Dam Construction

Dams are among the oldest structures built by humans for collective use. A dam is a barrier that is constructed across a river or stream so the water can be held back or impounded to supply water for drinking or irrigation, to control flooding, and to generate power. The main kinds of dams are earth fill, rock fill, concrete gravity, concrete arch, and arch gravity. The last three types are all made of concrete, reinforced concrete, or masonry. (The term masonry can mean concrete, bricks, or blocks of excavated rock.) Fill dams include all dams made of earth materials (soil and rock) that are compacted together. One type of fill dam called a tailings dam is constructed of fine waste that results from processing rock during mining; at mine sites, this soil-like waste is compacted to form an embankment that holds water for the mining and milling processes or to retain the tailings themselves in water.
Of the main categories of dams listed above, all have been built since ancient times although many refinements were developed in the nineteenth and twentieth centuries with improved engineering technology. Dams that leak have failed to do their job, either because they simply can't hold water or because the water seeping through them eats materials away from the inside of the dam causing it to fail structurally. In modern times, most fill dams are also built with zones including a clay center or core, filter and drainage layers, coarser materials sandwiching the clay core, and rock on the upstream (water) face to prevent erosion. These zones can be seen clearly when a cross section is cut from the upstream to the downstream side of the dam. All fill dams depend on weight to remain stable.
Fill embankments are usually less expensive to construct than concrete dams. Soil or rock are present at the site, and construction techniques, though complex, are also less costly than for concrete construction. For these reasons of available materials, low cost, and stability with