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<br />Why Dam Failure? <br /> <br />Dam failure floods are a result of hydrologic and geologic events and <br /> <br />structural deficiencies. The operation of a reservoir can also influence the <br /> <br />safety of the structure. <br /> <br />The most significant hydrologic deficiency is inadequate spillway capa- <br /> <br />city which can cause the dam structure to be overtopped at times of high <br /> <br />inflow to the reservoir,6 due to excessive runoff after unusually heavy <br /> <br />precipitation in the basin or snowmelt. Large waves generated from landslides <br /> <br />into a reservoir or the sudden inflow from upstream dam failures are other <br /> <br />causes of hydrologic dam failure. Overtopping is especially dangerous for an <br /> <br />earth dam because the flow of water over the crest will erode the dam face <br /> <br />and, if continued long enough, will breach the dam embankment and release all <br /> <br />the stored water suddenly into the downstream floodplain. Spillway inadequa- <br /> <br />cies exist due to the rapidly developing science of meteorology and hydrology <br />indicating that prior determinations of the magnitude of floods are less than <br /> <br />required or desired. Related to this, is the great expense involved in <br /> <br />the enlargement of a dam's spillway. <br /> <br />Examples of structural deficiencies include excessive seepage through the <br /> <br />embankment, piping along internal conduits, erosion, cracking, sliding, <br /> <br />overturning, or other weakness in the structure. Old age and neglect are <br /> <br />often at the root of structural deficiencies.? The State Engineer's safety <br /> <br />inspection program is aimed at reducing these deficiencies to an acceptable <br /> <br />level. Dam safety, however, cannot be guaranteed. <br /> <br />-12- <br />