Resolution No. 5303 - Laserfiche WebLink

Home Browse Search

Eugene -Springfield Area Natural Hazards Mitigation Plan 2. Hazard Descriptions Table 2-6 Extreme Weather - Impact Civil Unrest Risks Low Dam or Levee Failure No Known Epidemic No Known Hazardous Materials Low 2.4.8 Existing Hazard Mitigation Activities Extreme Weather is a new addition to this NHMP update, so hazard specific mitigation activities have yet to occur. 2.5 Flood The probability of riverine flooding in Eugene and Springfield is moderate, and the probability is high for stormwater system flooding. The vulnerability in Eugene and Springfield for riverine flooding is moderate and for stormwater system flooding is low. A moderate vulnerability indicates 10% to 69% of the population would be impacted, and a low vulnerability indicates less than 9% of the population would be impacted (Table 4-1). 2.6.1 Cause and Characteristics of the Hazard The Eugene -Springfield area considers two primary flood hazard categories: riverine flooding and stormwater system (urban) flooding. Riverine flooding occurs when water overtops the banks of a naturally occurring waterway, while urban flooding is most often caused by inadequate stormwater drainage systems or maintenance. The Eugene -Springfield area is subject to flooding from several sources, including: Riverine flooding from the Middle Fork of the Willamette River, the Willamette River, and the McKenzie River; • Riverine flooding from numerous smaller creeks and sloughs; and • Local stormwater drainage flooding. Flooding in Eugene and Springfield typically occurs in December and January. Incidents are usually associated with La Nina conditions, which result in prolonged rain and rapid snowmelt on saturated or frozen ground. This sudden influx of water causes rivers to swell, forcing tributary streams to back up and flood communities. Eugene -Springfield is largely protected from riverine flooding by multiple upstream flood control dams in both the McKenzie and Willamette River watersheds. 2-29 January 2020