Resolution No. 4814 - Laserfiche WebLink

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FLOOD HAZARDS The Eugene/Springfield Metro Area is subject to flooding from several flood sources, including: 1) over bank flooding from the Middle Fork of the Willamette River, the Willamette River, and the McKenzie River, 2) over bank flooding from numerous smaller creeks and sloughs 3) local storm water drainage flooding. Major flooding events generally result from large winter storms with intense rainfall, with flooding sometimes exacerbated by snow-melt runoff. These large winter storms often result in simultaneous flooding on all rivers and streams in an affected area. However, because of differences in drainage areas, slopes, and other watershed characteristics, the severity of flooding in any given rainfall event often varies significantly from stream to stream. 6.1 Historical Floods in the Eugene/Springfield Metro Area Flooding has occurred in the Eugene/Springfield Metro Area throughout the recorded history of the area, ever since the first European settlers arrived in the area in the mid- 1800$~ The FEMA Flood Insurance Study for Lane County (June 2, 1999) has a brief history of major historical floods in the Eugene/Springfield Metro Area. Major floods occurred in 1861, 1890, t945, 1956, and 1964. The 1964 flood was the largest flood event recorded in Lane County. In considering these past major floods in Eugene/Springfield and in Lane County it is important to recognize that construction of major dams upstream from the 1940s to the 1960s has substantially reduced the potential for major floods on the major rivers. These dams have reduced the expected 100-year stream discharges (volume of water flowing in the rivers). Accordingly, expected flood elevations and overall flood potential for major flood events along the major rivers have been substantially reduced. The flood hazard areas shown on the current Flood Insurance Study (FIS) and Flood Insurance Rate Maps (FIRM) for Eugene/Springfield assume that the dams are operating properly. Dam failure hazards are not addressed by the FIS or the FIRM. Despite the reduction in flood potential from construction of the dams, the Eugene/ Springfield Metro Area continues to have flood risk from major rivers as well as from the numerous creeks and sloughs running through the Eugene/Springfield Metro Area. Flood risk on these smaller streams has not been reduced by the dams on the larger rivers. 6.2 The 1996 Flood The most recent major flood event in occurred in February 1996. Unusually heavy rains over the four-day period from February 5th to February 8th resulted in significant Public Review Draft: August 6, 2004 6-1