IT is widely recognised that all dams in the world have adverse impacts, down stream, at dam site and also up stream. Larger the dam harsher and deeper is the problem. Obviously for this is mandatory requirement of EIA for a dam project, India prepared an EIA for Tipaimukh Dam covering a large area up to the border with Bangladesh. As per international convention for common drainage basin. ELA should be prepared for both the upstream and downstream riparians and damages to economy and environment should be quantified both in physical and monetary terms in order to ascertain the cost of mitigation and apportion it between the disputing parties. Generally, as per environmental rule "Polluters Pay" should be applied.

Since the ELA prepared by India excluded the lower riparian, an independent EIA should be mandatorily conducted for possible affected areas of Bangladesh. This will show, among others things, the adverse impacts on economy and environment which are apprehended irrespective of diversion or no diversion of water for irrigation in India.

Some less treaded areas of numerous adverse impacts such as release of clear water from the dam in the river channels downstream is no less damaging. The released water lacks sediment which affects soil-fertility, agriculture and fishery. Recycling of released water from dam back to reservoir in the desperate drought period and continuing filling of reservoir in case the reservoir was over designed are not compatible with available runoff from the catchments. During monsoon dam and spillway release causes high flood, submerging even higher lands. Low flow during lean period adversely affects irrigation, agriculture and navigation; causes deposition of rudiment for slack water which raises bed level of river channels that accentuate higher flood. Agreement for fair and equitable sharing of water and its validity and tenure should be compatible with the long life of the dam transcending say, half a dozen of generations.

Inflow and reservoir impoundment

Generally the design of reservoir capac- ity of a dam is based upon the average annual runoff at the dam site from the catchments. If we have discharge reports and data, we can check capacity of the reservoir and other components of the dam, spillways, outlets etc. If we have required data of rainfall, discharge etc we can find out what kindTipaimukdam is, whether the dam is designed compatible with annual flow and losses and demand of water for hydropower, irrigation, water supply etc or it is over-designed.

A reservoir is designed on annual inflow and demand. Its implication is that in dry season, average low flow in India, as it is this year, reported to be the lowest in 133 years of records, may create crisis in augmenting the impoundment to full capacity on an annual basis. It may be repeated and prolonged in enhanced intensity, when the dam authority may resort to conserve and augment every drop of water released from the dam and within the reservoir. This will be done by recycling the turbine release pumped back upstream to the reservoir. This will deprive the channels downstream.

A kind of crisis will ensue during the rainless dry season as supply may fall short of demand and "mining" of water in the reservoir will take place to the detriment of Bangladesh. Hot, dry and hostile climate will invite dreaded effect with concomitant adverse impact and damage to its economy and environment.

High and low flows and adverse impacts

High flow: We learnt that there would be no barrage or any form of diversion

structure for irrigation in India, we can take that the entire water after flowing over the turbines, would flow unobstructed to Bangladesh. During high monsoon the water level will further rise for the additional influx of flow from the spillways and outlets which remain open for ensuring safety of the dam. This high flood level in the lower riparian is apprehended to occur irrespective of irrigation or no irrigation in India. Erstwhile high lands will be flooded.

Low flow-whether there is irrigation or no irrigation in India, low flow will affect agriculture and fishery, navigation, create pollution and a state of drought and environmental degradation during the dry season. Low flow with slack water will enhance deposition of sediment and raise river bed level, causingsnags in navigation.

Water-sharing: Some suggestions

Any agreement on water sharing on an equitable and fair basis for rivers sharing common drainage basin should be long-ranged, depending on circumstances, particularly on the life of the project/structure in question. Like the Tipaimukh dam with modern design and a strong structure may have a life of 100 years or more outliving and transcending five to six generations of people. Agreement should be such that it can successfully face the test of time within its tenure and currency. An equitable and fair share of water that will flow to Bangladesh during low flow season should not fall below an agreed rate of flow, clearly stated in cusecs (cubic feet per second) or cumcs (cubic meters per second).

As no agreement is sacrosanct, there should be provision for modification or any relevant major change in the document which suits the mutual interest of the two participating parties as and when the situation necessitates it. In case of serious disagreement, the case may be referred to an impartial and expert arbitrator whose verdict would be deemed binding on the disputing parties.

International experience

Now a days high large dams are rarely built and vehemently discouraged in USA, perhaps also in EU countries. Protests from the Green Groups are formidable. A fully designed large hydroelectric dam on Hadeja Jama-are river, could not see the light of the day as government was forced to abandon the construction for the protests of the environmental groups in Nigeria in early nineties. Large-dams are now built only in the Third World developing countries, obviously prioritizing economy over environment. Reportedly, some dams are being broken for flow if severs in USA.

China ranks first in the number of dams (still building in full swing and aggressively). India (still going on) second and USA third (no more dam). Dams in China, India and USA number three to five thousand in each country. China is unilaterally building Mega Dams on the Brahmaputra and Mekong rivers within its territory with apprehension of seriously jeopardizing economic activities and creating monumental environmen-

tal crisis in India and Bangladesh, and Laos, Thailand, Cambodia and Vietnam in South, and South East Asia, respectively. China appears to have an insatiable hunger for dams and a parched desert thirst for dam waters.

Conclusion

Considering the strong outcry and protests, from the environmental groups and the knowledgeable people of civil societies, both in India itself and Bangladesh, for cogent reasons that the dam not being helpful in any way, for Bangladesh, our government may request our friendly neighbour. India, to reconsider, better stop its construction.

Our request would be very much in the with the recent assertion and assurance pronounced by the Prime Minister of India himself and two other leaders, like India's External Affairs and Power Ministers that "India will not do anything that harms Bangladesh". '

Pertinent data and information, collected by the Bangladesh parliamentary delegation who visited India recently are now being analyzed and studied by an expert committee set up at the instance of the Prime Minister. It is expected to come up with much-awaited plausible recommendations and guideline which can help the government arrive at a prudent decision for considering the next appropriate move to deal with the intricately complex and expressly urgent problem.

The writer, a water/river specialist, is a professor of civil engineering, World University of Bangladesh, Dhaka