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Amazon Creek Enhancement(ACE) PE-HY File No.6512 <br /> Project <br /> Study Purpose <br /> The purpose of this study is to evaluate the City of Eugene's Amazon Creek <br /> Enhancement (ACE)Project to determine the level of riparian vegetation growth that <br /> would be allowable to not exceed previous flood conditions. The ACE project evaluated <br /> is located between Bailey Hill Road (Channel Station 374+00) and the Southern Pacific <br /> Railroad Bridge (Station 237+00). <br /> The work on this project was performed under the Corps of Engineers Support for Others <br /> program. <br /> Study Scope <br /> The scope of this study was to evaluate the conveyance of the ACE project reach with <br /> fully developed vegetation growth. Composite Manning's roughness values were <br /> developed for altered channel cross-sections based on fully developed vegetation growth <br /> as shown in Figure 2. Limited hydraulic model runs were performed utilizing the <br /> original HEC-2 model developed in 1995 from the original ACE project design and the <br /> updated Manning's roughness values. Model runs were limited to the 100-year FEMA <br /> flood peak flows from the City of Eugene Flood Insurance Study of 1986. A field <br /> investigation of the constructed channel was performed. Comparison of historic <br /> photographs with those taken after construction was also performed. The final element of <br /> this project was to qualitatively assess future maintenance activities necessary to maintain <br /> conveyance levels within the altered channel. <br /> Study Assumptions <br /> Several assumptions were made in formulating this analysis. A key assumption was that <br /> the historic channel area will maintain its historic conveyance properties. Thus, the <br /> historic channel shall be maintained free of vegetation, debris and sedimentation. It was <br /> assumed that a composite Manning's roughness, which was derived based on the various <br /> regions of each cross-section, would adequately define the overall channel roughness for <br /> each full-flowing cross-section. It was also assumed that bridge cross-sections remain <br /> free of woody vegetation and maintain their historic channel conveyance properties. <br /> Channel Capacity Analysis <br /> a. HEC-2 Modeling <br /> During the design phase of this project an HEC-2 model was developed for this section of <br /> Amazon Creek by the USACE, Portland District. This one-dimensional, steady-state <br /> model was used in this analysis. The model was not altered other than Manning's <br /> roughness coefficients were updated based on increased vegetation growth within the <br /> constructed channel. The following table lists Manning's roughness values applied to <br /> sub-sections of each cross-section: <br /> Date: 08/26/98 Page 1 Channel Maintenance Analysis <br /> CENWP-PE-HY;MTK <br />