Resolution No. 4814 - Laserfiche WebLink

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McKenzie River, with flooding potential extending downstream including the Eugene/Springfield Metro Area. The worst case scenario would probably be failure of a debris dam that had impounded a substantial quantity of water. Major flooding could occur along the McKenzie River, with the most flood prone area being very similar to the FEMA-mapped floodplains of the McKenzie River. Importantly, because of distance and topography, possible lahars and other distal zone effects would not affect the Blue River or Cougar Reservoirs in northeastern Lane County or any of the upstream reservoirs on the Willamette. Thus, the extent of volcanic hazards for the Eugene/Springfield Metro Area appears most likely to be limited to the possibility of minor ash falls from eruptions at the Three Sisters, at other locations in the Cascades or elsewhere (e.g., Mount St. Helens) and possible impacts on the water system. In all but the most extreme events, ash falls in the Eugene/Springfield Metro Area are likely to be very minor with an inch or less of ash likely. In addition, volcanic events in the Three Sisters area, the McKenzie Pass area or in the Santiam Pass area could temporarily close some highways thus affecting transportation to/from the Eugene/Springfield Metro Area to a minor extent. There is also a possibility that a major eruption in the Cascades could affect public water supplies via heavy ash falls or lahars into streams/rivers upstream from public water supply intakes. There is also a possibility that some major volcanic eruptions could result in major flooding downstream along the McKenzie River all the way to the Eugene/Springfield Metro Area. The potential impacts of volcanic eruptions on the Eugene/Springfield Metro Area are summarized below in Table 11.3. Table 11.3 Potential Impacts of Volcanic Eruptions on the Eugene/Springfield Metro Area Inventory Probable Impacts Portion of Eugene/SpdngfieM Metro Enbre C~ty and surrounding region Area affected Buildings Negligible impact, other than minor cleanup required Streets within Metro Area Negligible impact, other than minor cleanup required Roads to/from Metro Area Neglig,ble impact, other than minor cleanup required Electric power Power outages likely from short circuits caused by ash falls Negligible impact, other than minor cleanup required for most Other Utilities ublities. Potential to impact water treatment plants which may require additional maintenance to deal with high turbidity water Casualties Some potential for health impacts, especially for frail people with resplratow problems. Volcamc erupbons, especially of Three Sisters, have the potential McKenzie River Floodgain to cause major flooding along the McKenzie River. A worst case scenario would be fadure of debris dams ~mpound~n9 substanbal quanbties of water. Public Review Draft: October 11, 2004 11-6