Dams all over the world have caused enormous damage. There are some 45,000 large dams - those above 15 metres in height from foundation to crest. In all, more than 400,000 square kms of land have been drowned by dams worldwide. Dam failures have killed 243,000 people. And to top this all, they have caused between 40 to 80 million people to be displaced.
When a river does not reach its delta, the delta will die from lack of new silt and nutrients to replenish the old, and if it reaches the delta but with much less water, pollution tends to get more concentrated. The Colorado's delta, formed when the river used to reach the sea, due to this toxic concentration is now decimating waterfowl and mammals, killing off a once highly productive fishery and contributing towards the virtual extinction of the vaquita, the world's smallest porpoise.
The Aswan High Dam traps 98 percent of the silt that used to be carried by the Nile. As a result, its delta by the Mediterranean is sinking into the sea. Today the Nile no longer has a true delta. The delta was retreating at around 20 metres per year into the sea before the High Dam was constructed but it is more like 240 metres per year now. The delta, the size of Northern Ireland, constitutes two-thirds of Egypt's crop land.
Beach erosion
The delta created by the Mississippi is facing the same problem. The sediment deposited has more than halved since 1953 mainly due to dams on the Missouri, the Mississippi's main tributary. The result of sediment deprivation is causing 10,000 hectares of Louisiana to disappear into the sea each year. And since the 1920s, dams have reduced four-fifths of the sediment reaching the coast of Southern California. This has caused massive beach erosion.
The Ganges and the Indus in India have no outflow to the sea during the dry season due to dams. The Indus delta contains the world's fifth largest mangrove forest. In general, mangroves are very rich in wild life and marine life, a breeding place for shrimps and fishes. The Indus mangroves harbour a wide variety of wildlife, including several endangered species of birds and dolphins.
Similarly with the Ganges delta. With very little fresh water during the dry season, salinity is threatening the Sundarbans, one of the world's largest mangroves and home of the threatened Bengal tiger. The damaged mangroves are also threatening its fish habitat.
Before the Amu Darya River in Central Asia was dammed, an estimated 40 tons of silt were deposited annually on every hectare of the river's delta in the Aral Sea. Now it is a barren, toxic, salt-encrusted land with the shoreline miles away. The Aral Sea, now only half its original size, used to support 60,000 workers in the fishing industry. The industry stopped in 1982 with most of the fish gone - the freshwater has turned more saline than the sea.
The number of bird species dropped from 319 to 168, only 30 of the 70 mammal species are left, and the delta forests have died. The toxic land is causing a lot of new illnesses, affecting millions of the surrounding population. It is a terrible environmental disaster created by humans.
Environmental niches
Living things adapt to their local environmental niches over long periods of time. When a dam is constructed over a river, the environment of the river and its surrounding is not the same environment as before. A reservoir environment is not the same as a free flowing river environment. An environment rich in silt and its nutrients supports many species. Deprived, the river and its delta lose their ability to support a rich diversified life.
Dams disrupt this adaptation. They tend to fragment the riverine ecosystem, isolating populations of species up and downstream of the dam and cutting off migrations and other species movements.
According to biologist Mohd Zakaria Ismail of Universiti Malaya, for a reservoir, the hotter the surface temperature and the deeper it is, the less habitable it is. The Temenggor Dam, with a depth exceeding 60m and surface temperature exceeding 27 C, cannot support life below 20m. The number of fish starts to decrease substantially below 6m. High concentration of toxic gases, particularly hydrogen sulphide, and the lack of dissolved oxygen - due to plant decomposition - are two main reasons for the poor life support ability.
A report, Pilot Analysis of Global Ecosystems (Page): Freshwater Systems , released by the World Resources Institute, reveals that the world's freshwater systems are so degraded that its ability to support human, plant and animal life is greatly in peril. As a result, many freshwater species are facing rapid population decline or extinction and an increasing number of people will face serious water shortages.
Extinction of species
The Page report estimates that dams, diversions or canals, fragment almost 60 percent of the world's largest 227 rivers. Concerning forest fragmentation, Edward Wilson, an ecologist at Harvard, puts it thus, "We know at least this much: an Amazon forest chopped into many small fragments will become no more than a skeleton of its former self." This should apply to any forest system, Amazon or Malaysian. A continuos forest is not the same system as a forest fragmented by roads or dams even though of the same size. Animal mobility, for one, is reduced.
The movement of the salmon in temperate rivers is disrupted by dams. They spawn upriver and the young smolts then make their way down to live in the sea until its time for them in turn to return to spawn. According to Mohd Zakaria Ismail, in Malaysian rivers we have the ikan linang which also migrates between the river and the sea, as well the udang galah . Dams would be an obstruction and thus result in their demise, as has been done to the salmon.
Not only dams but roads to dams too encourage fragmentation of forests. The inevitable intrusion by cultivators seeking new pastures, for logging and for other human activities, lead to deforestation and its subsequent problems. The fragmentation into small populations can lead to inbreeding of species and the problems associated with it - poor genetic stocks - which in turn lead to their demise.
Dams are also the main reason why one-fifth of the world's freshwater fish are now either endangered or extinct. In countries heavily dammed, this gets worse - in the US, two-fifths, and in Germany, three-quarters, are endangered or extinct. Other riverine and wetland life forms are similarly threatened. Further, freshwater sources, because of a host of human assaults and particularly because of dams, are the most degraded of major ecosystems.
Organic decomposition in reservoirs produces much methane, a greenhouse gas more potent than carbon dioxide in its global warming potential. In studies, the production of methane from uncleared forest reservoirs for hydroelectricity in its contribution to global warming is about equal to the carbon dioxide produced from oil fired power plants. Dams are not such a clean technology after all. On the other hand, clear cutting the area to prevent decomposition results in much erosion, quickly silting up the reservoir making it useless.
Loss of nutrients
A free flowing river brings sediments rich in nutrients to the flood plains and on to the delta and the sea. The rich nutrients are plant and animal food for sea life. The sedimentation of silt and nutrients behind dams, together with over fishing, are the main reasons for the severe decline, and in some cases the complete collapse, of local fishing industries.
Before the Aswan was dammed, the Nile used to flood as regular as clockwork annually. The silt it deposited to the soil replenished its fertility. After the flood, farmers could start planting. The loss of the natural flooding and its silt deposit have affected agriculture badly. Now chemical fertilisers are required, which however, cannot maintain the integrity of the soil. Chemical fertilisers, too, are causing grave pollution world-wide.
The elimination of benefits provided by natural flooding may be the single most important ecological impact of dams. (Control of flooding is described in the Pahang dams Environmental Impact Assessment report as a benefit without any qualification.)
The discharge of Russia's Volga to the Caspian Sea, due to dams and diversions, is reduced by 70 percent. This, together with the severe pollution the Volga dumps into the Caspian, have caused the most valuable commercial fisheries to be reduced by between 90 to 98 percent. Sturgeon (from which caviar is obtained) catches in the Caspian Sea is now only one to two percent of historical catches. This fish, which has been around for 250 million years, surviving even the dinosaurs, might now meet its demise in our hands.
The lack of nutrients, trapped in the Aswan dams, virtually destroyed the sardine and the shrimp industries off the Nile delta.
Mangrove forests are a very important breeding ground for fish, shrimps, and other marine life because they are rich in food. Estuarine mangroves are especially rich in nutrients brought down by rivers. Near shore catches in some tropical areas are proportional to the extent of their mangroves. The 80 percent reduction of discharge through the Indus delta has killed off almost all of its mangroves.
Sea water intrusion
For the Sungai Selangor, the regulated water after extraction could leave only a flow of 300 million litres per day in the river. This is much lower than even during the dry season. The difference between normal flow and that after damming would lead to salt water intrusion inland. This would kill the berembang trees, the trees fireflies feed on. Without the trees the unique synchronous flashing display lights of the fireflies at Kampung Kuantan will be lost forever.
Salt water intrusion into surrounding land along the river will destroy land and agriculture around Kuala Selangor. This follows from examples everywhere where saltwater intrusion has occurred.
Further reading
1} Patrick McCully, Silenced Rivers: the ecology and politics of large dams. Zed Books: London, 1996.2) [#1] World Commission on Dams, Dams and development: a new framework for decision making [/#]
DR ROSLI OMAR is an academic interested in the impact of science and technology on society and environment (being bred on the white heat of technology creed himself), be they dams, biotechnology/genetic engineering, or polluting machines. He believes that science and technology, as used at present, is sustaining an unsustainable development - the worst of all possible paradoxes.
