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<br />Based on the very different behavior of Problem Area 6, it appears that this reach is <br />likely degrading. This can not be stated with certainty at this point, but the high transport rate <br />and cross-sectional shape suggest an incising reach. It is expected that this reach requires high <br />maintenance (Resource Consultants and Engineers, Inc. 1994). The abnormally high transport <br />capacity will likely cause deposition problems downstream as well, if this has not already <br />occurred. <br /> <br />The "Bristol Bridge" particle size distribution was used for this sub-reach for sediment <br />transport calculations. The sediment yield for this problem area under existing conditions was <br />63,800 tonslyr with a mean daily load of l75 tons/day. <br /> <br />Problem Area 7. Hydraulic modeling of Problem Area 7 indicated that the capacity <br />within the active channel banks is approximately 1 ,500 cfs. This is the value above which flow <br />begins to significantly inundate the overbank areas adjacent to the river channel. Potentially <br />damaging flows begin above approximately 3,000 cfs, though the flowpath that indicated for <br />this area is quite wide with large undeveloped areas inundated. The 3,000 cfs operational <br />discharge was modeled to indicate potential problem areas under current conditions. The flow <br />area extents for this discharge were connected to generate pseudo-floodplains, as described <br />above, and are shown on Sheet 5. <br /> <br />Examination of the profile indicated by the survey in this reach is relatively uniform, <br />with a reach-length weighted average slope ofO.00l22, and maximum and minimum <br />individual values of 0.00477 and 0.000l7, respectively. The aerial photography shows <br />relatively little encroachment (compared to other areas studied), with a reasonable buffer zone <br />on either side of the active channel. This appears to correspond with a better behaved bed <br />profile and illustrates the importance of the floodplain cross-section in stability. A profile plot <br />of this area is shown in Plate 5. <br /> <br />The "Bristol Bridge" particle size distribution was used for this sub-reach for sediment <br />transport calculations. The sediment yield for this problem area under existing conditions was <br />47,500 tonslyr with a mean daily load of 130 tons/day. <br /> <br />Table 3-3 summarizes the sediment yields for the five problem areas in their current <br />state. The large jump in yield from area 4 to area 5 is primarily due to the differing particle <br />size distributions used. However, this is not the case for Problem Area 6, and represents the <br />impact on channel morphology of the severe constriction from agricultural encroachment. <br /> <br />Hydraulic and Sediment Summarv <br /> <br />The hydraulic and sedinlent analyses performed indicate several things. First, the <br />conveyance capacity is less than the 3,000 cfs necessary for flood control releases in four of the <br />five areas. Additionally, the erratic hydraulics likely cause seepage problems from localized <br />high stages in other areas. Second, the channel form and profile are widely variable and these <br />in turn cause a broad range of sediment transport potentials within the individual reaches. The <br />profiles of some of the areas show marked disturbance. The "fits and starts" nature of the areas <br /> <br />23 <br />