How Are Floods Good?
From a historic human perspective, life at the river's edge has been prosperous. Floodplain soils are legendary for their fertility, renewed by seasonal floods and occasionally great floods. River waters have been harnessed for irrigation around the world. And for millennia, rivers were filled with fish and shellfish that could be eaten without fear of pollution. Add this to the convenient transportation afforded by waterways, and you have a pretty nice place to live.
As long as people did not build permanent dwellings in the obvious path of floods, floods were considered a good and helpful part of nature. The predictability of seasonal floods was very important to the development of early civilizations. In order for populations to exist for long periods of time in one place (and develop many of the social and cultural features that we associate with civilization), the soil fertility of their fields had to be renewed regularly. Without regular seasonal floods, the soils would be exhausted in a few years, and the population—facing famine—would have to break up and move on to new areas.
Egyptians referred to the annual flooding of the Nile River as the Gift of the Nile and they worshiped a god of inundation called Hapi. Every year the Nile waters would rise across the floodplain, and leave behind rich black soil when they retreated. Crops were planted right away and never needed fertilizer. Unfortunately, the Gift of the Nile is now a quaint tale for the history books. In 1970, the Aswan High Dam was built across the Nile, trapping not only water for irrigated agriculture, but the rich sediments that had formerly fertilized crops and maintained the Nile delta. Now farmers can grow crops all year round, but they must use large amounts of artificial fertilizer to do so. They also have serious problems with soil salinity (caused by irrigation), and the delta is eroding away. Short sighted? Some people think so. Others, near the dam, are glad to have the irrigation water to grow crops and the electricity generated by the dam.
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