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Amazon Creek Enhancement(ACE) PE-HY File No.6512 <br /> • Project <br /> Since field measurement and subsequent refinement of the existing hydraulic model were <br /> beyond the scope of this study, changes to conveyance for each of the four altered bridge <br /> cross-sections was only qualitatively assessed based on the photos presented. <br /> West 11th Avenue Bridge <br /> The West 11th Avenue bridge crossing appears to have been slightly excavated on the <br /> right bank for the bike path. Overall conveyance under the bridge is most likely about <br /> the same as before construction. However, the steel railing may trap debris during a large <br /> flood event. <br /> Bertelsen Road Bridge <br /> Once again, the right bank appears to have been excavated for the bike path. The steel <br /> railing may trap debris during large flood events. Noticeable woody vegetation growth <br /> on the upstream side of the bridge has occurred in the three-years between the two <br /> photos. Bridge crossings must be maintained free of woody vegetation (see"Channel <br /> Maintenance"). <br /> Beltline Road Bridge <br /> The right bank appears to have been excavated for the bike path. However, capacity may <br /> have been reduced due to the installation of the concrete guidewall blocking a significant <br /> portion of right bank flow. A good transitional entrance to the bridge crossing was <br /> created which may offset some of the loss in capacity. <br /> Danebo Avenue Bridge <br /> The right bank appears to have been excavated for the bike path. Woody vegetation on <br /> both sides of the bridge has become very large and needs to be maintained(see "Channel <br /> Maintenance"). The steel railing may trap debris during large flood events. <br /> Channel Morphology <br /> a. Channel Migration <br /> As mentioned previously, a key assumption for this analysis was that the historic portion <br /> of the Amazon channel retain it's historic conveyance properties. However, in areas <br /> where the creek was widened and placed into more of a"natural"condition, the channel <br /> will migrate. Channel migration is a natural process as the channel strives for an <br /> equilibrium to balance stream and sediment energy. All of the channel widening took <br /> place on the right overbank of the historic stream. Thus, on all left bends the channel will <br /> attempt to migrate to the outside of this widened area. Channel migration rates and <br /> Date: 08/26/98 Page 8 Channel Maintenance Analysis <br /> CENWP-PE-HY;MTK <br />