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Eugene -Springfield Area Natural Hazards Mitigation Plan <br />6. Appendices <br />Table H-2 Additional Data on NI D High Hazard Potential Dams <br />County <br />Dam <br />River <br />Storage <br />Year <br />Da <br />ner <br />Name <br />acre feet <br />Built <br />T e <br />Lane <br />Leaburg <br />McKenzie <br />459 <br />1930 <br />PGRE <br />Y <br />EWEB <br />Canal and <br />River <br />Foreba <br />Lane <br />Walterville <br />McKenzie <br />275 <br />1911 <br />CNPGR <br />Y <br />EWEB <br />Forebay <br />River <br />E <br />Lane <br />Santa <br />In System <br />64 <br />1976 <br />RE <br />Y <br />EWEB <br />Clara <br />Source Army Corps of Engineers National Inventory of Dams (NID) <br />The NID dam type classification includes the following types of dams: <br />• RE: rockfill/earthfill embankment dams, primarily rockfill (fill >3" size) <br />• ER: rockfill/earthfill embankment dams, primarily earthfill (fill <3" size) <br />• CN: Concrete <br />• PG: Gravity <br />Lane County's high hazard potential dams were built between 1911 and 1976. All dams <br />are rockfill/earthfill embankment dams, except Cougar which is an earthfill/rockfill <br />embankment dam. All dams are operated by the US Army Corps of Engineers and <br />Eugene Water & Electric Board (EWEB) and have emergency action plans in place. All <br />dams are maintained on a regular schedule and undergo regular inspections, with major <br />re -inspections every five years. Furthermore, the Corps is highly experienced in the <br />construction, operation, and maintenance of dams.8 <br />For embankment dams the most common failure modes are overtopping, structural <br />failures, and seepage through the dam.9 However, all the Corps dams were designed <br />and built with specific flood capacities. hi addition, the Hills Creek Dam likely has the <br />capacity to withstand floods at least as large as a 1,000-year flood event without <br />expected damage. The other Corps dams have similar margins of flood design safety. <br />Under normal or flood conditions, the probability of failure of the Corps operated dams <br />appears highly unlikely. However, all of Lane County's dams were designed and built <br />before seismic design standards were put in place. <br />e Army Corps of Engineers, `National Inventory of Dams, Interactive Map & Charts, 2018, <br />httos://nid.sec.usace.army.miF, (accessed 1 August 2019). <br />8 United States. Association of State Dam Safety Officials. Earth Dam Failures. 2019. <br />httos:Hdamsafety.org/dam-owners/earth-dam-failures Accessed August 2019. <br />6-134 January 2020 <br />