Resolution No. 4814 - Laserfiche WebLink

Home Browse Search

DAM SAFETY 12,1 Overview of Dams Dams are structures built to impound water. Dams are built for many purposes including water storage for potable water supply, ~ivestock water supply, irrigation, or fire suppression. Other dams are built for flood control recreation, navigation, hydroelectric power or to contain mine tailings. Many dams provide recreationa~ activities, but recreation is rarely the primary motivation for dam construction. Dams are also commonly multifunctional, serving two or more of these purposes. The National inventory of Dams, NID, which is maintained by the United States Army Corps of Engineers, is a database of approximately 76,000 dams in the United States~ The NID does not include all dams in the United States. Rather, the NID includes dams that are deemed to have a high or significant hazard potential and dams deemed to pose a Iow hazard if they meet inclusion criteria based on dam height and storage volume. Low hazard potential dams are included if they meet either of the following selection criteria: 1 ) exceeds 25 feet in height and 15 acre-feet of storage, or 2) exceeds 6 feet in height and 50-acre feet of storage. There are many thousands of dams too small to meet the NID selection criteria. However, these small dams are generally too small to have significant consequences if they fail and thus are generally not considered for purposes of risk assessment or mitigation planning. This N~D potentia~ hazard classification is solely a measure of the probable impacts Lf a dam fails. Thus, a dam classified as High Potential Hazard does no___t mean that the dam is unsafe or ~ikely to fail. The level of risk (probability of failure) of a given dam is not even considered in this classification scheme. Rather, the High Potential Hazard classification simply means that there are people at risk downstream from the dam in the inundation area, if the dam were to fail The N~D potentia~ hazard classification system for dams is as summarized below in Table 12.1. Table 12,1 N~D Hazard Potential Classification for Dams~ Hazard Potential Loss of Human Life Economic, Environmental, or Classification Lifeline Losses Low None expected Low and generally bruited to dam owner Sigmflcant None expected Yes High Probable, one or more expected Yes, but not necessary for th~s class~ficabon. Dams assigned the Iow hazard potential classification are those where failure or mis- operation results in no probable loss of human life and Iow economic and/or environmental losses. Losses are principally limited to the dam owner's property. Dams assigned to the significant hazard potential classification are those where failure or mis-operation results in no probable Doss of human life but can cause economic loss, environmental damage, or disruption of lifeline facilities. Significant hazard Public Review Draft: August 6, 2004 12-1