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Amazon Creek Enhancement(ACE) PE-HY File No.6512 <br /> • Project <br /> Conclusions <br /> At a meeting in July of 1998, the City of Eugene presented a cross-sectional depiction of <br /> planned future vegetation and flow properties of a typical section within the Amazon <br /> Creek Enhancement project reach (see Figure 2). The cross-section is composed from <br /> left to right as follows: a 20-foot section of willow trees on the existing top of left bank, <br /> an approximate 50-foot section of existing-historic channel, a variable width riparian area <br /> composed of willow bushes, a 25-foot wide-5:1 sloped bank that will be maintained for <br /> maintenance access and a 20-foot section of willow trees on the top of a 2:1 sloped right <br /> bank. This fully developed section was used throughout the project reach in this analysis. <br /> It has been determined that the cross-section as depicted, will have adequate conveyance <br /> to maintain historic flood carrying capacity of the Amazon Channel. To keep the channel <br /> in this state will require maintenance. Particularly within the historic 50-foot wide <br /> section and along the 5:1 sloped access section. <br /> Intuitively, one would expect channel conveyance to increase upon excavation of the <br /> cross-section. This has occurred within the project, however, overall conveyance through <br /> the reach has not increased substantially. Constrictions in the channel at bridge crossings <br /> tend to control the water surface profile through the reach. Thus, it is important that <br /> maintenance continue at all channel constrictions within the project. <br /> The Amazon Creek channel was designed in the 1940's and completed in 1956. The <br /> historic unlined trapezoidal channel in the project area was designed to carry 1840 cubic <br /> feet per second (cfs) roughly between the SPRR Bridge and Danebo Avenue. From <br /> about Danebo Avenue upstream to Bailey Hill Road, the channel was designed to carry <br /> 1160 cfs. At the time of the design, these flows were calculated to be about a 25-year <br /> event. More recent calculations of flow frequency for Amazon Creek indicate that these <br /> flows are between 2 and 10-year events. The difference between the recent data and the <br /> design data is partly due to the increase in urbanization in the basin and partly due to <br /> improvements in flow frequency computation methods. Flood insurance study data for <br /> Amazon Creek are outdated. Differences in flood peak frequency estimates along with <br /> changes in channel conditions give reason to review nad possibly revise the existing <br /> flood insurance study data for Amazon Creek. <br /> Date: 08/26/98 Page 10 Channel Maintenance Analysis <br /> CENWP-PE-HY;MTK <br />