further study is needed on getting data of release from dam. Share of Barak waters should be negotiated and regularly monitored as that agreed share would reach Bangladesh, not like as it happened with the Ganges for Farakka. For low flow the area will be affected by drought and desertification.
High flow: After the reservoir is filled to capacity with impoundment of 15 billion m3 of water, the entire excess flow will pass downstream through the spillways and outlets with all gates open for ensuring safety of the dam. Entire flow from the turbines will flow unobstructed to Bangladesh.
Dambreak or dam failure: For 1.0m depth of flood, the impoundment involved was stated to be 10 billion m3. Since the capacity of the dam is 15 billion m3 and spilled water will finally exit through the border of Bangladesh the wall of water from dam will submerge the area to a larger depth.
EIA: Since EIA conducted by India just stopped short of Bangladesh border, EIA study in Bangladesh for adverse impacts of the dam must be conducted.
Damages and deterioration of economy in all sectors and sub-sectors like agriculture, irrigation, water supply, water-logging, fishery, pollution and environment and industries must be identified and expressed in quantities in both physical and monetary terms and mitigation measures undertaken for correcting/ameliorating the damage and improving water level in channels, by sharing adequate water for irrigation, navigation, fishery etc. and combating pollution and environmental degradation, taking care of aquatic flora and fauna, particularity fishery, local and large industries like gas, power, fertilizer and so on. In all dam projects biodiversity becomes the worst victim around the world.
The writer is Professor of Civil Engineering, the World University of Bangladesh, Dhaka.
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