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dam-l LS. The Frontier Post: The myth of large dams (I)
>Return-Path: <owner-irn-narmada@igc.org>
>Date: Wed, 19 Aug 1998 22:08:58 -0800
>From: Maqbool Khan Aliani <maliani@fecrc.com> (by way of patrick@irn.org
(Patrick
> McCully))
>Sender: owner-irn-narmada@igc.org
>Subject: LS. The Frontier Post: The myth of large dams (I)
>To: irn-narmada@igc.apc.org
>X-Sender: patrick@pop.igc.org
>
>AUGUST 09, 1998 SUNDAY
>
>FULL STORY - The Frontier Post
>
> The myth of large dams
>
> Engr Javaid R. Leghare
>
> The most significant damage from the dam construction is, however,
>caused downstream. The impoundment prevents the silt
> from being carried to the fertile land downstream and the sea. That
>silt, which generally contains large quantities of feldspar,
> clay and organic matter, has a high nutrient value. For instance,
>before the damming of the Amu Darya River in the Soviet
> Union, an estimated 15 tons of silt were deposited by the river
>each year on every acre of the delta.
> According to the University of Moscow, the land received 250
>kilograms of humus, 200 kilograms of potassium oxide and 50
> kilograms of phosphoric oxide from this yearly deposit.
> Similarly, before the building of the Aswan Dam, the Nile River
>deposited about 100 million tons of sediments each year i.e
> about 40 tons of silt per acre. This was rich in Silica, aluminum
>and iron. These losses are now being increasingly felt in Egypt.
> Today, the Nile deposits only a few tons of sediment each year on
>the delta, and the annual cost of fertilisation now required
> by Egypt is about 100 million dollars a year. A similar cost will
>have to be borne by the farmers of Sindh if the Kalabagh dam is
> ever constructed. It has also been pointed out that the impounded
>silt within the reservoir of the Kalabagh dam will reduce its
> storage capacity from 7.9 MAF to 1 MAF, within 25 years. It is also
>likely that Tarbela will set up completely by 2020. Thus,
> the life span of these dams will shorten considerably and reduce or
>block their hydro-electric power generation capability.
> Another important consequence occurs when waters downstream of a
>dam are deprived of their silt content __ it causes
> large-scale erosion of the land in the delta. In the Nile today,
>the delta shoreline that was advancing through history is now
> receding. A major blow such an affect will have on the Indus delta
>will be the loss of the fertile lands and the rich mangrove
> forests, the sixth largest in the world.
> The dams impact on fisheries is also tremendous. By disturbing the
>ecological balance of the river it impounds, a dam can
> have serious effects on fish life within the river bases itself,
>and indeed, within the seas immediately beyond its estuary.
> According to the Ukrainian Academy of Sciences, river sectioned off
>by dams are no longer single ecosystems. The flow of
> suspended material and dissolved gases, which previously sustained
>the life of the river population, is interrupted. Also fish
> migration is disrupted and spawning and fattening conditions
>deteriorate. The total river population decreases substantially
> and some species disappear completely.
> Indeed, the impact of the Kalabagh dam on the Sindhi Palla and the
>endangered the 'blind dolphins, about one hundred of
> which exist today, will be total extinction. Also, with a loss of
>silt, which contains nutrients essential to fishes in the sea
> beyond, the marine life will be greatly depleted. Before the
>building of the Aswan Dam, the sardine fisheries along the eastern
> Mediterranean coast yielded some 18,000 tons of fish a year.
>Deprived of the Niles silt, the catches were down to 500 tons a
> year after the construction of the dam. According to a 1989 report
>of the National Commission of Agriculture, the marine and
> fisheries industries in the Indus delta and the Arabian Sea
>coastline have already decreased due to the lower discharge of the
> Indus caused by impoundments upstream.
>
> The building of water storage schemes had led to an increase in the
>salinity of many rivers. This is due partly to the return of
> highly saline drainage waters from the irrigated lands, and due
>partly to the reduced flow of the rivers themselves. This
> reduced flow leads to the intrusion of sea water into the estuaries
>and deltas of the rivers.
> Indeed, in some river basins, notably in Bangladesh, sea water has
>been known to intrude up to 100 kilometres inland. Also,
> the salt content of the lower reaches of many rivers is now so high
>that they no longer provide suitable habitats for fresh
> water fish. With domestic waste and industrial chemicals in cities
>upstream pouring into an already reduced river flow, it may
> led to the formation of cesspools and eventually to the complete
>eradication of marine life. The drinking water, with higher
> concentrations of toxic and bacterial wastes, would lead to
>widespread disease and health-related problems in Sindh.
> Design and earthquake problems should also be given consideration
>in the construction of large dams. The failure of the
> spillways to function properly led to the near-failure of the 4009
>feet high Tarbela Dam in 1975-1976. The Manchu II Dam in
> India overflowed during floods in 1979 and caused the death of
>1,500 people down streams. Probable earthquakes can also
> cause great loss of life when they damage dams.
>
> Interestingly, large reservoirs can also trigger earthquakes. This
>phenomena was scientifically agreed to at the Fourth World
> Congress on Earthquake Engineering (Chili 1969). UNESCO also
>concluded in 1970 that the impounding of certain reservoirs is
> responsible for triggering seismic phenomena. In the 60s, four
>earthquakes measuring between 5.8 and 6.5 on the Richter
> scale occurred because of large reservoir in China, Zimbabwe,
>Greece and India. Damage was subsequently caused to the dam
> itself.
>
> This knowledge, however, does not seem to have any influence on
>developing countries despite warnings given in advance.
> In India, for example, seismic activity has greatly increased due
>to the construction of the Tehri Dam on the Bhagirathi River in
> the mid Himalayas. Between 1971-1973, the yearly average was one or
>two earthquakes, in 1974, five earthquakes occurred,
> and in 1975, there were seven. NWFP is a high risk earthquake area.
>A large earthquake struck near Peshawar in October, 1990;
> which is near the site of proposed Kalabagh dam. The government of
>Pakistan should take all of this into account.
> Waterlogging and salination of agricultural land is known to
>increase with intense irrigation. This has been experienced in
> Pakistan because of the barrage phenomena. Twenty-five million of
>the 37 million acres under irrigation are estimated to be
> salinised, waterlogged or both. Of this land, five million acres
>are classified as severely affected, 10 million as partly saline, and
> 10 million as poorly drained.
>
> Continued
>
>
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>
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Dianne Murray,
Coordinator, Dam-Reservoir Working Group
Webmistress, Dam-Reservoir Impact and Information Archive
http://www.sandelman.ottawa.on.ca/dams
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