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• <br /> AMAZON CHANNEL MAINTENANCE STUDY <br /> INTRODUCTION <br /> The Amazon Channel provides a certain level of flood protection throughout the Amazon Basin. <br /> Periodic channel maintenance is required to maintain this flood conveyance capacity. Channel <br /> conveyance capacity and floodwater surface elevations are directly related to a hydraulic parameter <br /> called Manning's roughness coefficient or "n" value. Manning's 'n"value is in turn related to the <br /> type, density, and height of vegetation and woody material found in the channel. Existing <br /> maintenance practices include the removal of woody material and wetland vegetation. These <br /> practices lower the 'n" value, which increases channel capacity,but they create potential sediment <br /> erosion problems and they are not compatible with the goals or vision identified in the West Eugene <br /> Wetlands Special Area Study (Reference 1). <br /> The City of Eugene's Public Works Department has contracted OTAK to conduct a study needed to <br /> more closely examine the relationships between flood protection, Manning's 'n' value and existing <br /> maintenance practices along the Amazon Channel. The hydraulic analysis address the channel <br /> between Beltline Road and the S.P.R.R. track which is scheduled for maintenance this summer. <br /> However, other aspects of the study will provide a much broader understanding of the flood control- <br /> maintenance-wetland destruction dilemma described earlier. <br /> STUDY OBJECTIVES <br /> The objectives of the study were: <br /> 1. Investigate the Federal Emergency Management Agency (FEMA) requirements regarding <br /> maintenance of flood channels or floodways. How do these differ from the Levee Inspection <br /> Rating Guide the Corps of Engineer's use for the Amazon Channel? How does the lack of <br /> 100-year flood protection provided by the levee effect these maintenance requirements or <br /> perceptions? <br /> 2. Determine the relationship between Manning's"n" value and the relative height of <br /> floodwaters along the designated study reach. <br /> 3. Working with existing topographical information, estimate the increase in the aerial extent of <br /> flooding for various computed heights of floodwaters along the designated study reach. <br /> 4. Suggest a relationship between Manning's "n" value and the length of time following the <br /> application of existing maintenance practices. <br /> MANNING'S.ROUGHNESS <br /> A field rec3tf, R ssance was conducted on March 3, 1992. The Amazon Channel was observed and <br /> photographed from the diversion structure upstream to Jefferson Street. The entire lower channel <br /> (i.e. defined for the purposes of this study as from the diversion structure upstream to Beltline Road) <br /> was walked, whereas the upper channel (i.e. from Beltline Road to Madison Street) was observed at <br /> I <br /> 1 <br />