Modern earth-moving equipment has made it easier to move large amounts of material. Making an embankment of mil-lions of tons of rock or earth is often cheaper than building a slender arch of concrete. In 1980 the world’s tallest embankment dam, the Nourek Dam, was completed on the Vakhsh River in Tajikistan, USSR. It is 1040ft (317m) high and contains enough Fill to make a cube taller than the Empire State Building.
Arch-gravity dam The Hoover Dam on the Colorado River was completed in 1936. It is 577ft (176m) high and relies on its weight (gravity) and its shape (an arch) to hold 38 billion tons of water.
Embankment dams come in two types: the earth-filled dam (also called an earthen dam or terrain dam) made of compacted earth, and the rock-filled dam. A cross-section of an embankment dam shows a shape like a bank, or hill. Most have a central section or core composed of an impermeable material to stop water from seeping through the dam. The core can be of clay, concrete, or asphalt concrete. This dam type is a good choice for sites with wide valleys. They can be built on hard rock or softer soils.
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