Damming a river

Dams harm rivers. Photo: R S C Anjan/ Drik NewsZulfiquer Ahmed Amin

THE Farakka Barrage, when commissioned in 1970, seemed to be a venture by India for saving the Kolkata port from silting up. In next few decades, the outcome in the lower riparian Bangladesh was disastrous due to the dearth of water in the entire south-western region. The country also experienced continuous losses in the agricultural, fisheries, forestry, industry, navigation and other sectors. It also caused fatal damages over the years through floods, droughts, excessive salinity and depletion of groundwater.

The project also resulted in massive devastation in Malda on its upstream, Murshidabad in West Bengal and south-west of Bangladesh on its downstream. Excessive sedimentation, increasing flood intensity, and river erosion are some of its effects.

Bangladesh is facing desertification along the normal course of the Padma river, with no water in the water-body, and the mighty river has become the reason for continuous floods and bank erosion.

Farakka, thus, was a major breach of trust by India against Bangladesh as India had repeatedly claimed before it started the project that the dam would not cause any damage to Bangladesh. The same assurances are being given about the Tipaimukh dam.

Land and water are ecologically linked in a natural system called a watershed. Any river is the product of the land it inhabits -- the type of rock and soil, the shape of the land, and the amount of vegetation are some of the factors that determine the river's shape, size and flow. When these ties between the land and the river are breached by a large dam, the consequences are felt throughout the watershed, as well as by the web of life it supports.

The main hydraulic effect of a dam is the discharge of the collection basin to a stationary reservoir instead of a stream-bed. Therefore, an instant change will start downstream, which dries partially or totally whenever the reservoir begins to accumulate water. During this temporary or periodically repeating time interval, the hydrological balance can collapse, and structural damages are observed in the water dependent ecosystem.

Dams have a significant impact on the disruption of natural sediment movement processes in rivers, which is blocked by the dam. Sediment builds up in the reservoir behind the dam, while creating sediment starved conditions below the dam, which lead to channel bed degradation, channel narrowing and bank erosion. It is natural that the river, which is accustomed to carrying sediment and now has none, will pick up the sediment from the streambed below the dam.

Dams are engineered to withstand the force of a certain number of tons of water --however large the reservoir is planned to be. When the pressure builds up the dam bursts, killing people and destroying settlements downstream. This disruption of sediment movement often disconnects a river from its natural floodplain downstream or submerges riverine floodplains upstream of a dam. In some cases this leads to river systems that are no longer naturally sustainable.

Dams hinder growth, development and maturation of fishes. They hold back not only sediment but also debris, which includes leaves, twigs, branches, and whole trees, as well as the remains of dead animals. The lives of organisms, including fish in downstream, depend on the constant feeding of the river with debris.

Many fish must move upstream and downstream to complete their lifecycles. Dams act as a barrier in this migration. The cold, clear water of downstream will be starved of nutrients and provide little or no habitat for animals. A river with a dam eventually becomes little more than a dead channel of water.

About 7 to 8 percent of the water in Bangladesh is obtained through the river Barak to Surma-Kushiara river basins. Agriculture, irrigation, navigation, drinking water supply, fisheries, wildlife in numerous haors (wetlands) and low lying areas in entire Sylhet division, some areas of Comilla and Mymensingh districts, and some peripheral areas of Dhaka division depend on this water.

The river system also supports local industries like fertilizer, electricity, gas etc. Around five crore people of Sylhet and Dhaka division will face problems as Surma and Kushiara will lose five feetof water in the rainy season. Massive environmental degradation will take place, severely affecting weather and climate, turning a wet, cool environment into a hot, uncomfortable cauldron.

Haors around Surma-Kushiara river located in Sunamganj, Habiganj and Moulvibazar districts and Sylhet Sadar Upazila, as well as Kishoreganj and Netrokona districts, receive surface runoff water from rivers and channels in the rainy season and serve as the granaries and fisheries of the northeast. During dry season the water drains out, leaving an alluvial-rich soil suitable for cultivation of boro. The rice farmers plant when the water recedes in the winter, and harvest before the monsoon waters come.

The water carries not only fish larvae but also much-needed nutrients into the haor, which turns into a vast nursery for fish. When the water recedes in the winter, the nourished fish move out into the rivers and are caught by the fishermen. The total area of this wetland covers nearly 25,000 square kilometres and supports approximately 20 million people.

They literally live by the ebb and flow of the waters. Any artificial alteration of this haor could affect food security and bring disaster to the region.

The north-east region of India is one of the six major seismically active zones of the world, which includes California, Japan, Mexico, Taiwan and Turkey. The Tipaimukh site is located in Zone-V of the Seismic Zoning Map of India. As per available records, about 16 earthquakes of magnitude greater than 7.0 have occurred in this region, of which 2 had a magnitude more than 8.5. An earthquake of significant scale will destroy the dam, with unimaginable damage to life and property.

While Bangladesh is concerned over the dam on the Barak river, India, too, is busy raising concerns about China's plan to build a dam on the Yarlung Tsangpo (Brahmaputra) in Tibet to generate 40,000 Megawatt power, and to divert 200 billion cubic meters of waters to the Yellow River for easing water shortages in Shaanxi, Beijing and Tianjin in northern China.

India's proposed Tipaimukh dam and China's proposed dam over Yarlung Tsangpo bear much similarity in terms of scale of destruction, threats and challenges both in the upstream and the downstream portion of the rivers. India is playing a double game. While objecting against China's plan to dam Yarlung Tsangpo, India is aggressively pursuing mega-dams construction spree in India's north-east, notwithstanding concerns in the north-east and Bangladesh.

Against the backdrop of its nonviable cost-effectiveness, immense economic and environmental damage coupled with utter human sufferings, when worldwide decommissioning of dams has over-taken commissioning, India's insistence may cause deterioration of Indo-Bangla relations.

Dr. Zulfiquer Ahmed Amin is a physician and specialist in Public health Administration and Health Economics, and is presently working in Kuwait.