Resolution No. 4814 - Laserfiche WebLink

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time, the slow filling of the floodplain and even minor watercourse alterations due to development may push future floodwaters to unanticipated and unaware areas within the community. In at least one location, along Amazon Creek, the FEMA Flood Insurance Study appears to be already out of date. Evidently, recent significant improvements/ changes in the Amazon Creek channel are not reflected in the FEMA FIS or flood plain maps for Amazon Creek. The FEMA FIS and maps should be updated to reflect accurately current flood hazards along Amazon Creek. There are also significant portions of the floodplains in the Eugene/Springfield Metro Area that are mapped only as approximate Zone A areas. Zone A areas are based upon approximate and historical data for which detailed flood hazard studies have not been performed. Some of these areas, such as the River Road/Santa Clara area are rapidly developing, although they did not have enough development at the time of the FIS to warrant a detailed study. 6.4 Flood Hazards and Flood Risk: Outside of Mapped Floodplains Section 6.3 above applies ONLY to the limited portions of the Eugene/Springfield Metro Area that are within the FEMA-mapped floodplains of the major rivers and portions of some of the smaller streams and sloughs. For mitigation planning purposes, it is very important to recognize that flood risk for a community is not limited only to areas of mapped floodplains. Other portions of the Eugene/Springfield Metro Area outside of the mapped floodplains are also at relatively high risk from over bank flooding from streams too small to be mapped by FEIVlA or from local storm water drainage. Repetitive, damaging floods from storm water drainage affect many areas of the United States, including the Eugene/Springfield Metro Area. As in most cities, local storm water drainage systems are designed to handle only small to moderate size rainfall events. Storm water systems are sometimes designed to handle only 2-year or 5-year flood events, and are rarely designed to handle rainfall events greater than 10-year or 15-year events. For local rainfall events that exceed the collection and conveyance capacities of the storm water drainage system, some level of flooding inevitably occurs. In many cases, local storm water drainage systems are designed to allow minor street flooding to carry off storm waters that exceed the capacity of the storm water drainage system. In larger rainfall events, flooding may extend beyond streets to include yards. In major rainfall events, local storm water drainage flooding can also flood buildings. In extreme cases, local storm water drainage flooding can sometimes result in several feet of water in buildings, with correspondingly high damage levels. in the Eugene/Springfield Metro Area, the storm water drainage system includes a combination of natural and built systems that have evolved over time. The built system includes flood control structures on the major rivers, along with smaller scale local drainage systems. Public Review Draft: August 6, 2004 6-9