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Eugene -Springfield Area Natural Hazards Mitigation Plan <br />6. Appendices <br />Concrete dams are subject to failure due to seepage of water through foundations or <br />abutments. Waterways with more than one dam have downstream dams that are subject <br />to failure induced by the failure of an upstream dam. If an upstream dam fails, then <br />downstream dams also fail due to overtopping or hydrodynamic forces. <br />The following may lead to failure for any type of dam: <br />■ Improper design or construction. <br />■ Inadequate preparation of foundations and abutments. <br />■ Improper operation of a dam, such as failure to open gates or valves during high <br />flow periods. <br />■ Unusual hydrodynamic forces. <br />■ Landslides may cause surge waves to overtop dams or create hydrodynamic <br />forces. <br />■ Earthquakes can cause seiches (waves) in reservoirs that may overtop or <br />overload dam structures. <br />■ High winds, in rare cases, may cause waves to overtop or overload dam <br />structures. <br />■ Deliberate damage via sabotage or terrorism. <br />The Association of State Dam Officials, using data collected from the Dam Incident <br />Database between 2010-2017, indicated overtopping to be the most common cause of <br />dam failure in the United States. <br />H.3 History of the Hazard in Eugene -Springfield <br />There have been no reported dam failures in Oregon that have impacted Eugene - <br />Springfield. <br />HA Risk Assessment <br />HAA How are Hazard Areas Identified? <br />Although the likelihood of failure is very low, all dams upstream from the Eugene - <br />Springfield area have the potential of causing widespread flooding should they fail. All <br />dams in the Eugene -Springfield area have been inventoried by the Army Corps of <br />Engineers in the National Inventory of Dams (NID). The NID lists 26,983 dams in the <br />8 Army Corps of Engineers, `National Inventory of Dams, Interactive Map & Charts, 2018, <br />httos://nid.sec.usace.anny.miU, (accessed 1 August2019). <br />6-131 January 2020 <br />