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Few creations of big technology capture the imagination like giant dams.Perhaps it is humankinds long suffering at the mercy of flood and drought that makes the ideal of forcing the waters to do our bidding so fascinating.But to be fascinated is also, sometimes, to be blind.Several giant dam projects threaten to do more harm than good.The lesson from dams is that big is not always beautiful.It doesn't help that building a big, powerful dam has become a symbol of achievement for nations and people striving to assert themselves.Egypt leadership in the Arab world was cemented by the Aswan High Dam.Turkeys bid for( 争取) First World status includes the giant Ataturk Dam.But big dams tend not to work as intended.The Aswan Dam, for example, stopped the Nile flooding but deprived Egypt of the fertile silt that floods left - all in return for a giant reservoir of disease which is now so full of silt that it barely generates electricity.And yet, the myth of controlling the waters persists.This week, in the heart of civilized Europe, Slovaks and Hungarians stopped just short of sending in the troops in their contention over a dam on the Danube.The huge complex will probably have all the usual problems of big dams.But Slovakia is bidding for independence from the Czechs, and now needs a dam to prove itself.Meanwhile, in India, the Word Bank has given the go ahead to the even more wrongheaded Narmada Dam.And the bank has done this even though its advisors say the dam will cause hardship for the powerless and environmental destruction.The benefits are for the powerful, but they are far from guaranteed.Proper, scientific study of the impacts of dams and of the cost and benefits of controlling water can help to resolve these conflicts.Hydroelectric power and flood control and irrigation are possible without building monster dams.But when you are dealing with myths, it is hard to be either proper, or scientific.It is time that the world learned the lessons of Aswan.You don't need a dam to be saved.