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<br />FOCUS <br /> <br />Since before the dawn of history, civilizations in many <br />lands have built dams to impound water. In fact, attaining <br />the capability to organize men and materials to produce a <br />massive dam could well be considered a significant milestone <br />in the development of a civilization. Unfortunately, dams <br />not properly designed, constructed and maintained can fail-- <br />sometimes catastrophically. Only in recent decades has the <br />technology been available to permit reasonable assurance of <br />safety in the development and maintenance of dams, but this <br />technology still is not applied by all dam builders and <br />owners. Thus, while archeologists continue to find ruins of <br />failed dams in many locales where the civilizations that <br />produced these structures have long vanished, we still have <br />dam failures that are costly in terms of lives lost and <br />property damaged. <br /> <br />Prior to 1900, many low pioneer-type wooden or stone- <br />filled timber crib dams were built in the united States <br />to collect and store water supplies, as aids to navigation, <br />and to provide waterpower for grist mills, saw mills and <br />factories. In the same period some notable, larger stone <br />masonry dams were built, generally to provide urban water <br />supplies. Many of these structures failed; but, because of <br />their low heights and small impoundments, resulting damages <br />usually were not excessive. A notable exception was the <br />failure of a small dam at Johnstown, Pennsylvania, in 1889. <br />This failure was largely responsible for one of the worst <br />natural disasters ever experienced in this country. <br /> <br />The twentieth century has seen a tremendous increase in <br />dam building in the united states, both in the numbers of <br />dams constructed and in their sizes. Two sets of factors can <br />be identified as causes of this phenomenon. First, the <br />expansion and industrialization of our Nation and the growth <br />in our population have greatly multiplied needs for impound- <br />ments for many purposes. It has become particularly fashion- <br />able to impound artificial lakes to enhance the environment <br />at housing and recreational developments. Second, develop- <br />ments in construction methods, particularly in earth-moving <br />equipment, have made it economically feasible to meet those <br />needs. The result of this virtual explosion in dam building <br />in the united States was revealed by the National Inventory <br />of Dams completed in 1981 under the direction of the U.S. <br />Army corps of Engineers. This inventory found 63,419 <br />non-Federal dams having impounding heights of 25 feet or more <br />or having impounding capacity of 50 acre-feet or more. <br /> <br />Focus - page 3 <br />