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Amazon Creek Enhancement(ACE) PE-HY File No.6512 <br /> • Project <br /> locations will depend on the geologic strata, debris blockages and hydrologic conditions. <br /> Established riparian vegetation (i.e. fascine willow) may retard channel migration. The <br /> first few seasons will be critical in terms of channel migration. It will be necessary to <br /> monitor the project reach during this period to locate possible problematic areas. In some <br /> instances,channel migration may be beneficial, however, the channel cross-section needs <br /> to maintain its conveyance properties and changes in cross-sectional properties must be <br /> evaluated. <br /> b. Channel Deposition/Agradation <br /> Areas where channel widening has taken place should experience increased deposition. <br /> Deposition will most likely occur in areas where dramatic changes have taken place such <br /> as in the widened area upstream of West 11th Avenue near channel station 352+00. <br /> Deposition may also occur in widened areas below channel tributaries such as Willow <br /> Creek. Generally,channel deposition in widened areas should not be a cause for concern. <br /> However, channel deposition in areas where the channel is constricted must be monitored <br /> and maintained. Constricted areas include all bridge crossings and locations where the <br /> historic channel was not widened such as at some pipe outfalls. <br /> Channel Maintenance <br /> As mentioned throughout this report, the most critical locations for channel maintenance <br /> are within constricted areas,especially bridge crossings. For the project reach to function <br /> as modeled, bridge crossings must be maintained free of woody vegetation. Areas <br /> around bridge crossings to be maintained include; the area upstream approximately the <br /> distance of the width of the bridge opening, through the bridge crossing and downstream <br /> approximately the width of the bridge opening. As noted, many bridge openings <br /> currently have significant woody vegetation within the described area for maintenance. <br /> These areas need to be maintained. This is especially true upstream and downstream of <br /> Danebo Bridge. Danebo bridge was pointed out by city personnel as having relatively <br /> low flood capacity. As shown in the "Photographic Comparison," the area under the <br /> bridge is quickly becoming a jungle. The historic channel area also needs to be <br /> maintained in its original geometry. This includes cutting back of riparian vegetation and <br /> possible removal of sediments. The historic channel shall maintain itself, however, self- <br /> maintenance will be a function of natural and man-induced conditions. For instance, <br /> during dry years, riparian vegetation will encroach upon the channel. Also, sediments <br /> may be deposited in the channel as a result of construction or other disturbances in the <br /> urban watershed. <br /> It will be important to monitor the project reach on a regular basis for the first few years <br /> while the channel adjusts to changed conditions. It is impossible to predict the exact <br /> location and timing of conditions in the channel that will need maintenance. Thus, it will <br /> remain important to have city personnel familiar with the project, monitor the reach on a <br /> regular basis and report all noticeable changes to appropriate city staff. <br /> Date: 08/26/98 Page 9 Channel Maintenance Analysis <br /> CENWP-PE-HY;MTK <br />